cmd/protoc-gen-go: remove name mangling for MessageSet extensions

MessageSet are a proto1 feature only used by Google.
We no longer rely on the name mangling logic performed here,
so remove it.

Change-Id: I5d66ebd86875894632f0d0c1e9816ae47ee0d5f4
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/242657
Reviewed-by: Herbie Ong <herbie@google.com>
diff --git a/cmd/protoc-gen-go/internal_gengo/main.go b/cmd/protoc-gen-go/internal_gengo/main.go
index b2e3930..ea5d2e6 100644
--- a/cmd/protoc-gen-go/internal_gengo/main.go
+++ b/cmd/protoc-gen-go/internal_gengo/main.go
@@ -17,7 +17,6 @@
 	"unicode/utf8"
 
 	"google.golang.org/protobuf/compiler/protogen"
-	"google.golang.org/protobuf/internal/encoding/messageset"
 	"google.golang.org/protobuf/internal/encoding/tag"
 	"google.golang.org/protobuf/internal/genid"
 	"google.golang.org/protobuf/internal/version"
@@ -735,12 +734,6 @@
 
 	g.P("var ", extensionTypesVarName(f), " = []", protoimplPackage.Ident("ExtensionInfo"), "{")
 	for _, x := range f.allExtensions {
-		// For MessageSet extensions, the name used is the parent message.
-		name := x.Desc.FullName()
-		if messageset.IsMessageSetExtension(x.Desc) {
-			name = name.Parent()
-		}
-
 		g.P("{")
 		g.P("ExtendedType: (*", x.Extendee.GoIdent, ")(nil),")
 		goType, pointer := fieldGoType(g, f, x.Extension)
@@ -749,7 +742,7 @@
 		}
 		g.P("ExtensionType: (", goType, ")(nil),")
 		g.P("Field: ", x.Desc.Number(), ",")
-		g.P("Name: ", strconv.Quote(string(name)), ",")
+		g.P("Name: ", strconv.Quote(string(x.Desc.FullName())), ",")
 		g.P("Tag: ", strconv.Quote(fieldProtobufTagValue(x.Extension)), ",")
 		g.P("Filename: ", strconv.Quote(f.Desc.Path()), ",")
 		g.P("},")
diff --git a/cmd/protoc-gen-go/testdata/extensions/ext/ext.pb.go b/cmd/protoc-gen-go/testdata/extensions/ext/ext.pb.go
index b4c58c3..3c79fbc 100644
--- a/cmd/protoc-gen-go/testdata/extensions/ext/ext.pb.go
+++ b/cmd/protoc-gen-go/testdata/extensions/ext/ext.pb.go
@@ -763,7 +763,7 @@
 		ExtendedType:  (*base.MessageSetWireFormatMessage)(nil),
 		ExtensionType: (*MessageSetWireFormatExtension)(nil),
 		Field:         100,
-		Name:          "goproto.protoc.extension.ext.MessageSetWireFormatExtension",
+		Name:          "goproto.protoc.extension.ext.MessageSetWireFormatExtension.message_set_extension",
 		Tag:           "bytes,100,opt,name=message_set_extension",
 		Filename:      "cmd/protoc-gen-go/testdata/extensions/ext/ext.proto",
 	},
diff --git a/internal/testprotos/conformance/test_messages_proto2.pb.go b/internal/testprotos/conformance/test_messages_proto2.pb.go
index dafcc84..051bf28 100644
--- a/internal/testprotos/conformance/test_messages_proto2.pb.go
+++ b/internal/testprotos/conformance/test_messages_proto2.pb.go
@@ -1691,7 +1691,7 @@
 		ExtendedType:  (*TestAllTypesProto2_MessageSetCorrect)(nil),
 		ExtensionType: (*TestAllTypesProto2_MessageSetCorrectExtension1)(nil),
 		Field:         1547769,
-		Name:          "protobuf_test_messages.proto2.TestAllTypesProto2.MessageSetCorrectExtension1",
+		Name:          "protobuf_test_messages.proto2.TestAllTypesProto2.MessageSetCorrectExtension1.message_set_extension",
