fix(3700): fix index out of range panic when emitting whitespace-only jsx text (#3707)

Author: a-tarasyuk

internal/fourslash/tests/codeFixMissingTypeAnnotationOnExports_jsxWhitespaceText_test.go

@@ -0,0 +1,26 @@
+package fourslash_test
+
+import (
+	"testing"
+
+	"github.com/microsoft/typescript-go/internal/fourslash"
+	"github.com/microsoft/typescript-go/internal/testutil"
+)
+
+func TestCodeFixMissingTypeAnnotationOnExports_jsxWhitespaceText(t *testing.T) {
+	t.Parallel()
+	defer testutil.RecoverAndFail(t, "Panic on fourslash test")
+
+	const content = `// @isolatedDeclarations: true
+// @declaration: true
+// @module: preserve
+// @Filename: /test.tsx
+export const /**/elem = <div>
+    <span />
+</div>;`
+	f, done := fourslash.NewFourslash(t, nil /*capabilities*/, content)
+	defer done()
+
+	f.GoToMarker(t, "")
+	f.VerifyCodeFixAvailable(t, nil)
+}

internal/printer/changetrackerwriter.go

@@ -88,12 +88,11 @@ func (ct *ChangeTrackerWriter) getEnd(node triviaPositionKey) int {
 func (ct *ChangeTrackerWriter) setLastNonTriviaPosition(s string, force bool) {
 	if force || scanner.SkipTrivia(s, 0) != len(s) {
 		ct.lastNonTriviaPosition = ct.textWriter.GetTextPos()
-		i := 0
-		for stringutil.IsWhiteSpaceLike(rune(s[len(s)-i-1])) {
-			i++
-		}
 		// trim trailing whitespaces
-		ct.lastNonTriviaPosition -= i
+		pos := len(s) - 1
+		for ; pos >= 0 && stringutil.IsWhiteSpaceLike(rune(s[pos])); pos-- {
+		}
+		ct.lastNonTriviaPosition -= len(s) - 1 - pos
 	}
 }