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

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"
+//
+
+//
+`)
+}