src/librustc_mir/hair/cx/expr.rs

   1 use crate::hair::*;
   2 use crate::hair::cx::Cx;
   3 use crate::hair::cx::block;
   4 use crate::hair::cx::to_ref::ToRef;
   5 use crate::hair::util::UserAnnotatedTyHelpers;
   6 use rustc_data_structures::indexed_vec::Idx;
   7 use rustc::hir::def::{Def, CtorKind};
   8 use rustc::mir::interpret::{GlobalId, ErrorHandled};
   9 use rustc::ty::{self, AdtKind, Ty};
  10 use rustc::ty::adjustment::{Adjustment, Adjust, AutoBorrow, AutoBorrowMutability};
  11 use rustc::ty::cast::CastKind as TyCastKind;
  12 use rustc::hir;
  13 use rustc::hir::def_id::LocalDefId;
  14 use rustc::mir::BorrowKind;
  15 use syntax_pos::Span;
  16
  17 impl<'tcx> Mirror<'tcx> for &'tcx hir::Expr {
  18     type Output = Expr<'tcx>;
  19
  20     fn make_mirror<'a, 'gcx>(self, cx: &mut Cx<'a, 'gcx, 'tcx>) -> Expr<'tcx> {
  21         let temp_lifetime = cx.region_scope_tree.temporary_scope(self.hir_id.local_id);
  22         let expr_scope = region::Scope {
  23             id: self.hir_id.local_id,
  24             data: region::ScopeData::Node
  25         };
  26
  27         debug!("Expr::make_mirror(): id={}, span={:?}", self.id, self.span);
  28
  29         let mut expr = make_mirror_unadjusted(cx, self);
  30
  31         // Now apply adjustments, if any.
  32         for adjustment in cx.tables().expr_adjustments(self) {
  33             debug!("make_mirror: expr={:?} applying adjustment={:?}",
  34                    expr,
  35                    adjustment);
  36             expr = apply_adjustment(cx, self, expr, adjustment);
  37         }
  38
  39         // Next, wrap this up in the expr's scope.
  40         expr = Expr {
  41             temp_lifetime,
  42             ty: expr.ty,
  43             span: self.span,
  44             kind: ExprKind::Scope {
  45                 region_scope: expr_scope,
  46                 value: expr.to_ref(),
  47                 lint_level: cx.lint_level_of(self.id),
  48             },
  49         };
  50
  51         // Finally, create a destruction scope, if any.
  52         if let Some(region_scope) =
  53             cx.region_scope_tree.opt_destruction_scope(self.hir_id.local_id) {
  54                 expr = Expr {
  55                     temp_lifetime,
  56                     ty: expr.ty,
  57                     span: self.span,
  58                     kind: ExprKind::Scope {
  59                         region_scope,
  60                         value: expr.to_ref(),
  61                         lint_level: LintLevel::Inherited,
  62                     },
  63                 };
  64             }
  65
  66         // OK, all done!
  67         expr
  68     }
  69 }
  70
  71 fn apply_adjustment<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
  72                                     hir_expr: &'tcx hir::Expr,
  73                                     mut expr: Expr<'tcx>,
  74                                     adjustment: &Adjustment<'tcx>)
  75                                     -> Expr<'tcx> {
  76     let Expr { temp_lifetime, mut span, .. } = expr;
  77     let kind = match adjustment.kind {
  78         Adjust::ReifyFnPointer => {
  79             ExprKind::ReifyFnPointer { source: expr.to_ref() }
  80         }
  81         Adjust::UnsafeFnPointer => {
  82             ExprKind::UnsafeFnPointer { source: expr.to_ref() }
  83         }
  84         Adjust::ClosureFnPointer => {
  85             ExprKind::ClosureFnPointer { source: expr.to_ref() }
  86         }
  87         Adjust::NeverToAny => {
  88             ExprKind::NeverToAny { source: expr.to_ref() }
  89         }
  90         Adjust::MutToConstPointer => {
  91             ExprKind::Cast { source: expr.to_ref() }
  92         }
  93         Adjust::Deref(None) => {
  94             // Adjust the span from the block, to the last expression of the
  95             // block. This is a better span when returning a mutable reference
  96             // with too short a lifetime. The error message will use the span
  97             // from the assignment to the return place, which should only point
  98             // at the returned value, not the entire function body.
  99             //
 100             // fn return_short_lived<'a>(x: &'a mut i32) -> &'static mut i32 {
 101             //      x
 102             //   // ^ error message points at this expression.
 103             // }
 104             //
 105             // We don't need to do this adjustment in the next match arm since
 106             // deref coercions always start with a built-in deref.
 107             if let ExprKind::Block { body } = expr.kind {
 108                 if let Some(ref last_expr) = body.expr {
 109                     span = last_expr.span;
 110                     expr.span = span;
 111                 }
 112             }
 113             ExprKind::Deref { arg: expr.to_ref() }
 114         }
 115         Adjust::Deref(Some(deref)) => {
 116             let call = deref.method_call(cx.tcx(), expr.ty);
 117
 118             expr = Expr {
 119                 temp_lifetime,
 120                 ty: cx.tcx.mk_ref(deref.region,
 121                                   ty::TypeAndMut {
 122                                     ty: expr.ty,
 123                                     mutbl: deref.mutbl,
 124                                   }),
 125                 span,
 126                 kind: ExprKind::Borrow {
 127                     borrow_kind: deref.mutbl.to_borrow_kind(),
 128                     arg: expr.to_ref(),
 129                 },
 130             };
 131
 132             overloaded_place(cx, hir_expr, adjustment.target, Some(call), vec![expr.to_ref()])
 133         }
 134         Adjust::Borrow(AutoBorrow::Ref(_, m)) => {
 135             ExprKind::Borrow {
 136                 borrow_kind: m.to_borrow_kind(),
 137                 arg: expr.to_ref(),
 138             }
 139         }
 140         Adjust::Borrow(AutoBorrow::RawPtr(m)) => {
 141             // Convert this to a suitable `&foo` and
 142             // then an unsafe coercion.
