[New go generator] Implement declaring unions.

mojom/generators/go/templates/structs.go

Index: mojom/generators/go/templates/structs.go
diff --git a/mojom/generators/go/templates/structs.go b/mojom/generators/go/templates/structs.go
new file mode 100644
index 0000000000000000000000000000000000000000..9320185a8466cecbffbaabca95599f54df2ddac8
--- /dev/null
+++ b/mojom/generators/go/templates/structs.go
@@ -0,0 +1,101 @@
+// 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 (
+	"text/template"
+)
+
+const structTmplText = `
+{{- define "Struct" -}}
+{{$struct := . -}}
+{{ template "StructDecl" $struct }}
+
+{{ template "StructEncodingTmpl" $struct }}
+
+{{ template "StructVersions" $struct }}
+
+{{ template "StructDecodingTmpl" $struct }}
+{{- end -}}
+`
+
+const structDeclTmplText = `
+{{- define "StructDecl" -}}
+{{$struct := . -}}
+type {{$struct.Name}} struct {
+{{- range $field := $struct.Fields}}
+	{{$field.Name}} {{$field.Type}}
+{{- end}}
+}
+{{- end -}}
+`
+
+const structEncodingTmplText = `
+{{- define "StructEncodingTmpl" -}}
+{{ $struct := . }}
+func (s *{{$struct.Name}}) Encode(encoder *bindings.Encoder) error {
+	encoder.StartStruct({{$struct.CurVersionSize}}, {{$struct.CurVersionNumber}})
+	{{- range $field := $struct.Fields}}
+		{{ template "FieldEncodingTmpl" $field.EncodingInfo }}
+	{{- end}}
+
+	if err := encoder.Finish(); err != nil {
+		return err
+	}
+	return nil
+}
+{{- end -}}
+`
+
+const structVersions = `
+{{- define "StructVersions" -}}
+{{- $struct := . -}}
+var {{$struct.PrivateName}}_Versions []bindings.DataHeader = []bindings.DataHeader{
+	{{- range $version := $struct.Versions}}
+	bindings.DataHeader{ {{$version.NumBytes}}, {{$version.Version}} },
+	{{- end}}
+}
+{{- end -}}
+`
+
+const structDecodingTmplText = `
+{{- define "StructDecodingTmpl" -}}
+{{- $struct := . -}}
+func (s *{{$struct.Name}}) Decode(decoder *bindings.Decoder) error {
+	header, err := decoder.StartStruct()
+	if err != nil {
+		return err
+	}
+
+	index := sort.Search(len({{$struct.PrivateName}}_Versions), func(i int) bool {
+		return {{$struct.PrivateName}}_Versions[i].ElementsOrVersion >= header.ElementsOrVersion
+	})
+	if index < len({{$struct.PrivateName}}_Versions) {
+		if {{$struct.PrivateName}}_Versions[index].ElementsOrVersion > header.ElementsOrVersion {
+			index--
+		}
+		expectedSize := {{$struct.PrivateName}}_Versions[index].Size
+		if expectedSize != header.Size {
+			return &bindings.ValidationError{bindings.UnexpectedStructHeader,
+				fmt.Sprintf("invalid struct header size: should be %d, but was %d", expectedSize, header.Size),
+			}
+		}
+	}
+
+	{{- range $field := $struct.Fields}}
+	if header.ElementsOrVersion >= {{$field.MinVersion}} {
+		{{ template "FieldDecodingTmpl" $field.EncodingInfo }}
+	}
+	{{- end}}
+}
+{{- end -}}
+`
+
+func initStructTemplates() {
+	template.Must(goFileTmpl.Parse(structEncodingTmplText))
+	template.Must(goFileTmpl.Parse(structDeclTmplText))
+	template.Must(goFileTmpl.Parse(structVersions))
+	template.Must(goFileTmpl.Parse(structDecodingTmplText))
+}