Merge pull request #5936 from ObsidianMinor/csharp/proto2-feature/finale

C# Proto2 feature : Finale

Makefile.am

@@ -68,9 +68,12 @@ csharp_EXTRA_DIST=                                                           \
   csharp/protos/map_unittest_proto3.proto                                    \
   csharp/protos/unittest_custom_options_proto3.proto                         \
   csharp/protos/unittest_import_public_proto3.proto                          \
+  csharp/protos/unittest_import_public.proto                                 \
   csharp/protos/unittest_import_proto3.proto                                 \
+  csharp/protos/unittest_import.proto                                        \
   csharp/protos/unittest_issues.proto                                        \
   csharp/protos/unittest_proto3.proto                                        \
+  csharp/protos/unittest.proto                                               \
   csharp/src/AddressBook/AddPerson.cs                                        \
   csharp/src/AddressBook/Addressbook.cs                                      \
   csharp/src/AddressBook/AddressBook.csproj                                  \
@@ -100,9 +103,11 @@ csharp_EXTRA_DIST=                                                           \
   csharp/src/Google.Protobuf.Test/Compatibility/TypeExtensionsTest.cs        \
   csharp/src/Google.Protobuf.Test/DeprecatedMemberTest.cs                    \
   csharp/src/Google.Protobuf.Test/EqualityTester.cs                          \
+  csharp/src/Google.Protobuf.Test/ExtensionSetTest.cs                        \
   csharp/src/Google.Protobuf.Test/FieldCodecTest.cs                          \
   csharp/src/Google.Protobuf.Test/FieldMaskTreeTest.cs                       \
   csharp/src/Google.Protobuf.Test/GeneratedMessageTest.cs                    \
+  csharp/src/Google.Protobuf.Test/GeneratedMessageTest.Proto2.cs             \
   csharp/src/Google.Protobuf.Test/Google.Protobuf.Test.csproj                \
   csharp/src/Google.Protobuf.Test/IssuesTest.cs                              \
   csharp/src/Google.Protobuf.Test/JsonFormatterTest.cs                       \
@@ -119,13 +124,17 @@ csharp_EXTRA_DIST=                                                           \
   csharp/src/Google.Protobuf.Test/TestCornerCases.cs                         \
   csharp/src/Google.Protobuf.Test/TestProtos/ForeignMessagePartial.cs        \
   csharp/src/Google.Protobuf.Test/TestProtos/MapUnittestProto3.cs            \
+  csharp/src/Google.Protobuf.Test/TestProtos/TestMessagesProto2.cs           \
   csharp/src/Google.Protobuf.Test/TestProtos/TestMessagesProto3.cs           \
   csharp/src/Google.Protobuf.Test/TestProtos/UnittestCustomOptionsProto3.cs  \
   csharp/src/Google.Protobuf.Test/TestProtos/UnittestImportProto3.cs         \
   csharp/src/Google.Protobuf.Test/TestProtos/UnittestImportPublicProto3.cs   \
+  csharp/src/Google.Protobuf.Test/TestProtos/UnittestImportPublic.cs         \
+  csharp/src/Google.Protobuf.Test/TestProtos/UnittestImport.cs               \
   csharp/src/Google.Protobuf.Test/TestProtos/UnittestIssues.cs               \
   csharp/src/Google.Protobuf.Test/TestProtos/UnittestProto3.cs               \
   csharp/src/Google.Protobuf.Test/TestProtos/UnittestWellKnownTypes.cs       \
+  csharp/src/Google.Protobuf.Test/TestProtos/Unittest.cs                     \
   csharp/src/Google.Protobuf.Test/WellKnownTypes/AnyTest.cs                  \
   csharp/src/Google.Protobuf.Test/WellKnownTypes/DurationTest.cs             \
   csharp/src/Google.Protobuf.Test/WellKnownTypes/FieldMaskTest.cs            \

csharp/generate_protos.sh

@@ -52,8 +52,12 @@ $PROTOC -Isrc -Icsharp/protos \
     csharp/protos/unittest_proto3.proto \
     csharp/protos/unittest_import_proto3.proto \
     csharp/protos/unittest_import_public_proto3.proto \
+    csharp/protos/unittest.proto \
+    csharp/protos/unittest_import.proto \
+    csharp/protos/unittest_import_public.proto \
     src/google/protobuf/unittest_well_known_types.proto \
-    src/google/protobuf/test_messages_proto3.proto
+    src/google/protobuf/test_messages_proto3.proto \
+    src/google/protobuf/test_messages_proto2.proto
 
 # AddressBook sample protos
 $PROTOC -Iexamples -Isrc --csharp_out=csharp/src/AddressBook \

csharp/protos/unittest.proto

@@ -0,0 +1,1113 @@
+// 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.
+
+// Author: kenton@google.com (Kenton Varda)
+//  Based on original Protocol Buffers design by
+//  Sanjay Ghemawat, Jeff Dean, and others.
+//
+// A proto file we will use for unit testing.
+//
+// LINT: ALLOW_GROUPS, LEGACY_NAMES
+
+syntax = "proto2";
+
+// Some generic_services option(s) added automatically.
+// See:  http://go/proto2-generic-services-default
+option cc_generic_services = true;     // auto-added
+option java_generic_services = true;   // auto-added
+option py_generic_services = true;     // auto-added
+option cc_enable_arenas = true;
+
+import "unittest_import.proto";
+
+// We don't put this in a package within proto2 because we need to make sure
+// that the generated code doesn't depend on being in the proto2 namespace.
+// In test_util.h we do "using namespace unittest = protobuf_unittest".
+package protobuf_unittest_proto2;
+
+// Protos optimized for SPEED use a strict superset of the generated code
+// of equivalent ones optimized for CODE_SIZE, so we should optimize all our
+// tests for speed unless explicitly testing code size optimization.
+option optimize_for = SPEED;
+
+option csharp_namespace = "Google.Protobuf.TestProtos.Proto2";
+
+// This proto includes every type of field in both singular and repeated
+// forms.
+message TestAllTypes {
+  message NestedMessage {
+    // The field name "b" fails to compile in proto1 because it conflicts with
+    // a local variable named "b" in one of the generated methods.  Doh.
+    // This file needs to compile in proto1 to test backwards-compatibility.
+    optional int32 bb = 1;
+  }
+
+  enum NestedEnum {
+    FOO = 1;
+    BAR = 2;
+    BAZ = 3;
+    NEG = -1;  // Intentionally negative.
+  }
+
+  // Singular
+  optional    int32 optional_int32    =  1;
+  optional    int64 optional_int64    =  2;
+  optional   uint32 optional_uint32   =  3;
+  optional   uint64 optional_uint64   =  4;
+  optional   sint32 optional_sint32   =  5;
+  optional   sint64 optional_sint64   =  6;
+  optional  fixed32 optional_fixed32  =  7;
+  optional  fixed64 optional_fixed64  =  8;
+  optional sfixed32 optional_sfixed32 =  9;
+  optional sfixed64 optional_sfixed64 = 10;
+  optional    float optional_float    = 11;
+  optional   double optional_double   = 12;
+  optional     bool optional_bool     = 13;
+  optional   string optional_string   = 14;
+  optional    bytes optional_bytes    = 15;
+
+  optional group OptionalGroup = 16 {
+    optional int32 a = 17;
+  }
+
+  optional NestedMessage                        optional_nested_message  = 18;
+  optional ForeignMessage                       optional_foreign_message = 19;
+  optional protobuf_unittest_import_proto2.ImportMessage optional_import_message  = 20;
+
+  optional NestedEnum                           optional_nested_enum     = 21;
+  optional ForeignEnum                          optional_foreign_enum    = 22;
+  optional protobuf_unittest_import_proto2.ImportEnum    optional_import_enum     = 23;
+
+  optional string optional_string_piece = 24 [ctype=STRING_PIECE];
+  optional string optional_cord = 25 [ctype=CORD];
+
+  // Defined in unittest_import_public.proto
+  optional protobuf_unittest_import_proto2.PublicImportMessage
+      optional_public_import_message = 26;
+
+  optional NestedMessage optional_lazy_message = 27 [lazy=true];
+
+  // Repeated
+  repeated    int32 repeated_int32    = 31;
+  repeated    int64 repeated_int64    = 32;
+  repeated   uint32 repeated_uint32   = 33;
+  repeated   uint64 repeated_uint64   = 34;
+  repeated   sint32 repeated_sint32   = 35;
+  repeated   sint64 repeated_sint64   = 36;
+  repeated  fixed32 repeated_fixed32  = 37;
+  repeated  fixed64 repeated_fixed64  = 38;
+  repeated sfixed32 repeated_sfixed32 = 39;
+  repeated sfixed64 repeated_sfixed64 = 40;
+  repeated    float repeated_float    = 41;
+  repeated   double repeated_double   = 42;
+  repeated     bool repeated_bool     = 43;
+  repeated   string repeated_string   = 44;
+  repeated    bytes repeated_bytes    = 45;
+
+  repeated group RepeatedGroup = 46 {
+    optional int32 a = 47;
+  }
+
+  repeated NestedMessage                        repeated_nested_message  = 48;
+  repeated ForeignMessage                       repeated_foreign_message = 49;
+  repeated protobuf_unittest_import_proto2.ImportMessage repeated_import_message  = 50;
+
+  repeated NestedEnum                           repeated_nested_enum     = 51;
+  repeated ForeignEnum                          repeated_foreign_enum    = 52;
+  repeated protobuf_unittest_import_proto2.ImportEnum    repeated_import_enum     = 53;
+
+  repeated string repeated_string_piece = 54 [ctype=STRING_PIECE];
+  repeated string repeated_cord = 55 [ctype=CORD];
+
+  repeated NestedMessage repeated_lazy_message = 57 [lazy=true];
+
+  // Singular with defaults
+  optional    int32 default_int32    = 61 [default =  41    ];
+  optional    int64 default_int64    = 62 [default =  42    ];
+  optional   uint32 default_uint32   = 63 [default =  43    ];
+  optional   uint64 default_uint64   = 64 [default =  44    ];
+  optional   sint32 default_sint32   = 65 [default = -45    ];
+  optional   sint64 default_sint64   = 66 [default =  46    ];
+  optional  fixed32 default_fixed32  = 67 [default =  47    ];
+  optional  fixed64 default_fixed64  = 68 [default =  48    ];
+  optional sfixed32 default_sfixed32 = 69 [default =  49    ];
+  optional sfixed64 default_sfixed64 = 70 [default = -50    ];
+  optional    float default_float    = 71 [default =  51.5  ];
+  optional   double default_double   = 72 [default =  52e3  ];
+  optional     bool default_bool     = 73 [default = true   ];
+  optional   string default_string   = 74 [default = "hello"];
+  optional    bytes default_bytes    = 75 [default = "world"];
+
+  optional NestedEnum  default_nested_enum  = 81 [default = BAR        ];
+  optional ForeignEnum default_foreign_enum = 82 [default = FOREIGN_BAR];
+  optional protobuf_unittest_import_proto2.ImportEnum
+      default_import_enum = 83 [default = IMPORT_BAR];
+
+  optional string default_string_piece = 84 [ctype=STRING_PIECE,default="abc"];
+  optional string default_cord = 85 [ctype=CORD,default="123"];
+
+  // For oneof test
+  oneof oneof_field {
+    uint32 oneof_uint32 = 111;
+    NestedMessage oneof_nested_message = 112;
+    string oneof_string = 113;
+    bytes oneof_bytes = 114;
+  }
+}
+
+// This proto includes a recusively nested message.
+message NestedTestAllTypes {
+  optional NestedTestAllTypes child = 1;
+  optional TestAllTypes payload = 2;
+  repeated NestedTestAllTypes repeated_child = 3;
+}
+
+message TestDeprecatedFields {
+  optional int32 deprecated_int32 = 1 [deprecated=true];
+  oneof oneof_fields {
+    int32 deprecated_int32_in_oneof = 2 [deprecated=true];
+  }
+}
+
+message TestDeprecatedMessage {
+  option deprecated = true;
+}
+
+// Define these after TestAllTypes to make sure the compiler can handle
+// that.
+message ForeignMessage {
+  optional int32 c = 1;
+  optional int32 d = 2;
+}
+
+enum ForeignEnum {
+  FOREIGN_FOO = 4;
+  FOREIGN_BAR = 5;
+  FOREIGN_BAZ = 6;
+}
+
+message TestReservedFields {
+  reserved 2, 15, 9 to 11;
+  reserved "bar", "baz";
+}
+
+message TestAllExtensions {
+  extensions 1 to max;
+}
+
+extend TestAllExtensions {
+  // Singular
+  optional    int32 optional_int32_extension    =  1;
+  optional    int64 optional_int64_extension    =  2;
+  optional   uint32 optional_uint32_extension   =  3;
+  optional   uint64 optional_uint64_extension   =  4;
+  optional   sint32 optional_sint32_extension   =  5;
+  optional   sint64 optional_sint64_extension   =  6;
+  optional  fixed32 optional_fixed32_extension  =  7;
+  optional  fixed64 optional_fixed64_extension  =  8;
+  optional sfixed32 optional_sfixed32_extension =  9;
+  optional sfixed64 optional_sfixed64_extension = 10;
+  optional    float optional_float_extension    = 11;
+  optional   double optional_double_extension   = 12;
+  optional     bool optional_bool_extension     = 13;
+  optional   string optional_string_extension   = 14;
+  optional    bytes optional_bytes_extension    = 15;
+
+  optional group OptionalGroup_extension = 16 {
+    optional int32 a = 17;
+  }
+
+  optional TestAllTypes.NestedMessage optional_nested_message_extension = 18;
+  optional ForeignMessage optional_foreign_message_extension = 19;
+  optional protobuf_unittest_import_proto2.ImportMessage
+    optional_import_message_extension = 20;
+
+  optional TestAllTypes.NestedEnum optional_nested_enum_extension = 21;
+  optional ForeignEnum optional_foreign_enum_extension = 22;
+  optional protobuf_unittest_import_proto2.ImportEnum
+    optional_import_enum_extension = 23;
+
+  optional string optional_string_piece_extension = 24 [ctype=STRING_PIECE];
+  optional string optional_cord_extension = 25 [ctype=CORD];
+
+  optional protobuf_unittest_import_proto2.PublicImportMessage
+    optional_public_import_message_extension = 26;
+
+  optional TestAllTypes.NestedMessage
+    optional_lazy_message_extension = 27 [lazy=true];
+
+  // Repeated
+  repeated    int32 repeated_int32_extension    = 31;
+  repeated    int64 repeated_int64_extension    = 32;
+  repeated   uint32 repeated_uint32_extension   = 33;
+  repeated   uint64 repeated_uint64_extension   = 34;
+  repeated   sint32 repeated_sint32_extension   = 35;
+  repeated   sint64 repeated_sint64_extension   = 36;
+  repeated  fixed32 repeated_fixed32_extension  = 37;
+  repeated  fixed64 repeated_fixed64_extension  = 38;
+  repeated sfixed32 repeated_sfixed32_extension = 39;
+  repeated sfixed64 repeated_sfixed64_extension = 40;
+  repeated    float repeated_float_extension    = 41;
+  repeated   double repeated_double_extension   = 42;
+  repeated     bool repeated_bool_extension     = 43;
+  repeated   string repeated_string_extension   = 44;
+  repeated    bytes repeated_bytes_extension    = 45;
+
+  repeated group RepeatedGroup_extension = 46 {
+    optional int32 a = 47;
+  }
+
+  repeated TestAllTypes.NestedMessage repeated_nested_message_extension = 48;
+  repeated ForeignMessage repeated_foreign_message_extension = 49;
+  repeated protobuf_unittest_import_proto2.ImportMessage
+    repeated_import_message_extension = 50;
+
+  repeated TestAllTypes.NestedEnum repeated_nested_enum_extension = 51;
+  repeated ForeignEnum repeated_foreign_enum_extension = 52;
+  repeated protobuf_unittest_import_proto2.ImportEnum
+    repeated_import_enum_extension = 53;
+
+  repeated string repeated_string_piece_extension = 54 [ctype=STRING_PIECE];
+  repeated string repeated_cord_extension = 55 [ctype=CORD];
+
+  repeated TestAllTypes.NestedMessage
+    repeated_lazy_message_extension = 57 [lazy=true];
+
+  // Singular with defaults
+  optional    int32 default_int32_extension    = 61 [default =  41    ];
+  optional    int64 default_int64_extension    = 62 [default =  42    ];
+  optional   uint32 default_uint32_extension   = 63 [default =  43    ];
+  optional   uint64 default_uint64_extension   = 64 [default =  44    ];
+  optional   sint32 default_sint32_extension   = 65 [default = -45    ];
+  optional   sint64 default_sint64_extension   = 66 [default =  46    ];
+  optional  fixed32 default_fixed32_extension  = 67 [default =  47    ];
+  optional  fixed64 default_fixed64_extension  = 68 [default =  48    ];
+  optional sfixed32 default_sfixed32_extension = 69 [default =  49    ];
+  optional sfixed64 default_sfixed64_extension = 70 [default = -50    ];
+  optional    float default_float_extension    = 71 [default =  51.5  ];
+  optional   double default_double_extension   = 72 [default =  52e3  ];
+  optional     bool default_bool_extension     = 73 [default = true   ];
+  optional   string default_string_extension   = 74 [default = "hello"];
+  optional    bytes default_bytes_extension    = 75 [default = "world"];
+
+  optional TestAllTypes.NestedEnum
+    default_nested_enum_extension = 81 [default = BAR];
+  optional ForeignEnum
+    default_foreign_enum_extension = 82 [default = FOREIGN_BAR];
+  optional protobuf_unittest_import_proto2.ImportEnum
+    default_import_enum_extension = 83 [default = IMPORT_BAR];
+
+  optional string default_string_piece_extension = 84 [ctype=STRING_PIECE,
+                                                       default="abc"];
+  optional string default_cord_extension = 85 [ctype=CORD, default="123"];
+
+  // For oneof test
+  optional uint32 oneof_uint32_extension = 111;
+  optional TestAllTypes.NestedMessage oneof_nested_message_extension = 112;
+  optional string oneof_string_extension = 113;
+  optional bytes oneof_bytes_extension = 114;
+}
+
+message TestGroup {
+  optional group OptionalGroup = 16 {
+    optional int32 a = 17;
+  }
+  optional ForeignEnum optional_foreign_enum = 22;
+}
+
+message TestGroupExtension {
+  extensions 1 to max;
+}
+
+message TestNestedExtension {
+  extend TestAllExtensions {
+    // Check for bug where string extensions declared in tested scope did not
+    // compile.
+    optional string test = 1002 [default="test"];
+    // Used to test if generated extension name is correct when there are
+    // underscores.
+    optional string nested_string_extension = 1003;
+  }
+
+  extend TestGroupExtension {
+    optional group OptionalGroup_extension = 16 {
+      optional int32 a = 17;
+    }
+    optional ForeignEnum optional_foreign_enum_extension = 22;
+  }
+}
+
+// We have separate messages for testing required fields because it's
+// annoying to have to fill in required fields in TestProto in order to
+// do anything with it.  Note that we don't need to test every type of
+// required filed because the code output is basically identical to
+// optional fields for all types.
+message TestRequired {
+  required int32 a = 1;
+  optional int32 dummy2 = 2;
+  required int32 b = 3;
+
+  extend TestAllExtensions {
+    optional TestRequired single = 1000;
+    repeated TestRequired multi  = 1001;
+  }
+
+  // Pad the field count to 32 so that we can test that IsInitialized()
+  // properly checks multiple elements of has_bits_.
+  optional int32 dummy4  =  4;
+  optional int32 dummy5  =  5;
+  optional int32 dummy6  =  6;
+  optional int32 dummy7  =  7;
+  optional int32 dummy8  =  8;
+  optional int32 dummy9  =  9;
+  optional int32 dummy10 = 10;
+  optional int32 dummy11 = 11;
+  optional int32 dummy12 = 12;
+  optional int32 dummy13 = 13;
+  optional int32 dummy14 = 14;
+  optional int32 dummy15 = 15;
+  optional int32 dummy16 = 16;
+  optional int32 dummy17 = 17;
+  optional int32 dummy18 = 18;
+  optional int32 dummy19 = 19;
+  optional int32 dummy20 = 20;
+  optional int32 dummy21 = 21;
+  optional int32 dummy22 = 22;
+  optional int32 dummy23 = 23;
+  optional int32 dummy24 = 24;
+  optional int32 dummy25 = 25;
+  optional int32 dummy26 = 26;
+  optional int32 dummy27 = 27;
+  optional int32 dummy28 = 28;
+  optional int32 dummy29 = 29;
+  optional int32 dummy30 = 30;
+  optional int32 dummy31 = 31;
+  optional int32 dummy32 = 32;
+
+  required int32 c = 33;
+}
+
+message TestRequiredForeign {
+  optional TestRequired optional_message = 1;
+  repeated TestRequired repeated_message = 2;
+  optional int32 dummy = 3;
+}
+
+message TestRequiredMessage {
+  optional TestRequired optional_message = 1;
+  repeated TestRequired repeated_message = 2;
+  required TestRequired required_message = 3;
+}
+
+// Test that we can use NestedMessage from outside TestAllTypes.
+message TestForeignNested {
+  optional TestAllTypes.NestedMessage foreign_nested = 1;
+}
+
+// TestEmptyMessage is used to test unknown field support.
+message TestEmptyMessage {
+}
+
+// Like above, but declare all field numbers as potential extensions.  No
+// actual extensions should ever be defined for this type.
+message TestEmptyMessageWithExtensions {
+  extensions 1 to max;
+}
+
+message TestMultipleExtensionRanges {
+  extensions 42;
+  extensions 4143 to 4243;
+  extensions 65536 to max;
+}
+
+// Test that really large tag numbers don't break anything.
+message TestReallyLargeTagNumber {
+  // The largest possible tag number is 2^28 - 1, since the wire format uses
+  // three bits to communicate wire type.
+  optional int32 a = 1;
+  optional int32 bb = 268435455;
+}
+
+message TestRecursiveMessage {
+  optional TestRecursiveMessage a = 1;
+  optional int32 i = 2;
+}
+
+// Test that mutual recursion works.
+message TestMutualRecursionA {
+  message SubMessage {
+    optional TestMutualRecursionB b = 1;
+  }
+  optional TestMutualRecursionB bb = 1;
+  optional group SubGroup = 2 {
+    optional SubMessage sub_message = 3;  // Needed because of bug in javatest
+    optional TestAllTypes not_in_this_scc = 4;
+  }
+}
+
+message TestMutualRecursionB {
+  optional TestMutualRecursionA a = 1;
+  optional int32 optional_int32 = 2;
+}
+
+message TestIsInitialized {
+  message SubMessage {
+    optional group SubGroup = 1 {
+      required int32 i = 2;
+    }
+  }
+  optional SubMessage sub_message = 1;
+}
+
+// Test that groups have disjoint field numbers from their siblings and
+// parents.  This is NOT possible in proto1; only google.protobuf.  When attempting
+// to compile with proto1, this will emit an error; so we only include it
+// in protobuf_unittest_proto.
+message TestDupFieldNumber {                        // NO_PROTO1
+  optional int32 a = 1;                             // NO_PROTO1
+  optional group Foo = 2 { optional int32 a = 1; }  // NO_PROTO1
+  optional group Bar = 3 { optional int32 a = 1; }  // NO_PROTO1
+}                                                   // NO_PROTO1
+
+// Additional messages for testing lazy fields.
+message TestEagerMessage {
+  optional TestAllTypes sub_message = 1 [lazy=false];
+}
+message TestLazyMessage {
+  optional TestAllTypes sub_message = 1 [lazy=true];
+}
+
+// Needed for a Python test.
+message TestNestedMessageHasBits {
+  message NestedMessage {
+    repeated int32 nestedmessage_repeated_int32 = 1;
+    repeated ForeignMessage nestedmessage_repeated_foreignmessage = 2;
+  }
+  optional NestedMessage optional_nested_message = 1;
+}
+
+
+// Test an enum that has multiple values with the same number.
+enum TestEnumWithDupValue {
+  option allow_alias = true;
+
+  FOO1 = 1;
+  BAR1 = 2;
+  BAZ = 3;
+  FOO2 = 1;
+  BAR2 = 2;
+}
+
+// Test an enum with large, unordered values.
+enum TestSparseEnum {
+  SPARSE_A = 123;
+  SPARSE_B = 62374;
+  SPARSE_C = 12589234;
+  SPARSE_D = -15;
+  SPARSE_E = -53452;
+  SPARSE_F = 0;
+  SPARSE_G = 2;
+}
+
+// Test message with CamelCase field names.  This violates Protocol Buffer
+// standard style.
+message TestCamelCaseFieldNames {
+  optional int32 PrimitiveField = 1;
+  optional string StringField = 2;
+  optional ForeignEnum EnumField = 3;
+  optional ForeignMessage MessageField = 4;
+  optional string StringPieceField = 5 [ctype=STRING_PIECE];
+  optional string CordField = 6 [ctype=CORD];
+
+  repeated int32 RepeatedPrimitiveField = 7;
+  repeated string RepeatedStringField = 8;
+  repeated ForeignEnum RepeatedEnumField = 9;
+  repeated ForeignMessage RepeatedMessageField = 10;
+  repeated string RepeatedStringPieceField = 11 [ctype=STRING_PIECE];
+  repeated string RepeatedCordField = 12 [ctype=CORD];
+}
+
+
+// We list fields out of order, to ensure that we're using field number and not
+// field index to determine serialization order.
+message TestFieldOrderings {
+  optional string my_string = 11;
+  extensions 2 to 10;
+  optional int64 my_int = 1;
+  extensions 12 to 100;
+  optional float my_float = 101;
+  message NestedMessage {
+    optional int64 oo = 2;
+    // The field name "b" fails to compile in proto1 because it conflicts with
+    // a local variable named "b" in one of the generated methods.  Doh.
+    // This file needs to compile in proto1 to test backwards-compatibility.
+    optional int32 bb = 1;
+  }
+
+  optional NestedMessage optional_nested_message  = 200;
+}
+
+extend TestFieldOrderings {
+  optional string my_extension_string = 50;
+  optional int32 my_extension_int = 5;
+}
+
+message TestExtensionOrderings1 {
+  extend TestFieldOrderings {
+    optional TestExtensionOrderings1 test_ext_orderings1 = 13;
+  }
+  optional string my_string = 1;
+}
+
+message TestExtensionOrderings2 {
+  extend TestFieldOrderings {
+    optional TestExtensionOrderings2 test_ext_orderings2 = 12;
+  }
+  message TestExtensionOrderings3 {
+    extend TestFieldOrderings {
+      optional TestExtensionOrderings3 test_ext_orderings3 = 14;
+    }
+    optional string my_string = 1;
+  }
+  optional string my_string = 1;
+}
+
+message TestExtremeDefaultValues {
+  optional bytes escaped_bytes = 1 [default = "\0\001\a\b\f\n\r\t\v\\\'\"\xfe"];
+  optional uint32 large_uint32 = 2 [default = 0xFFFFFFFF];
+  optional uint64 large_uint64 = 3 [default = 0xFFFFFFFFFFFFFFFF];
+  optional  int32 small_int32  = 4 [default = -0x7FFFFFFF];
+  optional  int64 small_int64  = 5 [default = -0x7FFFFFFFFFFFFFFF];
+  optional  int32 really_small_int32 = 21 [default = -0x80000000];
+  optional  int64 really_small_int64 = 22 [default = -0x8000000000000000];
+
+  // The default value here is UTF-8 for "\u1234".  (We could also just type
+  // the UTF-8 text directly into this text file rather than escape it, but
+  // lots of people use editors that would be confused by this.)
+  optional string utf8_string = 6 [default = "\341\210\264"];
+
+  // Tests for single-precision floating-point values.
+  optional float zero_float = 7 [default = 0];
+  optional float one_float = 8 [default = 1];
+  optional float small_float = 9 [default = 1.5];
+  optional float negative_one_float = 10 [default = -1];
+  optional float negative_float = 11 [default = -1.5];
+  // Using exponents
+  optional float large_float = 12 [default = 2E8];
+  optional float small_negative_float = 13 [default = -8e-28];
+
+  // Text for nonfinite floating-point values.
+  optional double inf_double = 14 [default = inf];
+  optional double neg_inf_double = 15 [default = -inf];
+  optional double nan_double = 16 [default = nan];
+  optional float inf_float = 17 [default = inf];
+  optional float neg_inf_float = 18 [default = -inf];
+  optional float nan_float = 19 [default = nan];
+
+  // Tests for C++ trigraphs.
+  // Trigraphs should be escaped in C++ generated files, but they should not be
+  // escaped for other languages.
+  // Note that in .proto file, "\?" is a valid way to escape ? in string
+  // literals.
+  optional string cpp_trigraph = 20 [default = "? \? ?? \?? \??? ??/ ?\?-"];
+
+  // String defaults containing the character '\000'
+  optional string string_with_zero       = 23 [default = "hel\000lo"];
+  optional  bytes bytes_with_zero        = 24 [default = "wor\000ld"];
+  optional string string_piece_with_zero = 25 [ctype=STRING_PIECE,
+                                               default="ab\000c"];
+  optional string cord_with_zero         = 26 [ctype=CORD,
+                                               default="12\0003"];
+  optional string replacement_string     = 27 [default="${unknown}"];
+}
+
+message SparseEnumMessage {
+  optional TestSparseEnum sparse_enum = 1;
+}
+
+// Test String and Bytes: string is for valid UTF-8 strings
+message OneString {
+  optional string data = 1;
+}
+
+message MoreString {
+  repeated string data = 1;
+}
+
+message OneBytes {
+  optional bytes data = 1;
+}
+
+message MoreBytes {
+  repeated bytes data = 1;
+}
+
+// Test int32, uint32, int64, uint64, and bool are all compatible
+message Int32Message {
+  optional int32 data = 1;
+}
+
+message Uint32Message {
+  optional uint32 data = 1;
+}
+
+message Int64Message {
+  optional int64 data = 1;
+}
+
+message Uint64Message {
+  optional uint64 data = 1;
+}
+
+message BoolMessage {
+  optional bool data = 1;
+}
+
+// Test oneofs.
+message TestOneof {
+  oneof foo {
+    int32 foo_int = 1;
+    string foo_string = 2;
+    TestAllTypes foo_message = 3;
+    group FooGroup = 4 {
+      optional int32 a = 5;
+      optional string b = 6;
+    }
+  }
+}
+
+message TestOneofBackwardsCompatible {
+  optional int32 foo_int = 1;
+  optional string foo_string = 2;
+  optional TestAllTypes foo_message = 3;
+  optional group FooGroup = 4 {
+    optional int32 a = 5;
+    optional string b = 6;
+  }
+}
+
+message TestOneof2 {
+  oneof foo {
+    int32 foo_int = 1;
+    string foo_string = 2;
+    string foo_cord = 3 [ctype=CORD];
+    string foo_string_piece = 4 [ctype=STRING_PIECE];
+    bytes foo_bytes = 5;
+    NestedEnum foo_enum = 6;
+    NestedMessage foo_message = 7;
+    group FooGroup = 8 {
+      optional int32 a = 9;
+      optional string b = 10;
+    }
+    NestedMessage foo_lazy_message = 11 [lazy=true];
+  }
+
+  oneof bar {
+    int32 bar_int = 12 [default = 5];
+    string bar_string = 13 [default = "STRING"];
+    string bar_cord = 14 [ctype=CORD, default = "CORD"];
+    string bar_string_piece = 15 [ctype=STRING_PIECE, default = "SPIECE"];
+    bytes bar_bytes = 16 [default = "BYTES"];
+    NestedEnum bar_enum = 17 [default = BAR];
+  }
+
+  optional int32 baz_int = 18;
+  optional string baz_string = 19 [default = "BAZ"];
+
+  message NestedMessage {
+    optional int64 qux_int = 1;
+    repeated int32 corge_int = 2;
+  }
+
+  enum NestedEnum {
+    FOO = 1;
+    BAR = 2;
+    BAZ = 3;
+  }
+}
+
+message TestRequiredOneof {
+  oneof foo {
+    int32 foo_int = 1;
+    string foo_string = 2;
+    NestedMessage foo_message = 3;
+  }
+  message NestedMessage {
+    required double required_double = 1;
+  }
+}
+
+message TestRequiredMap {
+  map<int32, NestedMessage> foo = 1;
+  message NestedMessage {
+    required int32 required_int32 = 1;
+  }
+}
+
+// Test messages for packed fields
+
+message TestPackedTypes {
+  repeated    int32 packed_int32    =  90 [packed = true];
+  repeated    int64 packed_int64    =  91 [packed = true];
+  repeated   uint32 packed_uint32   =  92 [packed = true];
+  repeated   uint64 packed_uint64   =  93 [packed = true];
+  repeated   sint32 packed_sint32   =  94 [packed = true];
+  repeated   sint64 packed_sint64   =  95 [packed = true];
+  repeated  fixed32 packed_fixed32  =  96 [packed = true];
+  repeated  fixed64 packed_fixed64  =  97 [packed = true];
+  repeated sfixed32 packed_sfixed32 =  98 [packed = true];
+  repeated sfixed64 packed_sfixed64 =  99 [packed = true];
+  repeated    float packed_float    = 100 [packed = true];
+  repeated   double packed_double   = 101 [packed = true];
+  repeated     bool packed_bool     = 102 [packed = true];
+  repeated ForeignEnum packed_enum  = 103 [packed = true];
+}
+
+// A message with the same fields as TestPackedTypes, but without packing. Used
+// to test packed <-> unpacked wire compatibility.
+message TestUnpackedTypes {
+  repeated    int32 unpacked_int32    =  90 [packed = false];
+  repeated    int64 unpacked_int64    =  91 [packed = false];
+  repeated   uint32 unpacked_uint32   =  92 [packed = false];
+  repeated   uint64 unpacked_uint64   =  93 [packed = false];
+  repeated   sint32 unpacked_sint32   =  94 [packed = false];
+  repeated   sint64 unpacked_sint64   =  95 [packed = false];
+  repeated  fixed32 unpacked_fixed32  =  96 [packed = false];
+  repeated  fixed64 unpacked_fixed64  =  97 [packed = false];
+  repeated sfixed32 unpacked_sfixed32 =  98 [packed = false];
+  repeated sfixed64 unpacked_sfixed64 =  99 [packed = false];
+  repeated    float unpacked_float    = 100 [packed = false];
+  repeated   double unpacked_double   = 101 [packed = false];
+  repeated     bool unpacked_bool     = 102 [packed = false];
+  repeated ForeignEnum unpacked_enum  = 103 [packed = false];
+}
+
+message TestPackedExtensions {
+  extensions 1 to max;
+}
+
+extend TestPackedExtensions {
+  repeated    int32 packed_int32_extension    =  90 [packed = true];
+  repeated    int64 packed_int64_extension    =  91 [packed = true];
+  repeated   uint32 packed_uint32_extension   =  92 [packed = true];
+  repeated   uint64 packed_uint64_extension   =  93 [packed = true];
+  repeated   sint32 packed_sint32_extension   =  94 [packed = true];
+  repeated   sint64 packed_sint64_extension   =  95 [packed = true];
+  repeated  fixed32 packed_fixed32_extension  =  96 [packed = true];
+  repeated  fixed64 packed_fixed64_extension  =  97 [packed = true];
+  repeated sfixed32 packed_sfixed32_extension =  98 [packed = true];
+  repeated sfixed64 packed_sfixed64_extension =  99 [packed = true];
+  repeated    float packed_float_extension    = 100 [packed = true];
+  repeated   double packed_double_extension   = 101 [packed = true];
+  repeated     bool packed_bool_extension     = 102 [packed = true];
+  repeated ForeignEnum packed_enum_extension  = 103 [packed = true];
+}
+
+message TestUnpackedExtensions {
+  extensions 1 to max;
+}
+
+extend TestUnpackedExtensions {
+  repeated    int32 unpacked_int32_extension    =  90 [packed = false];
+  repeated    int64 unpacked_int64_extension    =  91 [packed = false];
+  repeated   uint32 unpacked_uint32_extension   =  92 [packed = false];
+  repeated   uint64 unpacked_uint64_extension   =  93 [packed = false];
+  repeated   sint32 unpacked_sint32_extension   =  94 [packed = false];
+  repeated   sint64 unpacked_sint64_extension   =  95 [packed = false];
+  repeated  fixed32 unpacked_fixed32_extension  =  96 [packed = false];
+  repeated  fixed64 unpacked_fixed64_extension  =  97 [packed = false];
+  repeated sfixed32 unpacked_sfixed32_extension =  98 [packed = false];
+  repeated sfixed64 unpacked_sfixed64_extension =  99 [packed = false];
+  repeated    float unpacked_float_extension    = 100 [packed = false];
+  repeated   double unpacked_double_extension   = 101 [packed = false];
+  repeated     bool unpacked_bool_extension     = 102 [packed = false];
+  repeated ForeignEnum unpacked_enum_extension  = 103 [packed = false];
+}
+
+// Used by ExtensionSetTest/DynamicExtensions.  The test actually builds
+// a set of extensions to TestAllExtensions dynamically, based on the fields
+// of this message type.
+message TestDynamicExtensions {
+  enum DynamicEnumType {
+    DYNAMIC_FOO = 2200;
+    DYNAMIC_BAR = 2201;
+    DYNAMIC_BAZ = 2202;
+  }
+  message DynamicMessageType {
+    optional int32 dynamic_field = 2100;
+  }
+
+  optional fixed32 scalar_extension = 2000;
+  optional ForeignEnum enum_extension = 2001;
+  optional DynamicEnumType dynamic_enum_extension = 2002;
+
+  optional ForeignMessage message_extension = 2003;
+  optional DynamicMessageType dynamic_message_extension = 2004;
+
+  repeated string repeated_extension = 2005;
+  repeated sint32 packed_extension = 2006 [packed = true];
+}
+
+message TestRepeatedScalarDifferentTagSizes {
+  // Parsing repeated fixed size values used to fail. This message needs to be
+  // used in order to get a tag of the right size; all of the repeated fields
+  // in TestAllTypes didn't trigger the check.
+  repeated fixed32 repeated_fixed32 = 12;
+  // Check for a varint type, just for good measure.
+  repeated int32   repeated_int32   = 13;
+
+  // These have two-byte tags.
+  repeated fixed64 repeated_fixed64 = 2046;
+  repeated int64   repeated_int64   = 2047;
+
+  // Three byte tags.
+  repeated float   repeated_float   = 262142;
+  repeated uint64  repeated_uint64  = 262143;
+}
+
+// Test that if an optional or required message/group field appears multiple
+// times in the input, they need to be merged.
+message TestParsingMerge {
+  // RepeatedFieldsGenerator defines matching field types as TestParsingMerge,
+  // except that all fields are repeated. In the tests, we will serialize the
+  // RepeatedFieldsGenerator to bytes, and parse the bytes to TestParsingMerge.
+  // Repeated fields in RepeatedFieldsGenerator are expected to be merged into
+  // the corresponding required/optional fields in TestParsingMerge.
+  message RepeatedFieldsGenerator {
+    repeated TestAllTypes field1 = 1;
+    repeated TestAllTypes field2 = 2;
+    repeated TestAllTypes field3 = 3;
+    repeated group Group1 = 10 {
+      optional TestAllTypes field1 = 11;
+    }
+    repeated group Group2 = 20 {
+      optional TestAllTypes field1 = 21;
+    }
+    repeated TestAllTypes ext1 = 1000;
+    repeated TestAllTypes ext2 = 1001;
+  }
+  required TestAllTypes required_all_types = 1;
+  optional TestAllTypes optional_all_types = 2;
+  repeated TestAllTypes repeated_all_types = 3;
+  optional group OptionalGroup = 10 {
+    optional TestAllTypes optional_group_all_types = 11;
+  }
+  repeated group RepeatedGroup = 20 {
+    optional TestAllTypes repeated_group_all_types = 21;
+  }
+  extensions 1000 to max;
+  extend TestParsingMerge {
+    optional TestAllTypes optional_ext = 1000;
+    repeated TestAllTypes repeated_ext = 1001;
+  }
+}
+
+message TestCommentInjectionMessage {
+  // */ <- This should not close the generated doc comment
+  optional string a = 1 [default="*/ <- Neither should this."];
+}
+
+
+// Test that RPC services work.
+message FooRequest  {}
+message FooResponse {}
+
+message FooClientMessage {}
+message FooServerMessage{}
+
+service TestService {
+  rpc Foo(FooRequest) returns (FooResponse);
+  rpc Bar(BarRequest) returns (BarResponse);
+}
+
+
+message BarRequest  {}
+message BarResponse {}
+
+message TestJsonName {
+  optional int32 field_name1 = 1;
+  optional int32 fieldName2 = 2;
+  optional int32 FieldName3 = 3;
+  optional int32 _field_name4 = 4;
+  optional int32 FIELD_NAME5 = 5;
+  optional int32 field_name6 = 6 [json_name = "@type"];
+}
+
+message TestHugeFieldNumbers {
+  optional int32 optional_int32 = 536870000;
+  optional int32 fixed_32 = 536870001;
+  repeated int32 repeated_int32 = 536870002 [packed = false];
+  repeated int32 packed_int32 = 536870003 [packed = true];
+
+  optional ForeignEnum optional_enum = 536870004;
+  optional string optional_string = 536870005;
+  optional bytes optional_bytes = 536870006;
+  optional ForeignMessage optional_message = 536870007;
+
+  optional group OptionalGroup = 536870008 {
+    optional int32 group_a = 536870009;
+  }
+
+  map<string, string> string_string_map = 536870010;
+
+  oneof oneof_field {
+    uint32 oneof_uint32 = 536870011;
+    TestAllTypes oneof_test_all_types = 536870012;
+    string oneof_string = 536870013;
+    bytes oneof_bytes = 536870014;
+  }
+
+  extensions  536860000 to 536869999;
+}
+
+extend TestHugeFieldNumbers {
+  optional TestAllTypes test_all_types = 536860000;
+}
+
+message TestExtensionInsideTable {
+  optional int32 field1 = 1;
+  optional int32 field2 = 2;
+  optional int32 field3 = 3;
+  optional int32 field4 = 4;
+  extensions 5 to 5;
+  optional int32 field6 = 6;
+  optional int32 field7 = 7;
+  optional int32 field8 = 8;
+  optional int32 field9 = 9;
+  optional int32 field10 = 10;
+}
+
+extend TestExtensionInsideTable {
+  optional int32 test_extension_inside_table_extension = 5;
+}
+
+enum VeryLargeEnum {
+  ENUM_LABEL_DEFAULT = 0;
+  ENUM_LABEL_1 = 1;
+  ENUM_LABEL_2 = 2;
+  ENUM_LABEL_3 = 3;
+  ENUM_LABEL_4 = 4;
+  ENUM_LABEL_5 = 5;
+  ENUM_LABEL_6 = 6;
+  ENUM_LABEL_7 = 7;
+  ENUM_LABEL_8 = 8;
+  ENUM_LABEL_9 = 9;
+  ENUM_LABEL_10 = 10;
+  ENUM_LABEL_11 = 11;
+  ENUM_LABEL_12 = 12;
+  ENUM_LABEL_13 = 13;
+  ENUM_LABEL_14 = 14;
+  ENUM_LABEL_15 = 15;
+  ENUM_LABEL_16 = 16;
+  ENUM_LABEL_17 = 17;
+  ENUM_LABEL_18 = 18;
+  ENUM_LABEL_19 = 19;
+  ENUM_LABEL_20 = 20;
+  ENUM_LABEL_21 = 21;
+  ENUM_LABEL_22 = 22;
+  ENUM_LABEL_23 = 23;
+  ENUM_LABEL_24 = 24;
+  ENUM_LABEL_25 = 25;
+  ENUM_LABEL_26 = 26;
+  ENUM_LABEL_27 = 27;
+  ENUM_LABEL_28 = 28;
+  ENUM_LABEL_29 = 29;
+  ENUM_LABEL_30 = 30;
+  ENUM_LABEL_31 = 31;
+  ENUM_LABEL_32 = 32;
+  ENUM_LABEL_33 = 33;
+  ENUM_LABEL_34 = 34;
+  ENUM_LABEL_35 = 35;
+  ENUM_LABEL_36 = 36;
+  ENUM_LABEL_37 = 37;
+  ENUM_LABEL_38 = 38;
+  ENUM_LABEL_39 = 39;
+  ENUM_LABEL_40 = 40;
+  ENUM_LABEL_41 = 41;
+  ENUM_LABEL_42 = 42;
+  ENUM_LABEL_43 = 43;
+  ENUM_LABEL_44 = 44;
+  ENUM_LABEL_45 = 45;
+  ENUM_LABEL_46 = 46;
+  ENUM_LABEL_47 = 47;
+  ENUM_LABEL_48 = 48;
+  ENUM_LABEL_49 = 49;
+  ENUM_LABEL_50 = 50;
+  ENUM_LABEL_51 = 51;
+  ENUM_LABEL_52 = 52;
+  ENUM_LABEL_53 = 53;
+  ENUM_LABEL_54 = 54;
+  ENUM_LABEL_55 = 55;
+  ENUM_LABEL_56 = 56;
+  ENUM_LABEL_57 = 57;
+  ENUM_LABEL_58 = 58;
+  ENUM_LABEL_59 = 59;
+  ENUM_LABEL_60 = 60;
+  ENUM_LABEL_61 = 61;
+  ENUM_LABEL_62 = 62;
+  ENUM_LABEL_63 = 63;
+  ENUM_LABEL_64 = 64;
+  ENUM_LABEL_65 = 65;
+  ENUM_LABEL_66 = 66;
+  ENUM_LABEL_67 = 67;
+  ENUM_LABEL_68 = 68;
+  ENUM_LABEL_69 = 69;
+  ENUM_LABEL_70 = 70;
+  ENUM_LABEL_71 = 71;
+  ENUM_LABEL_72 = 72;
+  ENUM_LABEL_73 = 73;
+  ENUM_LABEL_74 = 74;
+  ENUM_LABEL_75 = 75;
+  ENUM_LABEL_76 = 76;
+  ENUM_LABEL_77 = 77;
+  ENUM_LABEL_78 = 78;
+  ENUM_LABEL_79 = 79;
+  ENUM_LABEL_80 = 80;
+  ENUM_LABEL_81 = 81;
+  ENUM_LABEL_82 = 82;
+  ENUM_LABEL_83 = 83;
+  ENUM_LABEL_84 = 84;
+  ENUM_LABEL_85 = 85;
+  ENUM_LABEL_86 = 86;
+  ENUM_LABEL_87 = 87;
+  ENUM_LABEL_88 = 88;
+  ENUM_LABEL_89 = 89;
+  ENUM_LABEL_90 = 90;
+  ENUM_LABEL_91 = 91;
+  ENUM_LABEL_92 = 92;
+  ENUM_LABEL_93 = 93;
+  ENUM_LABEL_94 = 94;
+  ENUM_LABEL_95 = 95;
+  ENUM_LABEL_96 = 96;
+  ENUM_LABEL_97 = 97;
+  ENUM_LABEL_98 = 98;
+  ENUM_LABEL_99 = 99;
+  ENUM_LABEL_100 = 100;
+};

