Rollup merge of #133218 - compiler-errors:const-opaque, r=fee1-dead

Implement `~const` item bounds in RPIT

an RPIT in a `const fn` is allowed to be conditionally const itself :)

r? fee1-dead or reroll

compiler/rustc_hir_analysis/src/check/check.rs

@@ -339,6 +339,8 @@ 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.
     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

@@ -2083,7 +2083,7 @@ pub(super) fn check_type_bounds<'tcx>(
     // 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(
-            tcx.implied_const_bounds(trait_ty.def_id)
+            tcx.explicit_implied_const_bounds(trait_ty.def_id)
                 .iter_instantiated_copied(tcx, rebased_args)
                 .map(|(c, span)| {
                     traits::Obligation::new(

compiler/rustc_hir_analysis/src/collect.rs

@@ -78,7 +78,7 @@ pub fn provide(providers: &mut Providers) {
             predicates_of::explicit_supertraits_containing_assoc_item,
         trait_explicit_predicates_and_bounds: predicates_of::trait_explicit_predicates_and_bounds,
         const_conditions: predicates_of::const_conditions,
-        implied_const_bounds: predicates_of::implied_const_bounds,
+        explicit_implied_const_bounds: predicates_of::explicit_implied_const_bounds,
         type_param_predicates: predicates_of::type_param_predicates,
         trait_def,
         adt_def,
@@ -340,6 +340,10 @@ impl<'tcx> Visitor<'tcx> for CollectItemTypesVisitor<'tcx> {
         self.tcx.ensure().explicit_item_super_predicates(def_id);
         self.tcx.ensure().item_bounds(def_id);
         self.tcx.ensure().item_super_predicates(def_id);
+        if self.tcx.is_conditionally_const(def_id) {
+            self.tcx.ensure().explicit_implied_const_bounds(def_id);
+            self.tcx.ensure().const_conditions(def_id);
+        }
         intravisit::walk_opaque_ty(self, opaque);
     }
 
@@ -682,6 +686,10 @@ fn lower_item(tcx: TyCtxt<'_>, item_id: hir::ItemId) {
                 tcx.ensure().generics_of(item.owner_id);
                 tcx.ensure().type_of(item.owner_id);
                 tcx.ensure().predicates_of(item.owner_id);
+                if tcx.is_conditionally_const(def_id) {
+                    tcx.ensure().explicit_implied_const_bounds(def_id);
+                    tcx.ensure().const_conditions(def_id);
+                }
                 match item.kind {
                     hir::ForeignItemKind::Fn(..) => {
                         tcx.ensure().codegen_fn_attrs(item.owner_id);

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -959,6 +959,12 @@ pub(super) fn const_conditions<'tcx>(
             hir::ForeignItemKind::Fn(_, _, generics) => (generics, None, false),
             _ => bug!("const_conditions called on wrong item: {def_id:?}"),
         },
+        Node::OpaqueTy(opaque) => match opaque.origin {
+            hir::OpaqueTyOrigin::FnReturn { parent, .. } => return tcx.const_conditions(parent),
+            hir::OpaqueTyOrigin::AsyncFn { .. } | hir::OpaqueTyOrigin::TyAlias { .. } => {
+                unreachable!()
+            }
+        },
         // N.B. Tuple ctors are unconditionally constant.
         Node::Ctor(hir::VariantData::Tuple { .. }) => return Default::default(),
         _ => bug!("const_conditions called on wrong item: {def_id:?}"),
@@ -1018,7 +1024,7 @@ pub(super) fn const_conditions<'tcx>(
     }
 }
 
-pub(super) fn implied_const_bounds<'tcx>(
+pub(super) fn explicit_implied_const_bounds<'tcx>(
     tcx: TyCtxt<'tcx>,
     def_id: LocalDefId,
 ) -> ty::EarlyBinder<'tcx, &'tcx [(ty::PolyTraitRef<'tcx>, Span)]> {
@@ -1034,10 +1040,11 @@ pub(super) fn implied_const_bounds<'tcx>(
                 PredicateFilter::SelfConstIfConst,
             )
         }
-        Node::TraitItem(hir::TraitItem { kind: hir::TraitItemKind::Type(..), .. }) => {
+        Node::TraitItem(hir::TraitItem { kind: hir::TraitItemKind::Type(..), .. })
+        | Node::OpaqueTy(_) => {
             explicit_item_bounds_with_filter(tcx, def_id, PredicateFilter::ConstIfConst)
         }
-        _ => bug!("implied_const_bounds called on wrong item: {def_id:?}"),
+        _ => bug!("explicit_implied_const_bounds called on wrong item: {def_id:?}"),
     };
 
     bounds.map_bound(|bounds| {

compiler/rustc_infer/src/infer/opaque_types/mod.rs

@@ -574,9 +574,8 @@ impl<'tcx> InferCtxt<'tcx> {
         // unexpected region errors.
         goals.push(Goal::new(tcx, param_env, ty::ClauseKind::WellFormed(hidden_ty.into())));
 
