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// Copyright 2019 The Go 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 lazytemplate is a thin wrapper over text/template, allowing the use
// of global template variables without forcing them to be parsed at init.
package lazytemplate
import (
// Template is a wrapper around text/template.Template, where the underlying
// template will be parsed the first time it is needed.
type Template struct {
name, text string
once sync.Once
tmpl *template.Template
func (r *Template) tp() *template.Template {
return r.tmpl
func (r *Template) build() {
r.tmpl = template.Must(template.New(, r.text = "", ""
func (r *Template) Execute(w io.Writer, data interface{}) error {
return, data)
var inTest = len(os.Args) > 0 && strings.HasSuffix(strings.TrimSuffix(os.Args[0], ".exe"), ".test")
// New creates a new lazy template, delaying the parsing work until it is first
// needed. If the code is being run as part of tests, the template parsing will
// happen immediately.
func New(name, text string) *Template {
lt := &Template{name: name, text: text}
if inTest {
// In tests, always parse the templates early.
return lt