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Traverse ParamSpec prefix where we should #19800

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merged 1 commit into from
Sep 6, 2025
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Traverse ParamSpec prefix where we should #19800

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2 changes: 1 addition & 1 deletion mypy/checkexpr.py
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Original file line number Diff line number Diff line change
Expand Up @@ -6435,7 +6435,7 @@ def visit_type_var(self, t: TypeVarType) -> bool:

def visit_param_spec(self, t: ParamSpecType) -> bool:
default = [t.default] if t.has_default() else []
return self.query_types([t.upper_bound, *default])
return self.query_types([t.upper_bound, *default, t.prefix])

def visit_type_var_tuple(self, t: TypeVarTupleType) -> bool:
default = [t.default] if t.has_default() else []
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1 change: 1 addition & 0 deletions mypy/erasetype.py
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Expand Up @@ -222,6 +222,7 @@ def visit_type_var_tuple(self, t: TypeVarTupleType) -> Type:
return t

def visit_param_spec(self, t: ParamSpecType) -> Type:
# TODO: we should probably preserve prefix here.
if self.erase_id is None or self.erase_id(t.id):
return self.replacement
return t
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1 change: 1 addition & 0 deletions mypy/fixup.py
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Expand Up @@ -347,6 +347,7 @@ def visit_type_var(self, tvt: TypeVarType) -> None:
def visit_param_spec(self, p: ParamSpecType) -> None:
p.upper_bound.accept(self)
p.default.accept(self)
p.prefix.accept(self)

def visit_type_var_tuple(self, t: TypeVarTupleType) -> None:
t.tuple_fallback.accept(self)
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1 change: 1 addition & 0 deletions mypy/indirection.py
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Expand Up @@ -93,6 +93,7 @@ def visit_type_var(self, t: types.TypeVarType) -> None:
def visit_param_spec(self, t: types.ParamSpecType) -> None:
self._visit(t.upper_bound)
self._visit(t.default)
self._visit(t.prefix)

def visit_type_var_tuple(self, t: types.TypeVarTupleType) -> None:
self._visit(t.upper_bound)
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1 change: 1 addition & 0 deletions mypy/server/astdiff.py
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Expand Up @@ -435,6 +435,7 @@ def visit_param_spec(self, typ: ParamSpecType) -> SnapshotItem:
typ.flavor,
snapshot_type(typ.upper_bound),
snapshot_type(typ.default),
snapshot_type(typ.prefix),
)

def visit_type_var_tuple(self, typ: TypeVarTupleType) -> SnapshotItem:
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1 change: 1 addition & 0 deletions mypy/server/astmerge.py
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Expand Up @@ -489,6 +489,7 @@ def visit_type_var(self, typ: TypeVarType) -> None:
def visit_param_spec(self, typ: ParamSpecType) -> None:
typ.upper_bound.accept(self)
typ.default.accept(self)
typ.prefix.accept(self)
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Should NodeReplaceVisitor above do the same? More importantly, why isn't its process_param_spec_def actually ever called (as well as process_type_var_tuple_def)?

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This leads to #14872 where process_param_spec_def was added, but apparently not connected to anything? It should probably be...

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ParamSpec definitions cannot have prefixes, it is purely mypy-internal thing to represent Concatenate in the type system. Also I noticed that process_param_spec_def() and process_type_var_tuple_def() are not called anywhere. Probably they should be called from visit_class_def(). But this is definitely a topic for a separate issue/PR.

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Yep, I remember what a PSpec prefix means:) I just wasn't able to make sure that process_param_spec_def is actually called on definitions and not on other ParamSpec occurrences


def visit_type_var_tuple(self, typ: TypeVarTupleType) -> None:
typ.upper_bound.accept(self)
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17 changes: 5 additions & 12 deletions mypy/server/deps.py
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Expand Up @@ -1037,10 +1037,8 @@ def visit_type_var(self, typ: TypeVarType) -> list[str]:
triggers = []
if typ.fullname:
triggers.append(make_trigger(typ.fullname))
if typ.upper_bound:
triggers.extend(self.get_type_triggers(typ.upper_bound))
if typ.default:
triggers.extend(self.get_type_triggers(typ.default))
triggers.extend(self.get_type_triggers(typ.upper_bound))
triggers.extend(self.get_type_triggers(typ.default))
for val in typ.values:
triggers.extend(self.get_type_triggers(val))
return triggers
Expand All @@ -1049,22 +1047,17 @@ def visit_param_spec(self, typ: ParamSpecType) -> list[str]:
triggers = []
if typ.fullname:
triggers.append(make_trigger(typ.fullname))
if typ.upper_bound:
triggers.extend(self.get_type_triggers(typ.upper_bound))
if typ.default:
triggers.extend(self.get_type_triggers(typ.default))
triggers.extend(self.get_type_triggers(typ.upper_bound))
triggers.extend(self.get_type_triggers(typ.default))
triggers.extend(self.get_type_triggers(typ.prefix))
return triggers

def visit_type_var_tuple(self, typ: TypeVarTupleType) -> list[str]:
triggers = []
if typ.fullname:
triggers.append(make_trigger(typ.fullname))
if typ.upper_bound:
triggers.extend(self.get_type_triggers(typ.upper_bound))
if typ.default:
triggers.extend(self.get_type_triggers(typ.default))
triggers.extend(self.get_type_triggers(typ.upper_bound))
triggers.extend(self.get_type_triggers(typ.default))
return triggers

