html/template: export the parse.Tree for the escaped template

The underlying parse tree is visible in text/template, so it should be visible here.
Done by copying the underlying *parse.Tree up to the top level of the struct, and then making sure it's kept up to date.
Fixes #6318.

R=mikesamuel
CC=golang-dev
https://golang.org/cl/13479044

src/pkg/html/template/escape.go

@@ -35,11 +35,13 @@ func escapeTemplates(tmpl *Template, names ...string) error {
 			for _, name := range names {
 				if t := tmpl.set[name]; t != nil {
 					t.text.Tree = nil
+					t.Tree = nil
 				}
 			}
 			return err
 		}
 		tmpl.escaped = true
+		tmpl.Tree = tmpl.text.Tree
 	}
 	e.commit()
 	return nil

src/pkg/html/template/escape_test.go

@@ -673,6 +673,10 @@ func TestEscape(t *testing.T) {
 			t.Errorf("%s: escaped output for pointer: want\n\t%q\ngot\n\t%q", test.name, w, g)
 			continue
 		}
+		if tmpl.Tree != tmpl.text.Tree {
+			t.Errorf("%s: tree mismatch", test.name)
+			continue
+		}
 	}
 }
 

src/pkg/html/template/template.go

@@ -21,7 +21,9 @@ type Template struct {
 	// We could embed the text/template field, but it's safer not to because
 	// we need to keep our version of the name space and the underlying
 	// template's in sync.
-	text       *template.Template
+	text *template.Template
+	// The underlying template's parse tree, updated to be HTML-safe.
+	Tree       *parse.Tree
 	*nameSpace // common to all associated templates
 }
 
@@ -149,6 +151,7 @@ func (t *Template) AddParseTree(name string, tree *parse.Tree) (*Template, error
 	ret := &Template{
 		false,
 		text,
+		text.Tree,
 		t.nameSpace,
 	}
 	t.set[name] = ret
@@ -176,6 +179,7 @@ func (t *Template) Clone() (*Template, error) {
 	ret := &Template{
 		false,
 		textClone,
+		textClone.Tree,
 		&nameSpace{
 			set: make(map[string]*Template),
 		},
@@ -195,6 +199,7 @@ func (t *Template) Clone() (*Template, error) {
 		ret.set[name] = &Template{
 			false,
 			x,
+			x.Tree,
 			ret.nameSpace,
 		}
 	}
@@ -206,6 +211,7 @@ func New(name string) *Template {
 	tmpl := &Template{
 		false,
 		template.New(name),
+		nil,
 		&nameSpace{
 			set: make(map[string]*Template),
 		},
@@ -228,6 +234,7 @@ func (t *Template) new(name string) *Template {
 	tmpl := &Template{
 		false,
 		t.text.New(name),
+		nil,
 		t.nameSpace,
 	}
 	tmpl.set[name] = tmpl