bindings/scripts/blink_idl_lexer.py

# Copyright (C) 2013 Google Inc. All rights reserved.
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"""Lexer for Blink IDL.

The lexer uses the PLY (Python Lex-Yacc) library to build a tokenizer which
understands the Blink dialect of Web IDL and produces a token stream suitable
for the Blink IDL parser.

Blink IDL is identical to Web IDL at the token level, but the base lexer
does not discard comments. We need to override (and not include comments in
the token stream), as otherwise comments must be explicitly included in the
phrase grammar of the parser.

FIXME: Change base lexer to discard comments, and simply used the base
lexer, eliminating this separate lexer.

Web IDL:
    http://www.w3.org/TR/WebIDL/
Web IDL Grammar:
    http://www.w3.org/TR/WebIDL/#idl-grammar
PLY:
    http://www.dabeaz.com/ply/

Design doc:
http://www.chromium.org/developers/design-documents/idl-compiler#TOC-Front-end
"""

# Disable attribute validation, as lint can't import parent class to check
# pylint: disable=E1101

import os.path
import sys

# PLY is in Chromium src/third_party/ply
module_path, module_name = os.path.split(__file__)
third_party = os.path.join(module_path, os.pardir, os.pardir, os.pardir, os.pardir)
# Insert at front to override system libraries, and after path[0] == script dir
sys.path.insert(1, third_party)
from ply import lex

# Base lexer is in Chromium src/tools/idl_parser
tools_dir = os.path.join(third_party, os.pardir, 'tools')
sys.path.append(tools_dir)
from idl_parser.idl_lexer import IDLLexer

LEXTAB = 'lextab'


class BlinkIDLLexer(IDLLexer):
    def __init__(self, debug=False, optimize=True, outputdir=None,
                 rewrite_tables=False):
        if debug:
            # Turn off optimization and caching to help debugging
            optimize = False
            outputdir = None
        if outputdir:
            # Need outputdir in path because lex imports the cached lex table
            # as a Python module
            sys.path.append(outputdir)

            if rewrite_tables:
                tablefile_root = os.path.join(outputdir, LEXTAB)
                # Also remove the .pyc/.pyo files, or they'll be used even if
                # the .py file doesn't exist.
                for ext in ('.py', '.pyc', '.pyo'):
                    try:
                        os.unlink(tablefile_root + ext)
                    except OSError:
                        pass

            lextab = LEXTAB
        else:
            lextab = None

        IDLLexer.__init__(self)
        # Optimized mode substantially decreases startup time (by disabling
        # error checking), and also allows use of Python's optimized mode.
        # See: Optimized Mode
        # http://www.dabeaz.com/ply/ply.html#ply_nn15
        self._lexobj = lex.lex(object=self,
                               debug=debug,
                               optimize=optimize,
                               lextab=lextab,
                               outputdir=outputdir)


################################################################################

def main(argv):
    # If file itself executed, build and cache lex table
    try:
        outputdir = argv[1]
    except IndexError as err:
        print 'Usage: %s OUTPUT_DIR' % argv[0]
        return 1
    # 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.
    lexer = BlinkIDLLexer(outputdir=outputdir, rewrite_tables=True)


if __name__ == '__main__':
    sys.exit(main(sys.argv))