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[ty] type[T] is assignable to an inferable typevar #21766

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Merged
ibraheemdev merged 1 commit into from
Dec 2, 2025
Merged

[ty] type[T] is assignable to an inferable typevar #21766

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11 changes: 11 additions & 0 deletions crates/ty_python_semantic/resources/mdtest/type_of/generics.md
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Original file line number Diff line number Diff line change
Expand Up @@ -227,6 +227,17 @@ def _[T: (int | str, int)](_: T):
static_assert(not is_disjoint_from(type[int], type[T]))
```

```py
class X[T]:
value: T

def get(self) -> T:
return self.value

def _[T](x: X[type[T]]):
reveal_type(x.get()) # revealed: type[T@_]
```

## Generic Type Inference

```py
Expand Down
125 changes: 73 additions & 52 deletions crates/ty_python_semantic/src/types.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2105,33 +2105,52 @@ impl<'db> Type<'db> {
})
.is_never_satisfied(db) =>
{
// TODO: The repetition here isn't great, but we really need the fallthrough logic,
// where this arm only engages if it returns true.
let this_instance = Type::TypeVar(subclass_of.into_type_var().unwrap());
target.to_instance(db).when_some_and(|other_instance| {
this_instance.has_relation_to_impl(
db,
other_instance,
inferable,
relation,
relation_visitor,
disjointness_visitor,
)
})
// TODO: The repetition here isn't great, but we need the fallthrough logic.
subclass_of
.into_type_var()
.zip(target.to_instance(db))
.when_some_and(|(this_instance, other_instance)| {
Type::TypeVar(this_instance).has_relation_to_impl(
db,
other_instance,
inferable,
relation,
relation_visitor,
disjointness_visitor,
)
})
}

(_, Type::SubclassOf(subclass_of)) if subclass_of.is_type_var() => {
let other_instance = Type::TypeVar(subclass_of.into_type_var().unwrap());
self.to_instance(db).when_some_and(|this_instance| {
this_instance.has_relation_to_impl(
db,
other_instance,
inferable,
relation,
relation_visitor,
disjointness_visitor,
)
})
(_, Type::SubclassOf(subclass_of))
if !subclass_of
.into_type_var()
.zip(self.to_instance(db))
.when_some_and(|(other_instance, this_instance)| {
this_instance.has_relation_to_impl(
db,
Type::TypeVar(other_instance),
inferable,
relation,
relation_visitor,
disjointness_visitor,
)
})
.is_never_satisfied(db) =>
{
// TODO: The repetition here isn't great, but we need the fallthrough logic.
subclass_of
.into_type_var()
.zip(self.to_instance(db))
.when_some_and(|(other_instance, this_instance)| {
this_instance.has_relation_to_impl(
db,
Type::TypeVar(other_instance),
inferable,
relation,
relation_visitor,
disjointness_visitor,
)
})
}

// A fully static typevar is a subtype of its upper bound, and to something similar to
Expand Down Expand Up @@ -2656,7 +2675,9 @@ impl<'db> Type<'db> {
disjointness_visitor,
),

(Type::SubclassOf(subclass_of), _) if subclass_of.is_type_var() => {
(Type::SubclassOf(subclass_of), _) | (_, Type::SubclassOf(subclass_of))
if subclass_of.is_type_var() =>
{
ConstraintSet::from(false)
}

Expand Down Expand Up @@ -3116,33 +3137,33 @@ impl<'db> Type<'db> {

// `type[T]` is disjoint from a class object `A` if every instance of `T` is disjoint from an instance of `A`.
(Type::SubclassOf(subclass_of), other) | (other, Type::SubclassOf(subclass_of))
if subclass_of.is_type_var()
&& (other.to_instance(db).is_some()
|| other.as_typevar().is_some_and(|type_var| {
type_var.typevar(db).bound_or_constraints(db).is_none()
})) =>
if !subclass_of
.into_type_var()
.zip(other.to_instance(db))
.when_none_or(|(this_instance, other_instance)| {
Type::TypeVar(this_instance).is_disjoint_from_impl(
db,
other_instance,
inferable,
disjointness_visitor,
relation_visitor,
)
})
.is_always_satisfied(db) =>
{
let this_instance = Type::TypeVar(subclass_of.into_type_var().unwrap());
let other_instance = match other {
// An unbounded typevar `U` may have instances of type `object` if specialized to
// an instance of `type`.
Type::TypeVar(typevar)
if typevar.typevar(db).bound_or_constraints(db).is_none() =>
{
Some(Type::object())
}
_ => other.to_instance(db),
};

other_instance.when_none_or(|other_instance| {
this_instance.is_disjoint_from_impl(
db,
other_instance,
inferable,
disjointness_visitor,
relation_visitor,
)
})
// TODO: The repetition here isn't great, but we need the fallthrough logic.
subclass_of
.into_type_var()
.zip(other.to_instance(db))
.when_none_or(|(this_instance, other_instance)| {
Type::TypeVar(this_instance).is_disjoint_from_impl(
db,
other_instance,
inferable,
disjointness_visitor,
relation_visitor,
)
})
}

// A typevar is never disjoint from itself, since all occurrences of the typevar must
Expand Down
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