[ty] Track when type variables are inferable or not (#19786)

`Type::TypeVar` now distinguishes whether the typevar in question is
inferable or not.

A typevar is _not inferable_ inside the body of the generic class or
function that binds it:

```py
def f[T](t: T) -> T:
    return t
```

The infered type of `t` in the function body is `TypeVar(T,
NotInferable)`. This represents how e.g. assignability checks need to be
valid for all possible specializations of the typevar. Most of the
existing assignability/etc logic only applies to non-inferable typevars.

Outside of the function body, the typevar is _inferable_:

```py
f(4)
```

Here, the parameter type of `f` is `TypeVar(T, Inferable)`. This
represents how e.g. assignability doesn't need to hold for _all_
specializations; instead, we need to find the constraints under which
this specific assignability check holds.

This is in support of starting to perform specialization inference _as
part of_ performing the assignability check at the call site.

In the [[POPL2015][]] paper, this concept is called _monomorphic_ /
_polymorphic_, but I thought _non-inferable_ / _inferable_ would be
clearer for us.

Depends on #19784 

[POPL2015]: https://doi.org/10.1145/2676726.2676991

---------

Co-authored-by: Carl Meyer <carl@astral.sh>

crates/ty_ide/src/completion.rs

@@ -1247,7 +1247,7 @@ quux.<CURSOR>
         __init_subclass__ :: bound method Quux.__init_subclass__() -> None
         __module__ :: str
         __ne__ :: bound method Quux.__ne__(value: object, /) -> bool
-        __new__ :: bound method Quux.__new__() -> Self@__new__
+        __new__ :: bound method Quux.__new__() -> Quux
         __reduce__ :: bound method Quux.__reduce__() -> str | tuple[Any, ...]
         __reduce_ex__ :: bound method Quux.__reduce_ex__(protocol: SupportsIndex, /) -> str | tuple[Any, ...]
         __repr__ :: bound method Quux.__repr__() -> str
@@ -1292,7 +1292,7 @@ quux.b<CURSOR>
         __init_subclass__ :: bound method Quux.__init_subclass__() -> None
         __module__ :: str
         __ne__ :: bound method Quux.__ne__(value: object, /) -> bool
-        __new__ :: bound method Quux.__new__() -> Self@__new__
+        __new__ :: bound method Quux.__new__() -> Quux
         __reduce__ :: bound method Quux.__reduce__() -> str | tuple[Any, ...]
         __reduce_ex__ :: bound method Quux.__reduce_ex__(protocol: SupportsIndex, /) -> str | tuple[Any, ...]
         __repr__ :: bound method Quux.__repr__() -> str

crates/ty_ide/src/semantic_tokens.rs

@@ -337,7 +337,9 @@ impl<'db> SemanticTokenVisitor<'db> {
 
         match ty {
             Type::ClassLiteral(_) => (SemanticTokenType::Class, modifiers),
-            Type::TypeVar(_) => (SemanticTokenType::TypeParameter, modifiers),
+            Type::NonInferableTypeVar(_) | Type::TypeVar(_) => {
+                (SemanticTokenType::TypeParameter, modifiers)
+            }
             Type::FunctionLiteral(_) => {
                 // Check if this is a method based on current scope
                 if self.in_class_scope {

crates/ty_python_semantic/resources/mdtest/annotations/self.md

@@ -1,16 +1,16 @@
 # Self
 
+```toml
+[environment]
+python-version = "3.11"
+```
+
 `Self` is treated as if it were a `TypeVar` bound to the class it's being used on.
 
 `typing.Self` is only available in Python 3.11 and later.
 
 ## Methods
 
-```toml
-[environment]
-python-version = "3.11"
-```
-
 ```py
 from typing import Self
 
@@ -74,11 +74,6 @@ reveal_type(C().method())  # revealed: C
 
 ## Class Methods
 
-```toml
-[environment]
-python-version = "3.11"
-```
-
 ```py
 from typing import Self, TypeVar
 
@@ -101,11 +96,6 @@ reveal_type(Shape.bar())  # revealed: Unknown
 
 ## Attributes
 
-```toml
-[environment]
-python-version = "3.11"
-```
-
 TODO: The use of `Self` to annotate the `next_node` attribute should be
 [modeled as a property][self attribute], using `Self` in its parameter and return type.
 
@@ -127,11 +117,6 @@ reveal_type(LinkedList().next())  # revealed: LinkedList
 
 ## Generic Classes
 
-```toml
-[environment]
-python-version = "3.11"
-```
-
 ```py
 from typing import Self, Generic, TypeVar
 
@@ -153,11 +138,6 @@ TODO: <https://typing.python.org/en/latest/spec/generics.html#use-in-protocols>
 
 ## Annotations
 
-```toml
-[environment]
-python-version = "3.11"
-```
-
 ```py
 from typing import Self
 
@@ -171,11 +151,6 @@ class Shape:
 
 `Self` cannot be used in the signature of a function or variable.
 
-```toml
-[environment]
-python-version = "3.11"
-```
-
 ```py
 from typing import Self, Generic, TypeVar
 
@@ -218,4 +193,33 @@ class MyMetaclass(type):
         return super().__new__(cls)
 ```
 
+## Binding a method fixes `Self`
+
+When a method is bound, any instances of `Self` in its signature are "fixed", since we now know the
+specific type of the bound parameter.
+
+```py
+from typing import Self
+
+class C:
+    def instance_method(self, other: Self) -> Self:
+        return self
+
+    @classmethod
+    def class_method(cls) -> Self:
+        return cls()
+
+# revealed: bound method C.instance_method(other: C) -> C
+reveal_type(C().instance_method)
+# revealed: bound method <class 'C'>.class_method() -> C
+reveal_type(C.class_method)
+
+class D(C): ...
+
+# revealed: bound method D.instance_method(other: D) -> D
+reveal_type(D().instance_method)
+# revealed: bound method <class 'D'>.class_method() -> D
+reveal_type(D.class_method)
+```
+
 [self attribute]: https://typing.python.org/en/latest/spec/generics.html#use-in-attribute-annotations

crates/ty_python_semantic/resources/mdtest/generics/legacy/classes.md

@@ -491,6 +491,24 @@ class A(Generic[T]):
 reveal_type(A(x=1))  # revealed: A[int]
 ```
 
+### Class typevar has another typevar as a default
+
+```py
+from typing import Generic, TypeVar
+
+T = TypeVar("T")
+U = TypeVar("U", default=T)
+
+class C(Generic[T, U]): ...
+
+reveal_type(C())  # revealed: C[Unknown, Unknown]
+
+class D(Generic[T, U]):
+    def __init__(self) -> None: ...
+
+reveal_type(D())  # revealed: D[Unknown, Unknown]
+```
+
 ## Generic subclass
 
 When a generic subclass fills its superclass's type parameter with one of its own, the actual types

crates/ty_python_semantic/resources/mdtest/generics/pep695/classes.md

@@ -438,6 +438,19 @@ class A[T]:
 reveal_type(A(x=1))  # revealed: A[int]
 ```
 
+### Class typevar has another typevar as a default
+
+```py
+class C[T, U = T]: ...
+
+reveal_type(C())  # revealed: C[Unknown, Unknown]
+
+class D[T, U = T]:
+    def __init__(self) -> None: ...
+
+reveal_type(D())  # revealed: D[Unknown, Unknown]
+```
+
 ## Generic subclass
 