 143             expr = Expr {
 144                 temp_lifetime,
 145                 ty: cx.tcx.mk_ref(cx.tcx.types.re_erased,
 146                                   ty::TypeAndMut {
 147                                     ty: expr.ty,
 148                                     mutbl: m,
 149                                   }),
 150                 span,
 151                 kind: ExprKind::Borrow {
 152                     borrow_kind: m.to_borrow_kind(),
 153                     arg: expr.to_ref(),
 154                 },
 155             };
 156             let cast_expr = Expr {
 157                 temp_lifetime,
 158                 ty: adjustment.target,
 159                 span,
 160                 kind: ExprKind::Cast { source: expr.to_ref() }
 161             };
 162
 163             // To ensure that both implicit and explicit coercions are
 164             // handled the same way, we insert an extra layer of indirection here.
 165             // For explicit casts (e.g., 'foo as *const T'), the source of the 'Use'
 166             // will be an ExprKind::Hair with the appropriate cast expression. Here,
 167             // we make our Use source the generated Cast from the original coercion.
 168             //
 169             // In both cases, this outer 'Use' ensures that the inner 'Cast' is handled by
 170             // as_operand, not by as_rvalue - causing the cast result to be stored in a temporary.
 171             // Ordinary, this is identical to using the cast directly as an rvalue. However, if the
 172             // source of the cast was previously borrowed as mutable, storing the cast in a
 173             // temporary gives the source a chance to expire before the cast is used. For
 174             // structs with a self-referential *mut ptr, this allows assignment to work as
 175             // expected.
 176             //
 177             // For example, consider the type 'struct Foo { field: *mut Foo }',
 178             // The method 'fn bar(&mut self) { self.field = self }'
 179             // triggers a coercion from '&mut self' to '*mut self'. In order
 180             // for the assignment to be valid, the implicit borrow
 181             // of 'self' involved in the coercion needs to end before the local
 182             // containing the '*mut T' is assigned to 'self.field' - otherwise,
 183             // we end up trying to assign to 'self.field' while we have another mutable borrow
 184             // active.
 185             //
 186             // We only need to worry about this kind of thing for coercions from refs to ptrs,
 187             // since they get rid of a borrow implicitly.
 188             ExprKind::Use { source: cast_expr.to_ref() }
 189         }
 190         Adjust::Unsize => {
 191             // See the above comment for Adjust::Deref
 192             if let ExprKind::Block { body } = expr.kind {
 193                 if let Some(ref last_expr) = body.expr {
 194                     span = last_expr.span;
 195                     expr.span = span;
 196                 }
 197             }
 198             ExprKind::Unsize { source: expr.to_ref() }
 199         }
 200     };
 201
 202     Expr {
 203         temp_lifetime,
 204         ty: adjustment.target,
 205         span,
 206         kind,
 207     }
 208 }
 209
 210 fn make_mirror_unadjusted<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
 211                                           expr: &'tcx hir::Expr)
 212                                           -> Expr<'tcx> {
 213     let expr_ty = cx.tables().expr_ty(expr);
 214     let temp_lifetime = cx.region_scope_tree.temporary_scope(expr.hir_id.local_id);
 215
 216     let kind = match expr.node {
 217         // Here comes the interesting stuff:
 218         hir::ExprKind::MethodCall(_, method_span, ref args) => {
 219             // Rewrite a.b(c) into UFCS form like Trait::b(a, c)
 220             let expr = method_callee(cx, expr, method_span,None);
 221             let args = args.iter()
 222                 .map(|e| e.to_ref())
 223                 .collect();
 224             ExprKind::Call {
 225                 ty: expr.ty,
 226                 fun: expr.to_ref(),
 227                 args,
 228                 from_hir_call: true,
 229             }
 230         }
 231
 232         hir::ExprKind::Call(ref fun, ref args) => {
 233             if cx.tables().is_method_call(expr) {
 234                 // The callee is something implementing Fn, FnMut, or FnOnce.
 235                 // Find the actual method implementation being called and
 236                 // build the appropriate UFCS call expression with the
 237                 // callee-object as expr parameter.
 238
 239                 // rewrite f(u, v) into FnOnce::call_once(f, (u, v))
 240
 241                 let method = method_callee(cx, expr, fun.span,None);
 242
 243                 let arg_tys = args.iter().map(|e| cx.tables().expr_ty_adjusted(e));
 244                 let tupled_args = Expr {
 245                     ty: cx.tcx.mk_tup(arg_tys),
 246                     temp_lifetime,
 247                     span: expr.span,
 248                     kind: ExprKind::Tuple { fields: args.iter().map(ToRef::to_ref).collect() },
 249                 };
 250
 251                 ExprKind::Call {
 252                     ty: method.ty,
 253                     fun: method.to_ref(),
 254                     args: vec![fun.to_ref(), tupled_args.to_ref()],
 255                     from_hir_call: true,
 256                 }
 257             } else {
 258                 let adt_data = if let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) =
 259                     fun.node
 260                 {
 261                     // Tuple-like ADTs are represented as ExprKind::Call. We convert them here.
