BUGFIX: Repeated use of optional rules tripped up the simplifier, manifesting when aliases were used (Issue #197)

lark/load_grammar.py

@@ -235,6 +235,7 @@ class SimplifyRule_Visitor(Visitor):
                 tree.children = [self.visit(ST('expansion', [option if i==j else other
                                                             for j, other in enumerate(tree.children)]))
                                     for option in set(child.children)]
+                self._flatten(tree)
                 break
 
     def alias(self, tree):

tests/test_parser.py

@@ -148,6 +148,9 @@ class TestParsers(unittest.TestCase):
         self.assertEqual( r.children, ["<c>"] )
 
 
+    def test_alias(self):
+        Lark("""start: ["a"] "b" ["c"] "e" ["f"] ["g"] ["h"] "x" -> d """)
+
 
 
 def _make_full_earley_test(LEXER):