Fix interaction between typing_extensions and collections.abc

[ilevkivskyi]

Fixes #501

The idea is straightforward: special classes in typing_extensions that have __extra__ should use a metaclass that fixes the problem in GenericMeta.__subclasscheck__ on older versions of typing.

Note that overriding __subclasscheck__ tries to mimic the behaviour in the new versions of typing. (I can't just use super().__subclasscheck__ on unaffected versions, since this changes call stack depth and therefore breaks a sys._getframe hack on some other versions of typing.)

@jabdoa2 Could you please check that this fixes the crash you found in dropbox/pyannotate#36

[jabdoa2]

Installed typing from your repository:
sudo pip3 install git+https://github.com/ilevkivskyi/typehinting.git@fix-abc-extensions --upgrade

Unfortunately, the error still persists for me:

pyannotate mpf
Traceback (most recent call last):
  File "/usr/local/bin/pyannotate", line 11, in <module>
    load_entry_point('pyannotate', 'console_scripts', 'pyannotate')()
  File "/data/home/jan/cloud/flipper/src/pyannotate/pyannotate_tools/annotations/__main__.py", line 56, in main
    show_diffs=not args.quiet)
  File "/usr/lib/python3.5/lib2to3/main.py", line 63, in __init__
    super(StdoutRefactoringTool, self).__init__(fixers, options, explicit)
  File "/usr/lib/python3.5/lib2to3/refactor.py", line 698, in __init__
    super(MultiprocessRefactoringTool, self).__init__(*args, **kwargs)
  File "/usr/lib/python3.5/lib2to3/refactor.py", line 210, in __init__
    self.pre_order, self.post_order = self.get_fixers()
  File "/usr/lib/python3.5/lib2to3/refactor.py", line 255, in get_fixers
    fixer = fix_class(self.options, self.fixer_log)
  File "/usr/lib/python3.5/lib2to3/fixer_base.py", line 58, in __init__
    self.compile_pattern()
  File "/usr/lib/python3.5/lib2to3/fixer_base.py", line 67, in compile_pattern
    PC = PatternCompiler()
  File "/usr/lib/python3.5/lib2to3/patcomp.py", line 50, in __init__
    self.grammar = driver.load_grammar(grammar_file)
  File "/usr/lib/python3.5/lib2to3/pgen2/driver.py", line 120, in load_grammar
    logger.info("Generating grammar tables from %s", gt)
  File "/usr/lib/python3.5/logging/__init__.py", line 1279, in info
    self._log(INFO, msg, args, **kwargs)
  File "/usr/lib/python3.5/logging/__init__.py", line 1414, in _log
    exc_info, func, extra, sinfo)
  File "/usr/lib/python3.5/logging/__init__.py", line 1384, in makeRecord
    sinfo)
  File "/usr/lib/python3.5/logging/__init__.py", line 269, in __init__
    if (args and len(args) == 1 and isinstance(args[0], collections.Mapping)
  File "/usr/lib/python3.5/abc.py", line 191, in __instancecheck__
    return cls.__subclasscheck__(subclass)
  File "/usr/lib/python3.5/abc.py", line 226, in __subclasscheck__
    if issubclass(subclass, scls):
  File "/usr/lib/python3.5/abc.py", line 226, in __subclasscheck__
    if issubclass(subclass, scls):
  File "/usr/lib/python3.5/abc.py", line 226, in __subclasscheck__
    if issubclass(subclass, scls):
  File "/usr/lib/python3.5/typing.py", line 1081, in __subclasscheck__
    return issubclass(cls, self.__extra__)
  File "/usr/lib/python3.5/abc.py", line 226, in __subclasscheck__
    if issubclass(subclass, scls):
  File "/usr/lib/python3.5/typing.py", line 1081, in __subclasscheck__
    return issubclass(cls, self.__extra__)
  File "/usr/lib/python3.5/abc.py", line 226, in __subclasscheck__
    if issubclass(subclass, scls):
  File "/usr/lib/python3.5/typing.py", line 1081, in __subclasscheck__
    return issubclass(cls, self.__extra__)
  File "/usr/lib/python3.5/abc.py", line 226, in __subclasscheck__
    if issubclass(subclass, scls):
  File "/usr/lib/python3.5/typing.py", line 1081, in __subclasscheck__
    return issubclass(cls, self.__extra__)
  File "/usr/lib/python3.5/abc.py", line 226, in __subclasscheck__
    if issubclass(subclass, scls):
  File "/usr/lib/python3.5/typing.py", line 1081, in __subclasscheck__
    return issubclass(cls, self.__extra__)
  File "/usr/lib/python3.5/abc.py", line 226, in __subclasscheck__
    if issubclass(subclass, scls):
  File "/usr/lib/python3.5/typing.py", line 1081, in __subclasscheck__
[...]
 File "/usr/lib/python3.5/abc.py", line 197, in __subclasscheck__
    if subclass in cls._abc_cache:
RecursionError: maximum recursion depth exceeded

[ilevkivskyi]

@jabdoa2 I don't think that command actually installed typing_extensions (typing is not touched in this PR, this is intentional). I am not a big pip expert, but I think you can just clone, then typing_extensions/src_py3 and run setup.py from there.

[jabdoa2]

That pip command should do the same as calling setup.py manually. I can try setup.py tomorrow to be sure.

[ilevkivskyi]

@jabdoa2

That pip command should do the same as calling setup.py manually. I can try setup.py tomorrow to be sure.

I think that command does not install typing_extensions because it runs setup.py from typing, not from the folder I said.

[jabdoa2]

Makes sense. Will give it a try

[jabdoa2]

Works fine. Thanks for the fix!

[ilevkivskyi]

@gvanrossum If you don't have objections for this, then I will merge this PR soon.

[gvanrossum]

Go ahead! I didn't try to follow all the details but I agree with the high level idea, and the OP is happy with it.