Add const effect syntax to the parser for all function headers

Author: oli-obk

compiler/rustc_ast/src/ast.rs

@@ -323,7 +323,7 @@ impl ParenthesizedArgs {
 
 pub use crate::node_id::{CRATE_NODE_ID, DUMMY_NODE_ID, NodeId};
 
-/// Modifiers on a trait bound like `~const`, `?` and `!`.
+/// Modifiers on a trait bound like `[const]`, `?` and `!`.
 #[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug)]
 pub struct TraitBoundModifiers {
     pub constness: BoundConstness,
@@ -3111,7 +3111,7 @@ pub enum BoundConstness {
     Never,
     /// `Type: const Trait`
     Always(Span),
-    /// `Type: ~const Trait`
+    /// `Type: [const] Trait`
     Maybe(Span),
 }
 
@@ -3120,7 +3120,7 @@ impl BoundConstness {
         match self {
             Self::Never => "",
             Self::Always(_) => "const",
-            Self::Maybe(_) => "~const",
+            Self::Maybe(_) => "[const]",
         }
     }
 }

compiler/rustc_ast_passes/messages.ftl

@@ -64,6 +64,8 @@ ast_passes_const_and_coroutine = functions cannot be both `const` and `{$corouti
 
 ast_passes_const_bound_trait_object = const trait bounds are not allowed in trait object types
 
+ast_passes_const_in_trait = `const fn` in traits is unstable
+
 ast_passes_const_without_body =
     free constant item without body
     .suggestion = provide a definition for the constant
@@ -232,17 +234,17 @@ ast_passes_static_without_body =
     free static item without body
     .suggestion = provide a definition for the static
 
-ast_passes_tilde_const_disallowed = `~const` is not allowed here
-    .closure = closures cannot have `~const` trait bounds
-    .function = this function is not `const`, so it cannot have `~const` trait bounds
-    .trait = this trait is not a `#[const_trait]`, so it cannot have `~const` trait bounds
-    .trait_impl = this impl is not `const`, so it cannot have `~const` trait bounds
-    .impl = inherent impls cannot have `~const` trait bounds
-    .trait_assoc_ty = associated types in non-`#[const_trait]` traits cannot have `~const` trait bounds
-    .trait_impl_assoc_ty = associated types in non-const impls cannot have `~const` trait bounds
-    .inherent_assoc_ty = inherent associated types cannot have `~const` trait bounds
-    .object = trait objects cannot have `~const` trait bounds
-    .item = this item cannot have `~const` trait bounds
+ast_passes_tilde_const_disallowed = `[const]` is not allowed here
+    .closure = closures cannot have `[const]` trait bounds
+    .function = this function is not `const`, so it cannot have `[const]` trait bounds
+    .trait = this trait is not a `#[const_trait]`, so it cannot have `[const]` trait bounds
+    .trait_impl = this impl is not `const`, so it cannot have `[const]` trait bounds
+    .impl = inherent impls cannot have `[const]` trait bounds
+    .trait_assoc_ty = associated types in non-`#[const_trait]` traits cannot have `[const]` trait bounds
+    .trait_impl_assoc_ty = associated types in non-const impls cannot have `[const]` trait bounds
+    .inherent_assoc_ty = inherent associated types cannot have `[const]` trait bounds
+    .object = trait objects cannot have `[const]` trait bounds
+    .item = this item cannot have `[const]` trait bounds
 
 ast_passes_trait_fn_const =
     functions in {$in_impl ->

compiler/rustc_const_eval/src/check_consts/check.rs

@@ -421,7 +421,7 @@ impl<'mir, 'tcx> Checker<'mir, 'tcx> {
             Some(ConstConditionsHold::Yes)
         } else {
             tcx.dcx()
-                .span_delayed_bug(call_span, "this should have reported a ~const error in HIR");
+                .span_delayed_bug(call_span, "this should have reported a [const] error in HIR");
             Some(ConstConditionsHold::No)
         }
     }

