From 529bd2bf988e653b078b7aca2c5559d951cc3033 Mon Sep 17 00:00:00 2001
From: Clayton Coleman <ccoleman@redhat.com>
Date: Mon, 4 Apr 2016 23:00:35 -0400
Subject: [PATCH] Support protobuf.as=Message for aliasing

In order to allow a Go type to have a different internal representation,
provide the comment `// +protobuf.as=MESSAGENAME` which substitutes the
current message's members with the named message's members. Used by the
unversioned.Time type to have the same fields as unversioned.Timestamp
and to have an alternate serialization.
---
 .../go-to-protobuf/protobuf/generator.go      | 34 +++++++++++++++----
 .../go2idl/go-to-protobuf/protobuf/namer.go   |  6 +++-
 2 files changed, 33 insertions(+), 7 deletions(-)

diff --git a/cmd/libs/go2idl/go-to-protobuf/protobuf/generator.go b/cmd/libs/go2idl/go-to-protobuf/protobuf/generator.go
index e81c8140021..5d1a8320013 100644
--- a/cmd/libs/go2idl/go-to-protobuf/protobuf/generator.go
+++ b/cmd/libs/go2idl/go-to-protobuf/protobuf/generator.go
@@ -135,8 +135,9 @@ func (g *genProtoIDL) GenerateType(c *generator.Context, t *types.Type, w io.Wri
 	sw := generator.NewSnippetWriter(w, c, "$", "$")
 	b := bodyGen{
 		locator: &protobufLocator{
-			namer:   c.Namers["proto"].(ProtobufFromGoNamer),
-			tracker: g.imports,
+			namer:    c.Namers["proto"].(ProtobufFromGoNamer),
+			tracker:  g.imports,
+			universe: c.Universe,
 
 			localGoPackage: g.localGoPackage.Package,
 		},
@@ -164,12 +165,14 @@ type ProtobufFromGoNamer interface {
 
 type ProtobufLocator interface {
 	ProtoTypeFor(t *types.Type) (*types.Type, error)
+	GoTypeForName(name types.Name) *types.Type
 	CastTypeName(name types.Name) string
 }
 
 type protobufLocator struct {
-	namer   ProtobufFromGoNamer
-	tracker namer.ImportTracker
+	namer    ProtobufFromGoNamer
+	tracker  namer.ImportTracker
+	universe types.Universe
 
 	localGoPackage string
 }
@@ -183,6 +186,13 @@ func (p protobufLocator) CastTypeName(name types.Name) string {
 	return name.String()
 }
 
+func (p protobufLocator) GoTypeForName(name types.Name) *types.Type {
+	if len(name.Package) == 0 {
+		name.Package = p.localGoPackage
+	}
+	return p.universe.Type(name)
+}
+
 // ProtoTypeFor locates a Protobuf type for the provided Go type (if possible).
 func (p protobufLocator) ProtoTypeFor(t *types.Type) (*types.Type, error) {
 	switch {
@@ -231,6 +241,7 @@ func (b bodyGen) doStruct(sw *generator.SnippetWriter) error {
 		return nil
 	}
 
+	var alias *types.Type
 	var fields []protoField
 	options := []string{}
 	allOptions := types.ExtractCommentTags("+", b.t.CommentLines)
@@ -254,6 +265,14 @@ func (b bodyGen) doStruct(sw *generator.SnippetWriter) error {
 					options = append(options, fmt.Sprintf("%s = %s", key, v))
 				}
 			}
+		// protobuf.as allows a type to have the same message contents as another Go type
+		case k == "protobuf.as":
+			fields = nil
+			if alias = b.locator.GoTypeForName(types.Name{Name: v}); alias == nil {
+				return fmt.Errorf("type %v references alias %q which does not exist", b.t, v)
+			}
+		// protobuf.embed instructs the generator to use the named type in this package
+		// as an embedded message.
 		case k == "protobuf.embed":
 			fields = []protoField{
 				{
@@ -270,10 +289,13 @@ func (b bodyGen) doStruct(sw *generator.SnippetWriter) error {
 			}
 		}
 	}
+	if alias == nil {
+		alias = b.t
+	}
 
 	// If we don't explicitly embed anything, generate fields by traversing fields.
 	if fields == nil {
-		memberFields, err := membersToFields(b.locator, b.t, b.localPackage, b.omitFieldTypes)
+		memberFields, err := membersToFields(b.locator, alias, b.localPackage, b.omitFieldTypes)
 		if err != nil {
 			return fmt.Errorf("type %v cannot be converted to protobuf: %v", b.t, err)
 		}
@@ -454,7 +476,7 @@ func memberTypeToProtobufField(locator ProtobufLocator, field *protoField, t *ty
 
 // protobufTagToField extracts information from an existing protobuf tag
 func protobufTagToField(tag string, field *protoField, m types.Member, t *types.Type, localPackage types.Name) error {
-	if len(tag) == 0 {
+	if len(tag) == 0 || tag == "-" {
 		return nil
 	}
 
diff --git a/cmd/libs/go2idl/go-to-protobuf/protobuf/namer.go b/cmd/libs/go2idl/go-to-protobuf/protobuf/namer.go
index 662206c0e5c..9e2b9853462 100644
--- a/cmd/libs/go2idl/go-to-protobuf/protobuf/namer.go
+++ b/cmd/libs/go2idl/go-to-protobuf/protobuf/namer.go
@@ -131,7 +131,11 @@ func assignGoTypeToProtoPackage(p *protobufPackage, t *types.Type, local, global
 			continue
 		}
 		field := &protoField{}
-		if err := protobufTagToField(reflect.StructTag(m.Tags).Get("protobuf"), field, m, t, p.ProtoTypeName()); err == nil && field.Type != nil {
+		tag := reflect.StructTag(m.Tags).Get("protobuf")
+		if tag == "-" {
+			continue
+		}
+		if err := protobufTagToField(tag, field, m, t, p.ProtoTypeName()); err == nil && field.Type != nil {
 			assignGoTypeToProtoPackage(p, field.Type, local, global)
 			continue
 		}