message: test mutable string slice indexing
diff: @@ -18,10 +18,17 @@ fn fat_pointer_on_32_bit() {
  Some(5).expect("foo");
  }
  +fn str_indexing() {
  + let mut x = "Hello".to_string();
  + let _v = &mut x[..3]; // Test IndexMut on String.
  +}
  +
  fn main() {
  assert_eq!(empty(), "");
  assert_eq!(hello(), "Hello, world!");
  assert_eq!(hello_bytes(), b"Hello, world!");
  assert_eq!(hello_bytes_fat(), b"Hello, world!");
  +
  fat_pointer_on_32_bit(); // Should run without crashing.
  + str_indexing();
  }
  