libgo: Update to go1.6rc1.

    
    Reviewed-on: https://go-review.googlesource.com/19200

From-SVN: r233110

9 files changed, 211 insertions, 97 deletions

diff --git a/libgo/go/html/escape.go b/libgo/go/html/escape.go
index f50a4b9..ab6fd1c 100644
--- a/libgo/go/html/escape.go
+++ b/libgo/go/html/escape.go
@@ -57,8 +57,9 @@ var replacementTable = [...]rune{
 // unescapeEntity reads an entity like "<" from b[src:] and writes the
 // corresponding "<" to b[dst:], returning the incremented dst and src cursors.
 // Precondition: b[src] == '&' && dst <= src.
-// attribute should be true if parsing an attribute value.
-func unescapeEntity(b []byte, dst, src int, attribute bool) (dst1, src1 int) {
+func unescapeEntity(b []byte, dst, src int) (dst1, src1 int) {
+	const attribute = false
+
 	// http://www.whatwg.org/specs/web-apps/current-work/multipage/tokenization.html#consume-a-character-reference
 
 	// i starts at 1 because we already know that s[0] == '&'.
@@ -139,14 +140,14 @@ func unescapeEntity(b []byte, dst, src int, attribute bool) (dst1, src1 int) {
 		break
 	}
 
-	entityName := string(s[1:i])
-	if entityName == "" {
+	entityName := s[1:i]
+	if len(entityName) == 0 {
 		// No-op.
 	} else if attribute && entityName[len(entityName)-1] != ';' && len(s) > i && s[i] == '=' {
 		// No-op.
-	} else if x := entity[entityName]; x != 0 {
+	} else if x := entity[string(entityName)]; x != 0 {
 		return dst + utf8.EncodeRune(b[dst:], x), src + i
-	} else if x := entity2[entityName]; x[0] != 0 {
+	} else if x := entity2[string(entityName)]; x[0] != 0 {
 		dst1 := dst + utf8.EncodeRune(b[dst:], x[0])
 		return dst1 + utf8.EncodeRune(b[dst1:], x[1]), src + i
 	} else if !attribute {
@@ -155,7 +156,7 @@ func unescapeEntity(b []byte, dst, src int, attribute bool) (dst1, src1 int) {
 			maxLen = longestEntityWithoutSemicolon
 		}
 		for j := maxLen; j > 1; j-- {
-			if x := entity[entityName[:j]]; x != 0 {
+			if x := entity[string(entityName[:j])]; x != 0 {
 				return dst + utf8.EncodeRune(b[dst:], x), src + j + 1
 			}
 		}
@@ -166,26 +167,6 @@ func unescapeEntity(b []byte, dst, src int, attribute bool) (dst1, src1 int) {
 	return dst1, src1
 }
 
-// unescape unescapes b's entities in-place, so that "a&lt;b" becomes "a<b".
-func unescape(b []byte) []byte {
-	for i, c := range b {
-		if c == '&' {
-			dst, src := unescapeEntity(b, i, i, false)
-			for src < len(b) {
-				c := b[src]
-				if c == '&' {
-					dst, src = unescapeEntity(b, dst, src, false)
-				} else {
-					b[dst] = c
-					dst, src = dst+1, src+1
-				}
-			}
-			return b[0:dst]
-		}
-	}
-	return b
-}
-
 var htmlEscaper = strings.NewReplacer(
 	`&`, "&amp;",
 	`'`, "&#39;", // "&#39;" is shorter than "&apos;" and apos was not in HTML until HTML5.
@@ -208,8 +189,29 @@ func EscapeString(s string) string {
 // UnescapeString(EscapeString(s)) == s always holds, but the converse isn't
 // always true.
 func UnescapeString(s string) string {
-	if !strings.Contains(s, "&") {
+	i := strings.IndexByte(s, '&')
+
+	if i < 0 {
 		return s
 	}
-	return string(unescape([]byte(s)))
+
+	b := []byte(s)
+	dst, src := unescapeEntity(b, i, i)
+	for len(s[src:]) > 0 {
+		if s[src] == '&' {
+			i = 0
+		} else {
+			i = strings.IndexByte(s[src:], '&')
+		}
+		if i < 0 {
+			dst += copy(b[dst:], s[src:])
+			break
+		}
+
+		if i > 0 {
+			copy(b[dst:], s[src:src+i])
+		}
+		dst, src = unescapeEntity(b, dst+i, src+i)
+	}
+	return string(b[:dst])
 }
diff --git a/libgo/go/html/escape_test.go b/libgo/go/html/escape_test.go
index 3702626..8b51a55 100644
--- a/libgo/go/html/escape_test.go
+++ b/libgo/go/html/escape_test.go
@@ -118,8 +118,10 @@ func TestUnescapeEscape(t *testing.T) {
 }
 
