Overcome the `ref struct` limitation for pre-roslyn compilers by introducing GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE for generated code (#7490)

* enable compatibility mode in codegen

* regenerate protos

* improve readability

* more robust way of figuring out path to old C# compiler

* add recent C# changes

CHANGES.txt

@@ -13,6 +13,17 @@ Unreleased Changes
   * Improved the error message when AttributeError is returned from __getattr__
     in EnumTypeWrapper.
 
+  C#:
+  * Dropped support for netstandard1.0 (replaced by support for netstandard1.1).
+    This was required to modernize the parsing stack to use the `Span<byte>`
+    type internally. (#7351)
+  * Add `ParseFrom(ReadOnlySequence<byte>)` method to enable GC friendly
+    parsing with reduced allocations and buffer copies. (#7351)
+  * Add `GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE` define to make
+    generated code compatible with old C# compilers (pre-roslyn compilers
+    from .NET framework and old versions of mono) that do not support
+    ref structs. (#7490)
+
 2020-05-26 version 3.12.2 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
 
   C++

Makefile.am

@@ -127,6 +127,7 @@ csharp_EXTRA_DIST=                                                           \
   csharp/src/Google.Protobuf.Test/MessageParsingHelpers.cs                   \
   csharp/src/Google.Protobuf.Test/Proto3OptionalTest.cs                      \
   csharp/src/Google.Protobuf.Test/ReadOnlySequenceFactory.cs                 \
+  csharp/src/Google.Protobuf.Test/RefStructCompatibilityTest.cs              \
   csharp/src/Google.Protobuf.Test/Reflection/CustomOptionsTest.cs            \
   csharp/src/Google.Protobuf.Test/Reflection/DescriptorDeclarationTest.cs    \
   csharp/src/Google.Protobuf.Test/Reflection/DescriptorsTest.cs              \

csharp/src/AddressBook/Addressbook.cs

@@ -49,7 +49,11 @@ namespace Google.Protobuf.Examples.AddressBook {
   /// <summary>
   /// [START messages]
   /// </summary>
-  public sealed partial class Person : pb::IMessage<Person>, pb::IBufferMessage {
+  public sealed partial class Person : pb::IMessage<Person>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Person> _parser = new pb::MessageParser<Person>(() => new Person());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -256,9 +260,44 @@ namespace Google.Protobuf.Examples.AddressBook {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            Name = input.ReadString();
+            break;
+          }
+          case 16: {
+            Id = input.ReadInt32();
+            break;
+          }
+          case 26: {
+            Email = input.ReadString();
+            break;
+          }
+          case 34: {
+            phones_.AddEntriesFrom(input, _repeated_phones_codec);
+            break;
+          }
+          case 42: {
+            if (lastUpdated_ == null) {
+              LastUpdated = new global::Google.Protobuf.WellKnownTypes.Timestamp();
+            }
+            input.ReadMessage(LastUpdated);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -293,6 +332,7 @@ namespace Google.Protobuf.Examples.AddressBook {
         }
       }
     }
+    #endif
 
     #region Nested types
     /// <summary>Container for nested types declared in the Person message type.</summary>
@@ -304,7 +344,11 @@ namespace Google.Protobuf.Examples.AddressBook {
         [pbr::OriginalName("WORK")] Work = 2,
       }
 
-      public sealed partial class PhoneNumber : pb::IMessage<PhoneNumber>, pb::IBufferMessage {
+      public sealed partial class PhoneNumber : pb::IMessage<PhoneNumber>
+      #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+          , pb::IBufferMessage
+      #endif
+      {
         private static readonly pb::MessageParser<PhoneNumber> _parser = new pb::MessageParser<PhoneNumber>(() => new PhoneNumber());
         private pb::UnknownFieldSet _unknownFields;
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -441,9 +485,29 @@ namespace Google.Protobuf.Examples.AddressBook {
 
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         public void MergeFrom(pb::CodedInputStream input) {
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
           input.ReadRawMessage(this);
+        #else
+          uint tag;
+          while ((tag = input.ReadTag()) != 0) {
+            switch(tag) {
+              default:
+                _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+                break;
+              case 10: {
+                Number = input.ReadString();
+                break;
+              }
+              case 16: {
+                Type = (global::Google.Protobuf.Examples.AddressBook.Person.Types.PhoneType) input.ReadEnum();
+                break;
+              }
+            }
+          }
+        #endif
         }
 
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
           uint tag;
@@ -463,6 +527,7 @@ namespace Google.Protobuf.Examples.AddressBook {
             }
           }
         }
+        #endif
 
       }
 
@@ -474,7 +539,11 @@ namespace Google.Protobuf.Examples.AddressBook {
   /// <summary>
   /// Our address book file is just one of these.
   /// </summary>
-  public sealed partial class AddressBook : pb::IMessage<AddressBook>, pb::IBufferMessage {
+  public sealed partial class AddressBook : pb::IMessage<AddressBook>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<AddressBook> _parser = new pb::MessageParser<AddressBook>(() => new AddressBook());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -579,9 +648,25 @@ namespace Google.Protobuf.Examples.AddressBook {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            people_.AddEntriesFrom(input, _repeated_people_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -597,6 +682,7 @@ namespace Google.Protobuf.Examples.AddressBook {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf.Benchmarks/BenchmarkMessage1Proto3.cs

@@ -64,7 +64,11 @@ namespace Benchmarks.Proto3 {
 
   }
   #region Messages
-  public sealed partial class GoogleMessage1 : pb::IMessage<GoogleMessage1>, pb::IBufferMessage {
+  public sealed partial class GoogleMessage1 : pb::IMessage<GoogleMessage1>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<GoogleMessage1> _parser = new pb::MessageParser<GoogleMessage1>(() => new GoogleMessage1());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1132,9 +1136,189 @@ namespace Benchmarks.Proto3 {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            Field1 = input.ReadString();
+            break;
+          }
+          case 16: {
+            Field2 = input.ReadInt32();
+            break;
+          }
+          case 24: {
+            Field3 = input.ReadInt32();
+            break;
+          }
+          case 34: {
+            Field4 = input.ReadString();
+            break;
+          }
+          case 42:
+          case 41: {
+            field5_.AddEntriesFrom(input, _repeated_field5_codec);
+            break;
+          }
+          case 48: {
+            Field6 = input.ReadInt32();
+            break;
+          }
+          case 58: {
+            Field7 = input.ReadString();
+            break;
+          }
+          case 74: {
+            Field9 = input.ReadString();
+            break;
+          }
+          case 96: {
+            Field12 = input.ReadBool();
+            break;
+          }
+          case 104: {
+            Field13 = input.ReadBool();
+            break;
+          }
+          case 112: {
+            Field14 = input.ReadBool();
+            break;
+          }
+          case 122: {
+            if (field15_ == null) {
+              Field15 = new global::Benchmarks.Proto3.GoogleMessage1SubMessage();
+            }
+            input.ReadMessage(Field15);
+            break;
+          }
+          case 128: {
+            Field16 = input.ReadInt32();
+            break;
+          }
+          case 136: {
+            Field17 = input.ReadBool();
+            break;
+          }
+          case 146: {
+            Field18 = input.ReadString();
+            break;
+          }
+          case 176: {
+            Field22 = input.ReadInt64();
+            break;
+          }
+          case 184: {
+            Field23 = input.ReadInt32();
+            break;
+          }
+          case 192: {
+            Field24 = input.ReadBool();
+            break;
+          }
+          case 200: {
+            Field25 = input.ReadInt32();
+            break;
+          }
+          case 232: {
+            Field29 = input.ReadInt32();
+            break;
+          }
+          case 240: {
+            Field30 = input.ReadBool();
+            break;
+          }
+          case 472: {
+            Field59 = input.ReadBool();
+            break;
+          }
+          case 480: {
+            Field60 = input.ReadInt32();
+            break;
+          }
+          case 536: {
+            Field67 = input.ReadInt32();
+            break;
+          }
+          case 544: {
+            Field68 = input.ReadInt32();
+            break;
+          }
+          case 624: {
+            Field78 = input.ReadBool();
+            break;
+          }
+          case 640: {
+            Field80 = input.ReadBool();
+            break;
+          }
+          case 648: {
+            Field81 = input.ReadBool();
+            break;
+          }
+          case 800: {
+            Field100 = input.ReadInt32();
+            break;
+          }
+          case 808: {
+            Field101 = input.ReadInt32();
+            break;
+          }
+          case 818: {
+            Field102 = input.ReadString();
+            break;
+          }
+          case 826: {
+            Field103 = input.ReadString();
+            break;
+          }
+          case 832: {
+            Field104 = input.ReadInt32();
+            break;
+          }
+          case 1024: {
+            Field128 = input.ReadInt32();
+            break;
+          }
+          case 1034: {
+            Field129 = input.ReadString();
+            break;
+          }
+          case 1040: {
+            Field130 = input.ReadInt32();
+            break;
+          }
+          case 1048: {
+            Field131 = input.ReadInt32();
+            break;
+          }
+          case 1200: {
+            Field150 = input.ReadInt32();
+            break;
+          }
+          case 2168: {
+            Field271 = input.ReadInt32();
+            break;
+          }
+          case 2176: {
+            Field272 = input.ReadInt32();
+            break;
+          }
+          case 2240: {
+            Field280 = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1314,10 +1498,15 @@ namespace Benchmarks.Proto3 {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class GoogleMessage1SubMessage : pb::IMessage<GoogleMessage1SubMessage>, pb::IBufferMessage {
+  public sealed partial class GoogleMessage1SubMessage : pb::IMessage<GoogleMessage1SubMessage>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<GoogleMessage1SubMessage> _parser = new pb::MessageParser<GoogleMessage1SubMessage>(() => new GoogleMessage1SubMessage());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1886,9 +2075,101 @@ namespace Benchmarks.Proto3 {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            Field1 = input.ReadInt32();
+            break;
+          }
+          case 16: {
+            Field2 = input.ReadInt32();
+            break;
+          }
+          case 24: {
+            Field3 = input.ReadInt32();
+            break;
+          }
+          case 96: {
+            Field12 = input.ReadBool();
+            break;
+          }
+          case 104: {
+            Field13 = input.ReadInt64();
+            break;
+          }
+          case 112: {
+            Field14 = input.ReadInt64();
+            break;
+          }
+          case 122: {
+            Field15 = input.ReadString();
+            break;
+          }
+          case 128: {
+            Field16 = input.ReadInt32();
+            break;
+          }
+          case 152: {
+            Field19 = input.ReadInt32();
+            break;
+          }
+          case 160: {
+            Field20 = input.ReadBool();
+            break;
+          }
+          case 169: {
+            Field21 = input.ReadFixed64();
+            break;
+          }
+          case 176: {
+            Field22 = input.ReadInt32();
+            break;
+          }
+          case 184: {
+            Field23 = input.ReadBool();
+            break;
+          }
+          case 224: {
+            Field28 = input.ReadBool();
+            break;
+          }
+          case 1629: {
+            Field203 = input.ReadFixed32();
+            break;
+          }
+          case 1632: {
+            Field204 = input.ReadInt32();
+            break;
+          }
+          case 1642: {
+            Field205 = input.ReadString();
+            break;
+          }
+          case 1648: {
+            Field206 = input.ReadBool();
+            break;
+          }
+          case 1656: {
+            Field207 = input.ReadUInt64();
+            break;
+          }
+          case 2400: {
+            Field300 = input.ReadUInt64();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1980,6 +2261,7 @@ namespace Benchmarks.Proto3 {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf.Benchmarks/Benchmarks.cs

@@ -38,7 +38,11 @@ namespace Benchmarks {
 
   }
   #region Messages
-  public sealed partial class BenchmarkDataset : pb::IMessage<BenchmarkDataset>, pb::IBufferMessage {
+  public sealed partial class BenchmarkDataset : pb::IMessage<BenchmarkDataset>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<BenchmarkDataset> _parser = new pb::MessageParser<BenchmarkDataset>(() => new BenchmarkDataset());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -219,9 +223,33 @@ namespace Benchmarks {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            Name = input.ReadString();
+            break;
+          }
+          case 18: {
+            MessageName = input.ReadString();
+            break;
+          }
+          case 26: {
+            payload_.AddEntriesFrom(input, _repeated_payload_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -245,6 +273,7 @@ namespace Benchmarks {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf.Conformance/Conformance.cs

@@ -107,7 +107,11 @@ namespace Conformance {
   /// This will be known by message_type == "conformance.FailureSet", a conformance
   /// test should return a serialized FailureSet in protobuf_payload.
   /// </summary>
-  public sealed partial class FailureSet : pb::IMessage<FailureSet>, pb::IBufferMessage {
+  public sealed partial class FailureSet : pb::IMessage<FailureSet>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<FailureSet> _parser = new pb::MessageParser<FailureSet>(() => new FailureSet());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -212,9 +216,25 @@ namespace Conformance {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            failure_.AddEntriesFrom(input, _repeated_failure_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -230,6 +250,7 @@ namespace Conformance {
         }
       }
     }
+    #endif
 
   }
 
@@ -240,7 +261,11 @@ namespace Conformance {
   ///   2. parse the protobuf or JSON payload in "payload" (which may fail)
   ///   3. if the parse succeeded, serialize the message in the requested format.
   /// </summary>
-  public sealed partial class ConformanceRequest : pb::IMessage<ConformanceRequest>, pb::IBufferMessage {
+  public sealed partial class ConformanceRequest : pb::IMessage<ConformanceRequest>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<ConformanceRequest> _parser = new pb::MessageParser<ConformanceRequest>(() => new ConformanceRequest());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -608,9 +633,60 @@ namespace Conformance {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            ProtobufPayload = input.ReadBytes();
+            break;
+          }
+          case 18: {
+            JsonPayload = input.ReadString();
+            break;
+          }
+          case 24: {
+            RequestedOutputFormat = (global::Conformance.WireFormat) input.ReadEnum();
+            break;
+          }
+          case 34: {
+            MessageType = input.ReadString();
+            break;
+          }
+          case 40: {
+            TestCategory = (global::Conformance.TestCategory) input.ReadEnum();
+            break;
+          }
+          case 50: {
+            if (jspbEncodingOptions_ == null) {
+              JspbEncodingOptions = new global::Conformance.JspbEncodingConfig();
+            }
+            input.ReadMessage(JspbEncodingOptions);
+            break;
+          }
+          case 58: {
+            JspbPayload = input.ReadString();
+            break;
+          }
+          case 66: {
+            TextPayload = input.ReadString();
+            break;
+          }
+          case 72: {
+            PrintUnknownFields = input.ReadBool();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -661,13 +737,18 @@ namespace Conformance {
         }
       }
     }
+    #endif
 
   }
 
   /// <summary>
   /// Represents a single test case's output.
   /// </summary>
-  public sealed partial class ConformanceResponse : pb::IMessage<ConformanceResponse>, pb::IBufferMessage {
+  public sealed partial class ConformanceResponse : pb::IMessage<ConformanceResponse>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<ConformanceResponse> _parser = new pb::MessageParser<ConformanceResponse>(() => new ConformanceResponse());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1035,9 +1116,53 @@ namespace Conformance {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            ParseError = input.ReadString();
+            break;
+          }
+          case 18: {
+            RuntimeError = input.ReadString();
+            break;
+          }
+          case 26: {
+            ProtobufPayload = input.ReadBytes();
+            break;
+          }
+          case 34: {
+            JsonPayload = input.ReadString();
+            break;
+          }
+          case 42: {
+            Skipped = input.ReadString();
+            break;
+          }
+          case 50: {
+            SerializeError = input.ReadString();
+            break;
+          }
+          case 58: {
+            JspbPayload = input.ReadString();
+            break;
+          }
+          case 66: {
+            TextPayload = input.ReadString();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1081,13 +1206,18 @@ namespace Conformance {
         }
       }
     }
+    #endif
 
   }
 
   /// <summary>
   /// Encoding options for jspb format.
   /// </summary>
-  public sealed partial class JspbEncodingConfig : pb::IMessage<JspbEncodingConfig>, pb::IBufferMessage {
+  public sealed partial class JspbEncodingConfig : pb::IMessage<JspbEncodingConfig>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<JspbEncodingConfig> _parser = new pb::MessageParser<JspbEncodingConfig>(() => new JspbEncodingConfig());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1203,9 +1333,25 @@ namespace Conformance {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            UseJspbArrayAnyFormat = input.ReadBool();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1221,6 +1367,7 @@ namespace Conformance {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf.Test.TestProtos/MapUnittestProto3.cs

@@ -176,7 +176,11 @@ namespace Google.Protobuf.TestProtos {
   /// <summary>
   /// Tests maps.
   /// </summary>
-  public sealed partial class TestMap : pb::IMessage<TestMap>, pb::IBufferMessage {
+  public sealed partial class TestMap : pb::IMessage<TestMap>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<TestMap> _parser = new pb::MessageParser<TestMap>(() => new TestMap());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -537,9 +541,89 @@ namespace Google.Protobuf.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            mapInt32Int32_.AddEntriesFrom(input, _map_mapInt32Int32_codec);
+            break;
+          }
+          case 18: {
+            mapInt64Int64_.AddEntriesFrom(input, _map_mapInt64Int64_codec);
+            break;
+          }
+          case 26: {
+            mapUint32Uint32_.AddEntriesFrom(input, _map_mapUint32Uint32_codec);
+            break;
+          }
+          case 34: {
+            mapUint64Uint64_.AddEntriesFrom(input, _map_mapUint64Uint64_codec);
+            break;
+          }
+          case 42: {
+            mapSint32Sint32_.AddEntriesFrom(input, _map_mapSint32Sint32_codec);
+            break;
+          }
+          case 50: {
+            mapSint64Sint64_.AddEntriesFrom(input, _map_mapSint64Sint64_codec);
+            break;
+          }
+          case 58: {
+            mapFixed32Fixed32_.AddEntriesFrom(input, _map_mapFixed32Fixed32_codec);
+            break;
+          }
+          case 66: {
+            mapFixed64Fixed64_.AddEntriesFrom(input, _map_mapFixed64Fixed64_codec);
+            break;
+          }
+          case 74: {
+            mapSfixed32Sfixed32_.AddEntriesFrom(input, _map_mapSfixed32Sfixed32_codec);
+            break;
+          }
+          case 82: {
+            mapSfixed64Sfixed64_.AddEntriesFrom(input, _map_mapSfixed64Sfixed64_codec);
+            break;
+          }
+          case 90: {
+            mapInt32Float_.AddEntriesFrom(input, _map_mapInt32Float_codec);
+            break;
+          }
+          case 98: {
+            mapInt32Double_.AddEntriesFrom(input, _map_mapInt32Double_codec);
+            break;
+          }
+          case 106: {
+            mapBoolBool_.AddEntriesFrom(input, _map_mapBoolBool_codec);
+            break;
+          }
+          case 114: {
+            mapStringString_.AddEntriesFrom(input, _map_mapStringString_codec);
+            break;
+          }
+          case 122: {
+            mapInt32Bytes_.AddEntriesFrom(input, _map_mapInt32Bytes_codec);
+            break;
+          }
+          case 130: {
+            mapInt32Enum_.AddEntriesFrom(input, _map_mapInt32Enum_codec);
+            break;
+          }
+          case 138: {
+            mapInt32ForeignMessage_.AddEntriesFrom(input, _map_mapInt32ForeignMessage_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -619,10 +703,15 @@ namespace Google.Protobuf.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class TestMapSubmessage : pb::IMessage<TestMapSubmessage>, pb::IBufferMessage {
+  public sealed partial class TestMapSubmessage : pb::IMessage<TestMapSubmessage>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<TestMapSubmessage> _parser = new pb::MessageParser<TestMapSubmessage>(() => new TestMapSubmessage());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -738,9 +827,28 @@ namespace Google.Protobuf.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            if (testMap_ == null) {
+              TestMap = new global::Google.Protobuf.TestProtos.TestMap();
+            }
+            input.ReadMessage(TestMap);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -759,10 +867,15 @@ namespace Google.Protobuf.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class TestMessageMap : pb::IMessage<TestMessageMap>, pb::IBufferMessage {
+  public sealed partial class TestMessageMap : pb::IMessage<TestMessageMap>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<TestMessageMap> _parser = new pb::MessageParser<TestMessageMap>(() => new TestMessageMap());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -867,9 +980,25 @@ namespace Google.Protobuf.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            mapInt32Message_.AddEntriesFrom(input, _map_mapInt32Message_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -885,13 +1014,18 @@ namespace Google.Protobuf.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
   /// <summary>
   /// Two map fields share the same entry default instance.
   /// </summary>
-  public sealed partial class TestSameTypeMap : pb::IMessage<TestSameTypeMap>, pb::IBufferMessage {
+  public sealed partial class TestSameTypeMap : pb::IMessage<TestSameTypeMap>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<TestSameTypeMap> _parser = new pb::MessageParser<TestSameTypeMap>(() => new TestSameTypeMap());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1012,9 +1146,29 @@ namespace Google.Protobuf.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            map1_.AddEntriesFrom(input, _map_map1_codec);
+            break;
+          }
+          case 18: {
+            map2_.AddEntriesFrom(input, _map_map2_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1034,10 +1188,15 @@ namespace Google.Protobuf.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class TestArenaMap : pb::IMessage<TestArenaMap>, pb::IBufferMessage {
+  public sealed partial class TestArenaMap : pb::IMessage<TestArenaMap>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<TestArenaMap> _parser = new pb::MessageParser<TestArenaMap>(() => new TestArenaMap());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1366,9 +1525,81 @@ namespace Google.Protobuf.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            mapInt32Int32_.AddEntriesFrom(input, _map_mapInt32Int32_codec);
+            break;
+          }
+          case 18: {
+            mapInt64Int64_.AddEntriesFrom(input, _map_mapInt64Int64_codec);
+            break;
+          }
+          case 26: {
+            mapUint32Uint32_.AddEntriesFrom(input, _map_mapUint32Uint32_codec);
+            break;
+          }
+          case 34: {
+            mapUint64Uint64_.AddEntriesFrom(input, _map_mapUint64Uint64_codec);
+            break;
+          }
+          case 42: {
+            mapSint32Sint32_.AddEntriesFrom(input, _map_mapSint32Sint32_codec);
+            break;
+          }
+          case 50: {
+            mapSint64Sint64_.AddEntriesFrom(input, _map_mapSint64Sint64_codec);
+            break;
+          }
+          case 58: {
+            mapFixed32Fixed32_.AddEntriesFrom(input, _map_mapFixed32Fixed32_codec);
+            break;
+          }
+          case 66: {
+            mapFixed64Fixed64_.AddEntriesFrom(input, _map_mapFixed64Fixed64_codec);
+            break;
+          }
+          case 74: {
+            mapSfixed32Sfixed32_.AddEntriesFrom(input, _map_mapSfixed32Sfixed32_codec);
+            break;
+          }
+          case 82: {
+            mapSfixed64Sfixed64_.AddEntriesFrom(input, _map_mapSfixed64Sfixed64_codec);
+            break;
+          }
+          case 90: {
+            mapInt32Float_.AddEntriesFrom(input, _map_mapInt32Float_codec);
+            break;
+          }
+          case 98: {
+            mapInt32Double_.AddEntriesFrom(input, _map_mapInt32Double_codec);
+            break;
+          }
+          case 106: {
+            mapBoolBool_.AddEntriesFrom(input, _map_mapBoolBool_codec);
+            break;
+          }
+          case 114: {
+            mapInt32Enum_.AddEntriesFrom(input, _map_mapInt32Enum_codec);
+            break;
+          }
+          case 122: {
+            mapInt32ForeignMessage_.AddEntriesFrom(input, _map_mapInt32ForeignMessage_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1440,6 +1671,7 @@ namespace Google.Protobuf.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
@@ -1447,7 +1679,11 @@ namespace Google.Protobuf.TestProtos {
   /// Previously, message containing enum called Type cannot be used as value of
   /// map field.
   /// </summary>
-  public sealed partial class MessageContainingEnumCalledType : pb::IMessage<MessageContainingEnumCalledType>, pb::IBufferMessage {
+  public sealed partial class MessageContainingEnumCalledType : pb::IMessage<MessageContainingEnumCalledType>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<MessageContainingEnumCalledType> _parser = new pb::MessageParser<MessageContainingEnumCalledType>(() => new MessageContainingEnumCalledType());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1552,9 +1788,25 @@ namespace Google.Protobuf.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            type_.AddEntriesFrom(input, _map_type_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1570,6 +1822,7 @@ namespace Google.Protobuf.TestProtos {
         }
       }
     }
+    #endif
 
