[New go generator] Implement declaring unions.

mojom/generators/go/templates/decoding.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
 
-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 -}}
-`
+import (
+        "text/template"
+)
 
 const fieldDecodingTmplText = `
 {{- define "FieldDecodingTmpl" -}}
 {{- $info := . -}}
 {{- if $info.IsPointer -}}
 pointer, err := decoder.ReadPointer()
 if err != nil {
         return err
 }
 if pointer == 0 {
@@ skipping 81 matching lines @@
         return &bindings.ValidationError{bindings.DifferentSizedArraysInMap,
                 fmt.Sprintf("Number of keys %d is different from number of values %d",
                 len({{$keyInfo.Identifier}}), len({{$valueInfo.Identifier}}))}
 }
 for i := 0; i < len({{$keyInfo.Identifier}}); i++ {
         (*{{$info.Identifier}})[{{$keyInfo.Identifier}}[i]] = {{$valueInfo.Identifier}}[i]
 }
 {{- end -}}
 {{- end -}}
 `
+
+func initDecodingTemplates() {
+        template.Must(goFileTmpl.Parse(nonNullableFieldDecodingTmplText))
+        template.Must(goFileTmpl.Parse(fieldDecodingTmplText))
+}