Fix remap_constness

`~const Drop` was renamed to `~const Destruct` and this special case should
be removed

Author: fee1-dead

compiler/rustc_middle/src/ty/mod.rs

@@ -790,22 +790,15 @@ pub struct TraitPredicate<'tcx> {
 pub type PolyTraitPredicate<'tcx> = ty::Binder<'tcx, TraitPredicate<'tcx>>;
 
 impl<'tcx> TraitPredicate<'tcx> {
-    pub fn remap_constness(&mut self, tcx: TyCtxt<'tcx>, param_env: &mut ParamEnv<'tcx>) {
-        if std::intrinsics::unlikely(Some(self.trait_ref.def_id) == tcx.lang_items().drop_trait()) {
-            // remap without changing constness of this predicate.
-            // this is because `T: ~const Drop` has a different meaning to `T: Drop`
-            // FIXME(fee1-dead): remove this logic after beta bump
-            param_env.remap_constness_with(self.constness)
-        } else {
-            *param_env = param_env.with_constness(self.constness.and(param_env.constness()))
-        }
+    pub fn remap_constness(&mut self, param_env: &mut ParamEnv<'tcx>) {
+        *param_env = param_env.with_constness(self.constness.and(param_env.constness()))
     }
 
     /// Remap the constness of this predicate before emitting it for diagnostics.
     pub fn remap_constness_diag(&mut self, param_env: ParamEnv<'tcx>) {
         // this is different to `remap_constness` that callees want to print this predicate
         // in case of selection errors. `T: ~const Drop` bounds cannot end up here when the
-        // param_env is not const because we it is always satisfied in non-const contexts.
+        // param_env is not const because it is always satisfied in non-const contexts.
         if let hir::Constness::NotConst = param_env.constness() {
             self.constness = ty::BoundConstness::NotConst;
         }

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -789,7 +789,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let mut param_env = obligation.param_env;
 
         fresh_trait_pred = fresh_trait_pred.map_bound(|mut pred| {
-            pred.remap_constness(self.tcx(), &mut param_env);
+            pred.remap_constness(&mut param_env);
             pred
         });
 
@@ -1321,7 +1321,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         }
         let tcx = self.tcx();
         let mut pred = cache_fresh_trait_pred.skip_binder();
-        pred.remap_constness(tcx, &mut param_env);
+        pred.remap_constness(&mut param_env);
 
         if self.can_use_global_caches(param_env) {
             if let Some(res) = tcx.selection_cache.get(&(param_env, pred), tcx) {
@@ -1375,7 +1375,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let tcx = self.tcx();
         let mut pred = cache_fresh_trait_pred.skip_binder();
 
-        pred.remap_constness(tcx, &mut param_env);
+        pred.remap_constness(&mut param_env);
 
         if !self.can_cache_candidate(&candidate) {
             debug!(?pred, ?candidate, "insert_candidate_cache - candidate is not cacheable");