     #region Nested types
     /// <summary>Container for nested types declared in the MessageContainingEnumCalledType message type.</summary>
@@ -1587,7 +1840,11 @@ namespace Google.Protobuf.TestProtos {
   /// <summary>
   /// Previously, message cannot contain map field called "entry".
   /// </summary>
-  public sealed partial class MessageContainingMapCalledEntry : pb::IMessage<MessageContainingMapCalledEntry>, pb::IBufferMessage {
+  public sealed partial class MessageContainingMapCalledEntry : pb::IMessage<MessageContainingMapCalledEntry>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<MessageContainingMapCalledEntry> _parser = new pb::MessageParser<MessageContainingMapCalledEntry>(() => new MessageContainingMapCalledEntry());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1692,9 +1949,25 @@ namespace Google.Protobuf.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            entry_.AddEntriesFrom(input, _map_entry_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1710,6 +1983,7 @@ namespace Google.Protobuf.TestProtos {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf.Test.TestProtos/TestMessagesProto2.cs

@@ -244,7 +244,11 @@ namespace ProtobufTestMessages.Proto2 {
   /// could trigger bugs that occur in any message type in this file.  We verify
   /// this stays true in a unit test.
   /// </summary>
-  public sealed partial class TestAllTypesProto2 : pb::IExtendableMessage<TestAllTypesProto2>, pb::IBufferMessage {
+  public sealed partial class TestAllTypesProto2 : pb::IExtendableMessage<TestAllTypesProto2>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<TestAllTypesProto2> _parser = new pb::MessageParser<TestAllTypesProto2>(() => new TestAllTypesProto2());
     private pb::UnknownFieldSet _unknownFields;
     private pb::ExtensionSet<TestAllTypesProto2> _extensions;
@@ -3311,9 +3315,556 @@ namespace ProtobufTestMessages.Proto2 {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            if (!pb::ExtensionSet.TryMergeFieldFrom(ref _extensions, input)) {
+              _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            }
+            break;
+          case 8: {
+            OptionalInt32 = input.ReadInt32();
+            break;
+          }
+          case 16: {
+            OptionalInt64 = input.ReadInt64();
+            break;
+          }
+          case 24: {
+            OptionalUint32 = input.ReadUInt32();
+            break;
+          }
+          case 32: {
+            OptionalUint64 = input.ReadUInt64();
+            break;
+          }
+          case 40: {
+            OptionalSint32 = input.ReadSInt32();
+            break;
+          }
+          case 48: {
+            OptionalSint64 = input.ReadSInt64();
+            break;
+          }
+          case 61: {
+            OptionalFixed32 = input.ReadFixed32();
+            break;
+          }
+          case 65: {
+            OptionalFixed64 = input.ReadFixed64();
+            break;
+          }
+          case 77: {
+            OptionalSfixed32 = input.ReadSFixed32();
+            break;
+          }
+          case 81: {
+            OptionalSfixed64 = input.ReadSFixed64();
+            break;
+          }
+          case 93: {
+            OptionalFloat = input.ReadFloat();
+            break;
+          }
+          case 97: {
+            OptionalDouble = input.ReadDouble();
+            break;
+          }
+          case 104: {
+            OptionalBool = input.ReadBool();
+            break;
+          }
+          case 114: {
+            OptionalString = input.ReadString();
+            break;
+          }
+          case 122: {
+            OptionalBytes = input.ReadBytes();
+            break;
+          }
+          case 146: {
+            if (optionalNestedMessage_ == null) {
+              OptionalNestedMessage = new global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.NestedMessage();
+            }
+            input.ReadMessage(OptionalNestedMessage);
+            break;
+          }
+          case 154: {
+            if (optionalForeignMessage_ == null) {
+              OptionalForeignMessage = new global::ProtobufTestMessages.Proto2.ForeignMessageProto2();
+            }
+            input.ReadMessage(OptionalForeignMessage);
+            break;
+          }
+          case 168: {
+            OptionalNestedEnum = (global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.NestedEnum) input.ReadEnum();
+            break;
+          }
+          case 176: {
+            OptionalForeignEnum = (global::ProtobufTestMessages.Proto2.ForeignEnumProto2) input.ReadEnum();
+            break;
+          }
+          case 194: {
+            OptionalStringPiece = input.ReadString();
+            break;
+          }
+          case 202: {
+            OptionalCord = input.ReadString();
+            break;
+          }
+          case 218: {
+            if (recursiveMessage_ == null) {
+              RecursiveMessage = new global::ProtobufTestMessages.Proto2.TestAllTypesProto2();
+            }
+            input.ReadMessage(RecursiveMessage);
+            break;
+          }
+          case 250:
+          case 248: {
+            repeatedInt32_.AddEntriesFrom(input, _repeated_repeatedInt32_codec);
+            break;
+          }
+          case 258:
+          case 256: {
+            repeatedInt64_.AddEntriesFrom(input, _repeated_repeatedInt64_codec);
+            break;
+          }
+          case 266:
+          case 264: {
+            repeatedUint32_.AddEntriesFrom(input, _repeated_repeatedUint32_codec);
+            break;
+          }
+          case 274:
+          case 272: {
+            repeatedUint64_.AddEntriesFrom(input, _repeated_repeatedUint64_codec);
+            break;
+          }
+          case 282:
+          case 280: {
+            repeatedSint32_.AddEntriesFrom(input, _repeated_repeatedSint32_codec);
+            break;
+          }
+          case 290:
+          case 288: {
+            repeatedSint64_.AddEntriesFrom(input, _repeated_repeatedSint64_codec);
+            break;
+          }
+          case 298:
+          case 301: {
+            repeatedFixed32_.AddEntriesFrom(input, _repeated_repeatedFixed32_codec);
+            break;
+          }
+          case 306:
+          case 305: {
+            repeatedFixed64_.AddEntriesFrom(input, _repeated_repeatedFixed64_codec);
+            break;
+          }
+          case 314:
+          case 317: {
+            repeatedSfixed32_.AddEntriesFrom(input, _repeated_repeatedSfixed32_codec);
+            break;
+          }
+          case 322:
+          case 321: {
+            repeatedSfixed64_.AddEntriesFrom(input, _repeated_repeatedSfixed64_codec);
+            break;
+          }
+          case 330:
+          case 333: {
+            repeatedFloat_.AddEntriesFrom(input, _repeated_repeatedFloat_codec);
+            break;
+          }
+          case 338:
+          case 337: {
+            repeatedDouble_.AddEntriesFrom(input, _repeated_repeatedDouble_codec);
+            break;
+          }
+          case 346:
+          case 344: {
+            repeatedBool_.AddEntriesFrom(input, _repeated_repeatedBool_codec);
+            break;
+          }
+          case 354: {
+            repeatedString_.AddEntriesFrom(input, _repeated_repeatedString_codec);
+            break;
+          }
+          case 362: {
+            repeatedBytes_.AddEntriesFrom(input, _repeated_repeatedBytes_codec);
+            break;
+          }
+          case 386: {
+            repeatedNestedMessage_.AddEntriesFrom(input, _repeated_repeatedNestedMessage_codec);
+            break;
+          }
+          case 394: {
+            repeatedForeignMessage_.AddEntriesFrom(input, _repeated_repeatedForeignMessage_codec);
+            break;
+          }
+          case 410:
+          case 408: {
+            repeatedNestedEnum_.AddEntriesFrom(input, _repeated_repeatedNestedEnum_codec);
+            break;
+          }
+          case 418:
+          case 416: {
+            repeatedForeignEnum_.AddEntriesFrom(input, _repeated_repeatedForeignEnum_codec);
+            break;
+          }
+          case 434: {
+            repeatedStringPiece_.AddEntriesFrom(input, _repeated_repeatedStringPiece_codec);
+            break;
+          }
+          case 442: {
+            repeatedCord_.AddEntriesFrom(input, _repeated_repeatedCord_codec);
+            break;
+          }
+          case 450: {
+            mapInt32Int32_.AddEntriesFrom(input, _map_mapInt32Int32_codec);
+            break;
+          }
+          case 458: {
+            mapInt64Int64_.AddEntriesFrom(input, _map_mapInt64Int64_codec);
+            break;
+          }
+          case 466: {
+            mapUint32Uint32_.AddEntriesFrom(input, _map_mapUint32Uint32_codec);
+            break;
+          }
+          case 474: {
+            mapUint64Uint64_.AddEntriesFrom(input, _map_mapUint64Uint64_codec);
+            break;
+          }
+          case 482: {
+            mapSint32Sint32_.AddEntriesFrom(input, _map_mapSint32Sint32_codec);
+            break;
+          }
+          case 490: {
+            mapSint64Sint64_.AddEntriesFrom(input, _map_mapSint64Sint64_codec);
+            break;
+          }
+          case 498: {
+            mapFixed32Fixed32_.AddEntriesFrom(input, _map_mapFixed32Fixed32_codec);
+            break;
+          }
+          case 506: {
+            mapFixed64Fixed64_.AddEntriesFrom(input, _map_mapFixed64Fixed64_codec);
+            break;
+          }
+          case 514: {
+            mapSfixed32Sfixed32_.AddEntriesFrom(input, _map_mapSfixed32Sfixed32_codec);
+            break;
+          }
+          case 522: {
+            mapSfixed64Sfixed64_.AddEntriesFrom(input, _map_mapSfixed64Sfixed64_codec);
+            break;
+          }
+          case 530: {
+            mapInt32Float_.AddEntriesFrom(input, _map_mapInt32Float_codec);
+            break;
+          }
+          case 538: {
+            mapInt32Double_.AddEntriesFrom(input, _map_mapInt32Double_codec);
+            break;
+          }
+          case 546: {
+            mapBoolBool_.AddEntriesFrom(input, _map_mapBoolBool_codec);
+            break;
+          }
+          case 554: {
+            mapStringString_.AddEntriesFrom(input, _map_mapStringString_codec);
+            break;
+          }
+          case 562: {
+            mapStringBytes_.AddEntriesFrom(input, _map_mapStringBytes_codec);
+            break;
+          }
+          case 570: {
+            mapStringNestedMessage_.AddEntriesFrom(input, _map_mapStringNestedMessage_codec);
+            break;
+          }
+          case 578: {
+            mapStringForeignMessage_.AddEntriesFrom(input, _map_mapStringForeignMessage_codec);
+            break;
+          }
+          case 586: {
+            mapStringNestedEnum_.AddEntriesFrom(input, _map_mapStringNestedEnum_codec);
+            break;
+          }
+          case 594: {
+            mapStringForeignEnum_.AddEntriesFrom(input, _map_mapStringForeignEnum_codec);
+            break;
+          }
+          case 602:
+          case 600: {
+            packedInt32_.AddEntriesFrom(input, _repeated_packedInt32_codec);
+            break;
+          }
+          case 610:
+          case 608: {
+            packedInt64_.AddEntriesFrom(input, _repeated_packedInt64_codec);
+            break;
+          }
+          case 618:
+          case 616: {
+            packedUint32_.AddEntriesFrom(input, _repeated_packedUint32_codec);
+            break;
+          }
+          case 626:
+          case 624: {
+            packedUint64_.AddEntriesFrom(input, _repeated_packedUint64_codec);
+            break;
+          }
+          case 634:
+          case 632: {
+            packedSint32_.AddEntriesFrom(input, _repeated_packedSint32_codec);
+            break;
+          }
+          case 642:
+          case 640: {
+            packedSint64_.AddEntriesFrom(input, _repeated_packedSint64_codec);
+            break;
+          }
+          case 650:
+          case 653: {
+            packedFixed32_.AddEntriesFrom(input, _repeated_packedFixed32_codec);
+            break;
+          }
+          case 658:
+          case 657: {
+            packedFixed64_.AddEntriesFrom(input, _repeated_packedFixed64_codec);
+            break;
+          }
+          case 666:
+          case 669: {
+            packedSfixed32_.AddEntriesFrom(input, _repeated_packedSfixed32_codec);
+            break;
+          }
+          case 674:
+          case 673: {
+            packedSfixed64_.AddEntriesFrom(input, _repeated_packedSfixed64_codec);
+            break;
+          }
+          case 682:
+          case 685: {
+            packedFloat_.AddEntriesFrom(input, _repeated_packedFloat_codec);
+            break;
+          }
+          case 690:
+          case 689: {
+            packedDouble_.AddEntriesFrom(input, _repeated_packedDouble_codec);
+            break;
+          }
+          case 698:
+          case 696: {
+            packedBool_.AddEntriesFrom(input, _repeated_packedBool_codec);
+            break;
+          }
+          case 706:
+          case 704: {
+            packedNestedEnum_.AddEntriesFrom(input, _repeated_packedNestedEnum_codec);
+            break;
+          }
+          case 714:
+          case 712: {
+            unpackedInt32_.AddEntriesFrom(input, _repeated_unpackedInt32_codec);
+            break;
+          }
+          case 722:
+          case 720: {
+            unpackedInt64_.AddEntriesFrom(input, _repeated_unpackedInt64_codec);
+            break;
+          }
+          case 730:
+          case 728: {
+            unpackedUint32_.AddEntriesFrom(input, _repeated_unpackedUint32_codec);
+            break;
+          }
+          case 738:
+          case 736: {
+            unpackedUint64_.AddEntriesFrom(input, _repeated_unpackedUint64_codec);
+            break;
+          }
+          case 746:
+          case 744: {
+            unpackedSint32_.AddEntriesFrom(input, _repeated_unpackedSint32_codec);
+            break;
+          }
+          case 754:
+          case 752: {
+            unpackedSint64_.AddEntriesFrom(input, _repeated_unpackedSint64_codec);
+            break;
+          }
+          case 762:
+          case 765: {
+            unpackedFixed32_.AddEntriesFrom(input, _repeated_unpackedFixed32_codec);
+            break;
+          }
+          case 770:
+          case 769: {
+            unpackedFixed64_.AddEntriesFrom(input, _repeated_unpackedFixed64_codec);
+            break;
+          }
+          case 778:
+          case 781: {
+            unpackedSfixed32_.AddEntriesFrom(input, _repeated_unpackedSfixed32_codec);
+            break;
+          }
+          case 786:
+          case 785: {
+            unpackedSfixed64_.AddEntriesFrom(input, _repeated_unpackedSfixed64_codec);
+            break;
+          }
+          case 794:
+          case 797: {
+            unpackedFloat_.AddEntriesFrom(input, _repeated_unpackedFloat_codec);
+            break;
+          }
+          case 802:
+          case 801: {
+            unpackedDouble_.AddEntriesFrom(input, _repeated_unpackedDouble_codec);
+            break;
+          }
+          case 810:
+          case 808: {
+            unpackedBool_.AddEntriesFrom(input, _repeated_unpackedBool_codec);
+            break;
+          }
+          case 818:
+          case 816: {
+            unpackedNestedEnum_.AddEntriesFrom(input, _repeated_unpackedNestedEnum_codec);
+            break;
+          }
+          case 888: {
+            OneofUint32 = input.ReadUInt32();
+            break;
+          }
+          case 898: {
+            global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.NestedMessage subBuilder = new global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.NestedMessage();
+            if (oneofFieldCase_ == OneofFieldOneofCase.OneofNestedMessage) {
+              subBuilder.MergeFrom(OneofNestedMessage);
+            }
+            input.ReadMessage(subBuilder);
+            OneofNestedMessage = subBuilder;
+            break;
+          }
+          case 906: {
+            OneofString = input.ReadString();
+            break;
+          }
+          case 914: {
+            OneofBytes = input.ReadBytes();
+            break;
+          }
+          case 920: {
+            OneofBool = input.ReadBool();
+            break;
+          }
+          case 928: {
+            OneofUint64 = input.ReadUInt64();
+            break;
+          }
+          case 941: {
+            OneofFloat = input.ReadFloat();
+            break;
+          }
+          case 945: {
+            OneofDouble = input.ReadDouble();
+            break;
+          }
+          case 952: {
+            oneofField_ = input.ReadEnum();
+            oneofFieldCase_ = OneofFieldOneofCase.OneofEnum;
+            break;
+          }
+          case 1611: {
+            if (!HasData) {
+              Data = new global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.Data();
+            }
+            input.ReadGroup(Data);
+            break;
+          }
+          case 3208: {
+            Fieldname1 = input.ReadInt32();
+            break;
+          }
+          case 3216: {
+            FieldName2 = input.ReadInt32();
+            break;
+          }
+          case 3224: {
+            FieldName3 = input.ReadInt32();
+            break;
+          }
+          case 3232: {
+            FieldName4 = input.ReadInt32();
+            break;
+          }
+          case 3240: {
+            Field0Name5 = input.ReadInt32();
+            break;
+          }
+          case 3248: {
+            Field0Name6 = input.ReadInt32();
+            break;
+          }
+          case 3256: {
+            FieldName7 = input.ReadInt32();
+            break;
+          }
+          case 3264: {
+            FieldName8 = input.ReadInt32();
+            break;
+          }
+          case 3272: {
+            FieldName9 = input.ReadInt32();
+            break;
+          }
+          case 3280: {
+            FieldName10 = input.ReadInt32();
+            break;
+          }
+          case 3288: {
+            FIELDNAME11 = input.ReadInt32();
+            break;
+          }
+          case 3296: {
+            FIELDName12 = input.ReadInt32();
+            break;
+          }
+          case 3304: {
+            FieldName13 = input.ReadInt32();
+            break;
+          }
+          case 3312: {
+            FieldName14 = input.ReadInt32();
+            break;
+          }
+          case 3320: {
+            FieldName15 = input.ReadInt32();
+            break;
+          }
+          case 3328: {
+            FieldName16 = input.ReadInt32();
+            break;
+          }
+          case 3336: {
+            FieldName17 = input.ReadInt32();
+            break;
+          }
+          case 3344: {
+            FieldName18 = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -3860,6 +4411,7 @@ namespace ProtobufTestMessages.Proto2 {
         }
       }
     }
+    #endif
 
     public TValue GetExtension<TValue>(pb::Extension<TestAllTypesProto2, TValue> extension) {
       return pb::ExtensionSet.Get(ref _extensions, extension);
@@ -3897,7 +4449,11 @@ namespace ProtobufTestMessages.Proto2 {
         [pbr::OriginalName("NEG")] Neg = -1,
       }
 
