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Fix crash on partial type used as context #19216

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Merged
merged 1 commit into from
Jun 3, 2025
Merged

Fix crash on partial type used as context #19216

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4 changes: 3 additions & 1 deletion mypy/checker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3427,7 +3427,9 @@ def check_compatibility_all_supers(self, lvalue: RefExpr, rvalue: Expression) ->
# store the rvalue type on the variable.
actual_lvalue_type = None
if lvalue_node.is_inferred and not lvalue_node.explicit_self_type:
rvalue_type = self.expr_checker.accept(rvalue, lvalue_node.type)
# Don't use partial types as context, similar to regular code path.
ctx = lvalue_node.type if not isinstance(lvalue_node.type, PartialType) else None
rvalue_type = self.expr_checker.accept(rvalue, ctx)
actual_lvalue_type = lvalue_node.type
lvalue_node.type = rvalue_type
lvalue_type, _ = self.node_type_from_base(lvalue_node.name, lvalue_node.info, lvalue)
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21 changes: 21 additions & 0 deletions test-data/unit/check-inference.test
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Expand Up @@ -4128,3 +4128,24 @@ T = TypeVar("T")
def f(x: Optional[T]) -> T: ...
reveal_type(f(a)) # N: Revealed type is "Any"
reveal_type(f(oa)) # N: Revealed type is "Any"

[case testNoCrashOnPartialTypeAsContext]
from typing import overload, TypeVar, Optional, Protocol

T = TypeVar("T")
class DbManager(Protocol):
@overload
def get(self, key: str) -> Optional[T]:
pass

@overload
def get(self, key: str, default: T) -> T:
pass

class Foo:
def __init__(self, db: DbManager, bar: bool) -> None:
if bar:
self.qux = db.get("qux")
else:
self.qux = {} # E: Need type annotation for "qux" (hint: "qux: dict[<type>, <type>] = ...")
[builtins fixtures/dict.pyi]