Added ToBuilder and WeakToBuilder

src/AddressBook/AddressBookProtos.cs

@@ -179,6 +179,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
         public static Builder CreateBuilder() { return new Builder(); }
+        public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(PhoneNumber prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
@@ -435,6 +436,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(Person prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -732,6 +734,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(AddressBook prototype) {
       return (Builder) new Builder().MergeFrom(prototype);

src/ProtoBench/BenchmarkProtoFile.cs

@@ -525,6 +525,7 @@ namespace Google.ProtocolBuffers.ProtoBench {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(Message1 prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -1568,6 +1569,7 @@ namespace Google.ProtocolBuffers.ProtoBench {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(Message2 prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -2194,6 +2196,7 @@ namespace Google.ProtocolBuffers.ProtoBench {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
         public static Builder CreateBuilder() { return new Builder(); }
+        public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(Group1 prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
@@ -2886,6 +2889,7 @@ namespace Google.ProtocolBuffers.ProtoBench {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(Message3 prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -3670,6 +3674,7 @@ namespace Google.ProtocolBuffers.ProtoBench {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(Message4 prototype) {
       return (Builder) new Builder().MergeFrom(prototype);

src/ProtoBench/BenchmarkSpeedProtoFile.cs

@@ -803,6 +803,7 @@ namespace Google.ProtocolBuffers.ProtoBench {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(SpeedMessage1 prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -2320,6 +2321,7 @@ namespace Google.ProtocolBuffers.ProtoBench {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(SpeedMessage2 prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -3267,6 +3269,7 @@ namespace Google.ProtocolBuffers.ProtoBench {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
         public static Builder CreateBuilder() { return new Builder(); }
+        public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(Group1 prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
@@ -4339,6 +4342,7 @@ namespace Google.ProtocolBuffers.ProtoBench {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(SpeedMessage3 prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -5463,6 +5467,7 @@ namespace Google.ProtocolBuffers.ProtoBench {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(SpeedMessage4 prototype) {
       return (Builder) new Builder().MergeFrom(prototype);

src/ProtoGen/MessageGenerator.cs

@@ -267,6 +267,7 @@ namespace Google.ProtocolBuffers.ProtoGen {
 
     private void GenerateBuilder(TextGenerator writer) {
       writer.WriteLine("public static Builder CreateBuilder() { return new Builder(); }");
+      writer.WriteLine("public override Builder ToBuilder() { return CreateBuilder(this); }");
       writer.WriteLine("public override Builder CreateBuilderForType() { return new Builder(); }");
       writer.WriteLine("public static Builder CreateBuilder({0} prototype) {{", ClassName);
       writer.WriteLine("  return (Builder) new Builder().MergeFrom(prototype);");

src/ProtocolBuffers.Test/AbstractMessageTest.cs

@@ -297,6 +297,10 @@ namespace Google.ProtocolBuffers {
         return new Builder(wrappedMessage.WeakCreateBuilderForType());
       }
 
+      public override Builder ToBuilder() {
+        return new Builder(wrappedMessage.WeakToBuilder());
+      }
+      
       internal class Builder : AbstractBuilder<AbstractMessageWrapper, Builder> {
         private readonly IBuilder wrappedBuilder;
 

src/ProtocolBuffers.Test/DynamicMessageTest.cs

@@ -1,3 +1,4 @@
+using System.Collections.Generic;
 using Google.ProtocolBuffers.TestProtos;
 // Protocol Buffers - Google's data interchange format
 // Copyright 2008 Google Inc.  All rights reserved.
@@ -173,5 +174,26 @@ namespace Google.ProtocolBuffers {
       DynamicMessage copy = DynamicMessage.CreateBuilder(message).Build();
       reflectionTester.AssertAllFieldsSetViaReflection(copy);
     }
+
+    [Test]
+    public void ToBuilder() {
+      DynamicMessage.Builder builder =
+          DynamicMessage.CreateBuilder(TestAllTypes.Descriptor);
+      reflectionTester.SetAllFieldsViaReflection(builder);
+      int unknownFieldNum = 9;
+      ulong unknownFieldVal = 90;
+      builder.SetUnknownFields(UnknownFieldSet.CreateBuilder()
+          .AddField(unknownFieldNum,
+              UnknownField.CreateBuilder().AddVarint(unknownFieldVal).Build())
+          .Build());
+      DynamicMessage message = builder.Build();
+
+      DynamicMessage derived = message.ToBuilder().Build();
+      reflectionTester.AssertAllFieldsSetViaReflection(derived);
+
+      IList<ulong> values = derived.UnknownFields.FieldDictionary[unknownFieldNum].VarintList;
+      Assert.AreEqual(1, values.Count);
+      Assert.AreEqual(unknownFieldVal, values[0]);
+    }
   }
 }

