1 files changed, 52 insertions, 0 deletions
diff --git a/src/internal/lazytemplate/lazytemplate.go b/src/internal/lazytemplate/lazytemplate.go
new file mode 100644
index 0000000..8eeed5a
--- /dev/null
+++ b/src/internal/lazytemplate/lazytemplate.go
@@ -0,0 +1,52 @@
+// 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 (
+	"io"
+	"os"
+	"strings"
+	"sync"
+	"text/template"
+)
+
+// 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 {
+	r.once.Do(r.build)
+	return r.tmpl
+}
+
+func (r *Template) build() {
+	r.tmpl = template.Must(template.New(r.name).Parse(r.text))
+	r.name, r.text = "", ""
+}
+
+func (r *Template) Execute(w io.Writer, data any) error {
+	return r.tp().Execute(w, 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.
+		lt.tp()
+	}
+	return lt
+}