borrowck: consolidate mut suggestions

src/librustc/hir/lowering.rs

@@ -907,6 +907,13 @@ impl<'a> LoweringContext<'a> {
                 FunctionRetTy::Default(span) => hir::DefaultReturn(span),
             },
             variadic: decl.variadic,
+            has_implicit_self: decl.inputs.get(0).map_or(false, |arg| {
+                match arg.ty.node {
+                    TyKind::ImplicitSelf => true,
+                    TyKind::Rptr(_, ref mt) => mt.ty.node == TyKind::ImplicitSelf,
+                    _ => false
+                }
+            })
         })
     }
 

src/librustc/hir/mod.rs

@@ -1379,6 +1379,9 @@ pub struct FnDecl {
     pub inputs: HirVec<P<Ty>>,
     pub output: FunctionRetTy,
     pub variadic: bool,
+    /// True if this function has an `self`, `&self` or `&mut self` receiver
+    /// (but not a `self: Xxx` one).
+    pub has_implicit_self: bool,
 }
 
 #[derive(Copy, Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]

src/librustc/middle/mem_categorization.rs

@@ -194,76 +194,75 @@ pub struct cmt_<'tcx> {
 
 pub type cmt<'tcx> = Rc<cmt_<'tcx>>;
 
+pub enum ImmutabilityBlame<'tcx> {
+    ImmLocal(ast::NodeId),
+    ClosureEnv(ast::NodeId),
+    LocalDeref(ast::NodeId),
+    AdtFieldDeref(&'tcx ty::AdtDef, &'tcx ty::FieldDef)
+}
+
 impl<'tcx> cmt_<'tcx> {
-    pub fn get_def(&self) -> Option<ast::NodeId> {
-        match self.cat {
-            Categorization::Deref(ref cmt, ..) |
-            Categorization::Interior(ref cmt, _) |
-            Categorization::Downcast(ref cmt, _) => {
-                if let Categorization::Local(nid) = cmt.cat {
-                    Some(nid)
-                } else {
-                    None
-                }
+    fn resolve_field(&self, field_name: FieldName) -> (&'tcx ty::AdtDef, &'tcx ty::FieldDef)
+    {
+        let adt_def = self.ty.ty_adt_def().unwrap_or_else(|| {
+            bug!("interior cmt {:?} is not an ADT", self)
+        });
+        let variant_def = match self.cat {
+            Categorization::Downcast(_, variant_did) => {
+                adt_def.variant_with_id(variant_did)
             }
-            _ => None
-        }
+            _ => {
+                assert!(adt_def.is_univariant());
+                &adt_def.variants[0]
+            }
+        };
+        let field_def = match field_name {
+            NamedField(name) => variant_def.field_named(name),
+            PositionalField(idx) => &variant_def.fields[idx]
+        };
+        (adt_def, field_def)
     }
 
