[ty] Add separate type for typevar "identity" (#20813)

As part of #20598, we added `is_identical_to` methods to
`TypeVarInstance` and `BoundTypeVarInstance`, which compare when two
typevar instances refer to "the same" underlying typevar, even if we
have forced their lazy bounds/constraints as part of marking typevars as
inferable. (Doing so results in a different salsa interned struct ID,
since we've changed the contents of the `bounds_or_constraints` field.)

It turns out that marking typevars as inferable is not the only way that
we might force lazy bounds/constraints; it also happens when we
materialize a type containing a typevar. This surfaced as ecosystem
report failures on #20677.

That means that we need a more long-term fix to this problem.
(`is_identical_to`, and its underlying `original` field, were meant to
be a temporary fix until we removed the `MarkTypeVarsInferable` type
mapping.)

This PR extracts out a separate type (`TypeVarIdentity`) that only
includes the fields that actually inform whether two typevars are "the
same". All other properties of the typevar (default, bounds/constraints,
etc) still live in `TypeVarInstance`. Call sites that care about typevar
identity can now either store just `TypeVarIdentity` (if they never need
access to those other properties), or continue to store
`TypeVarInstance` but pull out its `identity` when performing those "are
they the same typevar" comparisons. (All of this also applies
respectively to `BoundTypeVar{Identity,Instance}`.) In particular,
constraint sets now work on `BoundTypeVarIdentity`, and generic contexts
still _store_ a `BoundTypeVarInstance` (since we might need access to
defaults when specializing), but are keyed on `BoundTypeVarIdentity`.

crates/ty_python_semantic/src/types.rs

@@ -1674,7 +1674,7 @@ impl<'db> Type<'db> {
             (
                 Type::NonInferableTypeVar(lhs_bound_typevar),
                 Type::NonInferableTypeVar(rhs_bound_typevar),
-            ) if lhs_bound_typevar.is_identical_to(db, rhs_bound_typevar) => {
+            ) if lhs_bound_typevar.identity(db) == rhs_bound_typevar.identity(db) => {
                 ConstraintSet::from(true)
             }
 
@@ -2443,7 +2443,9 @@ impl<'db> Type<'db> {
             (
                 Type::NonInferableTypeVar(self_bound_typevar),
                 Type::NonInferableTypeVar(other_bound_typevar),
-            ) if self_bound_typevar == other_bound_typevar => ConstraintSet::from(false),
+            ) if self_bound_typevar.identity(db) == other_bound_typevar.identity(db) => {
+                ConstraintSet::from(false)
+            }
 
             (tvar @ Type::NonInferableTypeVar(_), Type::Intersection(intersection))
             | (Type::Intersection(intersection), tvar @ Type::NonInferableTypeVar(_))
@@ -7789,7 +7791,32 @@ pub enum TypeVarKind {
     TypingSelf,
 }
 
-/// A type variable that has not been bound to a generic context yet.
+/// The identity of a type variable.
+///
+/// This represents the core identity of a typevar, independent of its bounds or constraints. Two
+/// typevars have the same identity if they represent the same logical typevar, even if their
+/// bounds have been materialized differently.
+///
+/// # Ordering
+/// Ordering is based on the identity's salsa-assigned id and not on its values.
+/// The id may change between runs, or when the identity was garbage collected and recreated.
+#[salsa::interned(debug, heap_size=ruff_memory_usage::heap_size)]
+#[derive(PartialOrd, Ord)]
+pub struct TypeVarIdentity<'db> {
+    /// The name of this TypeVar (e.g. `T`)
+    #[returns(ref)]
+    pub(crate) name: ast::name::Name,
+
+    /// The type var's definition (None if synthesized)
+    pub(crate) definition: Option<Definition<'db>>,
+
+    /// The kind of typevar (PEP 695, Legacy, or TypingSelf)
+    pub(crate) kind: TypeVarKind,
+}
+
+impl get_size2::GetSize for TypeVarIdentity<'_> {}
+
+/// A specific instance of a type variable that has not been bound to a generic context yet.
 ///
 /// This is usually not the type that you want; if you are working with a typevar, in a generic
 /// context, which might be specialized to a concrete type, you want [`BoundTypeVarInstance`]. This
@@ -7828,12 +7855,8 @@ pub enum TypeVarKind {
 #[salsa::interned(debug, heap_size=ruff_memory_usage::heap_size)]
 #[derive(PartialOrd, Ord)]
 pub struct TypeVarInstance<'db> {
-    /// The name of this TypeVar (e.g. `T`)
-    #[returns(ref)]
-    name: ast::name::Name,
-
-    /// The type var's definition (None if synthesized)
-    pub definition: Option<Definition<'db>>,
+    /// The identity of this typevar
+    pub(crate) identity: TypeVarIdentity<'db>,
 
