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Pass through ParamSpec relation check for non-overloaded signatures #23927

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dhruvmanila merged 2 commits into from
Mar 17, 2026
Merged

Pass through ParamSpec relation check for non-overloaded signatures #23927

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Pass through ParamSpec relation check for non-overloaded signatures
dhruvmanila Mar 13, 2026
d67a9a3
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dhruvmanila Mar 17, 2026
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170 changes: 87 additions & 83 deletions crates/ty_python_semantic/src/types/signatures.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -942,24 +942,15 @@ impl<'c, 'db> TypeRelationChecker<'_, 'c, 'db> {
let target_is_single_paramspec =
CallableSignature::signatures_is_single_paramspec(target_overloads);

// If either callable is a ParamSpec, the constraint set should bind the ParamSpec to
// the other callable's signature. We also need to compare the return types — for
// instance, to verify in `Callable[P, int]` that the return type is assignable to
// `int`, or in `Callable[P, T]` to bind `T` to the return type of the other callable.
match (source_is_single_paramspec, target_is_single_paramspec) {
(Some((source_tvar, source_return)), Some((target_tvar, target_return))) => {
let param_spec_matches = ConstraintSet::constrain_typevar(
db,
self.constraints,
source_tvar,
Type::TypeVar(target_tvar),
Type::TypeVar(target_tvar),
);
let return_types_match = self.check_type_pair(db, source_return, target_return);
return param_spec_matches.and(db, self.constraints, || return_types_match);
}
// TODO: Adding proper support for overloads with ParamSpec will likely require some
// changes here.

(Some((source_tvar, source_return)), None) => {
// Only handle ParamSpec here when we still need the whole overload set. Once we're
// down to a single signature on both sides, let
// `TypeRelationChecker::check_signature_pair_inner` handle the ParamSpec binding
// instead.
match (source_is_single_paramspec, target_is_single_paramspec) {
(Some((source_tvar, source_return)), None) if target_overloads.len() > 1 => {
let upper = Type::Callable(CallableType::new(
db,
CallableSignature::from_overloads(target_overloads.iter().map(
Expand Down Expand Up @@ -991,7 +982,7 @@ impl<'c, 'db> TypeRelationChecker<'_, 'c, 'db> {
return param_spec_matches.and(db, self.constraints, return_types_match);
}

(None, Some((target_tvar, target_return))) => {
(None, Some((target_tvar, target_return))) if source_overloads.len() > 1 => {
let lower = Type::Callable(CallableType::new(
db,
CallableSignature::from_overloads(source_overloads.iter().map(
Expand Down Expand Up @@ -1023,22 +1014,29 @@ impl<'c, 'db> TypeRelationChecker<'_, 'c, 'db> {
return param_spec_matches.and(db, self.constraints, return_types_match);
}

(None, None) => {}
_ => {}
}
}

match (source_overloads, target_overloads) {
([self_signature], [other_signature]) => {
([source_signature], [target_signature]) => {
// Base case: both callable types contain a single signature.
self.check_signature_pair(db, self_signature, other_signature)
if self.relation.is_constraint_set_assignability()
&& (source_signature.parameters.as_paramspec().is_some()
|| target_signature.parameters.as_paramspec().is_some())
{
self.check_signature_pair_inner(db, source_signature, target_signature)
} else {
self.check_signature_pair(db, source_signature, target_signature)
}
}

// `self` is possibly overloaded while `other` is definitely not overloaded.
(_, [other_signature]) => {
// source is possibly overloaded while target is definitely not overloaded.
(_, [target_signature]) => {
if let Some(aggregate_relation) = self.try_unary_overload_aggregate_relation(
db,
source_overloads,
other_signature,
target_signature,
) {
return aggregate_relation;
}
Expand All @@ -1054,7 +1052,7 @@ impl<'c, 'db> TypeRelationChecker<'_, 'c, 'db> {
})
}

// `self` is definitely not overloaded while `other` is possibly overloaded.
// source is definitely not overloaded while target is possibly overloaded.
([_], _) => {
target_overloads
.iter()
Expand All @@ -1067,7 +1065,7 @@ impl<'c, 'db> TypeRelationChecker<'_, 'c, 'db> {
})
}

// `self` is definitely overloaded while `other` is possibly overloaded.
// source is definitely overloaded while target is possibly overloaded.
(_, _) => target_overloads
.iter()
.when_all(db, self.constraints, |target_signature| {
Expand Down Expand Up @@ -1216,72 +1214,33 @@ impl<'c, 'db> TypeRelationChecker<'_, 'c, 'db> {
.is_never_satisfied(db)
};

// Return types are covariant.
if !check_types(source.return_ty, target.return_ty) {
return result;
}

// A gradual parameter list is a supertype of the "bottom" parameter list (*args: object,
// **kwargs: object).
if target.parameters.is_gradual()
&& !source.parameters.is_top()
&& source
.parameters
.variadic()
.is_some_and(|(_, param)| param.annotated_type().is_object())
&& source
.parameters
.keyword_variadic()
.is_some_and(|(_, param)| param.annotated_type().is_object())
{
return self.always();
}