csharp/protos/unittest_import.proto

@@ -0,0 +1,69 @@
+// 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.
+
+// Author: kenton@google.com (Kenton Varda)
+//  Based on original Protocol Buffers design by
+//  Sanjay Ghemawat, Jeff Dean, and others.
+//
+// A proto file which is imported by unittest.proto to test importing.
+
+syntax = "proto2";
+
+// We don't put this in a package within proto2 because we need to make sure
+// that the generated code doesn't depend on being in the proto2 namespace.
+// In test_util.h we do
+// "using namespace unittest_import = protobuf_unittest_import".
+package protobuf_unittest_import_proto2;
+
+option optimize_for = SPEED;
+option cc_enable_arenas = true;
+
+option csharp_namespace = "Google.Protobuf.TestProtos.Proto2";
+
+// Test public import
+import public "unittest_import_public.proto";
+
+message ImportMessage {
+  optional int32 d = 1;
+}
+
+enum ImportEnum {
+  IMPORT_FOO = 7;
+  IMPORT_BAR = 8;
+  IMPORT_BAZ = 9;
+}
+
+
+// To use an enum in a map, it must has the first value as 0.
+enum ImportEnumForMap {
+  UNKNOWN = 0;
+  FOO = 1;
+  BAR = 2;
+}

csharp/protos/unittest_import_public.proto

@@ -0,0 +1,41 @@
+// 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.
+
+// Author: liujisi@google.com (Pherl Liu)
+
+syntax = "proto2";
+
+package protobuf_unittest_import_proto2;
+
+option csharp_namespace = "Google.Protobuf.TestProtos.Proto2";
+
+message PublicImportMessage {
+  optional int32 e = 1;
+}

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

@@ -48,7 +48,9 @@ namespace Google.Protobuf.Conformance
             // This way we get the binary streams instead of readers/writers.
             var input = new BinaryReader(Console.OpenStandardInput());
             var output = new BinaryWriter(Console.OpenStandardOutput());
-            var typeRegistry = TypeRegistry.FromMessages(ProtobufTestMessages.Proto3.TestAllTypesProto3.Descriptor);
+            var typeRegistry = TypeRegistry.FromMessages(
+                ProtobufTestMessages.Proto3.TestAllTypesProto3.Descriptor,
+                ProtobufTestMessages.Proto2.TestAllTypesProto2.Descriptor);
 
             int count = 0;
             while (RunTest(input, output, typeRegistry))
@@ -81,7 +83,7 @@ namespace Google.Protobuf.Conformance
 
         private static ConformanceResponse PerformRequest(ConformanceRequest request, TypeRegistry typeRegistry)
         {
-            ProtobufTestMessages.Proto3.TestAllTypesProto3 message;
+            IMessage message;
             try
             {
                 switch (request.PayloadCase)
@@ -101,7 +103,13 @@ namespace Google.Protobuf.Conformance
                         }
                         else if (request.MessageType.Equals("protobuf_test_messages.proto2.TestAllTypesProto2"))
                         {
-                            return new ConformanceResponse { Skipped = "CSharp doesn't support proto2" };
+                            ExtensionRegistry registry = new ExtensionRegistry()
+                            {
+                                ProtobufTestMessages.Proto2.TestMessagesProto2Extensions.ExtensionInt32,
+                                ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.MessageSetCorrectExtension1.Extensions.MessageSetExtension,
+                                ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.MessageSetCorrectExtension2.Extensions.MessageSetExtension
+                            };
+                            message = ProtobufTestMessages.Proto2.TestAllTypesProto2.Parser.WithExtensionRegistry(registry).ParseFrom(request.ProtobufPayload);
                         }
                         else
                         {

