text/template/parse: fix data race on lexer initialization

Before this change, `startParse` would write `lex.breakOK` and `lex.continueOK` when the lexer goroutine is already running, which is a potential race condition.

Makes `breakOK` and `continueOK` configuration flags passed when `lexer` is created, similarly to how `emitComment` works.

Fixes #53234

Change-Id: Ia65f6135509a758cd4c5a453b249a174f4fb3e21
Reviewed-on: https://go-review.googlesource.com/c/go/+/410414
Reviewed-by: Eli Bendersky <eliben@google.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>

src/text/template/parse/lex.go

@@ -211,7 +211,7 @@ func (l *lexer) drain() {
 }
 
 // lex creates a new scanner for the input string.
-func lex(name, input, left, right string, emitComment bool) *lexer {
+func lex(name, input, left, right string, emitComment, breakOK, continueOK bool) *lexer {
 	if left == "" {
 		left = leftDelim
 	}
@@ -224,6 +224,8 @@ func lex(name, input, left, right string, emitComment bool) *lexer {
 		leftDelim:   left,
 		rightDelim:  right,
 		emitComment: emitComment,
+		breakOK:     breakOK,
+		continueOK:  continueOK,
 		items:       make(chan item),
 		line:        1,
 		startLine:   1,

src/text/template/parse/lex_test.go

@@ -394,7 +394,7 @@ var lexTests = []lexTest{
 
 // collect gathers the emitted items into a slice.
 func collect(t *lexTest, left, right string) (items []item) {
-	l := lex(t.name, t.input, left, right, true)
+	l := lex(t.name, t.input, left, right, true, true, true)
 	for {
 		item := l.nextItem()
 		items = append(items, item)
@@ -550,7 +550,7 @@ func TestPos(t *testing.T) {
 func TestShutdown(t *testing.T) {
 	// We need to duplicate template.Parse here to hold on to the lexer.
 	const text = "erroneous{{define}}{{else}}1234"
-	lexer := lex("foo", text, "{{", "}}", false)
+	lexer := lex("foo", text, "{{", "}}", false, true, true)
 	_, err := New("root").parseLexer(lexer)
 	if err == nil {
 		t.Fatalf("expected error")

src/text/template/parse/parse.go

@@ -224,8 +224,6 @@ func (t *Tree) startParse(funcs []map[string]any, lex *lexer, treeSet map[string
 	t.vars = []string{"$"}
 	t.funcs = funcs
 	t.treeSet = treeSet
-	lex.breakOK = !t.hasFunction("break")
-	lex.continueOK = !t.hasFunction("continue")
 }
 
 // stopParse terminates parsing.
@@ -244,7 +242,10 @@ func (t *Tree) Parse(text, leftDelim, rightDelim string, treeSet map[string]*Tre
 	defer t.recover(&err)
 	t.ParseName = t.Name
 	emitComment := t.Mode&ParseComments != 0
-	t.startParse(funcs, lex(t.Name, text, leftDelim, rightDelim, emitComment), treeSet)
+	breakOK := !t.hasFunction("break")
+	continueOK := !t.hasFunction("continue")
+	lexer := lex(t.Name, text, leftDelim, rightDelim, emitComment, breakOK, continueOK)
+	t.startParse(funcs, lexer, treeSet)
 	t.text = text
 	t.parse()
 	t.add()