Get rid of OnlySelfBounds

compiler/rustc_hir_analysis/src/bounds.rs

@@ -9,7 +9,7 @@ use rustc_middle::ty::{self, Ty, TyCtxt, Upcast};
 use rustc_span::Span;
 use rustc_span::def_id::DefId;
 
-use crate::hir_ty_lowering::OnlySelfBounds;
+use crate::hir_ty_lowering::PredicateFilter;
 
 /// Collects together a list of type bounds. These lists of bounds occur in many places
 /// in Rust's syntax:
@@ -52,7 +52,7 @@ impl<'tcx> Bounds<'tcx> {
         span: Span,
         polarity: ty::PredicatePolarity,
         constness: ty::BoundConstness,
-        only_self_bounds: OnlySelfBounds,
+        predicate_filter: PredicateFilter,
     ) {
         let clause = (
             bound_trait_ref
@@ -72,9 +72,18 @@ impl<'tcx> Bounds<'tcx> {
         // FIXME(effects): Lift this out of `push_trait_bound`, and move it somewhere else.
         // Perhaps moving this into `lower_poly_trait_ref`, just like we lower associated
         // type bounds.
-        if !tcx.features().effects || only_self_bounds.0 {
+        if !tcx.features().effects {
             return;
         }
+        match predicate_filter {
+            PredicateFilter::SelfOnly | PredicateFilter::SelfThatDefines(_) => {
+                return;
+            }
+            PredicateFilter::All | PredicateFilter::SelfAndAssociatedTypeBounds => {
+                // Ok.
+            }
+        }
+
         // For `T: ~const Tr` or `T: const Tr`, we need to add an additional bound on the
         // associated type of `<T as Tr>` and make sure that the effect is compatible.
         let compat_val = match (tcx.def_kind(defining_def_id), constness) {

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -16,7 +16,7 @@ use crate::bounds::Bounds;
 use crate::collect::ItemCtxt;
 use crate::constrained_generic_params as cgp;
 use crate::delegation::inherit_predicates_for_delegation_item;
-use crate::hir_ty_lowering::{HirTyLowerer, OnlySelfBounds, PredicateFilter, RegionInferReason};
+use crate::hir_ty_lowering::{HirTyLowerer, PredicateFilter, RegionInferReason};
 
 /// Returns a list of all type predicates (explicit and implicit) for the definition with
 /// ID `def_id`. This includes all predicates returned by `explicit_predicates_of`, plus
@@ -270,7 +270,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
                     bound_pred.bounds.iter(),
                     &mut bounds,
                     bound_vars,
-                    OnlySelfBounds(false),
+                    PredicateFilter::All,
                 );
                 predicates.extend(bounds.clauses(tcx));
                 effects_min_tys.extend(bounds.effects_min_tys());
@@ -825,20 +825,6 @@ impl<'tcx> ItemCtxt<'tcx> {
                 continue;
             };
 
-            // Subtle: If we're collecting `SelfAndAssociatedTypeBounds`, then we
-            // want to only consider predicates with `Self: ...`, but we don't want
-            // `OnlySelfBounds(true)` since we want to collect the nested associated
-            // type bound as well.
-            let (only_self_bounds, assoc_name) = match filter {
-                PredicateFilter::All | PredicateFilter::SelfAndAssociatedTypeBounds => {
-                    (OnlySelfBounds(false), None)
-                }
-                PredicateFilter::SelfOnly => (OnlySelfBounds(true), None),
-                PredicateFilter::SelfThatDefines(assoc_name) => {
-                    (OnlySelfBounds(true), Some(assoc_name))
-                }
-            };
-
             let bound_ty = if predicate.is_param_bound(param_def_id.to_def_id()) {
                 ty
             } else if matches!(filter, PredicateFilter::All) {
@@ -850,31 +836,13 @@ impl<'tcx> ItemCtxt<'tcx> {
             let bound_vars = self.tcx.late_bound_vars(predicate.hir_id);
             self.lowerer().lower_poly_bounds(
                 bound_ty,
-                predicate.bounds.iter().filter(|bound| {
-                    assoc_name
-                        .map_or(true, |assoc_name| self.bound_defines_assoc_item(bound, assoc_name))
-                }),
+                predicate.bounds.iter(),
                 &mut bounds,
                 bound_vars,
-                only_self_bounds,
+                filter,
             );
         }
 
