Always canonicalize skolemized regions

Since `ReSkolemized` has the flag `KEEP_IN_LOCAL_TCX`, and
canonicalization is meant to ensure that flag is no longer present, it
implicitly is depending on the existence of the leak check. However,
since we want to remove that in rust-lang#48407, we can no longer make that
assumption.

This is related to rust-lang#48696, but does not resolve it. This does unblock that
PR, however. It could have been tacked on there, but I wanted to make
sure this is a reasonable short term approach separately from that.

Author: sgrif

src/librustc/infer/canonical.rs

@@ -557,31 +557,24 @@ impl<'cx, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for Canonicalizer<'cx, 'gcx, 'tcx>
                     .unwrap()
                     .borrow_region_constraints()
                     .opportunistic_resolve_var(self.tcx, vid);
-                let info = CanonicalVarInfo {
-                    kind: CanonicalVarKind::Region,
-                };
                 debug!(
                     "canonical: region var found with vid {:?}, \
                      opportunistically resolved to {:?}",
                     vid, r
                 );
-                let cvar = self.canonical_var(info, Kind::from(r));
-                self.tcx().mk_region(ty::ReCanonical(cvar))
+                self.canonicalize_region(r)
             }
 
+            ty::ReSkolemized(..) => self.canonicalize_region(r),
+
             ty::ReStatic
             | ty::ReEarlyBound(..)
             | ty::ReFree(_)
             | ty::ReScope(_)
-            | ty::ReSkolemized(..)
             | ty::ReEmpty
             | ty::ReErased => {
                 if self.canonicalize_all_free_regions.0 {
-                    let info = CanonicalVarInfo {
-                        kind: CanonicalVarKind::Region,
-                    };
-                    let cvar = self.canonical_var(info, Kind::from(r));
-                    self.tcx().mk_region(ty::ReCanonical(cvar))
+                    self.canonicalize_region(r)
                 } else {
                     r
                 }
@@ -764,6 +757,14 @@ impl<'cx, 'gcx, 'tcx> Canonicalizer<'cx, 'gcx, 'tcx> {
             self.tcx().mk_infer(ty::InferTy::CanonicalTy(cvar))
         }
     }
+
+    fn canonicalize_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
+        let info = CanonicalVarInfo {
+            kind: CanonicalVarKind::Region,
+        };
+        let cvar = self.canonical_var(info, Kind::from(r));
+        self.tcx().mk_region(ty::ReCanonical(cvar))
+    }
 }
 
 impl<'tcx, V> Canonical<'tcx, V> {