     /// The upper bound or constraint on the type of this TypeVar, if any. Don't use this field
     /// directly; use the `bound_or_constraints` (or `upper_bound` and `constraints`) methods
@@ -7846,14 +7869,6 @@ pub struct TypeVarInstance<'db> {
     /// The default type for this TypeVar, if any. Don't use this field directly, use the
     /// `default_type` method instead (to evaluate any lazy default).
     _default: Option<TypeVarDefaultEvaluation<'db>>,
-
-    pub kind: TypeVarKind,
-
-    /// If this typevar was transformed from another typevar via `mark_typevars_inferable`, this
-    /// records the identity of the "original" typevar, so we can recognize them as the same
-    /// typevar in `bind_typevar`. TODO: this (and the `is_identical_to` methods) should be
-    /// removable once we remove `mark_typevars_inferable`.
-    pub(crate) original: Option<TypeVarInstance<'db>>,
 }
 
 // The Salsa heap is tracked separately.
@@ -7899,6 +7914,18 @@ impl<'db> TypeVarInstance<'db> {
         BoundTypeVarInstance::new(db, self, BindingContext::Definition(binding_context))
     }
 
+    pub(crate) fn name(self, db: &'db dyn Db) -> &'db ast::name::Name {
+        self.identity(db).name(db)
+    }
+
+    pub(crate) fn definition(self, db: &'db dyn Db) -> Option<Definition<'db>> {
+        self.identity(db).definition(db)
+    }
+
+    pub(crate) fn kind(self, db: &'db dyn Db) -> TypeVarKind {
+        self.identity(db).kind(db)
+    }
+
     pub(crate) fn is_self(self, db: &'db dyn Db) -> bool {
         matches!(self.kind(db), TypeVarKind::TypingSelf)
     }
@@ -7942,8 +7969,7 @@ impl<'db> TypeVarInstance<'db> {
     pub(crate) fn normalized_impl(self, db: &'db dyn Db, visitor: &NormalizedVisitor<'db>) -> Self {
         Self::new(
             db,
-            self.name(db),
-            self.definition(db),
+            self.identity(db),
             self._bound_or_constraints(db)
                 .and_then(|bound_or_constraints| match bound_or_constraints {
                     TypeVarBoundOrConstraintsEvaluation::Eager(bound_or_constraints) => {
@@ -7963,8 +7989,6 @@ impl<'db> TypeVarInstance<'db> {
                     .lazy_default(db)
                     .map(|ty| ty.normalized_impl(db, visitor).into()),
             }),
-            self.kind(db),
-            self.original(db),
         )
     }
 
@@ -7976,8 +8000,7 @@ impl<'db> TypeVarInstance<'db> {
     ) -> Self {
         Self::new(
             db,
-            self.name(db),
-            self.definition(db),
+            self.identity(db),
             self._bound_or_constraints(db)
                 .and_then(|bound_or_constraints| match bound_or_constraints {
                     TypeVarBoundOrConstraintsEvaluation::Eager(bound_or_constraints) => Some(
@@ -8009,8 +8032,6 @@ impl<'db> TypeVarInstance<'db> {
                     .lazy_default(db)
                     .map(|ty| ty.materialize(db, materialization_kind, visitor).into()),
             }),
-            self.kind(db),
-            self.original(db),
         )
     }
 
@@ -8047,33 +8068,15 @@ impl<'db> TypeVarInstance<'db> {
             }),
         });
 
-        // Ensure that we only modify the `original` field if we are going to modify one or both of
-        // `_bound_or_constraints` and `_default`; don't trigger creation of a new
-        // `TypeVarInstance` unnecessarily.
-        let new_original = if new_bound_or_constraints == self._bound_or_constraints(db)
-            && new_default == self._default(db)
-        {
-            self.original(db)
-        } else {
-            Some(self)
-        };
-
         Self::new(
             db,
-            self.name(db),
-            self.definition(db),
+            self.identity(db),
             new_bound_or_constraints,
             self.explicit_variance(db),
             new_default,
-            self.kind(db),
-            new_original,
         )
     }
 