 When a generic subclass fills its superclass's type parameter with one of its own, the actual types

crates/ty_python_semantic/resources/mdtest/named_tuple.md

@@ -243,7 +243,7 @@ class Person(NamedTuple):
 
 reveal_type(Person._field_defaults)  # revealed: dict[str, Any]
 reveal_type(Person._fields)  # revealed: tuple[str, ...]
-reveal_type(Person._make)  # revealed: bound method <class 'Person'>._make(iterable: Iterable[Any]) -> Self@_make
+reveal_type(Person._make)  # revealed: bound method <class 'Person'>._make(iterable: Iterable[Any]) -> Person
 reveal_type(Person._asdict)  # revealed: def _asdict(self) -> dict[str, Any]
 reveal_type(Person._replace)  # revealed: def _replace(self, **kwargs: Any) -> Self@_replace
 
@@ -304,8 +304,8 @@ satisfy:
 ```py
 def expects_named_tuple(x: typing.NamedTuple):
     reveal_type(x)  # revealed: tuple[object, ...] & NamedTupleLike
-    reveal_type(x._make)  # revealed: bound method type[NamedTupleLike]._make(iterable: Iterable[Any]) -> Self@_make
+    reveal_type(x._make)  # revealed: bound method type[NamedTupleLike]._make(iterable: Iterable[Any]) -> NamedTupleLike
-    reveal_type(x._replace)  # revealed: bound method NamedTupleLike._replace(**kwargs) -> Self@_replace
+    reveal_type(x._replace)  # revealed: bound method NamedTupleLike._replace(**kwargs) -> NamedTupleLike
     # revealed: Overload[(value: tuple[object, ...], /) -> tuple[object, ...], (value: tuple[_T@__add__, ...], /) -> tuple[object, ...]]
     reveal_type(x.__add__)
     reveal_type(x.__iter__)  # revealed: bound method tuple[object, ...].__iter__() -> Iterator[object]
@@ -328,7 +328,7 @@ class Point(NamedTuple):
     x: int
     y: int
 
-reveal_type(Point._make)  # revealed: bound method <class 'Point'>._make(iterable: Iterable[Any]) -> Self@_make
+reveal_type(Point._make)  # revealed: bound method <class 'Point'>._make(iterable: Iterable[Any]) -> Point
 reveal_type(Point._asdict)  # revealed: def _asdict(self) -> dict[str, Any]
 reveal_type(Point._replace)  # revealed: def _replace(self, **kwargs: Any) -> Self@_replace
 

crates/ty_python_semantic/src/semantic_model.rs

@@ -232,7 +232,7 @@ impl<'db> Completion<'db> {
                 | Type::BytesLiteral(_) => CompletionKind::Value,
                 Type::EnumLiteral(_) => CompletionKind::Enum,
                 Type::ProtocolInstance(_) => CompletionKind::Interface,
-                Type::TypeVar(_) => CompletionKind::TypeParameter,
+                Type::NonInferableTypeVar(_) | Type::TypeVar(_) => CompletionKind::TypeParameter,
                 Type::Union(union) => union.elements(db).iter().find_map(|&ty| imp(db, ty))?,
                 Type::Intersection(intersection) => {
                     intersection.iter_positive(db).find_map(|ty| imp(db, ty))?

crates/ty_python_semantic/src/types.rs

@@ -44,7 +44,7 @@ use crate::types::context::{LintDiagnosticGuard, LintDiagnosticGuardBuilder};
 use crate::types::diagnostic::{INVALID_AWAIT, INVALID_TYPE_FORM, UNSUPPORTED_BOOL_CONVERSION};
 use crate::types::enums::{enum_metadata, is_single_member_enum};
 use crate::types::function::{
-    DataclassTransformerParams, FunctionSpans, FunctionType, KnownFunction,
+    DataclassTransformerParams, FunctionDecorators, FunctionSpans, FunctionType, KnownFunction,
 };
 use crate::types::generics::{
     GenericContext, PartialSpecialization, Specialization, bind_typevar, walk_generic_context,
@@ -612,9 +612,15 @@ pub enum Type<'db> {
     LiteralString,
     /// A bytes literal
     BytesLiteral(BytesLiteralType<'db>),
-    /// An instance of a typevar in a generic class or function. When the generic class or function
+    /// An instance of a typevar in a context where we can infer a specialization for it. (This is
-    /// is specialized, we will replace this typevar with its specialization.
+    /// typically the signature of a generic function, or of a constructor of a generic class.)
+    /// When the generic class or function binding this typevar is specialized, we will replace the
+    /// typevar with its specialization.
     TypeVar(BoundTypeVarInstance<'db>),
+    /// An instance of a typevar where we cannot infer a specialization for it. (This is typically
+    /// the body of the generic function or class that binds the typevar.) In these positions,
+    /// properties like assignability must hold for all possible specializations.
+    NonInferableTypeVar(BoundTypeVarInstance<'db>),
     /// A bound super object like `super()` or `super(A, A())`
     /// This type doesn't handle an unbound super object like `super(A)`; for that we just use
     /// a `Type::NominalInstance` of `builtins.super`.
@@ -823,6 +829,9 @@ impl<'db> Type<'db> {
                 )
                 .build(),
             Type::TypeVar(bound_typevar) => Type::TypeVar(bound_typevar.materialize(db, variance)),
+            Type::NonInferableTypeVar(bound_typevar) => {
+                Type::NonInferableTypeVar(bound_typevar.materialize(db, variance))
+            }
             Type::TypeIs(type_is) => {
                 type_is.with_type(db, type_is.return_type(db).materialize(db, variance))
             }
@@ -1127,6 +1136,9 @@ impl<'db> Type<'db> {
             Type::TypeVar(bound_typevar) => visitor.visit(self, || {
                 Type::TypeVar(bound_typevar.normalized_impl(db, visitor))
             }),
+            Type::NonInferableTypeVar(bound_typevar) => visitor.visit(self, || {
+                Type::NonInferableTypeVar(bound_typevar.normalized_impl(db, visitor))
+            }),
             Type::KnownInstance(known_instance) => visitor.visit(self, || {
                 Type::KnownInstance(known_instance.normalized_impl(db, visitor))
             }),
@@ -1203,6 +1215,7 @@ impl<'db> Type<'db> {
             | Type::Union(_)
             | Type::Intersection(_)
             | Type::Callable(_)
+            | Type::NonInferableTypeVar(_)
             | Type::TypeVar(_)
             | Type::BoundSuper(_)
             | Type::TypeIs(_)
@@ -1283,6 +1296,7 @@ impl<'db> Type<'db> {
             | Type::KnownInstance(_)
             | Type::PropertyInstance(_)
             | Type::Intersection(_)
+            | Type::NonInferableTypeVar(_)
             | Type::TypeVar(_)
             | Type::BoundSuper(_) => None,
         }
@@ -1399,13 +1413,17 @@ impl<'db> Type<'db> {
             // However, there is one exception to this general rule: for any given typevar `T`,
             // `T` will always be a subtype of any union containing `T`.
             // A similar rule applies in reverse to intersection types.
-            (Type::TypeVar(_), Type::Union(union)) if union.elements(db).contains(&self) => true,
+            (Type::NonInferableTypeVar(_), Type::Union(union))
-            (Type::Intersection(intersection), Type::TypeVar(_))
+                if union.elements(db).contains(&self) =>
+            {
+                true
+            }
+            (Type::Intersection(intersection), Type::NonInferableTypeVar(_))
                 if intersection.positive(db).contains(&target) =>
             {
                 true
             }
-            (Type::Intersection(intersection), Type::TypeVar(_))
+            (Type::Intersection(intersection), Type::NonInferableTypeVar(_))
                 if intersection.negative(db).contains(&target) =>
             {
                 false
@@ -1416,16 +1434,15 @@ impl<'db> Type<'db> {
             //
             // Note that this is not handled by the early return at the beginning of this method,
             // since subtyping between a TypeVar and an arbitrary other type cannot be guaranteed to be reflexive.
