Fix comment formatting bug that mangled */ tokens (#1401)

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: jakebailey <[email protected]>
Co-authored-by: DanielRosenwasser <[email protected]>
Co-authored-by: weswigham <[email protected]>

Author: 4 people

internal/format/comment_test.go

@@ -0,0 +1,71 @@
+package format_test
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/microsoft/typescript-go/internal/ast"
+	"github.com/microsoft/typescript-go/internal/core"
+	"github.com/microsoft/typescript-go/internal/format"
+	"github.com/microsoft/typescript-go/internal/parser"
+	"gotest.tools/v3/assert"
+)
+
+func TestCommentFormatting(t *testing.T) {
+	t.Parallel()
+
+	t.Run("format comment issue reproduction", 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")
+
+		// Original code that causes the bug
+		originalText := `class C {
+    /**
+     *
+    */
+    async x() {}
+}`
+
+		sourceFile := parser.ParseSourceFile(ast.SourceFileParseOptions{
+			FileName: "/test.ts",
+			Path:     "/test.ts",
+		}, originalText, core.ScriptKindTS)
+
+		// Apply formatting once
+		edits := format.FormatDocument(ctx, sourceFile)
+		firstFormatted := applyBulkEdits(originalText, edits)
+
+		// Check that the asterisk is not corrupted
+		assert.Check(t, !contains(firstFormatted, "*/\n   /"), "should not corrupt */ to /")
+		assert.Check(t, contains(firstFormatted, "*/"), "should preserve */ token")
+		assert.Check(t, contains(firstFormatted, "async"), "should preserve async keyword")
+
+		// Apply formatting a second time to test stability
+		sourceFile2 := parser.ParseSourceFile(ast.SourceFileParseOptions{
+			FileName: "/test.ts",
+			Path:     "/test.ts",
+		}, firstFormatted, core.ScriptKindTS)
+
+		edits2 := format.FormatDocument(ctx, sourceFile2)
+		secondFormatted := applyBulkEdits(firstFormatted, edits2)
+
+		// Check that second formatting doesn't introduce corruption
+		assert.Check(t, !contains(secondFormatted, " sync x()"), "should not corrupt async to sync")
+		assert.Check(t, contains(secondFormatted, "async"), "should preserve async keyword on second pass")
+	})
+}
+
+func contains(s, substr string) bool {
+	return len(substr) > 0 && strings.Contains(s, substr)
+}

internal/format/span.go

@@ -922,7 +922,7 @@ func (w *formatSpanWorker) indentMultilineComment(commentRange core.TextRange, i
 	for line := startLine; line < endLine; line++ {
 		endOfLine := scanner.GetEndLinePosition(w.sourceFile, line)
 		parts = append(parts, core.NewTextRange(startPos, endOfLine))
-		startPos = int(scanner.GetLineStarts(w.sourceFile)[line])
+		startPos = int(scanner.GetLineStarts(w.sourceFile)[line+1])
 	}
 
 	if indentFinalLine {