compiler/rustc_const_eval/src/check_consts/ops.rs

@@ -149,7 +149,7 @@ impl<'tcx> NonConstOp<'tcx> for FnCallNonConst<'tcx> {
                         debug!(?param_ty);
                         if let Some(generics) = tcx.hir_node_by_def_id(caller).generics() {
                             let constraint = with_no_trimmed_paths!(format!(
-                                "~const {}",
+                                "[const] {}",
                                 trait_ref.print_trait_sugared(),
                             ));
                             suggest_constraining_type_param(

compiler/rustc_const_eval/src/check_consts/qualifs.rs

@@ -170,14 +170,14 @@ impl Qualif for NeedsNonConstDrop {
 
     #[instrument(level = "trace", skip(cx), ret)]
     fn in_any_value_of_ty<'tcx>(cx: &ConstCx<'_, 'tcx>, ty: Ty<'tcx>) -> bool {
-        // If this doesn't need drop at all, then don't select `~const Destruct`.
+        // If this doesn't need drop at all, then don't select `[const] Destruct`.
         if !ty.needs_drop(cx.tcx, cx.typing_env) {
             return false;
         }
 
-        // We check that the type is `~const Destruct` since that will verify that
-        // the type is both `~const Drop` (if a drop impl exists for the adt), *and*
-        // that the components of this type are also `~const Destruct`. This
+        // We check that the type is `[const] Destruct` since that will verify that
+        // the type is both `[const] Drop` (if a drop impl exists for the adt), *and*
+        // that the components of this type are also `[const] Destruct`. This
         // amounts to verifying that there are no values in this ADT that may have
         // a non-const drop.
         let destruct_def_id = cx.tcx.require_lang_item(LangItem::Destruct, cx.body.span);
@@ -203,9 +203,9 @@ impl Qualif for NeedsNonConstDrop {
     fn is_structural_in_adt_value<'tcx>(cx: &ConstCx<'_, 'tcx>, adt: AdtDef<'tcx>) -> bool {
         // As soon as an ADT has a destructor, then the drop becomes non-structural
         // in its value since:
-        // 1. The destructor may have `~const` bounds which are not present on the type.
+        // 1. The destructor may have `[const]` bounds which are not present on the type.
         //   Someone needs to check that those are satisfied.
-        //   While this could be instead satisfied by checking that the `~const Drop`
+        //   While this could be instead satisfied by checking that the `[const] Drop`
         //   impl holds (i.e. replicating part of the `in_any_value_of_ty` logic above),
         //   even in this case, we have another problem, which is,
         // 2. The destructor may *modify* the operand being dropped, so even if we

compiler/rustc_feature/src/removed.rs

@@ -86,7 +86,7 @@ declare_features! (
      Some("at compile-time, pointers do not have an integer value, so these casts cannot be properly supported"), 87020),
     /// Allows `T: ?const Trait` syntax in bounds.
     (removed, const_trait_bound_opt_out, "1.56.0", Some(67794),
-     Some("Removed in favor of `~const` bound in #![feature(const_trait_impl)]"), 88328),
+     Some("Removed in favor of `[const]` bound in #![feature(const_trait_impl)]"), 88328),
     /// Allows using `crate` as visibility modifier, synonymous with `pub(crate)`.
     (removed, crate_visibility_modifier, "1.63.0", Some(53120), Some("removed in favor of `pub(crate)`"), 97254),
     /// Allows using custom attributes (RFC 572).
@@ -122,7 +122,7 @@ declare_features! (
     /// [^1]: Formerly known as "object safe".
     (removed, dyn_compatible_for_dispatch, "1.87.0", Some(43561),
      Some("removed, not used heavily and represented additional complexity in dyn compatibility"), 136522),
-    /// Uses generic effect parameters for ~const bounds
+    /// Uses generic effect parameters for [const] bounds
     (removed, effects, "1.84.0", Some(102090),
      Some("removed, redundant with `#![feature(const_trait_impl)]`"), 132479),
     /// Allows defining `existential type`s.