def visit_unpack_type(self, typ: UnpackType) -> list[str]:
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2 changes: 1 addition & 1 deletion mypy/type_visitor.py
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Expand Up @@ -525,7 +525,7 @@ def visit_type_var(self, t: TypeVarType, /) -> bool:
return self.query_types([t.upper_bound, t.default] + t.values)

def visit_param_spec(self, t: ParamSpecType, /) -> bool:
return self.query_types([t.upper_bound, t.default])
return self.query_types([t.upper_bound, t.default, t.prefix])

def visit_type_var_tuple(self, t: TypeVarTupleType, /) -> bool:
return self.query_types([t.upper_bound, t.default])
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2 changes: 1 addition & 1 deletion mypy/typeanal.py
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Expand Up @@ -2615,7 +2615,7 @@ def visit_type_var(self, t: TypeVarType) -> None:
self.process_types([t.upper_bound, t.default] + t.values)

def visit_param_spec(self, t: ParamSpecType) -> None:
self.process_types([t.upper_bound, t.default])
self.process_types([t.upper_bound, t.default, t.prefix])

def visit_type_var_tuple(self, t: TypeVarTupleType) -> None:
self.process_types([t.upper_bound, t.default])
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1 change: 1 addition & 0 deletions mypy/typetraverser.py
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Expand Up @@ -64,6 +64,7 @@ def visit_type_var(self, t: TypeVarType, /) -> None:
t.default.accept(self)

def visit_param_spec(self, t: ParamSpecType, /) -> None:
# TODO: do we need to traverse prefix here?
t.default.accept(self)

def visit_parameters(self, t: Parameters, /) -> None:
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67 changes: 67 additions & 0 deletions test-data/unit/check-incremental.test
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Expand Up @@ -6897,3 +6897,70 @@ import does_not_exist
[builtins fixtures/ops.pyi]
[out]
[out2]

[case testIncrementalNoCrashOnParamSpecPrefixUpdateMethod]
import impl
[file impl.py]
from typing_extensions import ParamSpec
from lib import Sub

P = ParamSpec("P")
class Impl(Sub[P]):
def test(self, *args: P.args, **kwargs: P.kwargs) -> None:
self.meth(1, *args, **kwargs)

[file impl.py.2]
from typing_extensions import ParamSpec
from lib import Sub

P = ParamSpec("P")
class Impl(Sub[P]):
def test(self, *args: P.args, **kwargs: P.kwargs) -> None:
self.meth("no", *args, **kwargs)

[file lib.py]
from typing import Generic
from typing_extensions import ParamSpec, Concatenate

P = ParamSpec("P")
class Base(Generic[P]):
def meth(self, *args: P.args, **kwargs: P.kwargs) -> None: ...
class Sub(Base[Concatenate[int, P]]): ...
[builtins fixtures/paramspec.pyi]
[out]
[out2]
tmp/impl.py:7: error: Argument 1 to "meth" of "Base" has incompatible type "str"; expected "int"

[case testIncrementalNoCrashOnParamSpecPrefixUpdateMethodAlias]
import impl
[file impl.py]
from typing_extensions import ParamSpec
from lib import Sub

P = ParamSpec("P")
class Impl(Sub[P]):
def test(self, *args: P.args, **kwargs: P.kwargs) -> None:
self.alias(1, *args, **kwargs)

[file impl.py.2]
from typing_extensions import ParamSpec
from lib import Sub

P = ParamSpec("P")
class Impl(Sub[P]):
def test(self, *args: P.args, **kwargs: P.kwargs) -> None:
self.alias("no", *args, **kwargs)

[file lib.py]
from typing import Generic
from typing_extensions import ParamSpec, Concatenate

P = ParamSpec("P")
class Base(Generic[P]):
def meth(self, *args: P.args, **kwargs: P.kwargs) -> None: ...
alias = meth
class Sub(Base[Concatenate[int, P]]): ...
[builtins fixtures/paramspec.pyi]
[out]
[out2]
tmp/impl.py:7: error: Argument 1 has incompatible type "str"; expected "int"
33 changes: 33 additions & 0 deletions test-data/unit/fine-grained.test
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Expand Up @@ -11485,3 +11485,36 @@ class A:
[out]
==
main:3: error: Too few arguments

[case testFineGrainedParamSpecPrefixUpdateMethod]
import impl
[file impl.py]
from typing_extensions import ParamSpec
from lib import Sub

P = ParamSpec("P")
class Impl(Sub[P]):
def test(self, *args: P.args, **kwargs: P.kwargs) -> None:
self.meth(1, *args, **kwargs)

[file lib.py]
from typing import Generic
from typing_extensions import ParamSpec, Concatenate

P = ParamSpec("P")
class Base(Generic[P]):
def meth(self, *args: P.args, **kwargs: P.kwargs) -> None: ...
class Sub(Base[Concatenate[int, P]]): ...

[file lib.py.2]
from typing import Generic
from typing_extensions import ParamSpec, Concatenate

P = ParamSpec("P")
class Base(Generic[P]):
def meth(self, *args: P.args, **kwargs: P.kwargs) -> None: ...
class Sub(Base[Concatenate[str, P]]): ...
[builtins fixtures/paramspec.pyi]
[out]
==
impl.py:7: error: Argument 1 to "meth" of "Base" has incompatible type "int"; expected "str"
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