From 21ffe30cd5e9e8b5f03454ea0cae6dc4f8cfb33a Mon Sep 17 00:00:00 2001
From: ltdk <usr@ltdk.xyz>
Date: Thu, 23 Oct 2025 18:24:39 -0400
Subject: [PATCH] Add regression test for inference failures

(cherry picked from commit 4a4f3b0e8e9609136c10a190c3f5572d70bb33ee)
---
 .../generic-cow-inference-regression.rs       | 20 +++++++++++++++++++
 1 file changed, 20 insertions(+)
 create mode 100644 tests/ui/traits/generic-cow-inference-regression.rs

diff --git a/tests/ui/traits/generic-cow-inference-regression.rs b/tests/ui/traits/generic-cow-inference-regression.rs
new file mode 100644
index 000000000000..6fd4715f85bb
--- /dev/null
+++ b/tests/ui/traits/generic-cow-inference-regression.rs
@@ -0,0 +1,20 @@
+//@ run-pass
+
+// regression test for #147964:
+//   constification of these traits resulted in inference errors due to additional where clauses
+
+use std::borrow::{Cow, Borrow};
+
+pub fn generic_deref<'a, T: ToOwned<Owned = U>, U>(cow: Cow<'a, T>) {
+    let _: &T = &cow;
+}
+
+pub fn generic_borrow<'a, T: ToOwned<Owned = U>, U>(cow: Cow<'a, T>) {
+    let _: &T = cow.borrow();
+}
+
+pub fn generic_as_ref<'a, T: ToOwned<Owned = U>, U>(cow: Cow<'a, T>) {
+    let _: &T = cow.as_ref();
+}
+
+fn main() {}