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[ty] Don't confuse multiple occurrences of typing.Self when binding bound methods #21754

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Merged
dcreager merged 3 commits into from
Dec 2, 2025
Merged

[ty] Don't confuse multiple occurrences of typing.Self when binding bound methods #21754

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448e1b5
add failing test
dcreager Dec 2, 2025
0980f1b
only bind self from current definition
dcreager Dec 2, 2025
d8a7b90
fix renames in test case
dcreager Dec 2, 2025
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26 changes: 26 additions & 0 deletions crates/ty_python_semantic/resources/mdtest/annotations/self.md
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Original file line number Diff line number Diff line change
Expand Up @@ -232,6 +232,32 @@ class C:
reveal_type(not_a_method) # revealed: def not_a_method(self) -> Unknown
```

## Different occurrences of `Self` represent different types

Here, both `Foo.foo` and `Bar.bar` use `Self`. When accessing a bound method, we replace any
occurrences of `Self` with the bound `self` type. In this example, when we access `x.foo`, we only
want to substitute the occurrences of `Self` in `Foo.foo` — that is, occurrences of `Self@foo`. The
fact that `x` is an instance of `Foo[Self@bar]` (a completely different `Self` type) should not
affect that subtitution. If we blindly substitute all occurrences of `Self`, we would get
`Foo[Self@bar]` as the return type of the bound method.

```py
from typing import Self

class Foo[T]:
def foo(self: Self) -> T:
raise NotImplementedError

class Bar:
def bar(self: Self, x: Foo[Self]):
# revealed: bound method Foo[Self@bar].foo() -> Self@bar
reveal_type(x.foo)

def f[U: Bar](x: Foo[U]):
# revealed: bound method Foo[U@f].foo() -> U@f
reveal_type(x.foo)
```

## typing_extensions

```toml
Expand Down
31 changes: 19 additions & 12 deletions crates/ty_python_semantic/src/types.rs
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Expand Up @@ -7549,10 +7549,9 @@ impl<'db> Type<'db> {
// If we are binding `typing.Self`, and this type is what we are binding `Self` to, return
// early. This is not just an optimization, it also prevents us from infinitely expanding
// the type, if it's something that can contain a `Self` reference.
if let TypeMapping::BindSelf(self_type) = type_mapping
&& self == *self_type
{
return self;
match type_mapping {
TypeMapping::BindSelf { self_type, .. } if self == *self_type => return self,
_ => {}
}