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

@@ -0,0 +1,102 @@
+using Google.Protobuf.TestProtos.Proto2;
+using NUnit.Framework;
+
+using static Google.Protobuf.TestProtos.Proto2.UnittestExtensions;
+
+namespace Google.Protobuf
+{
+    public class ExtensionSetTest
+    {
+        [Test]
+        public void EmptyExtensionSet()
+        {
+            ExtensionSet<TestAllExtensions> extensions = new ExtensionSet<TestAllExtensions>();
+            Assert.AreEqual(0, extensions.CalculateSize());
+        }
+
+        [Test]
+        public void MergeExtensionSet()
+        {
+            ExtensionSet<TestAllExtensions> extensions = null;
+            ExtensionSet.Set(ref extensions, OptionalBoolExtension, true);
+
+            ExtensionSet<TestAllExtensions> other = null;
+
+            Assert.IsFalse(ExtensionSet.Has(ref other, OptionalBoolExtension));
+            ExtensionSet.MergeFrom(ref other, extensions);
+            Assert.IsTrue(ExtensionSet.Has(ref other, OptionalBoolExtension));
+        }
+
+        [Test]
+        public void TestMergeCodedInput()
+        {
+            var message = new TestAllExtensions();
+            message.SetExtension(OptionalBoolExtension, true);
+            var serialized = message.ToByteArray();
+
+            var other = TestAllExtensions.Parser
+                .WithExtensionRegistry(new ExtensionRegistry() { OptionalBoolExtension })
+                .ParseFrom(serialized);
+
+            Assert.AreEqual(message, other);
+            Assert.AreEqual(message.CalculateSize(), other.CalculateSize());
+        }
+
+        [Test]
+        public void TestMergeMessage()
+        {
+            var message = new TestAllExtensions();
+            message.SetExtension(OptionalBoolExtension, true);
+
+            var other = new TestAllExtensions();
+
+            Assert.AreNotEqual(message, other);
+            Assert.AreNotEqual(message.CalculateSize(), other.CalculateSize());
+
+            other.MergeFrom(message);
+
+            Assert.AreEqual(message, other);
+            Assert.AreEqual(message.CalculateSize(), other.CalculateSize());
+        }
+
+        [Test]
+        public void TestEquals()
+        {
+            var message = new TestAllExtensions();
+            message.SetExtension(OptionalBoolExtension, true);
+
+            var other = new TestAllExtensions();
+
+            Assert.AreNotEqual(message, other);
+            Assert.AreNotEqual(message.CalculateSize(), other.CalculateSize());
+
+            other.SetExtension(OptionalBoolExtension, true);
+
+            Assert.AreEqual(message, other);
+            Assert.AreEqual(message.CalculateSize(), other.CalculateSize());
+        }
+
+        [Test]
+        public void TestHashCode()
+        {
+            var message = new TestAllExtensions();
+            var hashCode = message.GetHashCode();
+
+            message.SetExtension(OptionalBoolExtension, true);
+
+            Assert.AreNotEqual(hashCode, message.GetHashCode());
+        }
+
+        [Test]
+        public void TestClone()
+        {
+            var message = new TestAllExtensions();
+            message.SetExtension(OptionalBoolExtension, true);
+
+            var other = message.Clone();
+
+            Assert.AreEqual(message, other);
+            Assert.AreEqual(message.CalculateSize(), message.CalculateSize());
+        }
+    }
+}

csharp/src/Google.Protobuf.Test/GeneratedMessageTest.Proto2.cs

@@ -0,0 +1,368 @@
+using Google.Protobuf.TestProtos.Proto2;
+using Proto2 = Google.Protobuf.TestProtos.Proto2;
+using NUnit.Framework;
+
+using static Google.Protobuf.TestProtos.Proto2.UnittestExtensions;
+
+namespace Google.Protobuf
+{
+    /// <summary>
+    /// Tests around the generated TestAllTypes message in unittest.proto
+    /// </summary>
+    public partial class GeneratedMessageTest
+    {
+        [Test]
+        public void DefaultProto2Values()
+        {
+            var message = new TestAllTypes();
+            Assert.AreEqual(false, message.OptionalBool);
+            Assert.AreEqual(ByteString.Empty, message.OptionalBytes);
+            Assert.AreEqual(0.0, message.OptionalDouble);
+            Assert.AreEqual(0, message.OptionalFixed32);
+            Assert.AreEqual(0L, message.OptionalFixed64);
+            Assert.AreEqual(0.0f, message.OptionalFloat);
+            Assert.AreEqual(ForeignEnum.ForeignFoo, message.OptionalForeignEnum);
+            Assert.IsNull(message.OptionalForeignMessage);
+            Assert.AreEqual(ImportEnum.ImportFoo, message.OptionalImportEnum);
+            Assert.IsNull(message.OptionalImportMessage);
+            Assert.AreEqual(0, message.OptionalInt32);
+            Assert.AreEqual(0L, message.OptionalInt64);
+            Assert.AreEqual(Proto2.TestAllTypes.Types.NestedEnum.Foo, message.OptionalNestedEnum);
+            Assert.IsNull(message.OptionalNestedMessage);
+            Assert.IsNull(message.OptionalPublicImportMessage);
+            Assert.AreEqual(0, message.OptionalSfixed32);
+            Assert.AreEqual(0L, message.OptionalSfixed64);
+            Assert.AreEqual(0, message.OptionalSint32);
+            Assert.AreEqual(0L, message.OptionalSint64);
+            Assert.AreEqual("", message.OptionalString);
+            Assert.AreEqual(0U, message.OptionalUint32);
+            Assert.AreEqual(0UL, message.OptionalUint64);
+
+            // Repeated fields
+            Assert.AreEqual(0, message.RepeatedBool.Count);
+            Assert.AreEqual(0, message.RepeatedBytes.Count);
+            Assert.AreEqual(0, message.RepeatedDouble.Count);
+            Assert.AreEqual(0, message.RepeatedFixed32.Count);
+            Assert.AreEqual(0, message.RepeatedFixed64.Count);
+            Assert.AreEqual(0, message.RepeatedFloat.Count);
+            Assert.AreEqual(0, message.RepeatedForeignEnum.Count);
+            Assert.AreEqual(0, message.RepeatedForeignMessage.Count);
+            Assert.AreEqual(0, message.RepeatedImportEnum.Count);
+            Assert.AreEqual(0, message.RepeatedImportMessage.Count);
+            Assert.AreEqual(0, message.RepeatedNestedEnum.Count);
+            Assert.AreEqual(0, message.RepeatedNestedMessage.Count);
+            Assert.AreEqual(0, message.RepeatedSfixed32.Count);
+            Assert.AreEqual(0, message.RepeatedSfixed64.Count);
+            Assert.AreEqual(0, message.RepeatedSint32.Count);
+            Assert.AreEqual(0, message.RepeatedSint64.Count);
+            Assert.AreEqual(0, message.RepeatedString.Count);
+            Assert.AreEqual(0, message.RepeatedUint32.Count);
+            Assert.AreEqual(0, message.RepeatedUint64.Count);
+
+            // Oneof fields
+            Assert.AreEqual(Proto2.TestAllTypes.OneofFieldOneofCase.None, message.OneofFieldCase);
+            Assert.AreEqual(0, message.OneofUint32);
+            Assert.AreEqual("", message.OneofString);
+            Assert.AreEqual(ByteString.Empty, message.OneofBytes);
+            Assert.IsNull(message.OneofNestedMessage);
+
+            Assert.AreEqual(true, message.DefaultBool);
+            Assert.AreEqual(ByteString.CopyFromUtf8("world"), message.DefaultBytes);
+            Assert.AreEqual("123", message.DefaultCord);
+            Assert.AreEqual(52e3, message.DefaultDouble);
+            Assert.AreEqual(47, message.DefaultFixed32);
+            Assert.AreEqual(48, message.DefaultFixed64);
+            Assert.AreEqual(51.5, message.DefaultFloat);
+            Assert.AreEqual(ForeignEnum.ForeignBar, message.DefaultForeignEnum);
+            Assert.AreEqual(ImportEnum.ImportBar, message.DefaultImportEnum);
+            Assert.AreEqual(41, message.DefaultInt32);
+            Assert.AreEqual(42, message.DefaultInt64);
+            Assert.AreEqual(Proto2.TestAllTypes.Types.NestedEnum.Bar, message.DefaultNestedEnum);
+            Assert.AreEqual(49, message.DefaultSfixed32);
+            Assert.AreEqual(-50, message.DefaultSfixed64);
+            Assert.AreEqual(-45, message.DefaultSint32);
+            Assert.AreEqual(46, message.DefaultSint64);
+            Assert.AreEqual("hello", message.DefaultString);
+            Assert.AreEqual("abc", message.DefaultStringPiece);
+            Assert.AreEqual(43, message.DefaultUint32);
+            Assert.AreEqual(44, message.DefaultUint64);
+
+            Assert.False(message.HasDefaultBool);
+            Assert.False(message.HasDefaultBytes);
+            Assert.False(message.HasDefaultCord);
+            Assert.False(message.HasDefaultDouble);
+            Assert.False(message.HasDefaultFixed32);
+            Assert.False(message.HasDefaultFixed64);
+            Assert.False(message.HasDefaultFloat);
+            Assert.False(message.HasDefaultForeignEnum);
+            Assert.False(message.HasDefaultImportEnum);
+            Assert.False(message.HasDefaultInt32);
+            Assert.False(message.HasDefaultInt64);
+            Assert.False(message.HasDefaultNestedEnum);
+            Assert.False(message.HasDefaultSfixed32);
+            Assert.False(message.HasDefaultSfixed64);
+            Assert.False(message.HasDefaultSint32);
+            Assert.False(message.HasDefaultSint64);
+            Assert.False(message.HasDefaultString);
+            Assert.False(message.HasDefaultStringPiece);
+            Assert.False(message.HasDefaultUint32);
+            Assert.False(message.HasDefaultUint64);
+        }
+
+        [Test]
+        public void DefaultExtensionValues()
+        {
+            var message = new TestAllExtensions();
+            Assert.AreEqual(false, message.GetExtension(OptionalBoolExtension));
+            Assert.AreEqual(ByteString.Empty, message.GetExtension(OptionalBytesExtension));
+            Assert.AreEqual(0.0, message.GetExtension(OptionalDoubleExtension));
+            Assert.AreEqual(0, message.GetExtension(OptionalFixed32Extension));
+            Assert.AreEqual(0L, message.GetExtension(OptionalFixed64Extension));
+            Assert.AreEqual(0.0f, message.GetExtension(OptionalFloatExtension));
+            Assert.AreEqual(ForeignEnum.ForeignFoo, message.GetExtension(OptionalForeignEnumExtension));
+            Assert.IsNull(message.GetExtension(OptionalForeignMessageExtension));
+            Assert.AreEqual(ImportEnum.ImportFoo, message.GetExtension(OptionalImportEnumExtension));
+            Assert.IsNull(message.GetExtension(OptionalImportMessageExtension));
+            Assert.AreEqual(0, message.GetExtension(OptionalInt32Extension));
+            Assert.AreEqual(0L, message.GetExtension(OptionalInt64Extension));
+            Assert.AreEqual(Proto2.TestAllTypes.Types.NestedEnum.Foo, message.GetExtension(OptionalNestedEnumExtension));
+            Assert.IsNull(message.GetExtension(OptionalNestedMessageExtension));
+            Assert.IsNull(message.GetExtension(OptionalPublicImportMessageExtension));
+            Assert.AreEqual(0, message.GetExtension(OptionalSfixed32Extension));
+            Assert.AreEqual(0L, message.GetExtension(OptionalSfixed64Extension));
+            Assert.AreEqual(0, message.GetExtension(OptionalSint32Extension));
+            Assert.AreEqual(0L, message.GetExtension(OptionalSint64Extension));
+            Assert.AreEqual("", message.GetExtension(OptionalStringExtension));
+            Assert.AreEqual(0U, message.GetExtension(OptionalUint32Extension));
+            Assert.AreEqual(0UL, message.GetExtension(OptionalUint64Extension));
+
+            // Repeated fields
+            Assert.IsNull(message.GetExtension(RepeatedBoolExtension));
+            Assert.IsNull(message.GetExtension(RepeatedBytesExtension));
+            Assert.IsNull(message.GetExtension(RepeatedDoubleExtension));
+            Assert.IsNull(message.GetExtension(RepeatedFixed32Extension));
+            Assert.IsNull(message.GetExtension(RepeatedFixed64Extension));
+            Assert.IsNull(message.GetExtension(RepeatedFloatExtension));
+            Assert.IsNull(message.GetExtension(RepeatedForeignEnumExtension));
+            Assert.IsNull(message.GetExtension(RepeatedForeignMessageExtension));
+            Assert.IsNull(message.GetExtension(RepeatedImportEnumExtension));
+            Assert.IsNull(message.GetExtension(RepeatedImportMessageExtension));
+            Assert.IsNull(message.GetExtension(RepeatedNestedEnumExtension));
+            Assert.IsNull(message.GetExtension(RepeatedNestedMessageExtension));
+            Assert.IsNull(message.GetExtension(RepeatedSfixed32Extension));
+            Assert.IsNull(message.GetExtension(RepeatedSfixed64Extension));
+            Assert.IsNull(message.GetExtension(RepeatedSint32Extension));
+            Assert.IsNull(message.GetExtension(RepeatedSint64Extension));
+            Assert.IsNull(message.GetExtension(RepeatedStringExtension));
+            Assert.IsNull(message.GetExtension(RepeatedUint32Extension));
+            Assert.IsNull(message.GetExtension(RepeatedUint64Extension));
+
+            // Oneof fields
+            Assert.AreEqual(0, message.GetExtension(OneofUint32Extension));
+            Assert.AreEqual("", message.GetExtension(OneofStringExtension));
+            Assert.AreEqual(ByteString.Empty, message.GetExtension(OneofBytesExtension));
+            Assert.IsNull(message.GetExtension(OneofNestedMessageExtension));
+
+            Assert.AreEqual(true, message.GetExtension(DefaultBoolExtension));
+            Assert.AreEqual(ByteString.CopyFromUtf8("world"), message.GetExtension(DefaultBytesExtension));
+            Assert.AreEqual("123", message.GetExtension(DefaultCordExtension));
+            Assert.AreEqual(52e3, message.GetExtension(DefaultDoubleExtension));
+            Assert.AreEqual(47, message.GetExtension(DefaultFixed32Extension));
+            Assert.AreEqual(48, message.GetExtension(DefaultFixed64Extension));
+            Assert.AreEqual(51.5, message.GetExtension(DefaultFloatExtension));
+            Assert.AreEqual(ForeignEnum.ForeignBar, message.GetExtension(DefaultForeignEnumExtension));
+            Assert.AreEqual(ImportEnum.ImportBar, message.GetExtension(DefaultImportEnumExtension));
+            Assert.AreEqual(41, message.GetExtension(DefaultInt32Extension));
+            Assert.AreEqual(42, message.GetExtension(DefaultInt64Extension));
+            Assert.AreEqual(Proto2.TestAllTypes.Types.NestedEnum.Bar, message.GetExtension(DefaultNestedEnumExtension));
+            Assert.AreEqual(49, message.GetExtension(DefaultSfixed32Extension));
+            Assert.AreEqual(-50, message.GetExtension(DefaultSfixed64Extension));
+            Assert.AreEqual(-45, message.GetExtension(DefaultSint32Extension));
+            Assert.AreEqual(46, message.GetExtension(DefaultSint64Extension));
+            Assert.AreEqual("hello", message.GetExtension(DefaultStringExtension));
+            Assert.AreEqual("abc", message.GetExtension(DefaultStringPieceExtension));
+            Assert.AreEqual(43, message.GetExtension(DefaultUint32Extension));
+            Assert.AreEqual(44, message.GetExtension(DefaultUint64Extension));
+
+            Assert.False(message.HasExtension(DefaultBoolExtension));
+            Assert.False(message.HasExtension(DefaultBytesExtension));
+            Assert.False(message.HasExtension(DefaultCordExtension));
+            Assert.False(message.HasExtension(DefaultDoubleExtension));
+            Assert.False(message.HasExtension(DefaultFixed32Extension));
+            Assert.False(message.HasExtension(DefaultFixed64Extension));
+            Assert.False(message.HasExtension(DefaultFloatExtension));
+            Assert.False(message.HasExtension(DefaultForeignEnumExtension));
+            Assert.False(message.HasExtension(DefaultImportEnumExtension));
+            Assert.False(message.HasExtension(DefaultInt32Extension));
+            Assert.False(message.HasExtension(DefaultInt64Extension));
+            Assert.False(message.HasExtension(DefaultNestedEnumExtension));
+            Assert.False(message.HasExtension(DefaultSfixed32Extension));
+            Assert.False(message.HasExtension(DefaultSfixed64Extension));
+            Assert.False(message.HasExtension(DefaultSint32Extension));
+            Assert.False(message.HasExtension(DefaultSint64Extension));
+            Assert.False(message.HasExtension(DefaultStringExtension));
+            Assert.False(message.HasExtension(DefaultStringPieceExtension));
+            Assert.False(message.HasExtension(DefaultUint32Extension));
+            Assert.False(message.HasExtension(DefaultUint64Extension));
+        }
+
+        [Test]
+        public void FieldPresence()
+        {
+            var message = new TestAllTypes();
+
+            Assert.False(message.HasOptionalBool);
+            Assert.False(message.OptionalBool);
+
+            message.OptionalBool = true;
+
+            Assert.True(message.HasOptionalBool);
+            Assert.True(message.OptionalBool);
+
+            message.OptionalBool = false;
+
+            Assert.True(message.HasOptionalBool);
+            Assert.False(message.OptionalBool);
+
+            message.ClearOptionalBool();
+
+            Assert.False(message.HasOptionalBool);
+            Assert.False(message.OptionalBool);
+
+            Assert.False(message.HasDefaultBool);
+            Assert.True(message.DefaultBool);
+
+            message.DefaultBool = false;
+
+            Assert.True(message.HasDefaultBool);
+            Assert.False(message.DefaultBool);
+
+            message.DefaultBool = true;
+
+            Assert.True(message.HasDefaultBool);
+            Assert.True(message.DefaultBool);
+
+            message.ClearDefaultBool();
+
+            Assert.False(message.HasDefaultBool);
+            Assert.True(message.DefaultBool);
+        }
+
+        [Test]
+        public void RequiredFields()
+        {
+            var message = new TestRequired();
+            Assert.False(message.IsInitialized());
+
+            message.A = 1;
+            message.B = 2;
+            message.C = 3;
+
+            Assert.True(message.IsInitialized());
+        }
+
+        [Test]
+        public void RequiredFieldsInExtensions()
+        {
+            var message = new TestAllExtensions();
+            Assert.True(message.IsInitialized());
+
+            message.SetExtension(TestRequired.Extensions.Single, new TestRequired());
+
+            Assert.False(message.IsInitialized());
+
+            var extensionMessage = message.GetExtension(TestRequired.Extensions.Single);
+            extensionMessage.A = 1;
+            extensionMessage.B = 2;
+            extensionMessage.C = 3;
+
+            Assert.True(message.IsInitialized());
+
+            message.GetOrInitializeExtension(TestRequired.Extensions.Multi);
+
+            Assert.True(message.IsInitialized());
+
+            message.GetExtension(TestRequired.Extensions.Multi).Add(new TestRequired());
+
+            Assert.False(message.IsInitialized());
+
+            extensionMessage = message.GetExtension(TestRequired.Extensions.Multi)[0];
+            extensionMessage.A = 1;
+            extensionMessage.B = 2;
+            extensionMessage.C = 3;
+
+            Assert.True(message.IsInitialized());
+
+            message.SetExtension(UnittestExtensions.OptionalBoolExtension, true);
+
+            Assert.True(message.IsInitialized());
+
+            message.GetOrInitializeExtension(UnittestExtensions.RepeatedBoolExtension).Add(true);
+
+            Assert.True(message.IsInitialized());
+        }
+
+        [Test]
+        public void RequiredFieldInNestedMessageMapValue()
+        {
+            var message = new TestRequiredMap();
+            message.Foo.Add(0, new TestRequiredMap.Types.NestedMessage());
+
+            Assert.False(message.IsInitialized());
+
+            message.Foo[0].RequiredInt32 = 12;
+
+            Assert.True(message.IsInitialized());
+        }
+
+        [Test]
+        public void RoundTrip_Groups()
+        {
+            var message = new TestAllTypes
+            {
+                OptionalGroup = new TestAllTypes.Types.OptionalGroup
+                {
+                    A = 10
+                },
+                RepeatedGroup =
+                {
+                    new TestAllTypes.Types.RepeatedGroup { A = 10 },
+                    new TestAllTypes.Types.RepeatedGroup { A = 20 },
+                    new TestAllTypes.Types.RepeatedGroup { A = 30 }
+                }
+            };
+
+            byte[] bytes = message.ToByteArray();
+            TestAllTypes parsed = Proto2.TestAllTypes.Parser.ParseFrom(bytes);
+            Assert.AreEqual(message, parsed);
+        }
+
+        [Test]
+        public void RoundTrip_ExtensionGroups()
+        {
+            var message = new TestAllExtensions();
+            message.SetExtension(UnittestExtensions.OptionalGroupExtension, new OptionalGroup_extension { A = 10 });
+            message.GetOrInitializeExtension(UnittestExtensions.RepeatedGroupExtension).AddRange(new[]
+            {
+                new RepeatedGroup_extension { A = 10 },
+                new RepeatedGroup_extension { A = 20 },
+                new RepeatedGroup_extension { A = 30 }
+            });
+
+            byte[] bytes = message.ToByteArray();
+            TestAllExtensions extendable_parsed = TestAllExtensions.Parser.WithExtensionRegistry(new ExtensionRegistry() { UnittestExtensions.OptionalGroupExtension, UnittestExtensions.RepeatedGroupExtension }).ParseFrom(bytes);
+            Assert.AreEqual(message, extendable_parsed);
+        }
+
+        [Test]
+        public void RoundTrip_NestedExtensionGroup()
+        {
+            var message = new TestGroupExtension();
+            message.SetExtension(TestNestedExtension.Extensions.OptionalGroupExtension, new TestNestedExtension.Types.OptionalGroup_extension { A = 10 });
+
+            byte[] bytes = message.ToByteArray();
+            TestGroupExtension extendable_parsed = TestGroupExtension.Parser.WithExtensionRegistry(new ExtensionRegistry() { TestNestedExtension.Extensions.OptionalGroupExtension }).ParseFrom(bytes);
+            Assert.AreEqual(message, extendable_parsed);
+        }
+    }
+}

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

@@ -33,6 +33,7 @@
 using System;
 using System.IO;
 using Google.Protobuf.TestProtos;
+using Proto2 = Google.Protobuf.TestProtos.Proto2;
 using NUnit.Framework;
 using System.Collections;
 using System.Collections.Generic;
@@ -44,7 +45,7 @@ namespace Google.Protobuf
     /// <summary>
     /// Tests around the generated TestAllTypes message.
     /// </summary>
-    public class GeneratedMessageTest
+    public partial class GeneratedMessageTest
     {
         [Test]
         public void EmptyMessageFieldDistinctFromMissingMessageField()

csharp/src/Google.Protobuf.Test/Reflection/CustomOptionsTest.cs

@@ -33,64 +33,19 @@
 using Google.Protobuf.Reflection;
 using Google.Protobuf.WellKnownTypes;
 using NUnit.Framework;
+using System;
 using System.IO;
 using System.Linq;
 using UnitTest.Issues.TestProtos;
 using static Google.Protobuf.WireFormat;
 using static UnitTest.Issues.TestProtos.ComplexOptionType2.Types;
+using static UnitTest.Issues.TestProtos.UnittestCustomOptionsProto3Extensions;
 using static UnitTest.Issues.TestProtos.DummyMessageContainingEnum.Types;
-using static Google.Protobuf.Test.Reflection.CustomOptionNumber;
+
+#pragma warning disable CS0618
 
 namespace Google.Protobuf.Test.Reflection
 {
-    // Internal enum to allow us to use "using static" for convenience.
-    // These are the options defined in unittest_custom_options_proto3.proto
-    internal enum CustomOptionNumber
-    {
-        FileOpt1 = 7736974,
-        MessageOpt1 = 7739036,
-        FieldOpt1 = 7740936,
-        OneofOpt1 = 7740111,
-        EnumOpt1 = 7753576,
-        EnumValueOpt1 = 1560678,
-        ServiceOpt1 = 7887650,
-        MethodOpt1 = 7890860,
-
-        // All message options...
-        BoolOpt = 7706090,
-        Int32Opt = 7705709,
-        Int64Opt = 7705542,
-        UInt32Opt = 7704880,
-        UInt64Opt = 7702367,
-        SInt32Opt = 7701568,
-        SInt64Opt = 7700863,
-        Fixed32Opt = 7700307,
-        Fixed64Opt = 7700194,
-        SFixed32Opt = 7698645,
-        SFixed64Opt = 7685475,
-        FloatOpt = 7675390,
-        DoubleOpt = 7673293,
-        StringOpt = 7673285,
-        BytesOpt = 7673238,
-        EnumOpt = 7673233,
-        MessageTypeOpt = 7665967,
-
-        // Miscellaneous
-        ComplexOpt4 = 7633546,
-        ComplexOpt1 = 7646756,
-        ComplexOpt2 = 7636949,
-        ComplexOpt3 = 7636463,
-
-        // Aggregates
-        AggregateFileOpt = 15478479,
-        AggregateMsgOpt = 15480088,
-        AggregateFieldOpt = 15481374,
-        AggregateEnumOpt = 15483218,
-        AggregateEnumValueOpt = 15486921,
-        AggregateServiceOpt = 15497145,
-        AggregateMethodOpt = 15512713,
-    }
-
     /// <summary>
     /// The majority of the testing here is done via parsed descriptors. That's simpler to
     /// achieve (and more important) than constructing a CodedInputStream manually.
@@ -99,23 +54,41 @@ namespace Google.Protobuf.Test.Reflection
     {
         delegate bool OptionFetcher<T>(int field, out T value);
 
+        OptionFetcher<E> EnumFetcher<E>(CustomOptions options)
+        {
+            return (int i, out E v) => {
+                if (options.TryGetInt32(i, out int value))
+                {
+                    v = (E)(object)value;
+                    return true;
+                }
+                else
+                {
+                    v = default(E);
+                    return false;
+                }
+            };
+        }
+
         [Test]
         public void ScalarOptions()
         {
-            var options = CustomOptionOtherValues.Descriptor.CustomOptions;
-            AssertOption(-100, options.TryGetInt32, Int32Opt);
-            AssertOption(12.3456789f, options.TryGetFloat, FloatOpt);
-            AssertOption(1.234567890123456789d, options.TryGetDouble, DoubleOpt);
-            AssertOption("Hello, \"World\"", options.TryGetString, StringOpt);
-            AssertOption(ByteString.CopyFromUtf8("Hello\0World"), options.TryGetBytes, BytesOpt);
-            AssertOption((int)TestEnumType.TestOptionEnumType2, options.TryGetInt32, EnumOpt);
+            var d = CustomOptionOtherValues.Descriptor;
+            var options = d.CustomOptions;
+            AssertOption(-100, options.TryGetInt32, Int32Opt, d.GetOption);
+            AssertOption(12.3456789f, options.TryGetFloat, FloatOpt, d.GetOption);
+            AssertOption(1.234567890123456789d, options.TryGetDouble, DoubleOpt, d.GetOption);
+            AssertOption("Hello, \"World\"", options.TryGetString, StringOpt, d.GetOption);
+            AssertOption(ByteString.CopyFromUtf8("Hello\0World"), options.TryGetBytes, BytesOpt, d.GetOption);
+            AssertOption(TestEnumType.TestOptionEnumType2, EnumFetcher<TestEnumType>(options), EnumOpt, d.GetOption);
         }
 
         [Test]
         public void MessageOptions()
         {
-            var options = VariousComplexOptions.Descriptor.CustomOptions;
-            AssertOption(new ComplexOptionType1 { Foo = 42, Foo4 = { 99, 88 } }, options.TryGetMessage, ComplexOpt1);
+            var d = VariousComplexOptions.Descriptor;
+            var options = d.CustomOptions;
+            AssertOption(new ComplexOptionType1 { Foo = 42, Foo4 = { 99, 88 } }, options.TryGetMessage, ComplexOpt1, d.GetOption);
             AssertOption(new ComplexOptionType2
             {
                 Baz = 987,
@@ -123,72 +96,74 @@ namespace Google.Protobuf.Test.Reflection
                 Fred = new ComplexOptionType4 { Waldo = 321 },
                 Barney = { new ComplexOptionType4 { Waldo = 101 }, new ComplexOptionType4 { Waldo = 212 } }
             },
-                options.TryGetMessage, ComplexOpt2);
-            AssertOption(new ComplexOptionType3 { Qux = 9 }, options.TryGetMessage, ComplexOpt3);
+                options.TryGetMessage, ComplexOpt2, d.GetOption);
+            AssertOption(new ComplexOptionType3 { Qux = 9 }, options.TryGetMessage, ComplexOpt3, d.GetOption);
         }
 
