hir_analysis: add missing sizedness bounds

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -660,6 +660,14 @@ pub(super) fn implied_predicates_with_filter<'tcx>(
         | PredicateFilter::SelfOnly
         | PredicateFilter::SelfTraitThatDefines(_)
         | PredicateFilter::SelfAndAssociatedTypeBounds => {
+            icx.lowerer().add_sizedness_bounds(
+                &mut bounds,
+                self_param_ty,
+                superbounds,
+                None,
+                Some(trait_def_id),
+                item.span,
+            );
             icx.lowerer().add_default_super_traits(
                 trait_def_id,
                 &mut bounds,

compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs

@@ -64,8 +64,13 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
         self.add_default_traits(&mut user_written_bounds, dummy_self, &ast_bounds, None, span);
 
-        let (elaborated_trait_bounds, elaborated_projection_bounds) =
+        let (mut elaborated_trait_bounds, elaborated_projection_bounds) =
             traits::expand_trait_aliases(tcx, user_written_bounds.iter().copied());
+
+        // FIXME(sized-hierarchy): https://github.com/rust-lang/rust/pull/142712#issuecomment-3013231794
+        let meta_sized_did = tcx.require_lang_item(LangItem::MetaSized, span);
+        elaborated_trait_bounds.retain(|(pred, _)| pred.def_id() != meta_sized_did);
+
         let (regular_traits, mut auto_traits): (Vec<_>, Vec<_>) = elaborated_trait_bounds
             .into_iter()
             .partition(|(trait_ref, _)| !tcx.trait_is_auto(trait_ref.def_id()));

compiler/rustc_middle/src/ty/context.rs

@@ -493,6 +493,10 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
         self.is_default_trait(def_id)
     }
 
+    fn is_sizedness_trait(self, def_id: DefId) -> bool {
+        self.is_sizedness_trait(def_id)
+    }
+
     fn as_lang_item(self, def_id: DefId) -> Option<TraitSolverLangItem> {
         lang_item_to_trait_lang_item(self.lang_items().from_def_id(def_id)?)
     }
@@ -1645,6 +1649,10 @@ impl<'tcx> TyCtxt<'tcx> {
             .any(|&default_trait| self.lang_items().get(default_trait) == Some(def_id))
     }
 
+    pub fn is_sizedness_trait(self, def_id: DefId) -> bool {
+        matches!(self.as_lang_item(def_id), Some(LangItem::Sized | LangItem::MetaSized))
+    }
+
     /// Returns a range of the start/end indices specified with the
     /// `rustc_layout_scalar_valid_range` attribute.
     // FIXME(eddyb) this is an awkward spot for this method, maybe move it?

compiler/rustc_next_trait_solver/src/solve/trait_goals.rs

@@ -1343,6 +1343,7 @@ where
     #[instrument(level = "debug", skip(self), ret)]
     pub(super) fn merge_trait_candidates(
         &mut self,
+        prefer_alias_over_param_candidates: bool,
         mut candidates: Vec<Candidate<I>>,
     ) -> Result<(CanonicalResponse<I>, Option<TraitGoalProvenVia>), NoSolution> {
         if let TypingMode::Coherence = self.typing_mode() {
@@ -1368,6 +1369,26 @@ where
             return Ok((candidate.result, Some(TraitGoalProvenVia::Misc)));
         }
 
+        let potential_alias_bound_response =
+            candidates.iter().any(|c| matches!(c.source, CandidateSource::AliasBound)).then(|| {
+                let alias_bounds: Vec<_> = candidates
+                    .iter()
+                    .filter(|c| matches!(c.source, CandidateSource::AliasBound))
+                    .map(|c| c.result)
+                    .collect();
+                if let Some(response) = self.try_merge_responses(&alias_bounds) {
+                    (response, Some(TraitGoalProvenVia::AliasBound))
+                } else {
+                    (self.bail_with_ambiguity(&alias_bounds), None)
+                }
+            });
+
+        if prefer_alias_over_param_candidates
+            && let Some(alias_bound_response) = potential_alias_bound_response
+        {
+            return Ok(alias_bound_response);
+        }
+
         // If there are non-global where-bounds, prefer where-bounds
         // (including global ones) over everything else.
         let has_non_global_where_bounds = candidates
@@ -1386,17 +1407,8 @@ where
             };
         }
 