-      public sealed partial class NestedMessage : pb::IMessage<NestedMessage>, pb::IBufferMessage {
+      public sealed partial class NestedMessage : pb::IMessage<NestedMessage>
+      #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+          , pb::IBufferMessage
+      #endif
+      {
         private static readonly pb::MessageParser<NestedMessage> _parser = new pb::MessageParser<NestedMessage>(() => new NestedMessage());
         private pb::UnknownFieldSet _unknownFields;
         private int _hasBits0;
@@ -4052,9 +4608,32 @@ namespace ProtobufTestMessages.Proto2 {
 
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         public void MergeFrom(pb::CodedInputStream input) {
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
           input.ReadRawMessage(this);
+        #else
+          uint tag;
+          while ((tag = input.ReadTag()) != 0) {
+            switch(tag) {
+              default:
+                _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+                break;
+              case 8: {
+                A = input.ReadInt32();
+                break;
+              }
+              case 18: {
+                if (corecursive_ == null) {
+                  Corecursive = new global::ProtobufTestMessages.Proto2.TestAllTypesProto2();
+                }
+                input.ReadMessage(Corecursive);
+                break;
+              }
+            }
+          }
+        #endif
         }
 
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
           uint tag;
@@ -4077,13 +4656,18 @@ namespace ProtobufTestMessages.Proto2 {
             }
           }
         }
+        #endif
 
       }
 
       /// <summary>
       /// groups
       /// </summary>
-      public sealed partial class Data : pb::IMessage<Data>, pb::IBufferMessage {
+      public sealed partial class Data : pb::IMessage<Data>
+      #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+          , pb::IBufferMessage
+      #endif
+      {
         private static readonly pb::MessageParser<Data> _parser = new pb::MessageParser<Data>(() => new Data());
         private pb::UnknownFieldSet _unknownFields;
         private int _hasBits0;
@@ -4248,9 +4832,31 @@ namespace ProtobufTestMessages.Proto2 {
 
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         public void MergeFrom(pb::CodedInputStream input) {
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
           input.ReadRawMessage(this);
+        #else
+          uint tag;
+          while ((tag = input.ReadTag()) != 0) {
+            switch(tag) {
+              case 1612:
+                return;
+              default:
+                _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+                break;
+              case 1616: {
+                GroupInt32 = input.ReadInt32();
+                break;
+              }
+              case 1624: {
+                GroupUint32 = input.ReadUInt32();
+                break;
+              }
+            }
+          }
+        #endif
         }
 
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
           uint tag;
@@ -4272,13 +4878,18 @@ namespace ProtobufTestMessages.Proto2 {
             }
           }
         }
+        #endif
 
       }
 
       /// <summary>
       /// message_set test case.
       /// </summary>
-      public sealed partial class MessageSetCorrect : pb::IExtendableMessage<MessageSetCorrect>, pb::IBufferMessage {
+      public sealed partial class MessageSetCorrect : pb::IExtendableMessage<MessageSetCorrect>
+      #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+          , pb::IBufferMessage
+      #endif
+      {
         private static readonly pb::MessageParser<MessageSetCorrect> _parser = new pb::MessageParser<MessageSetCorrect>(() => new MessageSetCorrect());
         private pb::UnknownFieldSet _unknownFields;
         private pb::ExtensionSet<MessageSetCorrect> _extensions;
@@ -4383,9 +4994,23 @@ namespace ProtobufTestMessages.Proto2 {
 
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         public void MergeFrom(pb::CodedInputStream input) {
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
           input.ReadRawMessage(this);
+        #else
+          uint tag;
+          while ((tag = input.ReadTag()) != 0) {
+            switch(tag) {
+              default:
+                if (!pb::ExtensionSet.TryMergeFieldFrom(ref _extensions, input)) {
+                  _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+                }
+                break;
+            }
+          }
+        #endif
         }
 
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
           uint tag;
@@ -4399,6 +5024,7 @@ namespace ProtobufTestMessages.Proto2 {
             }
           }
         }
+        #endif
 
         public TValue GetExtension<TValue>(pb::Extension<MessageSetCorrect, TValue> extension) {
           return pb::ExtensionSet.Get(ref _extensions, extension);
@@ -4424,7 +5050,11 @@ namespace ProtobufTestMessages.Proto2 {
 
       }
 
-      public sealed partial class MessageSetCorrectExtension1 : pb::IMessage<MessageSetCorrectExtension1>, pb::IBufferMessage {
+      public sealed partial class MessageSetCorrectExtension1 : pb::IMessage<MessageSetCorrectExtension1>
+      #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+          , pb::IBufferMessage
+      #endif
+      {
         private static readonly pb::MessageParser<MessageSetCorrectExtension1> _parser = new pb::MessageParser<MessageSetCorrectExtension1>(() => new MessageSetCorrectExtension1());
         private pb::UnknownFieldSet _unknownFields;
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -4549,9 +5179,25 @@ namespace ProtobufTestMessages.Proto2 {
 
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         public void MergeFrom(pb::CodedInputStream input) {
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
           input.ReadRawMessage(this);
+        #else
+          uint tag;
+          while ((tag = input.ReadTag()) != 0) {
+            switch(tag) {
+              default:
+                _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+                break;
+              case 202: {
+                Str = input.ReadString();
+                break;
+              }
+            }
+          }
+        #endif
         }
 
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
           uint tag;
@@ -4567,6 +5213,7 @@ namespace ProtobufTestMessages.Proto2 {
             }
           }
         }
+        #endif
 
         #region Extensions
         /// <summary>Container for extensions for other messages declared in the MessageSetCorrectExtension1 message type.</summary>
@@ -4579,7 +5226,11 @@ namespace ProtobufTestMessages.Proto2 {
 
       }
 
-      public sealed partial class MessageSetCorrectExtension2 : pb::IMessage<MessageSetCorrectExtension2>, pb::IBufferMessage {
+      public sealed partial class MessageSetCorrectExtension2 : pb::IMessage<MessageSetCorrectExtension2>
+      #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+          , pb::IBufferMessage
+      #endif
+      {
         private static readonly pb::MessageParser<MessageSetCorrectExtension2> _parser = new pb::MessageParser<MessageSetCorrectExtension2>(() => new MessageSetCorrectExtension2());
         private pb::UnknownFieldSet _unknownFields;
         private int _hasBits0;
@@ -4707,9 +5358,25 @@ namespace ProtobufTestMessages.Proto2 {
 
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         public void MergeFrom(pb::CodedInputStream input) {
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
           input.ReadRawMessage(this);
+        #else
+          uint tag;
+          while ((tag = input.ReadTag()) != 0) {
+            switch(tag) {
+              default:
+                _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+                break;
+              case 72: {
+                I = input.ReadInt32();
+                break;
+              }
+            }
+          }
+        #endif
         }
 
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
           uint tag;
@@ -4725,6 +5392,7 @@ namespace ProtobufTestMessages.Proto2 {
             }
           }
         }
+        #endif
 
         #region Extensions
         /// <summary>Container for extensions for other messages declared in the MessageSetCorrectExtension2 message type.</summary>
@@ -4742,7 +5410,11 @@ namespace ProtobufTestMessages.Proto2 {
 
   }
 
-  public sealed partial class ForeignMessageProto2 : pb::IMessage<ForeignMessageProto2>, pb::IBufferMessage {
+  public sealed partial class ForeignMessageProto2 : pb::IMessage<ForeignMessageProto2>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<ForeignMessageProto2> _parser = new pb::MessageParser<ForeignMessageProto2>(() => new ForeignMessageProto2());
     private pb::UnknownFieldSet _unknownFields;
     private int _hasBits0;
@@ -4870,9 +5542,25 @@ namespace ProtobufTestMessages.Proto2 {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            C = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -4888,10 +5576,15 @@ namespace ProtobufTestMessages.Proto2 {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class UnknownToTestAllTypes : pb::IMessage<UnknownToTestAllTypes>, pb::IBufferMessage {
+  public sealed partial class UnknownToTestAllTypes : pb::IMessage<UnknownToTestAllTypes>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<UnknownToTestAllTypes> _parser = new pb::MessageParser<UnknownToTestAllTypes>(() => new UnknownToTestAllTypes());
     private pb::UnknownFieldSet _unknownFields;
     private int _hasBits0;
@@ -5173,9 +5866,52 @@ namespace ProtobufTestMessages.Proto2 {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8008: {
+            OptionalInt32 = input.ReadInt32();
+            break;
+          }
+          case 8018: {
+            OptionalString = input.ReadString();
+            break;
+          }
+          case 8026: {
+            if (nestedMessage_ == null) {
+              NestedMessage = new global::ProtobufTestMessages.Proto2.ForeignMessageProto2();
+            }
+            input.ReadMessage(NestedMessage);
+            break;
+          }
+          case 8035: {
+            if (!HasOptionalGroup) {
+              OptionalGroup = new global::ProtobufTestMessages.Proto2.UnknownToTestAllTypes.Types.OptionalGroup();
+            }
+            input.ReadGroup(OptionalGroup);
+            break;
+          }
+          case 8048: {
+            OptionalBool = input.ReadBool();
+            break;
+          }
+          case 8090:
+          case 8088: {
+            repeatedInt32_.AddEntriesFrom(input, _repeated_repeatedInt32_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -5218,12 +5954,17 @@ namespace ProtobufTestMessages.Proto2 {
         }
       }
     }
+    #endif
 
     #region Nested types
     /// <summary>Container for nested types declared in the UnknownToTestAllTypes message type.</summary>
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public static partial class Types {
-      public sealed partial class OptionalGroup : pb::IMessage<OptionalGroup>, pb::IBufferMessage {
+      public sealed partial class OptionalGroup : pb::IMessage<OptionalGroup>
+      #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+          , pb::IBufferMessage
+      #endif
+      {
         private static readonly pb::MessageParser<OptionalGroup> _parser = new pb::MessageParser<OptionalGroup>(() => new OptionalGroup());
         private pb::UnknownFieldSet _unknownFields;
         private int _hasBits0;
@@ -5351,9 +6092,27 @@ namespace ProtobufTestMessages.Proto2 {
 
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         public void MergeFrom(pb::CodedInputStream input) {
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
           input.ReadRawMessage(this);
+        #else
+          uint tag;
+          while ((tag = input.ReadTag()) != 0) {
+            switch(tag) {
+              case 8036:
+                return;
+              default:
+                _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+                break;
+              case 8: {
+                A = input.ReadInt32();
+                break;
+              }
+            }
+          }
+        #endif
         }
 
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
           uint tag;
@@ -5371,6 +6130,7 @@ namespace ProtobufTestMessages.Proto2 {
             }
           }
         }
+        #endif
 
