Make ui/span/borrowck-borrow-overloaded-auto-deref-mut.rs robust w.r.t. NLL.

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

@@ -14,6 +14,16 @@ LL | fn deref_extend_mut_field1(x: &Own<Point>) -> &mut isize {
 LL |     &mut x.y //~ ERROR cannot borrow
    |          ^ `x` is a `&` reference, so the data it refers to cannot be borrowed as mutable
 
+error[E0499]: cannot borrow `*x` as mutable more than once at a time
+  --> $DIR/borrowck-borrow-overloaded-auto-deref-mut.rs:88:19
+   |
+LL |     let _x = &mut x.x;
+   |                   - first mutable borrow occurs here
+LL |     let _y = &mut x.y; //~ ERROR cannot borrow
+   |                   ^ second mutable borrow occurs here
+LL |     use_mut(_x);
+   |             -- first borrow later used here
+
 error[E0596]: cannot borrow `x` as mutable, as it is not declared as mutable
   --> $DIR/borrowck-borrow-overloaded-auto-deref-mut.rs:98:5
    |
@@ -30,6 +40,16 @@ LL | fn assign_field2<'a>(x: &'a Own<Point>) {
 LL |     x.y = 3; //~ ERROR cannot borrow
    |     ^ `x` is a `&` reference, so the data it refers to cannot be borrowed as mutable
 
+error[E0499]: cannot borrow `*x` as mutable more than once at a time
+  --> $DIR/borrowck-borrow-overloaded-auto-deref-mut.rs:111:5
+   |
+LL |     let _p: &mut Point = &mut **x;
+   |                                -- first mutable borrow occurs here
+LL |     x.y = 3; //~ ERROR cannot borrow
+   |     ^ second mutable borrow occurs here
+LL |     use_mut(_p);
+   |             -- first borrow later used here
+
 error[E0596]: cannot borrow `x` as mutable, as it is not declared as mutable
   --> $DIR/borrowck-borrow-overloaded-auto-deref-mut.rs:119:5
    |
@@ -62,6 +82,7 @@ LL | fn assign_method2<'a>(x: &'a Own<Point>) {
 LL |     *x.y_mut() = 3; //~ ERROR cannot borrow
    |      ^ `x` is a `&` reference, so the data it refers to cannot be borrowed as mutable
 
-error: aborting due to 8 previous errors
+error: aborting due to 10 previous errors
 
-For more information about this error, try `rustc --explain E0596`.
+Some errors occurred: E0499, E0596.
+For more information about an error, try `rustc --explain E0499`.

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

@@ -86,8 +86,8 @@ fn deref_extend_mut_field3(x: &mut Own<Point>) {
 
     let _x = &mut x.x;
     let _y = &mut x.y; //~ ERROR cannot borrow
+    use_mut(_x);
 }
-
 fn deref_extend_mut_field4<'a>(x: &'a mut Own<Point>) {
     let p = &mut **x;
     let _x = &mut p.x;
@@ -109,8 +109,8 @@ fn assign_field3<'a>(x: &'a mut Own<Point>) {
 fn assign_field4<'a>(x: &'a mut Own<Point>) {
     let _p: &mut Point = &mut **x;
     x.y = 3; //~ ERROR cannot borrow
+    use_mut(_p);
 }
-
 fn deref_imm_method(x: Own<Point>) {
     let __isize = x.get();
 }
@@ -148,3 +148,5 @@ fn assign_method3<'a>(x: &'a mut Own<Point>) {
 }
 
 pub fn main() {}
+
+fn use_mut<T>(_: &mut T) {}

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

@@ -21,6 +21,7 @@ LL |     let _x = &mut x.x;
    |                   - first mutable borrow occurs here
 LL |     let _y = &mut x.y; //~ ERROR cannot borrow
    |                   ^ second mutable borrow occurs here
+LL |     use_mut(_x);
 LL | }
    | - first borrow ends here
 
@@ -47,6 +48,7 @@ LL |     let _p: &mut Point = &mut **x;
    |                                -- first mutable borrow occurs here
 LL |     x.y = 3; //~ ERROR cannot borrow
    |     ^ second mutable borrow occurs here
+LL |     use_mut(_p);
 LL | }
    | - first borrow ends here