-    fn is_identical_to(self, db: &'db dyn Db, other: Self) -> bool {
-        self == other || (self.original(db) == Some(other) || other.original(db) == Some(self))
-    }
-
     fn to_instance(self, db: &'db dyn Db) -> Option<Self> {
         let bound_or_constraints = match self.bound_or_constraints(db)? {
             TypeVarBoundOrConstraints::UpperBound(upper_bound) => {
@@ -8083,15 +8086,18 @@ impl<'db> TypeVarInstance<'db> {
                 TypeVarBoundOrConstraints::Constraints(constraints.to_instance(db)?.into_union()?)
             }
         };
-        Some(Self::new(
+        let identity = TypeVarIdentity::new(
             db,
             Name::new(format!("{}'instance", self.name(db))),
-            None,
+            None, // definition
+            self.kind(db),
+        );
+        Some(Self::new(
+            db,
+            identity,
             Some(bound_or_constraints.into()),
             self.explicit_variance(db),
-            None,
-            self.kind(db),
-            self.original(db),
+            None, // _default
         ))
     }
 
@@ -8222,6 +8228,18 @@ impl<'db> BindingContext<'db> {
     }
 }
 
+/// The identity of a bound type variable.
+///
+/// This identifies a specific binding of a typevar to a context (e.g., `T@ClassC` vs `T@FunctionF`),
+/// independent of the typevar's bounds or constraints. Two bound typevars have the same identity
+/// if they represent the same logical typevar bound in the same context, even if their bounds
+/// have been materialized differently.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, get_size2::GetSize)]
+pub struct BoundTypeVarIdentity<'db> {
+    pub(crate) identity: TypeVarIdentity<'db>,
+    pub(crate) binding_context: BindingContext<'db>,
+}
+
 /// A type variable that has been bound to a generic context, and which can be specialized to a
 /// concrete type.
 #[salsa::interned(debug, heap_size=ruff_memory_usage::heap_size)]
@@ -8235,6 +8253,17 @@ pub struct BoundTypeVarInstance<'db> {
 impl get_size2::GetSize for BoundTypeVarInstance<'_> {}
 
 impl<'db> BoundTypeVarInstance<'db> {
+    /// Get the identity of this bound typevar.
+    ///
+    /// This is used for comparing whether two bound typevars represent the same logical typevar,
+    /// regardless of e.g. differences in their bounds or constraints due to materialization.
+    pub(crate) fn identity(self, db: &'db dyn Db) -> BoundTypeVarIdentity<'db> {
+        BoundTypeVarIdentity {
+            identity: self.typevar(db).identity(db),
+            binding_context: self.binding_context(db),
+        }
+    }
+
     /// Create a new PEP 695 type variable that can be used in signatures
     /// of synthetic generic functions.
     pub(crate) fn synthetic(
@@ -8242,20 +8271,20 @@ impl<'db> BoundTypeVarInstance<'db> {
         name: &'static str,
         variance: TypeVarVariance,
     ) -> Self {
-        Self::new(
+        let identity = TypeVarIdentity::new(
             db,
-            TypeVarInstance::new(
-                db,
-                Name::new_static(name),
-                None, // definition
-                None, // _bound_or_constraints
-                Some(variance),
-                None, // _default
-                TypeVarKind::Pep695,
-                None,
-            ),
-            BindingContext::Synthetic,
-        )
+            Name::new_static(name),
+            None, // definition
+            TypeVarKind::Pep695,
+        );
+        let typevar = TypeVarInstance::new(
+            db,
+            identity,
+            None, // _bound_or_constraints
+            Some(variance),
+            None, // _default
+        );
+        Self::new(db, typevar, BindingContext::Synthetic)
     }
 