 262                     expr_ty.ty_adt_def().and_then(|adt_def| {
 263                         match path.def {
 264                             Def::VariantCtor(variant_id, CtorKind::Fn) => {
 265                                 Some((adt_def, adt_def.variant_index_with_id(variant_id)))
 266                             }
 267                             Def::StructCtor(_, CtorKind::Fn) |
 268                             Def::SelfCtor(..) => Some((adt_def, VariantIdx::new(0))),
 269                             _ => None,
 270                         }
 271                     })
 272                 } else {
 273                     None
 274                 };
 275                 if let Some((adt_def, index)) = adt_data {
 276                     let substs = cx.tables().node_substs(fun.hir_id);
 277                     let user_provided_types = cx.tables().user_provided_types();
 278                     let user_ty = user_provided_types.get(fun.hir_id)
 279                         .map(|u_ty| *u_ty)
 280                         .map(|mut u_ty| {
 281                             if let UserType::TypeOf(ref mut did, _) = &mut u_ty.value {
 282                                 *did = adt_def.did;
 283                             }
 284                             u_ty
 285                         });
 286                     debug!("make_mirror_unadjusted: (call) user_ty={:?}", user_ty);
 287
 288                     let field_refs = args.iter()
 289                         .enumerate()
 290                         .map(|(idx, e)| {
 291                             FieldExprRef {
 292                                 name: Field::new(idx),
 293                                 expr: e.to_ref(),
 294                             }
 295                         })
 296                         .collect();
 297                     ExprKind::Adt {
 298                         adt_def,
 299                         substs,
 300                         variant_index: index,
 301                         fields: field_refs,
 302                         user_ty,
 303                         base: None,
 304                     }
 305                 } else {
 306                     ExprKind::Call {
 307                         ty: cx.tables().node_type(fun.hir_id),
 308                         fun: fun.to_ref(),
 309                         args: args.to_ref(),
 310                         from_hir_call: true,
 311                     }
 312                 }
 313             }
 314         }
 315
 316         hir::ExprKind::AddrOf(mutbl, ref expr) => {
 317             ExprKind::Borrow {
 318                 borrow_kind: mutbl.to_borrow_kind(),
 319                 arg: expr.to_ref(),
 320             }
 321         }
 322
 323         hir::ExprKind::Block(ref blk, _) => ExprKind::Block { body: &blk },
 324
 325         hir::ExprKind::Assign(ref lhs, ref rhs) => {
 326             ExprKind::Assign {
 327                 lhs: lhs.to_ref(),
 328                 rhs: rhs.to_ref(),
 329             }
 330         }
 331
 332         hir::ExprKind::AssignOp(op, ref lhs, ref rhs) => {
 333             if cx.tables().is_method_call(expr) {
 334                 overloaded_operator(cx, expr, vec![lhs.to_ref(), rhs.to_ref()])
 335             } else {
 336                 ExprKind::AssignOp {
 337                     op: bin_op(op.node),
 338                     lhs: lhs.to_ref(),
 339                     rhs: rhs.to_ref(),
 340                 }
 341             }
 342         }
 343
 344         hir::ExprKind::Lit(ref lit) => ExprKind::Literal {
 345             literal: cx.tcx.mk_lazy_const(ty::LazyConst::Evaluated(
 346                 cx.const_eval_literal(&lit.node, expr_ty, lit.span, false)
 347             )),
 348             user_ty: None,
 349         },
 350
 351         hir::ExprKind::Binary(op, ref lhs, ref rhs) => {
 352             if cx.tables().is_method_call(expr) {
 353                 overloaded_operator(cx, expr, vec![lhs.to_ref(), rhs.to_ref()])
 354             } else {
 355                 // FIXME overflow
 356                 match (op.node, cx.constness) {
 357                     // FIXME(eddyb) use logical ops in constants when
 358                     // they can handle that kind of control-flow.
 359                     (hir::BinOpKind::And, hir::Constness::Const) => {
 360                         cx.control_flow_destroyed.push((
 361                             op.span,
 362                             "`&&` operator".into(),
 363                         ));
 364                         ExprKind::Binary {
 365                             op: BinOp::BitAnd,
 366                             lhs: lhs.to_ref(),
 367                             rhs: rhs.to_ref(),
 368                         }
 369                     }
 370                     (hir::BinOpKind::Or, hir::Constness::Const) => {
 371                         cx.control_flow_destroyed.push((
 372                             op.span,
 373                             "`||` operator".into(),
 374                         ));
 375                         ExprKind::Binary {
 376                             op: BinOp::BitOr,
 377                             lhs: lhs.to_ref(),
 378                             rhs: rhs.to_ref(),
 379                         }
 380                     }
 381
 382                     (hir::BinOpKind::And, hir::Constness::NotConst) => {
 383                         ExprKind::LogicalOp {
 384                             op: LogicalOp::And,
 385                             lhs: lhs.to_ref(),
 386                             rhs: rhs.to_ref(),
 387                         }
 388                     }
 389                     (hir::BinOpKind::Or, hir::Constness::NotConst) => {
 390                         ExprKind::LogicalOp {
 391                             op: LogicalOp::Or,
 392                             lhs: lhs.to_ref(),
 393                             rhs: rhs.to_ref(),
 394                         }
 395                     }
 396
 397                     _ => {
 398                         let op = bin_op(op.node);
 399                         ExprKind::Binary {
 400                             op,
 401                             lhs: lhs.to_ref(),
 402                             rhs: rhs.to_ref(),
 403                         }
 404                     }
 405                 }
 406             }
 407         }
 408
 409         hir::ExprKind::Index(ref lhs, ref index) => {
 410             if cx.tables().is_method_call(expr) {
 411                 overloaded_place(cx, expr, expr_ty, None, vec![lhs.to_ref(), index.to_ref()])
 412             } else {
 413                 ExprKind::Index {
 414                     lhs: lhs.to_ref(),
 415                     index: index.to_ref(),
 416                 }
 417             }
 418         }
 419
 420         hir::ExprKind::Unary(hir::UnOp::UnDeref, ref arg) => {
 421             if cx.tables().is_method_call(expr) {
 422                 overloaded_place(cx, expr, expr_ty, None, vec![arg.to_ref()])
 423             } else {
 424                 ExprKind::Deref { arg: arg.to_ref() }
 425             }
 426         }
 427
 428         hir::ExprKind::Unary(hir::UnOp::UnNot, ref arg) => {
 429             if cx.tables().is_method_call(expr) {
 430                 overloaded_operator(cx, expr, vec![arg.to_ref()])
 431             } else {
 432                 ExprKind::Unary {
 433                     op: UnOp::Not,
 434                     arg: arg.to_ref(),
 435                 }
 436             }
 437         }
 438
 439         hir::ExprKind::Unary(hir::UnOp::UnNeg, ref arg) => {
 440             if cx.tables().is_method_call(expr) {
 441                 overloaded_operator(cx, expr, vec![arg.to_ref()])
 442             } else {
 443                 if let hir::ExprKind::Lit(ref lit) = arg.node {
 444                     ExprKind::Literal {
 445                         literal: cx.tcx.mk_lazy_const(ty::LazyConst::Evaluated(
 446                             cx.const_eval_literal(&lit.node, expr_ty, lit.span, true)
 447                         )),
 448                         user_ty: None,
 449                     }
 450                 } else {
 451                     ExprKind::Unary {
 452                         op: UnOp::Neg,
 453                         arg: arg.to_ref(),
 454                     }
 455                 }
 456             }
 457         }
 458
 459         hir::ExprKind::Struct(ref qpath, ref fields, ref base) => {
 460             match expr_ty.sty {
 461                 ty::Adt(adt, substs) => {
 462                     match adt.adt_kind() {
 463                         AdtKind::Struct | AdtKind::Union => {
 464                             let user_provided_types = cx.tables().user_provided_types();
 465                             let user_ty = user_provided_types.get(expr.hir_id).map(|u_ty| *u_ty);