-            (Type::TypeVar(lhs_bound_typevar), Type::TypeVar(rhs_bound_typevar))
+            (
-                if lhs_bound_typevar == rhs_bound_typevar =>
+                Type::NonInferableTypeVar(lhs_bound_typevar),
-            {
+                Type::NonInferableTypeVar(rhs_bound_typevar),
-                true
+            ) if lhs_bound_typevar == rhs_bound_typevar => true,
-            }
 
             // A fully static typevar is a subtype of its upper bound, and to something similar to
             // the union of its constraints. An unbound, unconstrained, fully static typevar has an
             // implicit upper bound of `object` (which is handled above).
-            (Type::TypeVar(bound_typevar), _)
+            (Type::NonInferableTypeVar(bound_typevar), _)
                 if bound_typevar.typevar(db).bound_or_constraints(db).is_some() =>
             {
                 match bound_typevar.typevar(db).bound_or_constraints(db) {
@@ -1444,7 +1461,7 @@ impl<'db> Type<'db> {
             // If the typevar is constrained, there must be multiple constraints, and the typevar
             // might be specialized to any one of them. However, the constraints do not have to be
             // disjoint, which means an lhs type might be a subtype of all of the constraints.
-            (_, Type::TypeVar(bound_typevar))
+            (_, Type::NonInferableTypeVar(bound_typevar))
                 if bound_typevar
                     .typevar(db)
                     .constraints(db)
@@ -1496,7 +1513,10 @@ impl<'db> Type<'db> {
             // (If the typevar is bounded, it might be specialized to a smaller type than the
             // bound. This is true even if the bound is a final class, since the typevar can still
             // be specialized to `Never`.)
-            (_, Type::TypeVar(_)) => false,
+            (_, Type::NonInferableTypeVar(_)) => false,
+
+            // TODO: Infer specializations here
+            (Type::TypeVar(_), _) | (_, Type::TypeVar(_)) => false,
 
             // Note that the definition of `Type::AlwaysFalsy` depends on the return value of `__bool__`.
             // If `__bool__` always returns True or False, it can be treated as a subtype of `AlwaysTruthy` or `AlwaysFalsy`, respectively.
@@ -1756,7 +1776,7 @@ impl<'db> Type<'db> {
 
             // Other than the special cases enumerated above, `Instance` types and typevars are
             // never subtypes of any other variants
-            (Type::NominalInstance(_) | Type::TypeVar(_), _) => false,
+            (Type::NominalInstance(_) | Type::NonInferableTypeVar(_), _) => false,
         }
     }
 
@@ -1913,14 +1933,14 @@ impl<'db> Type<'db> {
             // be specialized to the same type. (This is an important difference between typevars
             // and `Any`!) Different typevars might be disjoint, depending on their bounds and
             // constraints, which are handled below.
-            (Type::TypeVar(self_bound_typevar), Type::TypeVar(other_bound_typevar))
+            (Type::NonInferableTypeVar(self_bound_typevar), Type::NonInferableTypeVar(other_bound_typevar))
                 if self_bound_typevar == other_bound_typevar =>
             {
                 false
             }
 
-            (tvar @ Type::TypeVar(_), Type::Intersection(intersection))
+            (tvar @ Type::NonInferableTypeVar(_), Type::Intersection(intersection))
-            | (Type::Intersection(intersection), tvar @ Type::TypeVar(_))
+            | (Type::Intersection(intersection), tvar @ Type::NonInferableTypeVar(_))
                 if intersection.negative(db).contains(&tvar) =>
             {
                 true
@@ -1930,7 +1950,7 @@ impl<'db> Type<'db> {
             // specialized to any type. A bounded typevar is not disjoint from its bound, and is
             // only disjoint from other types if its bound is. A constrained typevar is disjoint
             // from a type if all of its constraints are.
-            (Type::TypeVar(bound_typevar), other) | (other, Type::TypeVar(bound_typevar)) => {
+            (Type::NonInferableTypeVar(bound_typevar), other) | (other, Type::NonInferableTypeVar(bound_typevar)) => {
                 match bound_typevar.typevar(db).bound_or_constraints(db) {
                     None => false,
                     Some(TypeVarBoundOrConstraints::UpperBound(bound)) => {
@@ -1943,6 +1963,10 @@ impl<'db> Type<'db> {
                 }
             }
 
+            // TODO: Infer specializations here
+            (Type::TypeVar(_), _)
+            | (_, Type::TypeVar(_)) => false,
+
             (Type::Union(union), other) | (other, Type::Union(union)) => union
                 .elements(db)
                 .iter()
@@ -2383,7 +2407,7 @@ impl<'db> Type<'db> {
             // the bound is a final singleton class, since it can still be specialized to `Never`.
             // A constrained typevar is a singleton if all of its constraints are singletons. (Note
             // that you cannot specialize a constrained typevar to a subtype of a constraint.)
-            Type::TypeVar(bound_typevar) => {
+            Type::NonInferableTypeVar(bound_typevar) => {
                 match bound_typevar.typevar(db).bound_or_constraints(db) {
                     None => false,
                     Some(TypeVarBoundOrConstraints::UpperBound(_)) => false,
@@ -2394,6 +2418,8 @@ impl<'db> Type<'db> {
                 }
             }
 
+            Type::TypeVar(_) => false,
+
             // We eagerly transform `SubclassOf` to `ClassLiteral` for final types, so `SubclassOf` is never a singleton.
             Type::SubclassOf(..) => false,
             Type::BoundSuper(..) => false,
@@ -2513,7 +2539,7 @@ impl<'db> Type<'db> {
             // `Never`. A constrained typevar is single-valued if all of its constraints are
             // single-valued. (Note that you cannot specialize a constrained typevar to a subtype
             // of a constraint.)
-            Type::TypeVar(bound_typevar) => {
+            Type::NonInferableTypeVar(bound_typevar) => {
                 match bound_typevar.typevar(db).bound_or_constraints(db) {
                     None => false,
                     Some(TypeVarBoundOrConstraints::UpperBound(_)) => false,
@@ -2524,6 +2550,8 @@ impl<'db> Type<'db> {
                 }
             }
 
+            Type::TypeVar(_) => false,
+
             Type::SubclassOf(..) => {
                 // TODO: Same comment as above for `is_singleton`
                 false
@@ -2680,6 +2708,7 @@ impl<'db> Type<'db> {
             | Type::LiteralString
             | Type::BytesLiteral(_)
             | Type::EnumLiteral(_)
+            | Type::NonInferableTypeVar(_)
             | Type::TypeVar(_)
             | Type::NominalInstance(_)
             | Type::ProtocolInstance(_)
@@ -2790,7 +2819,7 @@ impl<'db> Type<'db> {
                 Type::object(db).instance_member(db, name)
             }
 
-            Type::TypeVar(bound_typevar) => {
+            Type::NonInferableTypeVar(bound_typevar) => {
                 match bound_typevar.typevar(db).bound_or_constraints(db) {
                     None => Type::object(db).instance_member(db, name),
                     Some(TypeVarBoundOrConstraints::UpperBound(bound)) => {
@@ -2803,6 +2832,16 @@ impl<'db> Type<'db> {
                 }
             }
 
+            Type::TypeVar(_) => {
+                debug_assert!(
+                    false,
+                    "should not be able to access instance member `{name}` \
+                    of type variable {} in inferable position",
+                    self.display(db)
+                );
+                Place::Unbound.into()
+            }