 		Tag:           "bytes,1547769,opt,name=message_set_extension",
 		Filename:      "google/protobuf/test_messages_proto2.proto",
 	},
@@ -1699,7 +1699,7 @@
 		ExtendedType:  (*TestAllTypesProto2_MessageSetCorrect)(nil),
 		ExtensionType: (*TestAllTypesProto2_MessageSetCorrectExtension2)(nil),
 		Field:         4135312,
-		Name:          "protobuf_test_messages.proto2.TestAllTypesProto2.MessageSetCorrectExtension2",
+		Name:          "protobuf_test_messages.proto2.TestAllTypesProto2.MessageSetCorrectExtension2.message_set_extension",
 		Tag:           "bytes,4135312,opt,name=message_set_extension",
 		Filename:      "google/protobuf/test_messages_proto2.proto",
 	},
diff --git a/internal/testprotos/messageset/msetextpb/msetextpb.pb.go b/internal/testprotos/messageset/msetextpb/msetextpb.pb.go
index af919ba..c9d2025 100644
--- a/internal/testprotos/messageset/msetextpb/msetextpb.pb.go
+++ b/internal/testprotos/messageset/msetextpb/msetextpb.pb.go
@@ -207,7 +207,7 @@
 		ExtendedType:  (*messagesetpb.MessageSet)(nil),
 		ExtensionType: (*Ext1)(nil),
 		Field:         1000,
-		Name:          "goproto.proto.messageset.Ext1",
+		Name:          "goproto.proto.messageset.Ext1.message_set_extension",
 		Tag:           "bytes,1000,opt,name=message_set_extension",
 		Filename:      "internal/testprotos/messageset/msetextpb/msetextpb.proto",
 	},
@@ -215,7 +215,7 @@
 		ExtendedType:  (*messagesetpb.MessageSet)(nil),
 		ExtensionType: (*Ext2)(nil),
 		Field:         1001,
-		Name:          "goproto.proto.messageset.Ext2",
+		Name:          "goproto.proto.messageset.Ext2.message_set_extension",
 		Tag:           "bytes,1001,opt,name=message_set_extension",
 		Filename:      "internal/testprotos/messageset/msetextpb/msetextpb.proto",
 	},
@@ -223,7 +223,7 @@
 		ExtendedType:  (*messagesetpb.MessageSet)(nil),
 		ExtensionType: (*ExtRequired)(nil),
 		Field:         1002,
-		Name:          "goproto.proto.messageset.ExtRequired",
+		Name:          "goproto.proto.messageset.ExtRequired.message_set_extension",
 		Tag:           "bytes,1002,opt,name=message_set_extension",
 		Filename:      "internal/testprotos/messageset/msetextpb/msetextpb.proto",
 	},
@@ -231,7 +231,7 @@
 		ExtendedType:  (*messagesetpb.MessageSet)(nil),
 		ExtensionType: (*ExtLargeNumber)(nil),
 		Field:         536870912,
-		Name:          "goproto.proto.messageset.ExtLargeNumber",
+		Name:          "goproto.proto.messageset.ExtLargeNumber.message_set_extension",
 		Tag:           "bytes,536870912,opt,name=message_set_extension",
 		Filename:      "internal/testprotos/messageset/msetextpb/msetextpb.proto",
 	},
diff --git a/internal/testprotos/textpb2/test.pb.go b/internal/testprotos/textpb2/test.pb.go
index c7d384c..65d351b 100644
--- a/internal/testprotos/textpb2/test.pb.go
+++ b/internal/testprotos/textpb2/test.pb.go
@@ -1734,7 +1734,7 @@
 		ExtendedType:  (*MessageSet)(nil),
 		ExtensionType: (*MessageSetExtension)(nil),
 		Field:         10,
-		Name:          "pb2.MessageSetExtension",
+		Name:          "pb2.MessageSetExtension.message_set_extension",
 		Tag:           "bytes,10,opt,name=message_set_extension",
 		Filename:      "internal/testprotos/textpb2/test.proto",
 	},