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compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs

@@ -1,4 +1,4 @@
-use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
+use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
 use rustc_errors::codes::*;
 use rustc_errors::struct_span_code_err;
 use rustc_hir as hir;
@@ -61,7 +61,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         }
 
         let mut trait_bounds = vec![];
-        let mut projection_bounds = vec![];
+        let mut projection_bounds = FxIndexMap::default();
         for (pred, span) in bounds.clauses() {
             let bound_pred = pred.kind();
             match bound_pred.skip_binder() {
@@ -70,7 +70,8 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     trait_bounds.push((bound_pred.rebind(trait_pred.trait_ref), span));
                 }
                 ty::ClauseKind::Projection(proj) => {
-                    projection_bounds.push((bound_pred.rebind(proj), span));
+                    let anon = tcx.anonymize_bound_vars(bound_pred.rebind(proj));
+                    projection_bounds.insert(anon, (bound_pred.rebind(proj), span));
                 }
                 ty::ClauseKind::TypeOutlives(_) => {
                     // Do nothing, we deal with regions separately
@@ -87,8 +88,12 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
         // Expand trait aliases recursively and check that only one regular (non-auto) trait
         // is used and no 'maybe' bounds are used.
-        let expanded_traits =
-            traits::expand_trait_aliases(tcx, trait_bounds.iter().map(|&(a, b)| (a, b)));
+        let mut trait_alias_projection_bounds = FxIndexSet::default();
+        let expanded_traits = traits::expand_trait_aliases(
+            tcx,
+            &mut trait_alias_projection_bounds,
+            trait_bounds.iter().map(|&(a, b)| (a, b)),
+        );
 
         let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
             expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
@@ -162,6 +167,12 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     }
                     ty::PredicateKind::Clause(ty::ClauseKind::Projection(pred)) => {
                         let pred = bound_predicate.rebind(pred);
+
+                        let pred_key = tcx.anonymize_bound_vars(pred);
+                        if !trait_alias_projection_bounds.contains(&pred_key) {
+                            projection_bounds.shift_remove(&pred_key);
+                        }
+
                         // A `Self` within the original bound will be instantiated with a
                         // `trait_object_dummy_self`, so check for that.
                         let references_self = match pred.skip_binder().term.unpack() {
@@ -188,8 +199,13 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
                         // the discussion in #56288 for alternatives.
                         if !references_self {
-                            // Include projections defined on supertraits.
-                            implied_projection_bounds.push(pred);
+                            if trait_alias_projection_bounds.contains(&pred_key) {
+                                // Include projections defined on supertraits.
+                                projection_bounds.insert(pred_key, (pred, supertrait_span));
+                            } else {
+                                // Include projections defined on supertraits.
+                                implied_projection_bounds.push(pred);
+                            }
                         }
 
                         self.check_elaborated_projection_mentions_input_lifetimes(
@@ -207,7 +223,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         // So every `Projection` clause is an `Assoc = Foo` bound. `associated_types` contains all associated
         // types's `DefId`, so the following loop removes all the `DefIds` of the associated types that have a
         // corresponding `Projection` clause
-        for (projection_bound, span) in &projection_bounds {
+        for (projection_bound, span) in projection_bounds.values() {
             let def_id = projection_bound.projection_def_id();
             let trait_ref = tcx.anonymize_bound_vars(
                 projection_bound.map_bound(|p| p.projection_term.trait_ref(tcx)),
@@ -314,7 +330,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             })
         });
 
-        let existential_projections = projection_bounds.iter().map(|(bound, _)| {
+        let existential_projections = projection_bounds.values().map(|(bound, _)| {
             bound.map_bound(|mut b| {
                 assert_eq!(b.projection_term.self_ty(), dummy_self);
 

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -903,6 +903,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
             // For trait aliases, recursively assume all explicitly named traits are relevant
             for expansion in traits::expand_trait_aliases(
                 self.tcx,
+                &mut Default::default(),
                 iter::once((ty::Binder::dummy(trait_ref), self.span)),
             ) {
                 let bound_trait_ref = expansion.trait_ref();

compiler/rustc_middle/src/ty/relate.rs

@@ -80,19 +80,12 @@ impl<'tcx> Relate<TyCtxt<'tcx>> for &'tcx ty::List<ty::PolyExistentialPredicate<
     ) -> RelateResult<'tcx, Self> {
         let tcx = relation.cx();
 