 466                             debug!("make_mirror_unadjusted: (struct/union) user_ty={:?}", user_ty);
 467                             ExprKind::Adt {
 468                                 adt_def: adt,
 469                                 variant_index: VariantIdx::new(0),
 470                                 substs,
 471                                 user_ty,
 472                                 fields: field_refs(cx, fields),
 473                                 base: base.as_ref().map(|base| {
 474                                     FruInfo {
 475                                         base: base.to_ref(),
 476                                         field_types: cx.tables()
 477                                                        .fru_field_types()[expr.hir_id]
 478                                                        .clone(),
 479                                     }
 480                                 }),
 481                             }
 482                         }
 483                         AdtKind::Enum => {
 484                             let def = cx.tables().qpath_def(qpath, expr.hir_id);
 485                             match def {
 486                                 Def::Variant(variant_id) => {
 487                                     assert!(base.is_none());
 488
 489                                     let index = adt.variant_index_with_id(variant_id);
 490                                     let user_provided_types = cx.tables().user_provided_types();
 491                                     let user_ty = user_provided_types.get(expr.hir_id)
 492                                         .map(|u_ty| *u_ty);
 493                                     debug!(
 494                                         "make_mirror_unadjusted: (variant) user_ty={:?}",
 495                                         user_ty
 496                                     );
 497                                     ExprKind::Adt {
 498                                         adt_def: adt,
 499                                         variant_index: index,
 500                                         substs,
 501                                         user_ty,
 502                                         fields: field_refs(cx, fields),
 503                                         base: None,
 504                                     }
 505                                 }
 506                                 _ => {
 507                                     span_bug!(expr.span, "unexpected def: {:?}", def);
 508                                 }
 509                             }
 510                         }
 511                     }
 512                 }
 513                 _ => {
 514                     span_bug!(expr.span,
 515                               "unexpected type for struct literal: {:?}",
 516                               expr_ty);
 517                 }
 518             }
 519         }
 520
 521         hir::ExprKind::Closure(..) => {
 522             let closure_ty = cx.tables().expr_ty(expr);
 523             let (def_id, substs, movability) = match closure_ty.sty {
 524                 ty::Closure(def_id, substs) => (def_id, UpvarSubsts::Closure(substs), None),
 525                 ty::Generator(def_id, substs, movability) => {
 526                     (def_id, UpvarSubsts::Generator(substs), Some(movability))
 527                 }
 528                 _ => {
 529                     span_bug!(expr.span, "closure expr w/o closure type: {:?}", closure_ty);
 530                 }
 531             };
 532             let upvars = cx.tcx.with_freevars(expr.id, |freevars| {
 533                 freevars.iter()
 534                     .zip(substs.upvar_tys(def_id, cx.tcx))
 535                     .map(|(fv, ty)| capture_freevar(cx, expr, fv, ty))
 536                     .collect()
 537             });
 538             ExprKind::Closure {
 539                 closure_id: def_id,
 540                 substs,
 541                 upvars,
 542                 movability,
 543             }
 544         }
 545
 546         hir::ExprKind::Path(ref qpath) => {
 547             let def = cx.tables().qpath_def(qpath, expr.hir_id);
 548             convert_path_expr(cx, expr, def)
 549         }
 550
 551         hir::ExprKind::InlineAsm(ref asm, ref outputs, ref inputs) => {
 552             ExprKind::InlineAsm {
 553                 asm,
 554                 outputs: outputs.to_ref(),
 555                 inputs: inputs.to_ref(),
 556             }
 557         }
 558
 559         // Now comes the rote stuff:
 560         hir::ExprKind::Repeat(ref v, ref count) => {
 561             let def_id = cx.tcx.hir().local_def_id(count.id);
 562             let substs = Substs::identity_for_item(cx.tcx.global_tcx(), def_id);
 563             let instance = ty::Instance::resolve(
 564                 cx.tcx.global_tcx(),
 565                 cx.param_env,
 566                 def_id,
 567                 substs,
 568             ).unwrap();
 569             let global_id = GlobalId {
 570                 instance,
 571                 promoted: None
 572             };
 573             let span = cx.tcx.def_span(def_id);
 574             let count = match cx.tcx.at(span).const_eval(cx.param_env.and(global_id)) {
 575                 Ok(cv) => cv.unwrap_usize(cx.tcx),
 576                 Err(ErrorHandled::Reported) => 0,
 577                 Err(ErrorHandled::TooGeneric) => {
 578                     cx.tcx.sess.span_err(span, "array lengths can't depend on generic parameters");
 579                     0
 580                 },
 581             };
 582
 583             ExprKind::Repeat {
 584                 value: v.to_ref(),
 585                 count,
 586             }
 587         }
 588         hir::ExprKind::Ret(ref v) => ExprKind::Return { value: v.to_ref() },
 589         hir::ExprKind::Break(dest, ref value) => {
 590             match dest.target_id {
 591                 Ok(target_id) => ExprKind::Break {
 592                     label: region::Scope {
 593                         id: cx.tcx.hir().node_to_hir_id(target_id).local_id,
 594                         data: region::ScopeData::Node
 595                     },
 596                     value: value.to_ref(),
 597                 },
 598                 Err(err) => bug!("invalid loop id for break: {}", err)
 599             }
 600         }
 601         hir::ExprKind::Continue(dest) => {
 602             match dest.target_id {
 603                 Ok(loop_id) => ExprKind::Continue {
 604                     label: region::Scope {
 605                         id: cx.tcx.hir().node_to_hir_id(loop_id).local_id,
 606                         data: region::ScopeData::Node
 607                     },
 608                 },
 609                 Err(err) => bug!("invalid loop id for continue: {}", err)
 610             }
 611         }
 612         hir::ExprKind::Match(ref discr, ref arms, _) => {
 613             ExprKind::Match {
 614                 discriminant: discr.to_ref(),
 615                 arms: arms.iter().map(|a| convert_arm(cx, a)).collect(),
 616             }
 617         }
 618         hir::ExprKind::If(ref cond, ref then, ref otherwise) => {
 619             ExprKind::If {
 620                 condition: cond.to_ref(),
 621                 then: then.to_ref(),
 622                 otherwise: otherwise.to_ref(),
 623             }
 624         }
 625         hir::ExprKind::While(ref cond, ref body, _) => {
 626             ExprKind::Loop {
 627                 condition: Some(cond.to_ref()),
 628                 body: block::to_expr_ref(cx, body),
 629             }
 630         }
 631         hir::ExprKind::Loop(ref body, _, _) => {
 632             ExprKind::Loop {
 633                 condition: None,
 634                 body: block::to_expr_ref(cx, body),
 635             }
 636         }
 637         hir::ExprKind::Field(ref source, ..) => {
 638             ExprKind::Field {
 639                 lhs: source.to_ref(),
 640                 name: Field::new(cx.tcx.field_index(expr.id, cx.tables)),
 641             }
 642         }
 643         hir::ExprKind::Cast(ref source, ref cast_ty) => {
 644             // Check for a user-given type annotation on this `cast`
 645             let user_provided_types = cx.tables.user_provided_types();
 646             let user_ty = user_provided_types.get(cast_ty.hir_id);
 647
 648             debug!(
 649                 "cast({:?}) has ty w/ hir_id {:?} and user provided ty {:?}",
 650                 expr,
 651                 cast_ty.hir_id,
 652                 user_ty,
 653             );
 654
 655             // Check to see if this cast is a "coercion cast", where the cast is actually done
 656             // using a coercion (or is a no-op).