     /// Create a new synthetic `Self` type variable with the given upper bound.
@@ -8264,32 +8293,20 @@ impl<'db> BoundTypeVarInstance<'db> {
         upper_bound: Type<'db>,
         binding_context: BindingContext<'db>,
     ) -> Self {
-        Self::new(
+        let identity = TypeVarIdentity::new(
             db,
-            TypeVarInstance::new(
-                db,
-                Name::new_static("Self"),
-                None,
-                Some(TypeVarBoundOrConstraints::UpperBound(upper_bound).into()),
-                Some(TypeVarVariance::Invariant),
-                None,
-                TypeVarKind::TypingSelf,
-                None,
-            ),
-            binding_context,
-        )
-    }
-
-    pub(crate) fn is_identical_to(self, db: &'db dyn Db, other: Self) -> bool {
-        if self == other {
-            return true;
-        }
-
-        if self.binding_context(db) != other.binding_context(db) {
-            return false;
-        }
-
-        self.typevar(db).is_identical_to(db, other.typevar(db))
+            Name::new_static("Self"),
+            None, // definition
+            TypeVarKind::TypingSelf,
+        );
+        let typevar = TypeVarInstance::new(
+            db,
+            identity,
+            Some(TypeVarBoundOrConstraints::UpperBound(upper_bound).into()),
+            Some(TypeVarVariance::Invariant),
+            None, // _default
+        );
+        Self::new(db, typevar, binding_context)
     }
 
     pub(crate) fn variance_with_polarity(

crates/ty_python_semantic/src/types/constraints.rs

@@ -60,7 +60,7 @@ use itertools::Itertools;
 use rustc_hash::FxHashSet;
 
 use crate::Db;
-use crate::types::{BoundTypeVarInstance, IntersectionType, Type, UnionType};
+use crate::types::{BoundTypeVarIdentity, IntersectionType, Type, UnionType};
 
 /// An extension trait for building constraint sets from [`Option`] values.
 pub(crate) trait OptionConstraintsExtension<T> {
@@ -223,7 +223,7 @@ impl<'db> ConstraintSet<'db> {
     pub(crate) fn range(
         db: &'db dyn Db,
         lower: Type<'db>,
-        typevar: BoundTypeVarInstance<'db>,
+        typevar: BoundTypeVarIdentity<'db>,
         upper: Type<'db>,
     ) -> Self {
         let lower = lower.bottom_materialization(db);
@@ -236,7 +236,7 @@ impl<'db> ConstraintSet<'db> {
     pub(crate) fn negated_range(
         db: &'db dyn Db,
         lower: Type<'db>,
-        typevar: BoundTypeVarInstance<'db>,
+        typevar: BoundTypeVarIdentity<'db>,
         upper: Type<'db>,
     ) -> Self {
         Self::range(db, lower, typevar, upper).negate(db)
@@ -258,7 +258,7 @@ impl From<bool> for ConstraintSet<'_> {
 #[salsa::interned(debug, heap_size=ruff_memory_usage::heap_size)]
 #[derive(PartialOrd, Ord)]
 pub(crate) struct ConstrainedTypeVar<'db> {
-    typevar: BoundTypeVarInstance<'db>,
+    typevar: BoundTypeVarIdentity<'db>,
     lower: Type<'db>,
     upper: Type<'db>,
 }
@@ -274,7 +274,7 @@ impl<'db> ConstrainedTypeVar<'db> {
     fn new_node(
         db: &'db dyn Db,
         lower: Type<'db>,
-        typevar: BoundTypeVarInstance<'db>,
+        typevar: BoundTypeVarIdentity<'db>,
         upper: Type<'db>,
     ) -> Node<'db> {
         debug_assert_eq!(lower, lower.bottom_materialization(db));

crates/ty_python_semantic/src/types/display.rs

@@ -24,7 +24,7 @@ use crate::types::signatures::{CallableSignature, Parameter, Parameters, Signatu
 use crate::types::tuple::TupleSpec;
 use crate::types::visitor::TypeVisitor;
 use crate::types::{
-    BoundTypeVarInstance, CallableType, IntersectionType, KnownBoundMethodType, KnownClass,
+    BoundTypeVarIdentity, CallableType, IntersectionType, KnownBoundMethodType, KnownClass,
     MaterializationKind, Protocol, ProtocolInstanceType, StringLiteralType, SubclassOfInner, Type,
     UnionType, WrapperDescriptorKind, visitor,
 };
@@ -561,7 +561,7 @@ impl Display for DisplayRepresentation<'_> {
                 literal_name = enum_literal.name(self.db)
             ),
             Type::NonInferableTypeVar(bound_typevar) | Type::TypeVar(bound_typevar) => {
-                bound_typevar.display(self.db).fmt(f)
+                bound_typevar.identity(self.db).display(self.db).fmt(f)
             }
             Type::AlwaysTruthy => f.write_str("AlwaysTruthy"),
             Type::AlwaysFalsy => f.write_str("AlwaysFalsy"),
@@ -598,24 +598,24 @@ impl Display for DisplayRepresentation<'_> {
     }
 }
 