 var (
-	benchEscapeData = strings.Repeat("AAAAA < BBBBB > CCCCC & DDDDD ' EEEEE \" ", 100)
-	benchEscapeNone = strings.Repeat("AAAAA x BBBBB x CCCCC x DDDDD x EEEEE x ", 100)
+	benchEscapeData     = strings.Repeat("AAAAA < BBBBB > CCCCC & DDDDD ' EEEEE \" ", 100)
+	benchEscapeNone     = strings.Repeat("AAAAA x BBBBB x CCCCC x DDDDD x EEEEE x ", 100)
+	benchUnescapeSparse = strings.Repeat(strings.Repeat("AAAAA x BBBBB x CCCCC x DDDDD x EEEEE x ", 10)+"&amp;", 10)
+	benchUnescapeDense  = strings.Repeat("&amp;&lt; &amp; &lt;", 100)
 )
 
 func BenchmarkEscape(b *testing.B) {
@@ -151,3 +153,17 @@ func BenchmarkUnescapeNone(b *testing.B) {
 		n += len(UnescapeString(s))
 	}
 }
+
+func BenchmarkUnescapeSparse(b *testing.B) {
+	n := 0
+	for i := 0; i < b.N; i++ {
+		n += len(UnescapeString(benchUnescapeSparse))
+	}
+}
+
+func BenchmarkUnescapeDense(b *testing.B) {
+	n := 0
+	for i := 0; i < b.N; i++ {
+		n += len(UnescapeString(benchUnescapeDense))
+	}
+}
diff --git a/libgo/go/html/template/clone_test.go b/libgo/go/html/template/clone_test.go
index c89d22a6..d7c62fa3 100644
--- a/libgo/go/html/template/clone_test.go
+++ b/libgo/go/html/template/clone_test.go
@@ -78,9 +78,17 @@ func TestClone(t *testing.T) {
 	Must(t0.Parse(`{{define "lhs"}} ( {{end}}`))
 	Must(t0.Parse(`{{define "rhs"}} ) {{end}}`))
 
-	// Clone t0 as t4. Redefining the "lhs" template should fail.
+	// Clone t0 as t4. Redefining the "lhs" template should not fail.
 	t4 := Must(t0.Clone())
-	if _, err := t4.Parse(`{{define "lhs"}} FAIL {{end}}`); err == nil {
+	if _, err := t4.Parse(`{{define "lhs"}} OK {{end}}`); err != nil {
+		t.Errorf(`redefine "lhs": got err %v want nil`, err)
+	}
+	// Cloning t1 should fail as it has been executed.
+	if _, err := t1.Clone(); err == nil {
+		t.Error("cloning t1: got nil err want non-nil")
+	}
+	// Redefining the "lhs" template in t1 should fail as it has been executed.
+	if _, err := t1.Parse(`{{define "lhs"}} OK {{end}}`); err == nil {
 		t.Error(`redefine "lhs": got nil err want non-nil`)
 	}
 
diff --git a/libgo/go/html/template/context.go b/libgo/go/html/template/context.go
index 59e794d..c90fc1f 100644
--- a/libgo/go/html/template/context.go
+++ b/libgo/go/html/template/context.go
@@ -310,7 +310,8 @@ func (e element) String() string {
 	return fmt.Sprintf("illegal element %d", int(e))
 }
 