-    pub fn get_field(&self, name: ast::Name) -> Option<DefId> {
+    pub fn immutability_blame(&self) -> Option<ImmutabilityBlame<'tcx>> {
         match self.cat {
-            Categorization::Deref(ref cmt, ..) |
-            Categorization::Interior(ref cmt, _) |
-            Categorization::Downcast(ref cmt, _) => {
-                if let Categorization::Local(_) = cmt.cat {
-                    if let ty::TyAdt(def, _) = self.ty.sty {
-                        if def.is_struct() {
-                            return def.struct_variant().find_field_named(name).map(|x| x.did);
+            Categorization::Deref(ref base_cmt, _, BorrowedPtr(ty::ImmBorrow, _)) |
+            Categorization::Deref(ref base_cmt, _, Implicit(ty::ImmBorrow, _)) => {
+                // try to figure out where the immutable reference came from
+                match base_cmt.cat {
+                    Categorization::Local(node_id) =>
+                        Some(ImmutabilityBlame::LocalDeref(node_id)),
+                    Categorization::Interior(ref base_cmt, InteriorField(field_name)) => {
+                        let (adt_def, field_def) = base_cmt.resolve_field(field_name);
+                        Some(ImmutabilityBlame::AdtFieldDeref(adt_def, field_def))
+                    }
+                    Categorization::Upvar(Upvar { id, .. }) => {
+                        if let NoteClosureEnv(..) = self.note {
+                            Some(ImmutabilityBlame::ClosureEnv(id.closure_expr_id))
+                        } else {
+                            None
                         }
                     }
-                    None
-                } else {
-                    cmt.get_field(name)
+                    _ => None
                 }
             }
-            _ => None
-        }
-    }
-
-    pub fn get_field_name(&self) -> Option<ast::Name> {
-        match self.cat {
-            Categorization::Interior(_, ref ik) => {
-                if let InteriorKind::InteriorField(FieldName::NamedField(name)) = *ik {
-                    Some(name)
-                } else {
-                    None
-                }
+            Categorization::Local(node_id) => {
+                Some(ImmutabilityBlame::ImmLocal(node_id))
             }
-            Categorization::Deref(ref cmt, ..) |
-            Categorization::Downcast(ref cmt, _) => {
-                cmt.get_field_name()
+            Categorization::Rvalue(..) |
+            Categorization::Upvar(..) |
+            Categorization::Deref(.., UnsafePtr(..)) => {
+                // This should not be reachable up to inference limitations.
+                None
             }
-            _ => None,
-        }
-    }
-
-    pub fn get_arg_if_immutable(&self, map: &hir_map::Map) -> Option<ast::NodeId> {
-        match self.cat {
-            Categorization::Deref(ref cmt, ..) |
-            Categorization::Interior(ref cmt, _) |
-            Categorization::Downcast(ref cmt, _) => {
-                if let Categorization::Local(nid) = cmt.cat {
-                    if let ty::TyAdt(_, _) = self.ty.sty {
-                        if let ty::TyRef(_, ty::TypeAndMut{mutbl: MutImmutable, ..}) = cmt.ty.sty {
-                            return Some(nid);
-                        }
-                    }
-                    None
-                } else {
-                    cmt.get_arg_if_immutable(map)
-                }
+            Categorization::Interior(ref base_cmt, _) |
+            Categorization::Downcast(ref base_cmt, _) |
+            Categorization::Deref(ref base_cmt, _, _) => {
+                base_cmt.immutability_blame()
+            }
+            Categorization::StaticItem => {
+                // Do we want to do something here?
+                None
             }
-            _ => None
         }
     }
 }
@@ -1282,9 +1281,6 @@ pub enum Aliasability {
 #[derive(Copy, Clone, Debug)]
 pub enum AliasableReason {
     AliasableBorrowed,
-    AliasableClosure(ast::NodeId), // Aliasable due to capture Fn closure env
-    AliasableOther,
-    UnaliasableImmutable, // Created as needed upon seeing ImmutableUnique
     AliasableStatic,
     AliasableStaticMut,
 }
@@ -1324,23 +1320,13 @@ impl<'tcx> cmt_<'tcx> {
             Categorization::Deref(ref b, _, Implicit(ty::MutBorrow, _)) |
             Categorization::Deref(ref b, _, BorrowedPtr(ty::UniqueImmBorrow, _)) |
             Categorization::Deref(ref b, _, Implicit(ty::UniqueImmBorrow, _)) |
+            Categorization::Deref(ref b, _, Unique) |
             Categorization::Downcast(ref b, _) |
             Categorization::Interior(ref b, _) => {
                 // Aliasability depends on base cmt
                 b.freely_aliasable()
             }
 
-            Categorization::Deref(ref b, _, Unique) => {
-                let sub = b.freely_aliasable();
-                if b.mutbl.is_mutable() {
-                    // Aliasability depends on base cmt alone
-                    sub
-                } else {
-                    // Do not allow mutation through an immutable box.
-                    ImmutableUnique(Box::new(sub))
-                }
-            }
-
             Categorization::Rvalue(..) |
             Categorization::Local(..) |
             Categorization::Upvar(..) |
@@ -1356,13 +1342,9 @@ impl<'tcx> cmt_<'tcx> {
                 }
             }
 
-            Categorization::Deref(ref base, _, BorrowedPtr(ty::ImmBorrow, _)) |
-            Categorization::Deref(ref base, _, Implicit(ty::ImmBorrow, _)) => {
-                match base.cat {
-                    Categorization::Upvar(Upvar{ id, .. }) =>
-                        FreelyAliasable(AliasableClosure(id.closure_expr_id)),
-                    _ => FreelyAliasable(AliasableBorrowed)
-                }
+            Categorization::Deref(_, _, BorrowedPtr(ty::ImmBorrow, _)) |
+            Categorization::Deref(_, _, Implicit(ty::ImmBorrow, _)) => {
+                FreelyAliasable(AliasableBorrowed)
             }
         }
     }

