From 5358ddae8857a0450f2a083ecdb7b9d2c0af9981 Mon Sep 17 00:00:00 2001
From: David Peter <sharkdp@users.noreply.github.com>
Date: Mon, 1 Dec 2025 13:52:36 +0100
Subject: [PATCH] [ty] Exhaustiveness checking for generic classes (#21726)

## Summary

We had tests for this already, but they used generic classes that were
bivariant in their type parameter, and so this case wasn't captured.

closes https://github.com/astral-sh/ty/issues/1702

## Test Plan

Updated Markdown tests
---
 .../resources/mdtest/exhaustiveness_checking.md     | 13 ++++++++++---
 .../src/semantic_index/reachability_constraints.rs  |  1 +
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/crates/ty_python_semantic/resources/mdtest/exhaustiveness_checking.md b/crates/ty_python_semantic/resources/mdtest/exhaustiveness_checking.md
index 4379498f2d..1d7cbfd401 100644
--- a/crates/ty_python_semantic/resources/mdtest/exhaustiveness_checking.md
+++ b/crates/ty_python_semantic/resources/mdtest/exhaustiveness_checking.md
@@ -284,10 +284,17 @@ python-version = "3.12"
 ```py
 from typing import assert_never
 
-class A[T]: ...
+class A[T]:
+    value: T
+
 class ASub[T](A[T]): ...
-class B[T]: ...
-class C[T]: ...
+
+class B[T]:
+    value: T
+
+class C[T]:
+    value: T
+
 class D: ...
 class E: ...
 class F: ...
diff --git a/crates/ty_python_semantic/src/semantic_index/reachability_constraints.rs b/crates/ty_python_semantic/src/semantic_index/reachability_constraints.rs
index d7ab0f621c..76ec1a70f0 100644
--- a/crates/ty_python_semantic/src/semantic_index/reachability_constraints.rs
+++ b/crates/ty_python_semantic/src/semantic_index/reachability_constraints.rs
@@ -336,6 +336,7 @@ fn pattern_kind_to_type<'db>(db: &'db dyn Db, kind: &PatternPredicateKind<'db>)
                 infer_expression_type(db, *class_expr, TypeContext::default())
                     .to_instance(db)
                     .unwrap_or(Type::Never)
+                    .top_materialization(db)
             } else {
                 Type::Never
             }