Quick mode crash when run twice in strict-optional mode

[gvanrossum]

In our codebase we have a case where running quick mode twice crashes.

@euresti reported this.

UPDATE: it's something like

$ rm -rf .mypy_cache
$ mypy -i --strict-optional <files>
<lots of errors>
$ mypy -quick --strict-optional <files>
<lots of errors>
$ mypy -quick --strict-optional <files>
<lots of errors>
<crash>
$

[gvanrossum]

There are lots of errors too. Traceback:

...
  File "/Users/david/src/client/.mypy/venv/lib/python3.6/site-packages/mypy/subtypes.py", line 33, in check_type_parameter
    return is_equivalent(lefta, righta, check_type_parameter)
  File "/Users/david/src/client/.mypy/venv/lib/python3.6/site-packages/mypy/subtypes.py", line 93, in is_equivalent
    is_subtype(a, b, type_parameter_checker, ignore_pos_arg_names=ignore_pos_arg_names)
  File "/Users/david/src/client/.mypy/venv/lib/python3.6/site-packages/mypy/subtypes.py", line 77, in is_subtype
    ignore_pos_arg_names=ignore_pos_arg_names))
  File "/Users/david/src/client/.mypy/venv/lib/python3.6/site-packages/mypy/types.py", line 381, in accept
    return visitor.visit_instance(self)  
  File "/Users/david/src/client/.mypy/venv/lib/python3.6/site-packages/mypy/subtypes.py", line 146, in visit_instance
    rname = right.type.fullname()
AttributeError: 'NoneType' object has no attribute 'fullname'

[gvanrossum]

Hm, I can repro this with an earlier mypy commit (a27963b, from last Thu) but not with master. The repro is kind of expensive so I won't bisect further (though I suspect it's Ivan's 8ecccda "Use dummy TypeInfo ..."), but I'm just going to close this as fixed.