IDL parser: fix rebuilding of (stale) cached parser tables

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 362 matching lines @@
             return ls[1].value
 
         if len(p) > 3:
             p[0] = unwrap_string(p[1]) + p[2] + p[3]
         else:
             p[0] = unwrap_string(p[1])
 
     def __init__(self,
                  # common parameters
                  debug=False,
+                 # local parameters
+                 rewrite_tables=False,
                  # idl_parser parameters
                  lexer=None, verbose=False, mute_error=False,
                  # yacc parameters
                  outputdir='', optimize=True, write_tables=False,
                  picklefile=None):
         if debug:
             # Turn off optimization and caching, and write out tables,
             # to help debugging
             optimize = False
             outputdir = None
             picklefile = None
             write_tables = True
         if outputdir:
             picklefile = picklefile or os.path.join(outputdir, 'parsetab.pickle')
+            if rewrite_tables:
+                try:
+                    os.unlink(picklefile)
+                except OSError:
+                    pass
 
         lexer = lexer or BlinkIDLLexer(debug=debug,
                                        outputdir=outputdir,
                                        optimize=optimize)
         self.lexer = lexer
         self.tokens = lexer.KnownTokens()
         # Using SLR (instead of LALR) generates the table faster,
         # but produces the same output. This is ok b/c Web IDL (and Blink IDL)
         # is an SLR grammar (as is often the case for simple LL(1) grammars).
         #
@@ skipping 25 matching lines @@
 
 ################################################################################
 
 def main(argv):
     # If file itself executed, cache parse table
     try:
         outputdir = argv[1]
     except IndexError as err:
         print 'Usage: %s OUTPUT_DIR' % argv[0]
         return 1
-    parser = BlinkIDLParser(outputdir=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))