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Prevent a crash when InitVar is redefined with a method in a subclass #19453

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merged 2 commits into from
Jul 16, 2025
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Prevent a crash when InitVar is redefined with a method in a subclass #19453

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0443f25
Prevent crash when InitVar is redefined with a method in a subclass
sterliakov Jul 15, 2025
c0ccf1c
Fix lineno in test
sterliakov Jul 15, 2025
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9 changes: 8 additions & 1 deletion mypy/checker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2188,7 +2188,14 @@ def check_method_override_for_base_with_name(
else:
override_class_or_static = defn.func.is_class or defn.func.is_static
typ, _ = self.node_type_from_base(defn.name, defn.info, defn)
assert typ is not None
if typ is None:
# This may only happen if we're checking `x-redefinition` member
# and `x` itself is for some reason gone. Normally the node should
# be reachable from the containing class by its name.
# The redefinition is never removed, use this as a sanity check to verify
# the reasoning above.
assert f"{defn.name}-redefinition" in defn.info.names
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@sterliakov What about multiple redefinitions? Will this fix still work? The current logic in semanal.py is

            if i == 1:
                new_name = f"{name}-redefinition"
            else:
                new_name = f"{name}-redefinition{i}"

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The first redefinition cannot be InitVar, so should not get deleted. I can replace this with any(name.startswith(f"{defn.name}-redifinition") for name in info.names), but I couldn't invent the case where name-redefinition is also gone

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OK, if you can't trigger it, it is fine.

return False

original_node = base_attr.node
# `original_type` can be partial if (e.g.) it is originally an
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16 changes: 16 additions & 0 deletions test-data/unit/check-dataclasses.test
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Expand Up @@ -2666,3 +2666,19 @@ class PersonBad(TypedDict):
class JobBad:
person: PersonBad = field(default_factory=PersonBad) # E: Argument "default_factory" to "field" has incompatible type "type[PersonBad]"; expected "Callable[[], PersonBad]"
[builtins fixtures/dict.pyi]

[case testDataclassInitVarRedefinitionNoCrash]
# https://github.com/python/mypy/issues/19443
from dataclasses import InitVar, dataclass

class ClassA:
def value(self) -> int:
return 0

@dataclass
class ClassB(ClassA):
value: InitVar[int]

def value(self) -> int: # E: Name "value" already defined on line 10
return 0
[builtins fixtures/dict.pyi]