Rollup merge of #112870 - compiler-errors:clause-2, r=oli-obk

Migrate `item_bounds` to `ty::Clause`

Should be simpler than the next PR that's coming up. Last three commits are the relevant ones.

r? ``@oli-obk`` or ``@lcnr``

compiler/rustc_trait_selection/src/solve/assembly/mod.rs

@@ -522,13 +522,11 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
 
         for assumption in self.tcx().item_bounds(alias_ty.def_id).subst(self.tcx(), alias_ty.substs)
         {
-            if let Some(clause) = assumption.as_clause() {
-                match G::consider_alias_bound_candidate(self, goal, clause) {
-                    Ok(result) => {
-                        candidates.push(Candidate { source: CandidateSource::AliasBound, result })
-                    }
-                    Err(NoSolution) => (),
+            match G::consider_alias_bound_candidate(self, goal, assumption) {
+                Ok(result) => {
+                    candidates.push(Candidate { source: CandidateSource::AliasBound, result })
                 }
+                Err(NoSolution) => (),
             }
         }
     }

compiler/rustc_trait_selection/src/solve/assembly/structural_traits.rs

@@ -353,7 +353,11 @@ pub(in crate::solve) fn predicates_for_object_candidate<'tcx>(
         // FIXME(associated_const_equality): Also add associated consts to
         // the requirements here.
         if item.kind == ty::AssocKind::Type {
-            requirements.extend(tcx.item_bounds(item.def_id).subst(tcx, trait_ref.substs));
+            requirements.extend(
+                tcx.item_bounds(item.def_id)
+                    .subst_iter(tcx, trait_ref.substs)
+                    .map(|clause| clause.as_predicate()),
+            );
         }
     }
 

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -1157,7 +1157,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 }
                 ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. }) => {
                     self.tcx.item_bounds(def_id).subst(self.tcx, substs).iter().find_map(|pred| {
-                        if let ty::PredicateKind::Clause(ty::ClauseKind::Projection(proj)) = pred.kind().skip_binder()
+                        if let ty::ClauseKind::Projection(proj) = pred.kind().skip_binder()
                         && Some(proj.projection_ty.def_id) == self.tcx.lang_items().fn_once_output()
                         // args tuple will always be substs[1]
                         && let ty::Tuple(args) = proj.projection_ty.substs.type_at(1).kind()

compiler/rustc_trait_selection/src/traits/object_safety.rs

@@ -271,7 +271,7 @@ fn bounds_reference_self(tcx: TyCtxt<'_>, trait_def_id: DefId) -> SmallVec<[Span
         .in_definition_order()
         .filter(|item| item.kind == ty::AssocKind::Type)
         .flat_map(|item| tcx.explicit_item_bounds(item.def_id).subst_identity_iter_copied())
-        .filter_map(|pred_span| predicate_references_self(tcx, pred_span))
+        .filter_map(|(clause, span)| predicate_references_self(tcx, (clause.as_predicate(), span)))
         .collect()
 }
 

compiler/rustc_trait_selection/src/traits/project.rs

@@ -1585,7 +1585,7 @@ fn assemble_candidates_from_trait_def<'cx, 'tcx>(
         obligation,
         candidate_set,
         ProjectionCandidate::TraitDef,
-        bounds.iter(),
+        bounds.iter().map(|clause| clause.as_predicate()),
         true,
     );
 }

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

@@ -170,7 +170,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         let candidate_predicate = tcx.item_bounds(def_id).map_bound(|i| i[idx]).subst(tcx, substs);
         let candidate = candidate_predicate
-            .to_opt_poly_trait_pred()
+            .as_trait_clause()
             .expect("projection candidate is not a trait predicate")
             .map_bound(|t| t.trait_ref);
         let mut obligations = Vec::new();
@@ -631,7 +631,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                         let assoc_ty_substs = tcx.mk_substs(&substs);
                         let bound =
                             bound.map_bound(|b| b.kind().skip_binder()).subst(tcx, assoc_ty_substs);
-                        tcx.mk_predicate(ty::Binder::bind_with_vars(bound, bound_vars))
+                        ty::Binder::bind_with_vars(bound, bound_vars).to_predicate(tcx)
                     };
                 let normalized_bound = normalize_with_depth_to(
                     self,

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

@@ -1668,9 +1668,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             .enumerate()
             .filter_map(|(idx, bound)| {
                 let bound_predicate = bound.kind();
-                if let ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) =
-                    bound_predicate.skip_binder()
-                {
+                if let ty::ClauseKind::Trait(pred) = bound_predicate.skip_binder() {
                     let bound = bound_predicate.rebind(pred.trait_ref);
                     if self.infcx.probe(|_| {
                         match self.match_normalize_trait_ref(