         [Test]
         public void OptionLocations()
         {
             var fileOptions = UnittestCustomOptionsProto3Reflection.Descriptor.CustomOptions;
-            AssertOption(9876543210UL, fileOptions.TryGetUInt64, FileOpt1);
+            AssertOption(9876543210UL, fileOptions.TryGetUInt64, FileOpt1, UnittestCustomOptionsProto3Reflection.Descriptor.GetOption);
 
             var messageOptions = TestMessageWithCustomOptions.Descriptor.CustomOptions;
-            AssertOption(-56, messageOptions.TryGetInt32, MessageOpt1);
+            AssertOption(-56, messageOptions.TryGetInt32, MessageOpt1, TestMessageWithCustomOptions.Descriptor.GetOption);
 
             var fieldOptions = TestMessageWithCustomOptions.Descriptor.Fields["field1"].CustomOptions;
-            AssertOption(8765432109UL, fieldOptions.TryGetFixed64, FieldOpt1);
+            AssertOption(8765432109UL, fieldOptions.TryGetFixed64, FieldOpt1, TestMessageWithCustomOptions.Descriptor.Fields["field1"].GetOption);
 
             var oneofOptions = TestMessageWithCustomOptions.Descriptor.Oneofs[0].CustomOptions;
-            AssertOption(-99, oneofOptions.TryGetInt32, OneofOpt1);
+            AssertOption(-99, oneofOptions.TryGetInt32, OneofOpt1, TestMessageWithCustomOptions.Descriptor.Oneofs[0].GetOption);
 
             var enumOptions = TestMessageWithCustomOptions.Descriptor.EnumTypes[0].CustomOptions;
-            AssertOption(-789, enumOptions.TryGetSFixed32, EnumOpt1);
+            AssertOption(-789, enumOptions.TryGetSFixed32, EnumOpt1, TestMessageWithCustomOptions.Descriptor.EnumTypes[0].GetOption);
 
             var enumValueOptions = TestMessageWithCustomOptions.Descriptor.EnumTypes[0].FindValueByNumber(2).CustomOptions;
-            AssertOption(123, enumValueOptions.TryGetInt32, EnumValueOpt1);
+            AssertOption(123, enumValueOptions.TryGetInt32, EnumValueOpt1, TestMessageWithCustomOptions.Descriptor.EnumTypes[0].FindValueByNumber(2).GetOption);
 
             var service = UnittestCustomOptionsProto3Reflection.Descriptor.Services
                 .Single(s => s.Name == "TestServiceWithCustomOptions");
             var serviceOptions = service.CustomOptions;
-            AssertOption(-9876543210, serviceOptions.TryGetSInt64, ServiceOpt1);
+            AssertOption(-9876543210, serviceOptions.TryGetSInt64, ServiceOpt1, service.GetOption);
 
             var methodOptions = service.Methods[0].CustomOptions;
-            AssertOption((int)UnitTest.Issues.TestProtos.MethodOpt1.Val2, methodOptions.TryGetInt32, CustomOptionNumber.MethodOpt1);
+            AssertOption(UnitTest.Issues.TestProtos.MethodOpt1.Val2, EnumFetcher<UnitTest.Issues.TestProtos.MethodOpt1>(methodOptions), UnittestCustomOptionsProto3Extensions.MethodOpt1, service.Methods[0].GetOption);
         }
 
         [Test]
         public void MinValues()
         {
-            var options = CustomOptionMinIntegerValues.Descriptor.CustomOptions;
-            AssertOption(false, options.TryGetBool, BoolOpt);
-            AssertOption(int.MinValue, options.TryGetInt32, Int32Opt);
-            AssertOption(long.MinValue, options.TryGetInt64, Int64Opt);
-            AssertOption(uint.MinValue, options.TryGetUInt32, UInt32Opt);
-            AssertOption(ulong.MinValue, options.TryGetUInt64, UInt64Opt);
-            AssertOption(int.MinValue, options.TryGetSInt32, SInt32Opt);
-            AssertOption(long.MinValue, options.TryGetSInt64, SInt64Opt);
-            AssertOption(uint.MinValue, options.TryGetUInt32, Fixed32Opt);
-            AssertOption(ulong.MinValue, options.TryGetUInt64, Fixed64Opt);
-            AssertOption(int.MinValue, options.TryGetInt32, SFixed32Opt);
-            AssertOption(long.MinValue, options.TryGetInt64, SFixed64Opt);
+            var d = CustomOptionMinIntegerValues.Descriptor;
+            var options = d.CustomOptions;
+            AssertOption(false, options.TryGetBool, BoolOpt, d.GetOption);
+            AssertOption(int.MinValue, options.TryGetInt32, Int32Opt, d.GetOption);
+            AssertOption(long.MinValue, options.TryGetInt64, Int64Opt, d.GetOption);
+            AssertOption(uint.MinValue, options.TryGetUInt32, Uint32Opt, d.GetOption);
+            AssertOption(ulong.MinValue, options.TryGetUInt64, Uint64Opt, d.GetOption);
+            AssertOption(int.MinValue, options.TryGetSInt32, Sint32Opt, d.GetOption);
+            AssertOption(long.MinValue, options.TryGetSInt64, Sint64Opt, d.GetOption);
+            AssertOption(uint.MinValue, options.TryGetUInt32, Fixed32Opt, d.GetOption);
+            AssertOption(ulong.MinValue, options.TryGetUInt64, Fixed64Opt, d.GetOption);
+            AssertOption(int.MinValue, options.TryGetInt32, Sfixed32Opt, d.GetOption);
+            AssertOption(long.MinValue, options.TryGetInt64, Sfixed64Opt, d.GetOption);
         }
 
         [Test]
         public void MaxValues()
         {
-            var options = CustomOptionMaxIntegerValues.Descriptor.CustomOptions;
-            AssertOption(true, options.TryGetBool, BoolOpt);
-            AssertOption(int.MaxValue, options.TryGetInt32, Int32Opt);
-            AssertOption(long.MaxValue, options.TryGetInt64, Int64Opt);
-            AssertOption(uint.MaxValue, options.TryGetUInt32, UInt32Opt);
-            AssertOption(ulong.MaxValue, options.TryGetUInt64, UInt64Opt);
-            AssertOption(int.MaxValue, options.TryGetSInt32, SInt32Opt);
-            AssertOption(long.MaxValue, options.TryGetSInt64, SInt64Opt);
-            AssertOption(uint.MaxValue, options.TryGetFixed32, Fixed32Opt);
-            AssertOption(ulong.MaxValue, options.TryGetFixed64, Fixed64Opt);
-            AssertOption(int.MaxValue, options.TryGetSFixed32, SFixed32Opt);
-            AssertOption(long.MaxValue, options.TryGetSFixed64, SFixed64Opt);
+            var d = CustomOptionMaxIntegerValues.Descriptor;
+            var options = d.CustomOptions;
+            AssertOption(true, options.TryGetBool, BoolOpt, d.GetOption);
+            AssertOption(int.MaxValue, options.TryGetInt32, Int32Opt, d.GetOption);
+            AssertOption(long.MaxValue, options.TryGetInt64, Int64Opt, d.GetOption);
+            AssertOption(uint.MaxValue, options.TryGetUInt32, Uint32Opt, d.GetOption);
+            AssertOption(ulong.MaxValue, options.TryGetUInt64, Uint64Opt, d.GetOption);
+            AssertOption(int.MaxValue, options.TryGetSInt32, Sint32Opt, d.GetOption);
+            AssertOption(long.MaxValue, options.TryGetSInt64, Sint64Opt, d.GetOption);
+            AssertOption(uint.MaxValue, options.TryGetFixed32, Fixed32Opt, d.GetOption);
+            AssertOption(ulong.MaxValue, options.TryGetFixed64, Fixed64Opt, d.GetOption);
+            AssertOption(int.MaxValue, options.TryGetSFixed32, Sfixed32Opt, d.GetOption);
+            AssertOption(long.MaxValue, options.TryGetSFixed64, Sfixed64Opt, d.GetOption);
         }
 
         [Test]
@@ -196,17 +171,19 @@ namespace Google.Protobuf.Test.Reflection
         {
             // Just two examples
             var messageOptions = AggregateMessage.Descriptor.CustomOptions;
-            AssertOption(new Aggregate { I = 101, S = "MessageAnnotation" }, messageOptions.TryGetMessage, AggregateMsgOpt);
+            AssertOption(new Aggregate { I = 101, S = "MessageAnnotation" }, messageOptions.TryGetMessage, Msgopt, AggregateMessage.Descriptor.GetOption);
 
             var fieldOptions = AggregateMessage.Descriptor.Fields["fieldname"].CustomOptions;
-            AssertOption(new Aggregate { S = "FieldAnnotation" }, fieldOptions.TryGetMessage, AggregateFieldOpt);
+            AssertOption(new Aggregate { S = "FieldAnnotation" }, fieldOptions.TryGetMessage, Fieldopt, AggregateMessage.Descriptor.Fields["fieldname"].GetOption);
         }
 
-        private void AssertOption<T>(T expected, OptionFetcher<T> fetcher, CustomOptionNumber field)
+        private void AssertOption<T, D>(T expected, OptionFetcher<T> fetcher, Extension<D, T> extension, Func<Extension<D, T>, T> descriptorOptionFetcher) where D : IExtendableMessage<D>
         {
-            T actual;
-            Assert.IsTrue(fetcher((int)field, out actual));
-            Assert.AreEqual(expected, actual);
+            T customOptionsValue;
+            T extensionValue = descriptorOptionFetcher(extension);
+            Assert.IsTrue(fetcher(extension.FieldNumber, out customOptionsValue));
+            Assert.AreEqual(expected, customOptionsValue);
+            Assert.AreEqual(expected, extensionValue);
         }
     }
 }

csharp/src/Google.Protobuf.Test/Reflection/FieldAccessTest.cs

@@ -31,11 +31,14 @@
 #endregion
 
 using Google.Protobuf.TestProtos;
+using Proto2 = Google.Protobuf.TestProtos.Proto2;
 using NUnit.Framework;
 using System;
 using System.Collections;
 using System.Collections.Generic;
 
+using static Google.Protobuf.TestProtos.Proto2.UnittestExtensions;
+
 namespace Google.Protobuf.Reflection
 {
     public class FieldAccessTest
@@ -44,36 +47,36 @@ namespace Google.Protobuf.Reflection
         public void GetValue()
         {
             var message = SampleMessages.CreateFullTestAllTypes();
-            var fields = TestAllTypes.Descriptor.Fields;
-            Assert.AreEqual(message.SingleBool, fields[TestAllTypes.SingleBoolFieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleBytes, fields[TestAllTypes.SingleBytesFieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleDouble, fields[TestAllTypes.SingleDoubleFieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleFixed32, fields[TestAllTypes.SingleFixed32FieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleFixed64, fields[TestAllTypes.SingleFixed64FieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleFloat, fields[TestAllTypes.SingleFloatFieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleForeignEnum, fields[TestAllTypes.SingleForeignEnumFieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleForeignMessage, fields[TestAllTypes.SingleForeignMessageFieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleImportEnum, fields[TestAllTypes.SingleImportEnumFieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleImportMessage, fields[TestAllTypes.SingleImportMessageFieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleInt32, fields[TestAllTypes.SingleInt32FieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleInt64, fields[TestAllTypes.SingleInt64FieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleNestedEnum, fields[TestAllTypes.SingleNestedEnumFieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleNestedMessage, fields[TestAllTypes.SingleNestedMessageFieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SinglePublicImportMessage, fields[TestAllTypes.SinglePublicImportMessageFieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleSint32, fields[TestAllTypes.SingleSint32FieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleSint64, fields[TestAllTypes.SingleSint64FieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleString, fields[TestAllTypes.SingleStringFieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleSfixed32, fields[TestAllTypes.SingleSfixed32FieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleSfixed64, fields[TestAllTypes.SingleSfixed64FieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleUint32, fields[TestAllTypes.SingleUint32FieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.SingleUint64, fields[TestAllTypes.SingleUint64FieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.OneofBytes, fields[TestAllTypes.OneofBytesFieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.OneofString, fields[TestAllTypes.OneofStringFieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.OneofNestedMessage, fields[TestAllTypes.OneofNestedMessageFieldNumber].Accessor.GetValue(message));
-            Assert.AreEqual(message.OneofUint32, fields[TestAllTypes.OneofUint32FieldNumber].Accessor.GetValue(message));
+            var fields = TestProtos.TestAllTypes.Descriptor.Fields;
+            Assert.AreEqual(message.SingleBool, fields[TestProtos.TestAllTypes.SingleBoolFieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleBytes, fields[TestProtos.TestAllTypes.SingleBytesFieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleDouble, fields[TestProtos.TestAllTypes.SingleDoubleFieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleFixed32, fields[TestProtos.TestAllTypes.SingleFixed32FieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleFixed64, fields[TestProtos.TestAllTypes.SingleFixed64FieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleFloat, fields[TestProtos.TestAllTypes.SingleFloatFieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleForeignEnum, fields[TestProtos.TestAllTypes.SingleForeignEnumFieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleForeignMessage, fields[TestProtos.TestAllTypes.SingleForeignMessageFieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleImportEnum, fields[TestProtos.TestAllTypes.SingleImportEnumFieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleImportMessage, fields[TestProtos.TestAllTypes.SingleImportMessageFieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleInt32, fields[TestProtos.TestAllTypes.SingleInt32FieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleInt64, fields[TestProtos.TestAllTypes.SingleInt64FieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleNestedEnum, fields[TestProtos.TestAllTypes.SingleNestedEnumFieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleNestedMessage, fields[TestProtos.TestAllTypes.SingleNestedMessageFieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SinglePublicImportMessage, fields[TestProtos.TestAllTypes.SinglePublicImportMessageFieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleSint32, fields[TestProtos.TestAllTypes.SingleSint32FieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleSint64, fields[TestProtos.TestAllTypes.SingleSint64FieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleString, fields[TestProtos.TestAllTypes.SingleStringFieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleSfixed32, fields[TestProtos.TestAllTypes.SingleSfixed32FieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleSfixed64, fields[TestProtos.TestAllTypes.SingleSfixed64FieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleUint32, fields[TestProtos.TestAllTypes.SingleUint32FieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.SingleUint64, fields[TestProtos.TestAllTypes.SingleUint64FieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.OneofBytes, fields[TestProtos.TestAllTypes.OneofBytesFieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.OneofString, fields[TestProtos.TestAllTypes.OneofStringFieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.OneofNestedMessage, fields[TestProtos.TestAllTypes.OneofNestedMessageFieldNumber].Accessor.GetValue(message));
+            Assert.AreEqual(message.OneofUint32, fields[TestProtos.TestAllTypes.OneofUint32FieldNumber].Accessor.GetValue(message));
 
             // Just one example for repeated fields - they're all just returning the list
-            var list = (IList) fields[TestAllTypes.RepeatedInt32FieldNumber].Accessor.GetValue(message);
+            var list = (IList) fields[TestProtos.TestAllTypes.RepeatedInt32FieldNumber].Accessor.GetValue(message);
             Assert.AreEqual(message.RepeatedInt32, list);
             Assert.AreEqual(message.RepeatedInt32[0], list[0]); // Just in case there was any doubt...
 
@@ -86,36 +89,35 @@ namespace Google.Protobuf.Reflection
         }
 
         [Test]
-        public void Clear()
+        public void GetValue_IncorrectType()
         {
-            var message = SampleMessages.CreateFullTestAllTypes();
-            var fields = TestAllTypes.Descriptor.Fields;
-            fields[TestAllTypes.SingleBoolFieldNumber].Accessor.Clear(message);
-            fields[TestAllTypes.SingleInt32FieldNumber].Accessor.Clear(message);
-            fields[TestAllTypes.SingleStringFieldNumber].Accessor.Clear(message);
-            fields[TestAllTypes.SingleBytesFieldNumber].Accessor.Clear(message);
-            fields[TestAllTypes.SingleForeignEnumFieldNumber].Accessor.Clear(message);
-            fields[TestAllTypes.SingleForeignMessageFieldNumber].Accessor.Clear(message);
-            fields[TestAllTypes.RepeatedDoubleFieldNumber].Accessor.Clear(message);
+            IMessage message = SampleMessages.CreateFullTestAllTypes();
+            var fields = message.Descriptor.Fields;
+            Assert.Throws<InvalidCastException>(() => fields[TestProtos.TestAllTypes.SingleBoolFieldNumber].Accessor.GetValue(new TestMap()));
+        }
 
-            var expected = new TestAllTypes(SampleMessages.CreateFullTestAllTypes())
-            {
-                SingleBool = false,
-                SingleInt32 = 0,
-                SingleString = "",
-                SingleBytes = ByteString.Empty,
-                SingleForeignEnum = 0,
-                SingleForeignMessage = null,
-            };
-            expected.RepeatedDouble.Clear();
+        [Test]
+        public void HasValue_Proto3()
+        {
+            IMessage message = SampleMessages.CreateFullTestAllTypes();
+            var fields = message.Descriptor.Fields;
+            Assert.Throws<InvalidOperationException>(() => fields[TestProtos.TestAllTypes.SingleBoolFieldNumber].Accessor.HasValue(message));
+        }
 
-            Assert.AreEqual(expected, message);
+        [Test]
+        public void HasValue()
+        {
+            IMessage message = new Proto2.TestAllTypes();
+            var fields = message.Descriptor.Fields;
+            var accessor = fields[Proto2.TestAllTypes.OptionalBoolFieldNumber].Accessor;
 
-            // Separately, maps.
-            var mapMessage = new TestMap { MapStringString = { { "key1", "value1" }, { "key2", "value2" } } };
-            fields = TestMap.Descriptor.Fields;
-            fields[TestMap.MapStringStringFieldNumber].Accessor.Clear(mapMessage);
-            Assert.AreEqual(0, mapMessage.MapStringString.Count);
+            Assert.False(accessor.HasValue(message));
+
+            accessor.SetValue(message, true);
+            Assert.True(accessor.HasValue(message));
+
+            accessor.Clear(message);
+            Assert.False(accessor.HasValue(message));
         }
 
         [Test]
@@ -123,14 +125,14 @@ namespace Google.Protobuf.Reflection
         {
             // Just a sample (primitives, messages, enums, strings, byte strings)
             var message = SampleMessages.CreateFullTestAllTypes();
-            var fields = TestAllTypes.Descriptor.Fields;
-            fields[TestAllTypes.SingleBoolFieldNumber].Accessor.SetValue(message, false);
-            fields[TestAllTypes.SingleInt32FieldNumber].Accessor.SetValue(message, 500);
-            fields[TestAllTypes.SingleStringFieldNumber].Accessor.SetValue(message, "It's a string");
-            fields[TestAllTypes.SingleBytesFieldNumber].Accessor.SetValue(message, ByteString.CopyFrom(99, 98, 97));
-            fields[TestAllTypes.SingleForeignEnumFieldNumber].Accessor.SetValue(message, ForeignEnum.ForeignFoo);
-            fields[TestAllTypes.SingleForeignMessageFieldNumber].Accessor.SetValue(message, new ForeignMessage { C = 12345 });
-            fields[TestAllTypes.SingleDoubleFieldNumber].Accessor.SetValue(message, 20150701.5);
+            var fields = TestProtos.TestAllTypes.Descriptor.Fields;
+            fields[TestProtos.TestAllTypes.SingleBoolFieldNumber].Accessor.SetValue(message, false);
+            fields[TestProtos.TestAllTypes.SingleInt32FieldNumber].Accessor.SetValue(message, 500);
+            fields[TestProtos.TestAllTypes.SingleStringFieldNumber].Accessor.SetValue(message, "It's a string");
+            fields[TestProtos.TestAllTypes.SingleBytesFieldNumber].Accessor.SetValue(message, ByteString.CopyFrom(99, 98, 97));
+            fields[TestProtos.TestAllTypes.SingleForeignEnumFieldNumber].Accessor.SetValue(message, ForeignEnum.ForeignFoo);
+            fields[TestProtos.TestAllTypes.SingleForeignMessageFieldNumber].Accessor.SetValue(message, new ForeignMessage { C = 12345 });
+            fields[TestProtos.TestAllTypes.SingleDoubleFieldNumber].Accessor.SetValue(message, 20150701.5);
 
             var expected = new TestAllTypes(SampleMessages.CreateFullTestAllTypes())
             {
@@ -151,7 +153,7 @@ namespace Google.Protobuf.Reflection
         {
             IMessage message = SampleMessages.CreateFullTestAllTypes();
             var fields = message.Descriptor.Fields;
-            Assert.Throws<InvalidCastException>(() => fields[TestAllTypes.SingleBoolFieldNumber].Accessor.SetValue(message, "This isn't a bool"));
+            Assert.Throws<InvalidCastException>(() => fields[TestProtos.TestAllTypes.SingleBoolFieldNumber].Accessor.SetValue(message, "This isn't a bool"));
         }
 
         [Test]
@@ -167,52 +169,100 @@ namespace Google.Protobuf.Reflection
         {
             IMessage message = SampleMessages.CreateFullTestAllTypes();
             var fields = message.Descriptor.Fields;
-            Assert.Throws<InvalidOperationException>(() => fields[TestAllTypes.RepeatedDoubleFieldNumber].Accessor.SetValue(message, new double[10]));
-        }
-
-        [Test]
-        public void GetValue_IncorrectType()
-        {
-            IMessage message = SampleMessages.CreateFullTestAllTypes();
-            var fields = message.Descriptor.Fields;
-            Assert.Throws<InvalidCastException>(() => fields[TestAllTypes.SingleBoolFieldNumber].Accessor.GetValue(new TestMap()));
+            Assert.Throws<InvalidOperationException>(() => fields[TestProtos.TestAllTypes.RepeatedDoubleFieldNumber].Accessor.SetValue(message, new double[10]));
         }
 
         [Test]
         public void Oneof()
         {
             var message = new TestAllTypes();
-            var descriptor = TestAllTypes.Descriptor;
+            var descriptor = TestProtos.TestAllTypes.Descriptor;
             Assert.AreEqual(1, descriptor.Oneofs.Count);
             var oneof = descriptor.Oneofs[0];
             Assert.AreEqual("oneof_field", oneof.Name);
             Assert.IsNull(oneof.Accessor.GetCaseFieldDescriptor(message));
 
             message.OneofString = "foo";
-            Assert.AreSame(descriptor.Fields[TestAllTypes.OneofStringFieldNumber], oneof.Accessor.GetCaseFieldDescriptor(message));
+            Assert.AreSame(descriptor.Fields[TestProtos.TestAllTypes.OneofStringFieldNumber], oneof.Accessor.GetCaseFieldDescriptor(message));
 
             message.OneofUint32 = 10;
-            Assert.AreSame(descriptor.Fields[TestAllTypes.OneofUint32FieldNumber], oneof.Accessor.GetCaseFieldDescriptor(message));
+            Assert.AreSame(descriptor.Fields[TestProtos.TestAllTypes.OneofUint32FieldNumber], oneof.Accessor.GetCaseFieldDescriptor(message));
 
             oneof.Accessor.Clear(message);
-            Assert.AreEqual(TestAllTypes.OneofFieldOneofCase.None, message.OneofFieldCase);
+            Assert.AreEqual(TestProtos.TestAllTypes.OneofFieldOneofCase.None, message.OneofFieldCase);
+        }
+
+        [Test]
+        public void Clear()
+        {
+            var message = SampleMessages.CreateFullTestAllTypes();
+            var fields = TestProtos.TestAllTypes.Descriptor.Fields;
+            fields[TestProtos.TestAllTypes.SingleBoolFieldNumber].Accessor.Clear(message);
+            fields[TestProtos.TestAllTypes.SingleInt32FieldNumber].Accessor.Clear(message);
+            fields[TestProtos.TestAllTypes.SingleStringFieldNumber].Accessor.Clear(message);
+            fields[TestProtos.TestAllTypes.SingleBytesFieldNumber].Accessor.Clear(message);
+            fields[TestProtos.TestAllTypes.SingleForeignEnumFieldNumber].Accessor.Clear(message);
+            fields[TestProtos.TestAllTypes.SingleForeignMessageFieldNumber].Accessor.Clear(message);
+            fields[TestProtos.TestAllTypes.RepeatedDoubleFieldNumber].Accessor.Clear(message);
+
+            var expected = new TestAllTypes(SampleMessages.CreateFullTestAllTypes())
+            {
+                SingleBool = false,
+                SingleInt32 = 0,
+                SingleString = "",
+                SingleBytes = ByteString.Empty,
+                SingleForeignEnum = 0,
+                SingleForeignMessage = null,
+            };
+            expected.RepeatedDouble.Clear();
+
+            Assert.AreEqual(expected, message);
+
+            // Separately, maps.
+            var mapMessage = new TestMap { MapStringString = { { "key1", "value1" }, { "key2", "value2" } } };
+            fields = TestMap.Descriptor.Fields;
+            fields[TestMap.MapStringStringFieldNumber].Accessor.Clear(mapMessage);
+            Assert.AreEqual(0, mapMessage.MapStringString.Count);
         }
 
         [Test]
         public void FieldDescriptor_ByName()
         {
-            var descriptor = TestAllTypes.Descriptor;
+            var descriptor = TestProtos.TestAllTypes.Descriptor;
             Assert.AreSame(
-                descriptor.Fields[TestAllTypes.SingleBoolFieldNumber],
+                descriptor.Fields[TestProtos.TestAllTypes.SingleBoolFieldNumber],
                 descriptor.Fields["single_bool"]);
         }
 
         [Test]
         public void FieldDescriptor_NotFound()
         {
-            var descriptor = TestAllTypes.Descriptor;
+            var descriptor = TestProtos.TestAllTypes.Descriptor;
             Assert.Throws<KeyNotFoundException>(() => descriptor.Fields[999999].ToString());
             Assert.Throws<KeyNotFoundException>(() => descriptor.Fields["not found"].ToString());
         }
+
+        [Test]
+        public void GetExtensionValue()
+        {
+            var message = SampleMessages.CreateFullTestAllExtensions();
+
+            // test that the reflector works, since the reflector just runs through IExtendableMessage
+            Assert.AreEqual(message.GetExtension(OptionalBoolExtension), Proto2.TestAllExtensions.Descriptor.FindFieldByNumber(OptionalBoolExtension.FieldNumber).Accessor.GetValue(message));
+        }
+
+        [Test]
+        public void GetRepeatedExtensionValue()
+        {
+            // check to make sure repeated accessor uses GetOrRegister
+            var message = new Proto2.TestAllExtensions();
+
+            Assert.IsNull(message.GetExtension(RepeatedBoolExtension));
+            Assert.IsNotNull(Proto2.TestAllExtensions.Descriptor.FindFieldByNumber(RepeatedBoolExtension.FieldNumber).Accessor.GetValue(message));
+            Assert.IsNotNull(message.GetExtension(RepeatedBoolExtension));
+
+            message.ClearExtension(RepeatedBoolExtension);
+            Assert.IsNull(message.GetExtension(RepeatedBoolExtension));
+        }
     }
 }

