From f93ee19fd7cd7016a8d6829b40ad7c087a6cd5c4 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Fri, 14 Jun 2024 14:59:03 -0400
Subject: [PATCH] Make ExternalConstraints just carry outlives

---
 compiler/rustc_middle/src/traits/solve.rs     |  3 +-
 .../src/solve/eval_ctxt/canonical.rs          | 40 ++++++++++---------
 2 files changed, 23 insertions(+), 20 deletions(-)

diff --git a/compiler/rustc_middle/src/traits/solve.rs b/compiler/rustc_middle/src/traits/solve.rs
index 0d9ce402c64..fea673eed77 100644
--- a/compiler/rustc_middle/src/traits/solve.rs
+++ b/compiler/rustc_middle/src/traits/solve.rs
@@ -4,7 +4,6 @@ use rustc_macros::{HashStable, TypeFoldable, TypeVisitable};
 use rustc_type_ir as ir;
 pub use rustc_type_ir::solve::*;
 
-use crate::infer::canonical::QueryRegionConstraints;
 use crate::ty::{
     self, FallibleTypeFolder, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeVisitable, TypeVisitor,
 };
@@ -52,7 +51,7 @@ impl<'tcx> std::ops::Deref for ExternalConstraints<'tcx> {
 #[derive(Debug, PartialEq, Eq, Clone, Hash, HashStable, Default, TypeVisitable, TypeFoldable)]
 pub struct ExternalConstraintsData<'tcx> {
     // FIXME: implement this.
-    pub region_constraints: QueryRegionConstraints<'tcx>,
+    pub region_constraints: Vec<ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>>,
     pub opaque_types: Vec<(ty::OpaqueTypeKey<'tcx>, Ty<'tcx>)>,
     pub normalization_nested_goals: NestedNormalizationGoals<'tcx>,
 }
diff --git a/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs b/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs
index 0e0b9e98339..ffbdc639f08 100644
--- a/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs
+++ b/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs
@@ -135,8 +135,7 @@ impl<'tcx> EvalCtxt<'_, InferCtxt<'tcx>> {
         // Remove any trivial region constraints once we've resolved regions
         external_constraints
             .region_constraints
-            .outlives
-            .retain(|(outlives, _)| outlives.0.as_region().map_or(true, |re| re != outlives.1));
+            .retain(|outlives| outlives.0.as_region().map_or(true, |re| re != outlives.1));
 
         let canonical = Canonicalizer::canonicalize(
             self.infcx,
@@ -193,19 +192,23 @@ impl<'tcx> EvalCtxt<'_, InferCtxt<'tcx>> {
             // Cannot use `take_registered_region_obligations` as we may compute the response
             // inside of a `probe` whenever we have multiple choices inside of the solver.
             let region_obligations = self.infcx.inner.borrow().region_obligations().to_owned();
-            let mut region_constraints = self.infcx.with_region_constraints(|region_constraints| {
-                make_query_region_constraints(
-                    self.interner(),
-                    region_obligations.iter().map(|r_o| {
-                        (r_o.sup_type, r_o.sub_region, r_o.origin.to_constraint_category())
-                    }),
-                    region_constraints,
-                )
-            });
-
+            let QueryRegionConstraints { outlives, member_constraints } =
+                self.infcx.with_region_constraints(|region_constraints| {
+                    make_query_region_constraints(
+                        self.interner(),
+                        region_obligations.iter().map(|r_o| {
+                            (r_o.sup_type, r_o.sub_region, r_o.origin.to_constraint_category())
+                        }),
+                        region_constraints,
+                    )
+                });
+            assert_eq!(member_constraints, vec![]);
             let mut seen = FxHashSet::default();
-            region_constraints.outlives.retain(|outlives| seen.insert(*outlives));
-            region_constraints
+            outlives
+                .into_iter()
+                .filter(|(outlives, _)| seen.insert(*outlives))
+                .map(|(outlives, _origin)| outlives)
+                .collect()
         } else {
             Default::default()
         };
@@ -369,16 +372,17 @@ impl<'tcx> EvalCtxt<'_, InferCtxt<'tcx>> {
         }
     }
 
-    fn register_region_constraints(&mut self, region_constraints: &QueryRegionConstraints<'tcx>) {
-        for &(ty::OutlivesPredicate(lhs, rhs), _) in &region_constraints.outlives {
+    fn register_region_constraints(
+        &mut self,
+        outlives: &[ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>],
+    ) {
+        for &ty::OutlivesPredicate(lhs, rhs) in outlives {
             match lhs.unpack() {
                 GenericArgKind::Lifetime(lhs) => self.register_region_outlives(lhs, rhs),
                 GenericArgKind::Type(lhs) => self.register_ty_outlives(lhs, rhs),
                 GenericArgKind::Const(_) => bug!("const outlives: {lhs:?}: {rhs:?}"),
             }
         }
-
-        assert!(region_constraints.member_constraints.is_empty());
     }
 
     fn register_new_opaque_types(&mut self, opaque_types: &[(ty::OpaqueTypeKey<'tcx>, Ty<'tcx>)]) {