Mir typeck Cast for ClosureFnPtr value

src/librustc_mir/transform/type_check.rs

@@ -1196,6 +1196,20 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
                         }
                     }
 
+                    CastKind::ClosureFnPointer => {
+                        let sig = match op.ty(mir, tcx).sty {
+                            ty::TyClosure(def_id, substs) => {
+                                substs.closure_sig_ty(def_id, tcx).fn_sig(tcx)
+                            }
+                            _ => bug!(),
+                        };
+                        let ty_fn_ptr_from = tcx.coerce_closure_fn_ty(sig);
+
+                        if let Err(terr) = self.eq_types(ty_fn_ptr_from, ty, location.at_self()) {
+                            span_mirbug!(self, "", "casting {:?}", terr);
+                        }
+                    }
+
                     CastKind::UnsafeFnPointer => {
                         let ty_fn_ptr_from = tcx.safe_to_unsafe_fn_ty(op.ty(mir, tcx).fn_sig(tcx));
 
@@ -1204,9 +1218,7 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
                         }
                     }
 
-                    CastKind::ClosureFnPointer |
-                    CastKind::Misc |
-                    CastKind::Unsize => {}
+                    CastKind::Misc | CastKind::Unsize => {}
                 }
             }
 

src/test/compile-fail/mir_check_cast_closure.rs

@@ -0,0 +1,22 @@
+// Copyright 2017 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.
+
+// compile-flags: -Z borrowck=mir -Z nll
+
+#![allow(dead_code)]
+
+fn bar<'a, 'b>() -> fn(&'a u32, &'b u32) -> &'a u32 {
+    let g: fn(_, _) -> _ = |_x, y| y;
+    g
+    //~^ WARNING not reporting region error due to -Znll
+    //~| ERROR free region `'b` does not outlive free region `'a`
+}
+
+fn main() {}