Use the power of adding helper function to simplify code w/ Mutability

compiler/rustc_ast/src/ast.rs

@@ -775,8 +775,9 @@ pub enum PatKind {
 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Copy)]
 #[derive(HashStable_Generic, Encodable, Decodable)]
 pub enum Mutability {
-    Mut,
+    // N.B. Order is deliberate, so that Not < Mut
     Not,
+    Mut,
 }
 
 impl Mutability {
@@ -787,12 +788,39 @@ impl Mutability {
         }
     }
 
-    pub fn prefix_str(&self) -> &'static str {
+    /// Returns `""` (empty string) or `"mut "` depending on the mutability.
+    pub fn prefix_str(self) -> &'static str {
         match self {
             Mutability::Mut => "mut ",
             Mutability::Not => "",
         }
     }
+
+    /// Returns `"&"` or `"&mut "` depending on the mutability.
+    pub fn ref_prefix_str(self) -> &'static str {
+        match self {
+            Mutability::Not => "&",
+            Mutability::Mut => "&mut ",
+        }
+    }
+
+    /// Returns `""` (empty string) or `"mutably "` depending on the mutability.
+    pub fn mutably_str(self) -> &'static str {
+        match self {
+            Mutability::Not => "",
+            Mutability::Mut => "mutably ",
+        }
+    }
+
+    /// Return `true` if self is mutable
+    pub fn is_mut(self) -> bool {
+        matches!(self, Self::Mut)
+    }
+
+    /// Return `true` if self is **not** mutable
+    pub fn is_not(self) -> bool {
+        matches!(self, Self::Not)
+    }
 }
 
 /// The kind of borrow in an `AddrOf` expression,

compiler/rustc_ast_lowering/src/lib.rs

@@ -1781,14 +1781,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     // Given we are only considering `ImplicitSelf` types, we needn't consider
                     // the case where we have a mutable pattern to a reference as that would
                     // no longer be an `ImplicitSelf`.
-                    TyKind::Rptr(_, mt)
-                        if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
-                    {
-                        hir::ImplicitSelfKind::MutRef
-                    }
-                    TyKind::Rptr(_, mt) if mt.ty.kind.is_implicit_self() => {
-                        hir::ImplicitSelfKind::ImmRef
-                    }
+                    TyKind::Rptr(_, mt) if mt.ty.kind.is_implicit_self() => match mt.mutbl {
+                        hir::Mutability::Not => hir::ImplicitSelfKind::ImmRef,
+                        hir::Mutability::Mut => hir::ImplicitSelfKind::MutRef,
+                    },
                     _ => hir::ImplicitSelfKind::None,
                 }
             }),

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -571,19 +571,12 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 let moved_place = &self.move_data.move_paths[move_out.path].place;
                 let move_spans = self.move_spans(moved_place.as_ref(), move_out.source);
                 let move_span = move_spans.args_or_use();
-                let suggestion = if borrow_level == hir::Mutability::Mut {
-                    "&mut ".to_string()
-                } else {
-                    "&".to_string()
-                };
+                let suggestion = borrow_level.ref_prefix_str().to_owned();
                 (move_span.shrink_to_lo(), suggestion)
             })
             .collect();
         err.multipart_suggestion_verbose(
-            &format!(
-                "consider {}borrowing {value_name}",
-                if borrow_level == hir::Mutability::Mut { "mutably " } else { "" }
-            ),
+            format!("consider {}borrowing {value_name}", borrow_level.mutably_str()),
             sugg,
             Applicability::MaybeIncorrect,
         );

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -389,13 +389,13 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
             // diagnostic: if the span starts with a mutable borrow of
             // a local variable, then just suggest the user remove it.
             PlaceRef { local: _, projection: [] }
-                if {
-                    if let Ok(snippet) = self.infcx.tcx.sess.source_map().span_to_snippet(span) {
-                        snippet.starts_with("&mut ")
-                    } else {
-                        false
-                    }
-                } =>
+                if self
+                    .infcx
+                    .tcx
+                    .sess
+                    .source_map()
+                    .span_to_snippet(span)
+                    .map_or(false, |snippet| snippet.starts_with("&mut ")) =>
             {
                 err.span_label(span, format!("cannot {ACT}", ACT = act));
                 err.span_suggestion(