+
             Type::IntLiteral(_) => KnownClass::Int.to_instance(db).instance_member(db, name),
             Type::BooleanLiteral(_) | Type::TypeIs(_) => {
                 KnownClass::Bool.to_instance(db).instance_member(db, name)
@@ -3329,6 +3368,7 @@ impl<'db> Type<'db> {
             | Type::BytesLiteral(..)
             | Type::EnumLiteral(..)
             | Type::LiteralString
+            | Type::NonInferableTypeVar(..)
             | Type::TypeVar(..)
             | Type::SpecialForm(..)
             | Type::KnownInstance(..)
@@ -3664,7 +3704,7 @@ impl<'db> Type<'db> {
                 }
             },
 
-            Type::TypeVar(bound_typevar) => {
+            Type::NonInferableTypeVar(bound_typevar) => {
                 match bound_typevar.typevar(db).bound_or_constraints(db) {
                     None => Truthiness::Ambiguous,
                     Some(TypeVarBoundOrConstraints::UpperBound(bound)) => {
@@ -3675,6 +3715,7 @@ impl<'db> Type<'db> {
                     }
                 }
             }
+            Type::TypeVar(_) => Truthiness::Ambiguous,
 
             Type::NominalInstance(instance) => instance
                 .class(db)
@@ -3767,7 +3808,7 @@ impl<'db> Type<'db> {
                     .into()
             }
 
-            Type::TypeVar(bound_typevar) => {
+            Type::NonInferableTypeVar(bound_typevar) => {
                 match bound_typevar.typevar(db).bound_or_constraints(db) {
                     None => CallableBinding::not_callable(self).into(),
                     Some(TypeVarBoundOrConstraints::UpperBound(bound)) => bound.bindings(db),
@@ -3780,6 +3821,15 @@ impl<'db> Type<'db> {
                 }
             }
 
+            Type::TypeVar(_) => {
+                debug_assert!(
+                    false,
+                    "should not be able to call type variable {} in inferable position",
+                    self.display(db)
+                );
+                CallableBinding::not_callable(self).into()
+            }
+
             Type::BoundMethod(bound_method) => {
                 let signature = bound_method.function(db).signature(db);
                 CallableBinding::from_overloads(self, signature.overloads.iter().cloned())
@@ -5111,20 +5161,22 @@ impl<'db> Type<'db> {
         // have the class's typevars still in the method signature when we attempt to call it. To
         // do this, we instead use the _identity_ specialization, which maps each of the class's
         // generic typevars to itself.
-        let (generic_origin, generic_context, self_type) =
+        let (generic_origin, generic_context, self_type) = match self {
-            match self {
+            Type::ClassLiteral(class) => match class.generic_context(db) {
-                Type::ClassLiteral(class) => match class.generic_context(db) {
+                Some(generic_context) => (
-                    Some(generic_context) => (
+                    Some(class),
-                        Some(class),
+                    Some(generic_context),
-                        Some(generic_context),
+                    Type::from(class.apply_specialization(db, |_| {
-                        Type::from(class.apply_specialization(db, |_| {
+                        // It is important that identity_specialization specializes the class with
-                            generic_context.identity_specialization(db)
+                        // _inferable_ typevars, so that our specialization inference logic will
-                        })),
+                        // try to find a specialization for them.
-                    ),
+                        generic_context.identity_specialization(db)
-                    _ => (None, None, self),
+                    })),
-                },
+                ),
                 _ => (None, None, self),
-            };
+            },
+            _ => (None, None, self),
+        };
 
         // As of now we do not model custom `__call__` on meta-classes, so the code below
         // only deals with interplay between `__new__` and `__init__` methods.
@@ -5281,32 +5333,10 @@ impl<'db> Type<'db> {
             // If there is no bound or constraints on a typevar `T`, `T: object` implicitly, which
             // has no instance type. Otherwise, synthesize a typevar with bound or constraints
             // mapped through `to_instance`.
-            Type::TypeVar(bound_typevar) => {
+            Type::NonInferableTypeVar(bound_typevar) => {
-                let typevar = bound_typevar.typevar(db);
+                Some(Type::NonInferableTypeVar(bound_typevar.to_instance(db)?))
-                let bound_or_constraints = match typevar.bound_or_constraints(db)? {
-                    TypeVarBoundOrConstraints::UpperBound(upper_bound) => {
-                        TypeVarBoundOrConstraints::UpperBound(upper_bound.to_instance(db)?)
-                    }
-                    TypeVarBoundOrConstraints::Constraints(constraints) => {
-                        TypeVarBoundOrConstraints::Constraints(
-                            constraints.to_instance(db)?.into_union()?,
-                        )
-                    }
-                };
-                Some(Type::TypeVar(BoundTypeVarInstance::new(
-                    db,
-                    TypeVarInstance::new(
-                        db,
-                        Name::new(format!("{}'instance", typevar.name(db))),
-                        None,
-                        Some(bound_or_constraints.into()),
-                        typevar.variance(db),
-                        None,
-                        typevar.kind(db),
-                    ),
-                    bound_typevar.binding_context(db),
-                )))
             }
+            Type::TypeVar(bound_typevar) => Some(Type::TypeVar(bound_typevar.to_instance(db)?)),
             Type::TypeAlias(alias) => alias.value_type(db).to_instance(db),
             Type::Intersection(_) => Some(todo_type!("Type::Intersection.to_instance")),
             Type::BooleanLiteral(_)
@@ -5390,6 +5420,7 @@ impl<'db> Type<'db> {
             | Type::LiteralString
             | Type::ModuleLiteral(_)
             | Type::StringLiteral(_)
+            | Type::NonInferableTypeVar(_)
             | Type::TypeVar(_)
             | Type::Callable(_)
             | Type::BoundMethod(_)
@@ -5423,7 +5454,7 @@ impl<'db> Type<'db> {
                         typevar_binding_context,
                         *typevar,
                     )
-                    .map(Type::TypeVar)
+                    .map(Type::NonInferableTypeVar)
                     .unwrap_or(*self))
                 }
                 KnownInstanceType::Deprecated(_) => Err(InvalidTypeExpressionError {
@@ -5506,7 +5537,7 @@ impl<'db> Type<'db> {
                         Some(TypeVarBoundOrConstraints::UpperBound(instance).into()),
                         TypeVarVariance::Invariant,
                         None,
-                        TypeVarKind::Implicit,
+                        TypeVarKind::TypingSelf,
                     );
                     Ok(bind_typevar(
                         db,
@@ -5516,7 +5547,7 @@ impl<'db> Type<'db> {
                         typevar_binding_context,
                         typevar,
                     )
-                    .map(Type::TypeVar)
+                    .map(Type::NonInferableTypeVar)
                     .unwrap_or(*self))
                 }
                 SpecialFormType::TypeAlias => Ok(Type::Dynamic(DynamicType::TodoTypeAlias)),
@@ -5685,7 +5716,7 @@ impl<'db> Type<'db> {
             }
             Type::Callable(_) | Type::DataclassTransformer(_) => KnownClass::Type.to_instance(db),
