Don't call drop when taking the address of unsized fields

src/librustc_trans/trans/expr.rs

@@ -730,8 +730,9 @@ fn trans_field<'blk, 'tcx, F>(bcx: Block<'blk, 'tcx>,
             let info = Load(bcx, get_len(bcx, base_datum.val));
             Store(bcx, info, get_len(bcx, scratch.val));
 
-            DatumBlock::new(bcx, scratch.to_expr_datum())
-
+            // Always generate an lvalue datum, because this pointer doesn't own
+            // the data and cleanup is scheduled elsewhere.
+            DatumBlock::new(bcx, Datum::new(scratch.val, scratch.ty, LvalueExpr))
         }
     })
 

src/test/run-pass/issue-25515.rs

@@ -0,0 +1,29 @@
+// 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.
+
+use std::rc::Rc;
+
+struct Foo<'r>(&'r mut i32);
+
+impl<'r> Drop for Foo<'r> {
+    fn drop(&mut self) {
+        *self.0 += 1;
+    }
+}
+
+fn main() {
+    let mut drops = 0;
+
+    {
+        let _: Rc<Send> = Rc::new(Foo(&mut drops));
+    }
+
+    assert_eq!(1, drops);
+}

src/test/run-pass/issue-25549-multiple-drop.rs

@@ -0,0 +1,41 @@
+// 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.
+
+struct Foo<'r>(&'r mut i32);
+
+impl<'r> Drop for Foo<'r> {
+    fn drop(&mut self) {
+        *self.0 += 1;
+    }
+}
+
+trait Trait {}
+impl<'r> Trait for Foo<'r> {}
+
+struct Holder<T: ?Sized>(T);
+
+fn main() {
+    let mut drops = 0;
+
+    {
+        let y = &Holder([Foo(&mut drops)]) as &Holder<[Foo]>;
+        // this used to cause an extra drop of the Foo instance
+        let x = &y.0;
+    }
+    assert_eq!(1, drops);
+
+    drops = 0;
+    {
+        let y = &Holder(Foo(&mut drops)) as &Holder<Trait>;
+        // this used to cause an extra drop of the Foo instance
+        let x = &y.0;
+    }
+    assert_eq!(1, drops);
+}