-        let item_bounds = tcx.explicit_item_bounds(def_id);
+        let replace_opaques_in = |clause: ty::Clause<'tcx>, goals: &mut Vec<_>| {
-        for (predicate, _) in item_bounds.iter_instantiated_copied(tcx, args) {
+            clause.fold_with(&mut BottomUpFolder {
-            let predicate = predicate.fold_with(&mut BottomUpFolder {
                 tcx,
                 ty_op: |ty| match *ty.kind() {
                     // We can't normalize associated types from `rustc_infer`,
@@ -612,11 +611,31 @@ impl<'tcx> InferCtxt<'tcx> {
                 },
                 lt_op: |lt| lt,
                 ct_op: |ct| ct,
-            });
+            })
+        };
+
+        let item_bounds = tcx.explicit_item_bounds(def_id);
+        for (predicate, _) in item_bounds.iter_instantiated_copied(tcx, args) {
+            let predicate = replace_opaques_in(predicate, goals);
+
+            // Require that the predicate holds for the concrete type.
+            debug!(?predicate);
+            goals.push(Goal::new(self.tcx, param_env, predicate));
+        }
+
+        // If this opaque is being defined and it's conditionally const,
+        if self.tcx.is_conditionally_const(def_id) {
+            let item_bounds = tcx.explicit_implied_const_bounds(def_id);
+            for (predicate, _) in item_bounds.iter_instantiated_copied(tcx, args) {
+                let predicate = replace_opaques_in(
+                    predicate.to_host_effect_clause(self.tcx, ty::BoundConstness::Maybe),
+                    goals,
+                );
 
                 // Require that the predicate holds for the concrete type.
                 debug!(?predicate);
                 goals.push(Goal::new(self.tcx, param_env, predicate));
             }
         }
+    }
 }

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -275,7 +275,7 @@ provide! { tcx, def_id, other, cdata,
     defaultness => { table_direct }
     constness => { table_direct }
     const_conditions => { table }
-    implied_const_bounds => { table_defaulted_array }
+    explicit_implied_const_bounds => { table_defaulted_array }
     coerce_unsized_info => {
         Ok(cdata
             .root

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1463,8 +1463,8 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 record_array!(self.tables.module_children_non_reexports[def_id] <-
                     module_children.iter().map(|child| child.res.def_id().index));
                 if self.tcx.is_const_trait(def_id) {
-                    record_defaulted_array!(self.tables.implied_const_bounds[def_id]
+                    record_defaulted_array!(self.tables.explicit_implied_const_bounds[def_id]
-                        <- self.tcx.implied_const_bounds(def_id).skip_binder());
+                        <- self.tcx.explicit_implied_const_bounds(def_id).skip_binder());
                 }
             }
             if let DefKind::TraitAlias = def_kind {
@@ -1532,6 +1532,10 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 self.encode_explicit_item_super_predicates(def_id);
                 record!(self.tables.opaque_ty_origin[def_id] <- self.tcx.opaque_ty_origin(def_id));
                 self.encode_precise_capturing_args(def_id);
+                if tcx.is_conditionally_const(def_id) {
+                    record_defaulted_array!(self.tables.explicit_implied_const_bounds[def_id]
+                        <- tcx.explicit_implied_const_bounds(def_id).skip_binder());
+                }
             }
             if tcx.impl_method_has_trait_impl_trait_tys(def_id)
                 && let Ok(table) = self.tcx.collect_return_position_impl_trait_in_trait_tys(def_id)
@@ -1654,8 +1658,8 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                     self.encode_explicit_item_bounds(def_id);
                     self.encode_explicit_item_super_predicates(def_id);
                     if tcx.is_conditionally_const(def_id) {
-                        record_defaulted_array!(self.tables.implied_const_bounds[def_id]
+                        record_defaulted_array!(self.tables.explicit_implied_const_bounds[def_id]
-                            <- self.tcx.implied_const_bounds(def_id).skip_binder());
+                            <- self.tcx.explicit_implied_const_bounds(def_id).skip_binder());
                     }
                 }
             }

