False negatives with dict.__(r)or__ #10678

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1. AlexWaygood commented on Sep 7, 2023

   

   AlexWaygood

   on Sep 7, 2023

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   In actual fact, the issue is our stubs for dict.__or__ and dict.__ror__:

   typeshed/stdlib/builtins.pyi

   Lines 1122 to 1129 in aa39b99

   	@overload
   	def __or__(self, __value: Mapping[_KT, _VT]) -> dict[_KT, _VT]: ...
   	@overload
   	def __or__(self, __value: Mapping[_T1, _T2]) -> dict[_KT | _T1, _VT | _T2]: ...
   	@overload
   	def __ror__(self, __value: Mapping[_KT, _VT]) -> dict[_KT, _VT]: ...
   	@overload
   	def __ror__(self, __value: Mapping[_T1, _T2]) -> dict[_KT | _T1, _VT | _T2]: ...

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   We currently claim that dict.__(r)or__ accepts any Mapping, but this isn't actually true. At runtime, the object passed to dict.__or__ has to be an instance of dict (and requests.structures.CaseInsensitiveDict is not a subclass of dict).

   Ideally we'd make this change, but I think we tried it recently, and it caused an unfortunate number of false positives:

   diff --git a/stdlib/builtins.pyi b/stdlib/builtins.pyi
   index 71cccee16..cf4f857c5 100644
   --- a/stdlib/builtins.pyi
   +++ b/stdlib/builtins.pyi
   @@ -1120,13 +1120,13 @@ class dict(MutableMapping[_KT, _VT], Generic[_KT, _VT]):
        if sys.version_info >= (3, 9):
            def __class_getitem__(cls, __item: Any) -> GenericAlias: ...
            @overload
   -        def __or__(self, __value: Mapping[_KT, _VT]) -> dict[_KT, _VT]: ...
   +        def __or__(self, __value: dict[_KT, _VT]) -> dict[_KT, _VT]: ...
            @overload
   -        def __or__(self, __value: Mapping[_T1, _T2]) -> dict[_KT | _T1, _VT | _T2]: ...
   +        def __or__(self, __value: dict[_T1, _T2]) -> dict[_KT | _T1, _VT | _T2]: ...
            @overload
   -        def __ror__(self, __value: Mapping[_KT, _VT]) -> dict[_KT, _VT]: ...
   +        def __ror__(self, __value: dict[_KT, _VT]) -> dict[_KT, _VT]: ...
            @overload
   -        def __ror__(self, __value: Mapping[_T1, _T2]) -> dict[_KT | _T1, _VT | _T2]: ...
   +        def __ror__(self, __value: dict[_T1, _T2]) -> dict[_KT | _T1, _VT | _T2]: ...
            # dict.__ior__ should be kept roughly in line with MutableMapping.update()
            @overload  # type: ignore[misc]
            def __ior__(self, __value: SupportsKeysAndGetItem[_KT, _VT]) -> Self: ...
2. AlexWaygood

   added

   stubs: false negativeType checkers do not report an error, but shouldType checkers do not report an error, but should

   on Sep 7, 2023
3. AlexWaygood

   changed the title [-]No error for [/-] [+]False negatives with `dict.__(r)or__`[/+] on Sep 7, 2023
4. AlexWaygood commented on Sep 7, 2023

   

   AlexWaygood

   on Sep 7, 2023

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   Okay, making the type hints more accurate here is actually less disruptive than I thought it would be! See #10679 (comment)
5. adamtheturtle commented on Sep 7, 2023

   

   adamtheturtle

   on Sep 7, 2023

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   Thank you for picking this up so quickly.

   👍React with 👍1Reacted by Alex Waygood
6. AlexWaygood

   closed this as completedin #10679on Sep 8, 2023
7. sobolevn commented on Oct 11, 2023

   

   sobolevn

   on Oct 11, 2023 · Hidden as off-topic

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8. sobolevn

   reopened this on Oct 11, 2023
9. AlexWaygood commented on Oct 12, 2023

   

   AlexWaygood

   on Oct 12, 2023 · Hidden as off-topic

   Last edited by AlexWaygood

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10. AlexWaygood commented on Oct 12, 2023

    

    AlexWaygood

    on Oct 12, 2023 · Hidden as off-topic

    Last edited by AlexWaygood

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11. AlexWaygood

    closed this as completedon Oct 18, 2023
12. sobolevn commented on Oct 18, 2023

    

    sobolevn

    on Oct 18, 2023 · Hidden as off-topic

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