Auto merge of #37129 - arielb1:erased-normal, r=eddyb

normalize types every time HR regions are erased

Associated type normalization is inhibited by higher-ranked regions.
Therefore, every time we erase them, we must re-normalize.

I was meaning to introduce this change some time ago, but we used
to erase regions in generic context, which broke this terribly (because
you can't always normalize in a generic context). That seems to be gone
now.

Ensure this by having a `erase_late_bound_regions_and_normalize`
function.

Fixes #37109 (the missing call was in mir::block).

r? @eddyb

src/librustc/infer/mod.rs

@@ -583,7 +583,8 @@ impl_trans_normalize!('gcx,
     ty::FnSig<'gcx>,
     &'gcx ty::BareFnTy<'gcx>,
     ty::ClosureSubsts<'gcx>,
-    ty::PolyTraitRef<'gcx>
+    ty::PolyTraitRef<'gcx>,
+    ty::ExistentialTraitRef<'gcx>
 );
 
 impl<'gcx> TransNormalize<'gcx> for LvalueTy<'gcx> {
@@ -603,6 +604,18 @@ impl<'gcx> TransNormalize<'gcx> for LvalueTy<'gcx> {
 
 // NOTE: Callable from trans only!
 impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
+    /// Currently, higher-ranked type bounds inhibit normalization. Therefore,
+    /// each time we erase them in translation, we need to normalize
+    /// the contents.
+    pub fn erase_late_bound_regions_and_normalize<T>(self, value: &ty::Binder<T>)
+        -> T
+        where T: TransNormalize<'tcx>
+    {
+        assert!(!value.needs_subst());
+        let value = self.erase_late_bound_regions(value);
+        self.normalize_associated_type(&value)
+    }
+
     pub fn normalize_associated_type<T>(self, value: &T) -> T
         where T: TransNormalize<'tcx>
     {