dmypy Suggest assertion error in `node_type_from_base`

Crash Report

Mypy Daemon crashed attempting to generate type suggestions for __reduce__ function in class with nonstandard __new__. (re-creating #15823)

Traceback

dmypy suggest crash.py:64: 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: 1.8.0
dmypy suggest crash.py: 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: 1.8.0
Daemon crashed!
Traceback (most recent call last):
  File "mypy/dmypy_server.py", line 236, in serve
  File "mypy/dmypy_server.py", line 285, in run_command
  File "mypy/dmypy_server.py", line 972, in cmd_suggest
  File "mypy/suggestions.py", line 267, in suggest
  File "mypy/suggestions.py", line 502, in get_suggestion
  File "mypy/suggestions.py", line 444, in find_best
  File "mypy/suggestions.py", line 675, in try_type
  File "mypy/server/update.py", line 314, in trigger
  File "mypy/server/update.py", line 881, in propagate_changes_using_dependencies
  File "mypy/server/update.py", line 1010, in reprocess_nodes
  File "mypy/semanal_main.py", line 144, in semantic_analysis_for_targets
  File "mypy/semanal_main.py", line 291, in process_top_level_function
  File "mypy/semanal_main.py", line 349, in semantic_analyze_target
  File "mypy/semanal.py", line 600, in refresh_partial
  File "mypy/semanal.py", line 6541, in accept
  File "mypy/errors.py", line 1261, in report_internal_error
  File "mypy/semanal.py", line 6539, in accept
  File "mypy/nodes.py", line 787, in accept
  File "mypy/semanal.py", line 833, in visit_func_def
  File "mypy/semanal.py", line 865, in analyze_func_def
  File "mypy/typeanal.py", line 1031, in visit_callable_type
  File "mypy/typeanal.py", line 1684, in anal_type
  File "mypy/types.py", line 2400, in accept
  File "mypy/typeanal.py", line 1133, in visit_tuple_type
  File "mypy/typeanal.py", line 1659, in anal_array
  File "mypy/typeanal.py", line 1684, in anal_type
  File "mypy/types.py", line 1970, in accept
  File "mypy/typeanal.py", line 980, in visit_callable_type
  File "mypy/typeanal.py", line 1614, in bind_function_type_variables
AssertionError

To Reproduce

dmypy suggest crash.py:

from __future__ import annotations

from collections.abc import Iterable, Callable
from typing import TYPE_CHECKING, TypeVar, Any, cast
import sys

if sys.version_info < (3, 11):
    from exceptiongroup import ExceptionGroup, BaseExceptionGroup

if TYPE_CHECKING:
    from types import TracebackType
    from typing_extensions import Self

NonBaseMultiError = ExceptionGroup


class MultiError(BaseExceptionGroup[BaseException]):
    def __init__(
        self, exceptions: list[BaseException], *, _collapse: bool = True
    ) -> None:
        self.collapse = _collapse

        # Avoid double initialization when _collapse is True and exceptions[0] returned
        # by __new__() happens to be a MultiError and subsequently __init__() is called.
        if _collapse and getattr(self, "exceptions", None) is not None:
            # This exception was already initialized.
            return

        super().__init__("multiple tasks failed", exceptions)

    def __new__(
        cls, exceptions: Iterable[BaseException], *, _collapse: bool = True
    ) -> MultiError | NonBaseMultiError[Exception] | Self:
        exceptions_union: list[BaseException | Exception] = list(exceptions)
        for exc in exceptions_union:
            if not isinstance(exc, BaseException):
                raise TypeError(f"Expected an exception object, not {exc!r}")
        class_sub: type[Self | NonBaseMultiError[Exception]] = cls
        if _collapse and len(exceptions_union) == 1:
            # If this lone object happens to itself be a MultiError, then
            # Python will implicitly call our __init__ on it again.  See
            # special handling in __init__.
            single = exceptions_union[0]
            assert isinstance(single, MultiError)
            return single
        else:
            # The base class __new__() implicitly invokes our __init__, which
            # is what we want.
            #
            # In an earlier version of the code, we didn't define __init__ and
            # simply set the `exceptions` attribute directly on the new object.
            # However, linters expect attributes to be initialized in __init__.
            if all(isinstance(exc, Exception) for exc in exceptions_union):
                exceptions_arg_one = cast("list[Exception]", exceptions_union)

                return super().__new__(
                    NonBaseMultiError, "multiple tasks failed", exceptions_arg_one
                )
            else:
                exceptions_arg_two = cast("list[BaseException]", exceptions_union)

                return super().__new__(cls, "multiple tasks failed", exceptions_arg_two)

    def __reduce__(self):
        return (
            self.__new__,
            (self.__class__, list(self.exceptions)),
            {"collapse": self.collapse},
        )

Run:

dmypy --status-file="<user path>/dmypy.json" run --timeout=1800 --log-file="<user path>/log.txt" --export-types "<user path>/dmypy suggest crash.py" -- --no-implicit-reexport --disallow-untyped-defs --show-error-codes --strict --warn-redundant-casts --cache-dir="<user path>" --show-error-end --no-color-output --no-error-summary --show-column-numbers --warn-unreachable --disallow-untyped-calls --warn-unused-ignores --cache-fine-grained --soft-error-limit=-1 --show-traceback --hide-error-context --show-absolute-path
dmypy --status-file="<user path>/dmypy.json" suggest "<user path>/dmypy suggest crash.py:65"

Your Environment

• Mypy version used: dmypy 1.8.0
• Mypy command-line flags: See above
• Mypy configuration options from mypy.ini (and other config files): See above
• Python version used: Python 3.12.0 (main, Oct 4 2023, 06:27:34) [GCC 13.2.0] on linux
• Operating system and version: 64 bit Linux Ubuntu Budgie 10.8 (Ubuntu 23.10) Linux 6.5.0-14-generic

Comienza con la reproducción de dmypy suggest indicada en el issue y, después, sigue la ruta de llamada reportada a través de mypy/suggestions.py y mypy/typeanal.py, especialmente bind_function_type_variables. Confirma el comportamiento con el crash.py proporcionado y determina cómo se alcanza la aserción durante el análisis de tipos. Se considera terminado cuando dmypy suggest gestiona este caso sin un INTERNAL ERROR ni un bloqueo del daemon.