[New go generator] Implement declaring unions.

mojom/generators/go/templates/declarations_test.go

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package templates
 
 import (
         "bytes"
         "fmt"
         "strings"
@@ skipping 33 matching lines @@
         s := translator.StructTemplate{
                 Name: "Foo",
                 Fields: []translator.StructFieldTemplate{
                         {Name: "Alpha", Type: "string"},
                         {Name: "Beta", Type: "uint32"},
                 },
         }
 
         check(t, expected, "StructDecl", s)
 }
+
+func TestUnionInterfaceDecl(t *testing.T) {
+        expected := `type SomeUnion interface {
+        Tag() uint32
+        Interface() interface{}
+        __Reflect(__SomeUnionReflect)
+        Encode(encoder *bindings.Encoder) error
+}
+
+type __SomeUnionReflect struct {
+        Alpha string
+        Beta  uint32
+}`
+
+        union := translator.UnionTemplate{
+                Name: "SomeUnion",
+                Fields: []translator.UnionFieldTemplate{
+                        {Name: "Alpha", Type: "string"},
+                        {Name: "Beta", Type: "uint32"},
+                },
+        }
+
+        check(t, expected, "UnionInterfaceDecl", union)
+}
+
+func TestUnionFieldDecl(t *testing.T) {
+        expected := `type SomeUnionAlpha struct{ Value string }
+
+func (u *SomeUnionAlpha) Tag() uint32                  { return 5 }
+func (u *SomeUnionAlpha) Interface() interface{}       { return u.Value }
+func (u *SomeUnionAlpha) __Reflect(__SomeUnionReflect) {}`
+
+        union := translator.UnionTemplate{Name: "SomeUnion"}
+
+        field := translator.UnionFieldTemplate{
+                Name:  "Alpha",
+                Type:  "string",
+                Tag:   5,
+                Union: &union,
+        }
+
+        check(t, expected, "UnionFieldDecl", field)
+}