From 79228526bfa37f2f0ee9b91671a4342064e85f73 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Tue, 6 Aug 2024 13:33:32 -0400
Subject: [PATCH] Cache supertrait outlives of impl header for soundness check

---
 compiler/rustc_hir_analysis/src/collect.rs    |  1 +
 .../src/collect/item_bounds.rs                | 21 ++++++++++
 compiler/rustc_middle/src/query/mod.rs        |  4 ++
 .../src/traits/select/mod.rs                  | 42 +++++++------------
 4 files changed, 42 insertions(+), 26 deletions(-)

diff --git a/compiler/rustc_hir_analysis/src/collect.rs b/compiler/rustc_hir_analysis/src/collect.rs
index 47ff748547a..8c1e5e78b75 100644
--- a/compiler/rustc_hir_analysis/src/collect.rs
+++ b/compiler/rustc_hir_analysis/src/collect.rs
@@ -67,6 +67,7 @@ pub fn provide(providers: &mut Providers) {
         item_super_predicates: item_bounds::item_super_predicates,
         explicit_item_super_predicates: item_bounds::explicit_item_super_predicates,
         item_non_self_assumptions: item_bounds::item_non_self_assumptions,
+        impl_super_outlives: item_bounds::impl_super_outlives,
         generics_of: generics_of::generics_of,
         predicates_of: predicates_of::predicates_of,
         predicates_defined_on,
diff --git a/compiler/rustc_hir_analysis/src/collect/item_bounds.rs b/compiler/rustc_hir_analysis/src/collect/item_bounds.rs
index 6bff99ea65f..ec48c781c0e 100644
--- a/compiler/rustc_hir_analysis/src/collect/item_bounds.rs
+++ b/compiler/rustc_hir_analysis/src/collect/item_bounds.rs
@@ -212,6 +212,8 @@ pub(super) fn item_super_predicates(
     })
 }
 
+/// This exists as an optimization to compute only the item bounds of the item
+/// that are not `Self` bounds.
 pub(super) fn item_non_self_assumptions(
     tcx: TyCtxt<'_>,
     def_id: DefId,
@@ -226,6 +228,25 @@ pub(super) fn item_non_self_assumptions(
     }
 }
 
+/// This exists as an optimization to compute only the supertraits of this impl's
+/// trait that are outlives bounds.
+pub(super) fn impl_super_outlives(
+    tcx: TyCtxt<'_>,
+    def_id: DefId,
+) -> ty::EarlyBinder<'_, ty::Clauses<'_>> {
+    tcx.impl_trait_header(def_id).expect("expected an impl of trait").trait_ref.map_bound(
+        |trait_ref| {
+            let clause: ty::Clause<'_> = trait_ref.upcast(tcx);
+            tcx.mk_clauses_from_iter(util::elaborate(tcx, [clause]).filter(|clause| {
+                matches!(
+                    clause.kind().skip_binder(),
+                    ty::ClauseKind::TypeOutlives(_) | ty::ClauseKind::RegionOutlives(_)
+                )
+            }))
+        },
+    )
+}
+
 struct AssocTyToOpaque<'tcx> {
     tcx: TyCtxt<'tcx>,
     fn_def_id: DefId,
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index c22c2e985ab..f69f78d4f0f 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -407,6 +407,10 @@ rustc_queries! {
         desc { |tcx| "elaborating item assumptions for `{}`", tcx.def_path_str(key) }
     }
 
+    query impl_super_outlives(key: DefId) -> ty::EarlyBinder<'tcx, ty::Clauses<'tcx>> {
+        desc { |tcx| "elaborating supertrait outlives for trait of `{}`", tcx.def_path_str(key) }
+    }
+
     /// Look up all native libraries this crate depends on.
     /// These are assembled from the following places:
     /// - `extern` blocks (depending on their `link` attributes)
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 1d9a90f0300..1b2767a6a62 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -17,7 +17,6 @@ use rustc_hir::LangItem;
 use rustc_infer::infer::relate::TypeRelation;
 use rustc_infer::infer::BoundRegionConversionTime::{self, HigherRankedType};
 use rustc_infer::infer::DefineOpaqueTypes;
-use rustc_infer::traits::util::elaborate;
 use rustc_infer::traits::TraitObligation;
 use rustc_middle::bug;
 use rustc_middle::dep_graph::{dep_kinds, DepNodeIndex};
@@ -2801,31 +2800,22 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
         }
 
         // Register any outlives obligations from the trait here, cc #124336.
-        if matches!(self.tcx().def_kind(def_id), DefKind::Impl { of_trait: true })
-            && let Some(header) = self.tcx().impl_trait_header(def_id)
-        {
-            let trait_clause: ty::Clause<'tcx> =
-                header.trait_ref.instantiate(self.tcx(), args).upcast(self.tcx());
-            for clause in elaborate(self.tcx(), [trait_clause]) {
-                if matches!(
-                    clause.kind().skip_binder(),
-                    ty::ClauseKind::TypeOutlives(..) | ty::ClauseKind::RegionOutlives(..)
-                ) {
-                    let clause = normalize_with_depth_to(
-                        self,
-                        param_env,
-                        cause.clone(),
-                        recursion_depth,
-                        clause,
-                        &mut obligations,
-                    );
-                    obligations.push(Obligation {
-                        cause: cause.clone(),
-                        recursion_depth,
-                        param_env,
-                        predicate: clause.as_predicate(),
-                    });
-                }
+        if matches!(tcx.def_kind(def_id), DefKind::Impl { of_trait: true }) {
+            for clause in tcx.impl_super_outlives(def_id).iter_instantiated(tcx, args) {
+                let clause = normalize_with_depth_to(
+                    self,
+                    param_env,
+                    cause.clone(),
+                    recursion_depth,
+                    clause,
+                    &mut obligations,
+                );
+                obligations.push(Obligation {
+                    cause: cause.clone(),
+                    recursion_depth,
+                    param_env,
+                    predicate: clause.as_predicate(),
+                });
             }
         }