Rollup merge of #91875 - b-naber:mir-transform-norm-erase-reg, r=Aaron1011

Use try_normalize_erasing_regions in RevealAllVisitor

Fixes https://github.com/rust-lang/rust/issues/91745

Thanks to ``@Aaron1011`` for [pointing out the problem](https://github.com/rust-lang/rust/issues/91745#issuecomment-991996008).

r? ``@Aaron1011``

2 files changed, 25 insertions, 1 deletions

diff --git a/compiler/rustc_mir_transform/src/reveal_all.rs b/compiler/rustc_mir_transform/src/reveal_all.rs
index a717dd3e0cd..ee661793a44 100644
--- a/compiler/rustc_mir_transform/src/reveal_all.rs
+++ b/compiler/rustc_mir_transform/src/reveal_all.rs
@@ -36,6 +36,9 @@ impl<'tcx> MutVisitor<'tcx> for RevealAllVisitor<'tcx> {
 
     #[inline]
     fn visit_ty(&mut self, ty: &mut Ty<'tcx>, _: TyContext) {
-        *ty = self.tcx.normalize_erasing_regions(self.param_env, ty);
+        // We have to use `try_normalize_erasing_regions` here, since it's
+        // possible that we visit impossible-to-satisfy where clauses here,
+        // see #91745
+        *ty = self.tcx.try_normalize_erasing_regions(self.param_env, *ty).unwrap_or(ty);
     }
 }
diff --git a/src/test/ui/mir/issue-91745.rs b/src/test/ui/mir/issue-91745.rs
new file mode 100644
index 00000000000..ca3d66b1c8e
--- /dev/null
+++ b/src/test/ui/mir/issue-91745.rs
@@ -0,0 +1,21 @@
+// check-pass
+
+pub trait Foo {
+    type Bar;
+}
+
+pub trait Broken {
+    type Assoc;
+    fn broken(&self) where Self::Assoc: Foo;
+}
+
+impl<T> Broken for T {
+    type Assoc = ();
+    fn broken(&self) where Self::Assoc: Foo {
+        let _x: <Self::Assoc as Foo>::Bar;
+    }
+}
+
+fn main() {
+    let _m: &dyn Broken<Assoc=()> = &();
+}