1 files changed, 37 insertions, 0 deletions
diff --git a/src/test/ui/borrowck/mut-borrow-of-mut-ref.rs b/src/test/ui/borrowck/mut-borrow-of-mut-ref.rs
new file mode 100644
index 000000000..7cdb16b28
--- /dev/null
+++ b/src/test/ui/borrowck/mut-borrow-of-mut-ref.rs
@@ -0,0 +1,37 @@
+// Suggest not mutably borrowing a mutable reference
+#![crate_type = "rlib"]
+
+pub fn f(b: &mut i32) {
+    //~^ NOTE the binding is already a mutable borrow
+    //~| NOTE the binding is already a mutable borrow
+    h(&mut b);
+    //~^ ERROR cannot borrow
+    //~| NOTE cannot borrow as mutable
+    //~| HELP try removing `&mut` here
+    g(&mut &mut b);
+    //~^ ERROR cannot borrow
+    //~| NOTE cannot borrow as mutable
+    //~| HELP try removing `&mut` here
+}
+
+pub fn g(b: &mut i32) { //~ NOTE the binding is already a mutable borrow
+    h(&mut &mut b);
+    //~^ ERROR cannot borrow
+    //~| NOTE cannot borrow as mutable
+    //~| HELP try removing `&mut` here
+}
+
+pub fn h(_: &mut i32) {}
+
+trait Foo {
+    fn bar(&mut self);
+}
+
+impl Foo for &mut String {
+    fn bar(&mut self) {}
+}
+
+pub fn baz(f: &mut String) { //~ HELP consider making the binding mutable
+    f.bar(); //~ ERROR cannot borrow `f` as mutable, as it is not declared as mutable
+    //~^ NOTE cannot borrow as mutable
+}