fix(lexer): treat trailing CR as line end so comment text is idempotent

Assisted-by: GLM 5.3 Flash

lexer/lexer_test.go

@@ -85,6 +85,19 @@ func TestLabelAndComment(t *testing.T) {
 		[]token.Kind{token.Ident, token.Colon, token.Ident, token.Ident, token.Comment})
 }
 
+func TestLineCommentTrailingWhitespace(t *testing.T) {
+	// A trailing run of CR, spaces and tabs is line-ending whitespace, not
+	// comment content.  The token text must not depend on what follows the
+	// comment: before the trim covered only a CR directly before the token's
+	// end, "// loop\r " kept the CR while "// loop\r\n" dropped it, and the
+	// formatter re-lexed its own output to a shorter comment.
+	eq(t, texts("// loop\r"), []string{"// loop"})
+	eq(t, texts("// loop\r "), []string{"// loop"})
+	eq(t, texts("// loop \r\t\nMOVQ AX, BX"), []string{"// loop", "MOVQ", "AX", ",", "BX"})
+	// A CR inside the comment is content and stays.
+	eq(t, texts("// loops\rall"), []string{"// loops\rall"})
+}
+
 func TestAVX512Mnemonics(t *testing.T) {
 	eq(t, texts("VFMADD231PD Z14, Z12, Z10"),
 		[]string{"VFMADD231PD", "Z14", ",", "Z12", ",", "Z10"})