html/template: add Clone and AddParseTree. Make text/template's Clone

return (*Template, error), not just *Template.

Fixes #2757.

R=r
CC=golang-dev
https://golang.org/cl/5665044

2 files changed, 171 insertions, 9 deletions

diff --git a/src/pkg/html/template/clone_test.go b/src/pkg/html/template/clone_test.go
index 39788173b9..384b4f0e83 100644
--- a/src/pkg/html/template/clone_test.go
+++ b/src/pkg/html/template/clone_test.go
@@ -7,9 +7,10 @@ package template
 import (
 	"bytes"
 	"testing"
+	"text/template/parse"
 )
 
-func TestClone(t *testing.T) {
+func TestCloneList(t *testing.T) {
 	tests := []struct {
 		input, want, wantClone string
 	}{
@@ -90,3 +91,107 @@ func TestClone(t *testing.T) {
 		}
 	}
 }
+
+func TestAddParseTree(t *testing.T) {
+	root := Must(New("root").Parse(`{{define "a"}} {{.}} {{template "b"}} {{.}} "></a>{{end}}`))
+	tree, err := parse.Parse("t", `{{define "b"}}<a href="{{end}}`, "", "", nil, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	added := Must(root.AddParseTree("b", tree["b"]))
+	b := new(bytes.Buffer)
+	err = added.ExecuteTemplate(b, "a", "1>0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got, want := b.String(), ` 1&gt;0 <a href=" 1%3e0 "></a>`; got != want {
+		t.Errorf("got %q want %q", got, want)
+	}
+}
+
+func TestClone(t *testing.T) {
+	// The {{.}} will be executed with data "<i>*/" in different contexts.
+	// In the t0 template, it will be in a text context.
+	// In the t1 template, it will be in a URL context.
+	// In the t2 template, it will be in a JavaScript context.
+	// In the t3 template, it will be in a CSS context.
+	const tmpl = `{{define "a"}}{{template "lhs"}}{{.}}{{template "rhs"}}{{end}}`
+	b := new(bytes.Buffer)
+
+	// Create an incomplete template t0.
+	t0 := Must(New("t0").Parse(tmpl))
+
+	// Clone t0 as t1.
+	t1 := Must(t0.Clone())
+	Must(t1.Parse(`{{define "lhs"}} <a href=" {{end}}`))
+	Must(t1.Parse(`{{define "rhs"}} "></a> {{end}}`))
+
+	// Execute t1.
+	b.Reset()
+	if err := t1.ExecuteTemplate(b, "a", "<i>*/"); err != nil {
+		t.Fatal(err)
+	}
+	if got, want := b.String(), ` <a href=" %3ci%3e*/ "></a> `; got != want {
+		t.Errorf("t1: got %q want %q", got, want)
+	}
+
+	// Clone t0 as t2.
+	t2 := Must(t0.Clone())
+	Must(t2.Parse(`{{define "lhs"}} <p onclick="javascript: {{end}}`))
+	Must(t2.Parse(`{{define "rhs"}} "></p> {{end}}`))
+
+	// Execute t2.
+	b.Reset()
+	if err := t2.ExecuteTemplate(b, "a", "<i>*/"); err != nil {
+		t.Fatal(err)
+	}
+	if got, want := b.String(), ` <p onclick="javascript: &#34;\u003ci\u003e*/&#34; "></p> `; got != want {
+		t.Errorf("t2: got %q want %q", got, want)
+	}
+
+	// Clone t0 as t3, but do not execute t3 yet.
+	t3 := Must(t0.Clone())
+	Must(t3.Parse(`{{define "lhs"}} <style> {{end}}`))
+	Must(t3.Parse(`{{define "rhs"}} </style> {{end}}`))
+
+	// Complete t0.
+	Must(t0.Parse(`{{define "lhs"}} ( {{end}}`))
+	Must(t0.Parse(`{{define "rhs"}} ) {{end}}`))
+
+	// Clone t0 as t4. Redefining the "lhs" template should fail.
+	t4 := Must(t0.Clone())
+	if _, err := t4.Parse(`{{define "lhs"}} FAIL {{end}}`); err == nil {
+		t.Error(`redefine "lhs": got nil err want non-nil`)
+	}
+
+	// Execute t0.
+	b.Reset()
+	if err := t0.ExecuteTemplate(b, "a", "<i>*/"); err != nil {
+		t.Fatal(err)
+	}
+	if got, want := b.String(), ` ( &lt;i&gt;*/ ) `; got != want {
+		t.Errorf("t0: got %q want %q", got, want)
+	}
+
+	// Clone t0. This should fail, as t0 has already executed.
+	if _, err := t0.Clone(); err == nil {
+		t.Error(`t0.Clone(): got nil err want non-nil`)
+	}
+
+	// Similarly, cloning sub-templates should fail.
+	if _, err := t0.Lookup("a").Clone(); err == nil {
+		t.Error(`t0.Lookup("a").Clone(): got nil err want non-nil`)
+	}
+	if _, err := t0.Lookup("lhs").Clone(); err == nil {
+		t.Error(`t0.Lookup("lhs").Clone(): got nil err want non-nil`)
+	}
+
+	// Execute t3.
+	b.Reset()
+	if err := t3.ExecuteTemplate(b, "a", "<i>*/"); err != nil {
+		t.Fatal(err)
+	}
+	if got, want := b.String(), ` <style> ZgotmplZ </style> `; got != want {
+		t.Errorf("t3: got %q want %q", got, want)
+	}
+}
diff --git a/src/pkg/html/template/template.go b/src/pkg/html/template/template.go
index 9ffe41413a..b0bae7a54f 100644
--- a/src/pkg/html/template/template.go
+++ b/src/pkg/html/template/template.go
@@ -50,7 +50,7 @@ func (t *Template) Execute(wr io.Writer, data interface{}) (err error) {
 // ExecuteTemplate applies the template associated with t that has the given
 // name to the specified data object and writes the output to wr.
 func (t *Template) ExecuteTemplate(wr io.Writer, name string, data interface{}) error {
-	tmpl, err := t.lookupAndEscapeTemplate(wr, name)
+	tmpl, err := t.lookupAndEscapeTemplate(name)
 	if err != nil {
 		return err
 	}
@@ -60,7 +60,7 @@ func (t *Template) ExecuteTemplate(wr io.Writer, name string, data interface{})
 // lookupAndEscapeTemplate guarantees that the template with the given name
 // is escaped, or returns an error if it cannot be. It returns the named
 // template.
-func (t *Template) lookupAndEscapeTemplate(wr io.Writer, name string) (tmpl *Template, err error) {
+func (t *Template) lookupAndEscapeTemplate(name string) (tmpl *Template, err error) {
 	t.nameSpace.mu.Lock()
 	defer t.nameSpace.mu.Unlock()
 	tmpl = t.set[name]
@@ -106,14 +106,71 @@ func (t *Template) Parse(src string) (*Template, error) {
 	return t, nil
 }
 
