Add test for #72554.

src/test/ui/issues/issue-72554.rs

@@ -0,0 +1,20 @@
+use std::collections::BTreeSet;
+
+#[derive(Hash)]
+pub enum ElemDerived { //~ ERROR recursive type `ElemDerived` has infinite size
+    A(ElemDerived)
+}
+
+pub enum Elem {
+    Derived(ElemDerived)
+}
+
+pub struct Set(BTreeSet<Elem>);
+
+impl Set {
+    pub fn into_iter(self) -> impl Iterator<Item = Elem> {
+        self.0.into_iter()
+    }
+}
+
+fn main() {}

src/test/ui/issues/issue-72554.stderr

@@ -0,0 +1,13 @@
+error[E0072]: recursive type `ElemDerived` has infinite size
+  --> $DIR/issue-72554.rs:4:1
+   |
+LL | pub enum ElemDerived {
+   | ^^^^^^^^^^^^^^^^^^^^ recursive type has infinite size
+LL |     A(ElemDerived)
+   |       ----------- recursive without indirection
+   |
+   = help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `ElemDerived` representable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0072`.