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

@@ -32,6 +32,9 @@
 
 using System;
 using Google.Protobuf.TestProtos;
+using Proto2 = Google.Protobuf.TestProtos.Proto2;
+
+using static Google.Protobuf.TestProtos.Proto2.UnittestExtensions;
 
 namespace Google.Protobuf
 {
@@ -60,7 +63,7 @@ namespace Google.Protobuf
                 SingleImportMessage = new ImportMessage { D = 20 },
                 SingleInt32 = 100,
                 SingleInt64 = 3210987654321,
-                SingleNestedEnum = TestAllTypes.Types.NestedEnum.Foo,
+                SingleNestedEnum = TestProtos.TestAllTypes.Types.NestedEnum.Foo,
                 SingleNestedMessage = new TestAllTypes.Types.NestedMessage { Bb = 35 },
                 SinglePublicImportMessage = new PublicImportMessage { E = 54 },
                 SingleSfixed32 = -123,
@@ -82,7 +85,7 @@ namespace Google.Protobuf
                 RepeatedImportMessage = { new ImportMessage { D = 20 }, new ImportMessage { D = 25 } },
                 RepeatedInt32 = { 100, 200 },
                 RepeatedInt64 = { 3210987654321, Int64.MaxValue },
-                RepeatedNestedEnum = { TestAllTypes.Types.NestedEnum.Foo, TestAllTypes.Types.NestedEnum.Neg },
+                RepeatedNestedEnum = { TestProtos.TestAllTypes.Types.NestedEnum.Foo, TestProtos.TestAllTypes.Types.NestedEnum.Neg },
                 RepeatedNestedMessage = { new TestAllTypes.Types.NestedMessage { Bb = 35 }, new TestAllTypes.Types.NestedMessage { Bb = 10 } },
                 RepeatedPublicImportMessage = { new PublicImportMessage { E = 54 }, new PublicImportMessage { E = -1 } },
                 RepeatedSfixed32 = { -123, 123 },
@@ -95,5 +98,110 @@ namespace Google.Protobuf
                 OneofString = "Oneof string"
             };
         }
+
+        public static Proto2.TestAllTypes CreateFullTestAllTypesProto2()
+        {
+            return new Proto2.TestAllTypes
+            {
+                OptionalBool = true,
+                OptionalBytes = ByteString.CopyFrom(1, 2, 3, 4),
+                OptionalDouble = 23.5,
+                OptionalFixed32 = 23,
+                OptionalFixed64 = 1234567890123,
+                OptionalFloat = 12.25f,
+                OptionalForeignEnum = Proto2.ForeignEnum.ForeignBar,
+                OptionalForeignMessage = new Proto2.ForeignMessage { C = 10 },
+                OptionalImportEnum = Proto2.ImportEnum.ImportBaz,
+                OptionalImportMessage = new Proto2.ImportMessage { D = 20 },
+                OptionalInt32 = 100,
+                OptionalInt64 = 3210987654321,
+                OptionalNestedEnum = Proto2.TestAllTypes.Types.NestedEnum.Foo,
+                OptionalNestedMessage = new Proto2.TestAllTypes.Types.NestedMessage { Bb = 35 },
+                OptionalPublicImportMessage = new Proto2.PublicImportMessage { E = 54 },
+                OptionalSfixed32 = -123,
+                OptionalSfixed64 = -12345678901234,
+                OptionalSint32 = -456,
+                OptionalSint64 = -12345678901235,
+                OptionalString = "test",
+                OptionalUint32 = UInt32.MaxValue,
+                OptionalUint64 = UInt64.MaxValue,
+                OptionalGroup = new Proto2.TestAllTypes.Types.OptionalGroup { A = 10 },
+                RepeatedBool = { true, false },
+                RepeatedBytes = { ByteString.CopyFrom(1, 2, 3, 4), ByteString.CopyFrom(5, 6), ByteString.CopyFrom(new byte[1000]) },
+                RepeatedDouble = { -12.25, 23.5 },
+                RepeatedFixed32 = { UInt32.MaxValue, 23 },
+                RepeatedFixed64 = { UInt64.MaxValue, 1234567890123 },
+                RepeatedFloat = { 100f, 12.25f },
+                RepeatedForeignEnum = { Proto2.ForeignEnum.ForeignFoo, Proto2.ForeignEnum.ForeignBar },
+                RepeatedForeignMessage = { new Proto2.ForeignMessage(), new Proto2.ForeignMessage { C = 10 } },
+                RepeatedImportEnum = { Proto2.ImportEnum.ImportBaz, Proto2.ImportEnum.ImportFoo },
+                RepeatedImportMessage = { new Proto2.ImportMessage { D = 20 }, new Proto2.ImportMessage { D = 25 } },
+                RepeatedInt32 = { 100, 200 },
+                RepeatedInt64 = { 3210987654321, Int64.MaxValue },
+                RepeatedNestedEnum = { Proto2.TestAllTypes.Types.NestedEnum.Foo, Proto2.TestAllTypes.Types.NestedEnum.Neg },
+                RepeatedNestedMessage = { new Proto2.TestAllTypes.Types.NestedMessage { Bb = 35 }, new Proto2.TestAllTypes.Types.NestedMessage { Bb = 10 } },
+                RepeatedSfixed32 = { -123, 123 },
+                RepeatedSfixed64 = { -12345678901234, 12345678901234 },
+                RepeatedSint32 = { -456, 100 },
+                RepeatedSint64 = { -12345678901235, 123 },
+                RepeatedString = { "foo", "bar" },
+                RepeatedUint32 = { UInt32.MaxValue, UInt32.MinValue },
+                RepeatedUint64 = { UInt64.MaxValue, UInt32.MinValue },
+                RepeatedGroup = { new Proto2.TestAllTypes.Types.RepeatedGroup { A = 10 }, new Proto2.TestAllTypes.Types.RepeatedGroup { A = 20 } },
+                OneofString = "Oneof string"
+            };
+        }
+
+        public static Proto2.TestAllExtensions CreateFullTestAllExtensions()
+        {
+            var message = new Proto2.TestAllExtensions();
+            message.SetExtension(OptionalBoolExtension, true);
+            message.SetExtension(OptionalBytesExtension, ByteString.CopyFrom(1, 2, 3, 4));
+            message.SetExtension(OptionalDoubleExtension, 23.5);
+            message.SetExtension(OptionalFixed32Extension, 23u);
+            message.SetExtension(OptionalFixed64Extension, 1234567890123u);
+            message.SetExtension(OptionalFloatExtension, 12.25f);
+            message.SetExtension(OptionalForeignEnumExtension, Proto2.ForeignEnum.ForeignBar);
+            message.SetExtension(OptionalForeignMessageExtension, new Proto2.ForeignMessage { C = 10 });
+            message.SetExtension(OptionalImportEnumExtension, Proto2.ImportEnum.ImportBaz);
+            message.SetExtension(OptionalImportMessageExtension, new Proto2.ImportMessage { D = 20 });
+            message.SetExtension(OptionalInt32Extension, 100);
+            message.SetExtension(OptionalInt64Extension, 3210987654321);
+            message.SetExtension(OptionalNestedEnumExtension, Proto2.TestAllTypes.Types.NestedEnum.Foo);
+            message.SetExtension(OptionalNestedMessageExtension, new Proto2.TestAllTypes.Types.NestedMessage { Bb = 35 });
+            message.SetExtension(OptionalPublicImportMessageExtension, new Proto2.PublicImportMessage { E = 54 });
+            message.SetExtension(OptionalSfixed32Extension, -123);
+            message.SetExtension(OptionalSfixed64Extension, -12345678901234);
+            message.SetExtension(OptionalSint32Extension, -456);
+            message.SetExtension(OptionalSint64Extension, -12345678901235);
+            message.SetExtension(OptionalStringExtension, "test");
+            message.SetExtension(OptionalUint32Extension, UInt32.MaxValue);
+            message.SetExtension(OptionalUint64Extension, UInt64.MaxValue);
+            message.SetExtension(OptionalGroupExtension, new Proto2.OptionalGroup_extension { A = 10 });
+            message.GetOrInitializeExtension(RepeatedBoolExtension).AddRange(new[] { true, false });
+            message.GetOrInitializeExtension(RepeatedBytesExtension).AddRange(new[] { ByteString.CopyFrom(1, 2, 3, 4), ByteString.CopyFrom(5, 6), ByteString.CopyFrom(new byte[1000]) });
+            message.GetOrInitializeExtension(RepeatedDoubleExtension).AddRange(new[] { -12.25, 23.5 });
+            message.GetOrInitializeExtension(RepeatedFixed32Extension).AddRange(new[] { UInt32.MaxValue, 23u });
+            message.GetOrInitializeExtension(RepeatedFixed64Extension).AddRange(new[] { UInt64.MaxValue, 1234567890123ul });
+            message.GetOrInitializeExtension(RepeatedFloatExtension).AddRange(new[] { 100f, 12.25f });
+            message.GetOrInitializeExtension(RepeatedForeignEnumExtension).AddRange(new[] { Proto2.ForeignEnum.ForeignFoo, Proto2.ForeignEnum.ForeignBar });
+            message.GetOrInitializeExtension(RepeatedForeignMessageExtension).AddRange(new[] { new Proto2.ForeignMessage(), new Proto2.ForeignMessage { C = 10 } });
+            message.GetOrInitializeExtension(RepeatedImportEnumExtension).AddRange(new[] { Proto2.ImportEnum.ImportBaz, Proto2.ImportEnum.ImportFoo });
+            message.GetOrInitializeExtension(RepeatedImportMessageExtension).AddRange(new[] { new Proto2.ImportMessage { D = 20 }, new Proto2.ImportMessage { D = 25 } });
+            message.GetOrInitializeExtension(RepeatedInt32Extension).AddRange(new[] { 100, 200 });
+            message.GetOrInitializeExtension(RepeatedInt64Extension).AddRange(new[] { 3210987654321, Int64.MaxValue });
+            message.GetOrInitializeExtension(RepeatedNestedEnumExtension).AddRange(new[] { Proto2.TestAllTypes.Types.NestedEnum.Foo, Proto2.TestAllTypes.Types.NestedEnum.Neg });
+            message.GetOrInitializeExtension(RepeatedNestedMessageExtension).AddRange(new[] { new Proto2.TestAllTypes.Types.NestedMessage { Bb = 35 }, new Proto2.TestAllTypes.Types.NestedMessage { Bb = 10 } });
+            message.GetOrInitializeExtension(RepeatedSfixed32Extension).AddRange(new[] { -123, 123 });
+            message.GetOrInitializeExtension(RepeatedSfixed64Extension).AddRange(new[] { -12345678901234, 12345678901234 });
+            message.GetOrInitializeExtension(RepeatedSint32Extension).AddRange(new[] { -456, 100 });
+            message.GetOrInitializeExtension(RepeatedSint64Extension).AddRange(new[] { -12345678901235, 123 });
+            message.GetOrInitializeExtension(RepeatedStringExtension).AddRange(new[] { "foo", "bar" });
+            message.GetOrInitializeExtension(RepeatedUint32Extension).AddRange(new[] { UInt32.MaxValue, UInt32.MinValue });
+            message.GetOrInitializeExtension(RepeatedUint64Extension).AddRange(new[] { UInt64.MaxValue, UInt32.MinValue });
+            message.GetOrInitializeExtension(RepeatedGroupExtension).AddRange(new[] { new Proto2.RepeatedGroup_extension { A = 10 }, new Proto2.RepeatedGroup_extension { A = 20 } });
+            message.SetExtension(OneofStringExtension, "Oneof string");
+            return message;
+        }
     }
 }

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

@@ -165,7 +165,7 @@ namespace UnitTest.Issues.TestProtos {
 
   }
   /// <summary>Holder for extension identifiers generated from the top level of unittest_custom_options_proto3.proto</summary>
-  internal static partial class UnittestCustomOptionsProto3Extensions {
+  public static partial class UnittestCustomOptionsProto3Extensions {
     public static readonly pb::Extension<global::Google.Protobuf.Reflection.FileOptions, ulong> FileOpt1 =
       new pb::Extension<global::Google.Protobuf.Reflection.FileOptions, ulong>(7736974, pb::FieldCodec.ForUInt64(61895792, 0UL));
     public static readonly pb::Extension<global::Google.Protobuf.Reflection.MessageOptions, int> MessageOpt1 =
@@ -2138,7 +2138,7 @@ namespace UnitTest.Issues.TestProtos {
         #region Extensions
         /// <summary>Container for extensions for other messages declared in the ComplexOptionType4 message type.</summary>
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
-        internal static partial class Extensions {
+        public static partial class Extensions {
           public static readonly pb::Extension<global::Google.Protobuf.Reflection.MessageOptions, global::UnitTest.Issues.TestProtos.ComplexOptionType2.Types.ComplexOptionType4> ComplexOpt4 =
             new pb::Extension<global::Google.Protobuf.Reflection.MessageOptions, global::UnitTest.Issues.TestProtos.ComplexOptionType2.Types.ComplexOptionType4>(7633546, pb::FieldCodec.ForMessage(61068370, global::UnitTest.Issues.TestProtos.ComplexOptionType2.Types.ComplexOptionType4.Parser));
         }

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

@@ -0,0 +1,210 @@
+// <auto-generated>
+//     Generated by the protocol buffer compiler.  DO NOT EDIT!
+//     source: unittest_import.proto
+// </auto-generated>
+#pragma warning disable 1591, 0612, 3021
+#region Designer generated code
+
+using pb = global::Google.Protobuf;
+using pbc = global::Google.Protobuf.Collections;
+using pbr = global::Google.Protobuf.Reflection;
+using scg = global::System.Collections.Generic;
+namespace Google.Protobuf.TestProtos.Proto2 {
+
+  /// <summary>Holder for reflection information generated from unittest_import.proto</summary>
+  public static partial class UnittestImportReflection {
+
+    #region Descriptor
+    /// <summary>File descriptor for unittest_import.proto</summary>
+    public static pbr::FileDescriptor Descriptor {
+      get { return descriptor; }
+    }
+    private static pbr::FileDescriptor descriptor;
+
+    static UnittestImportReflection() {
+      byte[] descriptorData = global::System.Convert.FromBase64String(
+          string.Concat(
+            "ChV1bml0dGVzdF9pbXBvcnQucHJvdG8SH3Byb3RvYnVmX3VuaXR0ZXN0X2lt",
+            "cG9ydF9wcm90bzIaHHVuaXR0ZXN0X2ltcG9ydF9wdWJsaWMucHJvdG8iGgoN",
+            "SW1wb3J0TWVzc2FnZRIJCgFkGAEgASgFKjwKCkltcG9ydEVudW0SDgoKSU1Q",
+            "T1JUX0ZPTxAHEg4KCklNUE9SVF9CQVIQCBIOCgpJTVBPUlRfQkFaEAkqMQoQ",
+            "SW1wb3J0RW51bUZvck1hcBILCgdVTktOT1dOEAASBwoDRk9PEAESBwoDQkFS",
+            "EAJCKUgB+AEBqgIhR29vZ2xlLlByb3RvYnVmLlRlc3RQcm90b3MuUHJvdG8y",
+            "UAA="));
+      descriptor = pbr::FileDescriptor.FromGeneratedCode(descriptorData,
+          new pbr::FileDescriptor[] { global::Google.Protobuf.TestProtos.Proto2.UnittestImportPublicReflection.Descriptor, },
+          new pbr::GeneratedClrTypeInfo(new[] {typeof(global::Google.Protobuf.TestProtos.Proto2.ImportEnum), typeof(global::Google.Protobuf.TestProtos.Proto2.ImportEnumForMap), }, null, new pbr::GeneratedClrTypeInfo[] {
+            new pbr::GeneratedClrTypeInfo(typeof(global::Google.Protobuf.TestProtos.Proto2.ImportMessage), global::Google.Protobuf.TestProtos.Proto2.ImportMessage.Parser, new[]{ "D" }, null, null, null, null)
+          }));
+    }
+    #endregion
+
+  }
+  #region Enums
+  public enum ImportEnum {
+    [pbr::OriginalName("IMPORT_FOO")] ImportFoo = 7,
+    [pbr::OriginalName("IMPORT_BAR")] ImportBar = 8,
+    [pbr::OriginalName("IMPORT_BAZ")] ImportBaz = 9,
+  }
+
+  /// <summary>
+  /// To use an enum in a map, it must has the first value as 0.
+  /// </summary>
+  public enum ImportEnumForMap {
+    [pbr::OriginalName("UNKNOWN")] Unknown = 0,
+    [pbr::OriginalName("FOO")] Foo = 1,
+    [pbr::OriginalName("BAR")] Bar = 2,
+  }
+
+  #endregion
+
+  #region Messages
+  public sealed partial class ImportMessage : pb::IMessage<ImportMessage> {
+    private static readonly pb::MessageParser<ImportMessage> _parser = new pb::MessageParser<ImportMessage>(() => new ImportMessage());
+    private pb::UnknownFieldSet _unknownFields;
+    private int _hasBits0;
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public static pb::MessageParser<ImportMessage> Parser { get { return _parser; } }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public static pbr::MessageDescriptor Descriptor {
+      get { return global::Google.Protobuf.TestProtos.Proto2.UnittestImportReflection.Descriptor.MessageTypes[0]; }
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    pbr::MessageDescriptor pb::IMessage.Descriptor {
+      get { return Descriptor; }
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public ImportMessage() {
+      OnConstruction();
+    }
+
+    partial void OnConstruction();
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public ImportMessage(ImportMessage other) : this() {
+      _hasBits0 = other._hasBits0;
+      d_ = other.d_;
+      _unknownFields = pb::UnknownFieldSet.Clone(other._unknownFields);
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public ImportMessage Clone() {
+      return new ImportMessage(this);
+    }
+
+    /// <summary>Field number for the "d" field.</summary>
+    public const int DFieldNumber = 1;
+    private readonly static int DDefaultValue = 0;
+
+    private int d_;
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public int D {
+      get { if ((_hasBits0 & 1) != 0) { return d_; } else { return DDefaultValue; } }
+      set {
+        _hasBits0 |= 1;
+        d_ = value;
+      }
+    }
+    /// <summary>Gets whether the "d" field is set</summary>
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public bool HasD {
+      get { return (_hasBits0 & 1) != 0; }
+    }
+    /// <summary>Clears the value of the "d" field</summary>
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public void ClearD() {
+      _hasBits0 &= ~1;
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public override bool Equals(object other) {
+      return Equals(other as ImportMessage);
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public bool Equals(ImportMessage other) {
+      if (ReferenceEquals(other, null)) {
+        return false;
+      }
+      if (ReferenceEquals(other, this)) {
+        return true;
+      }
+      if (D != other.D) return false;
+      return Equals(_unknownFields, other._unknownFields);
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public override int GetHashCode() {
+      int hash = 1;
+      if (HasD) hash ^= D.GetHashCode();
+      if (_unknownFields != null) {
+        hash ^= _unknownFields.GetHashCode();
+      }
+      return hash;
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public override string ToString() {
+      return pb::JsonFormatter.ToDiagnosticString(this);
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public void WriteTo(pb::CodedOutputStream output) {
+      if (HasD) {
+        output.WriteRawTag(8);
+        output.WriteInt32(D);
+      }
+      if (_unknownFields != null) {
+        _unknownFields.WriteTo(output);
+      }
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public int CalculateSize() {
+      int size = 0;
+      if (HasD) {
+        size += 1 + pb::CodedOutputStream.ComputeInt32Size(D);
+      }
+      if (_unknownFields != null) {
+        size += _unknownFields.CalculateSize();
+      }
+      return size;
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public void MergeFrom(ImportMessage other) {
+      if (other == null) {
+        return;
+      }
+      if (other.HasD) {
+        D = other.D;
+      }
+      _unknownFields = pb::UnknownFieldSet.MergeFrom(_unknownFields, other._unknownFields);
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public void MergeFrom(pb::CodedInputStream input) {
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            D = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    }
+
+  }
+
+  #endregion
+
+}
+
+#endregion Designer generated code

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

@@ -0,0 +1,188 @@
+// <auto-generated>
+//     Generated by the protocol buffer compiler.  DO NOT EDIT!
+//     source: unittest_import_public.proto
+// </auto-generated>
+#pragma warning disable 1591, 0612, 3021
+#region Designer generated code
+
+using pb = global::Google.Protobuf;
+using pbc = global::Google.Protobuf.Collections;
+using pbr = global::Google.Protobuf.Reflection;
+using scg = global::System.Collections.Generic;
+namespace Google.Protobuf.TestProtos.Proto2 {
+
+  /// <summary>Holder for reflection information generated from unittest_import_public.proto</summary>
+  public static partial class UnittestImportPublicReflection {
+
+    #region Descriptor
+    /// <summary>File descriptor for unittest_import_public.proto</summary>
+    public static pbr::FileDescriptor Descriptor {
+      get { return descriptor; }
+    }
+    private static pbr::FileDescriptor descriptor;
+
+    static UnittestImportPublicReflection() {
+      byte[] descriptorData = global::System.Convert.FromBase64String(
+          string.Concat(
+            "Chx1bml0dGVzdF9pbXBvcnRfcHVibGljLnByb3RvEh9wcm90b2J1Zl91bml0",
+            "dGVzdF9pbXBvcnRfcHJvdG8yIiAKE1B1YmxpY0ltcG9ydE1lc3NhZ2USCQoB",
+            "ZRgBIAEoBUIkqgIhR29vZ2xlLlByb3RvYnVmLlRlc3RQcm90b3MuUHJvdG8y"));
+      descriptor = pbr::FileDescriptor.FromGeneratedCode(descriptorData,
+          new pbr::FileDescriptor[] { },
+          new pbr::GeneratedClrTypeInfo(null, null, new pbr::GeneratedClrTypeInfo[] {
+            new pbr::GeneratedClrTypeInfo(typeof(global::Google.Protobuf.TestProtos.Proto2.PublicImportMessage), global::Google.Protobuf.TestProtos.Proto2.PublicImportMessage.Parser, new[]{ "E" }, null, null, null, null)
+          }));
+    }
+    #endregion
+
+  }
+  #region Messages
+  public sealed partial class PublicImportMessage : pb::IMessage<PublicImportMessage> {
+    private static readonly pb::MessageParser<PublicImportMessage> _parser = new pb::MessageParser<PublicImportMessage>(() => new PublicImportMessage());
+    private pb::UnknownFieldSet _unknownFields;
+    private int _hasBits0;
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public static pb::MessageParser<PublicImportMessage> Parser { get { return _parser; } }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public static pbr::MessageDescriptor Descriptor {
+      get { return global::Google.Protobuf.TestProtos.Proto2.UnittestImportPublicReflection.Descriptor.MessageTypes[0]; }
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    pbr::MessageDescriptor pb::IMessage.Descriptor {
+      get { return Descriptor; }
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public PublicImportMessage() {
+      OnConstruction();
+    }
+
+    partial void OnConstruction();
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public PublicImportMessage(PublicImportMessage other) : this() {
+      _hasBits0 = other._hasBits0;
+      e_ = other.e_;
+      _unknownFields = pb::UnknownFieldSet.Clone(other._unknownFields);
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public PublicImportMessage Clone() {
+      return new PublicImportMessage(this);
+    }
+
+    /// <summary>Field number for the "e" field.</summary>
+    public const int EFieldNumber = 1;
+    private readonly static int EDefaultValue = 0;
+
+    private int e_;
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public int E {
+      get { if ((_hasBits0 & 1) != 0) { return e_; } else { return EDefaultValue; } }
+      set {
+        _hasBits0 |= 1;
+        e_ = value;
+      }
+    }
+    /// <summary>Gets whether the "e" field is set</summary>
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public bool HasE {
+      get { return (_hasBits0 & 1) != 0; }
+    }
+    /// <summary>Clears the value of the "e" field</summary>
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public void ClearE() {
+      _hasBits0 &= ~1;
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public override bool Equals(object other) {
+      return Equals(other as PublicImportMessage);
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public bool Equals(PublicImportMessage other) {
+      if (ReferenceEquals(other, null)) {
+        return false;
+      }
+      if (ReferenceEquals(other, this)) {
+        return true;
+      }
+      if (E != other.E) return false;
+      return Equals(_unknownFields, other._unknownFields);
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public override int GetHashCode() {
+      int hash = 1;
+      if (HasE) hash ^= E.GetHashCode();
+      if (_unknownFields != null) {
+        hash ^= _unknownFields.GetHashCode();
+      }
+      return hash;
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public override string ToString() {
+      return pb::JsonFormatter.ToDiagnosticString(this);
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public void WriteTo(pb::CodedOutputStream output) {
+      if (HasE) {
+        output.WriteRawTag(8);
+        output.WriteInt32(E);
+      }
+      if (_unknownFields != null) {
+        _unknownFields.WriteTo(output);
+      }
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public int CalculateSize() {
+      int size = 0;
+      if (HasE) {
+        size += 1 + pb::CodedOutputStream.ComputeInt32Size(E);
+      }
+      if (_unknownFields != null) {
+        size += _unknownFields.CalculateSize();
+      }
+      return size;
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public void MergeFrom(PublicImportMessage other) {
+      if (other == null) {
+        return;
+      }
+      if (other.HasE) {
+        E = other.E;
+      }
+      _unknownFields = pb::UnknownFieldSet.MergeFrom(_unknownFields, other._unknownFields);
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    public void MergeFrom(pb::CodedInputStream input) {
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 8: {
+            E = input.ReadInt32();
+            break;
+          }
+        }
+      }
+    }
+
+  }
+
+  #endregion
+
+}
+
+#endregion Designer generated code

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

@@ -33,12 +33,25 @@
 using System;
 using System.IO;
 using Google.Protobuf.TestProtos;
+using Proto2 = Google.Protobuf.TestProtos.Proto2;
 using NUnit.Framework;
 
 namespace Google.Protobuf
 {
     public class UnknownFieldSetTest
     {
+        public class Data
+        {
+            public static System.Collections.IEnumerable Messages
+            {
+                get
+                {
+                    yield return SampleMessages.CreateFullTestAllTypesProto2();
+                    yield return SampleMessages.CreateFullTestAllTypes();
+                }
+            }
+        }
+
         [Test]
         public void EmptyUnknownFieldSet()
         {
@@ -60,24 +73,23 @@ namespace Google.Protobuf
         }
 
         [Test]
-        public void TestMergeCodedInput()
+        [TestCaseSource(typeof(Data), "Messages")]
+        public void TestMergeCodedInput(IMessage message)
         {
-            var message = SampleMessages.CreateFullTestAllTypes();
             var emptyMessage = new TestEmptyMessage();
             emptyMessage.MergeFrom(message.ToByteArray());
             Assert.AreEqual(message.CalculateSize(), emptyMessage.CalculateSize());
             Assert.AreEqual(message.ToByteArray(), emptyMessage.ToByteArray());
 
-            var newMessage = new TestAllTypes();
-            newMessage.MergeFrom(emptyMessage.ToByteArray());
+            var newMessage = message.Descriptor.Parser.ParseFrom(emptyMessage.ToByteArray());
             Assert.AreEqual(message, newMessage);
             Assert.AreEqual(message.CalculateSize(), newMessage.CalculateSize());
         }
 
         [Test]
-        public void TestMergeMessage()
+        [TestCaseSource(typeof(Data), "Messages")]
+        public void TestMergeMessage(IMessage message)
         {
-            var message = SampleMessages.CreateFullTestAllTypes();
             var emptyMessage = new TestEmptyMessage();
             var otherEmptyMessage = new TestEmptyMessage();
             emptyMessage.MergeFrom(message.ToByteArray());
@@ -88,9 +100,9 @@ namespace Google.Protobuf
         }
 
         [Test]
-        public void TestEquals()
+        [TestCaseSource(typeof(Data), "Messages")]
+        public void TestEquals(IMessage message)
         {
-            var message = SampleMessages.CreateFullTestAllTypes();
             var emptyMessage = new TestEmptyMessage();
             var otherEmptyMessage = new TestEmptyMessage();
             Assert.AreEqual(emptyMessage, otherEmptyMessage);
@@ -101,9 +113,9 @@ namespace Google.Protobuf
         }
 
         [Test]
-        public void TestHashCode()
+        [TestCaseSource(typeof(Data), "Messages")]
+        public void TestHashCode(IMessage message)
         {
-            var message = SampleMessages.CreateFullTestAllTypes();
             var emptyMessage = new TestEmptyMessage();
             int hashCode = emptyMessage.GetHashCode();
             emptyMessage.MergeFrom(message.ToByteArray());
@@ -111,7 +123,8 @@ namespace Google.Protobuf
         }
 
         [Test]
-        public void TestClone()
+        [TestCaseSource(typeof(Data), "Messages")]
+        public void TestClone(IMessage message)
         {
             var emptyMessage = new TestEmptyMessage();
             var otherEmptyMessage = new TestEmptyMessage();
@@ -119,7 +132,6 @@ namespace Google.Protobuf
             Assert.AreEqual(emptyMessage.CalculateSize(), otherEmptyMessage.CalculateSize());
             Assert.AreEqual(emptyMessage.ToByteArray(), otherEmptyMessage.ToByteArray());
 
