dict.setdefault on an unpinned dict always makes the dict nullable (overload evaluation premature pinning) #2668
Description
Describe the Bug
available_clients = {}
def process_device(source, device):
available_clients.setdefault(device.machineIdentifier, {"device": device}) # makes the value type dict | None
available_clients[device.machineIdentifier].setdefault("source", source) # error!The standard library type annotation on MutableMapping.setdefault weird here
class MutableMapping:
# This overload should be allowed only if the value type is compatible with None.
#
# Keep the following methods in line with MutableMapping.setdefault, modulo positional-only differences:
# -- collections.OrderedDict.setdefault
# -- collections.ChainMap.setdefault
# -- weakref.WeakKeyDictionary.setdefault
@overload
def setdefault(self: MutableMapping[_KT, _T | None], key: _KT, default: None = None, /) -> _T | None: ...
@overload
def setdefault(self, key: _KT, default: _VT, /) -> _VT: ...I think maybe overload evaluation is pinning the type too early based on the first overload, even when it was not selected.
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