             Type::ModuleLiteral(_) => KnownClass::ModuleType.to_class_literal(db),
-            Type::TypeVar(bound_typevar) => {
+            Type::NonInferableTypeVar(bound_typevar) => {
                 match bound_typevar.typevar(db).bound_or_constraints(db) {
                     None => KnownClass::Type.to_instance(db),
                     Some(TypeVarBoundOrConstraints::UpperBound(bound)) => bound.to_meta_type(db),
@@ -5696,6 +5727,7 @@ impl<'db> Type<'db> {
                     }
                 }
             }
+            Type::TypeVar(_) => KnownClass::Type.to_instance(db),
 
             Type::ClassLiteral(class) => class.metaclass(db),
             Type::GenericAlias(alias) => ClassType::from(*alias).metaclass(db),
@@ -5792,16 +5824,46 @@ impl<'db> Type<'db> {
                 TypeMapping::PartialSpecialization(partial) => {
                     partial.get(db, bound_typevar).unwrap_or(self)
                 }
-                TypeMapping::PromoteLiterals | TypeMapping::BindLegacyTypevars(_) => self,
+                TypeMapping::BindSelf(self_type) => {
+                    if bound_typevar.typevar(db).is_self(db) {
+                        *self_type
+                    } else {
+                        self
+                    }
+                }
+                TypeMapping::PromoteLiterals | TypeMapping::BindLegacyTypevars(_) |
+                TypeMapping::MarkTypeVarsInferable(_) => self,
+            }
+
+            Type::NonInferableTypeVar(bound_typevar) => match type_mapping {
+                TypeMapping::Specialization(specialization) => {
+                    specialization.get(db, bound_typevar).unwrap_or(self)
+                }
+                TypeMapping::PartialSpecialization(partial) => {
+                    partial.get(db, bound_typevar).unwrap_or(self)
+                }
+                TypeMapping::MarkTypeVarsInferable(binding_context) => {
+                    if bound_typevar.binding_context(db) == *binding_context {
+                        Type::TypeVar(bound_typevar)
+                    } else {
+                        self
+                    }
+                }
+                TypeMapping::PromoteLiterals |
+                TypeMapping::BindLegacyTypevars(_) |
+                TypeMapping::BindSelf(_)
+                    => self,
             }
 
             Type::KnownInstance(KnownInstanceType::TypeVar(typevar)) => match type_mapping {
-                TypeMapping::Specialization(_) |
-                TypeMapping::PartialSpecialization(_) |
-                TypeMapping::PromoteLiterals => self,
                 TypeMapping::BindLegacyTypevars(binding_context) => {
                     Type::TypeVar(BoundTypeVarInstance::new(db, typevar, *binding_context))
                 }
+                TypeMapping::Specialization(_) |
+                TypeMapping::PartialSpecialization(_) |
+                TypeMapping::PromoteLiterals |
+                TypeMapping::BindSelf(_) |
+                TypeMapping::MarkTypeVarsInferable(_) => self,
             }
 
             Type::FunctionLiteral(function) => {
@@ -5896,7 +5958,9 @@ impl<'db> Type<'db> {
             | Type::EnumLiteral(_) => match type_mapping {
                 TypeMapping::Specialization(_) |
                 TypeMapping::PartialSpecialization(_) |
-                TypeMapping::BindLegacyTypevars(_) => self,
+                TypeMapping::BindLegacyTypevars(_) |
+                TypeMapping::BindSelf(_) |
+                TypeMapping::MarkTypeVarsInferable(_) => self,
                 TypeMapping::PromoteLiterals => self.literal_fallback_instance(db)
                     .expect("literal type should have fallback instance type"),
             }
@@ -5929,10 +5993,10 @@ impl<'db> Type<'db> {
         typevars: &mut FxOrderSet<BoundTypeVarInstance<'db>>,
     ) {
         match self {
-            Type::TypeVar(bound_typevar) => {
+            Type::NonInferableTypeVar(bound_typevar) | Type::TypeVar(bound_typevar) => {
                 if matches!(
                     bound_typevar.typevar(db).kind(db),
-                    TypeVarKind::Legacy | TypeVarKind::Implicit
+                    TypeVarKind::Legacy | TypeVarKind::TypingSelf
                 ) && binding_context.is_none_or(|binding_context| {
                     bound_typevar.binding_context(db) == BindingContext::Definition(binding_context)
                 }) {
@@ -6145,6 +6209,7 @@ impl<'db> Type<'db> {
             | Self::PropertyInstance(_)
             | Self::BoundSuper(_) => self.to_meta_type(db).definition(db),
 
+            Self::NonInferableTypeVar(bound_typevar) |
             Self::TypeVar(bound_typevar) => Some(TypeDefinition::TypeVar(bound_typevar.typevar(db).definition(db)?)),
 
             Self::ProtocolInstance(protocol) => match protocol.inner {
@@ -6270,6 +6335,10 @@ pub enum TypeMapping<'a, 'db> {
     /// Binds a legacy typevar with the generic context (class, function, type alias) that it is
     /// being used in.
     BindLegacyTypevars(BindingContext<'db>),
+    /// Binds any `typing.Self` typevar with a particular `self` class.
+    BindSelf(Type<'db>),
+    /// Marks the typevars that are bound by a generic class or function as inferable.
+    MarkTypeVarsInferable(BindingContext<'db>),
 }
 
 fn walk_type_mapping<'db, V: visitor::TypeVisitor<'db> + ?Sized>(
@@ -6284,7 +6353,12 @@ fn walk_type_mapping<'db, V: visitor::TypeVisitor<'db> + ?Sized>(
         TypeMapping::PartialSpecialization(specialization) => {
             walk_partial_specialization(db, specialization, visitor);
         }
-        TypeMapping::PromoteLiterals | TypeMapping::BindLegacyTypevars(_) => {}
+        TypeMapping::BindSelf(self_type) => {
+            visitor.visit_type(db, *self_type);
+        }
+        TypeMapping::PromoteLiterals
+        | TypeMapping::BindLegacyTypevars(_)
+        | TypeMapping::MarkTypeVarsInferable(_) => {}
     }
 }
 
@@ -6301,6 +6375,10 @@ impl<'db> TypeMapping<'_, 'db> {
             TypeMapping::BindLegacyTypevars(binding_context) => {
                 TypeMapping::BindLegacyTypevars(*binding_context)
             }
+            TypeMapping::BindSelf(self_type) => TypeMapping::BindSelf(*self_type),
+            TypeMapping::MarkTypeVarsInferable(binding_context) => {
+                TypeMapping::MarkTypeVarsInferable(*binding_context)
+            }
         }
     }
 
@@ -6316,6 +6394,12 @@ impl<'db> TypeMapping<'_, 'db> {
             TypeMapping::BindLegacyTypevars(binding_context) => {
                 TypeMapping::BindLegacyTypevars(*binding_context)
             }
+            TypeMapping::BindSelf(self_type) => {
+                TypeMapping::BindSelf(self_type.normalized_impl(db, visitor))
+            }
+            TypeMapping::MarkTypeVarsInferable(binding_context) => {
+                TypeMapping::MarkTypeVarsInferable(*binding_context)
+            }
         }
     }
 }
@@ -6836,7 +6920,7 @@ pub enum TypeVarKind {
     /// `def foo[T](x: T) -> T: ...`
     Pep695,
     /// `typing.Self`
-    Implicit,
+    TypingSelf,
 }
 
 /// A type variable that has not been bound to a generic context yet.
@@ -6926,8 +7010,8 @@ impl<'db> TypeVarInstance<'db> {
         BoundTypeVarInstance::new(db, self, BindingContext::Definition(binding_context))
     }
 
-    pub(crate) fn is_implicit(self, db: &'db dyn Db) -> bool {
+    pub(crate) fn is_self(self, db: &'db dyn Db) -> bool {
-        matches!(self.kind(db), TypeVarKind::Implicit)
+        matches!(self.kind(db), TypeVarKind::TypingSelf)
     }
 
     pub(crate) fn upper_bound(self, db: &'db dyn Db) -> Option<Type<'db>> {
