resolve region bounds from components of type projection

compiler/rustc_borrowck/src/type_check/constraint_conversion.rs

@@ -12,6 +12,7 @@ use rustc_span::Span;
 use rustc_trait_selection::solve::deeply_normalize;
 use rustc_trait_selection::traits::query::type_op::custom::CustomTypeOp;
 use rustc_trait_selection::traits::query::type_op::{TypeOp, TypeOpOutput};
+use smallvec::SmallVec;
 
 use crate::{
     constraints::OutlivesConstraint,
@@ -147,8 +148,14 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
             region_bound_pairs,
             implicit_region_bound,
             known_type_outlives_obligations,
+            param_env,
             ..
         } = *self;
+        let projection_predicates: SmallVec<[_; 4]> = param_env
+            .caller_bounds()
+            .iter()
+            .filter_map(|clause| clause.as_projection_clause())
+            .collect();
 
         let mut outlives_predicates = vec![(predicate, constraint_category)];
         for iteration in 0.. {
@@ -191,6 +198,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
                             region_bound_pairs,
                             Some(implicit_region_bound),
                             known_type_outlives_obligations,
+                            &projection_predicates,
                         )
                         .type_must_outlive(
                             origin,

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -1129,6 +1129,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         data: &QueryRegionConstraints<'tcx>,
     ) {
         debug!("constraints generated: {:#?}", data);
+        debug!(?self.param_env);
 
         constraint_conversion::ConstraintConversion::new(
             self.infcx,

compiler/rustc_borrowck/src/universal_regions.rs

@@ -418,6 +418,7 @@ struct UniversalRegionsBuilder<'cx, 'tcx> {
 const FR: NllRegionVariableOrigin = NllRegionVariableOrigin::FreeRegion;
 
 impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
+    #[instrument(level = "debug", skip(self))]
     fn build(self) -> UniversalRegions<'tcx> {
         debug!("build(mir_def={:?})", self.mir_def);
 
@@ -851,8 +852,8 @@ impl<'tcx> UniversalRegionIndices<'tcx> {
     /// in later and instantiate the late-bound regions, and then we
     /// insert the `ReLateParam` version of those into the map as
     /// well. These are used for error reporting.
+    #[instrument(level = "debug", skip(self))]
     fn insert_late_bound_region(&mut self, r: ty::Region<'tcx>, vid: ty::RegionVid) {
-        debug!("insert_late_bound_region({:?}, {:?})", r, vid);
         self.indices.insert(r, vid);
     }
 

compiler/rustc_infer/src/infer/outlives/components.rs

@@ -211,9 +211,10 @@ pub(super) fn compute_alias_components_recursive<'tcx>(
     let ty::Alias(kind, alias_ty) = alias_ty.kind() else {
         unreachable!("can only call `compute_alias_components_recursive` on an alias type")
     };
-    let opt_variances = if *kind == ty::Opaque { tcx.variances_of(alias_ty.def_id) } else { &[] };
+    let opt_variances =
+        if matches!(kind, ty::Opaque) { tcx.variances_of(alias_ty.def_id) } else { &[] };
     for (index, child) in alias_ty.args.iter().enumerate() {
-        if opt_variances.get(index) == Some(&ty::Bivariant) {
+        if matches!(opt_variances.get(index), Some(ty::Bivariant)) {
             continue;
         }
         if !visited.insert(child) {

compiler/rustc_infer/src/infer/outlives/env.rs

@@ -26,7 +26,7 @@ use super::explicit_outlives_bounds;
 /// refactoring here, since the setup with NLL is quite different.
 /// For example, NLL has no need of `RegionRelations`, and is solely
 /// interested in the `OutlivesEnvironment`. -nmatsakis
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 pub struct OutlivesEnvironment<'tcx> {
     pub param_env: ty::ParamEnv<'tcx>,
     free_region_map: FreeRegionMap<'tcx>,

compiler/rustc_infer/src/infer/outlives/obligations.rs

@@ -89,13 +89,13 @@ impl<'tcx> InferCtxt<'tcx> {
         inner.region_obligations.push(obligation);
     }
 
