introduce closure_env_ty helper to compute ty of closure env arg

Previously the code was somewhat duplicated.

src/librustc/ty/mod.rs

@@ -1921,6 +1921,12 @@ impl<'a, 'gcx, 'tcx> FieldDef {
     }
 }
 
+/// Represents the various closure traits in the Rust language. This
+/// will determine the type of the environment (`self`, in the
+/// desuaring) argument that the closure expects.
+///
+/// You can get the environment type of a closure using
+/// `tcx.closure_env_ty()`.
 #[derive(Clone, Copy, PartialOrd, Ord, PartialEq, Eq, Hash, Debug, RustcEncodable, RustcDecodable)]
 pub enum ClosureKind {
     // Warning: Ordering is significant here! The ordering is chosen

src/librustc/ty/util.rs

@@ -634,6 +634,33 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         def_id
     }
 
+    /// Given the def-id and substs a closure, creates the type of
+    /// `self` argument that the closure expects. For example, for a
+    /// `Fn` closure, this would return a reference type `&T` where
+    /// `T=closure_ty`.
+    ///
+    /// Returns `None` if this closure's kind has not yet been inferred.
+    /// This should only be possible during type checking.
+    ///
+    /// Note that the return value is a late-bound region and hence
+    /// wrapped in a binder.
+    pub fn closure_env_ty(self,
+                          closure_def_id: DefId,
+                          closure_substs: ty::ClosureSubsts<'tcx>)
+                          -> Option<ty::Binder<Ty<'tcx>>>
+    {
+        let closure_ty = self.mk_closure(closure_def_id, closure_substs);
+        let env_region = ty::ReLateBound(ty::DebruijnIndex::new(1), ty::BrEnv);
+        let closure_kind_ty = closure_substs.closure_kind_ty(closure_def_id, self);
+        let closure_kind = closure_kind_ty.to_opt_closure_kind()?;
+        let env_ty = match closure_kind {
+            ty::ClosureKind::Fn => self.mk_imm_ref(self.mk_region(env_region), closure_ty),
+            ty::ClosureKind::FnMut => self.mk_mut_ref(self.mk_region(env_region), closure_ty),
+            ty::ClosureKind::FnOnce => closure_ty,
+        };
+        Some(ty::Binder(env_ty))
+    }
+
     /// Given the def-id of some item that has no type parameters, make
     /// a suitable "empty substs" for it.
     pub fn empty_substs_for_def_id(self, item_def_id: DefId) -> &'tcx ty::Substs<'tcx> {

src/librustc_mir/build/mod.rs

@@ -100,7 +100,7 @@ pub fn mir_build<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> Mir<'t
                     // HACK(eddyb) Avoid having RustCall on closures,
                     // as it adds unnecessary (and wrong) auto-tupling.
                     abi = Abi::Rust;
-                    Some((closure_self_ty(tcx, id, body_id), None))
+                    Some((liberated_closure_env_ty(tcx, id, body_id), None))
                 }
                 ty::TyGenerator(..) => {
                     let gen_ty = tcx.body_tables(body_id).node_id_to_type(fn_hir_id);
@@ -246,10 +246,10 @@ fn create_constructor_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 ///////////////////////////////////////////////////////////////////////////
 // BuildMir -- walks a crate, looking for fn items and methods to build MIR from
 
-pub fn closure_self_ty<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
-                                       closure_expr_id: ast::NodeId,
-                                       body_id: hir::BodyId)
-                                       -> Ty<'tcx> {
+fn liberated_closure_env_ty<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
+                                            closure_expr_id: ast::NodeId,
+                                            body_id: hir::BodyId)
+                                            -> Ty<'tcx> {
     let closure_expr_hir_id = tcx.hir.node_to_hir_id(closure_expr_id);
     let closure_ty = tcx.body_tables(body_id).node_id_to_type(closure_expr_hir_id);
 
@@ -258,24 +258,8 @@ pub fn closure_self_ty<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
         _ => bug!("closure expr does not have closure type: {:?}", closure_ty)
     };
 
-    let region = ty::ReFree(ty::FreeRegion {
-        scope: closure_def_id,
-        bound_region: ty::BoundRegion::BrEnv,
-    });
-    let region = tcx.mk_region(region);
-
-    match closure_substs.closure_kind_ty(closure_def_id, tcx).to_opt_closure_kind().unwrap() {
-        ty::ClosureKind::Fn =>
-            tcx.mk_ref(region,
-                       ty::TypeAndMut { ty: closure_ty,
-                                        mutbl: hir::MutImmutable }),
-        ty::ClosureKind::FnMut =>
-            tcx.mk_ref(region,
-                       ty::TypeAndMut { ty: closure_ty,
-                                        mutbl: hir::MutMutable }),
-        ty::ClosureKind::FnOnce =>
-            closure_ty
-    }
+    let closure_env_ty = tcx.closure_env_ty(closure_def_id, closure_substs).unwrap();
+    tcx.liberate_late_bound_regions(closure_def_id, &closure_env_ty)
 }
 
 struct Builder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {

src/librustc_trans/common.rs

@@ -395,15 +395,9 @@ pub fn ty_fn_sig<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
             let tcx = ccx.tcx();
             let sig = tcx.fn_sig(def_id).subst(tcx, substs.substs);
 
-            let env_region = ty::ReLateBound(ty::DebruijnIndex::new(1), ty::BrEnv);
-            let env_ty = match substs.closure_kind(def_id, tcx) {
-                ty::ClosureKind::Fn => tcx.mk_imm_ref(tcx.mk_region(env_region), ty),
-                ty::ClosureKind::FnMut => tcx.mk_mut_ref(tcx.mk_region(env_region), ty),
-                ty::ClosureKind::FnOnce => ty,
-            };
-
+            let env_ty = tcx.closure_env_ty(def_id, substs).unwrap();
             sig.map_bound(|sig| tcx.mk_fn_sig(
-                iter::once(env_ty).chain(sig.inputs().iter().cloned()),
+                iter::once(*env_ty.skip_binder()).chain(sig.inputs().iter().cloned()),
                 sig.output(),
                 sig.variadic,
                 sig.unsafety,