-impl<'db> BoundTypeVarInstance<'db> {
+impl<'db> BoundTypeVarIdentity<'db> {
     pub(crate) fn display(self, db: &'db dyn Db) -> impl Display {
-        DisplayBoundTypeVarInstance {
-            bound_typevar: self,
+        DisplayBoundTypeVarIdentity {
+            bound_typevar_identity: self,
             db,
         }
     }
 }
 
-struct DisplayBoundTypeVarInstance<'db> {
-    bound_typevar: BoundTypeVarInstance<'db>,
+struct DisplayBoundTypeVarIdentity<'db> {
+    bound_typevar_identity: BoundTypeVarIdentity<'db>,
     db: &'db dyn Db,
 }
 
-impl Display for DisplayBoundTypeVarInstance<'_> {
+impl Display for DisplayBoundTypeVarIdentity<'_> {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
-        f.write_str(self.bound_typevar.typevar(self.db).name(self.db))?;
-        if let Some(binding_context) = self.bound_typevar.binding_context(self.db).name(self.db) {
+        f.write_str(self.bound_typevar_identity.identity.name(self.db))?;
+        if let Some(binding_context) = self.bound_typevar_identity.binding_context.name(self.db) {
             write!(f, "@{binding_context}")?;
         }
         Ok(())

crates/ty_python_semantic/src/types/function.rs

@@ -1730,7 +1730,7 @@ impl KnownFunction {
                     return;
                 };
 
-                let constraints = ConstraintSet::range(db, *lower, *typevar, *upper);
+                let constraints = ConstraintSet::range(db, *lower, typevar.identity(db), *upper);
                 let tracked = TrackedConstraintSet::new(db, constraints);
                 overload.set_return_type(Type::KnownInstance(KnownInstanceType::ConstraintSet(
                     tracked,
@@ -1747,7 +1747,8 @@ impl KnownFunction {
                     return;
                 };
 
-                let constraints = ConstraintSet::negated_range(db, *lower, *typevar, *upper);
+                let constraints =
+                    ConstraintSet::negated_range(db, *lower, typevar.identity(db), *upper);
                 let tracked = TrackedConstraintSet::new(db, constraints);
                 overload.set_return_type(Type::KnownInstance(KnownInstanceType::ConstraintSet(
                     tracked,

crates/ty_python_semantic/src/types/generics.rs

@@ -14,11 +14,11 @@ use crate::types::instance::{Protocol, ProtocolInstanceType};
 use crate::types::signatures::{Parameter, Parameters, Signature};
 use crate::types::tuple::{TupleSpec, TupleType, walk_tuple_type};
 use crate::types::{
-    ApplyTypeMappingVisitor, BoundTypeVarInstance, ClassLiteral, FindLegacyTypeVarsVisitor,
-    HasRelationToVisitor, IsDisjointVisitor, IsEquivalentVisitor, KnownClass, KnownInstanceType,
-    MaterializationKind, NormalizedVisitor, Type, TypeContext, TypeMapping, TypeRelation,
-    TypeVarBoundOrConstraints, TypeVarInstance, TypeVarKind, TypeVarVariance, UnionType,
-    binding_type, declaration_type,
+    ApplyTypeMappingVisitor, BoundTypeVarIdentity, BoundTypeVarInstance, ClassLiteral,
+    FindLegacyTypeVarsVisitor, HasRelationToVisitor, IsDisjointVisitor, IsEquivalentVisitor,
+    KnownClass, KnownInstanceType, MaterializationKind, NormalizedVisitor, Type, TypeContext,
+    TypeMapping, TypeRelation, TypeVarBoundOrConstraints, TypeVarIdentity, TypeVarInstance,
+    TypeVarKind, TypeVarVariance, UnionType, binding_type, declaration_type,
 };
 use crate::{Db, FxOrderMap, FxOrderSet};
 
