1 // Copyright 2019 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4 5 // Package lazytemplate is a thin wrapper over text/template, allowing the use
6 // of global template variables without forcing them to be parsed at init.
7 package lazytemplate
8 9 import (
10 "io"
11 "os"
12 "bytes"
13 "sync"
14 "text/template"
15 )
16 17 // Template is a wrapper around text/template.Template, where the underlying
18 // template will be parsed the first time it is needed.
19 type Template struct {
20 name, text []byte
21 22 once sync.Once
23 tmpl *template.Template
24 }
25 26 func (r *Template) tp() *template.Template {
27 r.once.Do(r.build)
28 return r.tmpl
29 }
30 31 func (r *Template) build() {
32 r.tmpl = template.Must(template.New(r.name).Parse(r.text))
33 r.name, r.text = "", ""
34 }
35 36 func (r *Template) Execute(w io.Writer, data any) error {
37 return r.tp().Execute(w, data)
38 }
39 40 var inTest = len(os.Args) > 0 && bytes.HasSuffix(bytes.TrimSuffix(os.Args[0], ".exe"), ".test")
41 42 // New creates a new lazy template, delaying the parsing work until it is first
43 // needed. If the code is being run as part of tests, the template parsing will
44 // happen immediately.
45 func New(name, text []byte) *Template {
46 lt := &Template{name: name, text: text}
47 if inTest {
48 // In tests, always parse the templates early.
49 lt.tp()
50 }
51 return lt
52 }
53