 657             let cast = if let Some(&TyCastKind::CoercionCast) =
 658                 cx.tables()
 659                 .cast_kinds()
 660                 .get(source.hir_id)
 661             {
 662                 // Convert the lexpr to a vexpr.
 663                 ExprKind::Use { source: source.to_ref() }
 664             } else {
 665                 // check whether this is casting an enum variant discriminant
 666                 // to prevent cycles, we refer to the discriminant initializer
 667                 // which is always an integer and thus doesn't need to know the
 668                 // enum's layout (or its tag type) to compute it during const eval
 669                 // Example:
 670                 // enum Foo {
 671                 //     A,
 672                 //     B = A as isize + 4,
 673                 // }
 674                 // The correct solution would be to add symbolic computations to miri,
 675                 // so we wouldn't have to compute and store the actual value
 676                 let var = if let hir::ExprKind::Path(ref qpath) = source.node {
 677                     let def = cx.tables().qpath_def(qpath, source.hir_id);
 678                     cx
 679                         .tables()
 680                         .node_type(source.hir_id)
 681                         .ty_adt_def()
 682                         .and_then(|adt_def| {
 683                         match def {
 684                             Def::VariantCtor(variant_id, CtorKind::Const) => {
 685                                 let idx = adt_def.variant_index_with_id(variant_id);
 686                                 let (d, o) = adt_def.discriminant_def_for_variant(idx);
 687                                 use rustc::ty::util::IntTypeExt;
 688                                 let ty = adt_def.repr.discr_type();
 689                                 let ty = ty.to_ty(cx.tcx());
 690                                 Some((d, o, ty))
 691                             }
 692                             _ => None,
 693                         }
 694                     })
 695                 } else {
 696                     None
 697                 };
 698
 699                 let source = if let Some((did, offset, var_ty)) = var {
 700                     let mk_const = |literal| Expr {
 701                         temp_lifetime,
 702                         ty: var_ty,
 703                         span: expr.span,
 704                         kind: ExprKind::Literal {
 705                             literal: cx.tcx.mk_lazy_const(literal),
 706                             user_ty: None
 707                         },
 708                     }.to_ref();
 709                     let offset = mk_const(ty::LazyConst::Evaluated(ty::Const::from_bits(
 710                         cx.tcx,
 711                         offset as u128,
 712                         cx.param_env.and(var_ty),
 713                     )));
 714                     match did {
 715                         Some(did) => {
 716                             // in case we are offsetting from a computed discriminant
 717                             // and not the beginning of discriminants (which is always `0`)
 718                             let substs = Substs::identity_for_item(cx.tcx(), did);
 719                             let lhs = mk_const(ty::LazyConst::Unevaluated(did, substs));
 720                             let bin = ExprKind::Binary {
 721                                 op: BinOp::Add,
 722                                 lhs,
 723                                 rhs: offset,
 724                             };
 725                             Expr {
 726                                 temp_lifetime,
 727                                 ty: var_ty,
 728                                 span: expr.span,
 729                                 kind: bin,
 730                             }.to_ref()
 731                         },
 732                         None => offset,
 733                     }
 734                 } else {
 735                     source.to_ref()
 736                 };
 737
 738                 ExprKind::Cast { source }
 739             };
 740
 741             if let Some(user_ty) = user_ty {
 742                 // NOTE: Creating a new Expr and wrapping a Cast inside of it may be
 743                 //       inefficient, revisit this when performance becomes an issue.
 744                 let cast_expr = Expr {
 745                     temp_lifetime,
 746                     ty: expr_ty,
 747                     span: expr.span,
 748                     kind: cast,
 749                 };
 750                 debug!("make_mirror_unadjusted: (cast) user_ty={:?}", user_ty);
 751
 752                 ExprKind::ValueTypeAscription {
 753                     source: cast_expr.to_ref(),
 754                     user_ty: Some(*user_ty),
 755                 }
 756             } else {
 757                 cast
 758             }
 759         }
 760         hir::ExprKind::Type(ref source, ref ty) => {
 761             let user_provided_types = cx.tables.user_provided_types();
 762             let user_ty = user_provided_types.get(ty.hir_id).map(|u_ty| *u_ty);
 763             debug!("make_mirror_unadjusted: (type) user_ty={:?}", user_ty);
 764             if source.is_place_expr() {
 765                 ExprKind::PlaceTypeAscription {
 766                     source: source.to_ref(),
 767                     user_ty,
 768                 }
 769             } else {
 770                 ExprKind::ValueTypeAscription {
 771                     source: source.to_ref(),
 772                     user_ty,
 773                 }
 774             }
 775         }
 776         hir::ExprKind::Box(ref value) => {
 777             ExprKind::Box {
 778                 value: value.to_ref(),
 779             }
 780         }
 781         hir::ExprKind::Array(ref fields) => ExprKind::Array { fields: fields.to_ref() },
 782         hir::ExprKind::Tup(ref fields) => ExprKind::Tuple { fields: fields.to_ref() },
 783
 784         hir::ExprKind::Yield(ref v) => ExprKind::Yield { value: v.to_ref() },
 785         hir::ExprKind::Err => unreachable!(),
 786     };
 787
 788     Expr {
 789         temp_lifetime,
 790         ty: expr_ty,
 791         span: expr.span,
 792         kind,
 793     }
 794 }
 795
 796 fn user_substs_applied_to_def(
 797     cx: &mut Cx<'a, 'gcx, 'tcx>,
 798     hir_id: hir::HirId,
 799     def: &Def,
 800 ) -> Option<ty::CanonicalUserType<'tcx>> {
 801     debug!("user_substs_applied_to_def: def={:?}", def);
 802     let user_provided_type = match def {
 803         // A reference to something callable -- e.g., a fn, method, or
 804         // a tuple-struct or tuple-variant. This has the type of a
 805         // `Fn` but with the user-given substitutions.
