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false positive on interaction between @property, @lru_cache, and inheritance #16855

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@finite-state-machine

Description

@finite-state-machine

Bug Report

My thanks to @hauntsaninja for their excellent work on #5858! However, I suspect there's a related issue with the combination of @lru_cache and @property where inheritance is at play:

To Reproduce

Gists:
mypy-play.net
pyright-play.net (pyright handles this correctly, IMO)

from __future__ import annotations
from abc import ABC, abstractmethod
from functools import lru_cache

class AlfaBase(ABC):
    # (base class is shown as abstract, but it doesn't matter)
    @property
    @abstractmethod
    def meaning_of_life(self) -> int: ...

class AlfaImpl(AlfaBase):

    @property
    @lru_cache(maxsize=None)
    def meaning_of_life(self) -> int:     # ←───┐
        # (deep thought)                  #     │
        return 42                         #     │
                                          #     │
# actual behavior:  (here)──────────────────────┘
#
#   Signature of "meaning_…" incompatible with supertype "AlfaBase" [override]
#       Superclass:
#           int
#       Subclass:
#           _lru_cache_wrapper[int]
#
# expected: (no error)


# (without inheritance, everything works as it should:)

class BravoImpl:

    @property
    @lru_cache(maxsize=None)
    def meaning_of_life(self) -> int:  # no errors (as expected)
        return 42

Expected Behavior

The tool should accept the code without comment.

Actual Behavior

The tool believes the type of the inherited @property is incompatible with the definition in the base class.

Your Environment

  • Mypy version used: 1.8.0, master (2024-02-01)
  • Mypy command-line flags: none
  • Mypy configuration options from mypy.ini (and other config files): none
  • Python version used: 3.8, 3.12

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