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prevent false unreachable warnings for @final instances that occur when strict optional checking is disabled #20045

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merged 2 commits into from
Oct 12, 2025
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prevent false unreachable warnings for @final instances that occur when strict optional checking is disabled #20045

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Prevent false unreachable warnings for @final instances that occur wh…
tyralla Oct 10, 2025
13af01b
Do the same for enum literals.
tyralla Oct 11, 2025
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4 changes: 2 additions & 2 deletions mypy/typeops.py
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Original file line number Diff line number Diff line change
Expand Up @@ -789,9 +789,9 @@ def false_only(t: Type) -> ProperType:
if not ret_type.can_be_false:
return UninhabitedType(line=t.line)
elif isinstance(t, Instance):
if t.type.is_final or t.type.is_enum:
if (t.type.is_final or t.type.is_enum) and state.strict_optional:
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@ilevkivskyi ilevkivskyi Oct 11, 2025

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I think this should apply to the branch just below as well. I mean what if in your test you will have x: Optional[Literal[SomeEnum.Foo]]? Or those are not simplified when strict optional is False?

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@tyralla tyralla Oct 11, 2025

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Thanks, you're right. I did as suggested and added the corresponding test case testNoWrongUnreachableWarningWithNoStrictOptionalAndEnumLiteral.

return UninhabitedType(line=t.line)
elif isinstance(t, LiteralType) and t.is_enum_literal():
elif isinstance(t, LiteralType) and t.is_enum_literal() and state.strict_optional:
return UninhabitedType(line=t.line)

new_t = copy_type(t)
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25 changes: 25 additions & 0 deletions test-data/unit/check-inference.test
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Expand Up @@ -1964,6 +1964,31 @@ if 'x' in d: # E: "None" has no attribute "__iter__" (not iterable)
reveal_type(d) # N: Revealed type is "None"
[builtins fixtures/dict.pyi]

[case testNoWrongUnreachableWarningWithNoStrictOptionalAndFinalInstance]
# flags: --no-strict-optional --warn-unreachable
from typing import final, Optional

@final
class C: ...

x: Optional[C]
if not x:
x = C()
[builtins fixtures/dict.pyi]

[case testNoWrongUnreachableWarningWithNoStrictOptionalAndEnumLiteral]
# flags: --no-strict-optional --warn-unreachable
from enum import Enum
from typing import Literal, Optional

class E(Enum):
a = 1

x: Optional[Literal[E.a]]
if not x:
x = E.a
[builtins fixtures/dict.pyi]

[case testInferFromEmptyListWhenUsingInWithStrictEquality]
# flags: --strict-equality
def f() -> None:
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