text/template/parse: fix bug handling /*/

Incorrect syntax for comment was erroneously accepted.
Fixes #3919.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6453105

src/pkg/text/template/parse/lex.go

@@ -264,16 +264,17 @@ func lexText(l *lexer) stateFn {
 
 // lexLeftDelim scans the left delimiter, which is known to be present.
 func lexLeftDelim(l *lexer) stateFn {
-	if strings.HasPrefix(l.input[l.pos:], l.leftDelim+leftComment) {
+	l.pos += len(l.leftDelim)
+	if strings.HasPrefix(l.input[l.pos:], leftComment) {
 		return lexComment
 	}
-	l.pos += len(l.leftDelim)
 	l.emit(itemLeftDelim)
 	return lexInsideAction
 }
 
 // lexComment scans a comment. The left comment marker is known to be present.
 func lexComment(l *lexer) stateFn {
+	l.pos += len(leftComment)
 	i := strings.Index(l.input[l.pos:], rightComment+l.rightDelim)
 	if i < 0 {
 		return l.errorf("unclosed comment")

src/pkg/text/template/parse/lex_test.go

@@ -203,6 +203,10 @@ var lexTests = []lexTest{
 		tRight,
 		tEOF,
 	}},
+	{"text with bad comment", "hello-{{/*/}}-world", []item{
+		{itemText, 0, "hello-"},
+		{itemError, 0, `unclosed comment`},
+	}},
 }
 
 // collect gathers the emitted items into a slice.