text/template: catch unmatched right delimiter

It was simply a missing error case: when scanning plain text
outside of an action, a right delimiter should be an error.

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/13468045

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

@@ -217,6 +217,10 @@ func lexText(l *lexer) stateFn {
 			}
 			return lexLeftDelim
 		}
+		// Check for right after left in case they're the same.
+		if strings.HasPrefix(l.input[l.pos:], l.rightDelim) {
+			return l.errorf("unmatched right delimiter")
+		}
 		if l.next() == eof {
 			break
 		}

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

@@ -340,6 +340,9 @@ var lexTests = []lexTest{
 		{itemText, 0, "hello-"},
 		{itemError, 0, `comment ends before closing delimiter`},
 	}},
+	{"unmatched right delimiter", "hello-{.}}-world", []item{
+		{itemError, 0, `unmatched right delimiter`},
+	}},
 }
 
 // collect gathers the emitted items into a slice.

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

@@ -312,7 +312,7 @@ var isEmptyTests = []isEmptyTest{
 	{"spaces only", " \t\n \t\n", true},
 	{"definition", `{{define "x"}}something{{end}}`, true},
 	{"definitions and space", "{{define `x`}}something{{end}}\n\n{{define `y`}}something{{end}}\n\n", true},
-	{"definitions and text", "{{define `x`}}something{{end}}\nx\n{{define `y`}}something{{end}}\ny\n}}", false},
+	{"definitions and text", "{{define `x`}}something{{end}}\nx\n{{define `y`}}something{{end}}\ny\n", false},
 	{"definition and action", "{{define `x`}}something{{end}}{{if 3}}foo{{end}}", false},
 }