-            var message = SampleMessages.CreateFullTestAllTypes();
             emptyMessage.MergeFrom(message.ToByteArray());
             otherEmptyMessage = emptyMessage.Clone();
             Assert.AreEqual(message.CalculateSize(), otherEmptyMessage.CalculateSize());
@@ -127,9 +139,9 @@ namespace Google.Protobuf
         }
 
         [Test]
-        public void TestDiscardUnknownFields()
+        [TestCaseSource(typeof(Data), "Messages")]
+        public void TestDiscardUnknownFields(IMessage message)
         {
-            var message = SampleMessages.CreateFullTestAllTypes();
             var goldenEmptyMessage = new TestEmptyMessage();
             byte[] data = message.ToByteArray();
             int fullSize = message.CalculateSize();

csharp/src/Google.Protobuf/Collections/RepeatedField.cs

@@ -148,6 +148,10 @@ namespace Google.Protobuf.Collections
             {
                 var sizeCalculator = codec.ValueSizeCalculator;
                 int size = count * CodedOutputStream.ComputeRawVarint32Size(tag);
+                if (codec.EndTag != 0)
+                {
+                    size += count * CodedOutputStream.ComputeRawVarint32Size(codec.EndTag);
+                }
                 for (int i = 0; i < count; i++)
                 {
                     size += sizeCalculator(array[i]);

csharp/src/Google.Protobuf/ExtensionSet.cs

@@ -89,7 +89,7 @@ namespace Google.Protobuf
         /// <summary>
         /// Gets the value of the specified repeated extension, registering it if it doesn't exist
         /// </summary>
-        public static RepeatedField<TValue> GetOrRegister<TTarget, TValue>(ref ExtensionSet<TTarget> set, RepeatedExtension<TTarget, TValue> extension) where TTarget : IExtendableMessage<TTarget>
+        public static RepeatedField<TValue> GetOrInitialize<TTarget, TValue>(ref ExtensionSet<TTarget> set, RepeatedExtension<TTarget, TValue> extension) where TTarget : IExtendableMessage<TTarget>
         {
             IExtensionValue value;
             if (set == null)
@@ -115,6 +115,8 @@ namespace Google.Protobuf
         /// </summary>
         public static void Set<TTarget, TValue>(ref ExtensionSet<TTarget> set, Extension<TTarget, TValue> extension, TValue value) where TTarget : IExtendableMessage<TTarget>
         {
+            ProtoPreconditions.CheckNotNullUnconstrained(value, nameof(value));
+
             IExtensionValue extensionValue;
             if (set == null)
             {
@@ -330,5 +332,10 @@ namespace Google.Protobuf
                 value.WriteTo(stream);
             }
         }
+
+        internal bool IsInitialized()
+        {
+            return ValuesByNumber.Values.All(v => v.IsInitialized());
+        }
     }
 }

csharp/src/Google.Protobuf/ExtensionValue.cs

@@ -32,6 +32,7 @@
 
 using Google.Protobuf.Collections;
 using System;
+using System.Linq;
 
 namespace Google.Protobuf
 {
@@ -41,11 +42,11 @@ namespace Google.Protobuf
         void MergeFrom(IExtensionValue value);
         void WriteTo(CodedOutputStream output);
         int CalculateSize();
+        bool IsInitialized();
     }
 
     internal sealed class ExtensionValue<T> : IExtensionValue
     {
-        private bool hasValue;
         private T field;
         private FieldCodec<T> codec;
 
@@ -57,10 +58,6 @@ namespace Google.Protobuf
 
         public int CalculateSize()
         {
-            if (!hasValue)
-            {
-                return 0;
-            }
             return codec.CalculateSizeWithTag(field);
         }
 
@@ -68,7 +65,6 @@ namespace Google.Protobuf
         {
             return new ExtensionValue<T>(codec)
             {
-                hasValue = hasValue,
                 field = field is IDeepCloneable<T> ? (field as IDeepCloneable<T>).Clone() : field
             };
         }
@@ -80,7 +76,6 @@ namespace Google.Protobuf
 
             return other is ExtensionValue<T>
                 && codec.Equals((other as ExtensionValue<T>).codec)
-                && hasValue.Equals((other as ExtensionValue<T>).hasValue)
                 && Equals(field, (other as ExtensionValue<T>).field);
             // we check for equality in the codec since we could have equal field values however the values could be written in different ways
         }
@@ -90,7 +85,6 @@ namespace Google.Protobuf
             unchecked
             {
                 int hash = 17;
-                hash = hash * 31 + hasValue.GetHashCode();
                 hash = hash * 31 + field.GetHashCode();
                 hash = hash * 31 + codec.GetHashCode();
                 return hash;
@@ -99,7 +93,6 @@ namespace Google.Protobuf
 
         public void MergeFrom(CodedInputStream input)
         {
-            hasValue = true;
             codec.ValueMerger(input, ref field);
         }
 
@@ -107,24 +100,18 @@ namespace Google.Protobuf
         {
             if (value is ExtensionValue<T>)
             {
-                var extensionValue = value as ExtensionValue<T>;
-                if (extensionValue.hasValue)
-                {
-                    hasValue |= codec.FieldMerger(ref field, extensionValue.field);
-                }
+                var extensionValue = value as ExtensionValue<T>;
+                codec.FieldMerger(ref field, extensionValue.field);
             }
         }
 
         public void WriteTo(CodedOutputStream output)
         {
-            if (hasValue)
+            output.WriteTag(codec.Tag);
+            codec.ValueWriter(output, field);
+            if (codec.EndTag != 0)
             {
-                output.WriteTag(codec.Tag);
-                codec.ValueWriter(output, field);
-                if (codec.EndTag != 0)
-                {
-                    output.WriteTag(codec.EndTag);
-                }
+                output.WriteTag(codec.EndTag);
             }
         }
 
@@ -132,11 +119,20 @@ namespace Google.Protobuf
 
         public void SetValue(T value)
         {
-            hasValue = true;
             field = value;
         }
 
-        public bool HasValue => hasValue;
+        public bool IsInitialized()
+        {
+            if (field is IMessage)
+            {
+                return (field as IMessage).IsInitialized();
+            }
+            else
+            {
+                return true;
+            }
+        }
     }
 
     internal sealed class RepeatedExtensionValue<T> : IExtensionValue
@@ -203,5 +199,26 @@ namespace Google.Protobuf
         }
 
         public RepeatedField<T> GetValue() => field;
+
+        public bool IsInitialized()
+        {
+            for (int i = 0; i < field.Count; i++)
+            {
+                var element = field[i];
+                if (element is IMessage)
+                {
+                    if (!(element as IMessage).IsInitialized())
+                    {
+                        return false;
+                    }
+                }
+                else
+                {
+                    break;
+                }
+            }
+
+            return true;
+        }
     }
 }

csharp/src/Google.Protobuf/FieldCodec.cs

@@ -218,7 +218,7 @@ namespace Google.Protobuf
         /// <returns>A codec for the given tag.</returns>
         public static FieldCodec<string> ForString(uint tag, string defaultValue)
         {
-            return new FieldCodec<string>(input => input.ReadString(), (output, value) => output.WriteString(value), CodedOutputStream.ComputeStringSize, tag);
+            return new FieldCodec<string>(input => input.ReadString(), (output, value) => output.WriteString(value), CodedOutputStream.ComputeStringSize, tag, defaultValue);
         }
 
         /// <summary>
@@ -229,7 +229,7 @@ namespace Google.Protobuf
         /// <returns>A codec for the given tag.</returns>
         public static FieldCodec<ByteString> ForBytes(uint tag, ByteString defaultValue)
         {
-            return new FieldCodec<ByteString>(input => input.ReadBytes(), (output, value) => output.WriteBytes(value), CodedOutputStream.ComputeBytesSize, tag);
+            return new FieldCodec<ByteString>(input => input.ReadBytes(), (output, value) => output.WriteBytes(value), CodedOutputStream.ComputeBytesSize, tag, defaultValue);
         }
 
         /// <summary>
@@ -240,7 +240,7 @@ namespace Google.Protobuf
         /// <returns>A codec for the given tag.</returns>
         public static FieldCodec<bool> ForBool(uint tag, bool defaultValue)
         {
-            return new FieldCodec<bool>(input => input.ReadBool(), (output, value) => output.WriteBool(value), CodedOutputStream.BoolSize, tag);
+            return new FieldCodec<bool>(input => input.ReadBool(), (output, value) => output.WriteBool(value), CodedOutputStream.BoolSize, tag, defaultValue);
         }
 
         /// <summary>
@@ -251,7 +251,7 @@ namespace Google.Protobuf
         /// <returns>A codec for the given tag.</returns>
         public static FieldCodec<int> ForInt32(uint tag, int defaultValue)
         {
-            return new FieldCodec<int>(input => input.ReadInt32(), (output, value) => output.WriteInt32(value), CodedOutputStream.ComputeInt32Size, tag);
+            return new FieldCodec<int>(input => input.ReadInt32(), (output, value) => output.WriteInt32(value), CodedOutputStream.ComputeInt32Size, tag, defaultValue);
         }
 
         /// <summary>
@@ -262,7 +262,7 @@ namespace Google.Protobuf
         /// <returns>A codec for the given tag.</returns>
         public static FieldCodec<int> ForSInt32(uint tag, int defaultValue)
         {
-            return new FieldCodec<int>(input => input.ReadSInt32(), (output, value) => output.WriteSInt32(value), CodedOutputStream.ComputeSInt32Size, tag);
+            return new FieldCodec<int>(input => input.ReadSInt32(), (output, value) => output.WriteSInt32(value), CodedOutputStream.ComputeSInt32Size, tag, defaultValue);
         }
 
         /// <summary>
@@ -273,7 +273,7 @@ namespace Google.Protobuf
         /// <returns>A codec for the given tag.</returns>
         public static FieldCodec<uint> ForFixed32(uint tag, uint defaultValue)
         {
-            return new FieldCodec<uint>(input => input.ReadFixed32(), (output, value) => output.WriteFixed32(value), 4, tag);
+            return new FieldCodec<uint>(input => input.ReadFixed32(), (output, value) => output.WriteFixed32(value), 4, tag, defaultValue);
         }
 
         /// <summary>
@@ -284,7 +284,7 @@ namespace Google.Protobuf
         /// <returns>A codec for the given tag.</returns>
         public static FieldCodec<int> ForSFixed32(uint tag, int defaultValue)
         {
-            return new FieldCodec<int>(input => input.ReadSFixed32(), (output, value) => output.WriteSFixed32(value), 4, tag);
+            return new FieldCodec<int>(input => input.ReadSFixed32(), (output, value) => output.WriteSFixed32(value), 4, tag, defaultValue);
         }
 
         /// <summary>
@@ -295,7 +295,7 @@ namespace Google.Protobuf
         /// <returns>A codec for the given tag.</returns>
         public static FieldCodec<uint> ForUInt32(uint tag, uint defaultValue)
         {
-            return new FieldCodec<uint>(input => input.ReadUInt32(), (output, value) => output.WriteUInt32(value), CodedOutputStream.ComputeUInt32Size, tag);
+            return new FieldCodec<uint>(input => input.ReadUInt32(), (output, value) => output.WriteUInt32(value), CodedOutputStream.ComputeUInt32Size, tag, defaultValue);
         }
 
         /// <summary>
@@ -306,7 +306,7 @@ namespace Google.Protobuf
         /// <returns>A codec for the given tag.</returns>
         public static FieldCodec<long> ForInt64(uint tag, long defaultValue)
         {
-            return new FieldCodec<long>(input => input.ReadInt64(), (output, value) => output.WriteInt64(value), CodedOutputStream.ComputeInt64Size, tag);
+            return new FieldCodec<long>(input => input.ReadInt64(), (output, value) => output.WriteInt64(value), CodedOutputStream.ComputeInt64Size, tag, defaultValue);
         }
 
         /// <summary>
@@ -317,7 +317,7 @@ namespace Google.Protobuf
         /// <returns>A codec for the given tag.</returns>
         public static FieldCodec<long> ForSInt64(uint tag, long defaultValue)
         {
-            return new FieldCodec<long>(input => input.ReadSInt64(), (output, value) => output.WriteSInt64(value), CodedOutputStream.ComputeSInt64Size, tag);
+            return new FieldCodec<long>(input => input.ReadSInt64(), (output, value) => output.WriteSInt64(value), CodedOutputStream.ComputeSInt64Size, tag, defaultValue);
         }
 
         /// <summary>
@@ -328,7 +328,7 @@ namespace Google.Protobuf
         /// <returns>A codec for the given tag.</returns>
         public static FieldCodec<ulong> ForFixed64(uint tag, ulong defaultValue)
         {
-            return new FieldCodec<ulong>(input => input.ReadFixed64(), (output, value) => output.WriteFixed64(value), 8, tag);
+            return new FieldCodec<ulong>(input => input.ReadFixed64(), (output, value) => output.WriteFixed64(value), 8, tag, defaultValue);
         }
 
         /// <summary>
@@ -339,7 +339,7 @@ namespace Google.Protobuf
         /// <returns>A codec for the given tag.</returns>
         public static FieldCodec<long> ForSFixed64(uint tag, long defaultValue)
         {
-            return new FieldCodec<long>(input => input.ReadSFixed64(), (output, value) => output.WriteSFixed64(value), 8, tag);
+            return new FieldCodec<long>(input => input.ReadSFixed64(), (output, value) => output.WriteSFixed64(value), 8, tag, defaultValue);
         }
 
         /// <summary>
@@ -350,7 +350,7 @@ namespace Google.Protobuf
         /// <returns>A codec for the given tag.</returns>
         public static FieldCodec<ulong> ForUInt64(uint tag, ulong defaultValue)
         {
-            return new FieldCodec<ulong>(input => input.ReadUInt64(), (output, value) => output.WriteUInt64(value), CodedOutputStream.ComputeUInt64Size, tag);
+            return new FieldCodec<ulong>(input => input.ReadUInt64(), (output, value) => output.WriteUInt64(value), CodedOutputStream.ComputeUInt64Size, tag, defaultValue);
         }
 
         /// <summary>
@@ -361,7 +361,7 @@ namespace Google.Protobuf
         /// <returns>A codec for the given tag.</returns>
         public static FieldCodec<float> ForFloat(uint tag, float defaultValue)
         {
-            return new FieldCodec<float>(input => input.ReadFloat(), (output, value) => output.WriteFloat(value), CodedOutputStream.FloatSize, tag);
+            return new FieldCodec<float>(input => input.ReadFloat(), (output, value) => output.WriteFloat(value), CodedOutputStream.FloatSize, tag, defaultValue);
         }
 
         /// <summary>
@@ -372,7 +372,7 @@ namespace Google.Protobuf
         /// <returns>A codec for the given tag.</returns>
         public static FieldCodec<double> ForDouble(uint tag, double defaultValue)
         {
-            return new FieldCodec<double>(input => input.ReadDouble(), (output, value) => output.WriteDouble(value), CodedOutputStream.DoubleSize, tag);
+            return new FieldCodec<double>(input => input.ReadDouble(), (output, value) => output.WriteDouble(value), CodedOutputStream.DoubleSize, tag, defaultValue);
         }
 
         // Enums are tricky. We can probably use expression trees to build these delegates automatically,
@@ -391,7 +391,7 @@ namespace Google.Protobuf
             return new FieldCodec<T>(input => fromInt32(
                 input.ReadEnum()),
                 (output, value) => output.WriteEnum(toInt32(value)),
-                value => CodedOutputStream.ComputeEnumSize(toInt32(value)), tag);
+                value => CodedOutputStream.ComputeEnumSize(toInt32(value)), tag, defaultValue);
         }
 
         /// <summary>
@@ -402,8 +402,15 @@ namespace Google.Protobuf
         /// <returns>A codec for the given tag.</returns>
         public static FieldCodec<T> ForMessage<T>(uint tag, MessageParser<T> parser) where T : class, IMessage<T>
         {
-            return new FieldCodec<T>(input => { T message = parser.CreateTemplate(); input.ReadMessage(message); return message; },
-                (output, value) => output.WriteMessage(value), (CodedInputStream i, ref T v) => 
+            return new FieldCodec<T>(
+                input => 
+                { 
+                    T message = parser.CreateTemplate(); 
+                    input.ReadMessage(message); 
+                    return message; 
+                },
+                (output, value) => output.WriteMessage(value),
+                (CodedInputStream i, ref T v) => 
                 {
                     if (v == null)
                     {
@@ -427,7 +434,8 @@ namespace Google.Protobuf
                         v.MergeFrom(v2);
                     }
                     return true;
-                }, message => CodedOutputStream.ComputeMessageSize(message), tag);
+                }, 
+                message => CodedOutputStream.ComputeMessageSize(message), tag);
         }
 
         /// <summary>
@@ -439,8 +447,16 @@ namespace Google.Protobuf
         /// <returns>A codec for given tag</returns>
         public static FieldCodec<T> ForGroup<T>(uint startTag, uint endTag, MessageParser<T> parser) where T : class, IMessage<T>
         {
-            return new FieldCodec<T>(input => { T message = parser.CreateTemplate(); input.ReadGroup(message); return message; },
-                (output, value) => output.WriteGroup(value), (CodedInputStream i, ref T v) => {
+            return new FieldCodec<T>(
+                input => 
+                { 
+                    T message = parser.CreateTemplate();
+                    input.ReadGroup(message);
+                    return message;
+                },
+                (output, value) => output.WriteGroup(value), 
+                (CodedInputStream i, ref T v) => 
+                {
                     if (v == null)
                     {
                         v = parser.CreateTemplate();
@@ -463,7 +479,8 @@ namespace Google.Protobuf
                         v.MergeFrom(v2);
                     }
                     return true;
-                }, message => CodedOutputStream.ComputeGroupSize(message), startTag, endTag);
+                }, 
+                message => CodedOutputStream.ComputeGroupSize(message), startTag, endTag);
         }
 
         /// <summary>
@@ -689,7 +706,8 @@ namespace Google.Protobuf
                 Func<CodedInputStream, T> reader,
                 Action<CodedOutputStream, T> writer,
                 int fixedSize,
-                uint tag) : this(reader, writer, _ => fixedSize, tag)
+                uint tag,
+                T defaultValue) : this(reader, writer, _ => fixedSize, tag, defaultValue)
         {
             FixedSize = fixedSize;
         }
@@ -699,7 +717,7 @@ namespace Google.Protobuf
             Action<CodedOutputStream, T> writer,
             Func<T, int> sizeCalculator,
             uint tag,
-            uint endTag = 0) : this(reader, writer, (CodedInputStream i, ref T v) => v = reader(i), (ref T v, T v2) => { v = v2; return true; }, sizeCalculator, tag, endTag, DefaultDefault)
+            T defaultValue) : this(reader, writer, (CodedInputStream i, ref T v) => v = reader(i), (ref T v, T v2) => { v = v2; return true; }, sizeCalculator, tag, 0, defaultValue)
         {
         }
 
@@ -731,6 +749,7 @@ namespace Google.Protobuf
             ValueSizeCalculator = sizeCalculator;
             FixedSize = 0;
             Tag = tag;
+            EndTag = endTag;
             DefaultValue = defaultValue;
             tagSize = CodedOutputStream.ComputeRawVarint32Size(tag);
             if (endTag != 0)

csharp/src/Google.Protobuf/IExtendableMessage.cs

@@ -35,7 +35,8 @@ using Google.Protobuf.Collections;
 namespace Google.Protobuf
 {
     /// <summary>
-    /// Generic interface for a Protocol Buffers message containing one or more extensions, where the type parameter is expected to be the same type as the implementation class
+    /// Generic interface for a Protocol Buffers message containing one or more extensions, where the type parameter is expected to be the same type as the implementation class.
+    /// This interface is experiemental and is subject to change.
     /// </summary>
     public interface IExtendableMessage<T> : IMessage<T> where T : IExtendableMessage<T>
     {
@@ -46,14 +47,14 @@ namespace Google.Protobuf
 
         /// <summary>
         /// Gets the value of the specified repeated extension or null if the extension isn't registered in this set.
-        /// For a version of this method that never returns null, use <see cref="IExtendableMessage{T}.GetOrRegisterExtension{TValue}(RepeatedExtension{T, TValue})"/>
+        /// For a version of this method that never returns null, use <see cref="IExtendableMessage{T}.GetOrInitializeExtension{TValue}(RepeatedExtension{T, TValue})"/>
         /// </summary>
         RepeatedField<TValue> GetExtension<TValue>(RepeatedExtension<T, TValue> extension);
 
-        /// <summary>
-        /// Gets the value of the specified repeated extension, registering it if it isn't
+        /// <summary>
+        /// Gets the value of the specified repeated extension, registering it if it hasn't already been registered.
         /// </summary>
-        RepeatedField<TValue> GetOrRegisterExtension<TValue>(RepeatedExtension<T, TValue> extension);
+        RepeatedField<TValue> GetOrInitializeExtension<TValue>(RepeatedExtension<T, TValue> extension);
 
         /// <summary>
         /// Sets the value of the specified extension
@@ -65,13 +66,13 @@ namespace Google.Protobuf
         /// </summary>
         bool HasExtension<TValue>(Extension<T, TValue> extension);
 
-        /// <summary>
-        /// Clears the value of the specified extension
+        /// <summary>
+        /// Clears the value of the specified extension
         /// </summary>
         void ClearExtension<TValue>(Extension<T, TValue> extension);
 
-        /// <summary>
-        /// Clears the value of the specified repeated extension
+        /// <summary>
+        /// Clears the value of the specified repeated extension
         /// </summary>
         void ClearExtension<TValue>(RepeatedExtension<T, TValue> extension);
     }

csharp/src/Google.Protobuf/MessageExtensions.cs

@@ -148,11 +148,16 @@ namespace Google.Protobuf
         /// </summary>
         public static bool IsInitialized(this IMessage message)
         {
-            if (message.Descriptor.File.Proto.Syntax != "proto2")
+            if (message.Descriptor.File.Syntax == Syntax.Proto3)
             {
                 return true;
             }
 
+            if (!message.Descriptor.IsExtensionsInitialized(message))
+            {
+                return false;
+            }
+
             return message.Descriptor
                 .Fields
                 .InDeclarationOrder()
@@ -160,8 +165,16 @@ namespace Google.Protobuf
                 {
                     if (f.IsMap)
                     {
-                        var map = (IDictionary)f.Accessor.GetValue(message);
-                        return map.Values.OfType<IMessage>().All(IsInitialized);
+                        var valueField = f.MessageType.Fields[2];
+                        if (valueField.FieldType == FieldType.Message)
+                        {
+                            var map = (IDictionary)f.Accessor.GetValue(message);
+                            return map.Values.Cast<IMessage>().All(IsInitialized);
+                        }
+                        else
+                        {
+                            return true;
+                        }
                     }
                     else if (f.IsRepeated && f.FieldType == FieldType.Message || f.FieldType == FieldType.Group)
                     {

csharp/src/Google.Protobuf/Reflection/CustomOptions.cs

@@ -254,11 +254,8 @@ namespace Google.Protobuf.Reflection
                 if (extensionValue is ExtensionValue<T>)
                 {
                     ExtensionValue<T> single = extensionValue as ExtensionValue<T>;
-                    if (single.HasValue)
-                    {
-                        value = single.GetValue();
-                        return true;
-                    }
+                    value = single.GetValue();
+                    return true;
                 }
                 else if (extensionValue is RepeatedExtensionValue<T>)
                 {
@@ -279,11 +276,8 @@ namespace Google.Protobuf.Reflection
                         var typeArgs = typeInfo.GenericTypeArguments;
                         if (typeArgs.Length == 1 && typeArgs[0].GetTypeInfo().IsEnum)
                         {
-                            if ((bool)typeInfo.GetDeclaredProperty(nameof(ExtensionValue<T>.HasValue)).GetValue(extensionValue))
-                            {
-                                value = (T)typeInfo.GetDeclaredMethod(nameof(ExtensionValue<T>.GetValue)).Invoke(extensionValue, EmptyParameters);
-                                return true;
-                            }
+                            value = (T)typeInfo.GetDeclaredMethod(nameof(ExtensionValue<T>.GetValue)).Invoke(extensionValue, EmptyParameters);
+                            return true;
                         }
                     }
                     else if (type.GetGenericTypeDefinition() == typeof(RepeatedExtensionValue<>))

csharp/src/Google.Protobuf/Reflection/Descriptor.cs

@@ -12,7 +12,7 @@ using scg = global::System.Collections.Generic;
 namespace Google.Protobuf.Reflection {
 
   /// <summary>Holder for reflection information generated from google/protobuf/descriptor.proto</summary>
-  internal static partial class DescriptorReflection {
+  public static partial class DescriptorReflection {
 
     #region Descriptor
     /// <summary>File descriptor for google/protobuf/descriptor.proto</summary>
@@ -193,7 +193,7 @@ namespace Google.Protobuf.Reflection {
   /// The protocol compiler can output a FileDescriptorSet containing the .proto
   /// files it parses.
   /// </summary>
-  internal sealed partial class FileDescriptorSet : pb::IMessage<FileDescriptorSet> {
+  public sealed partial class FileDescriptorSet : pb::IMessage<FileDescriptorSet> {
     private static readonly pb::MessageParser<FileDescriptorSet> _parser = new pb::MessageParser<FileDescriptorSet>(() => new FileDescriptorSet());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -317,7 +317,7 @@ namespace Google.Protobuf.Reflection {
   /// <summary>
   /// Describes a complete .proto file.
   /// </summary>
-  internal sealed partial class FileDescriptorProto : pb::IMessage<FileDescriptorProto> {
+  public sealed partial class FileDescriptorProto : pb::IMessage<FileDescriptorProto> {
     private static readonly pb::MessageParser<FileDescriptorProto> _parser = new pb::MessageParser<FileDescriptorProto>(() => new FileDescriptorProto());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -800,7 +800,7 @@ namespace Google.Protobuf.Reflection {
   /// <summary>
   /// Describes a message type.
   /// </summary>
-  internal sealed partial class DescriptorProto : pb::IMessage<DescriptorProto> {
+  public sealed partial class DescriptorProto : pb::IMessage<DescriptorProto> {
     private static readonly pb::MessageParser<DescriptorProto> _parser = new pb::MessageParser<DescriptorProto>(() => new DescriptorProto());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -1151,7 +1151,7 @@ namespace Google.Protobuf.Reflection {
     /// <summary>Container for nested types declared in the DescriptorProto message type.</summary>
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public static partial class Types {
-      internal sealed partial class ExtensionRange : pb::IMessage<ExtensionRange> {
+      public sealed partial class ExtensionRange : pb::IMessage<ExtensionRange> {
         private static readonly pb::MessageParser<ExtensionRange> _parser = new pb::MessageParser<ExtensionRange>(() => new ExtensionRange());
         private pb::UnknownFieldSet _unknownFields;
         private int _hasBits0;
@@ -1391,7 +1391,7 @@ namespace Google.Protobuf.Reflection {
       /// fields or extension ranges in the same message. Reserved ranges may
       /// not overlap.
       /// </summary>
-      internal sealed partial class ReservedRange : pb::IMessage<ReservedRange> {
+      public sealed partial class ReservedRange : pb::IMessage<ReservedRange> {
         private static readonly pb::MessageParser<ReservedRange> _parser = new pb::MessageParser<ReservedRange>(() => new ReservedRange());
         private pb::UnknownFieldSet _unknownFields;
         private int _hasBits0;
@@ -1587,10 +1587,11 @@ namespace Google.Protobuf.Reflection {
 
