Auto merge of #132479 - compiler-errors:fx-feat-yeet, r=fee1-dead

Yeet the `effects` feature, move it onto `const_trait_impl`

This PR merges the `effects` feature into the `const_trait_impl` feature. There's really no need to have two feature gates for one feature.

After this PR, if `const_trait_impl` **is** enabled:
* Users can use and define const traits
* `HostEffect` const conditions will be enforced on the HIR
* We re-check the predicates in MIR just to make sure that we don't "leak" anything during MIR lowering

And if `const_trait_impl` **is not** enabled:
* Users cannot use nor define const traits
* `HostEffect` const conditions are not enforced on the HIR
* We will raise a const validation error if we call a function that has any const conditions (i.e. const traits and functions with any `~const` in their where clasues)

This should be the last step for us to be able to enable const traits in the standard library. We still need to re-constify `Drop` and `Destruct` and stuff for const traits to be particularly *useful* for some cases, but this is a good step :D

r? fee1-dead
cc `@rust-lang/project-const-traits`

4 files changed, 5 insertions, 7 deletions

diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
index 524b4139600..f5cd99222e3 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
@@ -538,7 +538,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     }
 
                     ty::PredicateKind::Clause(ty::ClauseKind::HostEffect(predicate)) => {
-                        // FIXME(effects): We should recompute the predicate with `~const`
+                        // FIXME(const_trait_impl): We should recompute the predicate with `~const`
                         // if it's `const`, and if it holds, explain that this bound only
                         // *conditionally* holds. If that fails, we should also do selection
                         // to drill this down to an impl or built-in source, so we can
@@ -2641,7 +2641,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         _span: Span,
     ) -> UnsatisfiedConst {
         let unsatisfied_const = UnsatisfiedConst(false);
-        // FIXME(effects)
+        // FIXME(const_trait_impl)
         unsatisfied_const
     }
 
@@ -3052,7 +3052,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 // Make a fresh inference variable so we can determine what the generic parameters
                 // of the trait are.
                 let var = self.next_ty_var(DUMMY_SP);
-                // FIXME(effects)
+                // FIXME(const_trait_impl)
                 let trait_ref = ty::TraitRef::new(self.tcx, trait_def_id, [ty.skip_binder(), var]);
                 let obligation = Obligation::new(
                     self.tcx,
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
index 07e3300f0f2..e155effa1e3 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
@@ -3751,7 +3751,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     trait_pred.skip_binder().self_ty(),
                     diagnostic_name,
                 ),
-                // FIXME(effects, const_trait_impl) derive_const as suggestion?
+                // FIXME(const_trait_impl) derive_const as suggestion?
                 format!("#[derive({diagnostic_name})]\n"),
                 Applicability::MaybeIncorrect,
             );
diff --git a/compiler/rustc_trait_selection/src/traits/fulfill.rs b/compiler/rustc_trait_selection/src/traits/fulfill.rs
index 29e60e3c428..e3d17a910cc 100644
--- a/compiler/rustc_trait_selection/src/traits/fulfill.rs
+++ b/compiler/rustc_trait_selection/src/traits/fulfill.rs
@@ -374,7 +374,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 | ty::PredicateKind::Coerce(_)
                 | ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(..))
                 | ty::PredicateKind::ConstEquate(..)
-                // FIXME(effects): We may need to do this using the higher-ranked
+                // FIXME(const_trait_impl): We may need to do this using the higher-ranked
                 // pred instead of just instantiating it with placeholders b/c of
                 // higher-ranked implied bound issues in the old solver.
                 | ty::PredicateKind::Clause(ty::ClauseKind::HostEffect(..)) => {
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 03fde1d1598..bf3f83ec827 100644
--- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -1170,8 +1170,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         _obligation: &PolyTraitObligation<'tcx>,
         candidates: &mut SelectionCandidateSet<'tcx>,
     ) {
-        // FIXME(effects): Destruct is not const yet, and it is implemented
-        // by all types today in non-const setting.
         candidates.vec.push(BuiltinCandidate { has_nested: false });
     }