@@ -7022,6 +7106,26 @@ impl<'db> TypeVarInstance<'db> {
         )
     }
 
+    fn to_instance(self, db: &'db dyn Db) -> Option<Self> {
+        let bound_or_constraints = match self.bound_or_constraints(db)? {
+            TypeVarBoundOrConstraints::UpperBound(upper_bound) => {
+                TypeVarBoundOrConstraints::UpperBound(upper_bound.to_instance(db)?)
+            }
+            TypeVarBoundOrConstraints::Constraints(constraints) => {
+                TypeVarBoundOrConstraints::Constraints(constraints.to_instance(db)?.into_union()?)
+            }
+        };
+        Some(Self::new(
+            db,
+            Name::new(format!("{}'instance", self.name(db))),
+            None,
+            Some(bound_or_constraints.into()),
+            self.variance(db),
+            None,
+            self.kind(db),
+        ))
+    }
+
     #[salsa::tracked]
     fn lazy_bound(self, db: &'db dyn Db) -> Option<TypeVarBoundOrConstraints<'db>> {
         let definition = self.definition(db)?;
@@ -7138,6 +7242,14 @@ impl<'db> BoundTypeVarInstance<'db> {
             self.binding_context(db),
         )
     }
+
+    fn to_instance(self, db: &'db dyn Db) -> Option<Self> {
+        Some(Self::new(
+            db,
+            self.typevar(db).to_instance(db)?,
+            self.binding_context(db),
+        ))
+    }
 }
 
 #[derive(Clone, Copy, Debug, Hash, PartialEq, Eq, salsa::Update, get_size2::GetSize)]
@@ -8328,16 +8440,35 @@ fn walk_bound_method_type<'db, V: visitor::TypeVisitor<'db> + ?Sized>(
     visitor.visit_type(db, method.self_instance(db));
 }
 
+#[salsa::tracked]
 impl<'db> BoundMethodType<'db> {
+    /// Returns the type that replaces any `typing.Self` annotations in the bound method signature.
+    /// This is normally the bound-instance type (the type of `self` or `cls`), but if the bound method is
+    /// a `@classmethod`, then it should be an instance of that bound-instance type.
+    pub(crate) fn typing_self_type(self, db: &'db dyn Db) -> Type<'db> {
+        let mut self_instance = self.self_instance(db);
+        if self
+            .function(db)
+            .has_known_decorator(db, FunctionDecorators::CLASSMETHOD)
+        {
+            self_instance = self_instance.to_instance(db).unwrap_or_else(Type::unknown);
+        }
+        self_instance
+    }
+
+    #[salsa::tracked(heap_size=ruff_memory_usage::heap_size)]
     pub(crate) fn into_callable_type(self, db: &'db dyn Db) -> CallableType<'db> {
+        let function = self.function(db);
+        let self_instance = self.typing_self_type(db);
+
         CallableType::new(
             db,
             CallableSignature::from_overloads(
-                self.function(db)
+                function
                     .signature(db)
                     .overloads
                     .iter()
-                    .map(signatures::Signature::bind_self),
+                    .map(|signature| signature.bind_self(db, Some(self_instance))),
             ),
             false,
         )
@@ -8435,7 +8566,7 @@ impl<'db> CallableType<'db> {
     pub(crate) fn bind_self(self, db: &'db dyn Db) -> Type<'db> {
         Type::Callable(CallableType::new(
             db,
-            self.signatures(db).bind_self(),
+            self.signatures(db).bind_self(db, None),
             false,
         ))
     }

crates/ty_python_semantic/src/types/builder.rs

@@ -983,7 +983,8 @@ impl<'db> InnerIntersectionBuilder<'db> {
         let mut positive_to_remove = SmallVec::<[usize; 1]>::new();
 
         for (typevar_index, ty) in self.positive.iter().enumerate() {
-            let Type::TypeVar(bound_typevar) = ty else {
+            let (Type::NonInferableTypeVar(bound_typevar) | Type::TypeVar(bound_typevar)) = ty
+            else {
                 continue;
             };
             let Some(TypeVarBoundOrConstraints::Constraints(constraints)) =

crates/ty_python_semantic/src/types/class.rs

@@ -966,6 +966,7 @@ impl<'db> ClassType<'db> {
 
     /// Return a callable type (or union of callable types) that represents the callable
     /// constructor signature of this class.
+    #[salsa::tracked(heap_size=ruff_memory_usage::heap_size)]
     pub(super) fn into_callable(self, db: &'db dyn Db) -> Type<'db> {
         let self_ty = Type::from(self);
         let metaclass_dunder_call_function_symbol = self_ty
@@ -1017,9 +1018,10 @@ impl<'db> ClassType<'db> {
                 })
             });
 
+            let instance_ty = Type::instance(db, self);
             let dunder_new_bound_method = Type::Callable(CallableType::new(
                 db,
-                dunder_new_signature.bind_self(),
+                dunder_new_signature.bind_self(db, Some(instance_ty)),
                 true,
             ));
 
@@ -1057,9 +1059,10 @@ impl<'db> ClassType<'db> {
 
                 if let Some(signature) = signature {
                     let synthesized_signature = |signature: &Signature<'db>| {
+                        let instance_ty = Type::instance(db, self);
                         Signature::new(signature.parameters().clone(), Some(correct_return_type))
                             .with_definition(signature.definition())
-                            .bind_self()
+                            .bind_self(db, Some(instance_ty))
                     };
 
                     let synthesized_dunder_init_signature = CallableSignature::from_overloads(

crates/ty_python_semantic/src/types/class_base.rs

@@ -155,6 +155,7 @@ impl<'db> ClassBase<'db> {
             | Type::StringLiteral(_)
             | Type::LiteralString
             | Type::ModuleLiteral(_)
+            | Type::NonInferableTypeVar(_)
             | Type::TypeVar(_)
             | Type::BoundSuper(_)
             | Type::ProtocolInstance(_)

crates/ty_python_semantic/src/types/display.rs

@@ -130,6 +130,8 @@ impl Display for DisplayRepresentation<'_> {
             Type::Callable(callable) => callable.display(self.db).fmt(f),
             Type::BoundMethod(bound_method) => {
                 let function = bound_method.function(self.db);
+                let self_ty = bound_method.self_instance(self.db);
+                let typing_self_ty = bound_method.typing_self_type(self.db);
 
                 match function.signature(self.db).overloads.as_slice() {
                     [signature] => {
@@ -142,9 +144,11 @@ impl Display for DisplayRepresentation<'_> {
                             f,
                             "bound method {instance}.{method}{type_parameters}{signature}",
                             method = function.name(self.db),
-                            instance = bound_method.self_instance(self.db).display(self.db),
+                            instance = self_ty.display(self.db),
                             type_parameters = type_parameters,
-                            signature = signature.bind_self().display(self.db)
+                            signature = signature
+                                .bind_self(self.db, Some(typing_self_ty))
+                                .display(self.db)
                         )
                     }
                     signatures => {
@@ -152,7 +156,11 @@ impl Display for DisplayRepresentation<'_> {
                         f.write_str("Overload[")?;
                         let mut join = f.join(", ");
                         for signature in signatures {
-                            join.entry(&signature.bind_self().display(self.db));
+                            join.entry(
+                                &signature
+                                    .bind_self(self.db, Some(typing_self_ty))
+                                    .display(self.db),