   }
 
-  internal sealed partial class ExtensionRangeOptions : pb::IExtendableMessage<ExtensionRangeOptions> {
+  public sealed partial class ExtensionRangeOptions : pb::IExtendableMessage<ExtensionRangeOptions> {
     private static readonly pb::MessageParser<ExtensionRangeOptions> _parser = new pb::MessageParser<ExtensionRangeOptions>(() => new ExtensionRangeOptions());
     private pb::UnknownFieldSet _unknownFields;
     internal pb::ExtensionSet<ExtensionRangeOptions> _extensions;
+    private pb::ExtensionSet<ExtensionRangeOptions> _Extensions => _extensions;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public static pb::MessageParser<ExtensionRangeOptions> Parser { get { return _parser; } }
 
@@ -1732,8 +1733,8 @@ namespace Google.Protobuf.Reflection {
     public pbc::RepeatedField<TValue> GetExtension<TValue>(pb::RepeatedExtension<ExtensionRangeOptions, TValue> extension) {
       return pb::ExtensionSet.Get(ref _extensions, extension);
     }
-    public pbc::RepeatedField<TValue> GetOrRegisterExtension<TValue>(pb::RepeatedExtension<ExtensionRangeOptions, TValue> extension) {
-      return pb::ExtensionSet.GetOrRegister(ref _extensions, extension);
+    public pbc::RepeatedField<TValue> GetOrInitializeExtension<TValue>(pb::RepeatedExtension<ExtensionRangeOptions, TValue> extension) {
+      return pb::ExtensionSet.GetOrInitialize(ref _extensions, extension);
     }
     public void SetExtension<TValue>(pb::Extension<ExtensionRangeOptions, TValue> extension, TValue value) {
       pb::ExtensionSet.Set(ref _extensions, extension, value);
@@ -1753,7 +1754,7 @@ namespace Google.Protobuf.Reflection {
   /// <summary>
   /// Describes a field within a message.
   /// </summary>
-  internal sealed partial class FieldDescriptorProto : pb::IMessage<FieldDescriptorProto> {
+  public sealed partial class FieldDescriptorProto : pb::IMessage<FieldDescriptorProto> {
     private static readonly pb::MessageParser<FieldDescriptorProto> _parser = new pb::MessageParser<FieldDescriptorProto>(() => new FieldDescriptorProto());
     private pb::UnknownFieldSet _unknownFields;
     private int _hasBits0;
@@ -2298,7 +2299,7 @@ namespace Google.Protobuf.Reflection {
     /// <summary>Container for nested types declared in the FieldDescriptorProto message type.</summary>
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public static partial class Types {
-      internal enum Type {
+      public enum Type {
         /// <summary>
         /// 0 is reserved for errors.
         /// Order is weird for historical reasons.
@@ -2349,7 +2350,7 @@ namespace Google.Protobuf.Reflection {
         [pbr::OriginalName("TYPE_SINT64")] Sint64 = 18,
       }
 
-      internal enum Label {
+      public enum Label {
         /// <summary>
         /// 0 is reserved for errors
         /// </summary>
@@ -2366,7 +2367,7 @@ namespace Google.Protobuf.Reflection {
   /// <summary>
   /// Describes a oneof.
   /// </summary>
-  internal sealed partial class OneofDescriptorProto : pb::IMessage<OneofDescriptorProto> {
+  public sealed partial class OneofDescriptorProto : pb::IMessage<OneofDescriptorProto> {
     private static readonly pb::MessageParser<OneofDescriptorProto> _parser = new pb::MessageParser<OneofDescriptorProto>(() => new OneofDescriptorProto());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -2554,7 +2555,7 @@ namespace Google.Protobuf.Reflection {
   /// <summary>
   /// Describes an enum type.
   /// </summary>
-  internal sealed partial class EnumDescriptorProto : pb::IMessage<EnumDescriptorProto> {
+  public sealed partial class EnumDescriptorProto : pb::IMessage<EnumDescriptorProto> {
     private static readonly pb::MessageParser<EnumDescriptorProto> _parser = new pb::MessageParser<EnumDescriptorProto>(() => new EnumDescriptorProto());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -2818,7 +2819,7 @@ namespace Google.Protobuf.Reflection {
       /// is inclusive such that it can appropriately represent the entire int32
       /// domain.
       /// </summary>
-      internal sealed partial class EnumReservedRange : pb::IMessage<EnumReservedRange> {
+      public sealed partial class EnumReservedRange : pb::IMessage<EnumReservedRange> {
         private static readonly pb::MessageParser<EnumReservedRange> _parser = new pb::MessageParser<EnumReservedRange>(() => new EnumReservedRange());
         private pb::UnknownFieldSet _unknownFields;
         private int _hasBits0;
@@ -3017,7 +3018,7 @@ namespace Google.Protobuf.Reflection {
   /// <summary>
   /// Describes a value within an enum.
   /// </summary>
-  internal sealed partial class EnumValueDescriptorProto : pb::IMessage<EnumValueDescriptorProto> {
+  public sealed partial class EnumValueDescriptorProto : pb::IMessage<EnumValueDescriptorProto> {
     private static readonly pb::MessageParser<EnumValueDescriptorProto> _parser = new pb::MessageParser<EnumValueDescriptorProto>(() => new EnumValueDescriptorProto());
     private pb::UnknownFieldSet _unknownFields;
     private int _hasBits0;
@@ -3248,7 +3249,7 @@ namespace Google.Protobuf.Reflection {
   /// <summary>
   /// Describes a service.
   /// </summary>
-  internal sealed partial class ServiceDescriptorProto : pb::IMessage<ServiceDescriptorProto> {
+  public sealed partial class ServiceDescriptorProto : pb::IMessage<ServiceDescriptorProto> {
     private static readonly pb::MessageParser<ServiceDescriptorProto> _parser = new pb::MessageParser<ServiceDescriptorProto>(() => new ServiceDescriptorProto());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -3456,7 +3457,7 @@ namespace Google.Protobuf.Reflection {
   /// <summary>
   /// Describes a method of a service.
   /// </summary>
-  internal sealed partial class MethodDescriptorProto : pb::IMessage<MethodDescriptorProto> {
+  public sealed partial class MethodDescriptorProto : pb::IMessage<MethodDescriptorProto> {
     private static readonly pb::MessageParser<MethodDescriptorProto> _parser = new pb::MessageParser<MethodDescriptorProto>(() => new MethodDescriptorProto());
     private pb::UnknownFieldSet _unknownFields;
     private int _hasBits0;
@@ -3815,10 +3816,11 @@ namespace Google.Protobuf.Reflection {
 
   }
 
-  internal sealed partial class FileOptions : pb::IExtendableMessage<FileOptions> {
+  public sealed partial class FileOptions : pb::IExtendableMessage<FileOptions> {
     private static readonly pb::MessageParser<FileOptions> _parser = new pb::MessageParser<FileOptions>(() => new FileOptions());
     private pb::UnknownFieldSet _unknownFields;
     internal pb::ExtensionSet<FileOptions> _extensions;
+    private pb::ExtensionSet<FileOptions> _Extensions => _extensions;
     private int _hasBits0;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public static pb::MessageParser<FileOptions> Parser { get { return _parser; } }
@@ -4869,8 +4871,8 @@ namespace Google.Protobuf.Reflection {
     public pbc::RepeatedField<TValue> GetExtension<TValue>(pb::RepeatedExtension<FileOptions, TValue> extension) {
       return pb::ExtensionSet.Get(ref _extensions, extension);
     }
-    public pbc::RepeatedField<TValue> GetOrRegisterExtension<TValue>(pb::RepeatedExtension<FileOptions, TValue> extension) {
-      return pb::ExtensionSet.GetOrRegister(ref _extensions, extension);
+    public pbc::RepeatedField<TValue> GetOrInitializeExtension<TValue>(pb::RepeatedExtension<FileOptions, TValue> extension) {
+      return pb::ExtensionSet.GetOrInitialize(ref _extensions, extension);
     }
     public void SetExtension<TValue>(pb::Extension<FileOptions, TValue> extension, TValue value) {
       pb::ExtensionSet.Set(ref _extensions, extension, value);
@@ -4892,7 +4894,7 @@ namespace Google.Protobuf.Reflection {
       /// <summary>
       /// Generated classes can be optimized for speed or code size.
       /// </summary>
-      internal enum OptimizeMode {
+      public enum OptimizeMode {
         /// <summary>
         /// Generate complete code for parsing, serialization,
         /// </summary>
@@ -4912,10 +4914,11 @@ namespace Google.Protobuf.Reflection {
 
   }
 
-  internal sealed partial class MessageOptions : pb::IExtendableMessage<MessageOptions> {
+  public sealed partial class MessageOptions : pb::IExtendableMessage<MessageOptions> {
     private static readonly pb::MessageParser<MessageOptions> _parser = new pb::MessageParser<MessageOptions>(() => new MessageOptions());
     private pb::UnknownFieldSet _unknownFields;
     internal pb::ExtensionSet<MessageOptions> _extensions;
+    private pb::ExtensionSet<MessageOptions> _Extensions => _extensions;
     private int _hasBits0;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public static pb::MessageParser<MessageOptions> Parser { get { return _parser; } }
@@ -5277,8 +5280,8 @@ namespace Google.Protobuf.Reflection {
     public pbc::RepeatedField<TValue> GetExtension<TValue>(pb::RepeatedExtension<MessageOptions, TValue> extension) {
       return pb::ExtensionSet.Get(ref _extensions, extension);
     }
-    public pbc::RepeatedField<TValue> GetOrRegisterExtension<TValue>(pb::RepeatedExtension<MessageOptions, TValue> extension) {
-      return pb::ExtensionSet.GetOrRegister(ref _extensions, extension);
+    public pbc::RepeatedField<TValue> GetOrInitializeExtension<TValue>(pb::RepeatedExtension<MessageOptions, TValue> extension) {
+      return pb::ExtensionSet.GetOrInitialize(ref _extensions, extension);
     }
     public void SetExtension<TValue>(pb::Extension<MessageOptions, TValue> extension, TValue value) {
       pb::ExtensionSet.Set(ref _extensions, extension, value);
@@ -5295,10 +5298,11 @@ namespace Google.Protobuf.Reflection {
 
   }
 
-  internal sealed partial class FieldOptions : pb::IExtendableMessage<FieldOptions> {
+  public sealed partial class FieldOptions : pb::IExtendableMessage<FieldOptions> {
     private static readonly pb::MessageParser<FieldOptions> _parser = new pb::MessageParser<FieldOptions>(() => new FieldOptions());
     private pb::UnknownFieldSet _unknownFields;
     internal pb::ExtensionSet<FieldOptions> _extensions;
+    private pb::ExtensionSet<FieldOptions> _Extensions => _extensions;
     private int _hasBits0;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public static pb::MessageParser<FieldOptions> Parser { get { return _parser; } }
@@ -5752,8 +5756,8 @@ namespace Google.Protobuf.Reflection {
     public pbc::RepeatedField<TValue> GetExtension<TValue>(pb::RepeatedExtension<FieldOptions, TValue> extension) {
       return pb::ExtensionSet.Get(ref _extensions, extension);
     }
-    public pbc::RepeatedField<TValue> GetOrRegisterExtension<TValue>(pb::RepeatedExtension<FieldOptions, TValue> extension) {
-      return pb::ExtensionSet.GetOrRegister(ref _extensions, extension);
+    public pbc::RepeatedField<TValue> GetOrInitializeExtension<TValue>(pb::RepeatedExtension<FieldOptions, TValue> extension) {
+      return pb::ExtensionSet.GetOrInitialize(ref _extensions, extension);
     }
     public void SetExtension<TValue>(pb::Extension<FieldOptions, TValue> extension, TValue value) {
       pb::ExtensionSet.Set(ref _extensions, extension, value);
@@ -5772,7 +5776,7 @@ namespace Google.Protobuf.Reflection {
     /// <summary>Container for nested types declared in the FieldOptions message type.</summary>
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public static partial class Types {
-      internal enum CType {
+      public enum CType {
         /// <summary>
         /// Default mode.
         /// </summary>
@@ -5781,7 +5785,7 @@ namespace Google.Protobuf.Reflection {
         [pbr::OriginalName("STRING_PIECE")] StringPiece = 2,
       }
 
-      internal enum JSType {
+      public enum JSType {
         /// <summary>
         /// Use the default type.
         /// </summary>
@@ -5801,10 +5805,11 @@ namespace Google.Protobuf.Reflection {
 
   }
 
-  internal sealed partial class OneofOptions : pb::IExtendableMessage<OneofOptions> {
+  public sealed partial class OneofOptions : pb::IExtendableMessage<OneofOptions> {
     private static readonly pb::MessageParser<OneofOptions> _parser = new pb::MessageParser<OneofOptions>(() => new OneofOptions());
     private pb::UnknownFieldSet _unknownFields;
     internal pb::ExtensionSet<OneofOptions> _extensions;
+    private pb::ExtensionSet<OneofOptions> _Extensions => _extensions;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public static pb::MessageParser<OneofOptions> Parser { get { return _parser; } }
 
@@ -5946,8 +5951,8 @@ namespace Google.Protobuf.Reflection {
     public pbc::RepeatedField<TValue> GetExtension<TValue>(pb::RepeatedExtension<OneofOptions, TValue> extension) {
       return pb::ExtensionSet.Get(ref _extensions, extension);
     }
-    public pbc::RepeatedField<TValue> GetOrRegisterExtension<TValue>(pb::RepeatedExtension<OneofOptions, TValue> extension) {
-      return pb::ExtensionSet.GetOrRegister(ref _extensions, extension);
+    public pbc::RepeatedField<TValue> GetOrInitializeExtension<TValue>(pb::RepeatedExtension<OneofOptions, TValue> extension) {
+      return pb::ExtensionSet.GetOrInitialize(ref _extensions, extension);
     }
     public void SetExtension<TValue>(pb::Extension<OneofOptions, TValue> extension, TValue value) {
       pb::ExtensionSet.Set(ref _extensions, extension, value);
@@ -5964,10 +5969,11 @@ namespace Google.Protobuf.Reflection {
 
   }
 
-  internal sealed partial class EnumOptions : pb::IExtendableMessage<EnumOptions> {
+  public sealed partial class EnumOptions : pb::IExtendableMessage<EnumOptions> {
     private static readonly pb::MessageParser<EnumOptions> _parser = new pb::MessageParser<EnumOptions>(() => new EnumOptions());
     private pb::UnknownFieldSet _unknownFields;
     internal pb::ExtensionSet<EnumOptions> _extensions;
+    private pb::ExtensionSet<EnumOptions> _Extensions => _extensions;
     private int _hasBits0;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public static pb::MessageParser<EnumOptions> Parser { get { return _parser; } }
@@ -6203,8 +6209,8 @@ namespace Google.Protobuf.Reflection {
     public pbc::RepeatedField<TValue> GetExtension<TValue>(pb::RepeatedExtension<EnumOptions, TValue> extension) {
       return pb::ExtensionSet.Get(ref _extensions, extension);
     }
-    public pbc::RepeatedField<TValue> GetOrRegisterExtension<TValue>(pb::RepeatedExtension<EnumOptions, TValue> extension) {
-      return pb::ExtensionSet.GetOrRegister(ref _extensions, extension);
+    public pbc::RepeatedField<TValue> GetOrInitializeExtension<TValue>(pb::RepeatedExtension<EnumOptions, TValue> extension) {
+      return pb::ExtensionSet.GetOrInitialize(ref _extensions, extension);
     }
     public void SetExtension<TValue>(pb::Extension<EnumOptions, TValue> extension, TValue value) {
       pb::ExtensionSet.Set(ref _extensions, extension, value);
@@ -6221,10 +6227,11 @@ namespace Google.Protobuf.Reflection {
 
   }
 
-  internal sealed partial class EnumValueOptions : pb::IExtendableMessage<EnumValueOptions> {
+  public sealed partial class EnumValueOptions : pb::IExtendableMessage<EnumValueOptions> {
     private static readonly pb::MessageParser<EnumValueOptions> _parser = new pb::MessageParser<EnumValueOptions>(() => new EnumValueOptions());
     private pb::UnknownFieldSet _unknownFields;
     internal pb::ExtensionSet<EnumValueOptions> _extensions;
+    private pb::ExtensionSet<EnumValueOptions> _Extensions => _extensions;
     private int _hasBits0;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public static pb::MessageParser<EnumValueOptions> Parser { get { return _parser; } }
@@ -6415,8 +6422,8 @@ namespace Google.Protobuf.Reflection {
     public pbc::RepeatedField<TValue> GetExtension<TValue>(pb::RepeatedExtension<EnumValueOptions, TValue> extension) {
       return pb::ExtensionSet.Get(ref _extensions, extension);
     }
-    public pbc::RepeatedField<TValue> GetOrRegisterExtension<TValue>(pb::RepeatedExtension<EnumValueOptions, TValue> extension) {
-      return pb::ExtensionSet.GetOrRegister(ref _extensions, extension);
+    public pbc::RepeatedField<TValue> GetOrInitializeExtension<TValue>(pb::RepeatedExtension<EnumValueOptions, TValue> extension) {
+      return pb::ExtensionSet.GetOrInitialize(ref _extensions, extension);
     }
     public void SetExtension<TValue>(pb::Extension<EnumValueOptions, TValue> extension, TValue value) {
       pb::ExtensionSet.Set(ref _extensions, extension, value);
@@ -6433,10 +6440,11 @@ namespace Google.Protobuf.Reflection {
 
   }
 
-  internal sealed partial class ServiceOptions : pb::IExtendableMessage<ServiceOptions> {
+  public sealed partial class ServiceOptions : pb::IExtendableMessage<ServiceOptions> {
     private static readonly pb::MessageParser<ServiceOptions> _parser = new pb::MessageParser<ServiceOptions>(() => new ServiceOptions());
     private pb::UnknownFieldSet _unknownFields;
     internal pb::ExtensionSet<ServiceOptions> _extensions;
+    private pb::ExtensionSet<ServiceOptions> _Extensions => _extensions;
     private int _hasBits0;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public static pb::MessageParser<ServiceOptions> Parser { get { return _parser; } }
@@ -6627,8 +6635,8 @@ namespace Google.Protobuf.Reflection {
     public pbc::RepeatedField<TValue> GetExtension<TValue>(pb::RepeatedExtension<ServiceOptions, TValue> extension) {
       return pb::ExtensionSet.Get(ref _extensions, extension);
     }
-    public pbc::RepeatedField<TValue> GetOrRegisterExtension<TValue>(pb::RepeatedExtension<ServiceOptions, TValue> extension) {
-      return pb::ExtensionSet.GetOrRegister(ref _extensions, extension);
+    public pbc::RepeatedField<TValue> GetOrInitializeExtension<TValue>(pb::RepeatedExtension<ServiceOptions, TValue> extension) {
+      return pb::ExtensionSet.GetOrInitialize(ref _extensions, extension);
     }
     public void SetExtension<TValue>(pb::Extension<ServiceOptions, TValue> extension, TValue value) {
       pb::ExtensionSet.Set(ref _extensions, extension, value);
@@ -6645,10 +6653,11 @@ namespace Google.Protobuf.Reflection {
 
   }
 
-  internal sealed partial class MethodOptions : pb::IExtendableMessage<MethodOptions> {
+  public sealed partial class MethodOptions : pb::IExtendableMessage<MethodOptions> {
     private static readonly pb::MessageParser<MethodOptions> _parser = new pb::MessageParser<MethodOptions>(() => new MethodOptions());
     private pb::UnknownFieldSet _unknownFields;
     internal pb::ExtensionSet<MethodOptions> _extensions;
+    private pb::ExtensionSet<MethodOptions> _Extensions => _extensions;
     private int _hasBits0;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public static pb::MessageParser<MethodOptions> Parser { get { return _parser; } }
@@ -6880,8 +6889,8 @@ namespace Google.Protobuf.Reflection {
     public pbc::RepeatedField<TValue> GetExtension<TValue>(pb::RepeatedExtension<MethodOptions, TValue> extension) {
       return pb::ExtensionSet.Get(ref _extensions, extension);
     }
-    public pbc::RepeatedField<TValue> GetOrRegisterExtension<TValue>(pb::RepeatedExtension<MethodOptions, TValue> extension) {
-      return pb::ExtensionSet.GetOrRegister(ref _extensions, extension);
+    public pbc::RepeatedField<TValue> GetOrInitializeExtension<TValue>(pb::RepeatedExtension<MethodOptions, TValue> extension) {
+      return pb::ExtensionSet.GetOrInitialize(ref _extensions, extension);
     }
     public void SetExtension<TValue>(pb::Extension<MethodOptions, TValue> extension, TValue value) {
       pb::ExtensionSet.Set(ref _extensions, extension, value);
@@ -6905,7 +6914,7 @@ namespace Google.Protobuf.Reflection {
       /// or neither? HTTP based RPC implementation may choose GET verb for safe
       /// methods, and PUT verb for idempotent methods instead of the default POST.
       /// </summary>
-      internal enum IdempotencyLevel {
+      public enum IdempotencyLevel {
         [pbr::OriginalName("IDEMPOTENCY_UNKNOWN")] IdempotencyUnknown = 0,
         /// <summary>
         /// implies idempotent
@@ -6930,7 +6939,7 @@ namespace Google.Protobuf.Reflection {
   /// or produced by Descriptor::CopyTo()) will never have UninterpretedOptions
   /// in them.
   /// </summary>
-  internal sealed partial class UninterpretedOption : pb::IMessage<UninterpretedOption> {
+  public sealed partial class UninterpretedOption : pb::IMessage<UninterpretedOption> {
     private static readonly pb::MessageParser<UninterpretedOption> _parser = new pb::MessageParser<UninterpretedOption>(() => new UninterpretedOption());
     private pb::UnknownFieldSet _unknownFields;
     private int _hasBits0;
@@ -7309,7 +7318,7 @@ namespace Google.Protobuf.Reflection {
       /// E.g.,{ ["foo", false], ["bar.baz", true], ["qux", false] } represents
       /// "foo.(bar.baz).qux".
       /// </summary>
-      internal sealed partial class NamePart : pb::IMessage<NamePart> {
+      public sealed partial class NamePart : pb::IMessage<NamePart> {
         private static readonly pb::MessageParser<NamePart> _parser = new pb::MessageParser<NamePart>(() => new NamePart());
         private pb::UnknownFieldSet _unknownFields;
         private int _hasBits0;
@@ -7502,7 +7511,7 @@ namespace Google.Protobuf.Reflection {
   /// Encapsulates information about the original source file from which a
   /// FileDescriptorProto was generated.
   /// </summary>
-  internal sealed partial class SourceCodeInfo : pb::IMessage<SourceCodeInfo> {
+  public sealed partial class SourceCodeInfo : pb::IMessage<SourceCodeInfo> {
     private static readonly pb::MessageParser<SourceCodeInfo> _parser = new pb::MessageParser<SourceCodeInfo>(() => new SourceCodeInfo());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -7670,7 +7679,7 @@ namespace Google.Protobuf.Reflection {
     /// <summary>Container for nested types declared in the SourceCodeInfo message type.</summary>
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public static partial class Types {
-      internal sealed partial class Location : pb::IMessage<Location> {
+      public sealed partial class Location : pb::IMessage<Location> {
         private static readonly pb::MessageParser<Location> _parser = new pb::MessageParser<Location>(() => new Location());
         private pb::UnknownFieldSet _unknownFields;
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -8004,7 +8013,7 @@ namespace Google.Protobuf.Reflection {
   /// file. A GeneratedCodeInfo message is associated with only one generated
   /// source file, but may contain references to different source .proto files.
   /// </summary>
-  internal sealed partial class GeneratedCodeInfo : pb::IMessage<GeneratedCodeInfo> {
+  public sealed partial class GeneratedCodeInfo : pb::IMessage<GeneratedCodeInfo> {
     private static readonly pb::MessageParser<GeneratedCodeInfo> _parser = new pb::MessageParser<GeneratedCodeInfo>(() => new GeneratedCodeInfo());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -8131,7 +8140,7 @@ namespace Google.Protobuf.Reflection {
     /// <summary>Container for nested types declared in the GeneratedCodeInfo message type.</summary>
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public static partial class Types {
-      internal sealed partial class Annotation : pb::IMessage<Annotation> {
+      public sealed partial class Annotation : pb::IMessage<Annotation> {
         private static readonly pb::MessageParser<Annotation> _parser = new pb::MessageParser<Annotation>(() => new Annotation());
         private pb::UnknownFieldSet _unknownFields;
         private int _hasBits0;

csharp/src/Google.Protobuf/Reflection/EnumDescriptor.cs

@@ -128,17 +128,16 @@ namespace Google.Protobuf.Reflection
         /// <summary>
         /// The (possibly empty) set of custom options for this enum.
         /// </summary>
-        //[Obsolete("CustomOptions are obsolete. Use GetOption")]
+        [Obsolete("CustomOptions are obsolete. Use GetOption")]
         public CustomOptions CustomOptions => new CustomOptions(Proto.Options._extensions?.ValuesByNumber);
 
-        /* // uncomment this in the full proto2 support PR
         /// <summary>
         /// Gets a single value enum option for this descriptor
         /// </summary>
         public T GetOption<T>(Extension<EnumOptions, T> extension)
         {
             var value = Proto.Options.GetExtension(extension);
-            return value is IDeepCloneable<T> clonable ? clonable.Clone() : value;
+            return value is IDeepCloneable<T> ? (value as IDeepCloneable<T>).Clone() : value;
         }
 
         /// <summary>
@@ -148,6 +147,5 @@ namespace Google.Protobuf.Reflection
         {
             return Proto.Options.GetExtension(extension).Clone();
         }
-        */
     }
 }

csharp/src/Google.Protobuf/Reflection/EnumValueDescriptor.cs

@@ -73,17 +73,16 @@ namespace Google.Protobuf.Reflection
         /// <summary>
         /// The (possibly empty) set of custom options for this enum value.
         /// </summary>
-        //[Obsolete("CustomOptions are obsolete. Use GetOption")]
+        [Obsolete("CustomOptions are obsolete. Use GetOption")]
         public CustomOptions CustomOptions => new CustomOptions(Proto.Options._extensions?.ValuesByNumber);
 
-        /* // uncomment this in the full proto2 support PR
         /// <summary>
         /// Gets a single value enum option for this descriptor
         /// </summary>
         public T GetOption<T>(Extension<EnumValueOptions, T> extension)
         {
             var value = Proto.Options.GetExtension(extension);
-            return value is IDeepCloneable<T> clonable ? clonable.Clone() : value;
+            return value is IDeepCloneable<T> ? (value as IDeepCloneable<T>).Clone() : value;
         }
 
