Fix formatting failure when whitespace-only line exists between single-line comments

internal/format/bug_test.go

@@ -0,0 +1,45 @@
+package format_test
+
+import (
+	"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/ls/lsutil"
+	"github.com/microsoft/typescript-go/internal/parser"
+	"gotest.tools/v3/assert"
+)
+
+func TestFormatWhitespaceBetweenComments(t *testing.T) {
+	t.Parallel()
+	// Regression test: whitespace-only line between two single-line comments
+	// should not cause overlapping/duplicate edits that break formatting.
+	text := "  const x = \"wont format\"\n//\n \n//\n"
+	ctx := format.WithFormatCodeSettings(t.Context(), lsutil.FormatCodeSettings{
+		EditorSettings: lsutil.EditorSettings{
+			TabSize:                4,
+			IndentSize:             4,
+			NewLineCharacter:       "\n",
+			ConvertTabsToSpaces:    core.TSTrue,
+			IndentStyle:            lsutil.IndentStyleSmart,
+			TrimTrailingWhitespace: core.TSTrue,
+		},
+	}, "\n")
+	sourceFile := parser.ParseSourceFile(ast.SourceFileParseOptions{
+		FileName: "/test.ts",
+		Path:     "/test.ts",
+	}, text, core.ScriptKindTS)
+	edits := format.FormatDocument(ctx, sourceFile)
+
+	// Verify no overlapping or duplicate edits
+	for i := 1; i < len(edits); i++ {
+		assert.Assert(t, edits[i].Pos() >= edits[i-1].End(),
+			"Overlapping edits: edit %d [%d,%d) overlaps with edit %d [%d,%d)",
+			i-1, edits[i-1].Pos(), edits[i-1].End(), i, edits[i].Pos(), edits[i].End())
+	}
+
+	// Verify edits can be applied without error
+	result := applyBulkEdits(text, edits)
+	assert.Assert(t, len(result) > 0)
+}

internal/format/span.go

@@ -795,7 +795,9 @@ func (w *formatSpanWorker) trimTrailingWhitespacesForRemainingRange(trivias []Te
 				w.trimTrailingWitespacesForPositions(startPos, trivia.Loc.Pos()-1, w.previousRange)
 			}
 
-			startPos = trivia.Loc.End() + 1
+			if trivia.Loc.End()+1 > startPos {
+				startPos = trivia.Loc.End() + 1
+			}
 		}
 	}
 

internal/fourslash/tests/formatWhitespaceBetweenComments_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 TestFormatWhitespaceBetweenComments(t *testing.T) {
+	t.Parallel()
+	defer testutil.RecoverAndFail(t, "Panic on fourslash test")
+	const content = `  const x = "wont format"
+//
+
+//
+`
+	f, done := fourslash.NewFourslash(t, nil /*capabilities*/, content)
+	defer done()
+	f.FormatDocument(t, "")
+	f.VerifyCurrentFileContent(t, `const x = "wont format"
+//
+
+//
+`)
+}