       }
 

csharp/src/Google.Protobuf.Test.TestProtos/TestMessagesProto3.cs

@@ -259,7 +259,11 @@ namespace ProtobufTestMessages.Proto3 {
   /// could trigger bugs that occur in any message type in this file.  We verify
   /// this stays true in a unit test.
   /// </summary>
-  public sealed partial class TestAllTypesProto3 : pb::IMessage<TestAllTypesProto3>, pb::IBufferMessage {
+  public sealed partial class TestAllTypesProto3 : pb::IMessage<TestAllTypesProto3>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<TestAllTypesProto3> _parser = new pb::MessageParser<TestAllTypesProto3>(() => new TestAllTypesProto3());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -3383,9 +3387,720 @@ namespace ProtobufTestMessages.Proto3 {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            OptionalInt32 = input.ReadInt32();
+            break;
+          }
+          case 16: {
+            OptionalInt64 = input.ReadInt64();
+            break;
+          }
+          case 24: {
+            OptionalUint32 = input.ReadUInt32();
+            break;
+          }
+          case 32: {
+            OptionalUint64 = input.ReadUInt64();
+            break;
+          }
+          case 40: {
+            OptionalSint32 = input.ReadSInt32();
+            break;
+          }
+          case 48: {
+            OptionalSint64 = input.ReadSInt64();
+            break;
+          }
+          case 61: {
+            OptionalFixed32 = input.ReadFixed32();
+            break;
+          }
+          case 65: {
+            OptionalFixed64 = input.ReadFixed64();
+            break;
+          }
+          case 77: {
+            OptionalSfixed32 = input.ReadSFixed32();
+            break;
+          }
+          case 81: {
+            OptionalSfixed64 = input.ReadSFixed64();
+            break;
+          }
+          case 93: {
+            OptionalFloat = input.ReadFloat();
+            break;
+          }
+          case 97: {
+            OptionalDouble = input.ReadDouble();
+            break;
+          }
+          case 104: {
+            OptionalBool = input.ReadBool();
+            break;
+          }
+          case 114: {
+            OptionalString = input.ReadString();
+            break;
+          }
+          case 122: {
+            OptionalBytes = input.ReadBytes();
+            break;
+          }
+          case 146: {
+            if (optionalNestedMessage_ == null) {
+              OptionalNestedMessage = new global::ProtobufTestMessages.Proto3.TestAllTypesProto3.Types.NestedMessage();
+            }
+            input.ReadMessage(OptionalNestedMessage);
+            break;
+          }
+          case 154: {
+            if (optionalForeignMessage_ == null) {
+              OptionalForeignMessage = new global::ProtobufTestMessages.Proto3.ForeignMessage();
+            }
+            input.ReadMessage(OptionalForeignMessage);
+            break;
+          }
+          case 168: {
+            OptionalNestedEnum = (global::ProtobufTestMessages.Proto3.TestAllTypesProto3.Types.NestedEnum) input.ReadEnum();
+            break;
+          }
+          case 176: {
+            OptionalForeignEnum = (global::ProtobufTestMessages.Proto3.ForeignEnum) input.ReadEnum();
+            break;
+          }
+          case 184: {
+            OptionalAliasedEnum = (global::ProtobufTestMessages.Proto3.TestAllTypesProto3.Types.AliasedEnum) input.ReadEnum();
+            break;
+          }
+          case 194: {
+            OptionalStringPiece = input.ReadString();
+            break;
+          }
+          case 202: {
+            OptionalCord = input.ReadString();
+            break;
+          }
+          case 218: {
+            if (recursiveMessage_ == null) {
+              RecursiveMessage = new global::ProtobufTestMessages.Proto3.TestAllTypesProto3();
+            }
+            input.ReadMessage(RecursiveMessage);
+            break;
+          }
+          case 250:
+          case 248: {
+            repeatedInt32_.AddEntriesFrom(input, _repeated_repeatedInt32_codec);
+            break;
+          }
+          case 258:
+          case 256: {
+            repeatedInt64_.AddEntriesFrom(input, _repeated_repeatedInt64_codec);
+            break;
+          }
+          case 266:
+          case 264: {
+            repeatedUint32_.AddEntriesFrom(input, _repeated_repeatedUint32_codec);
+            break;
+          }
+          case 274:
+          case 272: {
+            repeatedUint64_.AddEntriesFrom(input, _repeated_repeatedUint64_codec);
+            break;
+          }
+          case 282:
+          case 280: {
+            repeatedSint32_.AddEntriesFrom(input, _repeated_repeatedSint32_codec);
+            break;
+          }
+          case 290:
+          case 288: {
+            repeatedSint64_.AddEntriesFrom(input, _repeated_repeatedSint64_codec);
+            break;
+          }
+          case 298:
+          case 301: {
+            repeatedFixed32_.AddEntriesFrom(input, _repeated_repeatedFixed32_codec);
+            break;
+          }
+          case 306:
+          case 305: {
+            repeatedFixed64_.AddEntriesFrom(input, _repeated_repeatedFixed64_codec);
+            break;
+          }
+          case 314:
+          case 317: {
+            repeatedSfixed32_.AddEntriesFrom(input, _repeated_repeatedSfixed32_codec);
+            break;
+          }
+          case 322:
+          case 321: {
+            repeatedSfixed64_.AddEntriesFrom(input, _repeated_repeatedSfixed64_codec);
+            break;
+          }
+          case 330:
+          case 333: {
+            repeatedFloat_.AddEntriesFrom(input, _repeated_repeatedFloat_codec);
+            break;
+          }
+          case 338:
+          case 337: {
+            repeatedDouble_.AddEntriesFrom(input, _repeated_repeatedDouble_codec);
+            break;
+          }
+          case 346:
+          case 344: {
+            repeatedBool_.AddEntriesFrom(input, _repeated_repeatedBool_codec);
+            break;
+          }
+          case 354: {
+            repeatedString_.AddEntriesFrom(input, _repeated_repeatedString_codec);
+            break;
+          }
+          case 362: {
+            repeatedBytes_.AddEntriesFrom(input, _repeated_repeatedBytes_codec);
+            break;
+          }
+          case 386: {
+            repeatedNestedMessage_.AddEntriesFrom(input, _repeated_repeatedNestedMessage_codec);
+            break;
+          }
+          case 394: {
+            repeatedForeignMessage_.AddEntriesFrom(input, _repeated_repeatedForeignMessage_codec);
+            break;
+          }
+          case 410:
+          case 408: {
+            repeatedNestedEnum_.AddEntriesFrom(input, _repeated_repeatedNestedEnum_codec);
+            break;
+          }
+          case 418:
+          case 416: {
+            repeatedForeignEnum_.AddEntriesFrom(input, _repeated_repeatedForeignEnum_codec);
+            break;
+          }
+          case 434: {
+            repeatedStringPiece_.AddEntriesFrom(input, _repeated_repeatedStringPiece_codec);
+            break;
+          }
+          case 442: {
+            repeatedCord_.AddEntriesFrom(input, _repeated_repeatedCord_codec);
+            break;
+          }
+          case 450: {
+            mapInt32Int32_.AddEntriesFrom(input, _map_mapInt32Int32_codec);
+            break;
+          }
+          case 458: {
+            mapInt64Int64_.AddEntriesFrom(input, _map_mapInt64Int64_codec);
+            break;
+          }
+          case 466: {
+            mapUint32Uint32_.AddEntriesFrom(input, _map_mapUint32Uint32_codec);
+            break;
+          }
+          case 474: {
+            mapUint64Uint64_.AddEntriesFrom(input, _map_mapUint64Uint64_codec);
+            break;
+          }
+          case 482: {
+            mapSint32Sint32_.AddEntriesFrom(input, _map_mapSint32Sint32_codec);
+            break;
+          }
+          case 490: {
+            mapSint64Sint64_.AddEntriesFrom(input, _map_mapSint64Sint64_codec);
+            break;
+          }
+          case 498: {
+            mapFixed32Fixed32_.AddEntriesFrom(input, _map_mapFixed32Fixed32_codec);
+            break;
+          }
+          case 506: {
+            mapFixed64Fixed64_.AddEntriesFrom(input, _map_mapFixed64Fixed64_codec);
+            break;
+          }
+          case 514: {
+            mapSfixed32Sfixed32_.AddEntriesFrom(input, _map_mapSfixed32Sfixed32_codec);
+            break;
+          }
+          case 522: {
+            mapSfixed64Sfixed64_.AddEntriesFrom(input, _map_mapSfixed64Sfixed64_codec);
+            break;
+          }
+          case 530: {
+            mapInt32Float_.AddEntriesFrom(input, _map_mapInt32Float_codec);
+            break;
+          }
+          case 538: {
+            mapInt32Double_.AddEntriesFrom(input, _map_mapInt32Double_codec);
+            break;
+          }
+          case 546: {
+            mapBoolBool_.AddEntriesFrom(input, _map_mapBoolBool_codec);
+            break;
+          }
+          case 554: {
+            mapStringString_.AddEntriesFrom(input, _map_mapStringString_codec);
+            break;
+          }
+          case 562: {
+            mapStringBytes_.AddEntriesFrom(input, _map_mapStringBytes_codec);
+            break;
+          }
+          case 570: {
+            mapStringNestedMessage_.AddEntriesFrom(input, _map_mapStringNestedMessage_codec);
+            break;
+          }
+          case 578: {
+            mapStringForeignMessage_.AddEntriesFrom(input, _map_mapStringForeignMessage_codec);
+            break;
+          }
+          case 586: {
+            mapStringNestedEnum_.AddEntriesFrom(input, _map_mapStringNestedEnum_codec);
+            break;
+          }
+          case 594: {
+            mapStringForeignEnum_.AddEntriesFrom(input, _map_mapStringForeignEnum_codec);
+            break;
+          }
+          case 602:
+          case 600: {
+            packedInt32_.AddEntriesFrom(input, _repeated_packedInt32_codec);
+            break;
+          }
+          case 610:
+          case 608: {
+            packedInt64_.AddEntriesFrom(input, _repeated_packedInt64_codec);
+            break;
+          }
+          case 618:
+          case 616: {
+            packedUint32_.AddEntriesFrom(input, _repeated_packedUint32_codec);
+            break;
+          }
+          case 626:
+          case 624: {
+            packedUint64_.AddEntriesFrom(input, _repeated_packedUint64_codec);
+            break;
+          }
+          case 634:
+          case 632: {
+            packedSint32_.AddEntriesFrom(input, _repeated_packedSint32_codec);
+            break;
+          }
+          case 642:
+          case 640: {
+            packedSint64_.AddEntriesFrom(input, _repeated_packedSint64_codec);
+            break;
+          }
+          case 650:
+          case 653: {
+            packedFixed32_.AddEntriesFrom(input, _repeated_packedFixed32_codec);
+            break;
+          }
+          case 658:
+          case 657: {
+            packedFixed64_.AddEntriesFrom(input, _repeated_packedFixed64_codec);
+            break;
+          }
+          case 666:
+          case 669: {
+            packedSfixed32_.AddEntriesFrom(input, _repeated_packedSfixed32_codec);
+            break;
+          }
+          case 674:
+          case 673: {
+            packedSfixed64_.AddEntriesFrom(input, _repeated_packedSfixed64_codec);
+            break;
+          }
+          case 682:
+          case 685: {
+            packedFloat_.AddEntriesFrom(input, _repeated_packedFloat_codec);
+            break;
+          }
+          case 690:
+          case 689: {
+            packedDouble_.AddEntriesFrom(input, _repeated_packedDouble_codec);
+            break;
+          }
+          case 698:
+          case 696: {
+            packedBool_.AddEntriesFrom(input, _repeated_packedBool_codec);
+            break;
+          }
+          case 706:
+          case 704: {
+            packedNestedEnum_.AddEntriesFrom(input, _repeated_packedNestedEnum_codec);
+            break;
+          }
+          case 714:
+          case 712: {
+            unpackedInt32_.AddEntriesFrom(input, _repeated_unpackedInt32_codec);
+            break;
+          }
+          case 722:
+          case 720: {
+            unpackedInt64_.AddEntriesFrom(input, _repeated_unpackedInt64_codec);
+            break;
+          }
+          case 730:
+          case 728: {
+            unpackedUint32_.AddEntriesFrom(input, _repeated_unpackedUint32_codec);
+            break;
+          }
+          case 738:
+          case 736: {
+            unpackedUint64_.AddEntriesFrom(input, _repeated_unpackedUint64_codec);
+            break;
+          }
+          case 746:
+          case 744: {
+            unpackedSint32_.AddEntriesFrom(input, _repeated_unpackedSint32_codec);
+            break;
+          }
+          case 754:
+          case 752: {
+            unpackedSint64_.AddEntriesFrom(input, _repeated_unpackedSint64_codec);
+            break;
+          }
+          case 762:
+          case 765: {
+            unpackedFixed32_.AddEntriesFrom(input, _repeated_unpackedFixed32_codec);
+            break;
+          }
+          case 770:
+          case 769: {
+            unpackedFixed64_.AddEntriesFrom(input, _repeated_unpackedFixed64_codec);
+            break;
+          }
+          case 778:
+          case 781: {
+            unpackedSfixed32_.AddEntriesFrom(input, _repeated_unpackedSfixed32_codec);
+            break;
+          }
+          case 786:
+          case 785: {
+            unpackedSfixed64_.AddEntriesFrom(input, _repeated_unpackedSfixed64_codec);
+            break;
+          }
+          case 794:
+          case 797: {
+            unpackedFloat_.AddEntriesFrom(input, _repeated_unpackedFloat_codec);
+            break;
+          }
+          case 802:
+          case 801: {
+            unpackedDouble_.AddEntriesFrom(input, _repeated_unpackedDouble_codec);
+            break;
+          }
+          case 810:
+          case 808: {
+            unpackedBool_.AddEntriesFrom(input, _repeated_unpackedBool_codec);
+            break;
+          }
+          case 818:
+          case 816: {
+            unpackedNestedEnum_.AddEntriesFrom(input, _repeated_unpackedNestedEnum_codec);
+            break;
+          }
+          case 888: {
+            OneofUint32 = input.ReadUInt32();
+            break;
+          }
+          case 898: {
+            global::ProtobufTestMessages.Proto3.TestAllTypesProto3.Types.NestedMessage subBuilder = new global::ProtobufTestMessages.Proto3.TestAllTypesProto3.Types.NestedMessage();
+            if (oneofFieldCase_ == OneofFieldOneofCase.OneofNestedMessage) {
+              subBuilder.MergeFrom(OneofNestedMessage);
+            }
+            input.ReadMessage(subBuilder);
+            OneofNestedMessage = subBuilder;
+            break;
+          }
+          case 906: {
+            OneofString = input.ReadString();
+            break;
+          }
+          case 914: {
+            OneofBytes = input.ReadBytes();
+            break;
+          }
+          case 920: {
+            OneofBool = input.ReadBool();
+            break;
+          }
+          case 928: {
+            OneofUint64 = input.ReadUInt64();
+            break;
+          }
+          case 941: {
+            OneofFloat = input.ReadFloat();
+            break;
+          }
+          case 945: {
+            OneofDouble = input.ReadDouble();
+            break;
+          }
+          case 952: {
+            oneofField_ = input.ReadEnum();
+            oneofFieldCase_ = OneofFieldOneofCase.OneofEnum;
+            break;
+          }
+          case 1610: {
+            bool? value = _single_optionalBoolWrapper_codec.Read(input);
+            if (optionalBoolWrapper_ == null || value != false) {
+              OptionalBoolWrapper = value;
+            }
+            break;
+          }
+          case 1618: {
+            int? value = _single_optionalInt32Wrapper_codec.Read(input);
+            if (optionalInt32Wrapper_ == null || value != 0) {
+              OptionalInt32Wrapper = value;
+            }
+            break;
+          }
+          case 1626: {
+            long? value = _single_optionalInt64Wrapper_codec.Read(input);
+            if (optionalInt64Wrapper_ == null || value != 0L) {
+              OptionalInt64Wrapper = value;
+            }
+            break;
+          }
+          case 1634: {
+            uint? value = _single_optionalUint32Wrapper_codec.Read(input);
+            if (optionalUint32Wrapper_ == null || value != 0) {
+              OptionalUint32Wrapper = value;
+            }
+            break;
+          }
+          case 1642: {
+            ulong? value = _single_optionalUint64Wrapper_codec.Read(input);
+            if (optionalUint64Wrapper_ == null || value != 0UL) {
+              OptionalUint64Wrapper = value;
+            }
+            break;
+          }
+          case 1650: {
+            float? value = _single_optionalFloatWrapper_codec.Read(input);
+            if (optionalFloatWrapper_ == null || value != 0F) {
+              OptionalFloatWrapper = value;
+            }
+            break;
+          }
+          case 1658: {
+            double? value = _single_optionalDoubleWrapper_codec.Read(input);
+            if (optionalDoubleWrapper_ == null || value != 0D) {
+              OptionalDoubleWrapper = value;
+            }
+            break;
+          }
+          case 1666: {
+            string value = _single_optionalStringWrapper_codec.Read(input);
+            if (optionalStringWrapper_ == null || value != "") {
+              OptionalStringWrapper = value;
+            }
+            break;
+          }
+          case 1674: {
+            pb::ByteString value = _single_optionalBytesWrapper_codec.Read(input);
+            if (optionalBytesWrapper_ == null || value != pb::ByteString.Empty) {
+              OptionalBytesWrapper = value;
+            }
+            break;
+          }
+          case 1690: {
+            repeatedBoolWrapper_.AddEntriesFrom(input, _repeated_repeatedBoolWrapper_codec);
+            break;
+          }
+          case 1698: {
+            repeatedInt32Wrapper_.AddEntriesFrom(input, _repeated_repeatedInt32Wrapper_codec);
+            break;
+          }
+          case 1706: {
+            repeatedInt64Wrapper_.AddEntriesFrom(input, _repeated_repeatedInt64Wrapper_codec);
+            break;
+          }
+          case 1714: {
+            repeatedUint32Wrapper_.AddEntriesFrom(input, _repeated_repeatedUint32Wrapper_codec);
+            break;
+          }
+          case 1722: {
+            repeatedUint64Wrapper_.AddEntriesFrom(input, _repeated_repeatedUint64Wrapper_codec);
+            break;
+          }
+          case 1730: {
+            repeatedFloatWrapper_.AddEntriesFrom(input, _repeated_repeatedFloatWrapper_codec);
+            break;
+          }
+          case 1738: {
+            repeatedDoubleWrapper_.AddEntriesFrom(input, _repeated_repeatedDoubleWrapper_codec);
+            break;
+          }
+          case 1746: {
+            repeatedStringWrapper_.AddEntriesFrom(input, _repeated_repeatedStringWrapper_codec);
+            break;
+          }
+          case 1754: {
+            repeatedBytesWrapper_.AddEntriesFrom(input, _repeated_repeatedBytesWrapper_codec);
+            break;
+          }
+          case 2410: {
+            if (optionalDuration_ == null) {
+              OptionalDuration = new global::Google.Protobuf.WellKnownTypes.Duration();
+            }
+            input.ReadMessage(OptionalDuration);
+            break;
+          }
+          case 2418: {
+            if (optionalTimestamp_ == null) {
+              OptionalTimestamp = new global::Google.Protobuf.WellKnownTypes.Timestamp();
+            }
+            input.ReadMessage(OptionalTimestamp);
+            break;
+          }
+          case 2426: {
+            if (optionalFieldMask_ == null) {
+              OptionalFieldMask = new global::Google.Protobuf.WellKnownTypes.FieldMask();
+            }
+            input.ReadMessage(OptionalFieldMask);
+            break;
+          }
+          case 2434: {
+            if (optionalStruct_ == null) {
+              OptionalStruct = new global::Google.Protobuf.WellKnownTypes.Struct();
+            }
+            input.ReadMessage(OptionalStruct);
+            break;
+          }
+          case 2442: {
+            if (optionalAny_ == null) {
+              OptionalAny = new global::Google.Protobuf.WellKnownTypes.Any();
+            }
+            input.ReadMessage(OptionalAny);
+            break;
+          }
+          case 2450: {
+            if (optionalValue_ == null) {
+              OptionalValue = new global::Google.Protobuf.WellKnownTypes.Value();
+            }
+            input.ReadMessage(OptionalValue);
+            break;
+          }
+          case 2490: {
+            repeatedDuration_.AddEntriesFrom(input, _repeated_repeatedDuration_codec);
+            break;
+          }
+          case 2498: {
+            repeatedTimestamp_.AddEntriesFrom(input, _repeated_repeatedTimestamp_codec);
+            break;
+          }
+          case 2506: {
+            repeatedFieldmask_.AddEntriesFrom(input, _repeated_repeatedFieldmask_codec);
+            break;
+          }
+          case 2522: {
+            repeatedAny_.AddEntriesFrom(input, _repeated_repeatedAny_codec);
+            break;
+          }
+          case 2530: {
+            repeatedValue_.AddEntriesFrom(input, _repeated_repeatedValue_codec);
+            break;
+          }
+          case 2538: {
+            repeatedListValue_.AddEntriesFrom(input, _repeated_repeatedListValue_codec);
+            break;
+          }
+          case 2594: {
+            repeatedStruct_.AddEntriesFrom(input, _repeated_repeatedStruct_codec);
+            break;
+          }
+          case 3208: {
+            Fieldname1 = input.ReadInt32();
+            break;
+          }
+          case 3216: {
+            FieldName2 = input.ReadInt32();
+            break;
+          }
+          case 3224: {
+            FieldName3 = input.ReadInt32();
+            break;
+          }
+          case 3232: {
+            FieldName4 = input.ReadInt32();
+            break;
+          }
+          case 3240: {
+            Field0Name5 = input.ReadInt32();
+            break;
+          }
+          case 3248: {
+            Field0Name6 = input.ReadInt32();
+            break;
+          }
+          case 3256: {
+            FieldName7 = input.ReadInt32();
+            break;
+          }
+          case 3264: {
+            FieldName8 = input.ReadInt32();
+            break;
+          }
+          case 3272: {
+            FieldName9 = input.ReadInt32();
+            break;
+          }
+          case 3280: {
+            FieldName10 = input.ReadInt32();
+            break;
+          }
+          case 3288: {
+            FIELDNAME11 = input.ReadInt32();
+            break;
+          }
+          case 3296: {
+            FIELDName12 = input.ReadInt32();
+            break;
+          }
+          case 3304: {
+            FieldName13 = input.ReadInt32();
+            break;
+          }
+          case 3312: {
+            FieldName14 = input.ReadInt32();
+            break;
+          }
+          case 3320: {
+            FieldName15 = input.ReadInt32();
+            break;
+          }
+          case 3328: {
+            FieldName16 = input.ReadInt32();
+            break;
+          }
+          case 3336: {
+            FieldName17 = input.ReadInt32();
+            break;
+          }
+          case 3344: {
+            FieldName18 = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -4096,6 +4811,7 @@ namespace ProtobufTestMessages.Proto3 {
         }
       }
     }
+    #endif
 
     #region Nested types
     /// <summary>Container for nested types declared in the TestAllTypesProto3 message type.</summary>
@@ -4120,7 +4836,11 @@ namespace ProtobufTestMessages.Proto3 {
         [pbr::OriginalName("bAz", PreferredAlias = false)] BAz = 2,
       }
 
-      public sealed partial class NestedMessage : pb::IMessage<NestedMessage>, pb::IBufferMessage {
+      public sealed partial class NestedMessage : pb::IMessage<NestedMessage>
+      #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+          , pb::IBufferMessage
+      #endif
+      {
         private static readonly pb::MessageParser<NestedMessage> _parser = new pb::MessageParser<NestedMessage>(() => new NestedMessage());
         private pb::UnknownFieldSet _unknownFields;
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -4260,9 +4980,32 @@ namespace ProtobufTestMessages.Proto3 {
 
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         public void MergeFrom(pb::CodedInputStream input) {
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
           input.ReadRawMessage(this);
+        #else
+          uint tag;
+          while ((tag = input.ReadTag()) != 0) {
+            switch(tag) {
+              default:
+                _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+                break;
+              case 8: {
+                A = input.ReadInt32();
+                break;
+              }
+              case 18: {
+                if (corecursive_ == null) {
+                  Corecursive = new global::ProtobufTestMessages.Proto3.TestAllTypesProto3();
+                }
+                input.ReadMessage(Corecursive);
+                break;
+              }
+            }
+          }
+        #endif
         }
 
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
           uint tag;
@@ -4285,6 +5028,7 @@ namespace ProtobufTestMessages.Proto3 {
             }
           }
         }
+        #endif
 
       }
 
@@ -4293,7 +5037,11 @@ namespace ProtobufTestMessages.Proto3 {
 
   }
 
-  public sealed partial class ForeignMessage : pb::IMessage<ForeignMessage>, pb::IBufferMessage {
+  public sealed partial class ForeignMessage : pb::IMessage<ForeignMessage>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<ForeignMessage> _parser = new pb::MessageParser<ForeignMessage>(() => new ForeignMessage());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -4406,9 +5154,25 @@ namespace ProtobufTestMessages.Proto3 {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            C = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -4424,6 +5188,7 @@ namespace ProtobufTestMessages.Proto3 {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf.Test.TestProtos/UnittestCustomOptionsProto3.cs

@@ -257,7 +257,11 @@ namespace UnitTest.Issues.TestProtos {
   /// A test message with custom options at all possible locations (and also some
   /// regular options, to make sure they interact nicely).
   /// </summary>
-  public sealed partial class TestMessageWithCustomOptions : pb::IMessage<TestMessageWithCustomOptions>, pb::IBufferMessage {
+  public sealed partial class TestMessageWithCustomOptions : pb::IMessage<TestMessageWithCustomOptions>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<TestMessageWithCustomOptions> _parser = new pb::MessageParser<TestMessageWithCustomOptions>(() => new TestMessageWithCustomOptions());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -422,9 +426,29 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            Field1 = input.ReadString();
+            break;
+          }
+          case 16: {
+            OneofField = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -444,6 +468,7 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
     #region Nested types
     /// <summary>Container for nested types declared in the TestMessageWithCustomOptions message type.</summary>
@@ -464,7 +489,11 @@ namespace UnitTest.Issues.TestProtos {
   /// A test RPC service with custom options at all possible locations (and also
   /// some regular options, to make sure they interact nicely).
   /// </summary>
-  public sealed partial class CustomOptionFooRequest : pb::IMessage<CustomOptionFooRequest>, pb::IBufferMessage {
+  public sealed partial class CustomOptionFooRequest : pb::IMessage<CustomOptionFooRequest>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<CustomOptionFooRequest> _parser = new pb::MessageParser<CustomOptionFooRequest>(() => new CustomOptionFooRequest());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -553,9 +582,21 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -567,10 +608,15 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class CustomOptionFooResponse : pb::IMessage<CustomOptionFooResponse>, pb::IBufferMessage {
+  public sealed partial class CustomOptionFooResponse : pb::IMessage<CustomOptionFooResponse>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<CustomOptionFooResponse> _parser = new pb::MessageParser<CustomOptionFooResponse>(() => new CustomOptionFooResponse());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -659,9 +705,21 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -673,10 +731,15 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class CustomOptionFooClientMessage : pb::IMessage<CustomOptionFooClientMessage>, pb::IBufferMessage {
+  public sealed partial class CustomOptionFooClientMessage : pb::IMessage<CustomOptionFooClientMessage>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<CustomOptionFooClientMessage> _parser = new pb::MessageParser<CustomOptionFooClientMessage>(() => new CustomOptionFooClientMessage());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -765,9 +828,21 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -779,10 +854,15 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class CustomOptionFooServerMessage : pb::IMessage<CustomOptionFooServerMessage>, pb::IBufferMessage {
+  public sealed partial class CustomOptionFooServerMessage : pb::IMessage<CustomOptionFooServerMessage>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<CustomOptionFooServerMessage> _parser = new pb::MessageParser<CustomOptionFooServerMessage>(() => new CustomOptionFooServerMessage());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -871,9 +951,21 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -885,10 +977,15 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class DummyMessageContainingEnum : pb::IMessage<DummyMessageContainingEnum>, pb::IBufferMessage {
+  public sealed partial class DummyMessageContainingEnum : pb::IMessage<DummyMessageContainingEnum>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<DummyMessageContainingEnum> _parser = new pb::MessageParser<DummyMessageContainingEnum>(() => new DummyMessageContainingEnum());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -977,9 +1074,21 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -991,6 +1100,7 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
     #region Nested types
     /// <summary>Container for nested types declared in the DummyMessageContainingEnum message type.</summary>
@@ -1007,7 +1117,11 @@ namespace UnitTest.Issues.TestProtos {
 