-        if candidates.iter().any(|c| matches!(c.source, CandidateSource::AliasBound)) {
-            let alias_bounds: Vec<_> = candidates
-                .iter()
-                .filter(|c| matches!(c.source, CandidateSource::AliasBound))
-                .map(|c| c.result)
-                .collect();
-            return if let Some(response) = self.try_merge_responses(&alias_bounds) {
-                Ok((response, Some(TraitGoalProvenVia::AliasBound)))
-            } else {
-                Ok((self.bail_with_ambiguity(&alias_bounds), None))
-            };
+        if let Some(response) = potential_alias_bound_response {
+            return Ok(response);
         }
 
         self.filter_specialized_impls(AllowInferenceConstraints::No, &mut candidates);
@@ -1431,7 +1443,12 @@ where
         goal: Goal<I, TraitPredicate<I>>,
     ) -> Result<(CanonicalResponse<I>, Option<TraitGoalProvenVia>), NoSolution> {
         let candidates = self.assemble_and_evaluate_candidates(goal, AssembleCandidatesFrom::All);
-        self.merge_trait_candidates(candidates)
+
+        let did = goal.predicate.def_id();
+        let is_sizedness_or_auto_or_default_goal = self.cx().is_sizedness_trait(did)
+            || self.cx().trait_is_auto(did)
+            || self.cx().is_default_trait(did);
+        self.merge_trait_candidates(is_sizedness_or_auto_or_default_goal, candidates)
     }
 
     fn try_stall_coroutine_witness(

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

@@ -146,8 +146,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         obligation: &PolyTraitObligation<'tcx>,
         idx: usize,
     ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> {
-        let tcx = self.tcx();
-
         let placeholder_trait_predicate =
             self.infcx.enter_forall_and_leak_universe(obligation.predicate).trait_ref;
         let placeholder_self_ty = self.infcx.shallow_resolve(placeholder_trait_predicate.self_ty());
@@ -196,28 +194,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 .map_err(|_| SelectionError::Unimplemented)?,
         );
 
-        // FIXME(compiler-errors): I don't think this is needed.
-        if let ty::Alias(ty::Projection, alias_ty) = placeholder_self_ty.kind() {
-            let predicates = tcx.predicates_of(alias_ty.def_id).instantiate_own(tcx, alias_ty.args);
-            for (predicate, _) in predicates {
-                let normalized = normalize_with_depth_to(
-                    self,
-                    obligation.param_env,
-                    obligation.cause.clone(),
-                    obligation.recursion_depth + 1,
-                    predicate,
-                    &mut obligations,
-                );
-                obligations.push(Obligation::with_depth(
-                    self.tcx(),
-                    obligation.cause.clone(),
-                    obligation.recursion_depth + 1,
-                    obligation.param_env,
-                    normalized,
-                ));
-            }
-        }
-
         Ok(obligations)
     }
 

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

@@ -485,7 +485,15 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             }
         } else {
             let has_non_region_infer = stack.obligation.predicate.has_non_region_infer();
-            if let Some(candidate) = self.winnow_candidates(has_non_region_infer, candidates) {
+            let did = stack.obligation.predicate.def_id();
+            let is_sizedness_or_auto_or_default_predicate = self.tcx().is_sizedness_trait(did)
+                || self.tcx().trait_is_auto(did)
+                || self.tcx().is_default_trait(did);
+            if let Some(candidate) = self.winnow_candidates(
+                has_non_region_infer,
+                is_sizedness_or_auto_or_default_predicate,
+                candidates,
+            ) {
                 self.filter_reservation_impls(candidate)
             } else {
                 Ok(None)
@@ -1826,6 +1834,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
     fn winnow_candidates(
         &mut self,
         has_non_region_infer: bool,
+        prefer_alias_over_param_candidates: bool,
         mut candidates: Vec<EvaluatedCandidate<'tcx>>,
     ) -> Option<SelectionCandidate<'tcx>> {
         if candidates.len() == 1 {
@@ -1879,6 +1888,19 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
             break;
         }
 
