Regression test for #129541

Author: zachs18

tests/ui/traits/cow-self-field-sized.rs

@@ -0,0 +1,9 @@
+//@ check-pass
+// https://github.com/rust-lang/rust/issues/129541
+
+#[derive(Clone)]
+struct Test {
+    field: std::borrow::Cow<'static, [Self]>,
+}
+
+fn main(){}