Regression test for dropflag reinit issue.

Fix rust-lang#27401.

Author: pnkfelix

src/test/run-pass/issue-27401-dropflag-reinit.rs

@@ -0,0 +1,34 @@
+// 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.
+
+// Check that when a `let`-binding occurs in a loop, its associated
+// drop-flag is reinitialized (to indicate "needs-drop" at the end of
+// the owning variable's scope).
+
+struct A<'a>(&'a mut i32);
+
+impl<'a> Drop for A<'a> {
+    fn drop(&mut self) {
+        *self.0 += 1;
+    }
+}
+
+fn main() {
+    let mut cnt = 0;
+    for i in 0..2 {
+        let a = A(&mut cnt);
+        if i == 1 { // Note that
+            break;  //  both this break
+        }           //   and also
+        drop(a);    //    this move of `a`
+        // are necessary to expose the bug
+    }
+    assert_eq!(cnt, 2);
+}