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Fix type context for assert_type() #12612

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Apr 18, 2022
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Fix type context for assert_type() #12612

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2 changes: 1 addition & 1 deletion mypy/checkexpr.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3145,7 +3145,7 @@ def visit_cast_expr(self, expr: CastExpr) -> Type:
return target_type

def visit_assert_type_expr(self, expr: AssertTypeExpr) -> Type:
source_type = self.accept(expr.expr, type_context=AnyType(TypeOfAny.special_form),
source_type = self.accept(expr.expr, type_context=self.type_context[-1],
allow_none_return=True, always_allow_any=True)
target_type = expr.type
if not is_same_type(source_type, target_type):
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14 changes: 14 additions & 0 deletions test-data/unit/check-expressions.test
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Expand Up @@ -1049,6 +1049,20 @@ assert_type(a, Any) # E: Expression is of type "int", not "Any"
assert_type(a, Literal[1]) # E: Expression is of type "int", not "Literal[1]"
[builtins fixtures/tuple.pyi]

[case testAssertTypeGeneric]
from typing import assert_type, TypeVar, Generic
from typing_extensions import Literal
T = TypeVar("T")
def f(x: T) -> T: return x
assert_type(f(1), int)
class Gen(Generic[T]):
def __new__(cls, obj: T) -> Gen[T]: ...
assert_type(Gen(1), Gen[int])
# With type context, it infers Gen[Literal[1]] instead.
y: Gen[Literal[1]] = assert_type(Gen(1), Gen[Literal[1]])

[builtins fixtures/tuple.pyi]

-- None return type
-- ----------------

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