From cb9852b8e60b956421cbb6363a75d970d64372cc Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Tue, 28 Feb 2023 17:29:40 +0000
Subject: [PATCH] Erase **all** regions when probing for associated types in
 astconv

---
 compiler/rustc_hir_analysis/src/astconv/mod.rs           | 6 ++++--
 tests/ui/suggestions/suggest-trait-in-ufcs-in-hrtb.rs    | 8 ++++++++
 .../ui/suggestions/suggest-trait-in-ufcs-in-hrtb.stderr  | 9 +++++++++
 3 files changed, 21 insertions(+), 2 deletions(-)
 create mode 100644 tests/ui/suggestions/suggest-trait-in-ufcs-in-hrtb.rs
 create mode 100644 tests/ui/suggestions/suggest-trait-in-ufcs-in-hrtb.stderr

diff --git a/compiler/rustc_hir_analysis/src/astconv/mod.rs b/compiler/rustc_hir_analysis/src/astconv/mod.rs
index a15cf454df72f..7d6213dfc286c 100644
--- a/compiler/rustc_hir_analysis/src/astconv/mod.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/mod.rs
@@ -2403,8 +2403,10 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                                 infcx
                                     .can_eq(
                                         ty::ParamEnv::empty(),
-                                        tcx.erase_regions(impl_.self_ty()),
-                                        tcx.erase_regions(qself_ty),
+                                        impl_.self_ty(),
+                                        // Must fold past escaping bound vars too,
+                                        // since we have those at this point in astconv.
+                                        tcx.fold_regions(qself_ty, |_, _| tcx.lifetimes.re_erased),
                                     )
                             })
                             && tcx.impl_polarity(impl_def_id) != ty::ImplPolarity::Negative
diff --git a/tests/ui/suggestions/suggest-trait-in-ufcs-in-hrtb.rs b/tests/ui/suggestions/suggest-trait-in-ufcs-in-hrtb.rs
new file mode 100644
index 0000000000000..fbaf41245e9b6
--- /dev/null
+++ b/tests/ui/suggestions/suggest-trait-in-ufcs-in-hrtb.rs
@@ -0,0 +1,8 @@
+pub struct Bar<S>(S);
+
+pub trait Foo {}
+
+impl<S> Foo for Bar<S> where for<'a> <&'a S>::Item: Foo {}
+//~^ ERROR ambiguous associated type
+
+fn main() {}
diff --git a/tests/ui/suggestions/suggest-trait-in-ufcs-in-hrtb.stderr b/tests/ui/suggestions/suggest-trait-in-ufcs-in-hrtb.stderr
new file mode 100644
index 0000000000000..0ca5b9b920790
--- /dev/null
+++ b/tests/ui/suggestions/suggest-trait-in-ufcs-in-hrtb.stderr
@@ -0,0 +1,9 @@
+error[E0223]: ambiguous associated type
+  --> $DIR/suggest-trait-in-ufcs-in-hrtb.rs:5:38
+   |
+LL | impl<S> Foo for Bar<S> where for<'a> <&'a S>::Item: Foo {}
+   |                                      ^^^^^^^^^^^^^ help: use the fully-qualified path: `<&'a S as IntoIterator>::Item`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0223`.