compiler/rustc_codegen_cranelift/src/constant.rs

@@ -257,9 +257,9 @@ pub(crate) fn data_id_for_alloc_id(
     mutability: rustc_hir::Mutability,
 ) -> DataId {
     cx.todo.push(TodoItem::Alloc(alloc_id));
-    *cx.anon_allocs.entry(alloc_id).or_insert_with(|| {
-        module.declare_anonymous_data(mutability == rustc_hir::Mutability::Mut, false).unwrap()
-    })
+    *cx.anon_allocs
+        .entry(alloc_id)
+        .or_insert_with(|| module.declare_anonymous_data(mutability.is_mut(), false).unwrap())
 }
 
 fn data_id_for_static(
@@ -343,12 +343,7 @@ fn define_all_allocs(tcx: TyCtxt<'_>, module: &mut dyn Module, cx: &mut Constant
                     }
                 };
                 let data_id = *cx.anon_allocs.entry(alloc_id).or_insert_with(|| {
-                    module
-                        .declare_anonymous_data(
-                            alloc.inner().mutability == rustc_hir::Mutability::Mut,
-                            false,
-                        )
-                        .unwrap()
+                    module.declare_anonymous_data(alloc.inner().mutability.is_mut(), false).unwrap()
                 });
                 (data_id, alloc, None)
             }

compiler/rustc_codegen_llvm/src/intrinsic.rs

@@ -1500,7 +1500,7 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
         let (_, element_ty1) = arg_tys[1].simd_size_and_type(bx.tcx());
         let (_, element_ty2) = arg_tys[2].simd_size_and_type(bx.tcx());
         let (pointer_count, underlying_ty) = match element_ty1.kind() {
-            ty::RawPtr(p) if p.ty == in_elem && p.mutbl == hir::Mutability::Mut => {
+            ty::RawPtr(p) if p.ty == in_elem && p.mutbl.is_mut() => {
                 (ptr_count(element_ty1), non_ptr(element_ty1))
             }
             _ => {

compiler/rustc_hir/src/pat_util.rs

@@ -130,10 +130,7 @@ impl hir::Pat<'_> {
     pub fn contains_explicit_ref_binding(&self) -> Option<hir::Mutability> {
         let mut result = None;
         self.each_binding(|annotation, _, _, _| match annotation {
-            hir::BindingAnnotation::REF => match result {
-                None | Some(hir::Mutability::Not) => result = Some(hir::Mutability::Not),
-                _ => {}
-            },
+            hir::BindingAnnotation::REF if result.is_none() => result = Some(hir::Mutability::Not),
             hir::BindingAnnotation::REF_MUT => result = Some(hir::Mutability::Mut),
             _ => {}
         });

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(

compiler/rustc_hir_analysis/src/coherence/orphan.rs

@@ -292,7 +292,7 @@ fn emit_newtype_suggestion_for_raw_ptr(
     diag: &mut Diagnostic,
 ) {
     if !self_ty.needs_subst() {
-        let mut_key = if ptr_ty.mutbl == rustc_middle::mir::Mutability::Mut { "mut " } else { "" };
+        let mut_key = ptr_ty.mutbl.prefix_str();
         let msg_sugg = "consider introducing a new wrapper type".to_owned();
         let sugg = vec![
             (

compiler/rustc_hir_pretty/src/lib.rs

@@ -398,7 +398,7 @@ impl<'a> State<'a> {
             }
             hir::ForeignItemKind::Static(t, m) => {
                 self.head("static");
-                if m == hir::Mutability::Mut {
+                if m.is_mut() {
                     self.word_space("mut");
                 }
                 self.print_ident(item.ident);
@@ -519,7 +519,7 @@ impl<'a> State<'a> {
             }
             hir::ItemKind::Static(ty, m, expr) => {
                 self.head("static");
-                if m == hir::Mutability::Mut {
+                if m.is_mut() {
                     self.word_space("mut");
                 }
                 self.print_ident(item.ident);

compiler/rustc_hir_typeck/src/_match.rs

@@ -572,8 +572,5 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 }
 
 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()
 }

compiler/rustc_hir_typeck/src/callee.rs

@@ -258,15 +258,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         return None;
                     };
 