         /// <summary>
@@ -93,7 +92,6 @@ namespace Google.Protobuf.Reflection
         {
             return Proto.Options.GetExtension(extension).Clone();
         }
-        */
     }
 }
  

csharp/src/Google.Protobuf/Reflection/ExtensionCollection.cs

@@ -39,7 +39,7 @@ namespace Google.Protobuf.Reflection
     /// <summary>
     /// A collection to simplify retrieving the descriptors of extensions in a descriptor for a message
     /// </summary>
-    public class ExtensionCollection
+    public sealed class ExtensionCollection
     {
         private IDictionary<MessageDescriptor, IList<FieldDescriptor>> extensionsByTypeInDeclarationOrder;
         private IDictionary<MessageDescriptor, IList<FieldDescriptor>> extensionsByTypeInNumberOrder;

csharp/src/Google.Protobuf/Reflection/FieldDescriptor.cs

@@ -66,7 +66,10 @@ namespace Google.Protobuf.Reflection
 
         internal FieldDescriptorProto Proto { get; }
 
-        internal Extension Extension { get; }
+        /// <summary>
+        /// An extension identifier for this field, or <c>null</c> if this field isn't an extension.
+        /// </summary>
+        public Extension Extension { get; }
 
         internal FieldDescriptor(FieldDescriptorProto proto, FileDescriptor file,
                                  MessageDescriptor parent, int index, string propertyName, Extension extension)
@@ -201,7 +204,25 @@ namespace Google.Protobuf.Reflection
         /// <summary>
         /// Returns <c>true</c> if this field is a packed, repeated field; <c>false</c> otherwise.
         /// </summary>
-        public bool IsPacked => File.Proto.Syntax == "proto2" ? Proto.Options?.Packed ?? false : !Proto.Options.HasPacked || Proto.Options.Packed;
+        public bool IsPacked
+        {
+            get
+            {
+                if (File.Syntax != Syntax.Proto3)
+                {
+                    return Proto.Options?.Packed ?? false;
+                }
+                else
+                {
+                    return !Proto.Options.HasPacked || Proto.Options.Packed;
+                }
+            }
+        }
+
+        /// <summary>
+        /// Returns <c>true</c> if this field extends another message type; <c>false</c> otherwise.
+        /// </summary>
+        public bool IsExtension => Proto.HasExtendee;
 
         /// <summary>
         /// Returns the type of the field.
@@ -277,17 +298,16 @@ namespace Google.Protobuf.Reflection
         /// <summary>
         /// The (possibly empty) set of custom options for this field.
         /// </summary>
-        //[Obsolete("CustomOptions are obsolete. Use GetOption")]
+        [Obsolete("CustomOptions are obsolete. Use GetOption")]
         public CustomOptions CustomOptions => new CustomOptions(Proto.Options._extensions?.ValuesByNumber);
 
-        /* // uncomment this in the full proto2 support PR
         /// <summary>
         /// Gets a single value enum option for this descriptor
         /// </summary>
         public T GetOption<T>(Extension<FieldOptions, T> extension)
         {
             var value = Proto.Options.GetExtension(extension);
-            return value is IDeepCloneable<T> clonable ? clonable.Clone() : value;
+            return value is IDeepCloneable<T> ? (value as IDeepCloneable<T>).Clone() : value;
         }
 
         /// <summary>
@@ -297,7 +317,6 @@ namespace Google.Protobuf.Reflection
         {
             return Proto.Options.GetExtension(extension).Clone();
         }
-        */
 
         /// <summary>
         /// Look up and cross-link all field types etc.
@@ -378,6 +397,11 @@ namespace Google.Protobuf.Reflection
 
         private IFieldAccessor CreateAccessor()
         {
+            if (Extension != null)
+            {
+                return new ExtensionAccessor(this);
+            }
+
             // If we're given no property name, that's because we really don't want an accessor.
             // This could be because it's a map message, or it could be that we're loading a FileDescriptor dynamically.
             // TODO: Support dynamic messages.
@@ -386,10 +410,6 @@ namespace Google.Protobuf.Reflection
                 return null;
             }
 
-            if (Extension != null)
-            {
-                return new ExtensionAccessor(this);
-            }
             var property = ContainingType.ClrType.GetProperty(propertyName);
             if (property == null)
             {

csharp/src/Google.Protobuf/Reflection/FileDescriptor.cs

@@ -42,6 +42,25 @@ using static Google.Protobuf.Reflection.SourceCodeInfo.Types;
 
 namespace Google.Protobuf.Reflection
 {
+    /// <summary>
+    /// The syntax of a .proto file
+    /// </summary>
+    public enum Syntax
+    {
+        /// <summary>
+        /// Proto2 syntax
+        /// </summary>
+        Proto2,
+        /// <summary>
+        /// Proto3 syntax
+        /// </summary>
+        Proto3,
+        /// <summary>
+        /// An unknown declared syntax
+        /// </summary>
+        Unknown
+    }
+
     /// <summary>
     /// Describes a .proto file, including everything defined within.
     /// IDescriptor is implemented such that the File property returns this descriptor,
@@ -87,6 +106,19 @@ namespace Google.Protobuf.Reflection
             Extensions = new ExtensionCollection(this, generatedCodeInfo?.Extensions);
 
             declarations = new Lazy<Dictionary<IDescriptor, DescriptorDeclaration>>(CreateDeclarationMap, LazyThreadSafetyMode.ExecutionAndPublication);
+
+            if (!proto.HasSyntax || proto.Syntax == "proto2")
+            {
+                Syntax = Syntax.Proto2;
+            }
+            else if (proto.Syntax == "proto3")
+            {
+                Syntax = Syntax.Proto3;
+            }
+            else
+            {
+                Syntax = Syntax.Unknown;
+            }
         }
 
         private Dictionary<IDescriptor, DescriptorDeclaration> CreateDeclarationMap()
@@ -217,6 +249,11 @@ namespace Google.Protobuf.Reflection
         /// </value>
         internal FileDescriptorProto Proto { get; }
 
+        /// <summary>
+        /// The syntax of the file
+        /// </summary>
+        public Syntax Syntax { get; }
+
         /// <value>
         /// The file name.
         /// </value>
@@ -504,17 +541,16 @@ namespace Google.Protobuf.Reflection
         /// <summary>
         /// The (possibly empty) set of custom options for this file.
         /// </summary>
-        //[Obsolete("CustomOptions are obsolete. Use GetOption")]
+        [Obsolete("CustomOptions are obsolete. Use GetOption")]
         public CustomOptions CustomOptions => new CustomOptions(Proto.Options._extensions?.ValuesByNumber);
 
-        /* // uncomment this in the full proto2 support PR
         /// <summary>
         /// Gets a single value enum option for this descriptor
         /// </summary>
         public T GetOption<T>(Extension<FileOptions, T> extension)
         {
             var value = Proto.Options.GetExtension(extension);
-            return value is IDeepCloneable<T> clonable ? clonable.Clone() : value;
+            return value is IDeepCloneable<T> ? (value as IDeepCloneable<T>).Clone() : value;
         }
 
         /// <summary>
@@ -524,7 +560,6 @@ namespace Google.Protobuf.Reflection
         {
             return Proto.Options.GetExtension(extension).Clone();
         }
-        */
 
         /// <summary>
         /// Performs initialization for the given generic type argument.

csharp/src/Google.Protobuf/Reflection/IFieldAccessor.cs

@@ -51,11 +51,6 @@ namespace Google.Protobuf.Reflection
         /// </summary>
         void Clear(IMessage message);
 
-        /// <summary>
-        /// Indicates whether the field in the specified message is set. For proto3 fields, this throws an <see cref="InvalidOperationException"/>
-        /// </summary>
-        bool HasValue(IMessage message);
-
         /// <summary>
         /// Fetches the field value. For repeated values, this will be an
         /// <see cref="IList"/> implementation. For map values, this will be an
@@ -63,6 +58,11 @@ namespace Google.Protobuf.Reflection
         /// </summary>
         object GetValue(IMessage message);
 
+        /// <summary>
+        /// Indicates whether the field in the specified message is set. For proto3 fields, this throws an <see cref="InvalidOperationException"/>
+        /// </summary>
+        bool HasValue(IMessage message);
+
         /// <summary>
         /// Mutator for single "simple" fields only.
         /// </summary>

csharp/src/Google.Protobuf/Reflection/MessageDescriptor.cs

@@ -34,6 +34,7 @@ using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.Linq;
+using System.Reflection;
 #if NET35
 // Needed for ReadOnlyDictionary, which does not exist in .NET 3.5
 using Google.Protobuf.Collections;
@@ -63,6 +64,7 @@ namespace Google.Protobuf.Reflection
         private readonly IList<FieldDescriptor> fieldsInDeclarationOrder;
         private readonly IList<FieldDescriptor> fieldsInNumberOrder;
         private readonly IDictionary<string, FieldDescriptor> jsonFieldMap;
+        private Func<IMessage, bool> extensionSetIsInitialized;
 
         internal MessageDescriptor(DescriptorProto proto, FileDescriptor file, MessageDescriptor parent, int typeIndex, GeneratedClrTypeInfo generatedCodeInfo)
             : base(file, file.ComputeFullName(parent, proto.Name), typeIndex)
@@ -134,6 +136,21 @@ namespace Google.Protobuf.Reflection
 
         internal DescriptorProto Proto { get; }
 
+        internal bool IsExtensionsInitialized(IMessage message)
+        {
+            if (Proto.ExtensionRange.Count == 0)
+            {
+                return true;
+            }
+
+            if (extensionSetIsInitialized == null)
+            {
+                extensionSetIsInitialized = ReflectionUtil.CreateIsInitializedCaller(ClrType);
+            }
+
+            return extensionSetIsInitialized(message);
+        }
+
         /// <summary>
         /// The CLR type used to represent message instances from this descriptor.
         /// </summary>
@@ -243,17 +260,16 @@ namespace Google.Protobuf.Reflection
         /// <summary>
         /// The (possibly empty) set of custom options for this message.
         /// </summary>
-        //[Obsolete("CustomOptions are obsolete. Use GetOption")]
+        [Obsolete("CustomOptions are obsolete. Use GetOption")]
         public CustomOptions CustomOptions => new CustomOptions(Proto.Options._extensions?.ValuesByNumber);
 
-        /* // uncomment this in the full proto2 support PR
         /// <summary>
         /// Gets a single value enum option for this descriptor
         /// </summary>
         public T GetOption<T>(Extension<MessageOptions, T> extension)
         {
             var value = Proto.Options.GetExtension(extension);
-            return value is IDeepCloneable<T> clonable ? clonable.Clone() : value;
+            return value is IDeepCloneable<T> ? (value as IDeepCloneable<T>).Clone() : value;
         }
 
         /// <summary>
@@ -263,7 +279,6 @@ namespace Google.Protobuf.Reflection
         {
             return Proto.Options.GetExtension(extension).Clone();
         }
-        */
 
         /// <summary>
         /// Looks up and cross-links all fields and nested types.

csharp/src/Google.Protobuf/Reflection/MethodDescriptor.cs

@@ -73,17 +73,16 @@ namespace Google.Protobuf.Reflection
         /// <summary>
         /// The (possibly empty) set of custom options for this method.
         /// </summary>
-        //[Obsolete("CustomOptions are obsolete. Use GetOption")]
+        [Obsolete("CustomOptions are obsolete. Use GetOption")]
         public CustomOptions CustomOptions => new CustomOptions(Proto.Options._extensions?.ValuesByNumber);
 
-        /* // uncomment this in the full proto2 support PR
         /// <summary>
         /// Gets a single value enum option for this descriptor
         /// </summary>
         public T GetOption<T>(Extension<MethodOptions, T> extension)
         {
             var value = Proto.Options.GetExtension(extension);
-            return value is IDeepCloneable<T> clonable ? clonable.Clone() : value;
+            return value is IDeepCloneable<T> ? (value as IDeepCloneable<T>).Clone() : value;
         }
 
         /// <summary>
@@ -93,7 +92,6 @@ namespace Google.Protobuf.Reflection
         {
             return Proto.Options.GetExtension(extension).Clone();
         }
-        */
 
         internal MethodDescriptor(MethodDescriptorProto proto, FileDescriptor file,
                                   ServiceDescriptor parent, int index)

csharp/src/Google.Protobuf/Reflection/OneofDescriptor.cs

@@ -105,17 +105,16 @@ namespace Google.Protobuf.Reflection
         /// <summary>
         /// The (possibly empty) set of custom options for this oneof.
         /// </summary>
-        //[Obsolete("CustomOptions are obsolete. Use GetOption")]
+        [Obsolete("CustomOptions are obsolete. Use GetOption")]
         public CustomOptions CustomOptions => new CustomOptions(proto.Options._extensions?.ValuesByNumber);
 
-        /* // uncomment this in the full proto2 support PR
         /// <summary>
         /// Gets a single value enum option for this descriptor
         /// </summary>
         public T GetOption<T>(Extension<OneofOptions, T> extension)
         {
             var value = proto.Options.GetExtension(extension);
-            return value is IDeepCloneable<T> clonable ? clonable.Clone() : value;
+            return value is IDeepCloneable<T> ? (value as IDeepCloneable<T>).Clone() : value;
         }
 
         /// <summary>
@@ -125,7 +124,6 @@ namespace Google.Protobuf.Reflection
         {
             return proto.Options.GetExtension(extension).Clone();
         }
-        */
 
         internal void CrossLink()
         {

csharp/src/Google.Protobuf/Reflection/ReflectionUtil.cs

@@ -115,12 +115,15 @@ namespace Google.Protobuf.Reflection
         internal static Func<IMessage, bool> CreateFuncIMessageBool(MethodInfo method) =>
             GetReflectionHelper(method.DeclaringType, method.ReturnType).CreateFuncIMessageBool(method);
 
+        internal static Func<IMessage, bool> CreateIsInitializedCaller(Type msg) =>
+            ((IExtensionSetReflector)Activator.CreateInstance(typeof(ExtensionSetReflector<>).MakeGenericType(msg))).CreateIsInitializedCaller();
+
         /// <summary>
         /// Creates a delegate which will execute the given method after casting the first argument to
         /// the type that declares the method, and the second argument to the first parameter type of the method.
         /// </summary>
         internal static IExtensionReflectionHelper CreateExtensionHelper(Extension extension) =>
-            (IExtensionReflectionHelper)Activator.CreateInstance(typeof(ExtensionReflectionHelper<,>).MakeGenericType(extension.TargetType, extension.GetType().GenericTypeArguments[1]));
+            (IExtensionReflectionHelper)Activator.CreateInstance(typeof(ExtensionReflectionHelper<,>).MakeGenericType(extension.TargetType, extension.GetType().GenericTypeArguments[1]), extension);
 
         /// <summary>
         /// Creates a reflection helper for the given type arguments. Currently these are created on demand
@@ -150,6 +153,11 @@ namespace Google.Protobuf.Reflection
             void ClearExtension(IMessage message);
         }
 
+        private interface IExtensionSetReflector
+        {
+            Func<IMessage, bool> CreateIsInitializedCaller();
+        }
+
         private class ReflectionHelper<T1, T2> : IReflectionHelper
         {
 
@@ -222,7 +230,7 @@ namespace Google.Protobuf.Reflection
                 }
                 else if (extension is RepeatedExtension<T1, T3>)
                 {
-                    return extensionMessage.GetExtension(extension as RepeatedExtension<T1, T3>);
+                    return extensionMessage.GetOrInitializeExtension(extension as RepeatedExtension<T1, T3>);
                 }
                 else
                 {
@@ -300,6 +308,28 @@ namespace Google.Protobuf.Reflection
             }
         }
 
+        private class ExtensionSetReflector<T1> : IExtensionSetReflector where T1 : IExtendableMessage<T1>
+        {
+            public Func<IMessage, bool> CreateIsInitializedCaller()
+            {
+                var prop = typeof(T1).GetTypeInfo().GetDeclaredProperty("_Extensions");
+#if NET35
+                var getFunc = (Func<T1, ExtensionSet<T1>>)prop.GetGetMethod(true).CreateDelegate(typeof(Func<T1, ExtensionSet<T1>>));
+#else
+                var getFunc = (Func<T1, ExtensionSet<T1>>)prop.GetMethod.CreateDelegate(typeof(Func<T1, ExtensionSet<T1>>));
+#endif
+                var initializedFunc = (Func<ExtensionSet<T1>, bool>)
+                    typeof(ExtensionSet<T1>)
+                        .GetTypeInfo()
+                        .GetDeclaredMethod("IsInitialized")
+                        .CreateDelegate(typeof(Func<ExtensionSet<T1>, bool>));
+                return (m) => {
+                    var set = getFunc((T1)m);
+                    return set == null || initializedFunc(set);
+                };
+            }
+        }
+
         // Runtime compatibility checking code - see ReflectionHelper<T1, T2>.CreateFuncIMessageInt32 for
         // details about why we're doing this.
 

csharp/src/Google.Protobuf/Reflection/ServiceDescriptor.cs

@@ -94,17 +94,16 @@ namespace Google.Protobuf.Reflection
         /// <summary>
         /// The (possibly empty) set of custom options for this service.
         /// </summary>
-        //[Obsolete("CustomOptions are obsolete. Use GetOption")]
+        [Obsolete("CustomOptions are obsolete. Use GetOption")]
         public CustomOptions CustomOptions => new CustomOptions(Proto.Options._extensions?.ValuesByNumber);
 
-        /* // uncomment this in the full proto2 support PR
         /// <summary>
         /// Gets a single value enum option for this descriptor
         /// </summary>
         public T GetOption<T>(Extension<ServiceOptions, T> extension)
         {
             var value = Proto.Options.GetExtension(extension);
-            return value is IDeepCloneable<T> clonable ? clonable.Clone() : value;
+            return value is IDeepCloneable<T> ? (value as IDeepCloneable<T>).Clone() : value;
         }
 
         /// <summary>
@@ -114,7 +113,6 @@ namespace Google.Protobuf.Reflection
         {
             return Proto.Options.GetExtension(extension).Clone();
         }
-        */
 
         internal void CrossLink()
         {

csharp/src/Google.Protobuf/Reflection/SingleFieldAccessor.cs

@@ -57,20 +57,7 @@ namespace Google.Protobuf.Reflection
                 throw new ArgumentException("Not all required properties/methods available");
             }
             setValueDelegate = ReflectionUtil.CreateActionIMessageObject(property.GetSetMethod());
-            if (descriptor.File.Proto.Syntax == "proto2")
-            {
-                MethodInfo hasMethod = property.DeclaringType.GetRuntimeProperty("Has" + property.Name).GetMethod;
-                if (hasMethod == null) {
-                  throw new ArgumentException("Not all required properties/methods are available");
-                }
-                hasDelegate = ReflectionUtil.CreateFuncIMessageBool(hasMethod);
-                MethodInfo clearMethod = property.DeclaringType.GetRuntimeMethod("Clear" + property.Name, ReflectionUtil.EmptyTypes);
-                if (clearMethod == null) {
-                  throw new ArgumentException("Not all required properties/methods are available");
-                }
-                clearDelegate = ReflectionUtil.CreateActionIMessage(clearMethod);
-            }
-            else
+            if (descriptor.File.Syntax == Syntax.Proto3)
             {
                 hasDelegate = message => {
                   throw new InvalidOperationException("HasValue is not implemented for proto3 fields");
@@ -85,6 +72,19 @@ namespace Google.Protobuf.Reflection
                     : Activator.CreateInstance(clrType);
                 clearDelegate = message => SetValue(message, defaultValue);
             }
+            else
+            {
+                MethodInfo hasMethod = property.DeclaringType.GetRuntimeProperty("Has" + property.Name).GetMethod;
+                if (hasMethod == null) {
+                  throw new ArgumentException("Not all required properties/methods are available");
+                }
+                hasDelegate = ReflectionUtil.CreateFuncIMessageBool(hasMethod);
+                MethodInfo clearMethod = property.DeclaringType.GetRuntimeMethod("Clear" + property.Name, ReflectionUtil.EmptyTypes);
+                if (clearMethod == null) {
+                  throw new ArgumentException("Not all required properties/methods are available");
+                }
+                clearDelegate = ReflectionUtil.CreateActionIMessage(clearMethod);
+            }
         }
 
         public override void Clear(IMessage message)

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

@@ -306,7 +306,7 @@ std::string FieldGeneratorBase::GetStringDefaultValueInternal(const FieldDescrip
     if (descriptor->default_value_string().empty())
         return "\"\"";
     else
-        return "global::System.Encoding.UTF8.GetString(global::System.Convert.FromBase64String(\" +" + StringToBase64(descriptor->default_value_string()) + " +\"))";
+        return "global::System.Text.Encoding.UTF8.GetString(global::System.Convert.FromBase64String(\"" + StringToBase64(descriptor->default_value_string()) + "\"))";
 }
 
 std::string FieldGeneratorBase::GetBytesDefaultValueInternal(const FieldDescriptor* descriptor) {

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

@@ -63,12 +63,6 @@ bool Generator::Generate(
   std::vector<std::pair<string, string> > options;
   ParseGeneratorParameter(parameter, &options);
 
-  // We only support proto3 - but we make an exception for descriptor.proto.
-  if (file->syntax() != FileDescriptor::SYNTAX_PROTO3 && !IsDescriptorProto(file)) {
-    *error = "C# code generation only supports proto3 syntax";
-    return false;
-  }
-
   struct Options cli_options;
 
   for (int i = 0; i < options.size(); i++) {

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

@@ -284,15 +284,34 @@ std::string GetEnumValueName(const std::string& enum_name, const std::string& en
 
 uint GetGroupEndTag(const Descriptor* descriptor) {
   const Descriptor* containing_type = descriptor->containing_type();
-  if (containing_type == NULL) {
-    return 0;
-  }
-  const FieldDescriptor* field = containing_type->FindFieldByName(descriptor->name());
-  if (field != NULL && field->type() == FieldDescriptor::Type::TYPE_GROUP) {
-    return internal::WireFormatLite::MakeTag(field->number(), internal::WireFormatLite::WIRETYPE_LENGTH_DELIMITED);
+  if (containing_type != NULL) {
+    const FieldDescriptor* field;
+    for (int i = 0; i < containing_type->field_count(); i++) {
+      field = containing_type->field(i);
+      if (field->type() == FieldDescriptor::Type::TYPE_GROUP && field->message_type() == descriptor) {
+        return internal::WireFormatLite::MakeTag(field->number(), internal::WireFormatLite::WIRETYPE_END_GROUP);
+      }
+    }
+    for (int i = 0; i < containing_type->extension_count(); i++) {
+      field = containing_type->extension(i);
+      if (field->type() == FieldDescriptor::Type::TYPE_GROUP && field->message_type() == descriptor) {
+        return internal::WireFormatLite::MakeTag(field->number(), internal::WireFormatLite::WIRETYPE_END_GROUP);
+      }
+    }
   } else {
-    return 0;
+    const FileDescriptor* containing_file = descriptor->file();
+    if (containing_file != NULL) {
+      const FieldDescriptor* field;
+      for (int i = 0; i < containing_file->extension_count(); i++) {
+        field = containing_file->extension(i);
+        if (field->type() == FieldDescriptor::Type::TYPE_GROUP && field->message_type() == descriptor) {
+          return internal::WireFormatLite::MakeTag(field->number(), internal::WireFormatLite::WIRETYPE_END_GROUP);
+        }
+      }
+    }
   }
+
+  return 0;
 }
 
 std::string ToCSharpName(const std::string& name, const FileDescriptor* file) {

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

@@ -149,6 +149,8 @@ void MessageGenerator::Generate(io::Printer* printer) {
     } else {
       printer->Print(vars, "private pb::ExtensionSet<$class_name$> _extensions;\n");
     }
+
+    printer->Print(vars, "private pb::ExtensionSet<$class_name$> _Extensions => _extensions;\n"); // a read-only property for fast retrieval of the set in IsInitialized
   }
 
   for (int i = 0; i < has_bit_field_count_; i++) {
@@ -270,8 +272,8 @@ void MessageGenerator::Generate(io::Printer* printer) {
       "public pbc::RepeatedField<TValue> GetExtension<TValue>(pb::RepeatedExtension<$class_name$, TValue> extension) {\n"
       "  return pb::ExtensionSet.Get(ref _extensions, extension);\n"
       "}\n"
-      "public pbc::RepeatedField<TValue> GetOrRegisterExtension<TValue>(pb::RepeatedExtension<$class_name$, TValue> extension) {\n"
-      "  return pb::ExtensionSet.GetOrRegister(ref _extensions, extension);\n"
+      "public pbc::RepeatedField<TValue> GetOrInitializeExtension<TValue>(pb::RepeatedExtension<$class_name$, TValue> extension) {\n"
+      "  return pb::ExtensionSet.GetOrInitialize(ref _extensions, extension);\n"
       "}\n"
       "public void SetExtension<TValue>(pb::Extension<$class_name$, TValue> extension, TValue value) {\n"
       "  pb::ExtensionSet.Set(ref _extensions, extension, value);\n"
@@ -320,7 +322,7 @@ void MessageGenerator::Generate(io::Printer* printer) {
       "#region Extensions\n"
       "/// <summary>Container for extensions for other messages declared in the $class_name$ message type.</summary>\n");
     WriteGeneratedCodeAttributes(printer);
-    printer->Print("internal static partial class Extensions {\n");
+    printer->Print("public static partial class Extensions {\n");
     printer->Indent();
     for (int i = 0; i < descriptor_->extension_count(); i++) {
       std::unique_ptr<FieldGeneratorBase> generator(
@@ -625,7 +627,7 @@ void MessageGenerator::GenerateMergingMethods(io::Printer* printer) {
   printer->Indent();
   if (end_tag_ != 0) {
     printer->Print(
-      "$end_tag$:\n"
+      "case $end_tag$:\n"
       "  return;\n",
       "end_tag", StrCat(end_tag_));
   }
@@ -681,7 +683,7 @@ void MessageGenerator::GenerateMergingMethods(io::Printer* printer) {
 
 // it's a waste of space to track presence for all values, so we only track them if they're not nullable
 int MessageGenerator::GetPresenceIndex(const FieldDescriptor* descriptor) {
-  if (IsNullable(descriptor) || !IsProto2(descriptor_->file())) {
+  if (IsNullable(descriptor) || !IsProto2(descriptor->file()) || descriptor->is_extension()) {
     return -1;
   }
 

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

@@ -74,7 +74,7 @@ void ReflectionClassGenerator::Generate(io::Printer* printer) {
   if (file_->extension_count() > 0) {
     printer->Print(
         "/// <summary>Holder for extension identifiers generated from the top level of $file_name$</summary>\n"
-        "internal static partial class $class_name$ {\n",
+        "$access_level$ static partial class $class_name$ {\n",
         "access_level", class_access_level(),
         "class_name", extensionClassname_,
         "file_name", file_->name());

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

@@ -59,7 +59,7 @@ void SourceGeneratorBase::WriteGeneratedCodeAttributes(io::Printer* printer) {
 }
 
 std::string SourceGeneratorBase::class_access_level() {
-  return (IsDescriptorProto(descriptor_) || this->options()->internal_access) ? "internal" : "public";
+  return this->options()->internal_access ? "internal" : "public";
 }
 
 const Options* SourceGeneratorBase::options() {