Add regression test for #106630

tests/ui/impl-trait/not_general_enough_regression_106630.rs

@@ -0,0 +1,33 @@
+// edition:2018
+// run-pass
+
+use std::future::Future;
+
+trait AsyncCallback<'a> {
+    type Out;
+}
+
+impl<'a, Fut, T, F> AsyncCallback<'a> for F
+where
+    F: FnOnce(&'a mut ()) -> Fut,
+    Fut: Future<Output = T> + Send + 'a,
+{
+    type Out = T;
+}
+
+trait CallbackMarker {}
+
+impl<F, T> CallbackMarker for F
+where
+    T: 'static,
+    for<'a> F: AsyncCallback<'a, Out = T> + Send,
+{
+}
+
+fn do_sth<F: CallbackMarker>(_: F) {}
+
+async fn callback(_: &mut ()) -> impl Send {}
+
+fn main() {
+    do_sth(callback);
+}