drive-by: use is_const and is_const_if_const

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -7,7 +7,6 @@ use crate::interpret::{
 };
 
 use rustc_errors::ErrorReported;
-use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_middle::mir;
 use rustc_middle::mir::interpret::ErrorHandled;
@@ -216,7 +215,7 @@ pub fn eval_to_const_value_raw_provider<'tcx>(
     tcx: TyCtxt<'tcx>,
     key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
 ) -> ::rustc_middle::mir::interpret::EvalToConstValueResult<'tcx> {
-    assert!(key.param_env.constness() == hir::Constness::Const);
+    assert!(key.param_env.is_const());
     // see comment in eval_to_allocation_raw_provider for what we're doing here
     if key.param_env.reveal() == Reveal::All {
         let mut key = key;
@@ -251,7 +250,7 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
     tcx: TyCtxt<'tcx>,
     key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
 ) -> ::rustc_middle::mir::interpret::EvalToAllocationRawResult<'tcx> {
-    assert!(key.param_env.constness() == hir::Constness::Const);
+    assert!(key.param_env.is_const());
     // Because the constant is computed twice (once per value of `Reveal`), we are at risk of
     // reporting the same error twice here. To resolve this, we check whether we can evaluate the
     // constant in the more restrictive `Reveal::UserFacing`, which most likely already was

compiler/rustc_lint/src/traits.rs

@@ -86,7 +86,6 @@ declare_lint_pass!(
 
 impl<'tcx> LateLintPass<'tcx> for DropTraitConstraints {
     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
-        use rustc_middle::ty;
         use rustc_middle::ty::PredicateKind::*;
 
         let predicates = cx.tcx.explicit_predicates_of(item.def_id);
@@ -94,7 +93,7 @@ impl<'tcx> LateLintPass<'tcx> for DropTraitConstraints {
             let Trait(trait_predicate) = predicate.kind().skip_binder() else {
                 continue
             };
-            if trait_predicate.constness == ty::BoundConstness::ConstIfConst {
+            if trait_predicate.is_const_if_const() {
                 // `~const Drop` definitely have meanings so avoid linting here.
                 continue;
             }

compiler/rustc_middle/src/ty/mod.rs

@@ -784,6 +784,11 @@ impl<'tcx> TraitPredicate<'tcx> {
     pub fn self_ty(self) -> Ty<'tcx> {
         self.trait_ref.self_ty()
     }
+
+    #[inline]
+    pub fn is_const_if_const(self) -> bool {
+        self.constness == BoundConstness::ConstIfConst
+    }
 }
 
 impl<'tcx> PolyTraitPredicate<'tcx> {
@@ -804,8 +809,9 @@ impl<'tcx> PolyTraitPredicate<'tcx> {
         });
     }
 
-    pub fn is_const(self) -> bool {
+    #[inline]
-        self.skip_binder().constness == BoundConstness::ConstIfConst
+    pub fn is_const_if_const(self) -> bool {
+        self.skip_binder().is_const_if_const()
     }
 }
 
@@ -1392,6 +1398,7 @@ impl<'tcx> ParamEnv<'tcx> {
         self.packed.tag().constness
     }
 
+    #[inline]
     pub fn is_const(self) -> bool {
         self.packed.tag().constness == hir::Constness::Const
     }

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

@@ -440,7 +440,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                             err.span_label(span, explanation);
                         }
 
-                        if trait_predicate.is_const() && obligation.param_env.is_const() {
+                        if trait_predicate.is_const_if_const() && obligation.param_env.is_const() {
                             let non_const_predicate = trait_ref.without_const();
                             let non_const_obligation = Obligation {
                                 cause: obligation.cause.clone(),

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

@@ -305,7 +305,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             } else if lang_items.unsize_trait() == Some(def_id) {
                 self.assemble_candidates_for_unsizing(obligation, &mut candidates);
             } else if lang_items.drop_trait() == Some(def_id)
-                && obligation.predicate.skip_binder().constness == ty::BoundConstness::ConstIfConst
+                && obligation.predicate.is_const_if_const()
             {
                 self.assemble_const_drop_candidates(obligation, &mut candidates);
             } else {

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

@@ -72,9 +72,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // CheckPredicate(&A: Super)
         // CheckPredicate(A: ~const Super) // <- still const env, failure
         // ```
-        if obligation.param_env.constness() == Constness::Const
+        if obligation.param_env.is_const() && !obligation.predicate.is_const_if_const() {
-            && obligation.predicate.skip_binder().constness == ty::BoundConstness::NotConst
-        {
             new_obligation = TraitObligation {
                 cause: obligation.cause.clone(),
                 param_env: obligation.param_env.without_const(),

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

@@ -1173,9 +1173,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     ImplCandidate(def_id)
                         if tcx.impl_constness(def_id) == hir::Constness::Const => {}
                     // const param
-                    ParamCandidate(trait_pred)
+                    ParamCandidate(trait_pred) if trait_pred.is_const_if_const() => {}
-                        if trait_pred.skip_binder().constness
-                            == ty::BoundConstness::ConstIfConst => {}
                     // auto trait impl
                     AutoImplCandidate(..) => {}
                     // generator, this will raise error in other places