-        // FIXME: this is wasteful, but want to do a perf run to see how slow it is.
-        // We need to perform this deduplication as we sometimes generate duplicate projections
-        // in `a`.
-        let mut a_v: Vec<_> = a.into_iter().collect();
-        let mut b_v: Vec<_> = b.into_iter().collect();
-        a_v.dedup();
-        b_v.dedup();
-        if a_v.len() != b_v.len() {
+        if a.len() != b.len() {
             return Err(TypeError::ExistentialMismatch(ExpectedFound::new(a, b)));
         }
 
-        let v = iter::zip(a_v, b_v).map(|(ep_a, ep_b)| {
-            match (ep_a.skip_binder(), ep_b.skip_binder()) {
+        let v =
+            iter::zip(a, b).map(|(ep_a, ep_b)| match (ep_a.skip_binder(), ep_b.skip_binder()) {
                 (ty::ExistentialPredicate::Trait(a), ty::ExistentialPredicate::Trait(b)) => {
                     Ok(ep_a.rebind(ty::ExistentialPredicate::Trait(
                         relation.relate(ep_a.rebind(a), ep_b.rebind(b))?.skip_binder(),
@@ -109,8 +102,7 @@ impl<'tcx> Relate<TyCtxt<'tcx>> for &'tcx ty::List<ty::PolyExistentialPredicate<
                     ty::ExistentialPredicate::AutoTrait(b),
                 ) if a == b => Ok(ep_a.rebind(ty::ExistentialPredicate::AutoTrait(a))),
                 _ => Err(TypeError::ExistentialMismatch(ExpectedFound::new(a, b))),
-            }
-        });
+            });
         tcx.mk_poly_existential_predicates_from_iter(v)
     }
 }

compiler/rustc_trait_selection/src/traits/util.rs

@@ -1,6 +1,6 @@
 use std::collections::BTreeMap;
 
-use rustc_data_structures::fx::FxIndexMap;
+use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_errors::Diag;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::InferCtxt;
@@ -25,9 +25,11 @@ use tracing::debug;
 /// `Read + Write + Sync + Send`.
 /// Expansion is done via a DFS (depth-first search), and the `visited` field
 /// is used to avoid cycles.
-pub struct TraitAliasExpander<'tcx> {
+pub struct TraitAliasExpander<'a, 'tcx> {
     tcx: TyCtxt<'tcx>,
     stack: Vec<TraitAliasExpansionInfo<'tcx>>,
+    // TODO:
+    projection_bounds: &'a mut FxIndexSet<ty::PolyProjectionPredicate<'tcx>>,
 }
 
 /// Stores information about the expansion of a trait via a path of zero or more trait aliases.
@@ -85,16 +87,17 @@ impl<'tcx> TraitAliasExpansionInfo<'tcx> {
     }
 }
 
-pub fn expand_trait_aliases<'tcx>(
+pub fn expand_trait_aliases<'a, 'tcx>(
     tcx: TyCtxt<'tcx>,
+    projection_bounds: &'a mut FxIndexSet<ty::PolyProjectionPredicate<'tcx>>,
     trait_refs: impl Iterator<Item = (ty::PolyTraitRef<'tcx>, Span)>,
-) -> TraitAliasExpander<'tcx> {
+) -> TraitAliasExpander<'a, 'tcx> {
     let items: Vec<_> =
         trait_refs.map(|(trait_ref, span)| TraitAliasExpansionInfo::new(trait_ref, span)).collect();
-    TraitAliasExpander { tcx, stack: items }
+    TraitAliasExpander { tcx, stack: items, projection_bounds }
 }
 