compiler/rustc_feature/src/unstable.rs

@@ -437,7 +437,7 @@ declare_features! (
     (unstable, const_async_blocks, "1.53.0", Some(85368)),
     /// Allows `const || {}` closures in const contexts.
     (incomplete, const_closures, "1.68.0", Some(106003)),
-    /// Allows using `~const Destruct` bounds and calling drop impls in const contexts.
+    /// Allows using `[const] Destruct` bounds and calling drop impls in const contexts.
     (unstable, const_destruct, "1.85.0", Some(133214)),
     /// Allows `for _ in _` loops in const contexts.
     (unstable, const_for, "1.56.0", Some(87575)),

compiler/rustc_hir_analysis/src/check/check.rs

@@ -344,7 +344,7 @@ fn check_opaque_meets_bounds<'tcx>(
     let misc_cause = ObligationCause::misc(span, def_id);
     // FIXME: We should just register the item bounds here, rather than equating.
     // FIXME(const_trait_impl): When we do that, please make sure to also register
-    // the `~const` bounds.
+    // the `[const]` bounds.
     match ocx.eq(&misc_cause, param_env, opaque_ty, hidden_ty) {
         Ok(()) => {}
         Err(ty_err) => {

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -264,9 +264,9 @@ fn compare_method_predicate_entailment<'tcx>(
     }
 
     // If we're within a const implementation, we need to make sure that the method
-    // does not assume stronger `~const` bounds than the trait definition.
+    // does not assume stronger `[const]` bounds than the trait definition.
     //
-    // This registers the `~const` bounds of the impl method, which we will prove
+    // This registers the `[const]` bounds of the impl method, which we will prove
     // using the hybrid param-env that we earlier augmented with the const conditions
     // from the impl header and trait method declaration.
     if is_conditionally_const {
@@ -2335,7 +2335,7 @@ pub(super) fn check_type_bounds<'tcx>(
     )
     .collect();
 
-    // Only in a const implementation do we need to check that the `~const` item bounds hold.
+    // Only in a const implementation do we need to check that the `[const]` item bounds hold.
     if tcx.is_conditionally_const(impl_ty_def_id) {
         obligations.extend(util::elaborate(
             tcx,

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -1399,7 +1399,7 @@ fn check_impl<'tcx>(
                     }
                 }
 
-                // Ensure that the `~const` where clauses of the trait hold for the impl.
+                // Ensure that the `[const]` where clauses of the trait hold for the impl.
                 if tcx.is_conditionally_const(item.owner_id.def_id) {
                     for (bound, _) in
                         tcx.const_conditions(trait_ref.def_id).instantiate(tcx, trait_ref.args)

compiler/rustc_hir_analysis/src/collect/item_bounds.rs

@@ -54,7 +54,7 @@ fn associated_type_bounds<'tcx>(
                 );
                 icx.lowerer().add_default_traits(&mut bounds, item_ty, hir_bounds, None, span);
             }
-            // `ConstIfConst` is only interested in `~const` bounds.
+            // `ConstIfConst` is only interested in `[const]` bounds.
             PredicateFilter::ConstIfConst | PredicateFilter::SelfConstIfConst => {}
         }
 
@@ -351,7 +351,7 @@ fn opaque_type_bounds<'tcx>(
                 );
                 icx.lowerer().add_default_traits(&mut bounds, item_ty, hir_bounds, None, span);
             }
-            //`ConstIfConst` is only interested in `~const` bounds.
+            //`ConstIfConst` is only interested in `[const]` bounds.
             PredicateFilter::ConstIfConst | PredicateFilter::SelfConstIfConst => {}
         }
         debug!(?bounds);

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -666,7 +666,7 @@ pub(super) fn implied_predicates_with_filter<'tcx>(
                 item.span,
             );
         }
-        //`ConstIfConst` is only interested in `~const` bounds.
+        //`ConstIfConst` is only interested in `[const]` bounds.
         PredicateFilter::ConstIfConst | PredicateFilter::SelfConstIfConst => {}
     }
 
@@ -821,7 +821,7 @@ pub(super) fn assert_only_contains_predicates_from<'tcx>(
                         assert_eq!(
                             pred.constness,
                             ty::BoundConstness::Maybe,
-                            "expected `~const` predicate when computing `{filter:?}` \
+                            "expected `[const]` predicate when computing `{filter:?}` \
                             implied bounds: {clause:?}",
                         );
                         assert_eq!(
@@ -1009,7 +1009,7 @@ pub(super) fn const_conditions<'tcx>(
             }
             _ => bug!("const_conditions called on wrong item: {def_id:?}"),
         },
-        // While associated types are not really const, we do allow them to have `~const`
+        // While associated types are not really const, we do allow them to have `[const]`
         // bounds and where clauses. `const_conditions` is responsible for gathering
         // these up so we can check them in `compare_type_predicate_entailment`, and
         // in `HostEffect` goal computation.