-// attr identifies the most recent HTML attribute when inside a start tag.
+// attr identifies the current HTML attribute when inside the attribute,
+// that is, starting from stateAttrName until stateTag/stateText (exclusive).
 type attr uint8
 
 const (
diff --git a/libgo/go/html/template/escape_test.go b/libgo/go/html/template/escape_test.go
index bea2d13..707394e 100644
--- a/libgo/go/html/template/escape_test.go
+++ b/libgo/go/html/template/escape_test.go
@@ -1054,7 +1054,7 @@ func TestEscapeText(t *testing.T) {
 		},
 		{
 			`<a href=x`,
-			context{state: stateURL, delim: delimSpaceOrTagEnd, urlPart: urlPartPreQuery},
+			context{state: stateURL, delim: delimSpaceOrTagEnd, urlPart: urlPartPreQuery, attr: attrURL},
 		},
 		{
 			`<a href=x `,
@@ -1070,7 +1070,7 @@ func TestEscapeText(t *testing.T) {
 		},
 		{
 			`<a href ='`,
-			context{state: stateURL, delim: delimSingleQuote},
+			context{state: stateURL, delim: delimSingleQuote, attr: attrURL},
 		},
 		{
 			`<a href=''`,
@@ -1078,7 +1078,7 @@ func TestEscapeText(t *testing.T) {
 		},
 		{
 			`<a href= "`,
-			context{state: stateURL, delim: delimDoubleQuote},
+			context{state: stateURL, delim: delimDoubleQuote, attr: attrURL},
 		},
 		{
 			`<a href=""`,
@@ -1090,35 +1090,35 @@ func TestEscapeText(t *testing.T) {
 		},
 		{
 			`<a HREF='http:`,
-			context{state: stateURL, delim: delimSingleQuote, urlPart: urlPartPreQuery},
+			context{state: stateURL, delim: delimSingleQuote, urlPart: urlPartPreQuery, attr: attrURL},
 		},
 		{
 			`<a Href='/`,
-			context{state: stateURL, delim: delimSingleQuote, urlPart: urlPartPreQuery},
+			context{state: stateURL, delim: delimSingleQuote, urlPart: urlPartPreQuery, attr: attrURL},
 		},
 		{
 			`<a href='"`,
-			context{state: stateURL, delim: delimSingleQuote, urlPart: urlPartPreQuery},
+			context{state: stateURL, delim: delimSingleQuote, urlPart: urlPartPreQuery, attr: attrURL},
 		},
 		{
 			`<a href="'`,
-			context{state: stateURL, delim: delimDoubleQuote, urlPart: urlPartPreQuery},
+			context{state: stateURL, delim: delimDoubleQuote, urlPart: urlPartPreQuery, attr: attrURL},
 		},
 		{
 			`<a href='&apos;`,
-			context{state: stateURL, delim: delimSingleQuote, urlPart: urlPartPreQuery},
+			context{state: stateURL, delim: delimSingleQuote, urlPart: urlPartPreQuery, attr: attrURL},
 		},
 		{
 			`<a href="&quot;`,
-			context{state: stateURL, delim: delimDoubleQuote, urlPart: urlPartPreQuery},
+			context{state: stateURL, delim: delimDoubleQuote, urlPart: urlPartPreQuery, attr: attrURL},
 		},
 		{
 			`<a href="&#34;`,
-			context{state: stateURL, delim: delimDoubleQuote, urlPart: urlPartPreQuery},
+			context{state: stateURL, delim: delimDoubleQuote, urlPart: urlPartPreQuery, attr: attrURL},
 		},
 		{
 			`<a href=&quot;`,
-			context{state: stateURL, delim: delimSpaceOrTagEnd, urlPart: urlPartPreQuery},
+			context{state: stateURL, delim: delimSpaceOrTagEnd, urlPart: urlPartPreQuery, attr: attrURL},
 		},
 		{
 			`<img alt="1">`,
@@ -1138,83 +1138,83 @@ func TestEscapeText(t *testing.T) {
 		},
 		{
 			`<a onclick="`,
-			context{state: stateJS, delim: delimDoubleQuote},