 806         Def::Fn(_) |
 807         Def::Method(_) |
 808         Def::StructCtor(_, CtorKind::Fn) |
 809         Def::VariantCtor(_, CtorKind::Fn) |
 810         Def::Const(_) |
 811         Def::AssociatedConst(_) => cx.tables().user_provided_types().get(hir_id).map(|u_ty| *u_ty),
 812
 813         // A unit struct/variant which is used as a value (e.g.,
 814         // `None`). This has the type of the enum/struct that defines
 815         // this variant -- but with the substitutions given by the
 816         // user.
 817         Def::StructCtor(_def_id, CtorKind::Const) |
 818         Def::VariantCtor(_def_id, CtorKind::Const) =>
 819             cx.user_substs_applied_to_ty_of_hir_id(hir_id),
 820
 821         // `Self` is used in expression as a tuple struct constructor or an unit struct constructor
 822         Def::SelfCtor(_) =>
 823             cx.user_substs_applied_to_ty_of_hir_id(hir_id),
 824
 825         _ =>
 826             bug!("user_substs_applied_to_def: unexpected def {:?} at {:?}", def, hir_id)
 827     };
 828     debug!("user_substs_applied_to_def: user_provided_type={:?}", user_provided_type);
 829     user_provided_type
 830 }
 831
 832 fn method_callee<'a, 'gcx, 'tcx>(
 833     cx: &mut Cx<'a, 'gcx, 'tcx>,
 834     expr: &hir::Expr,
 835     span: Span,
 836     overloaded_callee: Option<(DefId, &'tcx Substs<'tcx>)>,
 837 ) -> Expr<'tcx> {
 838     let temp_lifetime = cx.region_scope_tree.temporary_scope(expr.hir_id.local_id);
 839     let (def_id, substs, user_ty) = match overloaded_callee {
 840         Some((def_id, substs)) => (def_id, substs, None),
 841         None => {
 842             let type_dependent_defs = cx.tables().type_dependent_defs();
 843             let def = type_dependent_defs
 844                 .get(expr.hir_id)
 845                 .unwrap_or_else(|| {
 846                     span_bug!(expr.span, "no type-dependent def for method callee")
 847                 });
 848             let user_ty = user_substs_applied_to_def(cx, expr.hir_id, def);
 849             debug!("method_callee: user_ty={:?}", user_ty);
 850             (def.def_id(), cx.tables().node_substs(expr.hir_id), user_ty)
 851         }
 852     };
 853     let ty = cx.tcx().mk_fn_def(def_id, substs);
 854     Expr {
 855         temp_lifetime,
 856         ty,
 857         span,
 858         kind: ExprKind::Literal {
 859             literal: cx.tcx().mk_lazy_const(ty::LazyConst::Evaluated(
 860                 ty::Const::zero_sized(ty)
 861             )),
 862             user_ty,
 863         },
 864     }
 865 }
 866
 867 trait ToBorrowKind { fn to_borrow_kind(&self) -> BorrowKind; }
 868
 869 impl ToBorrowKind for AutoBorrowMutability {
 870     fn to_borrow_kind(&self) -> BorrowKind {
 871         use rustc::ty::adjustment::AllowTwoPhase;
 872         match *self {
 873             AutoBorrowMutability::Mutable { allow_two_phase_borrow } =>
 874                 BorrowKind::Mut { allow_two_phase_borrow: match allow_two_phase_borrow {
 875                     AllowTwoPhase::Yes => true,
 876                     AllowTwoPhase::No => false
 877                 }},
 878             AutoBorrowMutability::Immutable =>
 879                 BorrowKind::Shared,
 880         }
 881     }
 882 }
 883
 884 impl ToBorrowKind for hir::Mutability {
 885     fn to_borrow_kind(&self) -> BorrowKind {
 886         match *self {
 887             hir::MutMutable => BorrowKind::Mut { allow_two_phase_borrow: false },
 888             hir::MutImmutable => BorrowKind::Shared,
 889         }
 890     }
 891 }
 892
 893 fn convert_arm<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>, arm: &'tcx hir::Arm) -> Arm<'tcx> {
 894     Arm {
 895         patterns: arm.pats.iter().map(|p| cx.pattern_from_hir(p)).collect(),
 896         guard: match arm.guard {
 897                 Some(hir::Guard::If(ref e)) => Some(Guard::If(e.to_ref())),
 898                 _ => None,
 899             },
 900         body: arm.body.to_ref(),
 901         // BUG: fix this
 902         lint_level: LintLevel::Inherited,
 903     }
 904 }
 905
 906 fn convert_path_expr<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
 907                                      expr: &'tcx hir::Expr,
 908                                      def: Def)
 909                                      -> ExprKind<'tcx> {
 910     let substs = cx.tables().node_substs(expr.hir_id);
 911     match def {
 912         // A regular function, constructor function or a constant.
 913         Def::Fn(_) |
 914         Def::Method(_) |
 915         Def::StructCtor(_, CtorKind::Fn) |
 916         Def::VariantCtor(_, CtorKind::Fn) |
 917         Def::SelfCtor(..) => {
 918             let user_ty = user_substs_applied_to_def(cx, expr.hir_id, &def);
 919             debug!("convert_path_expr: user_ty={:?}", user_ty);
 920             ExprKind::Literal {
 921                 literal: cx.tcx.mk_lazy_const(ty::LazyConst::Evaluated(ty::Const::zero_sized(
 922                     cx.tables().node_type(expr.hir_id),
 923                 ))),
 924                 user_ty,
 925             }
 926         },
 927
 928         Def::Const(def_id) |
 929         Def::AssociatedConst(def_id) => {
 930             let user_ty = user_substs_applied_to_def(cx, expr.hir_id, &def);
 931             debug!("convert_path_expr: (const) user_ty={:?}", user_ty);
 932             ExprKind::Literal {
 933                 literal: cx.tcx.mk_lazy_const(ty::LazyConst::Unevaluated(def_id, substs)),
 934                 user_ty,
 935             }
 936         },
 937
 938         Def::StructCtor(def_id, CtorKind::Const) |
 939         Def::VariantCtor(def_id, CtorKind::Const) => {
 940             let user_provided_types = cx.tables.user_provided_types();
 941             let user_provided_type = user_provided_types.get(expr.hir_id).map(|u_ty| *u_ty);
 942             debug!("convert_path_expr: user_provided_type={:?}", user_provided_type);
 943             match cx.tables().node_type(expr.hir_id).sty {
 944                 // A unit struct/variant which is used as a value.
