proto: remove Proto3UnknownFields flag (#497)

This flag was necessary inside Google for the transition to having
proto3 preserve unknown fields by default.
Outside of Google, this is unnecessary since the dev branch is
the transition.

proto/lib.go

@@ -274,12 +274,6 @@ import (
 	"sync"
 )
 
-// Proto3UnknownFields enables whether unknown fields are preserved when
-// unmarshaling proto3 messages. By default, this is disabled.
-// This variable should only be set at init time.
-// This variable is temporary and will go away soon. Do not rely on it.
-var Proto3UnknownFields = false
-
 var errInvalidUTF8 = errors.New("proto: invalid UTF-8 string")
 
 // Message is implemented by generated protocol buffer messages.

proto/proto3_test.go

@@ -145,13 +145,7 @@ func TestUnknownFieldPreservation(t *testing.T) {
 		t.Fatalf("proto.Unmarshal: %v", err)
 	}
 
-	if proto.Proto3UnknownFields {
-		if !bytes.Equal(m.XXX_unrecognized, []byte(b2)) {
-			t.Fatalf("mismatching unknown fields:\ngot  %q\nwant %q", m.XXX_unrecognized, b2)
-		}
-	} else {
-		if len(m.XXX_unrecognized) > 0 {
-			t.Fatalf("unexpected unknown fields: got %q", m.XXX_unrecognized)
-		}
+	if !bytes.Equal(m.XXX_unrecognized, []byte(b2)) {
+		t.Fatalf("mismatching unknown fields:\ngot  %q\nwant %q", m.XXX_unrecognized, b2)
 	}
 }

proto/table_unmarshal.go

@@ -344,11 +344,6 @@ func (u *unmarshalInfo) computeUnmarshalInfo() {
 	for i := 0; i < n; i++ {
 		f := t.Field(i)
 		if f.Name == "XXX_unrecognized" {
-			isProto3 := f.Tag.Get("protobuf_unrecognized") == "proto3"
-			if isProto3 && !Proto3UnknownFields {
-				continue // Explicit disabling of unknown fields in proto3
-			}
-
 			// The byte slice used to hold unrecognized input is special.
 			if f.Type != reflect.TypeOf(([]byte)(nil)) {
 				panic("bad type for XXX_unrecognized field: " + f.Type.Name())

protoc-gen-go/generator/generator.go

@@ -1978,12 +1978,7 @@ func (g *Generator) generateMessage(message *Descriptor) {
 		}
 		g.P(g.Pkg["proto"], ".XXX_InternalExtensions `", messageset, "json:\"-\"`")
 	}
-	if message.proto3() {
-		// TODO: Remove this when proto3 always preserves unknown fields.
-		g.P("XXX_unrecognized\t[]byte `protobuf_unrecognized:\"proto3\" json:\"-\"`")
-	} else {
-		g.P("XXX_unrecognized\t[]byte `json:\"-\"`")
-	}
+	g.P("XXX_unrecognized\t[]byte `json:\"-\"`")
 	g.P("XXX_sizecache\tint32 `json:\"-\"`")
 	g.Out()
 	g.P("}")