NLL: relate closure to parent fn

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -2619,6 +2619,28 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             );
         }
 
+        // Now equate closure substs to regions inherited from `typeck_root_def_id`. Fixes #98589.
+        let typeck_root_def_id = tcx.typeck_root_def_id(self.body.source.def_id());
+        let typeck_root_substs = ty::InternalSubsts::identity_for_item(tcx, typeck_root_def_id);
+
+        let parent_substs = match tcx.def_kind(def_id) {
+            DefKind::Closure => substs.as_closure().parent_substs(),
+            DefKind::Generator => substs.as_generator().parent_substs(),
+            DefKind::InlineConst => substs.as_inline_const().parent_substs(),
+            other => bug!("unexpected item {:?}", other),
+        };
+        let parent_substs = tcx.mk_substs(parent_substs.iter());
+
+        assert_eq!(typeck_root_substs.len(), parent_substs.len());
+        if let Err(_) = self.eq_substs(
+            typeck_root_substs,
+            parent_substs,
+            Locations::Single(location),
+            ConstraintCategory::BoringNoLocation,
+        ) {
+            bug!("we shouldn't error, this should only impose region constraints");
+        }
+
         tcx.predicates_of(def_id).instantiate(tcx, substs)
     }
 

compiler/rustc_borrowck/src/type_check/relate_tys.rs

@@ -38,6 +38,23 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         .relate(a, b)?;
         Ok(())
     }
+
+    /// Add sufficient constraints to ensure `a == b`. See also [Self::relate_types].
+    pub(super) fn eq_substs(
+        &mut self,
+        a: ty::SubstsRef<'tcx>,
+        b: ty::SubstsRef<'tcx>,
+        locations: Locations,
+        category: ConstraintCategory<'tcx>,
+    ) -> Fallible<()> {
+        let mut relation = TypeRelating::new(
+            self.infcx,
+            NllTypeRelatingDelegate::new(self, locations, category, UniverseInfo::other()),
+            ty::Variance::Invariant,
+        );
+        ty::relate::relate_substs(&mut relation, a, b)?;
+        Ok(())
+    }
 }
 
 struct NllTypeRelatingDelegate<'me, 'bccx, 'tcx> {