 945                 // We return a completely different ExprKind here to account for this special case.
 946                 ty::Adt(adt_def, substs) => {
 947                     ExprKind::Adt {
 948                         adt_def,
 949                         variant_index: adt_def.variant_index_with_id(def_id),
 950                         substs,
 951                         user_ty: user_provided_type,
 952                         fields: vec![],
 953                         base: None,
 954                     }
 955                 }
 956                 ref sty => bug!("unexpected sty: {:?}", sty),
 957             }
 958         }
 959
 960         Def::Static(node_id, _) => ExprKind::StaticRef { id: node_id },
 961
 962         Def::Local(..) | Def::Upvar(..) => convert_var(cx, expr, def),
 963
 964         _ => span_bug!(expr.span, "def `{:?}` not yet implemented", def),
 965     }
 966 }
 967
 968 fn convert_var<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
 969                                expr: &'tcx hir::Expr,
 970                                def: Def)
 971                                -> ExprKind<'tcx> {
 972     let temp_lifetime = cx.region_scope_tree.temporary_scope(expr.hir_id.local_id);
 973
 974     match def {
 975         Def::Local(id) => ExprKind::VarRef { id },
 976
 977         Def::Upvar(var_id, index, closure_expr_id) => {
 978             debug!("convert_var(upvar({:?}, {:?}, {:?}))",
 979                    var_id,
 980                    index,
 981                    closure_expr_id);
 982             let var_hir_id = cx.tcx.hir().node_to_hir_id(var_id);
 983             let var_ty = cx.tables().node_type(var_hir_id);
 984
 985             // FIXME free regions in closures are not right
 986             let closure_ty = cx.tables()
 987                                .node_type(cx.tcx.hir().node_to_hir_id(closure_expr_id));
 988
 989             // FIXME we're just hard-coding the idea that the
 990             // signature will be &self or &mut self and hence will
 991             // have a bound region with number 0
 992             let closure_def_id = cx.tcx.hir().local_def_id(closure_expr_id);
 993             let region = ty::ReFree(ty::FreeRegion {
 994                 scope: closure_def_id,
 995                 bound_region: ty::BoundRegion::BrAnon(0),
 996             });
 997             let region = cx.tcx.mk_region(region);
 998
 999             let self_expr = if let ty::Closure(_, closure_substs) = closure_ty.sty {
1000                 match cx.infcx.closure_kind(closure_def_id, closure_substs).unwrap() {
1001                     ty::ClosureKind::Fn => {
1002                         let ref_closure_ty = cx.tcx.mk_ref(region,
1003                                                            ty::TypeAndMut {
1004                                                                ty: closure_ty,
1005                                                                mutbl: hir::MutImmutable,
1006                                                            });
1007                         Expr {
1008                             ty: closure_ty,
1009                             temp_lifetime: temp_lifetime,
1010                             span: expr.span,
1011                             kind: ExprKind::Deref {
1012                                 arg: Expr {
1013                                     ty: ref_closure_ty,
1014                                     temp_lifetime,
1015                                     span: expr.span,
1016                                     kind: ExprKind::SelfRef,
1017                                 }
1018                                 .to_ref(),
1019                             },
1020                         }
1021                     }
1022                     ty::ClosureKind::FnMut => {
1023                         let ref_closure_ty = cx.tcx.mk_ref(region,
1024                                                            ty::TypeAndMut {
1025                                                                ty: closure_ty,
1026                                                                mutbl: hir::MutMutable,
1027                                                            });
1028                         Expr {
1029                             ty: closure_ty,
1030                             temp_lifetime,
1031                             span: expr.span,
1032                             kind: ExprKind::Deref {
1033                                 arg: Expr {
1034                                     ty: ref_closure_ty,
1035                                     temp_lifetime,
1036                                     span: expr.span,
1037                                     kind: ExprKind::SelfRef,
1038                                 }.to_ref(),
1039                             },
1040                         }
1041                     }
1042                     ty::ClosureKind::FnOnce => {
1043                         Expr {
1044                             ty: closure_ty,
1045                             temp_lifetime,
1046                             span: expr.span,
1047                             kind: ExprKind::SelfRef,
1048                         }
1049                     }
1050                 }
1051             } else {
1052                 Expr {
1053                     ty: closure_ty,
1054                     temp_lifetime,
1055                     span: expr.span,
1056                     kind: ExprKind::SelfRef,
1057                 }
1058             };
1059
1060             // at this point we have `self.n`, which loads up the upvar
1061             let field_kind = ExprKind::Field {
1062                 lhs: self_expr.to_ref(),
1063                 name: Field::new(index),
1064             };
1065
1066             // ...but the upvar might be an `&T` or `&mut T` capture, at which
1067             // point we need an implicit deref
1068             let upvar_id = ty::UpvarId {
1069                 var_path: ty::UpvarPath {hir_id: var_hir_id},
1070                 closure_expr_id: LocalDefId::from_def_id(closure_def_id),
1071             };
1072             match cx.tables().upvar_capture(upvar_id) {
1073                 ty::UpvarCapture::ByValue => field_kind,
1074                 ty::UpvarCapture::ByRef(borrow) => {
1075                     ExprKind::Deref {
1076                         arg: Expr {
1077                             temp_lifetime,
