Auto merge of #107614 - compiler-errors:allow-elaborator-to-filter-only-super-traits, r=oli-obk

Split implied and super predicate queries, then allow elaborator to filter only supertraits

Split the `super_predicates_of` query into a new `implied_predicates_of` query. The former now only returns the *real* supertraits of a trait alias, and the latter now returns the implied predicates (which include all of the `where` clauses of the trait alias). The behavior of these queries is identical for regular traits.

Now that the two queries are split, we can add a new filter method to the elaborator, `filter_only_self()`, which can be used in instances that we need only the *supertrait* predicates, such as during the elaboration used in closure signature deduction. This toggles the usage of `super_predicates_of` instead of `implied_predicates_of` during elaboration of a trait predicate.

This supersedes #104745, and fixes the four independent bugs identified in that PR.
Fixes #104719
Fixes #106238
Fixes #110023
Fixes #109514

r? types

Author: bors

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -1663,39 +1663,45 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             })
         });
 
-        let existential_projections = projection_bounds.iter().map(|(bound, _)| {
-            bound.map_bound(|mut b| {
-                assert_eq!(b.projection_ty.self_ty(), dummy_self);
-
-                // Like for trait refs, verify that `dummy_self` did not leak inside default type
-                // parameters.
-                let references_self = b.projection_ty.substs.iter().skip(1).any(|arg| {
-                    if arg.walk().any(|arg| arg == dummy_self.into()) {
-                        return true;
+        let existential_projections = projection_bounds
+            .iter()
+            // We filter out traits that don't have `Self` as their self type above,
+            // we need to do the same for projections.
+            .filter(|(bound, _)| bound.skip_binder().self_ty() == dummy_self)
+            .map(|(bound, _)| {
+                bound.map_bound(|mut b| {
+                    assert_eq!(b.projection_ty.self_ty(), dummy_self);
+
+                    // Like for trait refs, verify that `dummy_self` did not leak inside default type
+                    // parameters.
+                    let references_self = b.projection_ty.substs.iter().skip(1).any(|arg| {
+                        if arg.walk().any(|arg| arg == dummy_self.into()) {
+                            return true;
+                        }
+                        false
+                    });
+                    if references_self {
+                        let guar = tcx.sess.delay_span_bug(
+                            span,
+                            "trait object projection bounds reference `Self`",
+                        );
+                        let substs: Vec<_> = b
+                            .projection_ty
+                            .substs
+                            .iter()
+                            .map(|arg| {
+                                if arg.walk().any(|arg| arg == dummy_self.into()) {
+                                    return tcx.ty_error(guar).into();
+                                }
+                                arg
+                            })
+                            .collect();
+                        b.projection_ty.substs = tcx.mk_substs(&substs);
                     }
-                    false
-                });
-                if references_self {
-                    let guar = tcx
-                        .sess
-                        .delay_span_bug(span, "trait object projection bounds reference `Self`");
-                    let substs: Vec<_> = b
-                        .projection_ty
-                        .substs
-                        .iter()
-                        .map(|arg| {
-                            if arg.walk().any(|arg| arg == dummy_self.into()) {
-                                return tcx.ty_error(guar).into();
-                            }
-                            arg
-                        })
-                        .collect();
-                    b.projection_ty.substs = tcx.mk_substs(&substs);
-                }
 
-                ty::ExistentialProjection::erase_self_ty(tcx, b)
-            })
-        });
+                    ty::ExistentialProjection::erase_self_ty(tcx, b)
+                })
+            });
 
         let regular_trait_predicates = existential_trait_refs
             .map(|trait_ref| trait_ref.map_bound(ty::ExistentialPredicate::Trait));

compiler/rustc_hir_analysis/src/collect.rs

@@ -64,6 +64,7 @@ pub fn provide(providers: &mut Providers) {
         predicates_defined_on,
         explicit_predicates_of: predicates_of::explicit_predicates_of,
         super_predicates_of: predicates_of::super_predicates_of,
+        implied_predicates_of: predicates_of::implied_predicates_of,
         super_predicates_that_define_assoc_type:
             predicates_of::super_predicates_that_define_assoc_type,
         trait_explicit_predicates_and_bounds: predicates_of::trait_explicit_predicates_and_bounds,
@@ -596,6 +597,7 @@ fn convert_item(tcx: TyCtxt<'_>, item_id: hir::ItemId) {
         }
         hir::ItemKind::TraitAlias(..) => {
             tcx.ensure().generics_of(def_id);
+            tcx.at(it.span).implied_predicates_of(def_id);
             tcx.at(it.span).super_predicates_of(def_id);
             tcx.ensure().predicates_of(def_id);
         }