+    #[instrument(level = "debug", skip(self))]
     pub fn register_region_obligation_with_cause(
         &self,
         sup_type: Ty<'tcx>,
         sub_region: Region<'tcx>,
         cause: &ObligationCause<'tcx>,
     ) {
-        debug!(?sup_type, ?sub_region, ?cause);
         let origin = SubregionOrigin::from_obligation_cause(cause, || {
             infer::RelateParamBound(
                 cause.span,
@@ -125,7 +125,7 @@ impl<'tcx> InferCtxt<'tcx> {
     /// flow of the inferencer. The key point is that it is
     /// invoked after all type-inference variables have been bound --
     /// right before lexical region resolution.
-    #[instrument(level = "debug", skip(self, outlives_env, deeply_normalize_ty))]
+    #[instrument(level = "debug", skip(self, deeply_normalize_ty))]
     pub fn process_registered_region_obligations(
         &self,
         outlives_env: &OutlivesEnvironment<'tcx>,
@@ -185,6 +185,7 @@ impl<'tcx> InferCtxt<'tcx> {
                     outlives_env.region_bound_pairs(),
                     None,
                     &normalized_caller_bounds,
+                    &[],
                 );
                 let category = origin.to_constraint_category();
                 outlives.type_must_outlive(origin, sup_type, sub_region, category);
@@ -240,6 +241,7 @@ where
         region_bound_pairs: &'cx RegionBoundPairs<'tcx>,
         implicit_region_bound: Option<ty::Region<'tcx>>,
         caller_bounds: &'cx [ty::PolyTypeOutlivesPredicate<'tcx>],
+        projection_predicates: &'cx [ty::PolyTypeProjectionPredicate<'tcx>],
     ) -> Self {
         Self {
             delegate,
@@ -249,6 +251,7 @@ where
                 region_bound_pairs,
                 implicit_region_bound,
                 caller_bounds,
+                projection_predicates,
             ),
         }
     }
@@ -319,7 +322,10 @@ where
         region: ty::Region<'tcx>,
         param_ty: ty::ParamTy,
     ) {
-        let verify_bound = self.verify_bound.param_or_placeholder_bound(param_ty.to_ty(self.tcx));
+        let verify_bound = self
+            .verify_bound
+            .param_or_placeholder_bound(param_ty.to_ty(self.tcx), &mut Default::default());
+        debug!("param_ty_must_outlive: pushing {:?}", verify_bound);
         self.delegate.push_verify(origin, GenericKind::Param(param_ty), region, verify_bound);
     }
 
@@ -330,9 +336,11 @@ where
         region: ty::Region<'tcx>,
         placeholder_ty: ty::PlaceholderType,
     ) {
-        let verify_bound = self
-            .verify_bound
-            .param_or_placeholder_bound(Ty::new_placeholder(self.tcx, placeholder_ty));
+        let verify_bound = self.verify_bound.param_or_placeholder_bound(
+            Ty::new_placeholder(self.tcx, placeholder_ty),
+            &mut Default::default(),
+        );
+        debug!("placeholder_ty_must_outlive: pushing {:?}", verify_bound);
         self.delegate.push_verify(
             origin,
             GenericKind::Placeholder(placeholder_ty),

compiler/rustc_infer/src/infer/outlives/verify.rs

@@ -24,6 +24,7 @@ pub struct VerifyBoundCx<'cx, 'tcx> {
     /// setting  `'?0` to `'empty`.
     implicit_region_bound: Option<ty::Region<'tcx>>,
     caller_bounds: &'cx [ty::PolyTypeOutlivesPredicate<'tcx>],
+    projection_predicates: &'cx [ty::PolyTypeProjectionPredicate<'tcx>],
 }
 
 impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
@@ -32,12 +33,23 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
         region_bound_pairs: &'cx RegionBoundPairs<'tcx>,
         implicit_region_bound: Option<ty::Region<'tcx>>,
         caller_bounds: &'cx [ty::PolyTypeOutlivesPredicate<'tcx>],
+        projection_predicates: &'cx [ty::PolyTypeProjectionPredicate<'tcx>],
     ) -> Self {
-        Self { tcx, region_bound_pairs, implicit_region_bound, caller_bounds }
+        Self {
+            tcx,
+            region_bound_pairs,
+            implicit_region_bound,
+            caller_bounds,
+            projection_predicates,
+        }
     }
 
     #[instrument(level = "debug", skip(self))]
-    pub fn param_or_placeholder_bound(&self, ty: Ty<'tcx>) -> VerifyBound<'tcx> {
+    pub fn param_or_placeholder_bound(
+        &self,
+        ty: Ty<'tcx>,
+        visited: &mut SsoHashSet<GenericArg<'tcx>>,
+    ) -> VerifyBound<'tcx> {
         // Start with anything like `T: 'a` we can scrape from the
         // environment. If the environment contains something like
         // `for<'a> T: 'a`, then we know that `T` outlives everything.
@@ -56,6 +68,28 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
             }
         }
 