   }
 
-  public sealed partial class DummyMessageInvalidAsOptionType : pb::IMessage<DummyMessageInvalidAsOptionType>, pb::IBufferMessage {
+  public sealed partial class DummyMessageInvalidAsOptionType : pb::IMessage<DummyMessageInvalidAsOptionType>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<DummyMessageInvalidAsOptionType> _parser = new pb::MessageParser<DummyMessageInvalidAsOptionType>(() => new DummyMessageInvalidAsOptionType());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1096,9 +1210,21 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1110,10 +1236,15 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class CustomOptionMinIntegerValues : pb::IMessage<CustomOptionMinIntegerValues>, pb::IBufferMessage {
+  public sealed partial class CustomOptionMinIntegerValues : pb::IMessage<CustomOptionMinIntegerValues>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<CustomOptionMinIntegerValues> _parser = new pb::MessageParser<CustomOptionMinIntegerValues>(() => new CustomOptionMinIntegerValues());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1202,9 +1333,21 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1216,10 +1359,15 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class CustomOptionMaxIntegerValues : pb::IMessage<CustomOptionMaxIntegerValues>, pb::IBufferMessage {
+  public sealed partial class CustomOptionMaxIntegerValues : pb::IMessage<CustomOptionMaxIntegerValues>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<CustomOptionMaxIntegerValues> _parser = new pb::MessageParser<CustomOptionMaxIntegerValues>(() => new CustomOptionMaxIntegerValues());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1308,9 +1456,21 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1322,10 +1482,15 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class CustomOptionOtherValues : pb::IMessage<CustomOptionOtherValues>, pb::IBufferMessage {
+  public sealed partial class CustomOptionOtherValues : pb::IMessage<CustomOptionOtherValues>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<CustomOptionOtherValues> _parser = new pb::MessageParser<CustomOptionOtherValues>(() => new CustomOptionOtherValues());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1414,9 +1579,21 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1428,10 +1605,15 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class SettingRealsFromPositiveInts : pb::IMessage<SettingRealsFromPositiveInts>, pb::IBufferMessage {
+  public sealed partial class SettingRealsFromPositiveInts : pb::IMessage<SettingRealsFromPositiveInts>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<SettingRealsFromPositiveInts> _parser = new pb::MessageParser<SettingRealsFromPositiveInts>(() => new SettingRealsFromPositiveInts());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1520,9 +1702,21 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1534,10 +1728,15 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class SettingRealsFromNegativeInts : pb::IMessage<SettingRealsFromNegativeInts>, pb::IBufferMessage {
+  public sealed partial class SettingRealsFromNegativeInts : pb::IMessage<SettingRealsFromNegativeInts>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<SettingRealsFromNegativeInts> _parser = new pb::MessageParser<SettingRealsFromNegativeInts>(() => new SettingRealsFromNegativeInts());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1626,9 +1825,21 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1640,10 +1851,15 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class ComplexOptionType1 : pb::IMessage<ComplexOptionType1>, pb::IBufferMessage {
+  public sealed partial class ComplexOptionType1 : pb::IMessage<ComplexOptionType1>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<ComplexOptionType1> _parser = new pb::MessageParser<ComplexOptionType1>(() => new ComplexOptionType1());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1820,9 +2036,38 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            Foo = input.ReadInt32();
+            break;
+          }
+          case 16: {
+            Foo2 = input.ReadInt32();
+            break;
+          }
+          case 24: {
+            Foo3 = input.ReadInt32();
+            break;
+          }
+          case 34:
+          case 32: {
+            foo4_.AddEntriesFrom(input, _repeated_foo4_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1851,10 +2096,15 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class ComplexOptionType2 : pb::IMessage<ComplexOptionType2>, pb::IBufferMessage {
+  public sealed partial class ComplexOptionType2 : pb::IMessage<ComplexOptionType2>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<ComplexOptionType2> _parser = new pb::MessageParser<ComplexOptionType2>(() => new ComplexOptionType2());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -2037,9 +2287,43 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            if (bar_ == null) {
+              Bar = new global::UnitTest.Issues.TestProtos.ComplexOptionType1();
+            }
+            input.ReadMessage(Bar);
+            break;
+          }
+          case 16: {
+            Baz = input.ReadInt32();
+            break;
+          }
+          case 26: {
+            if (fred_ == null) {
+              Fred = new global::UnitTest.Issues.TestProtos.ComplexOptionType2.Types.ComplexOptionType4();
+            }
+            input.ReadMessage(Fred);
+            break;
+          }
+          case 34: {
+            barney_.AddEntriesFrom(input, _repeated_barney_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -2073,12 +2357,17 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
     #region Nested types
     /// <summary>Container for nested types declared in the ComplexOptionType2 message type.</summary>
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public static partial class Types {
-      public sealed partial class ComplexOptionType4 : pb::IMessage<ComplexOptionType4>, pb::IBufferMessage {
+      public sealed partial class ComplexOptionType4 : pb::IMessage<ComplexOptionType4>
+      #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+          , pb::IBufferMessage
+      #endif
+      {
         private static readonly pb::MessageParser<ComplexOptionType4> _parser = new pb::MessageParser<ComplexOptionType4>(() => new ComplexOptionType4());
         private pb::UnknownFieldSet _unknownFields;
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -2191,9 +2480,25 @@ namespace UnitTest.Issues.TestProtos {
 
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         public void MergeFrom(pb::CodedInputStream input) {
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
           input.ReadRawMessage(this);
+        #else
+          uint tag;
+          while ((tag = input.ReadTag()) != 0) {
+            switch(tag) {
+              default:
+                _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+                break;
+              case 8: {
+                Waldo = input.ReadInt32();
+                break;
+              }
+            }
+          }
+        #endif
         }
 
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
           uint tag;
@@ -2209,6 +2514,7 @@ namespace UnitTest.Issues.TestProtos {
             }
           }
         }
+        #endif
 
         #region Extensions
         /// <summary>Container for extensions for other messages declared in the ComplexOptionType4 message type.</summary>
@@ -2226,7 +2532,11 @@ namespace UnitTest.Issues.TestProtos {
 
   }
 
-  public sealed partial class ComplexOptionType3 : pb::IMessage<ComplexOptionType3>, pb::IBufferMessage {
+  public sealed partial class ComplexOptionType3 : pb::IMessage<ComplexOptionType3>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<ComplexOptionType3> _parser = new pb::MessageParser<ComplexOptionType3>(() => new ComplexOptionType3());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -2339,9 +2649,25 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            Qux = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -2357,13 +2683,18 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
   /// <summary>
   /// Note that we try various different ways of naming the same extension.
   /// </summary>
-  public sealed partial class VariousComplexOptions : pb::IMessage<VariousComplexOptions>, pb::IBufferMessage {
+  public sealed partial class VariousComplexOptions : pb::IMessage<VariousComplexOptions>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<VariousComplexOptions> _parser = new pb::MessageParser<VariousComplexOptions>(() => new VariousComplexOptions());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -2452,9 +2783,21 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -2466,13 +2809,18 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
   /// <summary>
   /// A helper type used to test aggregate option parsing
   /// </summary>
-  public sealed partial class Aggregate : pb::IMessage<Aggregate>, pb::IBufferMessage {
+  public sealed partial class Aggregate : pb::IMessage<Aggregate>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Aggregate> _parser = new pb::MessageParser<Aggregate>(() => new Aggregate());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -2639,9 +2987,36 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            I = input.ReadInt32();
+            break;
+          }
+          case 18: {
+            S = input.ReadString();
+            break;
+          }
+          case 26: {
+            if (sub_ == null) {
+              Sub = new global::UnitTest.Issues.TestProtos.Aggregate();
+            }
+            input.ReadMessage(Sub);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -2668,10 +3043,15 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class AggregateMessage : pb::IMessage<AggregateMessage>, pb::IBufferMessage {
+  public sealed partial class AggregateMessage : pb::IMessage<AggregateMessage>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<AggregateMessage> _parser = new pb::MessageParser<AggregateMessage>(() => new AggregateMessage());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -2784,9 +3164,25 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            Fieldname = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -2802,13 +3198,18 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
   /// <summary>
   /// Test custom options for nested type.
   /// </summary>
-  public sealed partial class NestedOptionType : pb::IMessage<NestedOptionType>, pb::IBufferMessage {
+  public sealed partial class NestedOptionType : pb::IMessage<NestedOptionType>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<NestedOptionType> _parser = new pb::MessageParser<NestedOptionType>(() => new NestedOptionType());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -2897,9 +3298,21 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -2911,6 +3324,7 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
     #region Nested types
     /// <summary>Container for nested types declared in the NestedOptionType message type.</summary>
@@ -2921,7 +3335,11 @@ namespace UnitTest.Issues.TestProtos {
         [pbr::OriginalName("NESTED_ENUM_VALUE")] Value = 1,
       }
 
-      public sealed partial class NestedMessage : pb::IMessage<NestedMessage>, pb::IBufferMessage {
+      public sealed partial class NestedMessage : pb::IMessage<NestedMessage>
+      #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+          , pb::IBufferMessage
+      #endif
+      {
         private static readonly pb::MessageParser<NestedMessage> _parser = new pb::MessageParser<NestedMessage>(() => new NestedMessage());
         private pb::UnknownFieldSet _unknownFields;
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -3034,9 +3452,25 @@ namespace UnitTest.Issues.TestProtos {
 
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         public void MergeFrom(pb::CodedInputStream input) {
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
           input.ReadRawMessage(this);
+        #else
+          uint tag;
+          while ((tag = input.ReadTag()) != 0) {
+            switch(tag) {
+              default:
+                _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+                break;
+              case 8: {
+                NestedField = input.ReadInt32();
+                break;
+              }
+            }
+          }
+        #endif
         }
 
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
           uint tag;
@@ -3052,6 +3486,7 @@ namespace UnitTest.Issues.TestProtos {
             }
           }
         }
+        #endif
 
       }
 

csharp/src/Google.Protobuf.Test.TestProtos/UnittestImport.cs

@@ -59,7 +59,11 @@ namespace Google.Protobuf.TestProtos.Proto2 {
   #endregion
 
   #region Messages
-  public sealed partial class ImportMessage : pb::IMessage<ImportMessage>, pb::IBufferMessage {
+  public sealed partial class ImportMessage : pb::IMessage<ImportMessage>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<ImportMessage> _parser = new pb::MessageParser<ImportMessage>(() => new ImportMessage());
     private pb::UnknownFieldSet _unknownFields;
     private int _hasBits0;
@@ -187,9 +191,25 @@ namespace Google.Protobuf.TestProtos.Proto2 {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            D = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -205,6 +225,7 @@ namespace Google.Protobuf.TestProtos.Proto2 {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf.Test.TestProtos/UnittestImportProto3.cs

@@ -50,7 +50,11 @@ namespace Google.Protobuf.TestProtos {
   #endregion
 
   #region Messages
-  public sealed partial class ImportMessage : pb::IMessage<ImportMessage>, pb::IBufferMessage {
+  public sealed partial class ImportMessage : pb::IMessage<ImportMessage>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<ImportMessage> _parser = new pb::MessageParser<ImportMessage>(() => new ImportMessage());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -163,9 +167,25 @@ namespace Google.Protobuf.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            D = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -181,6 +201,7 @@ namespace Google.Protobuf.TestProtos {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf.Test.TestProtos/UnittestImportPublic.cs

@@ -37,7 +37,11 @@ namespace Google.Protobuf.TestProtos.Proto2 {
 
   }
   #region Messages
-  public sealed partial class PublicImportMessage : pb::IMessage<PublicImportMessage>, pb::IBufferMessage {
+  public sealed partial class PublicImportMessage : pb::IMessage<PublicImportMessage>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<PublicImportMessage> _parser = new pb::MessageParser<PublicImportMessage>(() => new PublicImportMessage());
     private pb::UnknownFieldSet _unknownFields;
     private int _hasBits0;
@@ -165,9 +169,25 @@ namespace Google.Protobuf.TestProtos.Proto2 {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            E = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -183,6 +203,7 @@ namespace Google.Protobuf.TestProtos.Proto2 {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf.Test.TestProtos/UnittestImportPublicProto3.cs

@@ -38,7 +38,11 @@ namespace Google.Protobuf.TestProtos {
 
   }
   #region Messages
-  public sealed partial class PublicImportMessage : pb::IMessage<PublicImportMessage>, pb::IBufferMessage {
+  public sealed partial class PublicImportMessage : pb::IMessage<PublicImportMessage>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<PublicImportMessage> _parser = new pb::MessageParser<PublicImportMessage>(() => new PublicImportMessage());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -151,9 +155,25 @@ namespace Google.Protobuf.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            E = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -169,6 +189,7 @@ namespace Google.Protobuf.TestProtos {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf.Test.TestProtos/UnittestIssue6936B.cs

@@ -37,7 +37,11 @@ namespace UnitTest.Issues.TestProtos {
 
   }
   #region Messages
-  public sealed partial class Foo : pb::IMessage<Foo>, pb::IBufferMessage {
+  public sealed partial class Foo : pb::IMessage<Foo>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Foo> _parser = new pb::MessageParser<Foo>(() => new Foo());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -126,9 +130,21 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -140,6 +156,7 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf.Test.TestProtos/UnittestIssue6936C.cs

@@ -39,7 +39,11 @@ namespace UnitTest.Issues.TestProtos {
 
   }
   #region Messages
-  public sealed partial class Bar : pb::IMessage<Bar>, pb::IBufferMessage {
+  public sealed partial class Bar : pb::IMessage<Bar>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Bar> _parser = new pb::MessageParser<Bar>(() => new Bar());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -155,9 +159,28 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            if (foo_ == null) {
+              Foo = new global::UnitTest.Issues.TestProtos.Foo();
+            }
+            input.ReadMessage(Foo);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -176,6 +199,7 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf.Test.TestProtos/UnittestIssues.cs

@@ -88,7 +88,11 @@ namespace UnitTest.Issues.TestProtos {
   /// Issue 307: when generating doubly-nested types, any references
   /// should be of the form A.Types.B.Types.C.
   /// </summary>
-  public sealed partial class Issue307 : pb::IMessage<Issue307>, pb::IBufferMessage {
+  public sealed partial class Issue307 : pb::IMessage<Issue307>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Issue307> _parser = new pb::MessageParser<Issue307>(() => new Issue307());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -177,9 +181,21 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -191,12 +207,17 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
     #region Nested types
     /// <summary>Container for nested types declared in the Issue307 message type.</summary>
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public static partial class Types {
-      public sealed partial class NestedOnce : pb::IMessage<NestedOnce>, pb::IBufferMessage {
+      public sealed partial class NestedOnce : pb::IMessage<NestedOnce>
+      #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+          , pb::IBufferMessage
+      #endif
+      {
         private static readonly pb::MessageParser<NestedOnce> _parser = new pb::MessageParser<NestedOnce>(() => new NestedOnce());
         private pb::UnknownFieldSet _unknownFields;
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -285,9 +306,21 @@ namespace UnitTest.Issues.TestProtos {
 
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         public void MergeFrom(pb::CodedInputStream input) {
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
           input.ReadRawMessage(this);
+        #else
+          uint tag;
+          while ((tag = input.ReadTag()) != 0) {
+            switch(tag) {
+              default:
+                _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+                break;
+            }
+          }
+        #endif
         }
 
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
           uint tag;
@@ -299,12 +332,17 @@ namespace UnitTest.Issues.TestProtos {
             }
           }
         }
+        #endif
 
         #region Nested types
         /// <summary>Container for nested types declared in the NestedOnce message type.</summary>
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         public static partial class Types {
-          public sealed partial class NestedTwice : pb::IMessage<NestedTwice>, pb::IBufferMessage {
+          public sealed partial class NestedTwice : pb::IMessage<NestedTwice>
+          #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+              , pb::IBufferMessage
+          #endif
+          {
             private static readonly pb::MessageParser<NestedTwice> _parser = new pb::MessageParser<NestedTwice>(() => new NestedTwice());
             private pb::UnknownFieldSet _unknownFields;
             [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -393,9 +431,21 @@ namespace UnitTest.Issues.TestProtos {
 
             [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
             public void MergeFrom(pb::CodedInputStream input) {
+            #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
               input.ReadRawMessage(this);
+            #else
+              uint tag;
+              while ((tag = input.ReadTag()) != 0) {
+                switch(tag) {
+                  default:
+                    _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+                    break;
+                }
+              }
+            #endif
             }
 
+            #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
             [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
             void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
               uint tag;
@@ -407,6 +457,7 @@ namespace UnitTest.Issues.TestProtos {
                 }
               }
             }
+            #endif
 
           }
 
@@ -420,7 +471,11 @@ namespace UnitTest.Issues.TestProtos {
 
   }
 
-  public sealed partial class NegativeEnumMessage : pb::IMessage<NegativeEnumMessage>, pb::IBufferMessage {
+  public sealed partial class NegativeEnumMessage : pb::IMessage<NegativeEnumMessage>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<NegativeEnumMessage> _parser = new pb::MessageParser<NegativeEnumMessage>(() => new NegativeEnumMessage());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -565,9 +620,35 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            Value = (global::UnitTest.Issues.TestProtos.NegativeEnum) input.ReadEnum();
+            break;
+          }
+          case 18:
+          case 16: {
+            values_.AddEntriesFrom(input, _repeated_values_codec);
+            break;
+          }
+          case 26:
+          case 24: {
+            packedValues_.AddEntriesFrom(input, _repeated_packedValues_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -593,10 +674,15 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class DeprecatedChild : pb::IMessage<DeprecatedChild>, pb::IBufferMessage {
+  public sealed partial class DeprecatedChild : pb::IMessage<DeprecatedChild>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<DeprecatedChild> _parser = new pb::MessageParser<DeprecatedChild>(() => new DeprecatedChild());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -685,9 +771,21 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -699,10 +797,15 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class DeprecatedFieldsMessage : pb::IMessage<DeprecatedFieldsMessage>, pb::IBufferMessage {
+  public sealed partial class DeprecatedFieldsMessage : pb::IMessage<DeprecatedFieldsMessage>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<DeprecatedFieldsMessage> _parser = new pb::MessageParser<DeprecatedFieldsMessage>(() => new DeprecatedFieldsMessage());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -920,9 +1023,50 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            PrimitiveValue = input.ReadInt32();
+            break;
+          }
+          case 18:
+          case 16: {
+            primitiveArray_.AddEntriesFrom(input, _repeated_primitiveArray_codec);
+            break;
+          }
+          case 26: {
+            if (messageValue_ == null) {
+              MessageValue = new global::UnitTest.Issues.TestProtos.DeprecatedChild();
+            }
+            input.ReadMessage(MessageValue);
+            break;
+          }
+          case 34: {
+            messageArray_.AddEntriesFrom(input, _repeated_messageArray_codec);
+            break;
+          }
+          case 40: {
+            EnumValue = (global::UnitTest.Issues.TestProtos.DeprecatedEnum) input.ReadEnum();
+            break;
+          }
+          case 50:
+          case 48: {
+            enumArray_.AddEntriesFrom(input, _repeated_enumArray_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -963,13 +1107,18 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
   /// <summary>
   /// Issue 45: http://code.google.com/p/protobuf-csharp-port/issues/detail?id=45
   /// </summary>
-  public sealed partial class ItemField : pb::IMessage<ItemField>, pb::IBufferMessage {
+  public sealed partial class ItemField : pb::IMessage<ItemField>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<ItemField> _parser = new pb::MessageParser<ItemField>(() => new ItemField());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1082,9 +1231,25 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            Item = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1100,10 +1265,15 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class ReservedNames : pb::IMessage<ReservedNames>, pb::IBufferMessage {
+  public sealed partial class ReservedNames : pb::IMessage<ReservedNames>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<ReservedNames> _parser = new pb::MessageParser<ReservedNames>(() => new ReservedNames());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1240,9 +1410,29 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            Types_ = input.ReadInt32();
+            break;
+          }
+          case 16: {
+            Descriptor_ = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1262,6 +1452,7 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
     #region Nested types
     /// <summary>Container for nested types declared in the ReservedNames message type.</summary>
@@ -1270,7 +1461,11 @@ namespace UnitTest.Issues.TestProtos {
       /// <summary>
       /// Force a nested type called Types
       /// </summary>
-      public sealed partial class SomeNestedType : pb::IMessage<SomeNestedType>, pb::IBufferMessage {
+      public sealed partial class SomeNestedType : pb::IMessage<SomeNestedType>
+      #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+          , pb::IBufferMessage
+      #endif
+      {
         private static readonly pb::MessageParser<SomeNestedType> _parser = new pb::MessageParser<SomeNestedType>(() => new SomeNestedType());
         private pb::UnknownFieldSet _unknownFields;
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1359,9 +1554,21 @@ namespace UnitTest.Issues.TestProtos {
 
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         public void MergeFrom(pb::CodedInputStream input) {
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
           input.ReadRawMessage(this);
+        #else
+          uint tag;
+          while ((tag = input.ReadTag()) != 0) {
+            switch(tag) {
+              default:
+                _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+                break;
+            }
+          }
+        #endif
         }
 
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
           uint tag;
@@ -1373,6 +1580,7 @@ namespace UnitTest.Issues.TestProtos {
             }
           }
         }
+        #endif
 