-                    let mutbl = match mutbl {
-                        hir::Mutability::Not => AutoBorrowMutability::Not,
-                        hir::Mutability::Mut => AutoBorrowMutability::Mut {
-                            // For initial two-phase borrow
-                            // deployment, conservatively omit
-                            // overloaded function call ops.
-                            allow_two_phase_borrow: AllowTwoPhase::No,
-                        },
-                    };
+                    // For initial two-phase borrow
+                    // deployment, conservatively omit
+                    // overloaded function call ops.
+                    let mutbl = AutoBorrowMutability::new(*mutbl, AllowTwoPhase::No);
+
                     autoref = Some(Adjustment {
                         kind: Adjust::Borrow(AutoBorrow::Ref(*region, mutbl)),
                         target: method.sig.inputs()[0],

compiler/rustc_hir_typeck/src/cast.rs

@@ -951,7 +951,7 @@ impl<'a, 'tcx> CastCheck<'tcx> {
         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

compiler/rustc_hir_typeck/src/check.rs

@@ -197,7 +197,7 @@ fn check_panic_info_fn(
     let arg_is_panic_info = match *inputs[0].kind() {
         ty::Ref(region, ty, mutbl) => match *ty.kind() {
             ty::Adt(ref adt, _) => {
-                adt.did() == panic_info_did && mutbl == hir::Mutability::Not && !region.is_static()
+                adt.did() == panic_info_did && mutbl.is_not() && !region.is_static()
             }
             _ => false,
         },

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`.
@@ -456,7 +452,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
             return Err(err);
         };
 
-        if ty == a && mt_a.mutbl == hir::Mutability::Not && autoderef.step_count() == 1 {
+        if ty == a && mt_a.mutbl.is_not() && autoderef.step_count() == 1 {
             // As a special case, if we would produce `&'a *x`, that's
             // a total no-op. We end up with the type `&'a T` just as
             // we started with.  In that case, just skip it
@@ -468,7 +464,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
             // `self.x` both have `&mut `type would be a move of
             // `self.x`, but we auto-coerce it to `foo(&mut *self.x)`,
             // which is a borrow.
-            assert_eq!(mutbl_b, hir::Mutability::Not); // can only coerce &T -> &U
+            assert!(mutbl_b.is_not()); // can only coerce &T -> &U
             return success(vec![], ty, obligations);
         }
 
@@ -482,12 +478,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         let ty::Ref(r_borrow, _, _) = ty.kind() else {
             span_bug!(span, "expected a ref type, got {:?}", ty);
         };
-        let mutbl = match mutbl_b {
-            hir::Mutability::Not => AutoBorrowMutability::Not,
-            hir::Mutability::Mut => {
-                AutoBorrowMutability::Mut { allow_two_phase_borrow: self.allow_two_phase }
-            }
-        };
+        let mutbl = AutoBorrowMutability::new(mutbl_b, self.allow_two_phase);
         adjustments.push(Adjustment {
             kind: Adjust::Borrow(AutoBorrow::Ref(*r_borrow, mutbl)),
             target: ty,
@@ -556,15 +547,12 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
 
                 let coercion = Coercion(self.cause.span);
                 let r_borrow = self.next_region_var(coercion);
-                let mutbl = match mutbl_b {
-                    hir::Mutability::Not => AutoBorrowMutability::Not,
-                    hir::Mutability::Mut => AutoBorrowMutability::Mut {
-                        // We don't allow two-phase borrows here, at least for initial
-                        // implementation. If it happens that this coercion is a function argument,
-                        // the reborrow in coerce_borrowed_ptr will pick it up.
-                        allow_two_phase_borrow: AllowTwoPhase::No,
-                    },
-                };
+
+                // We don't allow two-phase borrows here, at least for initial
+                // implementation. If it happens that this coercion is a function argument,
+                // the reborrow in coerce_borrowed_ptr will pick it up.
+                let mutbl = AutoBorrowMutability::new(mutbl_b, AllowTwoPhase::No);
+
                 Some((
                     Adjustment { kind: Adjust::Deref(None), target: ty_a },
                     Adjustment {