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`

Author: bors

compiler/rustc_ast_passes/src/errors.rs

@@ -594,8 +594,8 @@ pub(crate) struct ConstBoundTraitObject {
     pub span: Span,
 }
 
-// FIXME(effects): Consider making the note/reason the message of the diagnostic.
-// FIXME(effects): Provide structured suggestions (e.g., add `const` / `#[const_trait]` here).
+// FIXME(const_trait_impl): Consider making the note/reason the message of the diagnostic.
+// FIXME(const_trait_impl): Provide structured suggestions (e.g., add `const` / `#[const_trait]` here).
 #[derive(Diagnostic)]
 #[diag(ast_passes_tilde_const_disallowed)]
 pub(crate) struct TildeConstDisallowed {

compiler/rustc_const_eval/src/check_consts/check.rs

@@ -20,7 +20,6 @@ use rustc_mir_dataflow::Analysis;
 use rustc_mir_dataflow::impls::MaybeStorageLive;
 use rustc_mir_dataflow::storage::always_storage_live_locals;
 use rustc_span::{Span, Symbol, sym};
-use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
 use rustc_trait_selection::traits::{
     Obligation, ObligationCause, ObligationCauseCode, ObligationCtxt,
 };
@@ -419,13 +418,8 @@ impl<'mir, 'tcx> Checker<'mir, 'tcx> {
 
         let errors = ocx.select_all_or_error();
         if !errors.is_empty() {
-            // FIXME(effects): Soon this should be unconditionally delaying a bug.
-            if matches!(call_source, CallSource::Normal) && tcx.features().effects() {
-                tcx.dcx()
-                    .span_delayed_bug(call_span, "this should have reported a ~const error in HIR");
-            } else {
-                infcx.err_ctxt().report_fulfillment_errors(errors);
-            }
+            tcx.dcx()
+                .span_delayed_bug(call_span, "this should have reported a ~const error in HIR");
         }
     }
 }
@@ -663,8 +657,9 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                     // typeck ensures the conditions for calling a const trait method are met,
                     // so we only error if the trait isn't const. We try to resolve the trait
                     // into the concrete method, and uses that for const stability checks.
-                    // FIXME(effects) we might consider moving const stability checks to typeck as well.
-                    if tcx.features().effects() && trait_is_const {
+                    // FIXME(const_trait_impl) we might consider moving const stability checks
+                    // to typeck as well.
+                    if tcx.features().const_trait_impl() && trait_is_const {
                         // This skips the check below that ensures we only call `const fn`.
                         is_trait = true;
 

compiler/rustc_const_eval/src/check_consts/ops.rs

@@ -120,7 +120,7 @@ impl<'tcx> NonConstOp<'tcx> for FnCallNonConst<'tcx> {
                     let implsrc = selcx.select(&obligation);
 
                     if let Ok(Some(ImplSource::UserDefined(data))) = implsrc {
-                        // FIXME(effects) revisit this
+                        // FIXME(const_trait_impl) revisit this
                         if !tcx.is_const_trait_impl(data.impl_def_id) {
                             let span = tcx.def_span(data.impl_def_id);
                             err.subdiagnostic(errors::NonConstImplNote { span });

compiler/rustc_const_eval/src/check_consts/qualifs.rs

@@ -192,7 +192,7 @@ impl Qualif for NeedsNonConstDrop {
             return false;
         }
 
-        // FIXME(effects): Reimplement const drop checking.
+        // FIXME(const_trait_impl): Reimplement const drop checking.
         NeedsDrop::in_any_value_of_ty(cx, ty)
     }
 

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -431,7 +431,7 @@ impl<'tcx> interpret::Machine<'tcx> for CompileTimeMachine<'tcx> {
             // sensitive check here. But we can at least rule out functions that are not const at
             // all. That said, we have to allow calling functions inside a trait marked with
             // #[const_trait]. These *are* const-checked!
-            // FIXME(effects): why does `is_const_fn` not classify them as const?
+            // FIXME(const_trait_impl): why does `is_const_fn` not classify them as const?
             if (!ecx.tcx.is_const_fn(def) && !ecx.tcx.is_const_default_method(def))
                 || ecx.tcx.has_attr(def, sym::rustc_do_not_const_check)
             {