src/ProtocolBuffers.Test/GeneratedMessageTest.cs

@@ -385,5 +385,13 @@ namespace Google.ProtocolBuffers {
       Assert.IsTrue(builder.IsInitialized);
       Assert.IsTrue(builder.BuildPartial().IsInitialized);
     }
+
+    [Test]
+    public void ToBuilder() {
+      TestAllTypes.Builder builder = TestAllTypes.CreateBuilder();
+      TestUtil.SetAllFields(builder);
+      TestAllTypes message = builder.Build();
+      TestUtil.AssertAllFieldsSet(message.ToBuilder().Build());
+    }
   }
 }

src/ProtocolBuffers.Test/TestProtos/UnitTestCustomOptionsProtoFile.cs

@@ -344,6 +344,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestMessageWithCustomOptions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -453,6 +454,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(CustomOptionFooRequest prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -543,6 +545,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(CustomOptionFooResponse prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -643,6 +646,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(DummyMessageContainingEnum prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -733,6 +737,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(DummyMessageInvalidAsOptionType prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -823,6 +828,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(CustomOptionMinIntegerValues prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -913,6 +919,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(CustomOptionMaxIntegerValues prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -1003,6 +1010,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(CustomOptionOtherValues prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -1093,6 +1101,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(SettingRealsFromPositiveInts prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -1183,6 +1192,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(SettingRealsFromNegativeInts prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -1282,6 +1292,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(ComplexOptionType1 prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -1425,6 +1436,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
         public static Builder CreateBuilder() { return new Builder(); }
+        public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(ComplexOptionType4 prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
@@ -1541,6 +1553,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(ComplexOptionType2 prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -1754,6 +1767,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
         public static Builder CreateBuilder() { return new Builder(); }
+        public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(ComplexOptionType5 prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
@@ -1861,6 +1875,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(ComplexOptionType3 prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -2014,6 +2029,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(ComplexOpt6 prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -2122,6 +2138,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(VariousComplexOptions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);

src/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs

@@ -146,6 +146,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestEmbedOptimizedForSize prototype) {
       return (Builder) new Builder().MergeFrom(prototype);

src/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs

@@ -129,6 +129,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(ImportMessage prototype) {
       return (Builder) new Builder().MergeFrom(prototype);

src/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs

@@ -143,6 +143,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestMessageSet prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -311,6 +312,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestMessageSetContainer prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -528,6 +530,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestMessageSetExtension1 prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -722,6 +725,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestMessageSetExtension2 prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -956,6 +960,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
         public static Builder CreateBuilder() { return new Builder(); }
+        public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(Item prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
@@ -1157,6 +1162,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(RawMessageSet prototype) {
       return (Builder) new Builder().MergeFrom(prototype);

src/ProtocolBuffers.Test/TestProtos/UnitTestOptimizeForProtoFile.cs

@@ -122,6 +122,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestOptimizedForSize prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -275,6 +276,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestRequiredOptimizedForSize prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -392,6 +394,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestOptionalOptimizedForSize prototype) {
       return (Builder) new Builder().MergeFrom(prototype);

src/ProtocolBuffers.Test/TestProtos/UnitTestProtoFile.cs

@@ -838,6 +838,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
         public static Builder CreateBuilder() { return new Builder(); }
+        public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(NestedMessage prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
@@ -1030,6 +1031,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
         public static Builder CreateBuilder() { return new Builder(); }
+        public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(OptionalGroup prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
@@ -1222,6 +1224,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
         public static Builder CreateBuilder() { return new Builder(); }
+        public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(RepeatedGroup prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
@@ -2580,6 +2583,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestAllTypes prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -4872,6 +4876,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(ForeignMessage prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -5053,6 +5058,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestAllExtensions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -5221,6 +5227,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(OptionalGroup_extension prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -5413,6 +5420,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(RepeatedGroup_extension prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -6093,6 +6101,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestRequired prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -7123,6 +7132,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestRequiredForeign prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -7411,6 +7421,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestForeignNested prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -7611,6 +7622,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestEmptyMessage prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -7767,6 +7779,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestEmptyMessageWithExtensions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -7950,6 +7963,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestReallyLargeTagNumber prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -8182,6 +8196,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestRecursiveMessage prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -8422,6 +8437,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestMutualRecursionA prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -8652,6 +8668,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestMutualRecursionB prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -8916,6 +8933,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
         public static Builder CreateBuilder() { return new Builder(); }
+        public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(Foo prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
@@ -9108,6 +9126,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
         public static Builder CreateBuilder() { return new Builder(); }
+        public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(Bar prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
@@ -9311,6 +9330,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestDupFieldNumber prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -9649,6 +9669,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
         public static Builder CreateBuilder() { return new Builder(); }
+        public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(NestedMessage prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
@@ -9879,6 +9900,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestNestedMessageHasBits prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -10308,6 +10330,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestCamelCaseFieldNames prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -10920,6 +10943,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestFieldOrderings prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -11239,6 +11263,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestExtremeDefaultValues prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -11937,6 +11962,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestPackedTypes prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -12644,6 +12670,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(TestPackedExtensions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -12797,6 +12824,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(FooRequest prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -12949,6 +12977,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(FooResponse prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -13101,6 +13130,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(BarRequest prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -13253,6 +13283,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(BarResponse prototype) {
       return (Builder) new Builder().MergeFrom(prototype);

src/ProtocolBuffers/AbstractMessage.cs

@@ -58,12 +58,17 @@ namespace Google.ProtocolBuffers {
     public abstract UnknownFieldSet UnknownFields { get; }
     public abstract TMessage DefaultInstanceForType { get; }
     public abstract TBuilder CreateBuilderForType();
+    public abstract TBuilder ToBuilder();
     #endregion
     
     public IBuilder WeakCreateBuilderForType() {
       return CreateBuilderForType();
     }
 
