From 0eb28df0b0506c6ffa8cb2b751ed61cd7cf00adf Mon Sep 17 00:00:00 2001
From: Charlie Marsh <charlie.r.marsh@gmail.com>
Date: Tue, 13 Jan 2026 20:36:53 -0500
Subject: [PATCH] Add more fast-paths

---
 .../ty_python_semantic/src/types/relation.rs  | 54 +++++++++++++------
 1 file changed, 39 insertions(+), 15 deletions(-)

diff --git a/crates/ty_python_semantic/src/types/relation.rs b/crates/ty_python_semantic/src/types/relation.rs
index 520d5e0e67..b7b3cd573f 100644
--- a/crates/ty_python_semantic/src/types/relation.rs
+++ b/crates/ty_python_semantic/src/types/relation.rs
@@ -823,23 +823,47 @@ impl<'db> Type<'db> {
                     })
                 }),
 
+            // Fast path for pure negations (~X): these are semantically `object & ~X`, so they're
+            // only assignable to types that `object` is assignable to. Since `object` is only
+            // assignable to `object`, dynamic types, unions/protocols/intersections that might
+            // contain `object`, we can short-circuit most cases directly.
+            (Type::Intersection(intersection), _) if intersection.positive(db).is_empty() => {
+                match target {
+                    // `object` is a subtype of `object`
+                    _ if target.is_object() => ConstraintSet::from(true),
+                    // `object` is a subtype of dynamic types
+                    Type::Dynamic(_) => ConstraintSet::from(true),
+                    // These cases need more complex checking - delegate to full machinery
+                    // (TypeVar needs special handling for inference)
+                    Type::Union(_)
+                    | Type::ProtocolInstance(_)
+                    | Type::Intersection(_)
+                    | Type::TypeVar(_) => Type::object().has_relation_to_impl(
+                        db,
+                        target,
+                        inferable,
+                        relation,
+                        relation_visitor,
+                        disjointness_visitor,
+                    ),
+                    // `object` is not a subtype of any other type
+                    _ => ConstraintSet::from(false),
+                }
+            }
+
             (Type::Intersection(intersection), _) => {
                 // An intersection type is a subtype of another type if at least one of its
-                // positive elements is a subtype of that type. If there are no positive elements,
-                // we treat `object` as the implicit positive element (e.g., `~str` is semantically
-                // `object & ~str`).
-                intersection
-                    .positive_elements_or_object(db)
-                    .when_any(db, |elem_ty| {
-                        elem_ty.has_relation_to_impl(
-                            db,
-                            target,
-                            inferable,
-                            relation,
-                            relation_visitor,
-                            disjointness_visitor,
-                        )
-                    })
+                // positive elements is a subtype of that type.
+                intersection.positive(db).iter().when_any(db, |&elem_ty| {
+                    elem_ty.has_relation_to_impl(
+                        db,
+                        target,
+                        inferable,
+                        relation,
+                        relation_visitor,
+                        disjointness_visitor,
+                    )
+                })
             }
 
             // Other than the special cases checked above, no other types are a subtype of a