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Fix crash on non-normalized parameters expansion #22123

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Merged
ilevkivskyi merged 1 commit into from
Oct 8, 2026
Merged

Fix crash on non-normalized parameters expansion #22123

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17 changes: 15 additions & 2 deletions mypy/expandtype.py
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Original file line number Diff line number Diff line change
Expand Up @@ -410,9 +410,22 @@ def expand_unpack(self, t: UnpackType) -> list[Type]:
raise RuntimeError(f"Invalid type replacement to expand: {repl}")

def visit_parameters(self, t: Parameters) -> Type:
return t.copy_modified(arg_types=self.expand_types(t.arg_types))
# This mimics the logic in visit_callable_type().
var_arg = t.var_arg()
needs_normalization = False

@JukkaL JukkaL Oct 8, 2026

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Should we also look at self.normalize_callables -- is it relevant here?

@ilevkivskyi ilevkivskyi Oct 8, 2026

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No, I think we are fine (even for callables we really need to keep original shape only for top-level callables).

if var_arg is not None and isinstance(var_arg.typ, UnpackType):
needs_normalization = True
arg_types = self.interpolate_args_for_unpack(t, var_arg.typ)
else:
arg_types = self.expand_types(t.arg_types)
expanded = t.copy_modified(arg_types=arg_types)
if needs_normalization:
expanded = expanded.with_normalized_var_args()
return expanded

def interpolate_args_for_unpack(self, t: CallableType, var_arg: UnpackType) -> list[Type]:
def interpolate_args_for_unpack(
self, t: CallableType | Parameters, var_arg: UnpackType
) -> list[Type]:
star_index = t.arg_kinds.index(ARG_STAR)
prefix = self.expand_types(t.arg_types[:star_index])
suffix = self.expand_types(t.arg_types[star_index + 1 :])
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