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -391,7 +391,7 @@ define_tables! {
     inferred_outlives_of: Table<DefIndex, LazyArray<(ty::Clause<'static>, Span)>>,
     explicit_super_predicates_of: Table<DefIndex, LazyArray<(ty::Clause<'static>, Span)>>,
     explicit_implied_predicates_of: Table<DefIndex, LazyArray<(ty::Clause<'static>, Span)>>,
-    implied_const_bounds: Table<DefIndex, LazyArray<(ty::PolyTraitRef<'static>, Span)>>,
+    explicit_implied_const_bounds: Table<DefIndex, LazyArray<(ty::PolyTraitRef<'static>, Span)>>,
     inherent_impls: Table<DefIndex, LazyArray<DefIndex>>,
     associated_types_for_impl_traits_in_associated_fn: Table<DefIndex, LazyArray<DefId>>,
     opt_rpitit_info: Table<DefIndex, Option<LazyValue<ty::ImplTraitInTraitData>>>,

compiler/rustc_middle/src/query/mod.rs

@@ -697,7 +697,7 @@ rustc_queries! {
         separate_provide_extern
     }
 
-    query implied_const_bounds(
+    query explicit_implied_const_bounds(
         key: DefId
     ) -> ty::EarlyBinder<'tcx, &'tcx [(ty::PolyTraitRef<'tcx>, Span)]> {
         desc { |tcx| "computing the implied `~const` bounds for `{}`",

compiler/rustc_middle/src/ty/context.rs

@@ -393,12 +393,12 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
         )
     }
 
-    fn implied_const_bounds(
+    fn explicit_implied_const_bounds(
         self,
         def_id: DefId,
     ) -> ty::EarlyBinder<'tcx, impl IntoIterator<Item = ty::Binder<'tcx, ty::TraitRef<'tcx>>>> {
         ty::EarlyBinder::bind(
-            self.implied_const_bounds(def_id).iter_identity_copied().map(|(c, _)| c),
+            self.explicit_implied_const_bounds(def_id).iter_identity_copied().map(|(c, _)| c),
         )
     }
 

compiler/rustc_middle/src/ty/mod.rs

@@ -2110,7 +2110,13 @@ impl<'tcx> TyCtxt<'tcx> {
                     _ => bug!("unexpected parent item of associated item: {parent_def_id:?}"),
                 }
             }
-            DefKind::Closure | DefKind::OpaqueTy => {
+            DefKind::OpaqueTy => match self.opaque_ty_origin(def_id) {
+                hir::OpaqueTyOrigin::FnReturn { parent, .. } => self.is_conditionally_const(parent),
+                hir::OpaqueTyOrigin::AsyncFn { .. } => false,
+                // FIXME(const_trait_impl): ATPITs could be conditionally const?
+                hir::OpaqueTyOrigin::TyAlias { .. } => false,
+            },
+            DefKind::Closure => {
                 // Closures and RPITs will eventually have const conditions
                 // for `~const` bounds.
                 false

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

@@ -102,7 +102,7 @@ where
 
     /// Assemble additional assumptions for an alias that are not included
     /// in the item bounds of the alias. For now, this is limited to the
-    /// `implied_const_bounds` for an associated type.
+    /// `explicit_implied_const_bounds` for an associated type.
     fn consider_additional_alias_assumptions(
         ecx: &mut EvalCtxt<'_, D>,
         goal: Goal<I, Self>,

compiler/rustc_next_trait_solver/src/solve/effect_goals.rs

@@ -84,12 +84,9 @@ where
         let cx = ecx.cx();
         let mut candidates = vec![];
 
-        // 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(
             cx,
-            cx.implied_const_bounds(alias_ty.def_id)
+            cx.explicit_implied_const_bounds(alias_ty.def_id)
                 .iter_instantiated(cx, alias_ty.args)
                 .map(|trait_ref| trait_ref.to_host_effect_clause(cx, goal.predicate.constness)),
         ) {

compiler/rustc_type_ir/src/elaborate.rs

@@ -157,7 +157,7 @@ impl<I: Interner, O: Elaboratable<I>> Elaborator<I, O> {
             }
             // `T: ~const Trait` implies `T: ~const Supertrait`.
             ty::ClauseKind::HostEffect(data) => self.extend_deduped(
-                cx.implied_const_bounds(data.def_id()).iter_identity().map(|trait_ref| {
+                cx.explicit_implied_const_bounds(data.def_id()).iter_identity().map(|trait_ref| {
                     elaboratable.child(
                         trait_ref
                             .to_host_effect_clause(cx, data.constness)