+    public IBuilder WeakToBuilder() {
+      return ToBuilder();
+    }
+
     public IMessage WeakDefaultInstanceForType {
       get { return DefaultInstanceForType; }
     }

src/ProtocolBuffers/DescriptorProtos/CSharpOptions.cs

@@ -143,6 +143,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(CSharpFileOptions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -334,6 +335,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(CSharpFieldOptions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);

src/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs

@@ -279,6 +279,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(FileDescriptorSet prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -631,6 +632,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(FileDescriptorProto prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -1165,6 +1167,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
         public static Builder CreateBuilder() { return new Builder(); }
+        public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(ExtensionRange prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
@@ -1478,6 +1481,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(DescriptorProto prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -2099,6 +2103,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(FieldDescriptorProto prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -2541,6 +2546,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(EnumDescriptorProto prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -2863,6 +2869,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(EnumValueDescriptorProto prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -3167,6 +3174,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(ServiceDescriptorProto prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -3504,6 +3512,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(MethodDescriptorProto prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -3876,6 +3885,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(FileOptions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -4223,6 +4233,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(MessageOptions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -4528,6 +4539,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(FieldOptions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -4834,6 +4846,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(EnumOptions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -5059,6 +5072,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(EnumValueOptions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -5284,6 +5298,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(ServiceOptions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -5509,6 +5524,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(MethodOptions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
@@ -5766,6 +5782,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
           return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
         }
         public static Builder CreateBuilder() { return new Builder(); }
+        public override Builder ToBuilder() { return CreateBuilder(this); }
         public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(NamePart prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
@@ -6045,6 +6062,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
       return ((Builder) CreateBuilder().MergeFrom(input, extensionRegistry)).BuildParsed();
     }
     public static Builder CreateBuilder() { return new Builder(); }
+    public override Builder ToBuilder() { return CreateBuilder(this); }
     public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(UninterpretedOption prototype) {
       return (Builder) new Builder().MergeFrom(prototype);

src/ProtocolBuffers/DynamicMessage.cs

@@ -74,7 +74,6 @@ namespace Google.ProtocolBuffers {
       Builder builder = CreateBuilder(type);
       Builder dynamicBuilder = builder.MergeFrom(input);
       return dynamicBuilder.BuildParsed();
-
     }
 
     /// <summary>
@@ -247,6 +246,10 @@ namespace Google.ProtocolBuffers {
       return new Builder(type);
     }
 
+    public override Builder ToBuilder() {
+      return CreateBuilderForType().MergeFrom(this);
+    }
+
     /// <summary>
     /// Verifies that the field is a field of this message.
     /// </summary>

src/ProtocolBuffers/FieldSet.cs

@@ -326,8 +326,7 @@ namespace Google.ProtocolBuffers {
           }
         } else if (field.MappedType == MappedType.Message && existingValue != null) {
           IMessage existingMessage = (IMessage)existingValue;
-          IMessage merged = existingMessage.WeakCreateBuilderForType()
-              .WeakMergeFrom(existingMessage)
+          IMessage merged = existingMessage.WeakToBuilder()
               .WeakMergeFrom((IMessage) entry.Value)
               .WeakBuild();
           this[field] = merged;

src/ProtocolBuffers/IMessage.cs

@@ -168,11 +168,18 @@ namespace Google.ProtocolBuffers {
 
     /// <summary>
     /// Creates a builder for the type, but in a weakly typed manner. This
-    /// is typically implemented by strongly typed builders by just returning
+    /// is typically implemented by strongly typed messages by just returning
     /// the result of CreateBuilderForType.
     /// </summary>
     IBuilder WeakCreateBuilderForType();
 
+    /// <summary>
+    /// Creates a builder with the same contents as this message. This
+    /// is typically implemented by strongly typed messages by just returning
+    /// the result of ToBuilder.
+    /// </summary>
+    IBuilder WeakToBuilder();
+
     IMessage WeakDefaultInstanceForType { get; }
   }
 
@@ -198,6 +205,12 @@ namespace Google.ProtocolBuffers {
     /// Constructs a new builder for a message of the same type as this message.
     /// </summary>
     TBuilder CreateBuilderForType();
+    /// <summary>
+    /// Creates a builder with the same contents as this current instance.
+    /// This is typically implemented by strongly typed messages by just
+    /// returning the result of ToBuilder().
+    /// </summary>
+    TBuilder ToBuilder();
     #endregion
   }
 }