Experimental parser: add tests for subgraph handling.

tools/lexer_generator/automaton.py

 # Copyright 2013 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 161 matching lines @@
 
   def matches(self, string):
     valid_states = self.start_set()
     for c in string:
       valid_states = Automaton.__transition_states_for_char(valid_states, c)
       if not valid_states:
         return False
     valid_states = self.epsilon_closure(valid_states)
     return len(self.terminal_set().intersection(valid_states)) > 0
 
-  def lex(self, string):
+  def lex(self, string, default_action):
     last_position = 0
     valid_states = self.start_set()
     for pos, c in enumerate(string):
       transitions = Automaton.__transition_states_for_char(valid_states, c)
       if transitions:
         valid_states = transitions
         continue
       action = Action.dominant_action(valid_states)
-      assert action # must invoke default action here
+      if not action:
+        assert default_action
+        action = default_action
       yield (action, last_position, pos)
       last_position = pos
       # lex next token
       valid_states = Automaton.__transition_states_for_char(self.start_set(), c)
       assert valid_states
     valid_states = self.epsilon_closure(valid_states)
     action = Action.dominant_action(valid_states)
-    assert action # must invoke default action here
+    if not action:
+      assert default_action
+      action = default_action
     yield (action, last_position, len(string))
 
   def to_dot(self):
 
     def escape(v):
       v = str(v)
       v = v.replace('\r', '\\\\r').replace('\t', '\\\\t').replace('\n', '\\\\n')
       v = v.replace('\\', '\\\\').replace('\"', '\\\"')
       return v
 
@@ skipping 33 matching lines @@
   node [shape = doublecircle, style=unfilled]; %s
   node [shape = circle];
 %s
 %s
 }
     ''' % (start_shape,
            start_number,
            " ".join(terminals),
            "\n".join(edge_content),
            "\n".join(node_content))