@@ -109,24 +109,25 @@ pub(crate) fn typing_self<'db>(
 ) -> Option<Type<'db>> {
     let index = semantic_index(db, scope_id.file(db));
 
-    let typevar = TypeVarInstance::new(
+    let identity = TypeVarIdentity::new(
         db,
         ast::name::Name::new_static("Self"),
         Some(class.definition(db)),
-        Some(
-            TypeVarBoundOrConstraints::UpperBound(Type::instance(
-                db,
-                class.identity_specialization(db, typevar_to_type),
-            ))
-            .into(),
-        ),
+        TypeVarKind::TypingSelf,
+    );
+    let bounds = TypeVarBoundOrConstraints::UpperBound(Type::instance(
+        db,
+        class.identity_specialization(db, typevar_to_type),
+    ));
+    let typevar = TypeVarInstance::new(
+        db,
+        identity,
+        Some(bounds.into()),
         // According to the [spec], we can consider `Self`
         // equivalent to an invariant type variable
         // [spec]: https://typing.python.org/en/latest/spec/generics.html#self
         Some(TypeVarVariance::Invariant),
         None,
-        TypeVarKind::TypingSelf,
-        None,
     );
 
     bind_typevar(
@@ -139,12 +140,20 @@ pub(crate) fn typing_self<'db>(
     .map(typevar_to_type)
 }
 
-#[derive(Copy, Clone, Debug, Default, Eq, Hash, PartialEq, get_size2::GetSize)]
-pub struct GenericContextTypeVarOptions {
+#[derive(Copy, Clone, Debug, Eq, Hash, PartialEq, get_size2::GetSize)]
+pub struct GenericContextTypeVar<'db> {
+    bound_typevar: BoundTypeVarInstance<'db>,
     should_promote_literals: bool,
 }
 
-impl GenericContextTypeVarOptions {
+impl<'db> GenericContextTypeVar<'db> {
+    fn new(bound_typevar: BoundTypeVarInstance<'db>) -> Self {
+        Self {
+            bound_typevar,
+            should_promote_literals: false,
+        }
+    }
+
     fn promote_literals(mut self) -> Self {
         self.should_promote_literals = true;
         self
@@ -160,7 +169,7 @@ impl GenericContextTypeVarOptions {
 #[derive(PartialOrd, Ord)]
 pub struct GenericContext<'db> {
     #[returns(ref)]
-    variables_inner: FxOrderMap<BoundTypeVarInstance<'db>, GenericContextTypeVarOptions>,
+    variables_inner: FxOrderMap<BoundTypeVarIdentity<'db>, GenericContextTypeVar<'db>>,
 }
 
 pub(super) fn walk_generic_context<'db, V: super::visitor::TypeVisitor<'db> + ?Sized>(
@@ -179,9 +188,15 @@ impl get_size2::GetSize for GenericContext<'_> {}
 impl<'db> GenericContext<'db> {
     fn from_variables(
         db: &'db dyn Db,
-        variables: impl IntoIterator<Item = (BoundTypeVarInstance<'db>, GenericContextTypeVarOptions)>,
+        variables: impl IntoIterator<Item = GenericContextTypeVar<'db>>,
     ) -> Self {
-        Self::new_internal(db, variables.into_iter().collect::<FxOrderMap<_, _>>())
+        Self::new_internal(
+            db,
+            variables
+                .into_iter()
+                .map(|variable| (variable.bound_typevar.identity(db), variable))
+                .collect::<FxOrderMap<_, _>>(),
+        )
     }
 
     /// Creates a generic context from a list of PEP-695 type parameters.
@@ -203,12 +218,7 @@ impl<'db> GenericContext<'db> {
         db: &'db dyn Db,
         type_params: impl IntoIterator<Item = BoundTypeVarInstance<'db>>,
     ) -> Self {
-        Self::from_variables(
-            db,
-            type_params
-                .into_iter()
-                .map(|bound_typevar| (bound_typevar, GenericContextTypeVarOptions::default())),
-        )
+        Self::from_variables(db, type_params.into_iter().map(GenericContextTypeVar::new))
     }
 
