From 9b9c7d0ecc9d902b3ed5eac2f06f8669fed57f43 Mon Sep 17 00:00:00 2001
From: Maybe Waffle <waffle.lapkin@gmail.com>
Date: Wed, 23 Nov 2022 18:22:26 +0000
Subject: [PATCH] Depend on `Mutability` ordering

---
 compiler/rustc_hir_analysis/src/coherence/builtin.rs | 2 +-
 compiler/rustc_hir_typeck/src/_match.rs              | 5 +----
 compiler/rustc_hir_typeck/src/cast.rs                | 2 +-
 compiler/rustc_hir_typeck/src/coercion.rs            | 6 +-----
 compiler/rustc_lint/src/builtin.rs                   | 4 ++--
 5 files changed, 6 insertions(+), 13 deletions(-)

diff --git a/compiler/rustc_hir_analysis/src/coherence/builtin.rs b/compiler/rustc_hir_analysis/src/coherence/builtin.rs
index 11661215ae1..70943eb7943 100644
--- a/compiler/rustc_hir_analysis/src/coherence/builtin.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/builtin.rs
@@ -370,7 +370,7 @@ pub fn coerce_unsized_info<'tcx>(tcx: TyCtxt<'tcx>, impl_did: DefId) -> CoerceUn
     let check_mutbl = |mt_a: ty::TypeAndMut<'tcx>,
                        mt_b: ty::TypeAndMut<'tcx>,
                        mk_ptr: &dyn Fn(Ty<'tcx>) -> Ty<'tcx>| {
-        if (mt_a.mutbl, mt_b.mutbl) == (hir::Mutability::Not, hir::Mutability::Mut) {
+        if mt_a.mutbl < mt_b.mutbl {
             infcx
                 .err_ctxt()
                 .report_mismatched_types(
diff --git a/compiler/rustc_hir_typeck/src/_match.rs b/compiler/rustc_hir_typeck/src/_match.rs
index 31432bb6e41..1d55378b91b 100644
--- a/compiler/rustc_hir_typeck/src/_match.rs
+++ b/compiler/rustc_hir_typeck/src/_match.rs
@@ -572,8 +572,5 @@ pub(crate) fn opt_suggest_box_span(
 }
 
 fn arms_contain_ref_bindings<'tcx>(arms: &'tcx [hir::Arm<'tcx>]) -> Option<hir::Mutability> {
-    arms.iter().filter_map(|a| a.pat.contains_explicit_ref_binding()).max_by_key(|m| match *m {
-        hir::Mutability::Mut => 1,
-        hir::Mutability::Not => 0,
-    })
+    arms.iter().filter_map(|a| a.pat.contains_explicit_ref_binding()).max()
 }
diff --git a/compiler/rustc_hir_typeck/src/cast.rs b/compiler/rustc_hir_typeck/src/cast.rs
index 5e1e44dcb6d..1cea8c9dadc 100644
--- a/compiler/rustc_hir_typeck/src/cast.rs
+++ b/compiler/rustc_hir_typeck/src/cast.rs
@@ -951,7 +951,7 @@ fn check_ref_cast(
         m_cast: ty::TypeAndMut<'tcx>,
     ) -> Result<CastKind, CastError> {
         // array-ptr-cast: allow mut-to-mut, mut-to-const, const-to-const
-        if m_expr.mutbl == hir::Mutability::Mut || m_cast.mutbl == hir::Mutability::Not {
+        if m_expr.mutbl >= m_cast.mutbl {
             if let ty::Array(ety, _) = m_expr.ty.kind() {
                 // Due to the limitations of LLVM global constants,
                 // region pointers end up pointing at copies of
diff --git a/compiler/rustc_hir_typeck/src/coercion.rs b/compiler/rustc_hir_typeck/src/coercion.rs
index 3f0d0a76027..0dffde40eeb 100644
--- a/compiler/rustc_hir_typeck/src/coercion.rs
+++ b/compiler/rustc_hir_typeck/src/coercion.rs
@@ -108,11 +108,7 @@ fn coerce_mutbls<'tcx>(
     from_mutbl: hir::Mutability,
     to_mutbl: hir::Mutability,
 ) -> RelateResult<'tcx, ()> {
-    match (from_mutbl, to_mutbl) {
-        (hir::Mutability::Mut, hir::Mutability::Mut | hir::Mutability::Not)
-        | (hir::Mutability::Not, hir::Mutability::Not) => Ok(()),
-        (hir::Mutability::Not, hir::Mutability::Mut) => Err(TypeError::Mutability),
-    }
+    if from_mutbl >= to_mutbl { Ok(()) } else { Err(TypeError::Mutability) }
 }
 
 /// Do not require any adjustments, i.e. coerce `x -> x`.
diff --git a/compiler/rustc_lint/src/builtin.rs b/compiler/rustc_lint/src/builtin.rs
index ada3c3b67fb..914ff1ab3da 100644
--- a/compiler/rustc_lint/src/builtin.rs
+++ b/compiler/rustc_lint/src/builtin.rs
@@ -1268,10 +1268,10 @@ fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
 
 impl<'tcx> LateLintPass<'tcx> for MutableTransmutes {
     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &hir::Expr<'_>) {
-        if let Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) =
+        if let Some((&ty::Ref(_, _, from_mutbl), &ty::Ref(_, _, to_mutbl))) =
             get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (ty1.kind(), ty2.kind()))
         {
-            if to_mt == hir::Mutability::Mut && from_mt == hir::Mutability::Not {
+            if from_mutbl < to_mutbl {
                 cx.struct_span_lint(
                     MUTABLE_TRANSMUTES,
                     expr.span,