stall generator witness obligations: add regression test

tests/ui/coroutine/dont-drop-stalled-generators.rs

@@ -0,0 +1,25 @@
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+//@ check-pass
+//@ edition: 2024
+
+// This test previously used the `is_copy_raw` query during
+// HIR typeck, dropping the list of generators from the current
+// body. This then caused a query cycle.
+
+struct W<T>(*const T);
+
+impl<T: Send> Clone for W<T> {
+    fn clone(&self) -> Self { W(self.0) }
+}
+
+impl<T: Send> Copy for W<T> {}
+
+fn main() {
+    let coro = async {};
+    let x = W(&raw const coro);
+    let c = || {
+        let x = x;
+    };
+}