cmd/protoc-gen-go: remove spurious . from enums with no package

Enums, for historical reasons, are registered with the proto package
under the name "<proto_package>.<go_type_name>". Don't include the dot
if there is no package statement in the .proto source file.

Change-Id: I6fb57d0803506668f60123a29fa06ae87fec523b
Reviewed-on: https://go-review.googlesource.com/c/140657
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>

cmd/protoc-gen-go/internal_gengo/main.go

@@ -296,6 +296,9 @@ func enumRegistryName(enum *protogen.Enum) string {
 		desc = p
 	}
 	fdesc := desc.(protoreflect.FileDescriptor)
+	if fdesc.Package() == "" {
+		return enum.GoIdent.GoName
+	}
 	return string(fdesc.Package()) + "." + enum.GoIdent.GoName
 }
 

cmd/protoc-gen-go/testdata/nopackage/nopackage.pb.go

@@ -0,0 +1,124 @@
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// source: nopackage/nopackage.proto
+
+package nopackage
+
+import (
+	fmt "fmt"
+	proto "github.com/golang/protobuf/proto"
+	math "math"
+)
+
+// Reference imports to suppress errors if they are not otherwise used.
+var _ = proto.Marshal
+var _ = fmt.Errorf
+var _ = math.Inf
+
+// This is a compile-time assertion to ensure that this generated file
+// is compatible with the proto package it is being compiled against.
+// A compilation error at this line likely means your copy of the
+// proto package needs to be updated.
+const _ = proto.ProtoPackageIsVersion2 // please upgrade the proto package
+
+type Enum int32
+
+const (
+	Enum_ZERO Enum = 0
+)
+
+var Enum_name = map[int32]string{
+	0: "ZERO",
+}
+
+var Enum_value = map[string]int32{
+	"ZERO": 0,
+}
+
+func (x Enum) Enum() *Enum {
+	p := new(Enum)
+	*p = x
+	return p
+}
+
+func (x Enum) String() string {
+	return proto.EnumName(Enum_name, int32(x))
+}
+
+func (x *Enum) UnmarshalJSON(data []byte) error {
+	value, err := proto.UnmarshalJSONEnum(Enum_value, data, "Enum")
+	if err != nil {
+		return err
+	}
+	*x = Enum(value)
+	return nil
+}
+
+func (Enum) EnumDescriptor() ([]byte, []int) {
+	return fileDescriptor_f33a1d5d178c43c9, []int{0}
+}
+
+type Message struct {
+	StringField          *string  `protobuf:"bytes,1,opt,name=string_field,json=stringField" json:"string_field,omitempty"`
+	EnumField            *Enum    `protobuf:"varint,2,opt,name=enum_field,json=enumField,enum=Enum" json:"enum_field,omitempty"`
+	XXX_NoUnkeyedLiteral struct{} `json:"-"`
+	XXX_unrecognized     []byte   `json:"-"`
+	XXX_sizecache        int32    `json:"-"`
+}
+
+func (m *Message) Reset()         { *m = Message{} }
+func (m *Message) String() string { return proto.CompactTextString(m) }
+func (*Message) ProtoMessage()    {}
+func (*Message) Descriptor() ([]byte, []int) {
+	return fileDescriptor_f33a1d5d178c43c9, []int{0}
+}
+
+func (m *Message) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_Message.Unmarshal(m, b)
+}
+func (m *Message) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_Message.Marshal(b, m, deterministic)
+}
+func (m *Message) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_Message.Merge(m, src)
+}
+func (m *Message) XXX_Size() int {
+	return xxx_messageInfo_Message.Size(m)
+}
+func (m *Message) XXX_DiscardUnknown() {
+	xxx_messageInfo_Message.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_Message proto.InternalMessageInfo
+
+func (m *Message) GetStringField() string {
+	if m != nil && m.StringField != nil {
+		return *m.StringField
+	}
+	return ""
+}
+
+func (m *Message) GetEnumField() Enum {
+	if m != nil && m.EnumField != nil {
+		return *m.EnumField
+	}
+	return Enum_ZERO
+}
+
+func init() {
+	proto.RegisterEnum("Enum", Enum_name, Enum_value)
+	proto.RegisterType((*Message)(nil), "Message")
+}
+
+func init() { proto.RegisterFile("nopackage/nopackage.proto", fileDescriptor_f33a1d5d178c43c9) }
+
+var fileDescriptor_f33a1d5d178c43c9 = []byte{
+	// 127 bytes of a gzipped FileDescriptorProto
+	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0xe2, 0x92, 0xcc, 0xcb, 0x2f, 0x48,
+	0x4c, 0xce, 0x4e, 0x4c, 0x4f, 0xd5, 0x87, 0xb3, 0xf4, 0x0a, 0x8a, 0xf2, 0x4b, 0xf2, 0x95, 0x82,
+	0xb8, 0xd8, 0x7d, 0x53, 0x8b, 0x8b, 0x13, 0xd3, 0x53, 0x85, 0x14, 0xb9, 0x78, 0x8a, 0x4b, 0x8a,
+	0x32, 0xf3, 0xd2, 0xe3, 0xd3, 0x32, 0x53, 0x73, 0x52, 0x24, 0x18, 0x15, 0x18, 0x35, 0x38, 0x83,
+	0xb8, 0x21, 0x62, 0x6e, 0x20, 0x21, 0x21, 0x15, 0x2e, 0xae, 0xd4, 0xbc, 0xd2, 0x5c, 0xa8, 0x02,
+	0x26, 0x05, 0x46, 0x0d, 0x3e, 0x23, 0x56, 0x3d, 0xd7, 0xbc, 0xd2, 0xdc, 0x20, 0x4e, 0x90, 0x04,
+	0x58, 0x95, 0x96, 0x00, 0x17, 0x0b, 0x48, 0x48, 0x88, 0x83, 0x8b, 0x25, 0xca, 0x35, 0xc8, 0x5f,
+	0x80, 0x01, 0x10, 0x00, 0x00, 0xff, 0xff, 0xb2, 0xbc, 0x78, 0x1f, 0x81, 0x00, 0x00, 0x00,
+}

cmd/protoc-gen-go/testdata/nopackage/nopackage.proto

@@ -0,0 +1,16 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+syntax = "proto2";
+
+// File contains no 'package' statement.
+
+enum Enum {
+  ZERO = 0;
+}
+
+message Message {
+  optional string string_field = 1;
+  optional Enum   enum_field   = 2;
+}