+        // A parameter or placeholder bound can also be aliased to an associated type
+        // so we need to inspect in the "reverse"
+        for &predicate in self.projection_predicates {
+            let ty::ProjectionPredicate { term, projection_ty } =
+                self.tcx.erase_regions(predicate).skip_binder();
+            if let Some(term) = term.ty()
+                && ty == term
+            {
+                debug!(?term, ?projection_ty, "found a matching predicate");
+                let alias_ty_as_ty = projection_ty.to_ty(self.tcx);
+                let mut components = smallvec![];
+                compute_alias_components_recursive(
+                    self.tcx,
+                    alias_ty_as_ty,
+                    &mut components,
+                    visited,
+                );
+                debug!(?components);
+                param_bounds.push(self.bound_from_components(&components, visited));
+            }
+        }
+
         // Add in the default bound of fn body that applies to all in
         // scope type parameters:
         if let Some(r) = self.implicit_region_bound {
@@ -163,10 +197,11 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     ) -> VerifyBound<'tcx> {
         match *component {
             Component::Region(lt) => VerifyBound::OutlivedBy(lt),
-            Component::Param(param_ty) => self.param_or_placeholder_bound(param_ty.to_ty(self.tcx)),
-            Component::Placeholder(placeholder_ty) => {
-                self.param_or_placeholder_bound(Ty::new_placeholder(self.tcx, placeholder_ty))
+            Component::Param(param_ty) => {
+                self.param_or_placeholder_bound(param_ty.to_ty(self.tcx), visited)
             }
+            Component::Placeholder(placeholder_ty) => self
+                .param_or_placeholder_bound(Ty::new_placeholder(self.tcx, placeholder_ty), visited),
             Component::Alias(alias_ty) => self.alias_bound(alias_ty, visited),
             Component::EscapingAlias(ref components) => {
                 self.bound_from_components(components, visited)

compiler/rustc_middle/src/ty/mod.rs

@@ -94,9 +94,9 @@ pub use self::predicate::{
     ExistentialTraitRef, NormalizesTo, OutlivesPredicate, PolyCoercePredicate,
     PolyExistentialPredicate, PolyExistentialProjection, PolyExistentialTraitRef,
     PolyProjectionPredicate, PolyRegionOutlivesPredicate, PolySubtypePredicate, PolyTraitPredicate,
-    PolyTraitRef, PolyTypeOutlivesPredicate, Predicate, PredicateKind, ProjectionPredicate,
-    RegionOutlivesPredicate, SubtypePredicate, ToPolyTraitRef, ToPredicate, TraitPredicate,
-    TraitRef, TypeOutlivesPredicate,
+    PolyTraitRef, PolyTypeOutlivesPredicate, PolyTypeProjectionPredicate, Predicate, PredicateKind,
+    ProjectionPredicate, RegionOutlivesPredicate, SubtypePredicate, ToPolyTraitRef, ToPredicate,
+    TraitPredicate, TraitRef, TypeOutlivesPredicate,
 };
 pub use self::region::{
     BoundRegion, BoundRegionKind, BoundRegionKind::*, EarlyParamRegion, LateParamRegion, Region,

compiler/rustc_middle/src/ty/predicate.rs

@@ -706,6 +706,7 @@ pub type RegionOutlivesPredicate<'tcx> = OutlivesPredicate<ty::Region<'tcx>, ty:
 pub type TypeOutlivesPredicate<'tcx> = OutlivesPredicate<Ty<'tcx>, ty::Region<'tcx>>;
 pub type PolyRegionOutlivesPredicate<'tcx> = ty::Binder<'tcx, RegionOutlivesPredicate<'tcx>>;
 pub type PolyTypeOutlivesPredicate<'tcx> = ty::Binder<'tcx, TypeOutlivesPredicate<'tcx>>;
+pub type PolyTypeProjectionPredicate<'tcx> = ty::Binder<'tcx, ProjectionPredicate<'tcx>>;
 
 /// Encodes that `a` must be a subtype of `b`. The `a_is_expected` flag indicates
 /// whether the `a` type is the type that we should label as "expected" when