Auto merge of #96593 - jackh726:issue-93262, r=compiler-errors

Revert "Prefer projection candidates instead of param_env candidates for Sized predicates"

Fixes #93262
Reopens #89352

This was a hack that seemed to have no negative side-effects at the time. Given that the latter has a workaround and likely less common than the former, it makes sense to revert this change.

r? `@compiler-errors`

2 files changed, 8 insertions, 16 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
index dbb6c54fcd9..07720ba71ca 100644
--- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -175,9 +175,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         let needs_infer = stack.obligation.predicate.has_infer_types_or_consts();
 
-        let sized_predicate = self.tcx().lang_items().sized_trait()
-            == Some(stack.obligation.predicate.skip_binder().def_id());
-
         // If there are STILL multiple candidates, we can further
         // reduce the list by dropping duplicates -- including
         // resolving specializations.
@@ -186,7 +183,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             while i < candidates.len() {
                 let is_dup = (0..candidates.len()).filter(|&j| i != j).any(|j| {
                     self.candidate_should_be_dropped_in_favor_of(
-                        sized_predicate,
                         &candidates[i],
                         &candidates[j],
                         needs_infer,
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index e69bf6eca90..9e2d0657029 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -1553,7 +1553,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     /// See the comment for "SelectionCandidate" for more details.
     fn candidate_should_be_dropped_in_favor_of(
         &mut self,
-        sized_predicate: bool,
         victim: &EvaluatedCandidate<'tcx>,
         other: &EvaluatedCandidate<'tcx>,
         needs_infer: bool,
@@ -1625,16 +1624,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             // Drop otherwise equivalent non-const fn pointer candidates
             (FnPointerCandidate { .. }, FnPointerCandidate { is_const: false }) => true,
 
-            // If obligation is a sized predicate or the where-clause bound is
-            // global, prefer the projection or object candidate. See issue
-            // #50825 and #89352.
-            (ObjectCandidate(_) | ProjectionCandidate(_), ParamCandidate(ref cand)) => {
-                sized_predicate || is_global(cand)
-            }
-            (ParamCandidate(ref cand), ObjectCandidate(_) | ProjectionCandidate(_)) => {
-                !(sized_predicate || is_global(cand))
-            }
-
             // Global bounds from the where clause should be ignored
             // here (see issue #50825). Otherwise, we have a where
             // clause so don't go around looking for impls.
@@ -1650,8 +1639,15 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 | BuiltinUnsizeCandidate
                 | TraitUpcastingUnsizeCandidate(_)
                 | BuiltinCandidate { .. }
-                | TraitAliasCandidate(..),
+                | TraitAliasCandidate(..)
+                | ObjectCandidate(_)
+                | ProjectionCandidate(_),
             ) => !is_global(cand),
+            (ObjectCandidate(_) | ProjectionCandidate(_), ParamCandidate(ref cand)) => {
+                // Prefer these to a global where-clause bound
+                // (see issue #50825).
+                is_global(cand)
+            }
             (
                 ImplCandidate(_)
                 | ClosureCandidate