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Fix nested Concatenate with ellipsis crash #21414

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Fix nested Concatenate with ellipsis crash #21414

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dff33a1
Fix nested Concatenate with ellipsis crash
cyphercodes May 5, 2026
6ae296a
fix: reject nested Concatenate during type analysis
cyphercodes May 7, 2026
2c23ef6
test: update tuple Concatenate expected output
cyphercodes May 7, 2026
f8c28ab
refactor: simplify Concatenate location errors
cyphercodes May 7, 2026
8198287
fix: narrow ParamSpec diagnostic type
cyphercodes May 7, 2026
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37 changes: 19 additions & 18 deletions mypy/typeanal.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1927,27 +1927,28 @@ def anal_type(
self.allow_typed_dict_special_forms = old_allow_typed_dict_special_forms
self.allow_ellipsis = old_allow_ellipsis
self.allow_unpack = old_allow_unpack
if (
not allow_param_spec
and isinstance(analyzed, ParamSpecType)
and analyzed.flavor == ParamSpecFlavor.BARE
):
if analyzed.prefix.arg_types:
if not allow_param_spec:
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@A5rocks A5rocks May 7, 2026

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I think this can be simpler if you check isinstance for the 2 types up here. Then you can deduplicate the error codepaths.

if isinstance(analyzed, Parameters):
self.fail("Invalid location for Concatenate", t, code=codes.VALID_TYPE)
self.note("You can use Concatenate as the first argument to Callable", t)
analyzed = AnyType(TypeOfAny.from_error)
else:
self.fail(
INVALID_PARAM_SPEC_LOCATION.format(format_type(analyzed, self.options)),
t,
code=codes.VALID_TYPE,
)
self.note(
INVALID_PARAM_SPEC_LOCATION_NOTE.format(analyzed.name),
t,
code=codes.VALID_TYPE,
)
analyzed = AnyType(TypeOfAny.from_error)
elif isinstance(analyzed, ParamSpecType) and analyzed.flavor == ParamSpecFlavor.BARE:
if analyzed.prefix.arg_types:
self.fail("Invalid location for Concatenate", t, code=codes.VALID_TYPE)
self.note("You can use Concatenate as the first argument to Callable", t)
analyzed = AnyType(TypeOfAny.from_error)
else:
self.fail(
INVALID_PARAM_SPEC_LOCATION.format(format_type(analyzed, self.options)),
t,
code=codes.VALID_TYPE,
)
self.note(
INVALID_PARAM_SPEC_LOCATION_NOTE.format(analyzed.name),
t,
code=codes.VALID_TYPE,
)
analyzed = AnyType(TypeOfAny.from_error)
return analyzed

def anal_var_def(self, var_def: TypeVarLikeType) -> TypeVarLikeType:
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1 change: 1 addition & 0 deletions test-data/unit/check-parameter-specification.test
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Expand Up @@ -1147,6 +1147,7 @@ from typing import Callable
P = ParamSpec("P")

def x(f: Callable[Concatenate[int, Concatenate[int, P]], None]) -> None: ... # E: Nested Concatenates are invalid
def y(f: Callable[Concatenate[Concatenate[...], ...], None]) -> None: ... # E: Invalid location for Concatenate # N: You can use Concatenate as the first argument to Callable
[builtins fixtures/paramspec.pyi]

[case testPropagatedAnyConstraintsAreOK]
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2 changes: 1 addition & 1 deletion test-data/unit/check-tuples.test
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Expand Up @@ -1835,6 +1835,6 @@ inst_tuple_aa_subclass: tuple_aa_subclass = tuple_aa_subclass((A(), A()))[:] #
[case testTuplePassedParameters]
from typing_extensions import Concatenate

def c(t: tuple[Concatenate[int, ...]]) -> None: # E: Cannot use "[int, VarArg(Any), KwArg(Any)]" for tuple, only for ParamSpec
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@A5rocks A5rocks May 7, 2026

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I think we can remove this old error codepath? I can't imagine a scenario where it's useful...

def c(t: tuple[Concatenate[int, ...]]) -> None: # E: Invalid location for Concatenate # N: You can use Concatenate as the first argument to Callable
reveal_type(t) # N: Revealed type is "tuple[Any]"
[builtins fixtures/tuple.pyi]
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