src/librustc_borrowck/borrowck/gather_loans/mod.rs

@@ -188,14 +188,6 @@ fn check_aliasability<'a, 'tcx>(bccx: &BorrowckCtxt<'a, 'tcx>,
             // user knows what they're doing in these cases.
             Ok(())
         }
-        (mc::Aliasability::ImmutableUnique(_), ty::MutBorrow) => {
-            bccx.report_aliasability_violation(
-                        borrow_span,
-                        loan_cause,
-                        mc::AliasableReason::UnaliasableImmutable,
-                        cmt);
-            Err(())
-        }
         (mc::Aliasability::FreelyAliasable(alias_cause), ty::UniqueImmBorrow) |
         (mc::Aliasability::FreelyAliasable(alias_cause), ty::MutBorrow) => {
             bccx.report_aliasability_violation(
@@ -510,4 +502,3 @@ impl<'a, 'tcx> GatherLoanCtxt<'a, 'tcx> {
         self.move_error_collector.report_potential_errors(self.bccx);
     }
 }
-

src/librustc_borrowck/diagnostics.rs

@@ -198,7 +198,7 @@ fn main() {
 ```
 "##,
 
-E0386: r##"
+/*E0386: r##"
 This error occurs when an attempt is made to mutate the target of a mutable
 reference stored inside an immutable container.
 
@@ -228,7 +228,7 @@ let x: i64 = 1;
 let y: Box<Cell<_>> = Box::new(Cell::new(x));
 y.set(2);
 ```
-"##,
+"##,*/
 
 E0387: r##"
 This error occurs when an attempt is made to mutate or mutably reference data
@@ -1117,6 +1117,6 @@ fn main() {
 }
 
 register_diagnostics! {
-    E0385, // {} in an aliasable location
+//    E0385, // {} in an aliasable location
     E0524, // two closures require unique access to `..` at the same time
 }

src/test/compile-fail/augmented-assignments.rs

@@ -27,7 +27,7 @@ fn main() {
     x;  //~ value moved here
 
     let y = Int(2);
-    //~^use `mut y` here to make mutable
+    //~^ consider changing this to `mut y`
     y   //~ error: cannot borrow immutable local variable `y` as mutable
         //~| cannot borrow
     +=

src/test/compile-fail/borrowck/borrowck-issue-14498.rs

@@ -23,7 +23,7 @@ fn indirect_write_to_imm_box() {
     let mut x: isize = 1;
     let y: Box<_> = box &mut x;
     let p = &y;
-    ***p = 2; //~ ERROR cannot assign to data in an immutable container
+    ***p = 2; //~ ERROR cannot assign to data in a `&` reference
     drop(p);
 }
 
@@ -43,7 +43,6 @@ fn borrow_in_var_from_var_via_imm_box() {
     let p = &y;
     let q = &***p;
     **y = 2; //~ ERROR cannot assign to `**y` because it is borrowed
-    //~^         ERROR cannot assign to data in an immutable container
     drop(p);
     drop(q);
 }
@@ -64,7 +63,6 @@ fn borrow_in_var_from_field_via_imm_box() {
     let p = &y;
     let q = &***p;
     **y = 2; //~ ERROR cannot assign to `**y` because it is borrowed
-    //~^         ERROR cannot assign to data in an immutable container
     drop(p);
     drop(q);
 }
@@ -85,7 +83,6 @@ fn borrow_in_field_from_var_via_imm_box() {
     let p = &y.a;
     let q = &***p;
     **y.a = 2; //~ ERROR cannot assign to `**y.a` because it is borrowed
-    //~^           ERROR cannot assign to data in an immutable container
     drop(p);
     drop(q);
 }
@@ -106,7 +103,6 @@ fn borrow_in_field_from_field_via_imm_box() {
     let p = &y.a;
     let q = &***p;
     **y.a = 2; //~ ERROR cannot assign to `**y.a` because it is borrowed
-    //~^           ERROR cannot assign to data in an immutable container
     drop(p);
     drop(q);
 }

src/test/compile-fail/issue-33819.rs

@@ -12,7 +12,7 @@ fn main() {
     match op {
         Some(ref v) => { let a = &mut v; },
         //~^ ERROR:cannot borrow immutable
-        //~| use `ref mut v` here to make mutable
+        //~| cannot borrow mutably
         None => {},
     }
 }

