Support for labels with no statement (#562)

* Add possibility to omit semicolon in labeled statement

* Add extra rule to properly parse semicolons so that the ASTs remain equal. Add test corroborating equality of ASTs

* Remove unnecesary rule for labeled statements

* Update label test to check the structure of the AST

---------

Co-authored-by: Ignacio Tiraboschi <ignacio.tiraboschi@eclypsium.com>

pycparser/c_parser.py

@@ -1580,6 +1580,10 @@ def p_labeled_statement_3(self, p):
         """ labeled_statement : DEFAULT COLON pragmacomp_or_statement """
         p[0] = c_ast.Default([p[3]], self._token_coord(p, 1))
 
+    def p_labeled_statement_4(self, p):
+        """ labeled_statement : ID COLON """
+        p[0] = c_ast.Label(p[1], c_ast.EmptyStatement(self._token_coord(p, 1)), self._token_coord(p, 1))
+
     def p_selection_statement_1(self, p):
         """ selection_statement : IF LPAREN expression RPAREN pragmacomp_or_statement """
         p[0] = c_ast.If(p[3], p[5], None, self._token_coord(p, 1))

tests/test_c_parser.py

@@ -2489,6 +2489,20 @@ def test_samescope_reuse_name(self):
             '''
         self.assertRaises(ParseError, self.parse, s2)
 
+    def test_label_empty_statement(self):
+        # Labels with empty statements and no semicolon should be parsed correctly
+        s1 = r'''
+            int main() {
+                int i = 0;
+                label0: i++;
+                label1:
+            }
+            '''
+        s1_ast : FileAST = self.parse(s1)
+        self.assertIsInstance(s1_ast.ext[0].body.block_items[1], Label)
+        self.assertIsInstance(s1_ast.ext[0].body.block_items[1].stmt, UnaryOp)
+        self.assertIsInstance(s1_ast.ext[0].body.block_items[2], Label)
+        self.assertIsInstance(s1_ast.ext[0].body.block_items[2].stmt, EmptyStatement)
 
 if __name__ == '__main__':
     #~ suite = unittest.TestLoader().loadTestsFromNames(