+			context{state: stateJS, delim: delimDoubleQuote, attr: attrScript},
 		},
 		{
 			`<a onclick="//foo`,
-			context{state: stateJSLineCmt, delim: delimDoubleQuote},
+			context{state: stateJSLineCmt, delim: delimDoubleQuote, attr: attrScript},
 		},
 		{
 			"<a onclick='//\n",
-			context{state: stateJS, delim: delimSingleQuote},
+			context{state: stateJS, delim: delimSingleQuote, attr: attrScript},
 		},
 		{
 			"<a onclick='//\r\n",
-			context{state: stateJS, delim: delimSingleQuote},
+			context{state: stateJS, delim: delimSingleQuote, attr: attrScript},
 		},
 		{
 			"<a onclick='//\u2028",
-			context{state: stateJS, delim: delimSingleQuote},
+			context{state: stateJS, delim: delimSingleQuote, attr: attrScript},
 		},
 		{
 			`<a onclick="/*`,
-			context{state: stateJSBlockCmt, delim: delimDoubleQuote},
+			context{state: stateJSBlockCmt, delim: delimDoubleQuote, attr: attrScript},
 		},
 		{
 			`<a onclick="/*/`,
-			context{state: stateJSBlockCmt, delim: delimDoubleQuote},
+			context{state: stateJSBlockCmt, delim: delimDoubleQuote, attr: attrScript},
 		},
 		{
 			`<a onclick="/**/`,
-			context{state: stateJS, delim: delimDoubleQuote},
+			context{state: stateJS, delim: delimDoubleQuote, attr: attrScript},
 		},
 		{
 			`<a onkeypress="&quot;`,
-			context{state: stateJSDqStr, delim: delimDoubleQuote},
+			context{state: stateJSDqStr, delim: delimDoubleQuote, attr: attrScript},
 		},
 		{
 			`<a onclick='&quot;foo&quot;`,
-			context{state: stateJS, delim: delimSingleQuote, jsCtx: jsCtxDivOp},
+			context{state: stateJS, delim: delimSingleQuote, jsCtx: jsCtxDivOp, attr: attrScript},
 		},
 		{
 			`<a onclick=&#39;foo&#39;`,
-			context{state: stateJS, delim: delimSpaceOrTagEnd, jsCtx: jsCtxDivOp},
+			context{state: stateJS, delim: delimSpaceOrTagEnd, jsCtx: jsCtxDivOp, attr: attrScript},
 		},
 		{
 			`<a onclick=&#39;foo`,
-			context{state: stateJSSqStr, delim: delimSpaceOrTagEnd},
+			context{state: stateJSSqStr, delim: delimSpaceOrTagEnd, attr: attrScript},
 		},
 		{
 			`<a onclick="&quot;foo'`,
-			context{state: stateJSDqStr, delim: delimDoubleQuote},
+			context{state: stateJSDqStr, delim: delimDoubleQuote, attr: attrScript},
 		},
 		{
 			`<a onclick="'foo&quot;`,
-			context{state: stateJSSqStr, delim: delimDoubleQuote},
+			context{state: stateJSSqStr, delim: delimDoubleQuote, attr: attrScript},
 		},
 		{
 			`<A ONCLICK="'`,
-			context{state: stateJSSqStr, delim: delimDoubleQuote},
+			context{state: stateJSSqStr, delim: delimDoubleQuote, attr: attrScript},
 		},
 		{
 			`<a onclick="/`,
-			context{state: stateJSRegexp, delim: delimDoubleQuote},
+			context{state: stateJSRegexp, delim: delimDoubleQuote, attr: attrScript},
 		},
 		{
 			`<a onclick="'foo'`,
-			context{state: stateJS, delim: delimDoubleQuote, jsCtx: jsCtxDivOp},
+			context{state: stateJS, delim: delimDoubleQuote, jsCtx: jsCtxDivOp, attr: attrScript},
 		},
 		{
 			`<a onclick="'foo\'`,
-			context{state: stateJSSqStr, delim: delimDoubleQuote},
+			context{state: stateJSSqStr, delim: delimDoubleQuote, attr: attrScript},
 		},
 		{
 			`<a onclick="'foo\'`,
