• Are you reporting a bug, or opening a feature request?

There's a bug when working with TypeQuery. It is literally unusable.

• Please insert below the code you are checking with mypy,
  or a mock-up repro if the source is private. We would appreciate
  if you try to simplify your case to a minimal repro.

Just take any type inside a plugin and pass it to TypeQuery:

from mypy.plugin import FunctionContext
from mypy.types import Type as MypyType
from mypy.types import TypeQuery
from mypy.plugin import Plugin

def analyze(ctx: FunctionContext) -> MypyType:
    print(ctx.default_return_type.accept(TypeQuery(any)))
    return ctx.default_return_type

class _ReturnsPlugin(Plugin):
    def get_function_hook(self, fullname):
        if fullname == 'ex.test':
            return analyze

def plugin(version: str):
    return _ReturnsPlugin

And provide any source code to trigger this plugin:

# ex.py
def test() -> int:
     return 1

• What is the actual behavior/output?

» PYTHONFAULTHANDLER=1 mypy ex.py
Fatal Python error: Segmentation fault

Current thread 0x0000000100b155c0 (most recent call first):
  File "/Users/sobolev/Documents/github/returns/returns/contrib/mypy/_features/decorators.py", line 18 in analyze
  File "/Users/sobolev/Documents/github/returns/.venv/lib/python3.7/site-packages/mypy/__main__.py", line 8 in console_entry
  File "/Users/sobolev/Documents/github/returns/.venv/bin/mypy", line 10 in <module>
[1]    22569 segmentation fault  PYTHONFAULTHANDLER=1 mypy ex.py

• What is the behavior/output you expect?

I would expect TypeQuery to work. Without the segfault.

• What are the versions of mypy and Python you are using?
  Do you see the same issue after installing mypy from Git master?

0.780

• What are the mypy flags you are using? (For example --strict-optional)

Full list: https://github.com/dry-python/returns/blob/master/setup.cfg#L122