Don't concatenate binders across types

src/test/ui/lifetimes/issue-83737-binders-across-types.rs

@@ -0,0 +1,14 @@
+// build-pass
+// compile-flags: --edition 2018
+// compile-flags: --crate-type rlib
+
+use std::future::Future;
+
+async fn handle<F>(slf: &F)
+where
+    F: Fn(&()) -> Box<dyn Future<Output = ()> + Unpin>,
+{
+    (slf)(&()).await;
+}
+
+fn main() {}