Fix panic in textDocument/formatting with slice bounds out of range

internal/format/comment_test.go

@@ -106,3 +106,42 @@ func TestCommentFormatting(t *testing.T) {
 func contains(s, substr string) bool {
 	return len(substr) > 0 && strings.Contains(s, substr)
 }
+
+func TestSliceBoundsPanic(t *testing.T) {
+	t.Parallel()
+
+	t.Run("format code with trailing semicolon should not panic", func(t *testing.T) {
+		t.Parallel()
+		ctx := format.WithFormatCodeSettings(t.Context(), &format.FormatCodeSettings{
+			EditorSettings: format.EditorSettings{
+				TabSize:                4,
+				IndentSize:             4,
+				BaseIndentSize:         4,
+				NewLineCharacter:       "\n",
+				ConvertTabsToSpaces:    true,
+				IndentStyle:            format.IndentStyleSmart,
+				TrimTrailingWhitespace: true,
+			},
+			InsertSpaceBeforeTypeAnnotation: core.TSTrue,
+		}, "\n")
+
+		// Code from the issue that causes slice bounds panic
+		originalText := `const _enableDisposeWithListenerWarning = false
+	// || Boolean("TRUE") // causes a linter warning so that it cannot be pushed
+	;
+`
+
+		sourceFile := parser.ParseSourceFile(ast.SourceFileParseOptions{
+			FileName: "/test.ts",
+			Path:     "/test.ts",
+		}, originalText, core.ScriptKindTS)
+
+		// This should not panic
+		edits := format.FormatDocument(ctx, sourceFile)
+		formatted := applyBulkEdits(originalText, edits)
+
+		// Basic sanity checks
+		assert.Check(t, len(formatted) > 0, "formatted text should not be empty")
+		assert.Check(t, contains(formatted, "_enableDisposeWithListenerWarning"), "should preserve variable name")
+	})
+}

internal/format/span.go

@@ -883,7 +883,12 @@ func (w *formatSpanWorker) characterToColumn(startLinePosition int, characterInL
 }
 
 func (w *formatSpanWorker) indentationIsDifferent(indentationString string, startLinePosition int) bool {
-	return indentationString != w.sourceFile.Text()[startLinePosition:startLinePosition+len(indentationString)]
+	// Check bounds to prevent slice panic
+	endPosition := startLinePosition + len(indentationString)
+	if endPosition > len(w.sourceFile.Text()) {
+		return true
+	}
+	return indentationString != w.sourceFile.Text()[startLinePosition:endPosition]
 }
 
 func (w *formatSpanWorker) indentTriviaItems(trivia []TextRangeWithKind, commentIndentation int, indentNextTokenOrTrivia bool, indentSingleLine func(item TextRangeWithKind)) bool {
@@ -969,6 +974,12 @@ func (w *formatSpanWorker) indentMultilineComment(commentRange core.TextRange, i
 }
 
 func getIndentationString(indentation int, options *FormatCodeSettings) string {
+	// Handle negative indentation (e.g., Constants.Unknown = -1)
+	// Return empty string like TypeScript's repeatString does when count is negative
+	if indentation < 0 {
+		return ""
+	}
+
 	// go's `strings.Repeat` already has static, global caching for repeated tabs and spaces, so there's no need to cache here like in strada
 	if !options.ConvertTabsToSpaces {
 		tabs := int(math.Floor(float64(indentation) / float64(options.TabSize)))