text/template: add lock for Template.tmpl to fix data race

This adds a new lock protecting "tmpl".

This is a copy of https://golang.org/cl/257817 by Andreas Fleig,
updated for current tip, and updated to start running the
html/template TestEscapeRace test.

Thanks to @bep for providing the test case.

Fixes #39807

Change-Id: Ic8874484290283a49116812eeaffb8608346dc70
Reviewed-on: https://go-review.googlesource.com/c/go/+/316669
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

1 files changed, 4 insertions, 5 deletions

diff --git a/src/text/template/exec.go b/src/text/template/exec.go
index f1305a29a0..5ad3b4ec58 100644
--- a/src/text/template/exec.go
+++ b/src/text/template/exec.go
@@ -179,10 +179,7 @@ func errRecover(errp *error) {
 // A template may be executed safely in parallel, although if parallel
 // executions share a Writer the output may be interleaved.
 func (t *Template) ExecuteTemplate(wr io.Writer, name string, data interface{}) error {
-	var tmpl *Template
-	if t.common != nil {
-		tmpl = t.tmpl[name]
-	}
+	tmpl := t.Lookup(name)
 	if tmpl == nil {
 		return fmt.Errorf("template: no template %q associated with template %q", name, t.name)
 	}
@@ -230,6 +227,8 @@ func (t *Template) DefinedTemplates() string {
 		return ""
 	}
 	var b strings.Builder
+	t.muTmpl.RLock()
+	defer t.muTmpl.RUnlock()
 	for name, tmpl := range t.tmpl {
 		if tmpl.Tree == nil || tmpl.Root == nil {
 			continue
@@ -401,7 +400,7 @@ func (s *state) walkRange(dot reflect.Value, r *parse.RangeNode) {
 
 func (s *state) walkTemplate(dot reflect.Value, t *parse.TemplateNode) {
 	s.at(t)
-	tmpl := s.tmpl.tmpl[t.Name]
+	tmpl := s.tmpl.Lookup(t.Name)
 	if tmpl == nil {
 		s.errorf("template %q not defined", t.Name)
 	}