// The top signature is supertype of (and assignable from) all other signatures. It is a
// subtype of no signature except itself, and assignable only to the gradual signature.
if target.parameters.is_top() {
return self.always();
} else if source.parameters.is_top() && !target.parameters.is_gradual() {
return self.never();
}

// If either of the parameter lists is gradual (`...`), then it is assignable to and from
// any other parameter list, but not a subtype or supertype of any other parameter list.
if source.parameters.is_gradual() || target.parameters.is_gradual() {
return match self.relation {
TypeRelation::Subtyping | TypeRelation::SubtypingAssuming => self.never(),
TypeRelation::Redundancy { .. } => result.intersect(
db,
self.constraints,
ConstraintSet::from_bool(
self.constraints,
source.parameters.is_gradual() && target.parameters.is_gradual(),
),
),
TypeRelation::Assignability | TypeRelation::ConstraintSetAssignability => result,
};
}
// Avoid returning early after checking the return types in case there is a `ParamSpec` type
// variable in either signature to ensure that the `ParamSpec` binding is still applied even
// if the return types are incompatible.
let return_type_checks = check_types(source.return_ty, target.return_ty);

if self.relation.is_constraint_set_assignability() {
let source_is_paramspec = source.parameters.as_paramspec();
let target_is_paramspec = target.parameters.as_paramspec();
let source_as_paramspec = source.parameters.as_paramspec();
let target_as_paramspec = target.parameters.as_paramspec();

// If either signature is a ParamSpec, the constraint set should bind the ParamSpec to
// the other signature.
match (source_is_paramspec, target_is_paramspec) {
(Some(source_tvar), Some(target_tvar)) => {
// the other signature before the return-type and gradual/top fast paths can return
// early. We also need to compare the return types here so a return-type mismatch still
// preserves the inferred ParamSpec binding.
match (source_as_paramspec, target_as_paramspec) {
(Some(source_bound_typevar), Some(target_bound_typevar)) => {
let param_spec_matches = ConstraintSet::constrain_typevar(
db,
self.constraints,
source_tvar,
Type::TypeVar(target_tvar),
Type::TypeVar(target_tvar),
source_bound_typevar,
Type::TypeVar(target_bound_typevar),
Type::TypeVar(target_bound_typevar),
);
result.intersect(db, self.constraints, param_spec_matches);
return result;
}

(Some(source_tvar), None) => {
(Some(source_bound_typevar), None) => {
let upper = Type::Callable(CallableType::new(
db,
CallableSignature::single(Signature::new_generic(
Expand All @@ -1294,15 +1253,15 @@ impl<'c, 'db> TypeRelationChecker<'_, 'c, 'db> {
let param_spec_matches = ConstraintSet::constrain_typevar(
db,
self.constraints,
source_tvar,
source_bound_typevar,
Type::Never,
upper,
);
result.intersect(db, self.constraints, param_spec_matches);
return result;
}

(None, Some(target_tvar)) => {
(None, Some(target_bound_typevar)) => {
let lower = Type::Callable(CallableType::new(
db,
CallableSignature::single(Signature::new_generic(
Expand All @@ -1315,7 +1274,7 @@ impl<'c, 'db> TypeRelationChecker<'_, 'c, 'db> {
let param_spec_matches = ConstraintSet::constrain_typevar(
db,
self.constraints,
target_tvar,
target_bound_typevar,
lower,
Type::object(),
);
Expand All @@ -1327,6 +1286,51 @@ impl<'c, 'db> TypeRelationChecker<'_, 'c, 'db> {
}
}

if !return_type_checks {
return result;
}

// A gradual parameter list is a supertype of the "bottom" parameter list (*args: object,
// **kwargs: object).
if target.parameters.is_gradual()
&& !source.parameters.is_top()
&& source
.parameters
.variadic()
.is_some_and(|(_, param)| param.annotated_type().is_object())
&& source
.parameters
.keyword_variadic()
.is_some_and(|(_, param)| param.annotated_type().is_object())
{
return self.always();
}

// The top signature is supertype of (and assignable from) all other signatures. It is a
// subtype of no signature except itself, and assignable only to the gradual signature.
if target.parameters.is_top() {
return self.always();
} else if source.parameters.is_top() && !target.parameters.is_gradual() {
return self.never();
}

// If either of the parameter lists is gradual (`...`), then it is assignable to and from
// any other parameter list, but not a subtype or supertype of any other parameter list.
if source.parameters.is_gradual() || target.parameters.is_gradual() {
return match self.relation {
TypeRelation::Subtyping | TypeRelation::SubtypingAssuming => self.never(),
TypeRelation::Redundancy { .. } => result.intersect(
db,
self.constraints,
ConstraintSet::from_bool(
self.constraints,
source.parameters.is_gradual() && target.parameters.is_gradual(),
),
),
TypeRelation::Assignability | TypeRelation::ConstraintSetAssignability => result,
};
}

let mut parameters = ParametersZip {
current_source: None,
current_target: None,
Expand Down
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