From efd3e75503074e93958a03fa1ee2b9a5abcad7e4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Steinbrink?= <bsteinbr@gmail.com>
Date: Mon, 25 May 2015 17:17:27 +0200
Subject: [PATCH] Fix auto_ref for fat pointers

Fat pointers aren't immediate, so in a datum, they're not actually
ByValue but ByRef.

Fixes #24589
---
 src/librustc_trans/trans/expr.rs |  4 +++-
 src/test/run-pass/issue-24589.rs | 26 ++++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 src/test/run-pass/issue-24589.rs

diff --git a/src/librustc_trans/trans/expr.rs b/src/librustc_trans/trans/expr.rs
index 3ebb56d1dd899..63158cdee9247 100644
--- a/src/librustc_trans/trans/expr.rs
+++ b/src/librustc_trans/trans/expr.rs
@@ -2180,7 +2180,9 @@ fn auto_ref<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
     // Construct the resulting datum, using what was the "by ref"
     // ValueRef of type `referent_ty` to be the "by value" ValueRef
     // of type `&referent_ty`.
-    DatumBlock::new(bcx, Datum::new(llref, ptr_ty, RvalueExpr(Rvalue::new(ByValue))))
+    // Pointers to DST types are non-immediate, and therefore still use ByRef.
+    let kind  = if type_is_sized(bcx.tcx(), referent_ty) { ByValue } else { ByRef };
+    DatumBlock::new(bcx, Datum::new(llref, ptr_ty, RvalueExpr(Rvalue::new(kind))))
 }
 
 fn deref_multiple<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
diff --git a/src/test/run-pass/issue-24589.rs b/src/test/run-pass/issue-24589.rs
new file mode 100644
index 0000000000000..2fa8c8e98c0de
--- /dev/null
+++ b/src/test/run-pass/issue-24589.rs
@@ -0,0 +1,26 @@
+// Copyright 2015 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.
+
+pub struct _X([u8]);
+
+impl std::ops::Deref for _X {
+    type Target = [u8];
+
+    fn deref(&self) -> &[u8] {
+        &self.0
+    }
+}
+
+pub fn _g(x: &_X) -> &[u8] {
+    x
+}
+
+fn main() {
+}