From ac3f0db809def6666fdb4cc19cf3ad367c6afa48 Mon Sep 17 00:00:00 2001
From: Douglas Creager <dcreager@dcreager.net>
Date: Tue, 6 Jan 2026 17:31:10 -0500
Subject: [PATCH] use subtyping

---
 .../src/types/constraints.rs                  | 10 +++++---
 .../ty_python_semantic/src/types/relation.rs  | 24 +++++++++++++++----
 2 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/crates/ty_python_semantic/src/types/constraints.rs b/crates/ty_python_semantic/src/types/constraints.rs
index c2d878b99b..ec9fb7fdb7 100644
--- a/crates/ty_python_semantic/src/types/constraints.rs
+++ b/crates/ty_python_semantic/src/types/constraints.rs
@@ -747,12 +747,16 @@ impl<'db> ConstrainedTypeVar<'db> {
         if !self.typevar(db).is_same_typevar_as(db, other.typevar(db)) {
             return false;
         }
+
+        // Note that we check that the bounds are _subtypes_ of each other, because we do not want
+        // dynamic types like `Any` to be pivots that we can use to compute transitive sequent map
+        // relationships.
         other
             .lower(db)
-            .is_constraint_set_assignable_to(db, self.lower(db))
+            .is_constraint_set_subtype_of(db, self.lower(db))
             && self
                 .upper(db)
-                .is_constraint_set_assignable_to(db, other.upper(db))
+                .is_constraint_set_subtype_of(db, other.upper(db))
     }
 
     /// Returns the intersection of two range constraints, or `None` if the intersection is empty.
@@ -763,7 +767,7 @@ impl<'db> ConstrainedTypeVar<'db> {
 
         // If `lower ≰ upper`, then the intersection is empty, since there is no type that is both
         // greater than `lower`, and less than `upper`.
-        if !lower.is_constraint_set_assignable_to(db, upper) {
+        if !lower.is_constraint_set_subtype_of(db, upper) {
             return IntersectionResult::Disjoint;
         }
 
diff --git a/crates/ty_python_semantic/src/types/relation.rs b/crates/ty_python_semantic/src/types/relation.rs
index 57f1945b67..13c966ea40 100644
--- a/crates/ty_python_semantic/src/types/relation.rs
+++ b/crates/ty_python_semantic/src/types/relation.rs
@@ -260,15 +260,17 @@ impl<'db> Type<'db> {
     }
 
     /// Return true if this type is assignable to type `target` using constraint-set assignability.
-    ///
-    /// This uses `TypeRelation::ConstraintSetAssignability`, which encodes typevar relations into
-    /// a constraint set and lets `satisfied_by_all_typevars` perform existential vs universal
-    /// reasoning depending on inferable typevars.
     pub fn is_constraint_set_assignable_to(self, db: &'db dyn Db, target: Type<'db>) -> bool {
         self.when_constraint_set_assignable_to(db, target, InferableTypeVars::None)
             .is_always_satisfied(db)
     }
 
+    /// Return true if this type is assignable to type `target` using constraint-set assignability.
+    pub fn is_constraint_set_subtype_of(self, db: &'db dyn Db, target: Type<'db>) -> bool {
+        self.when_constraint_set_subtype_of(db, target, InferableTypeVars::None)
+            .is_always_satisfied(db)
+    }
+
     pub(super) fn when_assignable_to(
         self,
         db: &'db dyn Db,
@@ -297,6 +299,20 @@ impl<'db> Type<'db> {
         )
     }
 
+    pub(super) fn when_constraint_set_subtype_of(
+        self,
+        db: &'db dyn Db,
+        target: Type<'db>,
+        inferable: InferableTypeVars<'_, 'db>,
+    ) -> ConstraintSet<'db> {
+        self.has_relation_to(
+            db,
+            target,
+            inferable,
+            TypeRelation::Subtyping(UseConstraintSets::Yes),
+        )
+    }
+
     /// Return `true` if it would be redundant to add `self` to a union that already contains `other`.
     ///
     /// See [`TypeRelation::Redundancy`] for more details.