+                            );
                         }
                         f.write_str("]")
                     }
@@ -214,7 +222,7 @@ impl Display for DisplayRepresentation<'_> {
                     name = enum_literal.name(self.db),
                 )
             }
-            Type::TypeVar(bound_typevar) => {
+            Type::NonInferableTypeVar(bound_typevar) | Type::TypeVar(bound_typevar) => {
                 f.write_str(bound_typevar.typevar(self.db).name(self.db))?;
                 if let Some(binding_context) = bound_typevar.binding_context(self.db).name(self.db)
                 {
@@ -455,7 +463,7 @@ impl Display for DisplayGenericContext<'_> {
 
         let non_implicit_variables: Vec<_> = variables
             .iter()
-            .filter(|bound_typevar| !bound_typevar.typevar(self.db).is_implicit(self.db))
+            .filter(|bound_typevar| !bound_typevar.typevar(self.db).is_self(self.db))
             .collect();
 
         if non_implicit_variables.is_empty() {

crates/ty_python_semantic/src/types/function.rs

@@ -1014,6 +1014,7 @@ fn is_instance_truthiness<'db>(
         | Type::PropertyInstance(..)
         | Type::AlwaysTruthy
         | Type::AlwaysFalsy
+        | Type::NonInferableTypeVar(..)
         | Type::TypeVar(..)
         | Type::BoundSuper(..)
         | Type::TypeIs(..)

crates/ty_python_semantic/src/types/generics.rs

@@ -236,7 +236,8 @@ impl<'db> GenericContext<'db> {
         db: &'db dyn Db,
         known_class: Option<KnownClass>,
     ) -> Specialization<'db> {
-        let partial = self.specialize_partial(db, &vec![None; self.variables(db).len()]);
+        let partial =
+            self.specialize_partial(db, std::iter::repeat_n(None, self.variables(db).len()));
         if known_class == Some(KnownClass::Tuple) {
             Specialization::new(
                 db,
@@ -249,6 +250,10 @@ impl<'db> GenericContext<'db> {
         }
     }
 
+    /// Returns a specialization of this generic context where each typevar is mapped to itself.
+    /// (And in particular, to an _inferable_ version of itself, since this will be used in our
+    /// class constructor invocation machinery to infer a specialization for the class from the
+    /// arguments passed to its constructor.)
     pub(crate) fn identity_specialization(self, db: &'db dyn Db) -> Specialization<'db> {
         let types = self
             .variables(db)
@@ -314,11 +319,12 @@ impl<'db> GenericContext<'db> {
     /// Creates a specialization of this generic context. Panics if the length of `types` does not
     /// match the number of typevars in the generic context. If any provided type is `None`, we
     /// will use the corresponding typevar's default type.
-    pub(crate) fn specialize_partial(
+    pub(crate) fn specialize_partial<I>(self, db: &'db dyn Db, types: I) -> Specialization<'db>
-        self,
+    where
-        db: &'db dyn Db,
+        I: IntoIterator<Item = Option<Type<'db>>>,
-        types: &[Option<Type<'db>>],
+        I::IntoIter: ExactSizeIterator,
-    ) -> Specialization<'db> {
+    {
+        let types = types.into_iter();
         let variables = self.variables(db);
         assert!(variables.len() == types.len());
 
@@ -331,9 +337,9 @@ impl<'db> GenericContext<'db> {
         // If there is a mapping for `T`, we want to map `U` to that type, not to `T`. To handle
         // this, we repeatedly apply the specialization to itself, until we reach a fixed point.
         let mut expanded = vec![Type::unknown(); types.len()];
-        for (idx, (ty, typevar)) in types.iter().zip(variables).enumerate() {
+        for (idx, (ty, typevar)) in types.zip(variables).enumerate() {
             if let Some(ty) = ty {
-                expanded[idx] = *ty;
+                expanded[idx] = ty;
                 continue;
             }
 
@@ -749,18 +755,12 @@ impl<'db> SpecializationBuilder<'db> {
     }
 
     pub(crate) fn build(&mut self, generic_context: GenericContext<'db>) -> Specialization<'db> {
-        let types: Box<[_]> = generic_context
+        let types = generic_context
             .variables(self.db)
             .iter()
-            .map(|variable| {
+            .map(|variable| self.types.get(variable).copied());
-                self.types
-                    .get(variable)
-                    .copied()
-                    .unwrap_or(variable.default_type(self.db).unwrap_or(Type::unknown()))
-            })
-            .collect();
         // TODO Infer the tuple spec for a tuple type
-        Specialization::new(self.db, generic_context, types, None)
+        generic_context.specialize_partial(self.db, types)
     }
 
     fn add_type_mapping(&mut self, bound_typevar: BoundTypeVarInstance<'db>, ty: Type<'db>) {
@@ -777,6 +777,10 @@ impl<'db> SpecializationBuilder<'db> {
         formal: Type<'db>,
         actual: Type<'db>,
     ) -> Result<(), SpecializationError<'db>> {
+        if formal == actual {
+            return Ok(());
+        }
+
         // If the actual type is a subtype of the formal type, then return without adding any new
         // type mappings. (Note that if the formal type contains any typevars, this check will
         // fail, since no non-typevar types are assignable to a typevar. Also note that we are

crates/ty_python_semantic/src/types/ide_support.rs

@@ -151,6 +151,7 @@ impl<'db> AllMembers<'db> {
             | Type::ProtocolInstance(_)
             | Type::SpecialForm(_)
             | Type::KnownInstance(_)
+            | Type::NonInferableTypeVar(_)
             | Type::TypeVar(_)
             | Type::BoundSuper(_)
             | Type::TypeIs(_) => match ty.to_meta_type(db) {

crates/ty_python_semantic/src/types/infer.rs

@@ -4025,6 +4025,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
             | Type::WrapperDescriptor(_)
             | Type::DataclassDecorator(_)
             | Type::DataclassTransformer(_)
+            | Type::NonInferableTypeVar(..)
             | Type::TypeVar(..)
             | Type::AlwaysTruthy
             | Type::AlwaysFalsy
@@ -7231,6 +7232,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
                 | Type::BytesLiteral(_)
                 | Type::EnumLiteral(_)
                 | Type::BoundSuper(_)
+                | Type::NonInferableTypeVar(_)
                 | Type::TypeVar(_)
                 | Type::TypeIs(_)
                 | Type::TypedDict(_),
@@ -7572,6 +7574,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
                 | Type::BytesLiteral(_)
                 | Type::EnumLiteral(_)
                 | Type::BoundSuper(_)
+                | Type::NonInferableTypeVar(_)
                 | Type::TypeVar(_)
                 | Type::TypeIs(_)
                 | Type::TypedDict(_),
@@ -7601,6 +7604,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
                 | Type::BytesLiteral(_)
                 | Type::EnumLiteral(_)
                 | Type::BoundSuper(_)
+                | Type::NonInferableTypeVar(_)
                 | Type::TypeVar(_)
                 | Type::TypeIs(_)
                 | Type::TypedDict(_),
@@ -8652,7 +8656,8 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
             .next()
             .expect("valid bindings should have matching overload");
         Type::from(generic_class.apply_specialization(self.db(), |_| {
-            generic_context.specialize_partial(self.db(), overload.parameter_types())
+            generic_context
+                .specialize_partial(self.db(), overload.parameter_types().iter().copied())
         }))
     }
 
@@ -10604,7 +10609,7 @@ impl<'db> TypeInferenceBuilder<'db, '_> {
 