       }
 
@@ -1393,7 +1601,11 @@ namespace UnitTest.Issues.TestProtos {
   /// Alternatively, consider just adding this to
   /// unittest_proto3.proto if multiple platforms want it.
   /// </summary>
-  public sealed partial class TestJsonFieldOrdering : pb::IMessage<TestJsonFieldOrdering>, pb::IBufferMessage {
+  public sealed partial class TestJsonFieldOrdering : pb::IMessage<TestJsonFieldOrdering>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<TestJsonFieldOrdering> _parser = new pb::MessageParser<TestJsonFieldOrdering>(() => new TestJsonFieldOrdering());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1688,9 +1900,45 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            PlainString = input.ReadString();
+            break;
+          }
+          case 18: {
+            O1String = input.ReadString();
+            break;
+          }
+          case 26: {
+            O2String = input.ReadString();
+            break;
+          }
+          case 32: {
+            PlainInt32 = input.ReadInt32();
+            break;
+          }
+          case 40: {
+            O1Int32 = input.ReadInt32();
+            break;
+          }
+          case 48: {
+            O2Int32 = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1726,10 +1974,15 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class TestJsonName : pb::IMessage<TestJsonName>, pb::IBufferMessage {
+  public sealed partial class TestJsonName : pb::IMessage<TestJsonName>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<TestJsonName> _parser = new pb::MessageParser<TestJsonName>(() => new TestJsonName());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1893,9 +2146,33 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            Name = input.ReadString();
+            break;
+          }
+          case 18: {
+            Description = input.ReadString();
+            break;
+          }
+          case 26: {
+            Guid = input.ReadString();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1919,6 +2196,7 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
@@ -1927,7 +2205,11 @@ namespace UnitTest.Issues.TestProtos {
   /// oneof case, which is itself a message type, the submessages should
   /// be merged.
   /// </summary>
-  public sealed partial class OneofMerging : pb::IMessage<OneofMerging>, pb::IBufferMessage {
+  public sealed partial class OneofMerging : pb::IMessage<OneofMerging>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<OneofMerging> _parser = new pb::MessageParser<OneofMerging>(() => new OneofMerging());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -2098,9 +2380,34 @@ namespace UnitTest.Issues.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            Text = input.ReadString();
+            break;
+          }
+          case 18: {
+            global::UnitTest.Issues.TestProtos.OneofMerging.Types.Nested subBuilder = new global::UnitTest.Issues.TestProtos.OneofMerging.Types.Nested();
+            if (valueCase_ == ValueOneofCase.Nested) {
+              subBuilder.MergeFrom(Nested);
+            }
+            input.ReadMessage(subBuilder);
+            Nested = subBuilder;
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -2125,12 +2432,17 @@ namespace UnitTest.Issues.TestProtos {
         }
       }
     }
+    #endif
 
     #region Nested types
     /// <summary>Container for nested types declared in the OneofMerging message type.</summary>
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public static partial class Types {
-      public sealed partial class Nested : pb::IMessage<Nested>, pb::IBufferMessage {
+      public sealed partial class Nested : pb::IMessage<Nested>
+      #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+          , pb::IBufferMessage
+      #endif
+      {
         private static readonly pb::MessageParser<Nested> _parser = new pb::MessageParser<Nested>(() => new Nested());
         private pb::UnknownFieldSet _unknownFields;
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -2267,9 +2579,29 @@ namespace UnitTest.Issues.TestProtos {
 
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         public void MergeFrom(pb::CodedInputStream input) {
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
           input.ReadRawMessage(this);
+        #else
+          uint tag;
+          while ((tag = input.ReadTag()) != 0) {
+            switch(tag) {
+              default:
+                _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+                break;
+              case 8: {
+                X = input.ReadInt32();
+                break;
+              }
+              case 16: {
+                Y = input.ReadInt32();
+                break;
+              }
+            }
+          }
+        #endif
         }
 
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
           uint tag;
@@ -2289,6 +2621,7 @@ namespace UnitTest.Issues.TestProtos {
             }
           }
         }
+        #endif
 
       }
 

csharp/src/Google.Protobuf.Test.TestProtos/UnittestProto3Optional.cs

@@ -67,7 +67,11 @@ namespace ProtobufUnittest {
 
   }
   #region Messages
-  public sealed partial class TestProto3Optional : pb::IMessage<TestProto3Optional>, pb::IBufferMessage {
+  public sealed partial class TestProto3Optional : pb::IMessage<TestProto3Optional>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<TestProto3Optional> _parser = new pb::MessageParser<TestProto3Optional>(() => new TestProto3Optional());
     private pb::UnknownFieldSet _unknownFields;
     private int _hasBits0;
@@ -858,9 +862,111 @@ namespace ProtobufUnittest {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            OptionalInt32 = input.ReadInt32();
+            break;
+          }
+          case 16: {
+            OptionalInt64 = input.ReadInt64();
+            break;
+          }
+          case 24: {
+            OptionalUint32 = input.ReadUInt32();
+            break;
+          }
+          case 32: {
+            OptionalUint64 = input.ReadUInt64();
+            break;
+          }
+          case 40: {
+            OptionalSint32 = input.ReadSInt32();
+            break;
+          }
+          case 48: {
+            OptionalSint64 = input.ReadSInt64();
+            break;
+          }
+          case 61: {
+            OptionalFixed32 = input.ReadFixed32();
+            break;
+          }
+          case 65: {
+            OptionalFixed64 = input.ReadFixed64();
+            break;
+          }
+          case 77: {
+            OptionalSfixed32 = input.ReadSFixed32();
+            break;
+          }
+          case 81: {
+            OptionalSfixed64 = input.ReadSFixed64();
+            break;
+          }
+          case 93: {
+            OptionalFloat = input.ReadFloat();
+            break;
+          }
+          case 97: {
+            OptionalDouble = input.ReadDouble();
+            break;
+          }
+          case 104: {
+            OptionalBool = input.ReadBool();
+            break;
+          }
+          case 114: {
+            OptionalString = input.ReadString();
+            break;
+          }
+          case 122: {
+            OptionalBytes = input.ReadBytes();
+            break;
+          }
+          case 130: {
+            OptionalCord = input.ReadString();
+            break;
+          }
+          case 146: {
+            if (optionalNestedMessage_ == null) {
+              OptionalNestedMessage = new global::ProtobufUnittest.TestProto3Optional.Types.NestedMessage();
+            }
+            input.ReadMessage(OptionalNestedMessage);
+            break;
+          }
+          case 154: {
+            if (lazyNestedMessage_ == null) {
+              LazyNestedMessage = new global::ProtobufUnittest.TestProto3Optional.Types.NestedMessage();
+            }
+            input.ReadMessage(LazyNestedMessage);
+            break;
+          }
+          case 168: {
+            OptionalNestedEnum = (global::ProtobufUnittest.TestProto3Optional.Types.NestedEnum) input.ReadEnum();
+            break;
+          }
+          case 176: {
+            SingularInt32 = input.ReadInt32();
+            break;
+          }
+          case 184: {
+            SingularInt64 = input.ReadInt64();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -962,6 +1068,7 @@ namespace ProtobufUnittest {
         }
       }
     }
+    #endif
 
     #region Nested types
     /// <summary>Container for nested types declared in the TestProto3Optional message type.</summary>
@@ -978,7 +1085,11 @@ namespace ProtobufUnittest {
         [pbr::OriginalName("NEG")] Neg = -1,
       }
 
-      public sealed partial class NestedMessage : pb::IMessage<NestedMessage>, pb::IBufferMessage {
+      public sealed partial class NestedMessage : pb::IMessage<NestedMessage>
+      #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+          , pb::IBufferMessage
+      #endif
+      {
         private static readonly pb::MessageParser<NestedMessage> _parser = new pb::MessageParser<NestedMessage>(() => new NestedMessage());
         private pb::UnknownFieldSet _unknownFields;
         private int _hasBits0;
@@ -1109,9 +1220,25 @@ namespace ProtobufUnittest {
 
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         public void MergeFrom(pb::CodedInputStream input) {
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
           input.ReadRawMessage(this);
+        #else
+          uint tag;
+          while ((tag = input.ReadTag()) != 0) {
+            switch(tag) {
+              default:
+                _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+                break;
+              case 8: {
+                Bb = input.ReadInt32();
+                break;
+              }
+            }
+          }
+        #endif
         }
 
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
           uint tag;
@@ -1127,6 +1254,7 @@ namespace ProtobufUnittest {
             }
           }
         }
+        #endif
 
       }
 

csharp/src/Google.Protobuf.Test.TestProtos/UnittestSelfreferentialOptions.cs

@@ -63,7 +63,11 @@ namespace UnitTest.Issues.TestProtos.SelfreferentialOptions {
   }
 
   #region Messages
-  public sealed partial class FooOptions : pb::IExtendableMessage<FooOptions>, pb::IBufferMessage {
+  public sealed partial class FooOptions : pb::IExtendableMessage<FooOptions>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<FooOptions> _parser = new pb::MessageParser<FooOptions>(() => new FooOptions());
     private pb::UnknownFieldSet _unknownFields;
     private pb::ExtensionSet<FooOptions> _extensions;
@@ -250,9 +254,31 @@ namespace UnitTest.Issues.TestProtos.SelfreferentialOptions {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            if (!pb::ExtensionSet.TryMergeFieldFrom(ref _extensions, input)) {
+              _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            }
+            break;
+          case 8: {
+            IntOpt = input.ReadInt32();
+            break;
+          }
+          case 16: {
+            Foo = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -274,6 +300,7 @@ namespace UnitTest.Issues.TestProtos.SelfreferentialOptions {
         }
       }
     }
+    #endif
 
     public TValue GetExtension<TValue>(pb::Extension<FooOptions, TValue> extension) {
       return pb::ExtensionSet.Get(ref _extensions, extension);

csharp/src/Google.Protobuf.Test.TestProtos/UnittestWellKnownTypes.cs

@@ -179,7 +179,11 @@ namespace Google.Protobuf.TestProtos {
   /// Each wrapper type is included separately, as languages
   /// map handle different wrappers in different ways.
   /// </summary>
-  public sealed partial class TestWellKnownTypes : pb::IMessage<TestWellKnownTypes>, pb::IBufferMessage {
+  public sealed partial class TestWellKnownTypes : pb::IMessage<TestWellKnownTypes>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<TestWellKnownTypes> _parser = new pb::MessageParser<TestWellKnownTypes>(() => new TestWellKnownTypes());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -784,9 +788,154 @@ namespace Google.Protobuf.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            if (anyField_ == null) {
+              AnyField = new global::Google.Protobuf.WellKnownTypes.Any();
+            }
+            input.ReadMessage(AnyField);
+            break;
+          }
+          case 18: {
+            if (apiField_ == null) {
+              ApiField = new global::Google.Protobuf.WellKnownTypes.Api();
+            }
+            input.ReadMessage(ApiField);
+            break;
+          }
+          case 26: {
+            if (durationField_ == null) {
+              DurationField = new global::Google.Protobuf.WellKnownTypes.Duration();
+            }
+            input.ReadMessage(DurationField);
+            break;
+          }
+          case 34: {
+            if (emptyField_ == null) {
+              EmptyField = new global::Google.Protobuf.WellKnownTypes.Empty();
+            }
+            input.ReadMessage(EmptyField);
+            break;
+          }
+          case 42: {
+            if (fieldMaskField_ == null) {
+              FieldMaskField = new global::Google.Protobuf.WellKnownTypes.FieldMask();
+            }
+            input.ReadMessage(FieldMaskField);
+            break;
+          }
+          case 50: {
+            if (sourceContextField_ == null) {
+              SourceContextField = new global::Google.Protobuf.WellKnownTypes.SourceContext();
+            }
+            input.ReadMessage(SourceContextField);
+            break;
+          }
+          case 58: {
+            if (structField_ == null) {
+              StructField = new global::Google.Protobuf.WellKnownTypes.Struct();
+            }
+            input.ReadMessage(StructField);
+            break;
+          }
+          case 66: {
+            if (timestampField_ == null) {
+              TimestampField = new global::Google.Protobuf.WellKnownTypes.Timestamp();
+            }
+            input.ReadMessage(TimestampField);
+            break;
+          }
+          case 74: {
+            if (typeField_ == null) {
+              TypeField = new global::Google.Protobuf.WellKnownTypes.Type();
+            }
+            input.ReadMessage(TypeField);
+            break;
+          }
+          case 82: {
+            double? value = _single_doubleField_codec.Read(input);
+            if (doubleField_ == null || value != 0D) {
+              DoubleField = value;
+            }
+            break;
+          }
+          case 90: {
+            float? value = _single_floatField_codec.Read(input);
+            if (floatField_ == null || value != 0F) {
+              FloatField = value;
+            }
+            break;
+          }
+          case 98: {
+            long? value = _single_int64Field_codec.Read(input);
+            if (int64Field_ == null || value != 0L) {
+              Int64Field = value;
+            }
+            break;
+          }
+          case 106: {
+            ulong? value = _single_uint64Field_codec.Read(input);
+            if (uint64Field_ == null || value != 0UL) {
+              Uint64Field = value;
+            }
+            break;
+          }
+          case 114: {
+            int? value = _single_int32Field_codec.Read(input);
+            if (int32Field_ == null || value != 0) {
+              Int32Field = value;
+            }
+            break;
+          }
+          case 122: {
+            uint? value = _single_uint32Field_codec.Read(input);
+            if (uint32Field_ == null || value != 0) {
+              Uint32Field = value;
+            }
+            break;
+          }
+          case 130: {
+            bool? value = _single_boolField_codec.Read(input);
+            if (boolField_ == null || value != false) {
+              BoolField = value;
+            }
+            break;
+          }
+          case 138: {
+            string value = _single_stringField_codec.Read(input);
+            if (stringField_ == null || value != "") {
+              StringField = value;
+            }
+            break;
+          }
+          case 146: {
+            pb::ByteString value = _single_bytesField_codec.Read(input);
+            if (bytesField_ == null || value != pb::ByteString.Empty) {
+              BytesField = value;
+            }
+            break;
+          }
+          case 154: {
+            if (valueField_ == null) {
+              ValueField = new global::Google.Protobuf.WellKnownTypes.Value();
+            }
+            input.ReadMessage(ValueField);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -931,13 +1080,18 @@ namespace Google.Protobuf.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
   /// <summary>
   /// A repeated field for each well-known type.
   /// </summary>
-  public sealed partial class RepeatedWellKnownTypes : pb::IMessage<RepeatedWellKnownTypes>, pb::IBufferMessage {
+  public sealed partial class RepeatedWellKnownTypes : pb::IMessage<RepeatedWellKnownTypes>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<RepeatedWellKnownTypes> _parser = new pb::MessageParser<RepeatedWellKnownTypes>(() => new RepeatedWellKnownTypes());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1317,9 +1471,93 @@ namespace Google.Protobuf.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            anyField_.AddEntriesFrom(input, _repeated_anyField_codec);
+            break;
+          }
+          case 18: {
+            apiField_.AddEntriesFrom(input, _repeated_apiField_codec);
+            break;
+          }
+          case 26: {
+            durationField_.AddEntriesFrom(input, _repeated_durationField_codec);
+            break;
+          }
+          case 34: {
+            emptyField_.AddEntriesFrom(input, _repeated_emptyField_codec);
+            break;
+          }
+          case 42: {
+            fieldMaskField_.AddEntriesFrom(input, _repeated_fieldMaskField_codec);
+            break;
+          }
+          case 50: {
+            sourceContextField_.AddEntriesFrom(input, _repeated_sourceContextField_codec);
+            break;
+          }
+          case 58: {
+            structField_.AddEntriesFrom(input, _repeated_structField_codec);
+            break;
+          }
+          case 66: {
+            timestampField_.AddEntriesFrom(input, _repeated_timestampField_codec);
+            break;
+          }
+          case 74: {
+            typeField_.AddEntriesFrom(input, _repeated_typeField_codec);
+            break;
+          }
+          case 82: {
+            doubleField_.AddEntriesFrom(input, _repeated_doubleField_codec);
+            break;
+          }
+          case 90: {
+            floatField_.AddEntriesFrom(input, _repeated_floatField_codec);
+            break;
+          }
+          case 98: {
+            int64Field_.AddEntriesFrom(input, _repeated_int64Field_codec);
+            break;
+          }
+          case 106: {
+            uint64Field_.AddEntriesFrom(input, _repeated_uint64Field_codec);
+            break;
+          }
+          case 114: {
+            int32Field_.AddEntriesFrom(input, _repeated_int32Field_codec);
+            break;
+          }
+          case 122: {
+            uint32Field_.AddEntriesFrom(input, _repeated_uint32Field_codec);
+            break;
+          }
+          case 130: {
+            boolField_.AddEntriesFrom(input, _repeated_boolField_codec);
+            break;
+          }
+          case 138: {
+            stringField_.AddEntriesFrom(input, _repeated_stringField_codec);
+            break;
+          }
+          case 146: {
+            bytesField_.AddEntriesFrom(input, _repeated_bytesField_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1403,10 +1641,15 @@ namespace Google.Protobuf.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
-  public sealed partial class OneofWellKnownTypes : pb::IMessage<OneofWellKnownTypes>, pb::IBufferMessage {
+  public sealed partial class OneofWellKnownTypes : pb::IMessage<OneofWellKnownTypes>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<OneofWellKnownTypes> _parser = new pb::MessageParser<OneofWellKnownTypes>(() => new OneofWellKnownTypes());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -2033,9 +2276,138 @@ namespace Google.Protobuf.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            global::Google.Protobuf.WellKnownTypes.Any subBuilder = new global::Google.Protobuf.WellKnownTypes.Any();
+            if (oneofFieldCase_ == OneofFieldOneofCase.AnyField) {
+              subBuilder.MergeFrom(AnyField);
+            }
+            input.ReadMessage(subBuilder);
+            AnyField = subBuilder;
+            break;
+          }
+          case 18: {
+            global::Google.Protobuf.WellKnownTypes.Api subBuilder = new global::Google.Protobuf.WellKnownTypes.Api();
+            if (oneofFieldCase_ == OneofFieldOneofCase.ApiField) {
+              subBuilder.MergeFrom(ApiField);
+            }
+            input.ReadMessage(subBuilder);
+            ApiField = subBuilder;
+            break;
+          }
+          case 26: {
+            global::Google.Protobuf.WellKnownTypes.Duration subBuilder = new global::Google.Protobuf.WellKnownTypes.Duration();
+            if (oneofFieldCase_ == OneofFieldOneofCase.DurationField) {
+              subBuilder.MergeFrom(DurationField);
+            }
+            input.ReadMessage(subBuilder);
+            DurationField = subBuilder;
+            break;
+          }
+          case 34: {
+            global::Google.Protobuf.WellKnownTypes.Empty subBuilder = new global::Google.Protobuf.WellKnownTypes.Empty();
+            if (oneofFieldCase_ == OneofFieldOneofCase.EmptyField) {
+              subBuilder.MergeFrom(EmptyField);
+            }
+            input.ReadMessage(subBuilder);
+            EmptyField = subBuilder;
+            break;
+          }
+          case 42: {
+            global::Google.Protobuf.WellKnownTypes.FieldMask subBuilder = new global::Google.Protobuf.WellKnownTypes.FieldMask();
+            if (oneofFieldCase_ == OneofFieldOneofCase.FieldMaskField) {
+              subBuilder.MergeFrom(FieldMaskField);
+            }
+            input.ReadMessage(subBuilder);
+            FieldMaskField = subBuilder;
+            break;
+          }
+          case 50: {
+            global::Google.Protobuf.WellKnownTypes.SourceContext subBuilder = new global::Google.Protobuf.WellKnownTypes.SourceContext();
+            if (oneofFieldCase_ == OneofFieldOneofCase.SourceContextField) {
+              subBuilder.MergeFrom(SourceContextField);
+            }
+            input.ReadMessage(subBuilder);
+            SourceContextField = subBuilder;
+            break;
+          }
+          case 58: {
+            global::Google.Protobuf.WellKnownTypes.Struct subBuilder = new global::Google.Protobuf.WellKnownTypes.Struct();
+            if (oneofFieldCase_ == OneofFieldOneofCase.StructField) {
+              subBuilder.MergeFrom(StructField);
+            }
+            input.ReadMessage(subBuilder);
+            StructField = subBuilder;
+            break;
+          }
+          case 66: {
+            global::Google.Protobuf.WellKnownTypes.Timestamp subBuilder = new global::Google.Protobuf.WellKnownTypes.Timestamp();
+            if (oneofFieldCase_ == OneofFieldOneofCase.TimestampField) {
+              subBuilder.MergeFrom(TimestampField);
+            }
+            input.ReadMessage(subBuilder);
+            TimestampField = subBuilder;
+            break;
+          }
+          case 74: {
+            global::Google.Protobuf.WellKnownTypes.Type subBuilder = new global::Google.Protobuf.WellKnownTypes.Type();
+            if (oneofFieldCase_ == OneofFieldOneofCase.TypeField) {
+              subBuilder.MergeFrom(TypeField);
+            }
+            input.ReadMessage(subBuilder);
+            TypeField = subBuilder;
+            break;
+          }
+          case 82: {
+            DoubleField = _oneof_doubleField_codec.Read(input);
+            break;
+          }
+          case 90: {
+            FloatField = _oneof_floatField_codec.Read(input);
+            break;
+          }
+          case 98: {
+            Int64Field = _oneof_int64Field_codec.Read(input);
+            break;
+          }
+          case 106: {
+            Uint64Field = _oneof_uint64Field_codec.Read(input);
+            break;
+          }
+          case 114: {
+            Int32Field = _oneof_int32Field_codec.Read(input);
+            break;
+          }
+          case 122: {
+            Uint32Field = _oneof_uint32Field_codec.Read(input);
+            break;
+          }
+          case 130: {
+            BoolField = _oneof_boolField_codec.Read(input);
+            break;
+          }
+          case 138: {
+            StringField = _oneof_stringField_codec.Read(input);
+            break;
+          }
+          case 146: {
+            BytesField = _oneof_bytesField_codec.Read(input);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -2164,6 +2536,7 @@ namespace Google.Protobuf.TestProtos {
         }
       }
     }
+    #endif
 
