1 files changed, 51 insertions, 0 deletions
diff --git a/libgo/go/go/doc/lazyre.go b/libgo/go/go/doc/lazyre.go
new file mode 100644
index 00000000000..3fd97d42de6
--- /dev/null
+++ b/libgo/go/go/doc/lazyre.go
@@ -0,0 +1,51 @@
+// Copyright 2018 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 doc
+
+import (
+	"os"
+	"regexp"
+	"strings"
+	"sync"
+)
+
+type lazyRE struct {
+	str  string
+	once sync.Once
+	rx   *regexp.Regexp
+}
+
+func (r *lazyRE) re() *regexp.Regexp {
+	r.once.Do(r.build)
+	return r.rx
+}
+
+func (r *lazyRE) build() {
+	r.rx = regexp.MustCompile(r.str)
+	r.str = ""
+}
+
+func (r *lazyRE) FindStringSubmatchIndex(s string) []int {
+	return r.re().FindStringSubmatchIndex(s)
+}
+
+func (r *lazyRE) ReplaceAllString(src, repl string) string {
+	return r.re().ReplaceAllString(src, repl)
+}
+
+func (r *lazyRE) MatchString(s string) bool {
+	return r.re().MatchString(s)
+}
+
+var inTest = len(os.Args) > 0 && strings.HasSuffix(strings.TrimSuffix(os.Args[0], ".exe"), ".test")
+
+func newLazyRE(str string) *lazyRE {
+	lr := &lazyRE{str: str}
+	if inTest {
+		// In tests, always compile the regexps early.
+		lr.re()
+	}
+	return lr
+}