         bounds.clauses(self.tcx).collect()
     }
-
-    #[instrument(level = "trace", skip(self))]
-    fn bound_defines_assoc_item(&self, b: &hir::GenericBound<'_>, assoc_name: Ident) -> bool {
-        match b {
-            hir::GenericBound::Trait(poly_trait_ref) => {
-                let trait_ref = &poly_trait_ref.trait_ref;
-                if let Some(trait_did) = trait_ref.trait_def_id() {
-                    self.tcx.trait_may_define_assoc_item(trait_did, assoc_name)
-                } else {
-                    false
-                }
-            }
-            _ => false,
-        }
-    }
 }

compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs

@@ -19,9 +19,7 @@ use tracing::{debug, instrument};
 use super::errors::GenericsArgsErrExtend;
 use crate::bounds::Bounds;
 use crate::errors;
-use crate::hir_ty_lowering::{
-    AssocItemQSelf, HirTyLowerer, OnlySelfBounds, PredicateFilter, RegionInferReason,
-};
+use crate::hir_ty_lowering::{AssocItemQSelf, HirTyLowerer, PredicateFilter, RegionInferReason};
 
 impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     /// Add a `Sized` bound to the `bounds` if appropriate.
@@ -150,11 +148,25 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         hir_bounds: I,
         bounds: &mut Bounds<'tcx>,
         bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
-        only_self_bounds: OnlySelfBounds,
+        predicate_filter: PredicateFilter,
     ) where
         'tcx: 'hir,
     {
         for hir_bound in hir_bounds {
+            // In order to avoid cycles, when we're lowering `SelfThatDefines`,
+            // we skip over any traits that don't define the given associated type.
+
+            if let PredicateFilter::SelfThatDefines(assoc_name) = predicate_filter {
+                if let Some(trait_ref) = hir_bound.trait_ref()
+                    && let Some(trait_did) = trait_ref.trait_def_id()
+                    && self.tcx().trait_may_define_assoc_item(trait_did, assoc_name)
+                {
+                    // Okay
+                } else {
+                    continue;
+                }
+            }
+
             match hir_bound {
                 hir::GenericBound::Trait(poly_trait_ref) => {
                     let (constness, polarity) = match poly_trait_ref.modifiers {
@@ -179,7 +191,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         polarity,
                         param_ty,
                         bounds,
-                        only_self_bounds,
+                        predicate_filter,
                     );
                 }
                 hir::GenericBound::Outlives(lifetime) => {
@@ -213,37 +225,16 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         &self,
         param_ty: Ty<'tcx>,
         hir_bounds: &[hir::GenericBound<'tcx>],
-        filter: PredicateFilter,
+        predicate_filter: PredicateFilter,
     ) -> Bounds<'tcx> {
         let mut bounds = Bounds::default();
 
-        let only_self_bounds = match filter {
-            PredicateFilter::All | PredicateFilter::SelfAndAssociatedTypeBounds => {
-                OnlySelfBounds(false)
-            }
-            PredicateFilter::SelfOnly | PredicateFilter::SelfThatDefines(_) => OnlySelfBounds(true),
-        };
-
         self.lower_poly_bounds(
             param_ty,
-            hir_bounds.iter().filter(|bound| match filter {
-                PredicateFilter::All
-                | PredicateFilter::SelfOnly
-                | PredicateFilter::SelfAndAssociatedTypeBounds => true,
-                PredicateFilter::SelfThatDefines(assoc_name) => {
-                    if let Some(trait_ref) = bound.trait_ref()
-                        && let Some(trait_did) = trait_ref.trait_def_id()
-                        && self.tcx().trait_may_define_assoc_item(trait_did, assoc_name)
-                    {
-                        true
-                    } else {
-                        false
-                    }
-                }
-            }),
+            hir_bounds.iter(),
             &mut bounds,
             ty::List::empty(),
-            only_self_bounds,
+            predicate_filter,
         );
         debug!(?bounds);
 
@@ -267,7 +258,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         bounds: &mut Bounds<'tcx>,
         duplicates: &mut FxIndexMap<DefId, Span>,
         path_span: Span,
-        only_self_bounds: OnlySelfBounds,
+        predicate_filter: PredicateFilter,
     ) -> Result<(), ErrorGuaranteed> {
         let tcx = self.tcx();
 