-			context{state: stateJSSqStr, delim: delimDoubleQuote},
+			context{state: stateJSSqStr, delim: delimDoubleQuote, attr: attrScript},
 		},
 		{
 			`<a onclick="/foo/`,
-			context{state: stateJS, delim: delimDoubleQuote, jsCtx: jsCtxDivOp},
+			context{state: stateJS, delim: delimDoubleQuote, jsCtx: jsCtxDivOp, attr: attrScript},
 		},
 		{
 			`<script>/foo/ /=`,
@@ -1222,111 +1222,111 @@ func TestEscapeText(t *testing.T) {
 		},
 		{
 			`<a onclick="1 /foo`,
-			context{state: stateJS, delim: delimDoubleQuote, jsCtx: jsCtxDivOp},
+			context{state: stateJS, delim: delimDoubleQuote, jsCtx: jsCtxDivOp, attr: attrScript},
 		},
 		{
 			`<a onclick="1 /*c*/ /foo`,
-			context{state: stateJS, delim: delimDoubleQuote, jsCtx: jsCtxDivOp},
+			context{state: stateJS, delim: delimDoubleQuote, jsCtx: jsCtxDivOp, attr: attrScript},
 		},
 		{
 			`<a onclick="/foo[/]`,
-			context{state: stateJSRegexp, delim: delimDoubleQuote},
+			context{state: stateJSRegexp, delim: delimDoubleQuote, attr: attrScript},
 		},
 		{
 			`<a onclick="/foo\/`,
-			context{state: stateJSRegexp, delim: delimDoubleQuote},
+			context{state: stateJSRegexp, delim: delimDoubleQuote, attr: attrScript},
 		},
 		{
 			`<a onclick="/foo/`,
-			context{state: stateJS, delim: delimDoubleQuote, jsCtx: jsCtxDivOp},
+			context{state: stateJS, delim: delimDoubleQuote, jsCtx: jsCtxDivOp, attr: attrScript},
 		},
 		{
 			`<input checked style="`,
-			context{state: stateCSS, delim: delimDoubleQuote},
+			context{state: stateCSS, delim: delimDoubleQuote, attr: attrStyle},
 		},
 		{
 			`<a style="//`,
-			context{state: stateCSSLineCmt, delim: delimDoubleQuote},
+			context{state: stateCSSLineCmt, delim: delimDoubleQuote, attr: attrStyle},
 		},
 		{
 			`<a style="//</script>`,
-			context{state: stateCSSLineCmt, delim: delimDoubleQuote},
+			context{state: stateCSSLineCmt, delim: delimDoubleQuote, attr: attrStyle},
 		},
 		{
 			"<a style='//\n",
-			context{state: stateCSS, delim: delimSingleQuote},
+			context{state: stateCSS, delim: delimSingleQuote, attr: attrStyle},
 		},
 		{
 			"<a style='//\r",
-			context{state: stateCSS, delim: delimSingleQuote},
+			context{state: stateCSS, delim: delimSingleQuote, attr: attrStyle},
 		},
 		{
 			`<a style="/*`,
-			context{state: stateCSSBlockCmt, delim: delimDoubleQuote},
+			context{state: stateCSSBlockCmt, delim: delimDoubleQuote, attr: attrStyle},
 		},
 		{
 			`<a style="/*/`,
-			context{state: stateCSSBlockCmt, delim: delimDoubleQuote},
+			context{state: stateCSSBlockCmt, delim: delimDoubleQuote, attr: attrStyle},
 		},
 		{
 			`<a style="/**/`,
-			context{state: stateCSS, delim: delimDoubleQuote},
+			context{state: stateCSS, delim: delimDoubleQuote, attr: attrStyle},
 		},
 		{
 			`<a style="background: '`,
-			context{state: stateCSSSqStr, delim: delimDoubleQuote},
+			context{state: stateCSSSqStr, delim: delimDoubleQuote, attr: attrStyle},
 		},
 		{
 			`<a style="background: &quot;`,
-			context{state: stateCSSDqStr, delim: delimDoubleQuote},
+			context{state: stateCSSDqStr, delim: delimDoubleQuote, attr: attrStyle},
 		},
 		{
 			`<a style="background: '/foo?img=`,