compiler/rustc_feature/src/removed.rs

@@ -100,6 +100,9 @@ declare_features! (
      Some("renamed to `doc_notable_trait`")),
     /// Allows using `#[unsafe_destructor_blind_to_params]` (RFC 1238).
     (removed, dropck_parametricity, "1.38.0", Some(28498), None),
+    /// Uses generic effect parameters for ~const bounds
+    (removed, effects, "CURRENT_RUSTC_VERSION", Some(102090),
+     Some("removed, redundant with `#![feature(const_trait_impl)]`")),
     /// Allows defining `existential type`s.
     (removed, existential_type, "1.38.0", Some(63063),
      Some("removed in favor of `#![feature(type_alias_impl_trait)]`")),

compiler/rustc_feature/src/unstable.rs

@@ -462,8 +462,6 @@ declare_features! (
     (unstable, doc_masked, "1.21.0", Some(44027)),
     /// Allows `dyn* Trait` objects.
     (incomplete, dyn_star, "1.65.0", Some(102425)),
-    /// Uses generic effect parameters for ~const bounds
-    (incomplete, effects, "1.72.0", Some(102090)),
     /// Allows exhaustive pattern matching on types that contain uninhabited types.
     (unstable, exhaustive_patterns, "1.13.0", Some(51085)),
     /// Allows explicit tail calls via `become` expression.

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -205,7 +205,6 @@ fn compare_method_predicate_entailment<'tcx>(
         trait_m_predicates.instantiate_own(tcx, trait_to_impl_args).map(|(predicate, _)| predicate),
     );
 
-    // FIXME(effects): This should be replaced with a more dedicated method.
     let is_conditionally_const = tcx.is_conditionally_const(impl_def_id);
     if is_conditionally_const {
         // Augment the hybrid param-env with the const conditions

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -563,7 +563,6 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         if let Err(guar) = ty.error_reported() {
                             return ty::Const::new_error(tcx, guar).into();
                         }
-                        // FIXME(effects) see if we should special case effect params here
                         if !infer_args && has_default {
                             tcx.const_param_default(param.def_id)
                                 .instantiate(tcx, preceding_args)

compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs

@@ -459,7 +459,7 @@ fn trait_predicates_eq<'tcx>(
     predicate1: ty::Predicate<'tcx>,
     predicate2: ty::Predicate<'tcx>,
 ) -> bool {
-    // FIXME(effects)
+    // FIXME(const_trait_impl)
     predicate1 == predicate2
 }
 

compiler/rustc_hir_typeck/src/callee.rs

@@ -461,7 +461,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 }
                 (fn_sig, Some(def_id))
             }
-            // FIXME(effects): these arms should error because we can't enforce them
+            // FIXME(const_trait_impl): these arms should error because we can't enforce them
             ty::FnPtr(sig_tys, hdr) => (sig_tys.with(hdr), None),
             _ => {
                 for arg in arg_exprs {
@@ -843,11 +843,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         callee_did: DefId,
         callee_args: GenericArgsRef<'tcx>,
     ) {
-        // FIXME(effects): We should be enforcing these effects unconditionally.
+        // FIXME(const_trait_impl): We should be enforcing these effects unconditionally.
         // This can be done as soon as we convert the standard library back to
         // using const traits, since if we were to enforce these conditions now,
         // we'd fail on basically every builtin trait call (i.e. `1 + 2`).
-        if !self.tcx.features().effects() {
+        if !self.tcx.features().const_trait_impl() {
             return;
         }
 
@@ -864,11 +864,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             None => return,
         };
 
-        // FIXME(effects): Should this be `is_const_fn_raw`? It depends on if we move
+        // FIXME(const_trait_impl): Should this be `is_const_fn_raw`? It depends on if we move
         // const stability checking here too, I guess.
         if self.tcx.is_conditionally_const(callee_did) {
             let q = self.tcx.const_conditions(callee_did);
-            // FIXME(effects): Use this span with a better cause code.
+            // FIXME(const_trait_impl): Use this span with a better cause code.
             for (cond, _) in q.instantiate(self.tcx, callee_args) {
                 self.register_predicate(Obligation::new(
                     self.tcx,
@@ -878,7 +878,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 ));
             }
         } else {
-            // FIXME(effects): This should eventually be caught here.
+            // FIXME(const_trait_impl): This should eventually be caught here.
             // For now, though, we defer some const checking to MIR.
         }
     }

compiler/rustc_middle/src/ty/context.rs

@@ -3125,7 +3125,6 @@ impl<'tcx> TyCtxt<'tcx> {
             }
     }
 
-    // FIXME(effects): Please remove this. It's a footgun.
     /// Whether the trait impl is marked const. This does not consider stability or feature gates.
     pub fn is_const_trait_impl(self, def_id: DefId) -> bool {
         self.def_kind(def_id) == DefKind::Impl { of_trait: true }

compiler/rustc_next_trait_solver/src/solve/effect_goals.rs

@@ -84,7 +84,7 @@ where
         let cx = ecx.cx();
         let mut candidates = vec![];
 
