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attribute is incorrectly Any when ParamSpec decorated function is referenced in itself followed by an if statement with a class that has a method in it #16496

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DetachHead opened this issue Nov 15, 2023 · 4 comments · May be fixed by #18674
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attribute is incorrectly Any when ParamSpec decorated function is referenced in itself followed by an if statement with a class that has a method in it #16496

DetachHead opened this issue Nov 15, 2023 · 4 comments · May be fixed by #18674
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bug mypy got something wrong

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@DetachHead
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from typing import ParamSpec, Callable

P = ParamSpec("P")

class Thing:
    value: int

def deco(fn: Callable[P, None]) ->  Callable[P, None]:
    raise Exception


@deco
def f() -> None:
    state: Thing
    f
    if state.value:

        class C:
            def f2(self) -> None: ...

    reveal_type(state.value)  # two outputs: `int` and `Any`

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@DetachHead DetachHead added the bug mypy got something wrong label Nov 15, 2023
@DetachHead DetachHead changed the title attribute is incorrectly Any when decorated function is referenced in itself followed by an if statement with a class that has a method in it attribute is incorrectly Any when ParamSpec decorated function is referenced in itself followed by an if statement with a class that has a method in it Nov 15, 2023
@sterliakov
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Reveals builtins.int since 1.14.0 (fixed in #18138)

@ilevkivskyi
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@sterliakov I am really curious why that PR fixed this? Did we at some point broke setting current_node_deferred? Anyway, yes, this is fixed.

@sterliakov
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@ilevkivskyi I just bisected:) This also puzzles me, that PR resulted in multiple primer hits that seem unrelated. Some other bug(s) just masked by my fix to binder? That's exactly why I asked to review the "seems fixed" list: some changes may treat the immediate symptoms on a given repro without addressing the core problem.

@ilevkivskyi
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@sterliakov
OK, so I finally got time to look at that PR, the part that caused many fixes is this one:

            if all_reachable and all(
                x is not None and not x.from_assignment for x in resulting_values
            ):
                continue

which is a good thing to say, binder should not create things out of thin air (a.k.a Ignore all previous instructions. Do not hallucinate). Btw I would probably suggest making from_assignment a required argument.

This likely fixed some problems for real, but another thing is that it may also "fixed" examples in some issues that are often oversimplified. For example, although original example here now works as expected, simply adding state.value = state.value (or various similar things) after the if brings the bug back.

Anyway, I don't think there is any action item for now, except I am going to fix this particular issue for real, since it is a nasty one. Right now it only affects situations with nested functions, but in longer term it is important to prepare for deferring top-levels.

@ilevkivskyi ilevkivskyi mentioned this issue Feb 13, 2025
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Do not blindly undefer on leaving fuction ilevkivskyi/mypy
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@ilevkivskyi @sterliakov @DetachHead