rustc: correctly transform memory_index mappings for generators.

src/test/ui/async-await/issue-61793.rs

@@ -0,0 +1,19 @@
+// This testcase used to ICE in codegen due to inconsistent field reordering
+// in the generator state, claiming a ZST field was after a non-ZST field,
+// while those two fields were at the same offset (which is impossible).
+// That is, memory ordering of `(X, ())`, but offsets of `((), X)`.
+
+// compile-pass
+// edition:2018
+
+#![feature(async_await)]
+#![allow(unused)]
+
+async fn foo<F>(_: &(), _: F) {}
+
+fn main() {
+    foo(&(), || {});
+    async {
+        foo(&(), || {}).await;
+    };
+}