match self {
Expand All @@ -7567,7 +7566,7 @@ impl<'db> Type<'db> {
TypeMapping::Specialization(_) |
TypeMapping::PartialSpecialization(_) |
TypeMapping::PromoteLiterals(_) |
TypeMapping::BindSelf(_) |
TypeMapping::BindSelf { .. } |
TypeMapping::ReplaceSelf { .. } |
TypeMapping::Materialize(_) |
TypeMapping::ReplaceParameterDefaults |
Expand Down Expand Up @@ -7743,7 +7742,7 @@ impl<'db> Type<'db> {
TypeMapping::Specialization(_) |
TypeMapping::PartialSpecialization(_) |
TypeMapping::BindLegacyTypevars(_) |
TypeMapping::BindSelf(_) |
TypeMapping::BindSelf { .. } |
TypeMapping::ReplaceSelf { .. } |
TypeMapping::Materialize(_) |
TypeMapping::ReplaceParameterDefaults |
Expand All @@ -7756,7 +7755,7 @@ impl<'db> Type<'db> {
TypeMapping::Specialization(_) |
TypeMapping::PartialSpecialization(_) |
TypeMapping::BindLegacyTypevars(_) |
TypeMapping::BindSelf(_) |
TypeMapping::BindSelf { .. } |
TypeMapping::ReplaceSelf { .. } |
TypeMapping::PromoteLiterals(_) |
TypeMapping::ReplaceParameterDefaults |
Expand Down Expand Up @@ -8420,7 +8419,10 @@ pub enum TypeMapping<'a, 'db> {
/// being used in.
BindLegacyTypevars(BindingContext<'db>),
/// Binds any `typing.Self` typevar with a particular `self` class.
BindSelf(Type<'db>),
BindSelf {
self_type: Type<'db>,
binding_context: Option<BindingContext<'db>>,
},
/// Replaces occurrences of `typing.Self` with a new `Self` type variable with the given upper bound.
ReplaceSelf { new_upper_bound: Type<'db> },
/// Create the top or bottom materialization of a type.
Expand Down Expand Up @@ -8448,7 +8450,7 @@ impl<'db> TypeMapping<'_, 'db> {
| TypeMapping::Materialize(_)
| TypeMapping::ReplaceParameterDefaults
| TypeMapping::EagerExpansion => context,
TypeMapping::BindSelf(_) => GenericContext::from_typevar_instances(
TypeMapping::BindSelf { .. } => GenericContext::from_typevar_instances(
db,
context
.variables(db)
Expand Down Expand Up @@ -8481,7 +8483,7 @@ impl<'db> TypeMapping<'_, 'db> {
TypeMapping::Specialization(_)
| TypeMapping::PartialSpecialization(_)
| TypeMapping::BindLegacyTypevars(_)
| TypeMapping::BindSelf(_)
| TypeMapping::BindSelf { .. }
| TypeMapping::ReplaceSelf { .. }
| TypeMapping::ReplaceParameterDefaults
| TypeMapping::EagerExpansion => self.clone(),
Expand Down Expand Up @@ -9836,8 +9838,13 @@ impl<'db> BoundTypeVarInstance<'db> {
TypeMapping::PartialSpecialization(partial) => {
partial.get(db, self).unwrap_or(Type::TypeVar(self))
}
TypeMapping::BindSelf(self_type) => {
if self.typevar(db).is_self(db) {
TypeMapping::BindSelf {
self_type,
binding_context,
} => {
if self.typevar(db).is_self(db)
&& binding_context.is_none_or(|context| self.binding_context(db) == context)
{
*self_type
} else {
Type::TypeVar(self)
Expand Down
38 changes: 19 additions & 19 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 @@ -29,9 +29,10 @@ use crate::types::generics::{
};
use crate::types::infer::nearest_enclosing_class;
use crate::types::{
ApplyTypeMappingVisitor, BoundTypeVarInstance, ClassLiteral, FindLegacyTypeVarsVisitor,
HasRelationToVisitor, IsDisjointVisitor, IsEquivalentVisitor, KnownClass, MaterializationKind,
NormalizedVisitor, TypeContext, TypeMapping, TypeRelation, VarianceInferable, todo_type,
ApplyTypeMappingVisitor, BindingContext, BoundTypeVarInstance, ClassLiteral,
FindLegacyTypeVarsVisitor, HasRelationToVisitor, IsDisjointVisitor, IsEquivalentVisitor,
KnownClass, MaterializationKind, NormalizedVisitor, TypeContext, TypeMapping, TypeRelation,
VarianceInferable, todo_type,
};
use crate::{Db, FxOrderSet};
use ruff_python_ast::{self as ast, name::Name};
Expand Down Expand Up @@ -667,19 +668,18 @@ impl<'db> Signature<'db> {
let mut parameters = Parameters::new(db, parameters);
let mut return_ty = self.return_ty;
if let Some(self_type) = self_type {
let self_mapping = TypeMapping::BindSelf {
self_type,
binding_context: self.definition.map(BindingContext::Definition),
};
parameters = parameters.apply_type_mapping_impl(
db,
&TypeMapping::BindSelf(self_type),
&self_mapping,
TypeContext::default(),
&ApplyTypeMappingVisitor::default(),
);
return_ty = return_ty.map(|ty| {
ty.apply_type_mapping(
db,
&TypeMapping::BindSelf(self_type),
TypeContext::default(),
)
});
return_ty = return_ty
.map(|ty| ty.apply_type_mapping(db, &self_mapping, TypeContext::default()));
}
Self {
generic_context: self.generic_context,
Expand All @@ -690,19 +690,19 @@ impl<'db> Signature<'db> {
}

pub(crate) fn apply_self(&self, db: &'db dyn Db, self_type: Type<'db>) -> Self {
let self_mapping = TypeMapping::BindSelf {
self_type,
binding_context: self.definition.map(BindingContext::Definition),
};
let parameters = self.parameters.apply_type_mapping_impl(
db,
&TypeMapping::BindSelf(self_type),
&self_mapping,
TypeContext::default(),
&ApplyTypeMappingVisitor::default(),
);
let return_ty = self.return_ty.map(|ty| {
ty.apply_type_mapping(
db,
&TypeMapping::BindSelf(self_type),
TypeContext::default(),
)
});
let return_ty = self
.return_ty
.map(|ty| ty.apply_type_mapping(db, &self_mapping, TypeContext::default()));
Self {
generic_context: self.generic_context,
definition: self.definition,
Expand Down
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