     /// Returns a copy of this generic context where we will promote literal types in any inferred
@@ -217,8 +227,8 @@ impl<'db> GenericContext<'db> {
         Self::from_variables(
             db,
             self.variables_inner(db)
-                .iter()
-                .map(|(bound_typevar, options)| (*bound_typevar, options.promote_literals())),
+                .values()
+                .map(|variable| variable.promote_literals()),
         )
     }
 
@@ -228,9 +238,9 @@ impl<'db> GenericContext<'db> {
         Self::from_variables(
             db,
             self.variables_inner(db)
-                .iter()
-                .chain(other.variables_inner(db).iter())
-                .map(|(bound_typevar, options)| (*bound_typevar, *options)),
+                .values()
+                .chain(other.variables_inner(db).values())
+                .copied(),
         )
     }
 
@@ -238,7 +248,9 @@ impl<'db> GenericContext<'db> {
         self,
         db: &'db dyn Db,
     ) -> impl ExactSizeIterator<Item = BoundTypeVarInstance<'db>> + Clone {
-        self.variables_inner(db).keys().copied()
+        self.variables_inner(db)
+            .values()
+            .map(|variable| variable.bound_typevar)
     }
 
     fn variable_from_type_param(
@@ -411,7 +423,7 @@ impl<'db> GenericContext<'db> {
     pub(crate) fn is_subset_of(self, db: &'db dyn Db, other: GenericContext<'db>) -> bool {
         let other_variables = other.variables_inner(db);
         self.variables(db)
-            .all(|bound_typevar| other_variables.contains_key(&bound_typevar))
+            .all(|bound_typevar| other_variables.contains_key(&bound_typevar.identity(db)))
     }
 
     pub(crate) fn binds_named_typevar(
@@ -428,8 +440,9 @@ impl<'db> GenericContext<'db> {
         db: &'db dyn Db,
         typevar: TypeVarInstance<'db>,
     ) -> Option<BoundTypeVarInstance<'db>> {
-        self.variables(db)
-            .find(|self_bound_typevar| self_bound_typevar.typevar(db).is_identical_to(db, typevar))
+        self.variables(db).find(|self_bound_typevar| {
+            self_bound_typevar.typevar(db).identity(db) == typevar.identity(db)
+        })
     }
 
     /// Creates a specialization of this generic context. Panics if the length of `types` does not
@@ -513,7 +526,7 @@ impl<'db> GenericContext<'db> {
     }
 
     fn heap_size(
-        (variables,): &(FxOrderMap<BoundTypeVarInstance<'db>, GenericContextTypeVarOptions>,),
+        (variables,): &(FxOrderMap<BoundTypeVarIdentity<'db>, GenericContextTypeVar<'db>>,),
     ) -> usize {
         ruff_memory_usage::order_map_heap_size(variables)
     }
@@ -765,7 +778,7 @@ impl<'db> Specialization<'db> {
         let restricted_variables = generic_context.variables(db);
         let restricted_types: Option<Box<[_]>> = restricted_variables
             .map(|variable| {
-                let index = self_variables.get_index_of(&variable)?;
+                let index = self_variables.get_index_of(&variable.identity(db))?;
                 self_types.get(index).copied()
             })
             .collect();
@@ -793,7 +806,7 @@ impl<'db> Specialization<'db> {
         let index = self
             .generic_context(db)
             .variables_inner(db)
-            .get_index_of(&bound_typevar)?;
+            .get_index_of(&bound_typevar.identity(db))?;
         self.types(db).get(index).copied()
     }
 
@@ -1146,7 +1159,7 @@ impl<'db> PartialSpecialization<'_, 'db> {
         let index = self
             .generic_context
             .variables_inner(db)
-            .get_index_of(&bound_typevar)?;
+            .get_index_of(&bound_typevar.identity(db))?;
         self.types.get(index).copied()
     }
 }
@@ -1155,7 +1168,7 @@ impl<'db> PartialSpecialization<'_, 'db> {
 /// specialization of a generic function.
 pub(crate) struct SpecializationBuilder<'db> {
     db: &'db dyn Db,
-    types: FxHashMap<BoundTypeVarInstance<'db>, Type<'db>>,
+    types: FxHashMap<BoundTypeVarIdentity<'db>, Type<'db>>,
 }
 
 impl<'db> SpecializationBuilder<'db> {
@@ -1175,20 +1188,21 @@ impl<'db> SpecializationBuilder<'db> {
             .annotation
             .and_then(|annotation| annotation.specialization_of(self.db, None));
 