-impl<'tcx> TraitAliasExpander<'tcx> {
+impl<'tcx> TraitAliasExpander<'_, 'tcx> {
     /// If `item` is a trait alias and its predicate has not yet been visited, then expands `item`
     /// to the definition, pushes the resulting expansion onto `self.stack`, and returns `false`.
     /// Otherwise, immediately returns `true` if `item` is a regular trait, or `false` if it is a
@@ -129,20 +132,26 @@ impl<'tcx> TraitAliasExpander<'tcx> {
         let predicates = tcx.explicit_super_predicates_of(trait_ref.def_id());
         debug!(?predicates);
 
-        let items = predicates.skip_binder().iter().rev().filter_map(|(pred, span)| {
-            pred.instantiate_supertrait(tcx, trait_ref)
-                .as_trait_clause()
-                .map(|trait_ref| item.clone_and_push(trait_ref.map_bound(|t| t.trait_ref), *span))
-        });
-        debug!("expand_trait_aliases: items={:?}", items.clone().collect::<Vec<_>>());
-
-        self.stack.extend(items);
+        for &(pred, span) in predicates.skip_binder().iter().rev() {
+            let pred = pred.instantiate_supertrait(tcx, trait_ref);
+            if let Some(trait_pred) = pred.as_trait_clause() {
+                // FIXME(negative_bounds): Polarity
+                self.stack.push(
+                    item.clone_and_push(
+                        trait_pred.map_bound(|trait_pred| trait_pred.trait_ref),
+                        span,
+                    ),
+                );
+            } else if let Some(proj) = pred.as_projection_clause() {
+                self.projection_bounds.insert(self.tcx.anonymize_bound_vars(proj));
+            }
+        }
 
         false
     }
 }
 
-impl<'tcx> Iterator for TraitAliasExpander<'tcx> {
+impl<'tcx> Iterator for TraitAliasExpander<'_, 'tcx> {
     type Item = TraitAliasExpansionInfo<'tcx>;
 
     fn size_hint(&self) -> (usize, Option<usize>) {

tests/ui/associated-types/issue-59324.rs

@@ -21,8 +21,6 @@ pub trait ThriftService<Bug: NotFoo>:
 }
 
 fn with_factory<H>(factory: dyn ThriftService<()>) {}
-//~^ ERROR the trait bound `(): Foo` is not satisfied
-//~| ERROR the trait bound `(): Foo` is not satisfied
-//~| ERROR cannot be known at compilation time
+//~^ ERROR cannot be known at compilation time
 
 fn main() {}

tests/ui/issues/issue-59326.rs

@@ -1,4 +1,3 @@
-//@ check-pass
 trait Service {
     type S;
 }
@@ -23,4 +22,5 @@ fn make_server<F: Framing>() -> Box<dyn HttpService<F, S = F::F>> {
 
 fn main() {
     build_server(|| make_server())
+    //~^ ERROR mismatched types
 }

tests/ui/issues/issue-59326.stderr

@@ -0,0 +1,12 @@
+error[E0308]: mismatched types
+  --> $DIR/issue-59326.rs:24:21
+   |
+LL |     build_server(|| make_server())
+   |                     ^^^^^^^^^^^^^ expected trait `HttpService<(), S = ()>`, found trait `HttpService<_>`
+   |
+   = note: expected struct `Box<(dyn HttpService<(), S = ()> + 'static)>`
+              found struct `Box<(dyn HttpService<_> + 'static)>`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.

tests/ui/traits/alias/dont-elaborate-non-self.stderr

@@ -1,10 +1,10 @@
-error[E0277]: the size for values of type `(dyn Fn<()> + 'static)` cannot be known at compilation time
+error[E0277]: the size for values of type `(dyn Fn() -> Fut + 'static)` cannot be known at compilation time
   --> $DIR/dont-elaborate-non-self.rs:7:14
    |
 LL | fn f<Fut>(a: dyn F<Fut>) {}
    |              ^^^^^^^^^^ doesn't have a size known at compile-time
    |
-   = help: the trait `Sized` is not implemented for `(dyn Fn<()> + 'static)`
+   = help: the trait `Sized` is not implemented for `(dyn Fn() -> Fut + 'static)`
    = help: unsized fn params are gated as an unstable feature
 help: you can use `impl Trait` as the argument type
    |