Crash on type: ignore in import

[drewhaven]

We have some code to the effect of

if IS_LINUX:
    from linux_class import SomeClass
elif IS_MAC:
    from mac_class import SomeClass
elif IS_WINDOWS:
    from windows_class import SomeClass

assert SomeClass

Because SomeClass doesn't have quite the same interface in all three places, I tried to add type: ignore to the second and third imports. This caused the following crash while running mypy:

  File "/code/client-all/client/.mypy_lint/mypy/mypy/main.py", line 51, in main
    type_check_only(sources, bin_dir, options)
  File "/code/client-all/client/.mypy_lint/mypy/mypy/main.py", line 95, in type_check_only
    python_path=options.python_path)
  File "/code/client-all/client/.mypy_lint/mypy/mypy/build.py", line 239, in build
    result = manager.process(initial_states)
  File "/code/client-all/client/.mypy_lint/mypy/mypy/build.py", line 456, in process
    next.process()
  File "/code/client-all/client/.mypy_lint/mypy/mypy/build.py", line 964, in process
    self.type_checker().visit_file(self.tree, self.tree.path)
  File "/code/client-all/client/.mypy_lint/mypy/mypy/checker.py", line 416, in visit_file
    self.accept(d)
  File "/code/client-all/client/.mypy_lint/mypy/mypy/checker.py", line 457, in accept
    typ = node.accept(self)
  File "/code/client-all/client/.mypy_lint/mypy/mypy/nodes.py", line 632, in accept
    return visitor.visit_assert_stmt(self)
  File "/code/client-all/client/.mypy_lint/mypy/mypy/checker.py", line 1710, in visit_assert_stmt
    self.accept(s.expr)
  File "/code/client-all/client/.mypy_lint/mypy/mypy/checker.py", line 457, in accept
    typ = node.accept(self)
  File "/code/client-all/client/.mypy_lint/mypy/mypy/nodes.py", line 902, in accept
    return visitor.visit_name_expr(self)
  File "/code/client-all/client/.mypy_lint/mypy/mypy/checker.py", line 1961, in visit_name_expr
    return self.expr_checker.visit_name_expr(e)
  File "/code/client-all/client/.mypy_lint/mypy/mypy/checkexpr.py", line 75, in visit_name_expr
    result = self.analyze_ref_expr(e)
  File "/code/client-all/client/.mypy_lint/mypy/mypy/checkexpr.py", line 103, in analyze_ref_expr
    result = type_object_type(node, self.named_type)
  File "/code/client-all/client/.mypy_lint/mypy/mypy/checkmember.py", line 320, in type_object_type
    init_method = info.get_method('__init__')
  File "/code/client-all/client/.mypy_lint/mypy/mypy/nodes.py", line 1593, in get_method
    for cls in self.mro:
TypeError: 'NoneType' object is not iterable

I've spent some time trying to get a small example of how to repro this, but haven't been able to yet.

[JukkaL]

This seems like a special case of #1107 that causes a crash. It would be useful to understand why this happens even if we won't implement #1107 very soon.