-// AddParseTree is unimplemented.
-func (t *Template) AddParseTree(name string, tree *parse.Tree) error {
-	return fmt.Errorf("html/template: AddParseTree unimplemented")
+// AddParseTree creates a new template with the name and parse tree
+// and associates it with t.
+//
+// It returns an error if t has already been executed.
+func (t *Template) AddParseTree(name string, tree *parse.Tree) (*Template, error) {
+	t.nameSpace.mu.Lock()
+	defer t.nameSpace.mu.Unlock()
+	if t.escaped {
+		return nil, fmt.Errorf("html/template: cannot AddParseTree to %q after it has executed", t.Name())
+	}
+	text, err := t.text.AddParseTree(name, tree)
+	if err != nil {
+		return nil, err
+	}
+	ret := &Template{
+		false,
+		text,
+		t.nameSpace,
+	}
+	t.set[name] = ret
+	return ret, nil
 }
 
-// Clone is unimplemented.
-func (t *Template) Clone(name string) error {
-	return fmt.Errorf("html/template: Clone unimplemented")
+// Clone returns a duplicate of the template, including all associated
+// templates. The actual representation is not copied, but the name space of
+// associated templates is, so further calls to Parse in the copy will add
+// templates to the copy but not to the original. Clone can be used to prepare
+// common templates and use them with variant definitions for other templates
+// by adding the variants after the clone is made.
+//
+// It returns an error if t has already been executed.
+func (t *Template) Clone() (*Template, error) {
+	t.nameSpace.mu.Lock()
+	defer t.nameSpace.mu.Unlock()
+	if t.escaped {
+		return nil, fmt.Errorf("html/template: cannot Clone %q after it has executed", t.Name())
+	}
+	textClone, err := t.text.Clone()
+	if err != nil {
+		return nil, err
+	}
+	ret := &Template{
+		false,
+		textClone,
+		&nameSpace{
+			set: make(map[string]*Template),
+		},
+	}
+	for _, x := range textClone.Templates() {
+		name := x.Name()
+		src := t.set[name]
+		if src == nil || src.escaped {
+			return nil, fmt.Errorf("html/template: cannot Clone %q after it has executed", t.Name())
+		}
+		x.Tree = &parse.Tree{
+			Name: x.Tree.Name,
+			Root: x.Tree.Root.CopyList(),
+		}
+		ret.set[name] = &Template{
+			false,
+			x,
+			ret.nameSpace,
+		}
+	}
+	return ret, nil
 }
 
 // New allocates a new HTML template with the given name.