-			context{state: stateCSSSqStr, delim: delimDoubleQuote, urlPart: urlPartQueryOrFrag},
+			context{state: stateCSSSqStr, delim: delimDoubleQuote, urlPart: urlPartQueryOrFrag, attr: attrStyle},
 		},
 		{
 			`<a style="background: '/`,
-			context{state: stateCSSSqStr, delim: delimDoubleQuote, urlPart: urlPartPreQuery},
+			context{state: stateCSSSqStr, delim: delimDoubleQuote, urlPart: urlPartPreQuery, attr: attrStyle},
 		},
 		{
 			`<a style="background: url(&#x22;/`,
-			context{state: stateCSSDqURL, delim: delimDoubleQuote, urlPart: urlPartPreQuery},
+			context{state: stateCSSDqURL, delim: delimDoubleQuote, urlPart: urlPartPreQuery, attr: attrStyle},
 		},
 		{
 			`<a style="background: url('/`,
-			context{state: stateCSSSqURL, delim: delimDoubleQuote, urlPart: urlPartPreQuery},
+			context{state: stateCSSSqURL, delim: delimDoubleQuote, urlPart: urlPartPreQuery, attr: attrStyle},
 		},
 		{
 			`<a style="background: url('/)`,
-			context{state: stateCSSSqURL, delim: delimDoubleQuote, urlPart: urlPartPreQuery},
+			context{state: stateCSSSqURL, delim: delimDoubleQuote, urlPart: urlPartPreQuery, attr: attrStyle},
 		},
 		{
 			`<a style="background: url('/ `,
-			context{state: stateCSSSqURL, delim: delimDoubleQuote, urlPart: urlPartPreQuery},
+			context{state: stateCSSSqURL, delim: delimDoubleQuote, urlPart: urlPartPreQuery, attr: attrStyle},
 		},
 		{
 			`<a style="background: url(/`,
-			context{state: stateCSSURL, delim: delimDoubleQuote, urlPart: urlPartPreQuery},
+			context{state: stateCSSURL, delim: delimDoubleQuote, urlPart: urlPartPreQuery, attr: attrStyle},
 		},
 		{
 			`<a style="background: url( `,
-			context{state: stateCSSURL, delim: delimDoubleQuote},
+			context{state: stateCSSURL, delim: delimDoubleQuote, attr: attrStyle},
 		},
 		{
 			`<a style="background: url( /image?name=`,
-			context{state: stateCSSURL, delim: delimDoubleQuote, urlPart: urlPartQueryOrFrag},
+			context{state: stateCSSURL, delim: delimDoubleQuote, urlPart: urlPartQueryOrFrag, attr: attrStyle},
 		},
 		{
 			`<a style="background: url(x)`,
-			context{state: stateCSS, delim: delimDoubleQuote},
+			context{state: stateCSS, delim: delimDoubleQuote, attr: attrStyle},
 		},
 		{
 			`<a style="background: url('x'`,
-			context{state: stateCSS, delim: delimDoubleQuote},
+			context{state: stateCSS, delim: delimDoubleQuote, attr: attrStyle},
 		},
 		{
 			`<a style="background: url( x `,
-			context{state: stateCSS, delim: delimDoubleQuote},
+			context{state: stateCSS, delim: delimDoubleQuote, attr: attrStyle},
 		},
 		{
 			`<!-- foo`,
@@ -1466,7 +1466,7 @@ func TestEscapeText(t *testing.T) {
 		},
 		{
 			`<a svg:style='`,
-			context{state: stateCSS, delim: delimSingleQuote},
+			context{state: stateCSS, delim: delimSingleQuote, attr: attrStyle},
 		},
 		{
 			`<svg:font-face`,
@@ -1474,7 +1474,11 @@ func TestEscapeText(t *testing.T) {
 		},
 		{
 			`<svg:a svg:onclick="`,
-			context{state: stateJS, delim: delimDoubleQuote},
+			context{state: stateJS, delim: delimDoubleQuote, attr: attrScript},
+		},
+		{
+			`<svg:a svg:onclick="x()">`,
+			context{},
 		},
 	}
 