src/test/compile-fail/mut-suggestion.rs

@@ -17,15 +17,15 @@ impl S {
 }
 
 fn func(arg: S) {
-    //~^ here to make mutable
+    //~^ consider changing this to `mut arg`
     arg.mutate();
     //~^ ERROR cannot borrow immutable argument
     //~| cannot borrow mutably
 }
 
 fn main() {
     let local = S;
-    //~^ here to make mutable
+    //~^ consider changing this to `mut local`
     local.mutate();
     //~^ ERROR cannot borrow immutable local variable
     //~| cannot borrow mutably

src/test/ui/codemap_tests/huge_multispan_highlight.stderr

@@ -2,7 +2,7 @@ error: cannot borrow immutable local variable `x` as mutable
    --> $DIR/huge_multispan_highlight.rs:100:18
     |
 12  |     let x = "foo";
-    |         - use `mut x` here to make mutable
+    |         - consider changing this to `mut x`
 ...
 100 |     let y = &mut x;
     |                  ^ cannot borrow mutably

src/test/ui/did_you_mean/issue-31424.stderr

@@ -10,6 +10,8 @@ error: cannot borrow immutable argument `self` as mutable
 error: cannot borrow immutable argument `self` as mutable
   --> $DIR/issue-31424.rs:23:15
    |
+22 |     fn bar(self: &mut Self) {
+   |            ---- consider changing this to `mut self`
 23 |         (&mut self).bar();
    |               ^^^^ cannot borrow mutably
 

src/test/ui/did_you_mean/issue-35937.rs

@@ -0,0 +1,31 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct Foo {
+    pub v: Vec<String>
+}
+
+fn main() {
+    let f = Foo { v: Vec::new() };
+    f.v.push("cat".to_string());
+}
+
+
+struct S {
+    x: i32,
+}
+fn foo() {
+    let s = S { x: 42 };
+    s.x += 1;
+}
+
+fn bar(s: S) {
+    s.x += 1;
+}

src/test/ui/did_you_mean/issue-35937.stderr

@@ -0,0 +1,26 @@
+error: cannot borrow immutable field `f.v` as mutable
+  --> $DIR/issue-35937.rs:17:5
+   |
+16 |     let f = Foo { v: Vec::new() };
+   |         - consider changing this to `mut f`
+17 |     f.v.push("cat".to_string());
+   |     ^^^ cannot mutably borrow immutable field
+
+error: cannot assign to immutable field `s.x`
+  --> $DIR/issue-35937.rs:26:5
+   |
+25 |     let s = S { x: 42 };
+   |         - consider changing this to `mut s`
+26 |     s.x += 1;
+   |     ^^^^^^^^ cannot mutably borrow immutable field
+
+error: cannot assign to immutable field `s.x`
+  --> $DIR/issue-35937.rs:30:5
+   |
+29 | fn bar(s: S) {
+   |        - consider changing this to `mut s`
+30 |     s.x += 1;
+   |     ^^^^^^^^ cannot mutably borrow immutable field
+
+error: aborting due to 3 previous errors
+

src/test/ui/did_you_mean/issue-38147-2.stderr

@@ -2,7 +2,7 @@ error: cannot borrow immutable borrowed content `*self.s` as mutable
   --> $DIR/issue-38147-2.rs:17:9
    |
 12 |     s: &'a String
-   |     ------------- use `&'a mut String` here to make mutable
+   |        ---------- use `&'a mut String` here to make mutable
 ...
 17 |         self.s.push('x');
    |         ^^^^^^ cannot borrow as mutable

src/test/ui/did_you_mean/issue-38147-3.stderr

@@ -2,10 +2,8 @@ error: cannot borrow immutable borrowed content `*self.s` as mutable
   --> $DIR/issue-38147-3.rs:17:9
    |
 12 |     s: &'a String
-   |     ------------- use `&'a mut String` here to make mutable
+   |        ---------- use `&'a mut String` here to make mutable
 ...
-16 |     fn f(&self) {
-   |          ----- use `&mut self` here to make mutable
 17 |         self.s.push('x');
    |         ^^^^^^ cannot borrow as mutable
 

src/test/ui/did_you_mean/issue-39544.rs

@@ -8,15 +8,46 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-enum X {
+pub enum X {
     Y
 }
 
