tpl: Add temporary patch to fix template data race

Keep this as a separate commit so we can reapply it if needed.

Fixes #7293

tpl/internal/go_templates/texttemplate/template.go

@@ -5,13 +5,15 @@
 package template
 
 import (
-	"github.com/gohugoio/hugo/tpl/internal/go_templates/texttemplate/parse"
 	"reflect"
 	"sync"
+
+	"github.com/gohugoio/hugo/tpl/internal/go_templates/texttemplate/parse"
 )
 
 // common holds the information shared by related templates.
 type common struct {
+	muTmpl sync.RWMutex         // protects tmpl (temporary Hugo-fix)
 	tmpl   map[string]*Template // Map from name to defined templates.
 	option option
 	// We use two maps, one for parsing and one for execution.
@@ -88,6 +90,9 @@ func (t *Template) Clone() (*Template, error) {
 	if t.common == nil {
 		return nt, nil
 	}
+	// temporary Hugo-fix
+	t.muTmpl.RLock()
+	defer t.muTmpl.RUnlock()
 	for k, v := range t.tmpl {
 		if k == t.name {
 			nt.tmpl[t.name] = nt
@@ -124,6 +129,9 @@ func (t *Template) copy(c *common) *Template {
 // its definition. If it has been defined and already has that name, the existing
 // definition is replaced; otherwise a new template is created, defined, and returned.
 func (t *Template) AddParseTree(name string, tree *parse.Tree) (*Template, error) {
+	// temporary Hugo-fix
+	t.muTmpl.Lock()
+	defer t.muTmpl.Unlock()
 	t.init()
 	nt := t
 	if name != t.name {
@@ -142,6 +150,9 @@ func (t *Template) Templates() []*Template {
 		return nil
 	}
 	// Return a slice so we don't expose the map.
+	// temporary Hugo-fix
+	t.muTmpl.RLock()
+	defer t.muTmpl.RUnlock()
 	m := make([]*Template, 0, len(t.tmpl))
 	for _, v := range t.tmpl {
 		m = append(m, v)
@@ -182,6 +193,9 @@ func (t *Template) Lookup(name string) *Template {
 	if t.common == nil {
 		return nil
 	}
+	// temporary Hugo-fix
+	t.muTmpl.RLock()
+	defer t.muTmpl.RUnlock()
 	return t.tmpl[name]
 }