From 4d92a20ed442c6181bc010f50b7a8b3a2985dfd1 Mon Sep 17 00:00:00 2001
From: Lukas Markeffsky <@>
Date: Mon, 5 Feb 2024 15:14:16 +0100
Subject: [PATCH] new solver: improve normalization of `Pointee::Metadata`

---
 compiler/rustc_middle/src/ty/predicate.rs     |  4 ++++
 .../src/solve/normalizes_to/mod.rs            | 20 +++++++++----------
 tests/ui/traits/pointee-normalize-equate.rs   |  2 ++
 3 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/compiler/rustc_middle/src/ty/predicate.rs b/compiler/rustc_middle/src/ty/predicate.rs
index 7c5b49512ae50..09913953127c1 100644
--- a/compiler/rustc_middle/src/ty/predicate.rs
+++ b/compiler/rustc_middle/src/ty/predicate.rs
@@ -814,6 +814,10 @@ impl<'tcx> NormalizesTo<'tcx> {
     pub fn def_id(self) -> DefId {
         self.alias.def_id
     }
+
+    pub fn as_projection(self) -> ProjectionPredicate<'tcx> {
+        ProjectionPredicate { projection_ty: self.alias, term: self.term }
+    }
 }
 
 pub trait ToPolyTraitRef<'tcx> {
diff --git a/compiler/rustc_trait_selection/src/solve/normalizes_to/mod.rs b/compiler/rustc_trait_selection/src/solve/normalizes_to/mod.rs
index 9f1b4a09a20ba..2eed7f057c586 100644
--- a/compiler/rustc_trait_selection/src/solve/normalizes_to/mod.rs
+++ b/compiler/rustc_trait_selection/src/solve/normalizes_to/mod.rs
@@ -378,6 +378,8 @@ impl<'tcx> assembly::GoalKind<'tcx> for NormalizesTo<'tcx> {
         goal: Goal<'tcx, Self>,
     ) -> QueryResult<'tcx> {
         let tcx = ecx.tcx();
+        let metadata_def_id = tcx.require_lang_item(LangItem::Metadata, None);
+        assert_eq!(metadata_def_id, goal.predicate.def_id());
         ecx.probe_misc_candidate("builtin pointee").enter(|ecx| {
             let metadata_ty = match goal.predicate.self_ty().kind() {
                 ty::Bool
@@ -422,13 +424,11 @@ impl<'tcx> assembly::GoalKind<'tcx> for NormalizesTo<'tcx> {
 
                 ty::Adt(def, args) if def.is_struct() => match def.non_enum_variant().tail_opt() {
                     None => tcx.types.unit,
-                    Some(field_def) => {
-                        let self_ty = field_def.ty(tcx, args);
+                    Some(tail_def) => {
+                        let tail_ty = tail_def.ty(tcx, args);
+                        let predicate = goal.predicate.with_self_ty(tcx, tail_ty).as_projection();
                         // FIXME(-Znext-solver=coinductive): Should this be `GoalSource::ImplWhereBound`?
-                        ecx.add_goal(
-                            GoalSource::Misc,
-                            goal.with(tcx, goal.predicate.with_self_ty(tcx, self_ty)),
-                        );
+                        ecx.add_goal(GoalSource::Misc, goal.with(tcx, predicate));
                         return ecx
                             .evaluate_added_goals_and_make_canonical_response(Certainty::Yes);
                     }
@@ -437,12 +437,10 @@ impl<'tcx> assembly::GoalKind<'tcx> for NormalizesTo<'tcx> {
 
                 ty::Tuple(elements) => match elements.last() {
                     None => tcx.types.unit,
-                    Some(&self_ty) => {
+                    Some(&tail_ty) => {
+                        let predicate = goal.predicate.with_self_ty(tcx, tail_ty).as_projection();
                         // FIXME(-Znext-solver=coinductive): Should this be `GoalSource::ImplWhereBound`?
-                        ecx.add_goal(
-                            GoalSource::Misc,
-                            goal.with(tcx, goal.predicate.with_self_ty(tcx, self_ty)),
-                        );
+                        ecx.add_goal(GoalSource::Misc, goal.with(tcx, predicate));
                         return ecx
                             .evaluate_added_goals_and_make_canonical_response(Certainty::Yes);
                     }
diff --git a/tests/ui/traits/pointee-normalize-equate.rs b/tests/ui/traits/pointee-normalize-equate.rs
index 218b5110ef2b3..e6267a134b228 100644
--- a/tests/ui/traits/pointee-normalize-equate.rs
+++ b/tests/ui/traits/pointee-normalize-equate.rs
@@ -1,4 +1,6 @@
 // check-pass
+// revisions: old next
+//[next] compile-flags: -Znext-solver
 
 #![feature(ptr_metadata)]