-struct Z {
+pub struct Z {
     x: X
 }
 
 fn main() {
     let z = Z { x: X::Y };
     let _ = &mut z.x;
 }
+
+impl Z {
+    fn foo<'z>(&'z self) {
+        let _ = &mut self.x;
+    }
+
+    fn foo1(&self, other: &Z) {
+        let _ = &mut self.x;
+        let _ = &mut other.x;
+    }
+
+    fn foo2<'a>(&'a self, other: &Z) {
+        let _ = &mut self.x;
+        let _ = &mut other.x;
+    }
+
+    fn foo3<'a>(self: &'a Self, other: &Z) {
+        let _ = &mut self.x;
+        let _ = &mut other.x;
+    }
+
+    fn foo4(other: &Z) {
+        let _ = &mut other.x;
+    }
+
+}
+
+pub fn with_arg(z: Z, w: &Z) {
+    let _ = &mut z.x;
+    let _ = &mut w.x;
+}

src/test/ui/did_you_mean/issue-39544.stderr

@@ -6,5 +6,89 @@ error: cannot borrow immutable field `z.x` as mutable
 21 |     let _ = &mut z.x;
    |                  ^^^ cannot mutably borrow immutable field
 
-error: aborting due to previous error
+error: cannot borrow immutable field `self.x` as mutable
+  --> $DIR/issue-39544.rs:26:22
+   |
+25 |     fn foo<'z>(&'z self) {
+   |                -------- use `&'z mut self` here to make mutable
+26 |         let _ = &mut self.x;
+   |                      ^^^^^^ cannot mutably borrow immutable field
+
+error: cannot borrow immutable field `self.x` as mutable
+  --> $DIR/issue-39544.rs:30:22
+   |
+29 |     fn foo1(&self, other: &Z) {
+   |             ----- use `&mut self` here to make mutable
+30 |         let _ = &mut self.x;
+   |                      ^^^^^^ cannot mutably borrow immutable field
+
+error: cannot borrow immutable field `other.x` as mutable
+  --> $DIR/issue-39544.rs:31:22
+   |
+29 |     fn foo1(&self, other: &Z) {
+   |                           -- use `&mut Z` here to make mutable
+30 |         let _ = &mut self.x;
+31 |         let _ = &mut other.x;
+   |                      ^^^^^^^ cannot mutably borrow immutable field
+
+error: cannot borrow immutable field `self.x` as mutable
+  --> $DIR/issue-39544.rs:35:22
+   |
+34 |     fn foo2<'a>(&'a self, other: &Z) {
+   |                 -------- use `&'a mut self` here to make mutable
+35 |         let _ = &mut self.x;
+   |                      ^^^^^^ cannot mutably borrow immutable field
+
+error: cannot borrow immutable field `other.x` as mutable
+  --> $DIR/issue-39544.rs:36:22
+   |
+34 |     fn foo2<'a>(&'a self, other: &Z) {
+   |                                  -- use `&mut Z` here to make mutable
+35 |         let _ = &mut self.x;
+36 |         let _ = &mut other.x;
+   |                      ^^^^^^^ cannot mutably borrow immutable field
+
+error: cannot borrow immutable field `self.x` as mutable
+  --> $DIR/issue-39544.rs:40:22
+   |
+39 |     fn foo3<'a>(self: &'a Self, other: &Z) {
+   |                       -------- use `&'a mut Self` here to make mutable
+40 |         let _ = &mut self.x;
+   |                      ^^^^^^ cannot mutably borrow immutable field
+
+error: cannot borrow immutable field `other.x` as mutable
+  --> $DIR/issue-39544.rs:41:22
+   |
+39 |     fn foo3<'a>(self: &'a Self, other: &Z) {
+   |                                        -- use `&mut Z` here to make mutable
+40 |         let _ = &mut self.x;
+41 |         let _ = &mut other.x;
+   |                      ^^^^^^^ cannot mutably borrow immutable field
+
+error: cannot borrow immutable field `other.x` as mutable
+  --> $DIR/issue-39544.rs:45:22
+   |
+44 |     fn foo4(other: &Z) {
+   |                    -- use `&mut Z` here to make mutable
+45 |         let _ = &mut other.x;
+   |                      ^^^^^^^ cannot mutably borrow immutable field
+
+error: cannot borrow immutable field `z.x` as mutable
+  --> $DIR/issue-39544.rs:51:18
+   |
+50 | pub fn with_arg(z: Z, w: &Z) {
+   |                 - consider changing this to `mut z`
+51 |     let _ = &mut z.x;
+   |                  ^^^ cannot mutably borrow immutable field
+
+error: cannot borrow immutable field `w.x` as mutable
+  --> $DIR/issue-39544.rs:52:18
+   |
+50 | pub fn with_arg(z: Z, w: &Z) {
+   |                          -- use `&mut Z` here to make mutable
+51 |     let _ = &mut z.x;
+52 |     let _ = &mut w.x;
+   |                  ^^^ cannot mutably borrow immutable field
+
+error: aborting due to 11 previous errors
 

