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use is_same_type when determining if a cast is redundant #18588

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use is_same_type when determining if a cast is redundant #18588

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d87bac9
use is_same_type when determining if a cast is redundant
asottile Feb 2, 2025
ffab4d4
don't report warn-redundant-cast to cast of Union of Any
asottile Feb 2, 2025
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4 changes: 2 additions & 2 deletions mypy/checkexpr.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4687,8 +4687,8 @@ def visit_cast_expr(self, expr: CastExpr) -> Type:
options = self.chk.options
if (
options.warn_redundant_casts
and not isinstance(get_proper_type(target_type), AnyType)
and source_type == target_type
and not is_same_type(target_type, AnyType(TypeOfAny.special_form))
and is_same_type(source_type, target_type)
):
self.msg.redundant_cast(target_type, expr)
if options.disallow_any_unimported and has_any_from_unimported_type(target_type):
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26 changes: 26 additions & 0 deletions test-data/unit/check-warnings.test
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Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,32 @@ a: Any
b = cast(Any, a)
[builtins fixtures/list.pyi]

[case testCastToObjectNotRedunant]
# flags: --warn-redundant-casts
from typing import cast

a = 1
b = cast(object, 1)

[case testCastFromLiteralRedundant]
# flags: --warn-redundant-casts
from typing import cast

cast(int, 1)
[out]
main:4: error: Redundant cast to "int"

[case testCastFromUnionOfAnyOk]
# flags: --warn-redundant-casts
from typing import Any, cast, Union

x = Any
y = Any
z = Any

def f(q: Union[x, y, z]) -> None:
cast(Union[x, y], q)

-- Unused 'type: ignore' comments
-- ------------------------------

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