+        let alias_bound = candidates
+            .iter()
+            .filter_map(|c| if let ProjectionCandidate(i) = c.candidate { Some(i) } else { None })
+            .try_reduce(|c1, c2| if has_non_region_infer { None } else { Some(c1.min(c2)) });
+
+        if prefer_alias_over_param_candidates {
+            match alias_bound {
+                Some(Some(index)) => return Some(ProjectionCandidate(index)),
+                Some(None) => {}
+                None => return None,
+            }
+        }
+
         // The next highest priority is for non-global where-bounds. However, while we don't
         // prefer global where-clauses here, we do bail with ambiguity when encountering both
         // a global and a non-global where-clause.
@@ -1912,10 +1934,6 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
         // fairly arbitrary but once again necessary for backwards compatibility.
         // If there are multiple applicable candidates which don't affect type inference,
         // choose the one with the lowest index.
-        let alias_bound = candidates
-            .iter()
-            .filter_map(|c| if let ProjectionCandidate(i) = c.candidate { Some(i) } else { None })
-            .try_reduce(|c1, c2| if has_non_region_infer { None } else { Some(c1.min(c2)) });
         match alias_bound {
             Some(Some(index)) => return Some(ProjectionCandidate(index)),
             Some(None) => {}

compiler/rustc_type_ir/src/interner.rs

@@ -300,6 +300,8 @@ pub trait Interner:
 
     fn is_default_trait(self, def_id: Self::DefId) -> bool;
 
+    fn is_sizedness_trait(self, def_id: Self::DefId) -> bool;
+
     fn as_lang_item(self, def_id: Self::DefId) -> Option<TraitSolverLangItem>;
 
     fn associated_type_def_ids(self, def_id: Self::DefId) -> impl IntoIterator<Item = Self::DefId>;

tests/ui/dyn-compatibility/assoc_type_bounds_sized_used.rs

@@ -9,7 +9,8 @@ trait Bop {
 
 fn bop<T: Bop + ?Sized>() {
     let _ = <T as Bop>::Bar::default();
-    //~^ ERROR: trait bounds were not satisfied
+    //~^ ERROR: the size for values of type `T` cannot be known at compilation time
+    //~| ERROR: the size for values of type `T` cannot be known at compilation time
     //~| ERROR: the size for values of type `T` cannot be known at compilation time
 }
 

tests/ui/dyn-compatibility/assoc_type_bounds_sized_used.stderr

@@ -24,21 +24,58 @@ help: consider relaxing the implicit `Sized` restriction
 LL |     type Bar: Default + ?Sized
    |                       ++++++++
 
-error[E0599]: the function or associated item `default` exists for associated type `<T as Bop>::Bar`, but its trait bounds were not satisfied
-  --> $DIR/assoc_type_bounds_sized_used.rs:11:30
+error[E0277]: the size for values of type `T` cannot be known at compilation time
+  --> $DIR/assoc_type_bounds_sized_used.rs:11:13
    |
+LL | fn bop<T: Bop + ?Sized>() {
+   |        - this type parameter needs to be `Sized`
 LL |     let _ = <T as Bop>::Bar::default();
-   |                              ^^^^^^^ function or associated item cannot be called on `<T as Bop>::Bar` due to unsatisfied trait bounds
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+note: required by a bound in `Bop::Bar`
+  --> $DIR/assoc_type_bounds_sized_used.rs:7:15
+   |
+LL |     type Bar: Default
+   |          --- required by a bound in this associated type
+LL |     where
+LL |         Self: Sized;
+   |               ^^^^^ required by this bound in `Bop::Bar`
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL - fn bop<T: Bop + ?Sized>() {
+LL + fn bop<T: Bop>() {
    |
-   = note: the following trait bounds were not satisfied:
-           `T: Sized`
-           which is required by `<T as Bop>::Bar: Default`
-help: consider restricting the type parameter to satisfy the trait bound
+help: consider relaxing the implicit `Sized` restriction
+   |
+LL |     type Bar: Default + ?Sized
+   |                       ++++++++
+
+error[E0277]: the size for values of type `T` cannot be known at compilation time
+  --> $DIR/assoc_type_bounds_sized_used.rs:11:13
    |
-LL | fn bop<T: Bop + ?Sized>() where T: Sized {
-   |                           ++++++++++++++
+LL | fn bop<T: Bop + ?Sized>() {
+   |        - this type parameter needs to be `Sized`
+LL |     let _ = <T as Bop>::Bar::default();
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+note: required by a bound in `Bop::Bar`
+  --> $DIR/assoc_type_bounds_sized_used.rs:7:15
+   |
+LL |     type Bar: Default
+   |          --- required by a bound in this associated type
+LL |     where
+LL |         Self: Sized;
+   |               ^^^^^ required by this bound in `Bop::Bar`
+help: consider removing the `?Sized` bound to make the type parameter `Sized`
+   |
+LL - fn bop<T: Bop + ?Sized>() {
+LL + fn bop<T: Bop>() {
+   |
+help: consider relaxing the implicit `Sized` restriction
+   |
+LL |     type Bar: Default + ?Sized
+   |                       ++++++++
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors
 