                 let mut signature_iter = callable_binding.into_iter().map(|binding| {
                     if argument_type.is_bound_method() {
-                        binding.signature.bind_self()
+                        binding.signature.bind_self(self.db(), Some(argument_type))
                     } else {
                         binding.signature.clone()
                     }

crates/ty_python_semantic/src/types/narrow.rs

@@ -215,7 +215,7 @@ impl ClassInfoConstraintFunction {
             Type::Union(union) => {
                 union.try_map(db, |element| self.generate_constraint(db, *element))
             }
-            Type::TypeVar(bound_typevar) => match bound_typevar
+            Type::NonInferableTypeVar(bound_typevar) => match bound_typevar
                 .typevar(db)
                 .bound_or_constraints(db)?
             {
@@ -259,6 +259,7 @@ impl ClassInfoConstraintFunction {
             | Type::IntLiteral(_)
             | Type::KnownInstance(_)
             | Type::TypeIs(_)
+            | Type::TypeVar(_)
             | Type::WrapperDescriptor(_)
             | Type::DataclassTransformer(_)
             | Type::TypedDict(_) => None,

crates/ty_python_semantic/src/types/signatures.rs

@@ -19,7 +19,8 @@ use super::{DynamicType, Type, TypeVarVariance, definition_expression_type};
 use crate::semantic_index::definition::Definition;
 use crate::types::generics::{GenericContext, walk_generic_context};
 use crate::types::{
-    BoundTypeVarInstance, KnownClass, NormalizedVisitor, TypeMapping, TypeRelation, todo_type,
+    BindingContext, BoundTypeVarInstance, KnownClass, NormalizedVisitor, TypeMapping, TypeRelation,
+    todo_type,
 };
 use crate::{Db, FxOrderSet};
 use ruff_python_ast::{self as ast, name::Name};
@@ -98,9 +99,16 @@ impl<'db> CallableSignature<'db> {
         }
     }
 
-    pub(crate) fn bind_self(&self) -> Self {
+    /// Binds the first (presumably `self`) parameter of this signature. If a `self_type` is
+    /// provided, we will replace any occurrences of `typing.Self` in the parameter and return
+    /// annotations with that type.
+    pub(crate) fn bind_self(&self, db: &'db dyn Db, self_type: Option<Type<'db>>) -> Self {
         Self {
-            overloads: self.overloads.iter().map(Signature::bind_self).collect(),
+            overloads: self
+                .overloads
+                .iter()
+                .map(|signature| signature.bind_self(db, self_type))
+                .collect(),
         }
     }
 
@@ -328,8 +336,11 @@ impl<'db> Signature<'db> {
         let parameters =
             Parameters::from_parameters(db, definition, function_node.parameters.as_ref());
         let return_ty = function_node.returns.as_ref().map(|returns| {
-            let plain_return_ty = definition_expression_type(db, definition, returns.as_ref());
+            let plain_return_ty = definition_expression_type(db, definition, returns.as_ref())
-
+                .apply_type_mapping(
+                    db,
+                    &TypeMapping::MarkTypeVarsInferable(BindingContext::Definition(definition)),
+                );
             if function_node.is_async && !is_generator {
                 KnownClass::CoroutineType
                     .to_specialized_instance(db, [Type::any(), Type::any(), plain_return_ty])
@@ -457,13 +468,20 @@ impl<'db> Signature<'db> {
         self.definition
     }
 
-    pub(crate) fn bind_self(&self) -> Self {
+    pub(crate) fn bind_self(&self, db: &'db dyn Db, self_type: Option<Type<'db>>) -> Self {
+        let mut parameters = Parameters::new(self.parameters().iter().skip(1).cloned());
+        let mut return_ty = self.return_ty;
+        if let Some(self_type) = self_type {
+            parameters = parameters.apply_type_mapping(db, &TypeMapping::BindSelf(self_type));
+            return_ty =
+                return_ty.map(|ty| ty.apply_type_mapping(db, &TypeMapping::BindSelf(self_type)));
+        }
         Self {
             generic_context: self.generic_context,
             inherited_generic_context: self.inherited_generic_context,
             definition: self.definition,
-            parameters: Parameters::new(self.parameters().iter().skip(1).cloned()),
+            parameters,
-            return_ty: self.return_ty,
+            return_ty,
         }
     }
 
@@ -1432,9 +1450,12 @@ impl<'db> Parameter<'db> {
         kind: ParameterKind<'db>,
     ) -> Self {
         Self {
-            annotated_type: parameter
+            annotated_type: parameter.annotation().map(|annotation| {
-                .annotation()
+                definition_expression_type(db, definition, annotation).apply_type_mapping(
-                .map(|annotation| definition_expression_type(db, definition, annotation)),
+                    db,
+                    &TypeMapping::MarkTypeVarsInferable(BindingContext::Definition(definition)),
+                )
+            }),
             kind,
             form: ParameterForm::Value,
         }

crates/ty_python_semantic/src/types/subclass_of.rs

@@ -91,7 +91,7 @@ impl<'db> SubclassOfType<'db> {
                 TypeVarVariance::Invariant => {
                     // We need to materialize this to `type[T]` but that isn't representable so
                     // we instead use a type variable with an upper bound of `type`.
-                    Type::TypeVar(BoundTypeVarInstance::new(
+                    Type::NonInferableTypeVar(BoundTypeVarInstance::new(
                         db,
                         TypeVarInstance::new(
                             db,

crates/ty_python_semantic/src/types/type_ordering.rs

@@ -142,6 +142,10 @@ pub(super) fn union_or_intersection_elements_ordering<'db>(
         (Type::ProtocolInstance(_), _) => Ordering::Less,
         (_, Type::ProtocolInstance(_)) => Ordering::Greater,
 
+        (Type::NonInferableTypeVar(left), Type::NonInferableTypeVar(right)) => left.cmp(right),
+        (Type::NonInferableTypeVar(_), _) => Ordering::Less,
+        (_, Type::NonInferableTypeVar(_)) => Ordering::Greater,
+
         (Type::TypeVar(left), Type::TypeVar(right)) => left.cmp(right),
         (Type::TypeVar(_), _) => Ordering::Less,
         (_, Type::TypeVar(_)) => Ordering::Greater,

crates/ty_python_semantic/src/types/visitor.rs

@@ -114,6 +114,7 @@ enum NonAtomicType<'db> {
     NominalInstance(NominalInstanceType<'db>),
     PropertyInstance(PropertyInstanceType<'db>),
     TypeIs(TypeIsType<'db>),
+    NonInferableTypeVar(BoundTypeVarInstance<'db>),
     TypeVar(BoundTypeVarInstance<'db>),
     ProtocolInstance(ProtocolInstanceType<'db>),
     TypedDict(TypedDictType<'db>),
@@ -177,6 +178,9 @@ impl<'db> From<Type<'db>> for TypeKind<'db> {
             Type::PropertyInstance(property) => {
                 TypeKind::NonAtomic(NonAtomicType::PropertyInstance(property))
             }
+            Type::NonInferableTypeVar(bound_typevar) => {
+                TypeKind::NonAtomic(NonAtomicType::NonInferableTypeVar(bound_typevar))
+            }
             Type::TypeVar(bound_typevar) => {
                 TypeKind::NonAtomic(NonAtomicType::TypeVar(bound_typevar))
             }
@@ -216,6 +220,9 @@ fn walk_non_atomic_type<'db, V: TypeVisitor<'db> + ?Sized>(
             visitor.visit_property_instance_type(db, property);
         }
         NonAtomicType::TypeIs(type_is) => visitor.visit_typeis_type(db, type_is),
+        NonAtomicType::NonInferableTypeVar(bound_typevar) => {
+            visitor.visit_bound_type_var_type(db, bound_typevar);
+        }
         NonAtomicType::TypeVar(bound_typevar) => {
             visitor.visit_bound_type_var_type(db, bound_typevar);
         }