diff --git a/libgo/go/html/template/example_test.go b/libgo/go/html/template/example_test.go
index 3ea3dca..de7cdbb 100644
--- a/libgo/go/html/template/example_test.go
+++ b/libgo/go/html/template/example_test.go
@@ -11,6 +11,7 @@ import (
 	"html/template"
 	"log"
 	"os"
+	"strings"
 )
 
 func Example() {
@@ -32,6 +33,7 @@ func Example() {
 		}
 	}
 	t, err := template.New("webpage").Parse(tpl)
+	check(err)
 
 	data := struct {
 		Title string
@@ -122,3 +124,38 @@ func Example_escape() {
 	// %22Fran+%26+Freddie%27s+Diner%2232%3Ctasty%40example.com%3E
 
 }
+
+// The following example is duplicated in text/template; keep them in sync.
+
+func ExampleTemplate_block() {
+	const (
+		master  = `Names:{{block "list" .}}{{"\n"}}{{range .}}{{println "-" .}}{{end}}{{end}}`
+		overlay = `{{define "list"}} {{join . ", "}}{{end}} `
+	)
+	var (
+		funcs     = template.FuncMap{"join": strings.Join}
+		guardians = []string{"Gamora", "Groot", "Nebula", "Rocket", "Star-Lord"}
+	)
+	masterTmpl, err := template.New("master").Funcs(funcs).Parse(master)
+	if err != nil {
+		log.Fatal(err)
+	}
+	overlayTmpl, err := template.Must(masterTmpl.Clone()).Parse(overlay)
+	if err != nil {
+		log.Fatal(err)
+	}
+	if err := masterTmpl.Execute(os.Stdout, guardians); err != nil {
+		log.Fatal(err)
+	}
+	if err := overlayTmpl.Execute(os.Stdout, guardians); err != nil {
+		log.Fatal(err)
+	}
+	// Output:
+	// Names:
+	// - Gamora
+	// - Groot
+	// - Nebula
+	// - Rocket
+	// - Star-Lord
+	// Names: Gamora, Groot, Nebula, Rocket, Star-Lord
+}
diff --git a/libgo/go/html/template/template.go b/libgo/go/html/template/template.go
index bb9140a..96ab268 100644
--- a/libgo/go/html/template/template.go
+++ b/libgo/go/html/template/template.go
@@ -17,7 +17,7 @@ import (
 // Template is a specialized Template from "text/template" that produces a safe
 // HTML document fragment.
 type Template struct {
-	// Sticky error if escaping fails.
+	// Sticky error if escaping fails, or escapeOK if succeeded.
 	escapeErr error
 	// 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
@@ -80,7 +80,7 @@ func (t *Template) escape() error {
 	defer t.nameSpace.mu.Unlock()
 	if t.escapeErr == nil {
 		if t.Tree == nil {
-			return fmt.Errorf("template: %q is an incomplete or empty template%s", t.Name(), t.text.DefinedTemplates())
+			return fmt.Errorf("template: %q is an incomplete or empty template%s", t.Name(), t.DefinedTemplates())
 		}
 		if err := escapeTemplate(t, t.text.Root, t.Name()); err != nil {
 			return err
@@ -143,6 +143,13 @@ func (t *Template) lookupAndEscapeTemplate(name string) (tmpl *Template, err err
 	return tmpl, err
 }
 
