8000 Use type variable bound when it appears as actual during inference by ilevkivskyi · Pull Request #16178 · python/mypy · GitHub
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Use type variable bound when it appears as actual during inference #16178

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Merged
merged 5 commits into from
Sep 27, 2023
Merged

Use type variable bound when it appears as actual during inference #16178

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1f1074d
Use type variable bound when it appears as actual during inference
ilevkivskyi Sep 25, 2023
0d23e85
Unions require specific ordering of steps
ilevkivskyi Sep 26, 2023
67d965c
add regression test
hauntsaninja Sep 26, 2023
5a3d0f1
Merge branch 'master' into infer-upper-bound
hauntsaninja Sep 26, 2023
ce79dbc
Cleanup the test
ilevkivskyi Sep 27, 2023
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Use type variable bound when it appears as actual during inference
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@ilevkivskyi
ilevkivskyi committed Sep 25, 2023
commit 1f1074d0c73c6c1215a59b73cbde4c6c47bb0148
5 changes: 5 additions & 0 deletions mypy/constraints.py
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Expand Up @@ -373,6 +373,11 @@ def _infer_constraints(
return handle_recursive_union(template, actual, direction)
return []

if isinstance(actual, TypeVarType) and not actual.id.is_meta_var():
# Unless template is also a type variable (that is handled above), using the upper
# bound for inference will usually give better result for actual that is a type variable.
actual = get_proper_type(actual.upper_bound)

# Remaining cases are handled by ConstraintBuilderVisitor.
return template.accept(ConstraintBuilderVisitor(actual, direction, skip_neg_op))

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12 changes: 12 additions & 0 deletions test-data/unit/check-inference.test
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Expand Up @@ -3686,3 +3686,15 @@ def g(*args: str) -> None: pass
reveal_type(f(g)) # N: Revealed type is "Tuple[Never, Never]" \
# E: Argument 1 to "f" has incompatible type "Callable[[VarArg(str)], None]"; expected "Call[Never]"
[builtins fixtures/list.pyi]

[case testInferenceAgainstTypeVarActualBound]
from typing import Callable, TypeVar

T = TypeVar("T")
S = TypeVar("S")
def test(f: Callable[[T], S]) -> Callable[[T], S]: ...

F = TypeVar("F", bound=Callable[..., object])
def dec(f: F) -> F:
reveal_type(test(f)) # N: Revealed type is "def (Any) -> builtins.object"
return f
0