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -125,7 +125,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
     // on a trait we need to add in the supertrait bounds and bounds found on
     // associated types.
     if let Some(_trait_ref) = is_trait {
-        predicates.extend(tcx.super_predicates_of(def_id).predicates.iter().cloned());
+        predicates.extend(tcx.implied_predicates_of(def_id).predicates.iter().cloned());
     }
 
     // In default impls, we can assume that the self type implements
@@ -534,31 +534,62 @@ pub(super) fn explicit_predicates_of<'tcx>(
     }
 }
 
+#[derive(Copy, Clone, Debug)]
+pub enum PredicateFilter {
+    /// All predicates may be implied by the trait
+    All,
+
+    /// Only traits that reference `Self: ..` are implied by the trait
+    SelfOnly,
+
+    /// Only traits that reference `Self: ..` and define an associated type
+    /// with the given ident are implied by the trait
+    SelfThatDefines(Ident),
+}
+
 /// Ensures that the super-predicates of the trait with a `DefId`
 /// of `trait_def_id` are converted and stored. This also ensures that
 /// the transitive super-predicates are converted.
 pub(super) fn super_predicates_of(
     tcx: TyCtxt<'_>,
     trait_def_id: LocalDefId,
 ) -> ty::GenericPredicates<'_> {
-    tcx.super_predicates_that_define_assoc_type((trait_def_id.to_def_id(), None))
+    implied_predicates_with_filter(tcx, trait_def_id.to_def_id(), PredicateFilter::SelfOnly)
+}
+
+pub(super) fn super_predicates_that_define_assoc_type(
+    tcx: TyCtxt<'_>,
+    (trait_def_id, assoc_name): (DefId, Ident),
+) -> ty::GenericPredicates<'_> {
+    implied_predicates_with_filter(tcx, trait_def_id, PredicateFilter::SelfThatDefines(assoc_name))
+}
+
+pub(super) fn implied_predicates_of(
+    tcx: TyCtxt<'_>,
+    trait_def_id: LocalDefId,
+) -> ty::GenericPredicates<'_> {
+    if tcx.is_trait_alias(trait_def_id.to_def_id()) {
+        implied_predicates_with_filter(tcx, trait_def_id.to_def_id(), PredicateFilter::All)
+    } else {
+        tcx.super_predicates_of(trait_def_id)
+    }
 }
 
 /// Ensures that the super-predicates of the trait with a `DefId`
 /// of `trait_def_id` are converted and stored. This also ensures that
 /// the transitive super-predicates are converted.
-pub(super) fn super_predicates_that_define_assoc_type(
+pub(super) fn implied_predicates_with_filter(
     tcx: TyCtxt<'_>,
-    (trait_def_id, assoc_name): (DefId, Option<Ident>),
+    trait_def_id: DefId,
+    filter: PredicateFilter,
 ) -> ty::GenericPredicates<'_> {
     let Some(trait_def_id) = trait_def_id.as_local() else {
         // if `assoc_name` is None, then the query should've been redirected to an
         // external provider
-        assert!(assoc_name.is_some());
+        assert!(matches!(filter, PredicateFilter::SelfThatDefines(_)));
         return tcx.super_predicates_of(trait_def_id);
     };
 
-    debug!("local trait");
     let trait_hir_id = tcx.hir().local_def_id_to_hir_id(trait_def_id);
 
     let Node::Item(item) = tcx.hir().get(trait_hir_id) else {
@@ -573,48 +604,66 @@ pub(super) fn super_predicates_that_define_assoc_type(
 
     let icx = ItemCtxt::new(tcx, trait_def_id);
 
