[New go generator] Implement declaring unions.

mojom/generators/go/templates/declarations_test.go

Index: mojom/generators/go/templates/declarations_test.go
diff --git a/mojom/generators/go/templates/declarations_test.go b/mojom/generators/go/templates/declarations_test.go
index 5b4b3329a6096069dcb38968d0a8a7cfd9463828..899ad97cf6917dfd9e43a3f79afc58968718f27e 100644
--- a/mojom/generators/go/templates/declarations_test.go
+++ b/mojom/generators/go/templates/declarations_test.go
@@ -51,3 +51,46 @@ func TestStructDecl(t *testing.T) {
 
 	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)
+}