-        // FIXME(effects): We elaborate here because the implied const bounds
+        // FIXME(const_trait_impl): We elaborate here because the implied const bounds
         // aren't necessarily elaborated. We probably should prefix this query
         // with `explicit_`...
         for clause in elaborate::elaborate(

compiler/rustc_next_trait_solver/src/solve/trait_goals.rs

@@ -609,8 +609,6 @@ where
             return Err(NoSolution);
         }
 
-        // FIXME(effects): Implement this when we get const working in the new solver
-
         // `Destruct` is automatically implemented for every type in
         // non-const environments.
         ecx.probe_builtin_trait_candidate(BuiltinImplSource::Misc)

compiler/rustc_passes/src/stability.rs

@@ -217,7 +217,7 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
 
         // `impl const Trait for Type` items forward their const stability to their
         // immediate children.
-        // FIXME(effects): how is this supposed to interact with `#[rustc_const_stable_indirect]`?
+        // FIXME(const_trait_impl): how is this supposed to interact with `#[rustc_const_stable_indirect]`?
         // Currently, once that is set, we do not inherit anything from the parent any more.
         if const_stab.is_none() {
             debug!("annotate: const_stab not found, parent = {:?}", self.parent_const_stab);

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,

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,
             );

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(..)) => {

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 });
     }
 

compiler/rustc_ty_utils/src/instance.rs

@@ -81,7 +81,6 @@ fn resolve_instance_raw<'tcx>(
             }
         } else {
             debug!(" => free item");
-            // FIXME(effects): we may want to erase the effect param if that is present on this item.
             ty::InstanceKind::Item(def_id)
         };
 

compiler/rustc_type_ir/src/predicate.rs

@@ -174,7 +174,6 @@ impl<I: Interner> UpcastFrom<I, TraitRef<I>> for TraitPredicate<I> {
 
 impl<I: Interner> fmt::Debug for TraitPredicate<I> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        // FIXME(effects) printing?
         write!(f, "TraitPredicate({:?}, polarity:{:?})", self.trait_ref, self.polarity)
     }
 }

library/core/src/ffi/c_str.rs

@@ -510,7 +510,7 @@ impl CStr {
     #[inline]
     #[must_use]
     const fn as_non_null_ptr(&self) -> NonNull<c_char> {
-        // FIXME(effects) replace with `NonNull::from`
+        // FIXME(const_trait_impl) replace with `NonNull::from`
         // SAFETY: a reference is never null
         unsafe { NonNull::new_unchecked(&self.inner as *const [c_char] as *mut [c_char]) }
             .as_non_null_ptr()

library/core/src/ops/drop.rs

@@ -203,7 +203,7 @@
 /// [nomicon]: ../../nomicon/phantom-data.html#an-exception-the-special-case-of-the-standard-library-and-its-unstable-may_dangle
 #[lang = "drop"]
 #[stable(feature = "rust1", since = "1.0.0")]
-// FIXME(effects) #[const_trait]
+// FIXME(const_trait_impl) #[const_trait]
 pub trait Drop {
     /// Executes the destructor for this type.
     ///

library/core/src/ops/function.rs

@@ -72,7 +72,7 @@ use crate::marker::Tuple;
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
 #[must_use = "closures are lazy and do nothing unless called"]
-// FIXME(effects) #[const_trait]
+// FIXME(const_trait_impl) #[const_trait]
 pub trait Fn<Args: Tuple>: FnMut<Args> {
     /// Performs the call operation.
     #[unstable(feature = "fn_traits", issue = "29625")]
@@ -159,7 +159,7 @@ pub trait Fn<Args: Tuple>: FnMut<Args> {
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
 #[must_use = "closures are lazy and do nothing unless called"]
-// FIXME(effects) #[const_trait]
+// FIXME(const_trait_impl) #[const_trait]
 pub trait FnMut<Args: Tuple>: FnOnce<Args> {
     /// Performs the call operation.
     #[unstable(feature = "fn_traits", issue = "29625")]
@@ -238,7 +238,7 @@ pub trait FnMut<Args: Tuple>: FnOnce<Args> {
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
 #[must_use = "closures are lazy and do nothing unless called"]
-// FIXME(effects) #[const_trait]
+// FIXME(const_trait_impl) #[const_trait]
 pub trait FnOnce<Args: Tuple> {
     /// The returned type after the call operator is used.
     #[lang = "fn_once_output"]

