Auto merge of #147299 - compiler-errors:hr-norm, r=jackh726

Don't normalize higher-ranked assumptions if they're not used

See the comment in the code.

Normalizing these assumptions may cause us to register things like new placeholder outlives obligations that cause higher-ranked lifetime errors, and this is problematic if we're not even using these assumptions in borrowck.

Fixes rust-lang/rust#147244
Fixes rust-lang/rust#147285

1 files changed, 51 insertions, 0 deletions

diff --git a/tests/ui/async-await/higher-ranked-normalize-assumptions.rs b/tests/ui/async-await/higher-ranked-normalize-assumptions.rs
new file mode 100644
index 00000000000..ec9cf3a1522
--- /dev/null
+++ b/tests/ui/async-await/higher-ranked-normalize-assumptions.rs
@@ -0,0 +1,51 @@
+//@ revisions: stock hr
+//@[hr] compile-flags: -Zhigher-ranked-assumptions
+//@ edition: 2024
+//@ check-pass
+
+// Test that we don't normalize the higher-ranked assumptions of an auto trait goal
+// unless we have `-Zhigher-ranked-assumptions`, since obligations that result from
+// this normalization may lead to higher-ranked lifetime errors when the flag is not
+// enabled.
+
+// Regression test for <https://github.com/rust-lang/rust/issues/147285>.
+
+pub trait Service {
+    type Response;
+}
+
+impl<T, R> Service for T
+where
+    T: FnMut() -> R,
+    R: 'static,
+{
+    type Response = R;
+}
+
+async fn serve<C>(_: C)
+where
+    C: Service,
+    C::Response: 'static,
+{
+    connect::<C>().await;
+}
+
+async fn connect<C>()
+where
+    C: Service,
+    C::Response: 'static,
+{
+}
+
+fn repro() -> impl Send {
+    async {
+        let server = || do_something();
+        serve(server).await;
+    }
+}
+
+fn do_something() -> Box<dyn std::error::Error> {
+    unimplemented!()
+}
+
+fn main() {}