-Some errors have detailed explanations: E0277, E0599.
-For more information about an error, try `rustc --explain E0277`.
+For more information about this error, try `rustc --explain E0277`.

tests/ui/generic-associated-types/bugs/issue-100013.stderr

@@ -1,25 +1,3 @@
-error: lifetime bound not satisfied
-  --> $DIR/issue-100013.rs:15:5
-   |
-LL | /     async { // a coroutine checked for autotrait impl `Send`
-LL | |         let x = None::<I::Future<'_, '_>>; // a type referencing GAT
-LL | |         async {}.await; // a yield point
-LL | |     }
-   | |_____^
-   |
-   = note: this is a known limitation that will be removed in the future (see issue #100013 <https://github.com/rust-lang/rust/issues/100013> for more information)
-
-error: lifetime bound not satisfied
-  --> $DIR/issue-100013.rs:22:5
-   |
-LL | /     async { // a coroutine checked for autotrait impl `Send`
-LL | |         let x = None::<I::Future<'a, 'b>>; // a type referencing GAT
-LL | |         async {}.await; // a yield point
-LL | |     }
-   | |_____^
-   |
-   = note: this is a known limitation that will be removed in the future (see issue #100013 <https://github.com/rust-lang/rust/issues/100013> for more information)
-
 error: lifetime may not live long enough
   --> $DIR/issue-100013.rs:23:17
    |
@@ -33,16 +11,5 @@ LL |         let x = None::<I::Future<'a, 'b>>; // a type referencing GAT
    |
    = help: consider adding the following bound: `'a: 'b`
 
-error: lifetime bound not satisfied
-  --> $DIR/issue-100013.rs:29:5
-   |
-LL | /     async { // a coroutine checked for autotrait impl `Send`
-LL | |         let x = None::<I::Future<'a, 'b>>; // a type referencing GAT
-LL | |         async {}.await; // a yield point
-LL | |     }
-   | |_____^
-   |
-   = note: this is a known limitation that will be removed in the future (see issue #100013 <https://github.com/rust-lang/rust/issues/100013> for more information)
-
-error: aborting due to 4 previous errors
+error: aborting due to 1 previous error
 

tests/ui/generic-associated-types/issue-92096.rs

@@ -1,3 +1,4 @@
+//@ check-pass
 //@ edition:2018
 
 use std::future::Future;
@@ -15,14 +16,6 @@ where
     C: Client + Send + Sync,
 {
     async move { c.connect().await }
-    //~^ ERROR `C` does not live long enough
-    //
-    // FIXME(#71723). This is because we infer at some point a value of
-    //
-    // impl Future<Output = <C as Client>::Connection<'_>>
-    //
-    // and then we somehow fail the WF check because `where C: 'a` is not known,
-    // but I'm not entirely sure how that comes about.
 }
 
 fn main() {}

tests/ui/higher-ranked/trait-bounds/normalize-under-binder/norm-before-method-resolution-opaque-type.next.stderr

@@ -0,0 +1,14 @@
+error[E0282]: type annotations needed for `<X as Trait<'static>>::Out<_>`
+  --> $DIR/norm-before-method-resolution-opaque-type.rs:21:9
+   |
+LL |     let x = *x;
+   |         ^
+   |
+help: consider giving `x` an explicit type, where the placeholders `_` are specified
+   |
+LL |     let x: <_ as Trait<'static>>::Out<_> = *x;
+   |          +++++++++++++++++++++++++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0282`.

tests/ui/higher-ranked/trait-bounds/normalize-under-binder/norm-before-method-resolution-opaque-type.old.stderr

@@ -1,5 +1,5 @@
 error[E0507]: cannot move out of `*x` which is behind a shared reference
-  --> $DIR/norm-before-method-resolution-opaque-type.rs:22:13
+  --> $DIR/norm-before-method-resolution-opaque-type.rs:21:13
    |
 LL |     let x = *x;
    |             ^^ move occurs because `*x` has type `<X as Trait<'_>>::Out<Foo>`, which does not implement the `Copy` trait