compiler/rustc_hir_analysis/src/errors/wrong_number_of_generic_args.rs

@@ -635,7 +635,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
                 self.suggest_adding_type_and_const_args(err);
             }
             ExcessTypesOrConsts { .. } => {
-                // this can happen with `~const T` where T isn't a const_trait.
+                // this can happen with `[const] T` where T isn't a const_trait.
             }
             _ => unreachable!(),
         }

compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs

@@ -492,7 +492,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     );
                 }
                 hir::GenericBound::Outlives(lifetime) => {
-                    // `ConstIfConst` is only interested in `~const` bounds.
+                    // `ConstIfConst` is only interested in `[const]` bounds.
                     if matches!(
                         predicate_filter,
                         PredicateFilter::ConstIfConst | PredicateFilter::SelfConstIfConst
@@ -708,7 +708,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     }
                     // SelfTraitThatDefines is only interested in trait predicates.
                     PredicateFilter::SelfTraitThatDefines(_) => {}
-                    // `ConstIfConst` is only interested in `~const` bounds.
+                    // `ConstIfConst` is only interested in `[const]` bounds.
                     PredicateFilter::ConstIfConst | PredicateFilter::SelfConstIfConst => {}
                 }
             }

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -80,10 +80,10 @@ pub enum PredicateFilter {
     /// and `<Self as Tr>::A: B`.
     SelfAndAssociatedTypeBounds,
 
-    /// Filter only the `~const` bounds, which are lowered into `HostEffect` clauses.
+    /// Filter only the `[const]` bounds, which are lowered into `HostEffect` clauses.
     ConstIfConst,
 
-    /// Filter only the `~const` bounds which are *also* in the supertrait position.
+    /// Filter only the `[const]` bounds which are *also* in the supertrait position.
     SelfConstIfConst,
 }
 
@@ -885,7 +885,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     }
                 }
                 // On the flip side, when filtering `ConstIfConst` bounds, we only need to convert
-                // `~const` bounds. All other predicates are handled in their respective queries.
+                // `[const]` bounds. All other predicates are handled in their respective queries.
                 //
                 // Note that like `PredicateFilter::SelfOnly`, we don't need to do any filtering
                 // here because we only call this on self bounds, and deal with the recursive case

compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs

@@ -402,22 +402,22 @@ fn check_predicates<'tcx>(
 /// as some predicate on the base impl (`predicate2`).
 ///
 /// This basically just checks syntactic equivalence, but is a little more
-/// forgiving since we want to equate `T: Tr` with `T: ~const Tr` so this can work:
+/// forgiving since we want to equate `T: Tr` with `T: [const] Tr` so this can work:
 ///
 /// ```ignore (illustrative)
 /// #[rustc_specialization_trait]
 /// trait Specialize { }
 ///
 /// impl<T: Bound> Tr for T { }
-/// impl<T: ~const Bound + Specialize> const Tr for T { }
+/// impl<T: [const] Bound + Specialize> const Tr for T { }
 /// ```
 ///
 /// However, we *don't* want to allow the reverse, i.e., when the bound on the
 /// specializing impl is not as const as the bound on the base impl:
 ///
 /// ```ignore (illustrative)
-/// impl<T: ~const Bound> const Tr for T { }
-/// impl<T: Bound + Specialize> const Tr for T { } // should be T: ~const Bound
+/// impl<T: [const] Bound> const Tr for T { }
+/// impl<T: Bound + Specialize> const Tr for T { } // should be T: [const] Bound
 /// ```
 ///
 /// So we make that check in this function and try to raise a helpful error message.