compiler/rustc_type_ir/src/interner.rs

@@ -229,7 +229,7 @@ pub trait Interner:
         self,
         def_id: Self::DefId,
     ) -> ty::EarlyBinder<Self, impl IntoIterator<Item = ty::Binder<Self, ty::TraitRef<Self>>>>;
-    fn implied_const_bounds(
+    fn explicit_implied_const_bounds(
         self,
         def_id: Self::DefId,
     ) -> ty::EarlyBinder<Self, impl IntoIterator<Item = ty::Binder<Self, ty::TraitRef<Self>>>>;

tests/ui/traits/const-traits/const-closure-parse-not-item.stderr

@@ -12,5 +12,13 @@ LL | const fn test() -> impl ~const Fn() {
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error: aborting due to 2 previous errors
+error: `~const` can only be applied to `#[const_trait]` traits
+  --> $DIR/const-closure-parse-not-item.rs:7:25
+   |
+LL | const fn test() -> impl ~const Fn() {
+   |                         ^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error: aborting due to 3 previous errors
 

tests/ui/traits/const-traits/const-opaque.no.stderr

@@ -0,0 +1,15 @@
+error[E0277]: the trait bound `(): const Foo` is not satisfied
+  --> $DIR/const-opaque.rs:31:18
+   |
+LL |     let opaque = bar(());
+   |                  ^^^^^^^
+
+error[E0277]: the trait bound `(): const Foo` is not satisfied
+  --> $DIR/const-opaque.rs:33:5
+   |
+LL |     opaque.method();
+   |     ^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/traits/const-traits/const-opaque.rs

@@ -0,0 +1,38 @@
+//@ revisions: yes no
+//@ compile-flags: -Znext-solver
+//@[yes] check-pass
+
+#![feature(const_trait_impl)]
+
+#[const_trait]
+trait Foo {
+    fn method(&self);
+}
+
+impl<T: ~const Foo> const Foo for (T,) {
+    fn method(&self) {}
+}
+
+#[cfg(yes)]
+impl const Foo for () {
+    fn method(&self) {}
+}
+
+#[cfg(no)]
+impl Foo for () {
+    fn method(&self) {}
+}
+
+const fn bar<T: ~const Foo>(t: T) -> impl ~const Foo {
+    (t,)
+}
+
+const _: () = {
+    let opaque = bar(());
+    //[no]~^ ERROR the trait bound `(): const Foo` is not satisfied
+    opaque.method();
+    //[no]~^ ERROR the trait bound `(): const Foo` is not satisfied
+    std::mem::forget(opaque);
+};
+
+fn main() {}

tests/ui/traits/const-traits/effects/ice-112822-expected-type-for-param.rs

@@ -3,6 +3,7 @@
 const fn test() -> impl ~const Fn() {
     //~^ ERROR `~const` can only be applied to `#[const_trait]` traits
     //~| ERROR `~const` can only be applied to `#[const_trait]` traits
+    //~| ERROR `~const` can only be applied to `#[const_trait]` traits
     const move || { //~ ERROR const closures are experimental
         let sl: &[u8] = b"foo";
 

tests/ui/traits/const-traits/effects/ice-112822-expected-type-for-param.stderr

@@ -1,5 +1,5 @@
 error[E0658]: const closures are experimental
-  --> $DIR/ice-112822-expected-type-for-param.rs:6:5
+  --> $DIR/ice-112822-expected-type-for-param.rs:7:5
    |
 LL |     const move || {
    |     ^^^^^
@@ -22,8 +22,16 @@ LL | const fn test() -> impl ~const Fn() {
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
+error: `~const` can only be applied to `#[const_trait]` traits
+  --> $DIR/ice-112822-expected-type-for-param.rs:3:25
+   |
+LL | const fn test() -> impl ~const Fn() {
+   |                         ^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
 error[E0015]: cannot call non-const operator in constant functions
-  --> $DIR/ice-112822-expected-type-for-param.rs:11:17
+  --> $DIR/ice-112822-expected-type-for-param.rs:12:17
    |
 LL |                 assert_eq!(first, &b'f');
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^
@@ -32,7 +40,7 @@ LL |                 assert_eq!(first, &b'f');
    = note: this error originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0015]: cannot call non-const fn `core::panicking::assert_failed::<&u8, &u8>` in constant functions
-  --> $DIR/ice-112822-expected-type-for-param.rs:11:17
+  --> $DIR/ice-112822-expected-type-for-param.rs:12:17
    |
 LL |                 assert_eq!(first, &b'f');
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^
@@ -40,7 +48,7 @@ LL |                 assert_eq!(first, &b'f');
    = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
    = note: this error originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 5 previous errors
+error: aborting due to 6 previous errors
 
 Some errors have detailed explanations: E0015, E0658.
 For more information about an error, try `rustc --explain E0015`.