1 files changed, 44 insertions, 0 deletions
diff --git a/tests/ui/methods/method-mut-self-modifies-mut-slice-lvalue.rs b/tests/ui/methods/method-mut-self-modifies-mut-slice-lvalue.rs
new file mode 100644
index 00000000000..daff037b27b
--- /dev/null
+++ b/tests/ui/methods/method-mut-self-modifies-mut-slice-lvalue.rs
@@ -0,0 +1,44 @@
+// run-pass
+// Test that an `&mut self` method, when invoked on a place whose
+// type is `&mut [u8]`, passes in a pointer to the place and not a
+// temporary. Issue #19147.
+
+use std::slice;
+use std::cmp;
+
+trait MyWriter {
+    fn my_write(&mut self, buf: &[u8]) -> Result<(), ()>;
+}
+
+impl<'a> MyWriter for &'a mut [u8] {
+    fn my_write(&mut self, buf: &[u8]) -> Result<(), ()> {
+        let amt = cmp::min(self.len(), buf.len());
+        self[..amt].clone_from_slice(&buf[..amt]);
+
+        let write_len = buf.len();
+        unsafe {
+            *self = slice::from_raw_parts_mut(
+                self.as_mut_ptr().add(write_len),
+                self.len() - write_len
+            );
+        }
+
+        Ok(())
+    }
+}
+
+fn main() {
+    let mut buf = [0; 6];
+
+    {
+        let mut writer: &mut [_] = &mut buf;
+        writer.my_write(&[0, 1, 2]).unwrap();
+        writer.my_write(&[3, 4, 5]).unwrap();
+    }
+
+    // If `my_write` is not modifying `buf` in place, then we will
+    // wind up with `[3, 4, 5, 0, 0, 0]` because the first call to
+    // `my_write()` doesn't update the starting point for the write.
+
+    assert_eq!(buf, [0, 1, 2, 3, 4, 5]);
+}