@@ -444,21 +435,23 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             // Lower a constraint like `Item: Debug` as found in HIR bound `T: Iterator<Item: Debug>`
             // to a bound involving a projection: `<T as Iterator>::Item: Debug`.
             hir::AssocItemConstraintKind::Bound { bounds: hir_bounds } => {
-                // NOTE: If `only_self_bounds` is true, do NOT expand this associated type bound into
-                // a trait predicate, since we only want to add predicates for the `Self` type.
-                if !only_self_bounds.0 {
-                    let projection_ty = projection_term
-                        .map_bound(|projection_term| projection_term.expect_ty(self.tcx()));
-                    // Calling `skip_binder` is okay, because `lower_bounds` expects the `param_ty`
-                    // parameter to have a skipped binder.
-                    let param_ty = Ty::new_alias(tcx, ty::Projection, projection_ty.skip_binder());
-                    self.lower_poly_bounds(
-                        param_ty,
-                        hir_bounds.iter(),
-                        bounds,
-                        projection_ty.bound_vars(),
-                        only_self_bounds,
-                    );
+                match predicate_filter {
+                    PredicateFilter::SelfOnly | PredicateFilter::SelfThatDefines(_) => {}
+                    PredicateFilter::All | PredicateFilter::SelfAndAssociatedTypeBounds => {
+                        let projection_ty = projection_term
+                            .map_bound(|projection_term| projection_term.expect_ty(self.tcx()));
+                        // Calling `skip_binder` is okay, because `lower_bounds` expects the `param_ty`
+                        // parameter to have a skipped binder.
+                        let param_ty =
+                            Ty::new_alias(tcx, ty::Projection, projection_ty.skip_binder());
+                        self.lower_poly_bounds(
+                            param_ty,
+                            hir_bounds.iter(),
+                            bounds,
+                            projection_ty.bound_vars(),
+                            predicate_filter,
+                        );
+                    }
                 }
             }
         }

compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_compatibility.rs

@@ -20,7 +20,7 @@ use tracing::{debug, instrument};
 use super::HirTyLowerer;
 use crate::bounds::Bounds;
 use crate::hir_ty_lowering::{
-    GenericArgCountMismatch, GenericArgCountResult, OnlySelfBounds, RegionInferReason,
+    GenericArgCountMismatch, GenericArgCountResult, PredicateFilter, RegionInferReason,
 };
 
 impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
@@ -55,9 +55,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 ty::PredicatePolarity::Positive,
                 dummy_self,
                 &mut bounds,
-                // True so we don't populate `bounds` with associated type bounds, even
-                // though they're disallowed from object types.
-                OnlySelfBounds(true),
+                PredicateFilter::SelfOnly,
             ) {
                 potential_assoc_types.extend(cur_potential_assoc_types);
             }

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -64,9 +64,6 @@ use crate::require_c_abi_if_c_variadic;
 #[derive(Debug)]
 pub struct GenericPathSegment(pub DefId, pub usize);
 
-#[derive(Copy, Clone, Debug)]
-pub struct OnlySelfBounds(pub bool);
-
 #[derive(Copy, Clone, Debug)]
 pub enum PredicateFilter {
     /// All predicates may be implied by the trait.
@@ -76,7 +73,8 @@ pub enum PredicateFilter {
     SelfOnly,
 
     /// Only traits that reference `Self: ..` and define an associated type
-    /// with the given ident are implied by the trait.
+    /// with the given ident are implied by the trait. This mode exists to
+    /// side-step query cycles when lowering associated types.
     SelfThatDefines(Ident),
 
     /// Only traits that reference `Self: ..` and their associated type bounds.
@@ -683,7 +681,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         polarity: ty::PredicatePolarity,
         self_ty: Ty<'tcx>,
         bounds: &mut Bounds<'tcx>,
-        only_self_bounds: OnlySelfBounds,
+        predicate_filter: PredicateFilter,
     ) -> GenericArgCountResult {
         let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
         let trait_segment = trait_ref.path.segments.last().unwrap();
@@ -720,7 +718,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             span,
             polarity,
             constness,
-            only_self_bounds,
+            predicate_filter,
         );
 
         let mut dup_constraints = FxIndexMap::default();
@@ -744,7 +742,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 bounds,
                 &mut dup_constraints,
                 constraint.span,
-                only_self_bounds,
+                predicate_filter,
             );
             // Okay to ignore `Err` because of `ErrorGuaranteed` (see above).
         }