Rollup merge of #61499 - varkor:issue-53457, r=oli-obk

Add regression test for existential type ICE #53457

Closes #53457.

src/test/ui/impl-trait/issues/issue-53457.rs

@@ -0,0 +1,15 @@
+// run-pass
+
+#![feature(existential_type)]
+
+existential type X: Clone;
+
+fn bar<F: Fn(&i32) + Clone>(f: F) -> F {
+    f
+}
+
+fn foo() -> X {
+    bar(|x| ())
+}
+
+fn main() {}