   }
 
@@ -2172,7 +2545,11 @@ namespace Google.Protobuf.TestProtos {
   /// need to worry about the value part of the map being the
   /// well-known types, as messages can't be map keys.
   /// </summary>
-  public sealed partial class MapWellKnownTypes : pb::IMessage<MapWellKnownTypes>, pb::IBufferMessage {
+  public sealed partial class MapWellKnownTypes : pb::IMessage<MapWellKnownTypes>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<MapWellKnownTypes> _parser = new pb::MessageParser<MapWellKnownTypes>(() => new MapWellKnownTypes());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -2549,9 +2926,93 @@ namespace Google.Protobuf.TestProtos {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            anyField_.AddEntriesFrom(input, _map_anyField_codec);
+            break;
+          }
+          case 18: {
+            apiField_.AddEntriesFrom(input, _map_apiField_codec);
+            break;
+          }
+          case 26: {
+            durationField_.AddEntriesFrom(input, _map_durationField_codec);
+            break;
+          }
+          case 34: {
+            emptyField_.AddEntriesFrom(input, _map_emptyField_codec);
+            break;
+          }
+          case 42: {
+            fieldMaskField_.AddEntriesFrom(input, _map_fieldMaskField_codec);
+            break;
+          }
+          case 50: {
+            sourceContextField_.AddEntriesFrom(input, _map_sourceContextField_codec);
+            break;
+          }
+          case 58: {
+            structField_.AddEntriesFrom(input, _map_structField_codec);
+            break;
+          }
+          case 66: {
+            timestampField_.AddEntriesFrom(input, _map_timestampField_codec);
+            break;
+          }
+          case 74: {
+            typeField_.AddEntriesFrom(input, _map_typeField_codec);
+            break;
+          }
+          case 82: {
+            doubleField_.AddEntriesFrom(input, _map_doubleField_codec);
+            break;
+          }
+          case 90: {
+            floatField_.AddEntriesFrom(input, _map_floatField_codec);
+            break;
+          }
+          case 98: {
+            int64Field_.AddEntriesFrom(input, _map_int64Field_codec);
+            break;
+          }
+          case 106: {
+            uint64Field_.AddEntriesFrom(input, _map_uint64Field_codec);
+            break;
+          }
+          case 114: {
+            int32Field_.AddEntriesFrom(input, _map_int32Field_codec);
+            break;
+          }
+          case 122: {
+            uint32Field_.AddEntriesFrom(input, _map_uint32Field_codec);
+            break;
+          }
+          case 130: {
+            boolField_.AddEntriesFrom(input, _map_boolField_codec);
+            break;
+          }
+          case 138: {
+            stringField_.AddEntriesFrom(input, _map_stringField_codec);
+            break;
+          }
+          case 146: {
+            bytesField_.AddEntriesFrom(input, _map_bytesField_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -2635,6 +3096,7 @@ namespace Google.Protobuf.TestProtos {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf.Test/RefStructCompatibilityTest.cs

@@ -0,0 +1,119 @@
+#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+
+using NUnit.Framework;
+using System.Diagnostics;
+using System;
+using System.Reflection;
+using System.IO;
+
+namespace Google.Protobuf
+{
+    public class RefStructCompatibilityTest
+    {
+        /// <summary>
+        /// Checks that the generated code can be compiler with an old C# compiler.
+        /// The reason why this test is needed is that even though dotnet SDK projects allow to set LangVersion,
+        /// this setting doesn't accurately simulate compilation with an actual old pre-roslyn C# compiler.
+        /// For instance, the "ref struct" types are only supported by C# 7.2 and higher, but even if
+        /// LangVersion is set low, the roslyn compiler still understands the concept of ref struct
+        /// and silently accepts them. Therefore we try to build the generated code with an actual old C# compiler
+        /// to be able to catch these sort of compatibility problems.
+        /// </summary>
+        [Test]
+        public void GeneratedCodeCompilesWithOldCsharpCompiler()
+        {
+            if (Environment.OSVersion.Platform != PlatformID.Win32NT)
+            {
+                // This tests needs old C# compiler which is only available on Windows. Skipping it on all other platforms.
+                return;
+            }
+
+            var currentAssemblyDir = Path.GetDirectoryName(typeof(RefStructCompatibilityTest).GetTypeInfo().Assembly.Location);
+            var testProtosProjectDir = Path.GetFullPath(Path.Combine(currentAssemblyDir, "..", "..", "..", "..", "Google.Protobuf.Test.TestProtos"));
+            var testProtosOutputDir = (currentAssemblyDir.Contains("bin/Debug/") || currentAssemblyDir.Contains("bin\\Debug\\")) ? "bin\\Debug\\net45" : "bin\\Release\\net45";
+
+            // If "ref struct" types are used in the generated code, compilation with an old compiler will fail with the following error:
+            // "XYZ is obsolete: 'Types with embedded references are not supported in this version of your compiler.'"
+            // We build the code with GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE to avoid the use of ref struct in the generated code.
+            var compatibilityFlag = "-define:GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE";
+            var sources = "*.cs";  // the generated sources from the TestProtos project
+            var args = $"-langversion:3 -target:library {compatibilityFlag} -reference:{testProtosOutputDir}\\Google.Protobuf.dll -out:{testProtosOutputDir}\\TestProtos.RefStructCompatibilityTest.OldCompiler.dll {sources}";
+            RunOldCsharpCompilerAndCheckSuccess(args, testProtosProjectDir);
+        }
+
+        /// <summary>
+        /// Invoke an old C# compiler in a subprocess and check it finished successful.
+        /// </summary>
+        /// <param name="args"></param>
+        /// <param name="workingDirectory"></param>
+        private void RunOldCsharpCompilerAndCheckSuccess(string args, string workingDirectory)
+        {  
+            using (var process = new Process())
+            {
+                // Get the path to the old C# 5 compiler from .NET framework. This approach is not 100% reliable, but works on most machines.
+                // Alternative way of getting the framework path is System.Runtime.InteropServices.RuntimeEnvironment.GetRuntimeDirectory()
+                // but it only works with the net45 target.
+                var oldCsharpCompilerPath = Path.Combine(Environment.GetEnvironmentVariable("WINDIR"), "Microsoft.NET", "Framework", "v4.0.30319", "csc.exe");
+                process.StartInfo.FileName = oldCsharpCompilerPath;
+                process.StartInfo.RedirectStandardOutput = true;
+                process.StartInfo.RedirectStandardError = true;
+                process.StartInfo.UseShellExecute = false;
+                process.StartInfo.Arguments = args;
+                process.StartInfo.WorkingDirectory = workingDirectory;
+
+                process.OutputDataReceived += (sender, e) =>
+                {
+                    if (e.Data != null)
+                    {
+                        Console.WriteLine(e.Data);
+                    }
+                };
+                process.ErrorDataReceived += (sender, e) =>
+                {
+                    if (e.Data != null)
+                    {
+                        Console.WriteLine(e.Data);
+                    }
+                };
+
+                process.Start();
+
+                process.BeginErrorReadLine();
+                process.BeginOutputReadLine();
+
+                process.WaitForExit();
+                Assert.AreEqual(0, process.ExitCode);
+            }
+        }
+    }
+}

csharp/src/Google.Protobuf/WellKnownTypes/Any.cs

@@ -119,7 +119,11 @@ namespace Google.Protobuf.WellKnownTypes {
   ///       "value": "1.212s"
   ///     }
   /// </summary>
-  public sealed partial class Any : pb::IMessage<Any>, pb::IBufferMessage {
+  public sealed partial class Any : pb::IMessage<Any>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Any> _parser = new pb::MessageParser<Any>(() => new Any());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -288,9 +292,29 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            TypeUrl = input.ReadString();
+            break;
+          }
+          case 18: {
+            Value = input.ReadBytes();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -310,6 +334,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf/WellKnownTypes/Api.cs

@@ -64,7 +64,11 @@ namespace Google.Protobuf.WellKnownTypes {
   /// this message itself. See https://cloud.google.com/apis/design/glossary for
   /// detailed terminology.
   /// </summary>
-  public sealed partial class Api : pb::IMessage<Api>, pb::IBufferMessage {
+  public sealed partial class Api : pb::IMessage<Api>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Api> _parser = new pb::MessageParser<Api>(() => new Api());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -341,9 +345,52 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            Name = input.ReadString();
+            break;
+          }
+          case 18: {
+            methods_.AddEntriesFrom(input, _repeated_methods_codec);
+            break;
+          }
+          case 26: {
+            options_.AddEntriesFrom(input, _repeated_options_codec);
+            break;
+          }
+          case 34: {
+            Version = input.ReadString();
+            break;
+          }
+          case 42: {
+            if (sourceContext_ == null) {
+              SourceContext = new global::Google.Protobuf.WellKnownTypes.SourceContext();
+            }
+            input.ReadMessage(SourceContext);
+            break;
+          }
+          case 50: {
+            mixins_.AddEntriesFrom(input, _repeated_mixins_codec);
+            break;
+          }
+          case 56: {
+            Syntax = (global::Google.Protobuf.WellKnownTypes.Syntax) input.ReadEnum();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -386,13 +433,18 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 
   /// <summary>
   /// Method represents a method of an API interface.
   /// </summary>
-  public sealed partial class Method : pb::IMessage<Method>, pb::IBufferMessage {
+  public sealed partial class Method : pb::IMessage<Method>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Method> _parser = new pb::MessageParser<Method>(() => new Method());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -662,9 +714,49 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            Name = input.ReadString();
+            break;
+          }
+          case 18: {
+            RequestTypeUrl = input.ReadString();
+            break;
+          }
+          case 24: {
+            RequestStreaming = input.ReadBool();
+            break;
+          }
+          case 34: {
+            ResponseTypeUrl = input.ReadString();
+            break;
+          }
+          case 40: {
+            ResponseStreaming = input.ReadBool();
+            break;
+          }
+          case 50: {
+            options_.AddEntriesFrom(input, _repeated_options_codec);
+            break;
+          }
+          case 56: {
+            Syntax = (global::Google.Protobuf.WellKnownTypes.Syntax) input.ReadEnum();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -704,6 +796,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 
@@ -787,7 +880,11 @@ namespace Google.Protobuf.WellKnownTypes {
   ///       ...
   ///     }
   /// </summary>
-  public sealed partial class Mixin : pb::IMessage<Mixin>, pb::IBufferMessage {
+  public sealed partial class Mixin : pb::IMessage<Mixin>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Mixin> _parser = new pb::MessageParser<Mixin>(() => new Mixin());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -931,9 +1028,29 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            Name = input.ReadString();
+            break;
+          }
+          case 18: {
+            Root = input.ReadString();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -953,6 +1070,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf/WellKnownTypes/Duration.cs

@@ -100,7 +100,11 @@ namespace Google.Protobuf.WellKnownTypes {
   /// be expressed in JSON format as "3.000000001s", and 3 seconds and 1
   /// microsecond should be expressed in JSON format as "3.000001s".
   /// </summary>
-  public sealed partial class Duration : pb::IMessage<Duration>, pb::IBufferMessage {
+  public sealed partial class Duration : pb::IMessage<Duration>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Duration> _parser = new pb::MessageParser<Duration>(() => new Duration());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -250,9 +254,29 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            Seconds = input.ReadInt64();
+            break;
+          }
+          case 16: {
+            Nanos = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -272,6 +296,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf/WellKnownTypes/Empty.cs

@@ -50,7 +50,11 @@ namespace Google.Protobuf.WellKnownTypes {
   ///
   /// The JSON representation for `Empty` is empty JSON object `{}`.
   /// </summary>
-  public sealed partial class Empty : pb::IMessage<Empty>, pb::IBufferMessage {
+  public sealed partial class Empty : pb::IMessage<Empty>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Empty> _parser = new pb::MessageParser<Empty>(() => new Empty());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -139,9 +143,21 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -153,6 +169,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf/WellKnownTypes/FieldMask.cs

@@ -240,7 +240,11 @@ namespace Google.Protobuf.WellKnownTypes {
   /// request should verify the included field paths, and return an
   /// `INVALID_ARGUMENT` error if any path is unmappable.
   /// </summary>
-  public sealed partial class FieldMask : pb::IMessage<FieldMask>, pb::IBufferMessage {
+  public sealed partial class FieldMask : pb::IMessage<FieldMask>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<FieldMask> _parser = new pb::MessageParser<FieldMask>(() => new FieldMask());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -348,9 +352,25 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            paths_.AddEntriesFrom(input, _repeated_paths_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -366,6 +386,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf/WellKnownTypes/SourceContext.cs

@@ -44,7 +44,11 @@ namespace Google.Protobuf.WellKnownTypes {
   /// `SourceContext` represents information about the source of a
   /// protobuf element, like the file in which it is defined.
   /// </summary>
-  public sealed partial class SourceContext : pb::IMessage<SourceContext>, pb::IBufferMessage {
+  public sealed partial class SourceContext : pb::IMessage<SourceContext>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<SourceContext> _parser = new pb::MessageParser<SourceContext>(() => new SourceContext());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -161,9 +165,25 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            FileName = input.ReadString();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -179,6 +199,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf/WellKnownTypes/Struct.cs

@@ -77,7 +77,11 @@ namespace Google.Protobuf.WellKnownTypes {
   ///
   /// The JSON representation for `Struct` is JSON object.
   /// </summary>
-  public sealed partial class Struct : pb::IMessage<Struct>, pb::IBufferMessage {
+  public sealed partial class Struct : pb::IMessage<Struct>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Struct> _parser = new pb::MessageParser<Struct>(() => new Struct());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -185,9 +189,25 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            fields_.AddEntriesFrom(input, _map_fields_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -203,6 +223,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 
@@ -214,7 +235,11 @@ namespace Google.Protobuf.WellKnownTypes {
   ///
   /// The JSON representation for `Value` is JSON value.
   /// </summary>
-  public sealed partial class Value : pb::IMessage<Value>, pb::IBufferMessage {
+  public sealed partial class Value : pb::IMessage<Value>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Value> _parser = new pb::MessageParser<Value>(() => new Value());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -514,9 +539,56 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            kind_ = input.ReadEnum();
+            kindCase_ = KindOneofCase.NullValue;
+            break;
+          }
+          case 17: {
+            NumberValue = input.ReadDouble();
+            break;
+          }
+          case 26: {
+            StringValue = input.ReadString();
+            break;
+          }
+          case 32: {
+            BoolValue = input.ReadBool();
+            break;
+          }
+          case 42: {
+            global::Google.Protobuf.WellKnownTypes.Struct subBuilder = new global::Google.Protobuf.WellKnownTypes.Struct();
+            if (kindCase_ == KindOneofCase.StructValue) {
+              subBuilder.MergeFrom(StructValue);
+            }
+            input.ReadMessage(subBuilder);
+            StructValue = subBuilder;
+            break;
+          }
+          case 50: {
+            global::Google.Protobuf.WellKnownTypes.ListValue subBuilder = new global::Google.Protobuf.WellKnownTypes.ListValue();
+            if (kindCase_ == KindOneofCase.ListValue) {
+              subBuilder.MergeFrom(ListValue);
+            }
+            input.ReadMessage(subBuilder);
+            ListValue = subBuilder;
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -563,6 +635,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 
@@ -571,7 +644,11 @@ namespace Google.Protobuf.WellKnownTypes {
   ///
   /// The JSON representation for `ListValue` is JSON array.
   /// </summary>
-  public sealed partial class ListValue : pb::IMessage<ListValue>, pb::IBufferMessage {
+  public sealed partial class ListValue : pb::IMessage<ListValue>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<ListValue> _parser = new pb::MessageParser<ListValue>(() => new ListValue());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -679,9 +756,25 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            values_.AddEntriesFrom(input, _repeated_values_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -697,6 +790,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf/WellKnownTypes/Timestamp.cs

@@ -123,7 +123,11 @@ namespace Google.Protobuf.WellKnownTypes {
   /// http://www.joda.org/joda-time/apidocs/org/joda/time/format/ISODateTimeFormat.html#dateTime%2D%2D
   /// ) to obtain a formatter capable of generating timestamps in this format.
   /// </summary>
-  public sealed partial class Timestamp : pb::IMessage<Timestamp>, pb::IBufferMessage {
+  public sealed partial class Timestamp : pb::IMessage<Timestamp>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Timestamp> _parser = new pb::MessageParser<Timestamp>(() => new Timestamp());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -271,9 +275,29 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            Seconds = input.ReadInt64();
+            break;
+          }
+          case 16: {
+            Nanos = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -293,6 +317,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf/WellKnownTypes/Type.cs

@@ -94,7 +94,11 @@ namespace Google.Protobuf.WellKnownTypes {
   /// <summary>
   /// A protocol buffer message type.
   /// </summary>
-  public sealed partial class Type : pb::IMessage<Type>, pb::IBufferMessage {
+  public sealed partial class Type : pb::IMessage<Type>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Type> _parser = new pb::MessageParser<Type>(() => new Type());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -324,9 +328,48 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            Name = input.ReadString();
+            break;
+          }
+          case 18: {
+            fields_.AddEntriesFrom(input, _repeated_fields_codec);
+            break;
+          }
+          case 26: {
+            oneofs_.AddEntriesFrom(input, _repeated_oneofs_codec);
+            break;
+          }
+          case 34: {
+            options_.AddEntriesFrom(input, _repeated_options_codec);
+            break;
+          }
+          case 42: {
+            if (sourceContext_ == null) {
+              SourceContext = new global::Google.Protobuf.WellKnownTypes.SourceContext();
+            }
+            input.ReadMessage(SourceContext);
+            break;
+          }
+          case 48: {
+            Syntax = (global::Google.Protobuf.WellKnownTypes.Syntax) input.ReadEnum();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -365,13 +408,18 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 
   /// <summary>
   /// A single field of a message type.
   /// </summary>
-  public sealed partial class Field : pb::IMessage<Field>, pb::IBufferMessage {
+  public sealed partial class Field : pb::IMessage<Field>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Field> _parser = new pb::MessageParser<Field>(() => new Field());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -724,9 +772,61 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            Kind = (global::Google.Protobuf.WellKnownTypes.Field.Types.Kind) input.ReadEnum();
+            break;
+          }
+          case 16: {
+            Cardinality = (global::Google.Protobuf.WellKnownTypes.Field.Types.Cardinality) input.ReadEnum();
+            break;
+          }
+          case 24: {
+            Number = input.ReadInt32();
+            break;
+          }
+          case 34: {
+            Name = input.ReadString();
+            break;
+          }
+          case 50: {
+            TypeUrl = input.ReadString();
+            break;
+          }
+          case 56: {
+            OneofIndex = input.ReadInt32();
+            break;
+          }
+          case 64: {
+            Packed = input.ReadBool();
+            break;
+          }
+          case 74: {
+            options_.AddEntriesFrom(input, _repeated_options_codec);
+            break;
+          }
+          case 82: {
+            JsonName = input.ReadString();
+            break;
+          }
+          case 90: {
+            DefaultValue = input.ReadString();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -778,6 +878,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
     #region Nested types
     /// <summary>Container for nested types declared in the Field message type.</summary>
@@ -895,7 +996,11 @@ namespace Google.Protobuf.WellKnownTypes {
   /// <summary>
   /// Enum type definition.
   /// </summary>
-  public sealed partial class Enum : pb::IMessage<Enum>, pb::IBufferMessage {
+  public sealed partial class Enum : pb::IMessage<Enum>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Enum> _parser = new pb::MessageParser<Enum>(() => new Enum());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1106,9 +1211,44 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            Name = input.ReadString();
+            break;
+          }
+          case 18: {
+            enumvalue_.AddEntriesFrom(input, _repeated_enumvalue_codec);
+            break;
+          }
+          case 26: {
+            options_.AddEntriesFrom(input, _repeated_options_codec);
+            break;
+          }
+          case 34: {
+            if (sourceContext_ == null) {
+              SourceContext = new global::Google.Protobuf.WellKnownTypes.SourceContext();
+            }
+            input.ReadMessage(SourceContext);
+            break;
+          }
+          case 40: {
+            Syntax = (global::Google.Protobuf.WellKnownTypes.Syntax) input.ReadEnum();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1143,13 +1283,18 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 
   /// <summary>
   /// Enum value definition.
   /// </summary>
-  public sealed partial class EnumValue : pb::IMessage<EnumValue>, pb::IBufferMessage {
+  public sealed partial class EnumValue : pb::IMessage<EnumValue>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<EnumValue> _parser = new pb::MessageParser<EnumValue>(() => new EnumValue());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1311,9 +1456,33 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            Name = input.ReadString();
+            break;
+          }
+          case 16: {
+            Number = input.ReadInt32();
+            break;
+          }
+          case 26: {
+            options_.AddEntriesFrom(input, _repeated_options_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1337,6 +1506,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 
@@ -1344,7 +1514,11 @@ namespace Google.Protobuf.WellKnownTypes {
   /// A protocol buffer option, which can be attached to a message, field,
   /// enumeration, etc.
   /// </summary>
-  public sealed partial class Option : pb::IMessage<Option>, pb::IBufferMessage {
+  public sealed partial class Option : pb::IMessage<Option>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Option> _parser = new pb::MessageParser<Option>(() => new Option());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1496,9 +1670,32 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            Name = input.ReadString();
+            break;
+          }
+          case 18: {
+            if (value_ == null) {
+              Value = new global::Google.Protobuf.WellKnownTypes.Any();
+            }
+            input.ReadMessage(Value);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1521,6 +1718,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 

