Complex inheritance generates INTERNAL ERROR

[epenet]

Crash Report

On HomeAssistant project, a complex flow is generating an INTERNAL ERROR when trying to add type hints.
home-assistant/core#59503
I was able to reproduce the issue with a trimmed version of the code (see below).

Traceback

internal_error.py:36: error: INTERNAL ERROR -- Please try using mypy master on Github:
https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 0.920+dev.053a1beb94ee4e5b3260725594315d1b6776e42f
Traceback (most recent call last):
  File "/usr/local/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
  File "/usr/local/lib/python3.8/dist-packages/mypy/__main__.py", line 11, in console_entry
    main(None, sys.stdout, sys.stderr)
  File "/usr/local/lib/python3.8/dist-packages/mypy/main.py", line 92, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File "/usr/local/lib/python3.8/dist-packages/mypy/main.py", line 170, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/usr/local/lib/python3.8/dist-packages/mypy/build.py", line 180, in build
    result = _build(
  File "/usr/local/lib/python3.8/dist-packages/mypy/build.py", line 256, in _build
    graph = dispatch(sources, manager, stdout)
  File "/usr/local/lib/python3.8/dist-packages/mypy/build.py", line 2712, in dispatch
    process_graph(graph, manager)
  File "/usr/local/lib/python3.8/dist-packages/mypy/build.py", line 3043, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/usr/local/lib/python3.8/dist-packages/mypy/build.py", line 3150, in process_stale_scc
    if not graph[id].type_check_second_pass():
  File "/usr/local/lib/python3.8/dist-packages/mypy/build.py", line 2197, in type_check_second_pass
    return self.type_checker().check_second_pass()
  File "/usr/local/lib/python3.8/dist-packages/mypy/checker.py", line 366, in check_second_pass
    self.check_partial(node)
  File "/usr/local/lib/python3.8/dist-packages/mypy/checker.py", line 377, in check_partial
    self.accept(node)
  File "/usr/local/lib/python3.8/dist-packages/mypy/checker.py", line 422, in accept
    stmt.accept(self)
  File "/usr/local/lib/python3.8/dist-packages/mypy/nodes.py", line 727, in accept
    return visitor.visit_func_def(self)
  File "/usr/local/lib/python3.8/dist-packages/mypy/checker.py", line 754, in visit_func_def
    self._visit_func_def(defn)
  File "/usr/local/lib/python3.8/dist-packages/mypy/checker.py", line 765, in _visit_func_def
    self.check_method_override(defn)
  File "/usr/local/lib/python3.8/dist-packages/mypy/checker.py", line 1451, in check_method_override
    if self.check_method_or_accessor_override_for_base(defn, base):
  File "/usr/local/lib/python3.8/dist-packages/mypy/checker.py", line 1479, in check_method_or_accessor_override_for_base
    if self.check_method_override_for_base_with_name(defn, name, base):
  File "/usr/local/lib/python3.8/dist-packages/mypy/checker.py", line 1540, in check_method_override_for_base_with_name
    assert False, str(base_attr.node)
AssertionError: Var(async_specific)
internal_error.py:36: : note: use --pdb to drop into pdb

To Reproduce

from typing import Any, Dict, TypedDict, cast

GenericServiceInfoType = Dict[str, Any]


class SpecificServiceInfo(TypedDict):
    host: str
    port: int


class BaseFlow:
    async def async_generic(
        self,
        service_info: GenericServiceInfoType,
    ) -> bool:
        return True

    async def async_specific(
        self,
        service_info: SpecificServiceInfo,
    ) -> bool:
        return await self.async_generic(cast(dict, service_info))


class StandardFlow(BaseFlow):
    async def async_standard_generic(
        self,
        service_info: GenericServiceInfoType,
    ) -> bool:
        return True

    async_specific = async_standard_generic  # type: ignore


class ExtendedFlow(StandardFlow):
    async def async_specific(
        self,
        service_info: SpecificServiceInfo,
    ) -> bool:
        return await self.async_generic(cast(dict, service_info))

Your Environment

• Mypy version used: 0.920+dev.053a1beb94ee4e5b3260725594315d1b6776e42f
• Mypy command-line flags:
• Mypy configuration options from mypy.ini (and other config files):
• Python version used: 3.8.10
• Operating system and version: WSL (Ubuntu-20.04)

[A5rocks]

perhaps this is similar to #10134 and #5425 ?

Here's a simplified repro:

class BaseFlow:
    async_specific = int

class StandardFlow(BaseFlow):
    async_specific = str

class ExtendedFlow(StandardFlow):
    def async_specific(
        self,
        service_info: int,
    ) -> None:
        ...