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When checking python code that uses attrs dataclasses, Generic classes and inheritance, mypy fails to infer the actual type of a TypeVar.
Swapping attrs for std dataclasses removes the error.
Simplifying inheritance chain also removes the error.
I suspect this might be an issue in the mypy-attr plugin.
To Reproduce
can't put a playground link since it doesn't support attrs sorry.
importabcfromtypingimportGeneric, TypeVarfromattrimportfrozen# define a hierarchy of State typesclassBaseState(metaclass=abc.ABCMeta):
...
T_State=TypeVar("T_State", bound=BaseState, covariant=True)
@frozen()classJumpState(BaseState):
start: int# define a hierarchy of signals@frozen()classAbstractBaseSignal(metaclass=abc.ABCMeta):
passT_Signal=TypeVar("T_Signal", bound=AbstractBaseSignal)
@frozen()classSignalA(Generic[T_State], AbstractBaseSignal, metaclass=abc.ABCMeta):
state: T_State@frozen()classSignalAA(SignalA[T_State], metaclass=abc.ABCMeta):
pass# this signal specializes the generic type to a well defined JumpState typeclassSignalAAA(SignalAA[JumpState]):
passdeffoo(s: SignalAAA) ->None:
reveal_type(s) # SignalAAAreveal_type(s.state) # T_State instead of JumpStatereveal_type(s.state.start) # start is not found on T_State
if you swap all the frozen decorators for dataclass it suddendly works, s.state is correctly inferred as a JumpState.
if you remove the class SignalAA and have SignalAAA inherit directly from SignalA (i.e. short-circuit the inheritance chain) it works correctly as well.
Expected Behavior
I would expect this code to typecheck, especially since it does with standard dataclasses. I suspect a problem with the mypy-attrs plugin.
Actual Behavior
mypy output on this example:
type_test.py:47: note: Revealed type is "type_test.SignalAAA"
type_test.py:49: note: Revealed type is "T_State`1"
type_test.py:50: error: "T_State" has no attribute "start" [attr-defined]
type_test.py:50: note: Revealed type is "Any"
Found 1 error in 1 file (checked 1 source file)
Your Environment
Mypy version used: issue confirmed at least starting from 0.991 to latest version. It was working fine with version 0.910.
Mypy command-line flags: None
Mypy configuration options from mypy.ini (and other config files):
Bug Report
When checking python code that uses
attrs
dataclasses,Generic
classes and inheritance, mypy fails to infer the actual type of a TypeVar.Swapping
attrs
for std dataclasses removes the error.Simplifying inheritance chain also removes the error.
I suspect this might be an issue in the mypy-attr plugin.
To Reproduce
can't put a playground link since it doesn't support
attrs
sorry.if you swap all the
frozen
decorators fordataclass
it suddendly works,s.state
is correctly inferred as aJumpState
.if you remove the class
SignalAA
and haveSignalAAA
inherit directly fromSignalA
(i.e. short-circuit the inheritance chain) it works correctly as well.Expected Behavior
I would expect this code to typecheck, especially since it does with standard dataclasses. I suspect a problem with the mypy-attrs plugin.
Actual Behavior
mypy output on this example:
Your Environment
mypy.ini
(and other config files):attrs
package version: 23.1.0 (bug reproduced in 22.1.0 as well)The bug was observed first while updating our mypy version from 0.910 to 0.991.
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