From c91f60e22fccbd1ee7701b2a1b88457985f9df0b Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Mon, 30 Oct 2023 19:24:08 +0000
Subject: [PATCH] Don't super-fold types when we hit the recursion limit

---
 .../src/traits/query/normalize.rs                     | 11 ++++-------
 .../infinite-cycle-involving-weak.rs                  |  8 ++++++++
 .../infinite-cycle-involving-weak.stderr              |  9 +++++++++
 3 files changed, 21 insertions(+), 7 deletions(-)
 create mode 100644 tests/ui/type-alias-impl-trait/infinite-cycle-involving-weak.rs
 create mode 100644 tests/ui/type-alias-impl-trait/infinite-cycle-involving-weak.stderr

diff --git a/compiler/rustc_trait_selection/src/traits/query/normalize.rs b/compiler/rustc_trait_selection/src/traits/query/normalize.rs
index c761d0d103ea2..2e31b560b38ff 100644
--- a/compiler/rustc_trait_selection/src/traits/query/normalize.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/normalize.rs
@@ -230,17 +230,14 @@ impl<'cx, 'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for QueryNormalizer<'cx, 'tcx>
                     Reveal::All => {
                         let args = data.args.try_fold_with(self)?;
                         let recursion_limit = self.interner().recursion_limit();
+
                         if !recursion_limit.value_within_limit(self.anon_depth) {
-                            // A closure or coroutine may have itself as in its upvars.
-                            // This should be checked handled by the recursion check for opaque
-                            // types, but we may end up here before that check can happen.
-                            // In that case, we delay a bug to mark the trip, and continue without
-                            // revealing the opaque.
-                            self.infcx
+                            let guar = self
+                                .infcx
                                 .err_ctxt()
                                 .build_overflow_error(&ty, self.cause.span, true)
                                 .delay_as_bug();
-                            return ty.try_super_fold_with(self);
+                            return Ok(Ty::new_error(self.interner(), guar));
                         }
 
                         let generic_ty = self.interner().type_of(data.def_id);
diff --git a/tests/ui/type-alias-impl-trait/infinite-cycle-involving-weak.rs b/tests/ui/type-alias-impl-trait/infinite-cycle-involving-weak.rs
new file mode 100644
index 0000000000000..6609d4eb5a274
--- /dev/null
+++ b/tests/ui/type-alias-impl-trait/infinite-cycle-involving-weak.rs
@@ -0,0 +1,8 @@
+#![feature(type_alias_impl_trait)]
+
+type T = impl Copy;
+//~^ ERROR cannot resolve opaque type
+
+static STATIC: T = None::<&'static T>;
+
+fn main() {}
diff --git a/tests/ui/type-alias-impl-trait/infinite-cycle-involving-weak.stderr b/tests/ui/type-alias-impl-trait/infinite-cycle-involving-weak.stderr
new file mode 100644
index 0000000000000..50ae6f3864112
--- /dev/null
+++ b/tests/ui/type-alias-impl-trait/infinite-cycle-involving-weak.stderr
@@ -0,0 +1,9 @@
+error[E0720]: cannot resolve opaque type
+  --> $DIR/infinite-cycle-involving-weak.rs:3:10
+   |
+LL | type T = impl Copy;
+   |          ^^^^^^^^^ cannot resolve opaque type
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0720`.