library/core/src/slice/sort/shared/smallsort.rs

@@ -102,7 +102,7 @@ impl<T: FreezeMarker> UnstableSmallSortTypeImpl for T {
     }
 }
 
-/// FIXME(effects) use original ipnsort approach with choose_unstable_small_sort,
+/// FIXME(const_trait_impl) use original ipnsort approach with choose_unstable_small_sort,
 /// as found here <https://github.com/Voultapher/sort-research-rs/blob/438fad5d0495f65d4b72aa87f0b62fc96611dff3/ipnsort/src/smallsort.rs#L83C10-L83C36>.
 pub(crate) trait UnstableSmallSortFreezeTypeImpl: Sized + FreezeMarker {
     fn small_sort_threshold() -> usize;

src/librustdoc/clean/mod.rs

@@ -369,7 +369,7 @@ pub(crate) fn clean_predicate<'tcx>(
         ty::ClauseKind::ConstEvaluatable(..)
         | ty::ClauseKind::WellFormed(..)
         | ty::ClauseKind::ConstArgHasType(..)
-        // FIXME(effects): We can probably use this `HostEffect` pred to render `~const`.
+        // FIXME(const_trait_impl): We can probably use this `HostEffect` pred to render `~const`.
         | ty::ClauseKind::HostEffect(_) => None,
     }
 }
@@ -379,7 +379,7 @@ fn clean_poly_trait_predicate<'tcx>(
     cx: &mut DocContext<'tcx>,
 ) -> Option<WherePredicate> {
     // `T: ~const Destruct` is hidden because `T: Destruct` is a no-op.
-    // FIXME(effects) check constness
+    // FIXME(const_trait_impl) check constness
     if Some(pred.skip_binder().def_id()) == cx.tcx.lang_items().destruct_trait() {
         return None;
     }

src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs

@@ -404,15 +404,15 @@ fn is_stable_const_fn(tcx: TyCtxt<'_>, def_id: DefId, msrv: &Msrv) -> bool {
 }
 
 fn is_ty_const_destruct<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, body: &Body<'tcx>) -> bool {
-    // FIXME(effects, fee1-dead) revert to const destruct once it works again
+    // FIXME(const_trait_impl, fee1-dead) revert to const destruct once it works again
     #[expect(unused)]
     fn is_ty_const_destruct_unused<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, body: &Body<'tcx>) -> bool {
         // Avoid selecting for simple cases, such as builtin types.
         if ty::util::is_trivially_const_drop(ty) {
             return true;
         }
 
-        // FIXME(effects) constness
+        // FIXME(const_trait_impl) constness
         let obligation = Obligation::new(
             tcx,
             ObligationCause::dummy_with_span(body.span),

src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const.fixed

@@ -104,7 +104,7 @@ fn main() {}
 
 struct D;
 
-/* FIXME(effects)
+/* FIXME(const_trait_impl)
 impl const Drop for D {
     fn drop(&mut self) {
         todo!();
@@ -113,7 +113,7 @@ impl const Drop for D {
 */
 
 // Lint this, since it can be dropped in const contexts
-// FIXME(effects)
+// FIXME(const_trait_impl)
 const fn d(this: D) {}
 //~^ ERROR: this could be a `const fn`
 

src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const.rs

@@ -104,7 +104,7 @@ fn main() {}
 
 struct D;
 
-/* FIXME(effects)
+/* FIXME(const_trait_impl)
 impl const Drop for D {
     fn drop(&mut self) {
         todo!();
@@ -113,7 +113,7 @@ impl const Drop for D {
 */
 
 // Lint this, since it can be dropped in const contexts
-// FIXME(effects)
+// FIXME(const_trait_impl)
 fn d(this: D) {}
 //~^ ERROR: this could be a `const fn`