text/template/parse: fix confusion about markers near right delims

Fixes #52527.
Fixes #55336.

Change-Id: I8f5c521c693e74451a558788909e7e4ad1cc797a
Reviewed-on: https://go-review.googlesource.com/c/go/+/433036
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

Author: rsc

src/text/template/parse/lex.go

@@ -369,7 +369,7 @@ func lexComment(l *lexer) stateFn {
 
 // lexRightDelim scans the right delimiter, which is known to be present, possibly with a trim marker.
 func lexRightDelim(l *lexer) stateFn {
-	trimSpace := hasRightTrimMarker(l.input[l.pos:])
+	_, trimSpace := l.atRightDelim()
 	if trimSpace {
 		l.pos += trimMarkerLen
 		l.ignore()

src/text/template/parse/lex_test.go

@@ -491,6 +491,23 @@ func TestDelimsAlphaNumeric(t *testing.T) {
 	}
 }
 
+func TestDelimsAndMarkers(t *testing.T) {
+	test := lexTest{"delims that look like markers", "{{- .x -}} {{- - .x - -}}", []item{
+		mkItem(itemLeftDelim, "{{- "),
+		mkItem(itemField, ".x"),
+		mkItem(itemRightDelim, " -}}"),
+		mkItem(itemLeftDelim, "{{- "),
+		mkItem(itemField, ".x"),
+		mkItem(itemRightDelim, " -}}"),
+		tEOF,
+	}}
+	items := collect(&test, "{{- ", " -}}")
+
+	if !equal(items, test.items, false) {
+		t.Errorf("%s: got\n\t%v\nexpected\n\t%v", test.name, items, test.items)
+	}
+}
+
 var lexPosTests = []lexTest{
 	{"empty", "", []item{{itemEOF, 0, "", 1}}},
 	{"punctuation", "{{,@%#}}", []item{