-        let types = (generic_context.variables_inner(self.db).iter()).map(|(variable, options)| {
-            let mut ty = self.types.get(variable).copied();
+        let types =
+            (generic_context.variables_inner(self.db).iter()).map(|(identity, variable)| {
+                let mut ty = self.types.get(identity).copied();
 
-            // When inferring a specialization for a generic class typevar from a constructor call,
-            // promote any typevars that are inferred as a literal to the corresponding instance type.
-            if options.should_promote_literals {
-                let tcx = tcx_specialization
-                    .and_then(|specialization| specialization.get(self.db, *variable));
+                // When inferring a specialization for a generic class typevar from a constructor call,
+                // promote any typevars that are inferred as a literal to the corresponding instance type.
+                if variable.should_promote_literals {
+                    let tcx = tcx_specialization.and_then(|specialization| {
+                        specialization.get(self.db, variable.bound_typevar)
+                    });
+                    ty = ty.map(|ty| ty.promote_literals(self.db, TypeContext::new(tcx)));
+                }
 
-                ty = ty.map(|ty| ty.promote_literals(self.db, TypeContext::new(tcx)));
-            }
-
-            ty
-        });
+                ty
+            });
 
         // TODO Infer the tuple spec for a tuple type
         generic_context.specialize_partial(self.db, types)
@@ -1196,7 +1210,7 @@ impl<'db> SpecializationBuilder<'db> {
 
     fn add_type_mapping(&mut self, bound_typevar: BoundTypeVarInstance<'db>, ty: Type<'db>) {
         self.types
-            .entry(bound_typevar)
+            .entry(bound_typevar.identity(self.db))
             .and_modify(|existing| {
                 *existing = UnionType::from_elements(self.db, [*existing, ty]);
             })

crates/ty_python_semantic/src/types/infer/builder.rs

@@ -94,8 +94,9 @@ use crate::types::{
     MemberLookupPolicy, MetaclassCandidate, PEP695TypeAliasType, Parameter, ParameterForm,
     Parameters, SpecialFormType, SubclassOfType, TrackedConstraintSet, Truthiness, Type,
     TypeAliasType, TypeAndQualifiers, TypeContext, TypeQualifiers,
-    TypeVarBoundOrConstraintsEvaluation, TypeVarDefaultEvaluation, TypeVarInstance, TypeVarKind,
-    TypeVarVariance, TypedDictType, UnionBuilder, UnionType, binding_type, todo_type,
+    TypeVarBoundOrConstraintsEvaluation, TypeVarDefaultEvaluation, TypeVarIdentity,
+    TypeVarInstance, TypeVarKind, TypeVarVariance, TypedDictType, UnionBuilder, UnionType,
+    binding_type, todo_type,
 };
 use crate::types::{ClassBase, add_inferred_python_version_hint_to_diagnostic};
 use crate::unpack::{EvaluationMode, UnpackPosition};
@@ -3001,15 +3002,14 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
         if bound_or_constraint.is_some() || default.is_some() {
             self.deferred.insert(definition);
         }
+        let identity =
+            TypeVarIdentity::new(self.db(), &name.id, Some(definition), TypeVarKind::Pep695);
         let ty = Type::KnownInstance(KnownInstanceType::TypeVar(TypeVarInstance::new(
             self.db(),
-            &name.id,
-            Some(definition),
+            identity,
             bound_or_constraint,
-            None,
+            None, // explicit_variance
             default.as_deref().map(|_| TypeVarDefaultEvaluation::Lazy),
-            TypeVarKind::Pep695,
-            None,
         )));
         self.add_declaration_with_binding(
             node.into(),
@@ -4340,15 +4340,13 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
             self.deferred.insert(definition);
         }
 
+        let identity = TypeVarIdentity::new(db, target_name, Some(definition), TypeVarKind::Legacy);
         Type::KnownInstance(KnownInstanceType::TypeVar(TypeVarInstance::new(
             db,
-            target_name,
-            Some(definition),
+            identity,
             bound_or_constraints,
             Some(variance),
             default,
-            TypeVarKind::Legacy,
-            None,
         )))
     }