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Narrow type with typevar when the lower bound of its upper bound and that type is same #10658

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Merged
msullivan merged 2 commits into from
Jun 29, 2021
Merged

Narrow type with typevar when the lower bound of its upper bound and that type is same #10658

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e04dd2e
Narrow type with typevar when the lower bound of its upper bound and …
ethframe Jun 16, 2021
fafe542
Use is_subtype instead of combination of meet_types and is_same_type
ethframe Jun 19, 2021
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2 changes: 2 additions & 0 deletions mypy/meet.py
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Original file line number Diff line number Diff line change
Expand Up @@ -70,6 +70,8 @@ def narrow_declared_type(declared: Type, narrowed: Type) -> Type:
for x in narrowed.relevant_items()])
elif isinstance(narrowed, AnyType):
return narrowed
elif isinstance(narrowed, TypeVarType) and is_subtype(narrowed.upper_bound, declared):
return narrowed
elif isinstance(declared, TypeType) and isinstance(narrowed, TypeType):
return TypeType.make_normalized(narrow_declared_type(declared.item, narrowed.item))
elif (isinstance(declared, TypeType)
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20 changes: 20 additions & 0 deletions test-data/unit/check-narrowing.test
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Expand Up @@ -1073,3 +1073,23 @@ def f(t: Type[C]) -> None:
else:
reveal_type(t) # N: Revealed type is "Type[__main__.C]"
reveal_type(t) # N: Revealed type is "Type[__main__.C]"

[case testNarrowingUsingTypeVar]
# flags: --strict-optional
from typing import Type, TypeVar

class A: pass
class B(A): pass

T = TypeVar("T", bound=A)

def f(t: Type[T], a: A, b: B) -> None:
if type(a) is t:
reveal_type(a) # N: Revealed type is "T`-1"
else:
reveal_type(a) # N: Revealed type is "__main__.A"

if type(b) is t:
reveal_type(b) # N: Revealed type is "<nothing>"
else:
reveal_type(b) # N: Revealed type is "__main__.B"