csharp/src/Google.Protobuf/WellKnownTypes/Wrappers.cs

@@ -57,7 +57,11 @@ namespace Google.Protobuf.WellKnownTypes {
   ///
   /// The JSON representation for `DoubleValue` is JSON number.
   /// </summary>
-  public sealed partial class DoubleValue : pb::IMessage<DoubleValue>, pb::IBufferMessage {
+  public sealed partial class DoubleValue : pb::IMessage<DoubleValue>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<DoubleValue> _parser = new pb::MessageParser<DoubleValue>(() => new DoubleValue());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -173,9 +177,25 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 9: {
+            Value = input.ReadDouble();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -191,6 +211,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 
@@ -199,7 +220,11 @@ namespace Google.Protobuf.WellKnownTypes {
   ///
   /// The JSON representation for `FloatValue` is JSON number.
   /// </summary>
-  public sealed partial class FloatValue : pb::IMessage<FloatValue>, pb::IBufferMessage {
+  public sealed partial class FloatValue : pb::IMessage<FloatValue>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<FloatValue> _parser = new pb::MessageParser<FloatValue>(() => new FloatValue());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -315,9 +340,25 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 13: {
+            Value = input.ReadFloat();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -333,6 +374,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 
@@ -341,7 +383,11 @@ namespace Google.Protobuf.WellKnownTypes {
   ///
   /// The JSON representation for `Int64Value` is JSON string.
   /// </summary>
-  public sealed partial class Int64Value : pb::IMessage<Int64Value>, pb::IBufferMessage {
+  public sealed partial class Int64Value : pb::IMessage<Int64Value>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Int64Value> _parser = new pb::MessageParser<Int64Value>(() => new Int64Value());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -457,9 +503,25 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            Value = input.ReadInt64();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -475,6 +537,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 
@@ -483,7 +546,11 @@ namespace Google.Protobuf.WellKnownTypes {
   ///
   /// The JSON representation for `UInt64Value` is JSON string.
   /// </summary>
-  public sealed partial class UInt64Value : pb::IMessage<UInt64Value>, pb::IBufferMessage {
+  public sealed partial class UInt64Value : pb::IMessage<UInt64Value>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<UInt64Value> _parser = new pb::MessageParser<UInt64Value>(() => new UInt64Value());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -599,9 +666,25 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            Value = input.ReadUInt64();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -617,6 +700,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 
@@ -625,7 +709,11 @@ namespace Google.Protobuf.WellKnownTypes {
   ///
   /// The JSON representation for `Int32Value` is JSON number.
   /// </summary>
-  public sealed partial class Int32Value : pb::IMessage<Int32Value>, pb::IBufferMessage {
+  public sealed partial class Int32Value : pb::IMessage<Int32Value>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Int32Value> _parser = new pb::MessageParser<Int32Value>(() => new Int32Value());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -741,9 +829,25 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            Value = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -759,6 +863,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 
@@ -767,7 +872,11 @@ namespace Google.Protobuf.WellKnownTypes {
   ///
   /// The JSON representation for `UInt32Value` is JSON number.
   /// </summary>
-  public sealed partial class UInt32Value : pb::IMessage<UInt32Value>, pb::IBufferMessage {
+  public sealed partial class UInt32Value : pb::IMessage<UInt32Value>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<UInt32Value> _parser = new pb::MessageParser<UInt32Value>(() => new UInt32Value());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -883,9 +992,25 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            Value = input.ReadUInt32();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -901,6 +1026,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 
@@ -909,7 +1035,11 @@ namespace Google.Protobuf.WellKnownTypes {
   ///
   /// The JSON representation for `BoolValue` is JSON `true` and `false`.
   /// </summary>
-  public sealed partial class BoolValue : pb::IMessage<BoolValue>, pb::IBufferMessage {
+  public sealed partial class BoolValue : pb::IMessage<BoolValue>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<BoolValue> _parser = new pb::MessageParser<BoolValue>(() => new BoolValue());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1025,9 +1155,25 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            Value = input.ReadBool();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1043,6 +1189,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 
@@ -1051,7 +1198,11 @@ namespace Google.Protobuf.WellKnownTypes {
   ///
   /// The JSON representation for `StringValue` is JSON string.
   /// </summary>
-  public sealed partial class StringValue : pb::IMessage<StringValue>, pb::IBufferMessage {
+  public sealed partial class StringValue : pb::IMessage<StringValue>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<StringValue> _parser = new pb::MessageParser<StringValue>(() => new StringValue());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1167,9 +1318,25 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            Value = input.ReadString();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1185,6 +1352,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 
@@ -1193,7 +1361,11 @@ namespace Google.Protobuf.WellKnownTypes {
   ///
   /// The JSON representation for `BytesValue` is JSON string.
   /// </summary>
-  public sealed partial class BytesValue : pb::IMessage<BytesValue>, pb::IBufferMessage {
+  public sealed partial class BytesValue : pb::IMessage<BytesValue>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<BytesValue> _parser = new pb::MessageParser<BytesValue>(() => new BytesValue());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1309,9 +1481,25 @@ namespace Google.Protobuf.WellKnownTypes {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            Value = input.ReadBytes();
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -1327,6 +1515,7 @@ namespace Google.Protobuf.WellKnownTypes {
         }
       }
     }
+    #endif
 
   }
 

src/google/protobuf/compiler/csharp/csharp_field_base.cc

@@ -161,6 +161,12 @@ void FieldGeneratorBase::GenerateExtensionCode(io::Printer* printer) {
   // and repeated fields need this default is to not generate any code
 }
 
+void FieldGeneratorBase::GenerateParsingCode(io::Printer* printer, bool use_parse_context) {
+  // for some field types the value of "use_parse_context" doesn't matter,
+  // so we fallback to the default implementation.
+  GenerateParsingCode(printer);
+}
+
 void FieldGeneratorBase::AddDeprecatedFlag(io::Printer* printer) {
   if (descriptor_->options().deprecated()) {
     printer->Print("[global::System.ObsoleteAttribute]\n");

src/google/protobuf/compiler/csharp/csharp_field_base.h

@@ -61,6 +61,7 @@ class FieldGeneratorBase : public SourceGeneratorBase {
   virtual void GenerateMembers(io::Printer* printer) = 0;
   virtual void GenerateMergingCode(io::Printer* printer) = 0;
   virtual void GenerateParsingCode(io::Printer* printer) = 0;
+  virtual void GenerateParsingCode(io::Printer* printer, bool use_parse_context);
   virtual void GenerateSerializationCode(io::Printer* printer) = 0;
   virtual void GenerateSerializedSizeCode(io::Printer* printer) = 0;
 

src/google/protobuf/compiler/csharp/csharp_map_field.cc

@@ -94,9 +94,15 @@ void MapFieldGenerator::GenerateMergingCode(io::Printer* printer) {
 }
 
 void MapFieldGenerator::GenerateParsingCode(io::Printer* printer) {
+  GenerateParsingCode(printer, true);
+}
+
+void MapFieldGenerator::GenerateParsingCode(io::Printer* printer, bool use_parse_context) {
   printer->Print(
     variables_,
-    "$name$_.AddEntriesFrom(ref input, _map_$name$_codec);\n");
+    use_parse_context
+    ? "$name$_.AddEntriesFrom(ref input, _map_$name$_codec);\n"
+    : "$name$_.AddEntriesFrom(input, _map_$name$_codec);\n");
 }
 
 void MapFieldGenerator::GenerateSerializationCode(io::Printer* printer) {

src/google/protobuf/compiler/csharp/csharp_map_field.h

@@ -56,6 +56,7 @@ class MapFieldGenerator : public FieldGeneratorBase {
   virtual void GenerateMembers(io::Printer* printer);
   virtual void GenerateMergingCode(io::Printer* printer);
   virtual void GenerateParsingCode(io::Printer* printer);
+  virtual void GenerateParsingCode(io::Printer* printer, bool use_parse_context);
   virtual void GenerateSerializationCode(io::Printer* printer);
   virtual void GenerateSerializedSizeCode(io::Printer* printer);
 

src/google/protobuf/compiler/csharp/csharp_message.cc

@@ -125,13 +125,15 @@ void MessageGenerator::Generate(io::Printer* printer) {
     "$access_level$ sealed partial class $class_name$ : ");
 
   if (has_extension_ranges_) {
-    printer->Print(vars, "pb::IExtendableMessage<$class_name$>");
+    printer->Print(vars, "pb::IExtendableMessage<$class_name$>\n");
   }
   else {
-    printer->Print(vars, "pb::IMessage<$class_name$>");
+    printer->Print(vars, "pb::IMessage<$class_name$>\n");
   }
-  printer->Print(", pb::IBufferMessage");
-  printer->Print(" {\n");
+  printer->Print("#if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE\n");
+  printer->Print("    , pb::IBufferMessage\n");
+  printer->Print("#endif\n");
+  printer->Print("{\n");
   printer->Indent();
 
   // All static fields and properties
@@ -633,17 +635,34 @@ void MessageGenerator::GenerateMergingMethods(io::Printer* printer) {
   printer->Outdent();
   printer->Print("}\n\n");
 
-
   WriteGeneratedCodeAttributes(printer);
   printer->Print("public void MergeFrom(pb::CodedInputStream input) {\n");
+  printer->Print("#if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE\n");
   printer->Indent();
   printer->Print("input.ReadRawMessage(this);\n");
   printer->Outdent();
+  printer->Print("#else\n");
+  printer->Indent();
+  GenerateMainParseLoop(printer, false);
+  printer->Outdent();
+  printer->Print("#endif\n");
   printer->Print("}\n\n");
 
+  printer->Print("#if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE\n");
   WriteGeneratedCodeAttributes(printer);
   printer->Print("void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {\n");
   printer->Indent();
+  GenerateMainParseLoop(printer, true);
+  printer->Outdent();
+  printer->Print("}\n"); // method
+  printer->Print("#endif\n\n");
+
+}
+
+void MessageGenerator::GenerateMainParseLoop(io::Printer* printer, bool use_parse_context) {
+  std::map<string, string> vars;
+  vars["maybe_ref_input"] = use_parse_context ? "ref input" : "input";
+
   printer->Print(
     "uint tag;\n"
     "while ((tag = input.ReadTag()) != 0) {\n"
@@ -657,16 +676,16 @@ void MessageGenerator::GenerateMergingMethods(io::Printer* printer) {
         "end_tag", StrCat(end_tag_));
   }
   if (has_extension_ranges_) {
-    printer->Print(
+    printer->Print(vars,
       "default:\n"
-      "  if (!pb::ExtensionSet.TryMergeFieldFrom(ref _extensions, ref input)) {\n"
-      "    _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, ref input);\n"
+      "  if (!pb::ExtensionSet.TryMergeFieldFrom(ref _extensions, $maybe_ref_input$)) {\n"
+      "    _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, $maybe_ref_input$);\n"
       "  }\n"
       "  break;\n");
   } else {
-    printer->Print(
+    printer->Print(vars,
       "default:\n"
-      "  _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, ref input);\n"
+      "  _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, $maybe_ref_input$);\n"
       "  break;\n");
   }
   for (int i = 0; i < fields_by_number().size(); i++) {
@@ -693,7 +712,7 @@ void MessageGenerator::GenerateMergingMethods(io::Printer* printer) {
     printer->Indent();
     std::unique_ptr<FieldGeneratorBase> generator(
         CreateFieldGeneratorInternal(field));
-    generator->GenerateParsingCode(printer);
+    generator->GenerateParsingCode(printer, use_parse_context);
     printer->Print("break;\n");
     printer->Outdent();
     printer->Print("}\n");
@@ -702,8 +721,6 @@ void MessageGenerator::GenerateMergingMethods(io::Printer* printer) {
   printer->Print("}\n"); // switch
   printer->Outdent();
   printer->Print("}\n"); // while
-  printer->Outdent();
-  printer->Print("}\n\n"); // method
 }
 
 // it's a waste of space to track presence for all values, so we only track them if they're not nullable

src/google/protobuf/compiler/csharp/csharp_message.h

@@ -67,6 +67,7 @@ class MessageGenerator : public SourceGeneratorBase {
 
   void GenerateMessageSerializationMethods(io::Printer* printer);
   void GenerateMergingMethods(io::Printer* printer);
+  void GenerateMainParseLoop(io::Printer* printer, bool use_parse_context);
 
   int GetPresenceIndex(const FieldDescriptor* descriptor);
   FieldGeneratorBase* CreateFieldGeneratorInternal(

src/google/protobuf/compiler/csharp/csharp_repeated_enum_field.cc

@@ -78,9 +78,15 @@ void RepeatedEnumFieldGenerator::GenerateMergingCode(io::Printer* printer) {
 }
 
 void RepeatedEnumFieldGenerator::GenerateParsingCode(io::Printer* printer) {
+  GenerateParsingCode(printer, true);
+}
+
+void RepeatedEnumFieldGenerator::GenerateParsingCode(io::Printer* printer, bool use_parse_context) {
   printer->Print(
     variables_,
-    "$name$_.AddEntriesFrom(ref input, _repeated_$name$_codec);\n");
+    use_parse_context
+    ? "$name$_.AddEntriesFrom(ref input, _repeated_$name$_codec);\n"
+    : "$name$_.AddEntriesFrom(input, _repeated_$name$_codec);\n");
 }
 
 void RepeatedEnumFieldGenerator::GenerateSerializationCode(io::Printer* printer) {

src/google/protobuf/compiler/csharp/csharp_repeated_enum_field.h

@@ -59,6 +59,7 @@ class RepeatedEnumFieldGenerator : public FieldGeneratorBase {
   virtual void GenerateMembers(io::Printer* printer);
   virtual void GenerateMergingCode(io::Printer* printer);
   virtual void GenerateParsingCode(io::Printer* printer);
+  virtual void GenerateParsingCode(io::Printer* printer, bool use_parse_context);
   virtual void GenerateSerializationCode(io::Printer* printer);
   virtual void GenerateSerializedSizeCode(io::Printer* printer);
   virtual void GenerateExtensionCode(io::Printer* printer);

src/google/protobuf/compiler/csharp/csharp_repeated_message_field.cc

@@ -93,9 +93,15 @@ void RepeatedMessageFieldGenerator::GenerateMergingCode(io::Printer* printer) {
 }
 
 void RepeatedMessageFieldGenerator::GenerateParsingCode(io::Printer* printer) {
+  GenerateParsingCode(printer, true);
+}
+
+void RepeatedMessageFieldGenerator::GenerateParsingCode(io::Printer* printer, bool use_parse_context) {
   printer->Print(
     variables_,
-    "$name$_.AddEntriesFrom(ref input, _repeated_$name$_codec);\n");
+    use_parse_context
+    ? "$name$_.AddEntriesFrom(ref input, _repeated_$name$_codec);\n"
+    : "$name$_.AddEntriesFrom(input, _repeated_$name$_codec);\n");
 }
 
 void RepeatedMessageFieldGenerator::GenerateSerializationCode(io::Printer* printer) {

src/google/protobuf/compiler/csharp/csharp_repeated_message_field.h

@@ -59,6 +59,7 @@ class RepeatedMessageFieldGenerator : public FieldGeneratorBase {
   virtual void GenerateMembers(io::Printer* printer);
   virtual void GenerateMergingCode(io::Printer* printer);
   virtual void GenerateParsingCode(io::Printer* printer);
+  virtual void GenerateParsingCode(io::Printer* printer, bool use_parse_context);
   virtual void GenerateSerializationCode(io::Printer* printer);
   virtual void GenerateSerializedSizeCode(io::Printer* printer);
   virtual void GenerateExtensionCode(io::Printer* printer);

src/google/protobuf/compiler/csharp/csharp_repeated_primitive_field.cc

@@ -78,9 +78,15 @@ void RepeatedPrimitiveFieldGenerator::GenerateMergingCode(io::Printer* printer)
 }
 
 void RepeatedPrimitiveFieldGenerator::GenerateParsingCode(io::Printer* printer) {
+  GenerateParsingCode(printer, true);
+}
+
+void RepeatedPrimitiveFieldGenerator::GenerateParsingCode(io::Printer* printer, bool use_parse_context) {
   printer->Print(
     variables_,
-    "$name$_.AddEntriesFrom(ref input, _repeated_$name$_codec);\n");
+    use_parse_context
+    ? "$name$_.AddEntriesFrom(ref input, _repeated_$name$_codec);\n"
+    : "$name$_.AddEntriesFrom(input, _repeated_$name$_codec);\n");
 }
 
 void RepeatedPrimitiveFieldGenerator::GenerateSerializationCode(io::Printer* printer) {

src/google/protobuf/compiler/csharp/csharp_repeated_primitive_field.h

@@ -55,6 +55,7 @@ class RepeatedPrimitiveFieldGenerator : public FieldGeneratorBase {
   virtual void GenerateMembers(io::Printer* printer);
   virtual void GenerateMergingCode(io::Printer* printer);
   virtual void GenerateParsingCode(io::Printer* printer);
+  virtual void GenerateParsingCode(io::Printer* printer, bool use_parse_context);
   virtual void GenerateSerializationCode(io::Printer* printer);
   virtual void GenerateSerializedSizeCode(io::Printer* printer);
   virtual void GenerateExtensionCode(io::Printer* printer);

src/google/protobuf/compiler/csharp/csharp_wrapper_field.cc

@@ -114,12 +114,21 @@ void WrapperFieldGenerator::GenerateMergingCode(io::Printer* printer) {
 }
 
 void WrapperFieldGenerator::GenerateParsingCode(io::Printer* printer) {
+  GenerateParsingCode(printer, true);
+}
+
+void WrapperFieldGenerator::GenerateParsingCode(io::Printer* printer, bool use_parse_context) {
   printer->Print(
     variables_,
-    "$type_name$ value = _single_$name$_codec.Read(ref input);\n"
-    "if ($has_not_property_check$ || value != $default_value$) {\n"
-    "  $property_name$ = value;\n"
-    "}\n");
+    use_parse_context
+    ? "$type_name$ value = _single_$name$_codec.Read(ref input);\n"
+      "if ($has_not_property_check$ || value != $default_value$) {\n"
+      "  $property_name$ = value;\n"
+      "}\n"
+    : "$type_name$ value = _single_$name$_codec.Read(input);\n"
+      "if ($has_not_property_check$ || value != $default_value$) {\n"
+      "  $property_name$ = value;\n"
+      "}\n");
 }
 
 void WrapperFieldGenerator::GenerateSerializationCode(io::Printer* printer) {
@@ -248,9 +257,15 @@ void WrapperOneofFieldGenerator::GenerateMergingCode(io::Printer* printer) {
 }
 
 void WrapperOneofFieldGenerator::GenerateParsingCode(io::Printer* printer) {
+  GenerateParsingCode(printer, true);
+}
+
+void WrapperOneofFieldGenerator::GenerateParsingCode(io::Printer* printer, bool use_parse_context) {
   printer->Print(
     variables_,
-    "$property_name$ = _oneof_$name$_codec.Read(ref input);\n");
+    use_parse_context
+    ? "$property_name$ = _oneof_$name$_codec.Read(ref input);\n"
+    : "$property_name$ = _oneof_$name$_codec.Read(input);\n");
 }
 
 void WrapperOneofFieldGenerator::GenerateSerializationCode(io::Printer* printer) {

src/google/protobuf/compiler/csharp/csharp_wrapper_field.h

@@ -58,6 +58,7 @@ class WrapperFieldGenerator : public FieldGeneratorBase {
   virtual void GenerateMembers(io::Printer* printer);
   virtual void GenerateMergingCode(io::Printer* printer);
   virtual void GenerateParsingCode(io::Printer* printer);
+  virtual void GenerateParsingCode(io::Printer* printer, bool use_parse_context);
   virtual void GenerateSerializationCode(io::Printer* printer);
   virtual void GenerateSerializedSizeCode(io::Printer* printer);
   virtual void GenerateExtensionCode(io::Printer* printer);
@@ -83,6 +84,7 @@ class WrapperOneofFieldGenerator : public WrapperFieldGenerator {
   virtual void GenerateMembers(io::Printer* printer);
   virtual void GenerateMergingCode(io::Printer* printer);
   virtual void GenerateParsingCode(io::Printer* printer);
+  virtual void GenerateParsingCode(io::Printer* printer, bool use_parse_context);
   virtual void GenerateSerializationCode(io::Printer* printer);
   virtual void GenerateSerializedSizeCode(io::Printer* printer);
 };