IDL: Make caching lex table robust

Source/bindings/scripts/blink_idl_parser.py

 # Copyright (C) 2013 Google Inc. 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
@@ skipping 77 matching lines @@
                  'Comments',  # [0.1]
                  'CommentsRest',  # [0.2]
                 ]
 
 # Remove rules from base class
 # FIXME: add a class method upstream: @classmethod IDLParser._RemoveRules
 for rule in REMOVED_RULES:
     production_name = 'p_' + rule
     delattr(IDLParser, production_name)
 
+# The base name of cached lexer table generated by BlinkIDLLexer
+LEX_TABLE_BASENAME = 'lextab'
+
+
+def remove_cached_lex_table(outputdir):
+    table_files = [
+        os.path.join(outputdir, '%s.py' % LEX_TABLE_BASENAME),
+        os.path.join(outputdir, '%s.pyc' % LEX_TABLE_BASENAME),
+    ]
+    for table_file in table_files:
+        if os.path.exists(table_file):
+            os.unlink(table_file)
+
 
 class BlinkIDLParser(IDLParser):
     # [1]
     # FIXME: Need to duplicate rule for starting symbol here, with line number
     # *lower* than in the base parser (idl_parser.py).
     # This is a bug in PLY: it determines starting symbol by lowest line number.
     # This can be overridden by the 'start' parameter, but as of PLY 3.4 this
     # doesn't work correctly.
     def p_Definitions(self, p):
         """Definitions : ExtendedAttributeList Definition Definitions
@@ skipping 325 matching lines @@
         self._parse_errors = 0
         self._parse_warnings = 0
         self._last_error_msg = None
         self._last_error_lineno = 0
         self._last_error_pos = 0
 
 
 ################################################################################
 
 def main(argv):
-    # If file itself executed, cache parse table
+    # If file itself executed, cache parse table. Caching the parse table
+    # also caches lex table. Before caching these tables, we remove the
+    # previous cached lex table if exists so that the build system can keep
+    # track of dependencies. See http://crbug.com/397909
     try:
         outputdir = argv[1]
     except IndexError as err:
         print 'Usage: %s OUTPUT_DIR' % argv[0]
         return 1
+    remove_cached_lex_table(outputdir)
     # Important: rewrite_tables=True causes the cache file to be deleted if it
     # exists, thus making sure that PLY doesn't load it instead of regenerating
     # the parse table.
     parser = BlinkIDLParser(outputdir=outputdir, rewrite_tables=True)
 
 
 if __name__ == '__main__':
     sys.exit(main(sys.argv))