auto merge of #18729 : bkoropoff/rust/issue-18711, r=cmr

Closes #18711

src/librustc/middle/trans/closure.rs

@@ -489,10 +489,9 @@ pub fn trans_unboxed_closure<'blk, 'tcx>(
         closure_id,
         &bcx.fcx.param_substs.substs).unwrap();
 
-    let unboxed_closures = bcx.tcx().unboxed_closures.borrow();
-    let function_type = (*unboxed_closures)[closure_id]
-                                        .closure_type
-                                        .clone();
+    let function_type = (*bcx.tcx().unboxed_closures.borrow())[closure_id]
+                                                              .closure_type
+                                                              .clone();
     let function_type = ty::mk_closure(bcx.tcx(), function_type);
 
     let freevars: Vec<ty::Freevar> =

src/test/auxiliary/issue-18711.rs

@@ -0,0 +1,16 @@
+// 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.
+
+#![feature(unboxed_closures, overloaded_calls)]
+#![crate_type = "rlib"]
+
+pub fn inner<F>(f: F) -> F {
+    (move |:| f)()
+}

src/test/run-pass/issue-18711.rs

@@ -0,0 +1,21 @@
+// 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 we don't panic on a RefCell borrow conflict in certain
+// code paths involving unboxed closures.
+
+#![feature(unboxed_closures, overloaded_calls)]
+
+// aux-build:issue-18711.rs
+extern crate "issue-18711" as issue;
+
+fn main() {
+    (|:| issue::inner(()))();
+}