Extract coerce_closure_fn_ty function

src/librustc/ty/context.rs

@@ -1717,6 +1717,27 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         }))
     }
 
+    /// Create an unsafe fn ty based on a safe fn ty.
+    pub fn coerce_closure_fn_ty(self, sig: PolyFnSig<'tcx>) -> Ty<'tcx> {
+        let converted_sig = sig.map_bound(|s| {
+            let params_iter = match s.inputs()[0].sty {
+                ty::TyTuple(params, _) => {
+                    params.into_iter().cloned()
+                }
+                _ => bug!(),
+            };
+            self.mk_fn_sig(
+                params_iter,
+                s.output(),
+                s.variadic,
+                hir::Unsafety::Normal,
+                abi::Abi::Rust
+                )
+        });
+
+        self.mk_fn_ptr(converted_sig)
+    }
+
     // Interns a type/name combination, stores the resulting box in cx.interners,
     // and returns the box as cast to an unsafe ptr (see comments for Ty above).
     pub fn mk_ty(self, st: TypeVariants<'tcx>) -> Ty<'tcx> {

src/librustc_typeck/check/coercion.rs

@@ -75,7 +75,6 @@ use rustc::ty::fold::TypeFoldable;
 use rustc::ty::error::TypeError;
 use rustc::ty::relate::RelateResult;
 use errors::DiagnosticBuilder;
-use syntax::abi;
 use syntax::feature_gate;
 use syntax::ptr::P;
 use syntax_pos;
@@ -670,22 +669,7 @@ impl<'f, 'gcx, 'tcx> Coerce<'f, 'gcx, 'tcx> {
                 // to
                 //     `fn(arg0,arg1,...) -> _`
                 let sig = self.closure_sig(def_id_a, substs_a);
-                let converted_sig = sig.map_bound(|s| {
+                let pointer_ty = self.tcx.coerce_closure_fn_ty(sig);
-                    let params_iter = match s.inputs()[0].sty {
-                        ty::TyTuple(params, _) => {
-                            params.into_iter().cloned()
-                        }
-                        _ => bug!(),
-                    };
-                    self.tcx.mk_fn_sig(
-                        params_iter,
-                        s.output(),
-                        s.variadic,
-                        hir::Unsafety::Normal,
-                        abi::Abi::Rust
-                    )
-                });
-                let pointer_ty = self.tcx.mk_fn_ptr(converted_sig);
                 debug!("coerce_closure_to_fn(a={:?}, b={:?}, pty={:?})",
                        a, b, pointer_ty);
                 self.unify_and(pointer_ty, b, simple(Adjust::ClosureFnPointer))