-    // Convert the bounds that follow the colon, e.g., `Bar + Zed` in `trait Foo: Bar + Zed`.
     let self_param_ty = tcx.types.self_param;
-    let superbounds1 = if let Some(assoc_name) = assoc_name {
-        icx.astconv().compute_bounds_that_match_assoc_type(self_param_ty, bounds, assoc_name)
-    } else {
-        icx.astconv().compute_bounds(self_param_ty, bounds)
+    let (superbounds, where_bounds_that_match) = match filter {
+        PredicateFilter::All => (
+            // Convert the bounds that follow the colon (or equal in trait aliases)
+            icx.astconv().compute_bounds(self_param_ty, bounds),
+            // Also include all where clause bounds
+            icx.type_parameter_bounds_in_generics(
+                generics,
+                item.owner_id.def_id,
+                self_param_ty,
+                OnlySelfBounds(false),
+                None,
+            ),
+        ),
+        PredicateFilter::SelfOnly => (
+            // Convert the bounds that follow the colon (or equal in trait aliases)
+            icx.astconv().compute_bounds(self_param_ty, bounds),
+            // Include where clause bounds for `Self`
+            icx.type_parameter_bounds_in_generics(
+                generics,
+                item.owner_id.def_id,
+                self_param_ty,
+                OnlySelfBounds(true),
+                None,
+            ),
+        ),
+        PredicateFilter::SelfThatDefines(assoc_name) => (
+            // Convert the bounds that follow the colon (or equal) that reference the associated name
+            icx.astconv().compute_bounds_that_match_assoc_type(self_param_ty, bounds, assoc_name),
+            // Include where clause bounds for `Self` that reference the associated name
+            icx.type_parameter_bounds_in_generics(
+                generics,
+                item.owner_id.def_id,
+                self_param_ty,
+                OnlySelfBounds(true),
+                Some(assoc_name),
+            ),
+        ),
     };
 
-    let superbounds1 = superbounds1.predicates();
-
-    // Convert any explicit superbounds in the where-clause,
-    // e.g., `trait Foo where Self: Bar`.
-    // In the case of trait aliases, however, we include all bounds in the where-clause,
-    // so e.g., `trait Foo = where u32: PartialEq<Self>` would include `u32: PartialEq<Self>`
-    // as one of its "superpredicates".
-    let is_trait_alias = tcx.is_trait_alias(trait_def_id.to_def_id());
-    let superbounds2 = icx.type_parameter_bounds_in_generics(
-        generics,
-        item.owner_id.def_id,
-        self_param_ty,
-        OnlySelfBounds(!is_trait_alias),
-        assoc_name,
-    );
-
     // Combine the two lists to form the complete set of superbounds:
-    let superbounds = &*tcx.arena.alloc_from_iter(superbounds1.into_iter().chain(superbounds2));
-    debug!(?superbounds);
+    let implied_bounds = &*tcx
+        .arena
+        .alloc_from_iter(superbounds.predicates().into_iter().chain(where_bounds_that_match));
+    debug!(?implied_bounds);
 
     // Now require that immediate supertraits are converted,
     // which will, in turn, reach indirect supertraits.
-    if assoc_name.is_none() {
+    if matches!(filter, PredicateFilter::SelfOnly) {
         // Now require that immediate supertraits are converted,
         // which will, in turn, reach indirect supertraits.
-        for &(pred, span) in superbounds {
+        for &(pred, span) in implied_bounds {
             debug!("superbound: {:?}", pred);
             if let ty::PredicateKind::Clause(ty::Clause::Trait(bound)) = pred.kind().skip_binder() {
                 tcx.at(span).super_predicates_of(bound.def_id());
             }
         }
     }
 
-    ty::GenericPredicates { parent: None, predicates: superbounds }
+    ty::GenericPredicates { parent: None, predicates: implied_bounds }
 }
 
 /// Returns the predicates defined on `item_def_id` of the form

compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs

@@ -1749,8 +1749,7 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
             if trait_defines_associated_type_named(def_id) {
                 break Some(bound_vars.into_iter().collect());
             }
-            let predicates =
-                tcx.super_predicates_that_define_assoc_type((def_id, Some(assoc_name)));
+            let predicates = tcx.super_predicates_that_define_assoc_type((def_id, assoc_name));
             let obligations = predicates.predicates.iter().filter_map(|&(pred, _)| {
                 let bound_predicate = pred.kind();
                 match bound_predicate.skip_binder() {

compiler/rustc_hir_typeck/src/closure.rs

@@ -210,7 +210,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // and we want to keep inference generally in the same order of
             // the registered obligations.
             predicates.rev(),
-        ) {
+        )
+        // We only care about self bounds
+        .filter_only_self()
+        {
             debug!(?pred);
             let bound_predicate = pred.kind();
 

compiler/rustc_infer/src/traits/util.rs

@@ -69,6 +69,7 @@ impl<'tcx> Extend<ty::Predicate<'tcx>> for PredicateSet<'tcx> {
 pub struct Elaborator<'tcx, O> {
     stack: Vec<O>,
     visited: PredicateSet<'tcx>,
+    only_self: bool,
 }
 