1078                             ty: cx.tcx.mk_ref(borrow.region,
1079                                               ty::TypeAndMut {
1080                                                   ty: var_ty,
1081                                                   mutbl: borrow.kind.to_mutbl_lossy(),
1082                                               }),
1083                             span: expr.span,
1084                             kind: field_kind,
1085                         }.to_ref(),
1086                     }
1087                 }
1088             }
1089         }
1090
1091         _ => span_bug!(expr.span, "type of & not region"),
1092     }
1093 }
1094
1095
1096 fn bin_op(op: hir::BinOpKind) -> BinOp {
1097     match op {
1098         hir::BinOpKind::Add => BinOp::Add,
1099         hir::BinOpKind::Sub => BinOp::Sub,
1100         hir::BinOpKind::Mul => BinOp::Mul,
1101         hir::BinOpKind::Div => BinOp::Div,
1102         hir::BinOpKind::Rem => BinOp::Rem,
1103         hir::BinOpKind::BitXor => BinOp::BitXor,
1104         hir::BinOpKind::BitAnd => BinOp::BitAnd,
1105         hir::BinOpKind::BitOr => BinOp::BitOr,
1106         hir::BinOpKind::Shl => BinOp::Shl,
1107         hir::BinOpKind::Shr => BinOp::Shr,
1108         hir::BinOpKind::Eq => BinOp::Eq,
1109         hir::BinOpKind::Lt => BinOp::Lt,
1110         hir::BinOpKind::Le => BinOp::Le,
1111         hir::BinOpKind::Ne => BinOp::Ne,
1112         hir::BinOpKind::Ge => BinOp::Ge,
1113         hir::BinOpKind::Gt => BinOp::Gt,
1114         _ => bug!("no equivalent for ast binop {:?}", op),
1115     }
1116 }
1117
1118 fn overloaded_operator<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
1119                                        expr: &'tcx hir::Expr,
1120                                        args: Vec<ExprRef<'tcx>>)
1121                                        -> ExprKind<'tcx> {
1122     let fun = method_callee(cx, expr, expr.span, None);
1123     ExprKind::Call {
1124         ty: fun.ty,
1125         fun: fun.to_ref(),
1126         args,
1127         from_hir_call: false,
1128     }
1129 }
1130
1131 fn overloaded_place<'a, 'gcx, 'tcx>(
1132     cx: &mut Cx<'a, 'gcx, 'tcx>,
1133     expr: &'tcx hir::Expr,
1134     place_ty: Ty<'tcx>,
1135     overloaded_callee: Option<(DefId, &'tcx Substs<'tcx>)>,
1136     args: Vec<ExprRef<'tcx>>,
1137 ) -> ExprKind<'tcx> {
1138     // For an overloaded *x or x[y] expression of type T, the method
1139     // call returns an &T and we must add the deref so that the types
1140     // line up (this is because `*x` and `x[y]` represent places):
1141
1142     let recv_ty = match args[0] {
1143         ExprRef::Hair(e) => cx.tables().expr_ty_adjusted(e),
1144         ExprRef::Mirror(ref e) => e.ty
1145     };
1146
1147     // Reconstruct the output assuming it's a reference with the
1148     // same region and mutability as the receiver. This holds for
1149     // `Deref(Mut)::Deref(_mut)` and `Index(Mut)::index(_mut)`.
1150     let (region, mutbl) = match recv_ty.sty {
1151         ty::Ref(region, _, mutbl) => (region, mutbl),
1152         _ => span_bug!(expr.span, "overloaded_place: receiver is not a reference"),
1153     };
1154     let ref_ty = cx.tcx.mk_ref(region, ty::TypeAndMut {
1155         ty: place_ty,
1156         mutbl,
1157     });
1158
1159     // construct the complete expression `foo()` for the overloaded call,
1160     // which will yield the &T type
1161     let temp_lifetime = cx.region_scope_tree.temporary_scope(expr.hir_id.local_id);
1162     let fun = method_callee(cx, expr, expr.span, overloaded_callee);
1163     let ref_expr = Expr {
1164         temp_lifetime,
1165         ty: ref_ty,
1166         span: expr.span,
1167         kind: ExprKind::Call {
1168             ty: fun.ty,
1169             fun: fun.to_ref(),
1170             args,
1171             from_hir_call: false,
1172         },
1173     };
1174
1175     // construct and return a deref wrapper `*foo()`
1176     ExprKind::Deref { arg: ref_expr.to_ref() }
1177 }
1178
1179 fn capture_freevar<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
1180                                    closure_expr: &'tcx hir::Expr,
1181                                    freevar: &hir::Freevar,
1182                                    freevar_ty: Ty<'tcx>)
1183                                    -> ExprRef<'tcx> {
1184     let var_hir_id = cx.tcx.hir().node_to_hir_id(freevar.var_id());
1185     let upvar_id = ty::UpvarId {
1186         var_path: ty::UpvarPath { hir_id: var_hir_id },
1187         closure_expr_id: cx.tcx.hir().local_def_id(closure_expr.id).to_local(),
1188     };
1189     let upvar_capture = cx.tables().upvar_capture(upvar_id);
1190     let temp_lifetime = cx.region_scope_tree.temporary_scope(closure_expr.hir_id.local_id);
1191     let var_ty = cx.tables().node_type(var_hir_id);
1192     let captured_var = Expr {
1193         temp_lifetime,
1194         ty: var_ty,
1195         span: closure_expr.span,
1196         kind: convert_var(cx, closure_expr, freevar.def),
1197     };
1198     match upvar_capture {
1199         ty::UpvarCapture::ByValue => captured_var.to_ref(),
1200         ty::UpvarCapture::ByRef(upvar_borrow) => {
1201             let borrow_kind = match upvar_borrow.kind {
1202                 ty::BorrowKind::ImmBorrow => BorrowKind::Shared,
1203                 ty::BorrowKind::UniqueImmBorrow => BorrowKind::Unique,
1204                 ty::BorrowKind::MutBorrow => BorrowKind::Mut { allow_two_phase_borrow: false }
1205             };
1206             Expr {
1207                 temp_lifetime,
1208                 ty: freevar_ty,
1209                 span: closure_expr.span,
1210                 kind: ExprKind::Borrow {
1211                     borrow_kind,
1212                     arg: captured_var.to_ref(),
1213                 },
1214             }.to_ref()
1215         }
1216     }
1217 }
1218
1219 /// Converts a list of named fields (i.e., for struct-like struct/enum ADTs) into FieldExprRef.
1220 fn field_refs<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
1221                               fields: &'tcx [hir::Field])
1222                               -> Vec<FieldExprRef<'tcx>> {
1223     fields.iter()
1224         .map(|field| {
1225             FieldExprRef {
1226                 name: Field::new(cx.tcx.field_index(field.id, cx.tables)),
1227                 expr: field.expr.to_ref(),
1228             }
1229         })
1230         .collect()
1231 }