src/test/ui/did_you_mean/issue-40823.rs

@@ -0,0 +1,14 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn main() {
+    let mut buf = &[1, 2, 3, 4];
+    buf.iter_mut();
+}

src/test/ui/did_you_mean/issue-40823.stderr

@@ -0,0 +1,8 @@
+error: cannot borrow immutable borrowed content `*buf` as mutable
+  --> $DIR/issue-40823.rs:13:5
+   |
+13 |     buf.iter_mut();
+   |     ^^^ cannot borrow as mutable
+
+error: aborting due to previous error
+

src/test/ui/span/borrowck-borrow-overloaded-auto-deref-mut.stderr

@@ -2,7 +2,7 @@ error: cannot borrow immutable argument `x` as mutable
   --> $DIR/borrowck-borrow-overloaded-auto-deref-mut.rs:63:24
    |
 62 | fn deref_mut_field1(x: Own<Point>) {
-   |                     - use `mut x` here to make mutable
+   |                     - consider changing this to `mut x`
 63 |     let __isize = &mut x.y; //~ ERROR cannot borrow
    |                        ^ cannot borrow mutably
 
@@ -28,7 +28,7 @@ error: cannot borrow immutable argument `x` as mutable
   --> $DIR/borrowck-borrow-overloaded-auto-deref-mut.rs:98:5
    |
 97 | fn assign_field1<'a>(x: Own<Point>) {
-   |                      - use `mut x` here to make mutable
+   |                      - consider changing this to `mut x`
 98 |     x.y = 3; //~ ERROR cannot borrow
    |     ^ cannot borrow mutably
 
@@ -54,7 +54,7 @@ error: cannot borrow immutable argument `x` as mutable
    --> $DIR/borrowck-borrow-overloaded-auto-deref-mut.rs:119:5
     |
 118 | fn deref_mut_method1(x: Own<Point>) {
-    |                      - use `mut x` here to make mutable
+    |                      - consider changing this to `mut x`
 119 |     x.set(0, 0); //~ ERROR cannot borrow
     |     ^ cannot borrow mutably
 
@@ -70,7 +70,7 @@ error: cannot borrow immutable argument `x` as mutable
    --> $DIR/borrowck-borrow-overloaded-auto-deref-mut.rs:139:6
     |
 138 | fn assign_method1<'a>(x: Own<Point>) {
-    |                       - use `mut x` here to make mutable
+    |                       - consider changing this to `mut x`
 139 |     *x.y_mut() = 3; //~ ERROR cannot borrow
     |      ^ cannot borrow mutably
 

src/test/ui/span/borrowck-borrow-overloaded-deref-mut.stderr

@@ -2,7 +2,7 @@ error: cannot borrow immutable argument `x` as mutable
   --> $DIR/borrowck-borrow-overloaded-deref-mut.rs:39:25
    |
 38 | fn deref_mut1(x: Own<isize>) {
-   |               - use `mut x` here to make mutable
+   |               - consider changing this to `mut x`
 39 |     let __isize = &mut *x; //~ ERROR cannot borrow
    |                         ^ cannot borrow mutably
 
@@ -18,7 +18,7 @@ error: cannot borrow immutable argument `x` as mutable
   --> $DIR/borrowck-borrow-overloaded-deref-mut.rs:59:6
    |
 58 | fn assign1<'a>(x: Own<isize>) {
-   |                - use `mut x` here to make mutable
+   |                - consider changing this to `mut x`
 59 |     *x = 3; //~ ERROR cannot borrow
    |      ^ cannot borrow mutably
 

src/test/ui/span/borrowck-object-mutability.stderr

@@ -10,6 +10,9 @@ error: cannot borrow immutable borrowed content `*x` as mutable
 error: cannot borrow immutable `Box` content `*x` as mutable
   --> $DIR/borrowck-object-mutability.rs:29:5
    |
+27 | fn owned_receiver(x: Box<Foo>) {
+   |                   - consider changing this to `mut x`
+28 |     x.borrowed();
 29 |     x.borrowed_mut(); //~ ERROR cannot borrow
    |     ^ cannot borrow as mutable