text/template: allow using -}} with many spaces

lexSpace consumed all spaces, even if the last one was part of a right
delimiter like " -}}". Thus, "3  -}}" wouldn't lex as "3" and a right
delimiter, but as "3", "-", and "}}".

To fix that, make lexSpace stop if it encounters a right delimiter.

Fixes #30948.

Change-Id: I80a5546e5809e54f6823e2bf3a57a7e8808329be
Reviewed-on: https://go-review.googlesource.com/c/go/+/168457Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

src/text/template/parse/lex.go

@@ -107,17 +107,18 @@ type stateFn func(*lexer) stateFn
 
 // lexer holds the state of the scanner.
 type lexer struct {
-	name       string    // the name of the input; used only for error reports
-	input      string    // the string being scanned
-	leftDelim  string    // start of action
-	rightDelim string    // end of action
-	pos        Pos       // current position in the input
-	start      Pos       // start position of this item
-	width      Pos       // width of last rune read from input
-	items      chan item // channel of scanned items
-	parenDepth int       // nesting depth of ( ) exprs
-	line       int       // 1+number of newlines seen
-	startLine  int       // start line of this item
+	name           string    // the name of the input; used only for error reports
+	input          string    // the string being scanned
+	leftDelim      string    // start of action
+	rightDelim     string    // end of action
+	trimRightDelim string    // end of action with trim marker
+	pos            Pos       // current position in the input
+	start          Pos       // start position of this item
+	width          Pos       // width of last rune read from input
+	items          chan item // channel of scanned items
+	parenDepth     int       // nesting depth of ( ) exprs
+	line           int       // 1+number of newlines seen
+	startLine      int       // start line of this item
 }
 
 // next returns the next rune in the input.
@@ -210,13 +211,14 @@ func lex(name, input, left, right string) *lexer {
 		right = rightDelim
 	}
 	l := &lexer{
-		name:       name,
-		input:      input,
-		leftDelim:  left,
-		rightDelim: right,
-		items:      make(chan item),
-		line:       1,
-		startLine:  1,
+		name:           name,
+		input:          input,
+		leftDelim:      left,
+		rightDelim:     right,
+		trimRightDelim: rightTrimMarker + right,
+		items:          make(chan item),
+		line:           1,
+		startLine:      1,
 	}
 	go l.run()
 	return l
@@ -275,14 +277,12 @@ func rightTrimLength(s string) Pos {
 
 // atRightDelim reports whether the lexer is at a right delimiter, possibly preceded by a trim marker.
 func (l *lexer) atRightDelim() (delim, trimSpaces bool) {
-	if strings.HasPrefix(l.input[l.pos:], l.rightDelim) {
-		return true, false
-	}
-	// The right delim might have the marker before.
-	if strings.HasPrefix(l.input[l.pos:], rightTrimMarker) &&
-		strings.HasPrefix(l.input[l.pos+trimMarkerLen:], l.rightDelim) {
+	if strings.HasPrefix(l.input[l.pos:], l.trimRightDelim) { // With trim marker.
 		return true, true
 	}
+	if strings.HasPrefix(l.input[l.pos:], l.rightDelim) { // Without trim marker.
+		return true, false
+	}
 	return false, false
 }
 
@@ -366,6 +366,7 @@ func lexInsideAction(l *lexer) stateFn {
 	case r == eof || isEndOfLine(r):
 		return l.errorf("unclosed action")
 	case isSpace(r):
+		l.backup() // Put space back in case we have " -}}".
 		return lexSpace
 	case r == '=':
 		l.emit(itemAssign)
@@ -418,10 +419,26 @@ func lexInsideAction(l *lexer) stateFn {
 }
 
 // lexSpace scans a run of space characters.
-// One space has already been seen.
+// We have not consumed the first space, which is known to be present.
+// Take care if there is a trim-marked right delimiter, which starts with a space.
 func lexSpace(l *lexer) stateFn {
-	for isSpace(l.peek()) {
+	var r rune
+	var numSpaces int
+	for {
+		r = l.peek()
+		if !isSpace(r) {
+			break
+		}
 		l.next()
+		numSpaces++
+	}
+	// Be careful about a trim-marked closing delimiter, which has a minus
+	// after a space. We know there is a space, so check for the '-' that might follow.
+	if strings.HasPrefix(l.input[l.pos-1:], l.trimRightDelim) {
+		l.backup() // Before the space.
+		if numSpaces == 1 {
+			return lexRightDelim // On the delim, so go right to that.
+		}
 	}
 	l.emit(itemSpace)
 	return lexInsideAction

src/text/template/parse/parse_test.go

@@ -244,6 +244,7 @@ var parseTests = []parseTest{
 	{"trim left", "x \r\n\t{{- 3}}", noError, `"x"{{3}}`},
 	{"trim right", "{{3 -}}\n\n\ty", noError, `{{3}}"y"`},
 	{"trim left and right", "x \r\n\t{{- 3 -}}\n\n\ty", noError, `"x"{{3}}"y"`},
+	{"trim with extra spaces", "x\n{{-  3   -}}\ny", noError, `"x"{{3}}"y"`},
 	{"comment trim left", "x \r\n\t{{- /* hi */}}", noError, `"x"`},
 	{"comment trim right", "{{/* hi */ -}}\n\n\ty", noError, `"y"`},
 	{"comment trim left and right", "x \r\n\t{{- /* */ -}}\n\n\ty", noError, `"x""y"`},