compiler/rustc_hir_pretty/src/lib.rs

@@ -784,7 +784,7 @@ impl<'a> State<'a> {
         match constness {
             hir::BoundConstness::Never => {}
             hir::BoundConstness::Always(_) => self.word("const"),
-            hir::BoundConstness::Maybe(_) => self.word("~const"),
+            hir::BoundConstness::Maybe(_) => self.word("[const]"),
         }
         match polarity {
             hir::BoundPolarity::Positive => {}

compiler/rustc_hir_typeck/src/callee.rs

@@ -903,7 +903,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             return;
         }
 
-        // If we have `rustc_do_not_const_check`, do not check `~const` bounds.
+        // If we have `rustc_do_not_const_check`, do not check `[const]` bounds.
         if self.tcx.has_attr(self.body_id, sym::rustc_do_not_const_check) {
             return;
         }

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -281,7 +281,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     );
                 }
                 Adjust::Deref(None) => {
-                    // FIXME(const_trait_impl): We *could* enforce `&T: ~const Deref` here.
+                    // FIXME(const_trait_impl): We *could* enforce `&T: [const] Deref` here.
                 }
                 Adjust::Pointer(_pointer_coercion) => {
                     // FIXME(const_trait_impl): We should probably enforce these.

compiler/rustc_middle/src/middle/stability.rs

@@ -620,7 +620,7 @@ impl<'tcx> TyCtxt<'tcx> {
     /// instead of regular stability.
     ///
     /// This enforces *syntactical* const stability of const traits. In other words,
-    /// it enforces the ability to name `~const`/`const` traits in trait bounds in various
+    /// it enforces the ability to name `[const]`/`const` traits in trait bounds in various
     /// syntax positions in HIR (including in the trait of an impl header).
     pub fn check_const_stability(self, def_id: DefId, span: Span, const_kw_span: Span) {
         let is_staged_api = self.lookup_stability(def_id.krate.as_def_id()).is_some();

compiler/rustc_middle/src/query/mod.rs

@@ -850,14 +850,14 @@ rustc_queries! {
     }
 
     /// Compute the conditions that need to hold for a conditionally-const item to be const.
-    /// That is, compute the set of `~const` where clauses for a given item.
+    /// That is, compute the set of `[const]` where clauses for a given item.
     ///
-    /// This can be thought of as the `~const` equivalent of `predicates_of`. These are the
+    /// This can be thought of as the `[const]` equivalent of `predicates_of`. These are the
     /// predicates that need to be proven at usage sites, and can be assumed at definition.
     ///
-    /// This query also computes the `~const` where clauses for associated types, which are
-    /// not "const", but which have item bounds which may be `~const`. These must hold for
-    /// the `~const` item bound to hold.
+    /// This query also computes the `[const]` where clauses for associated types, which are
+    /// not "const", but which have item bounds which may be `[const]`. These must hold for
+    /// the `[const]` item bound to hold.
     query const_conditions(
         key: DefId
     ) -> ty::ConstConditions<'tcx> {
@@ -869,13 +869,13 @@ rustc_queries! {
 
     /// Compute the const bounds that are implied for a conditionally-const item.
     ///
-    /// This can be though of as the `~const` equivalent of `explicit_item_bounds`. These
+    /// This can be though of as the `[const]` equivalent of `explicit_item_bounds`. These
     /// are the predicates that need to proven at definition sites, and can be assumed at
     /// usage sites.
     query explicit_implied_const_bounds(
         key: DefId
     ) -> ty::EarlyBinder<'tcx, &'tcx [(ty::PolyTraitRef<'tcx>, Span)]> {
-        desc { |tcx| "computing the implied `~const` bounds for `{}`",
+        desc { |tcx| "computing the implied `[const]` bounds for `{}`",
             tcx.def_path_str(key)
         }
         separate_provide_extern

compiler/rustc_middle/src/ty/generics.rs

@@ -419,7 +419,7 @@ impl<'tcx> GenericPredicates<'tcx> {
     }
 }
 
-/// `~const` bounds for a given item. This is represented using a struct much like
+/// `[const]` bounds for a given item. This is represented using a struct much like
 /// `GenericPredicates`, where you can either choose to only instantiate the "own"
 /// bounds or all of the bounds including those from the parent. This distinction
 /// is necessary for code like `compare_method_predicate_entailment`.