From 24db8eaefd794624ba79569bfcfaed65d8134634 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Thu, 21 Mar 2024 16:50:10 -0400
Subject: [PATCH] Remove TypeAndMut from relate

---
 compiler/rustc_middle/src/ty/relate.rs | 61 ++++++++++++++------------
 1 file changed, 32 insertions(+), 29 deletions(-)

diff --git a/compiler/rustc_middle/src/ty/relate.rs b/compiler/rustc_middle/src/ty/relate.rs
index 990e78aff8af..764ee8d5652c 100644
--- a/compiler/rustc_middle/src/ty/relate.rs
+++ b/compiler/rustc_middle/src/ty/relate.rs
@@ -94,28 +94,6 @@ pub trait Relate<'tcx>: TypeFoldable<TyCtxt<'tcx>> + PartialEq + Copy {
 ///////////////////////////////////////////////////////////////////////////
 // Relate impls
 
-pub fn relate_type_and_mut<'tcx, R: TypeRelation<'tcx>>(
-    relation: &mut R,
-    a: ty::TypeAndMut<'tcx>,
-    b: ty::TypeAndMut<'tcx>,
-    base_ty: Ty<'tcx>,
-) -> RelateResult<'tcx, ty::TypeAndMut<'tcx>> {
-    debug!("{}.mts({:?}, {:?})", relation.tag(), a, b);
-    if a.mutbl != b.mutbl {
-        Err(TypeError::Mutability)
-    } else {
-        let mutbl = a.mutbl;
-        let (variance, info) = match mutbl {
-            hir::Mutability::Not => (ty::Covariant, ty::VarianceDiagInfo::None),
-            hir::Mutability::Mut => {
-                (ty::Invariant, ty::VarianceDiagInfo::Invariant { ty: base_ty, param_index: 0 })
-            }
-        };
-        let ty = relation.relate_with_variance(variance, info, a.ty, b.ty)?;
-        Ok(ty::TypeAndMut { ty, mutbl })
-    }
-}
-
 #[inline]
 pub fn relate_args_invariantly<'tcx, R: TypeRelation<'tcx>>(
     relation: &mut R,
@@ -465,17 +443,42 @@ pub fn structurally_relate_tys<'tcx, R: TypeRelation<'tcx>>(
             Ok(Ty::new_coroutine_closure(tcx, a_id, args))
         }
 
-        (&ty::RawPtr(a_mt), &ty::RawPtr(b_mt)) => {
-            let mt = relate_type_and_mut(relation, a_mt, b_mt, a)?;
-            Ok(Ty::new_ptr(tcx, mt))
+        (
+            &ty::RawPtr(ty::TypeAndMut { ty: a_ty, mutbl: a_mutbl }),
+            &ty::RawPtr(ty::TypeAndMut { ty: b_ty, mutbl: b_mutbl }),
+        ) => {
+            if a_mutbl != b_mutbl {
+                return Err(TypeError::Mutability);
+            }
+
+            let (variance, info) = match a_mutbl {
+                hir::Mutability::Not => (ty::Covariant, ty::VarianceDiagInfo::None),
+                hir::Mutability::Mut => {
+                    (ty::Invariant, ty::VarianceDiagInfo::Invariant { ty: a, param_index: 0 })
+                }
+            };
+
+            let ty = relation.relate_with_variance(variance, info, a_ty, b_ty)?;
+
+            Ok(Ty::new_ptr(tcx, ty::TypeAndMut { mutbl: a_mutbl, ty }))
         }
 
         (&ty::Ref(a_r, a_ty, a_mutbl), &ty::Ref(b_r, b_ty, b_mutbl)) => {
+            if a_mutbl != b_mutbl {
+                return Err(TypeError::Mutability);
+            }
+
+            let (variance, info) = match a_mutbl {
+                hir::Mutability::Not => (ty::Covariant, ty::VarianceDiagInfo::None),
+                hir::Mutability::Mut => {
+                    (ty::Invariant, ty::VarianceDiagInfo::Invariant { ty: a, param_index: 0 })
+                }
+            };
+
             let r = relation.relate(a_r, b_r)?;
-            let a_mt = ty::TypeAndMut { ty: a_ty, mutbl: a_mutbl };
-            let b_mt = ty::TypeAndMut { ty: b_ty, mutbl: b_mutbl };
-            let mt = relate_type_and_mut(relation, a_mt, b_mt, a)?;
-            Ok(Ty::new_ref(tcx, r, mt))
+            let ty = relation.relate_with_variance(variance, info, a_ty, b_ty)?;
+
+            Ok(Ty::new_ref(tcx, r, ty::TypeAndMut { mutbl: a_mutbl, ty }))
         }
 
         (&ty::Array(a_t, sz_a), &ty::Array(b_t, sz_b)) => {