 /// Describes how to elaborate an obligation into a sub-obligation.
@@ -170,7 +171,8 @@ pub fn elaborate<'tcx, O: Elaboratable<'tcx>>(
     tcx: TyCtxt<'tcx>,
     obligations: impl IntoIterator<Item = O>,
 ) -> Elaborator<'tcx, O> {
-    let mut elaborator = Elaborator { stack: Vec::new(), visited: PredicateSet::new(tcx) };
+    let mut elaborator =
+        Elaborator { stack: Vec::new(), visited: PredicateSet::new(tcx), only_self: false };
     elaborator.extend_deduped(obligations);
     elaborator
 }
@@ -185,14 +187,25 @@ impl<'tcx, O: Elaboratable<'tcx>> Elaborator<'tcx, O> {
         self.stack.extend(obligations.into_iter().filter(|o| self.visited.insert(o.predicate())));
     }
 
+    /// Filter to only the supertraits of trait predicates, i.e. only the predicates
+    /// that have `Self` as their self type, instead of all implied predicates.
+    pub fn filter_only_self(mut self) -> Self {
+        self.only_self = true;
+        self
+    }
+
     fn elaborate(&mut self, elaboratable: &O) {
         let tcx = self.visited.tcx;
 
         let bound_predicate = elaboratable.predicate().kind();
         match bound_predicate.skip_binder() {
             ty::PredicateKind::Clause(ty::Clause::Trait(data)) => {
-                // Get predicates declared on the trait.
-                let predicates = tcx.super_predicates_of(data.def_id());
+                // Get predicates implied by the trait, or only super predicates if we only care about self predicates.
+                let predicates = if self.only_self {
+                    tcx.super_predicates_of(data.def_id())
+                } else {
+                    tcx.implied_predicates_of(data.def_id())
+                };
 
                 let obligations =
                     predicates.predicates.iter().enumerate().map(|(index, &(mut pred, span))| {
@@ -350,18 +363,16 @@ pub fn supertraits<'tcx>(
     tcx: TyCtxt<'tcx>,
     trait_ref: ty::PolyTraitRef<'tcx>,
 ) -> impl Iterator<Item = ty::PolyTraitRef<'tcx>> {
-    let pred: ty::Predicate<'tcx> = trait_ref.to_predicate(tcx);
-    FilterToTraits::new(elaborate(tcx, [pred]))
+    elaborate(tcx, [trait_ref.to_predicate(tcx)]).filter_only_self().filter_to_traits()
 }
 
 pub fn transitive_bounds<'tcx>(
     tcx: TyCtxt<'tcx>,
     trait_refs: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
 ) -> impl Iterator<Item = ty::PolyTraitRef<'tcx>> {
-    FilterToTraits::new(elaborate(
-        tcx,
-        trait_refs.map(|trait_ref| -> ty::Predicate<'tcx> { trait_ref.to_predicate(tcx) }),
-    ))
+    elaborate(tcx, trait_refs.map(|trait_ref| trait_ref.to_predicate(tcx)))
+        .filter_only_self()
+        .filter_to_traits()
 }
 
 /// A specialized variant of `elaborate` that only elaborates trait references that may
@@ -381,10 +392,8 @@ pub fn transitive_bounds_that_define_assoc_type<'tcx>(
         while let Some(trait_ref) = stack.pop() {
             let anon_trait_ref = tcx.anonymize_bound_vars(trait_ref);
             if visited.insert(anon_trait_ref) {
-                let super_predicates = tcx.super_predicates_that_define_assoc_type((
-                    trait_ref.def_id(),
-                    Some(assoc_name),
-                ));
+                let super_predicates =
+                    tcx.super_predicates_that_define_assoc_type((trait_ref.def_id(), assoc_name));
                 for (super_predicate, _) in super_predicates.predicates {
                     let subst_predicate = super_predicate.subst_supertrait(tcx, &trait_ref);
                     if let Some(binder) = subst_predicate.to_opt_poly_trait_pred() {
@@ -404,18 +413,18 @@ pub fn transitive_bounds_that_define_assoc_type<'tcx>(
 // Other
 ///////////////////////////////////////////////////////////////////////////
 
+impl<'tcx> Elaborator<'tcx, ty::Predicate<'tcx>> {
+    fn filter_to_traits(self) -> FilterToTraits<Self> {
+        FilterToTraits { base_iterator: self }
+    }
+}
+
 /// A filter around an iterator of predicates that makes it yield up
 /// just trait references.
 pub struct FilterToTraits<I> {
     base_iterator: I,
 }
 
-impl<I> FilterToTraits<I> {
-    fn new(base: I) -> FilterToTraits<I> {
-        FilterToTraits { base_iterator: base }
-    }
-}
-
 impl<'tcx, I: Iterator<Item = ty::Predicate<'tcx>>> Iterator for FilterToTraits<I> {
     type Item = ty::PolyTraitRef<'tcx>;