During method resolution, only reborrow if we are not doing an auto-ref.

The current behavior leads to adjustments like `&&*` being applied
instead of just `&` (when the unmodified receiver is a `&T` or an `&mut
T`). This causes both safety errors and unexpected behavior. The safety
errors result from regionck not being prepared for auto-ref-ref-like
adjustments; this is worth fixing on its own, but I think the best way
to do it is to modify regionck to use expr-use-visitor (and fix
expr-use-visitor as well, which I don't think properly invokes `borrow`
for each level of auto-ref), and for now it's simpler to just not
produce the adjustment in question. (I have a separate patch porting
regionck to use exprusevisitor for a different bug, so that is coming.)

src/test/compile-fail/borrowck-return-variable-on-stack-via-clone.rs

@@ -0,0 +1,20 @@
+// Copyright 2014 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.
+
+// Check that when we clone a `&T` pointer we properly relate the
+// lifetime of the pointer which results to the pointer being cloned.
+// Bugs in method resolution have sometimes broken this connection.
+// Issue #19261.
+
+fn leak<'a, T>(x: T) -> &'a T {
+    (&x).clone() //~ ERROR `x` does not live long enough
+}
+
+fn main() { }

src/test/run-pass/method-mut-self-modifies-mut-slice-lvalue.rs

@@ -0,0 +1,54 @@
+// Copyright 2014 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.
+
+// Test that an `&mut self` method, when invoked on an lvalue whose
+// type is `&mut [u8]`, passes in a pointer to the lvalue and not a
+// temporary. Issue #19147.
+
+use std::raw;
+use std::mem;
+use std::slice;
+use std::io::IoResult;
+
+trait MyWriter {
+    fn my_write(&mut self, buf: &[u8]) -> IoResult<()>;
+}
+
+impl<'a> MyWriter for &'a mut [u8] {
+    fn my_write(&mut self, buf: &[u8]) -> IoResult<()> {
+        slice::bytes::copy_memory(*self, buf);
+
+        let write_len = buf.len();
+        unsafe {
+            *self = mem::transmute(raw::Slice {
+                data: self.as_ptr().offset(write_len as int),
+                len: self.len() - write_len,
+            });
+        }
+
+        Ok(())
+    }
+}
+
+fn main() {
+    let mut buf = [0_u8, .. 6];
+
+    {
+        let mut writer = buf.as_mut_slice();
+        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]);
+}