+// DefinedTemplates returns a string listing the defined templates,
+// prefixed by the string "; defined templates are: ". If there are none,
+// it returns the empty string. Used to generate an error message.
+func (t *Template) DefinedTemplates() string {
+	return t.text.DefinedTemplates()
+}
+
 // Parse parses a string into a template. Nested template definitions
 // will be associated with the top-level template t. Parse may be
 // called multiple times to parse definitions of templates to associate
@@ -169,6 +176,8 @@ func (t *Template) Parse(src string) (*Template, error) {
 		tmpl := t.set[name]
 		if tmpl == nil {
 			tmpl = t.new(name)
+		} else if tmpl.escapeErr != nil {
+			return nil, fmt.Errorf("html/template: cannot redefine %q after it has executed", name)
 		}
 		// Restore our record of this text/template to its unescaped original state.
 		tmpl.escapeErr = nil
@@ -228,6 +237,7 @@ func (t *Template) Clone() (*Template, error) {
 			set: make(map[string]*Template),
 		},
 	}
+	ret.set[ret.Name()] = ret
 	for _, x := range textClone.Templates() {
 		name := x.Name()
 		src := t.set[name]
@@ -413,3 +423,10 @@ func parseGlob(t *Template, pattern string) (*Template, error) {
 	}
 	return parseFiles(t, filenames...)
 }
+
+// IsTrue reports whether the value is 'true', in the sense of not the zero of its type,
+// and whether the value has a meaningful truth value. This is the definition of
+// truth used by if and other such actions.
+func IsTrue(val interface{}) (truth, ok bool) {
+	return template.IsTrue(val)
+}
diff --git a/libgo/go/html/template/template_test.go b/libgo/go/html/template/template_test.go
new file mode 100644
index 0000000..6f70d67
--- /dev/null
+++ b/libgo/go/html/template/template_test.go
@@ -0,0 +1,29 @@
+package template
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestTemplateClone(t *testing.T) {
+	// https://golang.org/issue/12996
+	orig := New("name")
+	clone, err := orig.Clone()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(clone.Templates()) != len(orig.Templates()) {
+		t.Fatalf("Invalid lenth of t.Clone().Templates()")
+	}
+
+	const want = "stuff"
+	parsed := Must(clone.Parse(want))
+	var buf bytes.Buffer
+	err = parsed.Execute(&buf, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := buf.String(); got != want {
+		t.Fatalf("got %q; want %q", got, want)
+	}
+}
diff --git a/libgo/go/html/template/transition.go b/libgo/go/html/template/transition.go
index d2e0287..aefe035 100644
--- a/libgo/go/html/template/transition.go
+++ b/libgo/go/html/template/transition.go
@@ -169,7 +169,7 @@ func tBeforeValue(c context, s []byte) (context, int) {
 	case '"':
 		delim, i = delimDoubleQuote, i+1
 	}
-	c.state, c.delim, c.attr = attrStartStates[c.attr], delim, attrNone
+	c.state, c.delim = attrStartStates[c.attr], delim
 	return c, i
 }