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_index::vec::Idx;
   7 use rustc::hir::def::{CtorOf, Res, DefKind, CtorKind};
   8 use rustc::mir::interpret::{GlobalId, ErrorHandled, ConstValue};
   9 use rustc::ty::{self, AdtKind, Ty};
  10 use rustc::ty::adjustment::{Adjustment, Adjust, AutoBorrow, AutoBorrowMutability, PointerCast};
  11 use rustc::ty::subst::{InternalSubsts, SubstsRef};
  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(self, cx: &mut Cx<'_, '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.hir_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: LintLevel::Explicit(self.hir_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, 'tcx>(
  72     cx: &mut Cx<'a, 'tcx>,
  73     hir_expr: &'tcx hir::Expr,
  74     mut expr: Expr<'tcx>,
  75     adjustment: &Adjustment<'tcx>
  76 ) -> Expr<'tcx> {
  77     let Expr { temp_lifetime, mut span, .. } = expr;
  78
  79     // Adjust the span from the block, to the last expression of the
  80     // block. This is a better span when returning a mutable reference
  81     // with too short a lifetime. The error message will use the span
  82     // from the assignment to the return place, which should only point
  83     // at the returned value, not the entire function body.
  84     //
  85     // fn return_short_lived<'a>(x: &'a mut i32) -> &'static mut i32 {
  86     //      x
  87     //   // ^ error message points at this expression.
  88     // }
  89     let mut adjust_span = |expr: &mut Expr<'tcx>| {
  90         if let ExprKind::Block { body } = expr.kind {
  91             if let Some(ref last_expr) = body.expr {
  92                 span = last_expr.span;
  93                 expr.span = span;
  94             }
  95         }
  96     };
  97
  98     let kind = match adjustment.kind {
  99         Adjust::Pointer(PointerCast::Unsize) => {
 100             adjust_span(&mut expr);
 101             ExprKind::Pointer { cast: PointerCast::Unsize, source: expr.to_ref() }
 102         }
 103         Adjust::Pointer(cast) => {
 104             ExprKind::Pointer { cast, source: expr.to_ref() }
 105         }
 106         Adjust::NeverToAny => {
 107             ExprKind::NeverToAny { source: expr.to_ref() }
 108         }
 109         Adjust::Deref(None) => {
 110             adjust_span(&mut expr);
 111             ExprKind::Deref { arg: expr.to_ref() }
 112         }
 113         Adjust::Deref(Some(deref)) => {
 114             // We don't need to do call adjust_span here since
 115             // deref coercions always start with a built-in 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.lifetimes.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     };
 191
 192     Expr {
 193         temp_lifetime,
 194         ty: adjustment.target,
 195         span,
 196         kind,
 197     }
 198 }
 199
 200 fn make_mirror_unadjusted<'a, 'tcx>(
 201     cx: &mut Cx<'a, 'tcx>,
 202     expr: &'tcx hir::Expr,
 203 ) -> Expr<'tcx> {
 204     let expr_ty = cx.tables().expr_ty(expr);
 205     let temp_lifetime = cx.region_scope_tree.temporary_scope(expr.hir_id.local_id);
 206
 207     let kind = match expr.kind {
 208         // Here comes the interesting stuff:
 209         hir::ExprKind::MethodCall(_, method_span, ref args) => {
 210             // Rewrite a.b(c) into UFCS form like Trait::b(a, c)
 211             let expr = method_callee(cx, expr, method_span,None);
 212             let args = args.iter()
 213                 .map(|e| e.to_ref())
 214                 .collect();
 215             ExprKind::Call {
 216                 ty: expr.ty,
 217                 fun: expr.to_ref(),
 218                 args,
 219                 from_hir_call: true,
 220             }
 221         }
 222
 223         hir::ExprKind::Call(ref fun, ref args) => {
 224             if cx.tables().is_method_call(expr) {
 225                 // The callee is something implementing Fn, FnMut, or FnOnce.
 226                 // Find the actual method implementation being called and
 227                 // build the appropriate UFCS call expression with the
 228                 // callee-object as expr parameter.
 229
 230                 // rewrite f(u, v) into FnOnce::call_once(f, (u, v))
 231
 232                 let method = method_callee(cx, expr, fun.span,None);
 233
 234                 let arg_tys = args.iter().map(|e| cx.tables().expr_ty_adjusted(e));
 235                 let tupled_args = Expr {
 236                     ty: cx.tcx.mk_tup(arg_tys),
 237                     temp_lifetime,
 238                     span: expr.span,
 239                     kind: ExprKind::Tuple { fields: args.iter().map(ToRef::to_ref).collect() },
 240                 };
 241
 242                 ExprKind::Call {
 243                     ty: method.ty,
 244                     fun: method.to_ref(),
 245                     args: vec![fun.to_ref(), tupled_args.to_ref()],
 246                     from_hir_call: true,
 247                 }
 248             } else {
 249                 let adt_data = if let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) =
 250                     fun.kind
 251                 {
 252                     // Tuple-like ADTs are represented as ExprKind::Call. We convert them here.
 253                     expr_ty.ty_adt_def().and_then(|adt_def| {
 254                         match path.res {
 255                             Res::Def(DefKind::Ctor(_, CtorKind::Fn), ctor_id) =>
 256                                 Some((adt_def, adt_def.variant_index_with_ctor_id(ctor_id))),
 257                             Res::SelfCtor(..) => Some((adt_def, VariantIdx::new(0))),
 258                             _ => None,
 259                         }
 260                     })
 261                 } else {
 262                     None
 263                 };
 264                 if let Some((adt_def, index)) = adt_data {
 265                     let substs = cx.tables().node_substs(fun.hir_id);
 266                     let user_provided_types = cx.tables().user_provided_types();
 267                     let user_ty = user_provided_types.get(fun.hir_id)
 268                         .map(|u_ty| *u_ty)
 269                         .map(|mut u_ty| {
 270                             if let UserType::TypeOf(ref mut did, _) = &mut u_ty.value {
 271                                 *did = adt_def.did;
 272                             }
 273                             u_ty
 274                         });
 275                     debug!("make_mirror_unadjusted: (call) user_ty={:?}", user_ty);
 276
 277                     let field_refs = args.iter()
 278                         .enumerate()
 279                         .map(|(idx, e)| {
 280                             FieldExprRef {
 281                                 name: Field::new(idx),
 282                                 expr: e.to_ref(),
 283                             }
 284                         })
 285                         .collect();
 286                     ExprKind::Adt {
 287                         adt_def,
 288                         substs,
 289                         variant_index: index,
 290                         fields: field_refs,
 291                         user_ty,
 292                         base: None,
 293                     }
 294                 } else {
 295                     ExprKind::Call {
 296                         ty: cx.tables().node_type(fun.hir_id),
 297                         fun: fun.to_ref(),
 298                         args: args.to_ref(),
 299                         from_hir_call: true,
 300                     }
 301                 }
 302             }
 303         }
 304
 305         hir::ExprKind::AddrOf(mutbl, ref expr) => {
 306             ExprKind::Borrow {
 307                 borrow_kind: mutbl.to_borrow_kind(),
 308                 arg: expr.to_ref(),
 309             }
 310         }
 311
 312         hir::ExprKind::Block(ref blk, _) => ExprKind::Block { body: &blk },
 313
 314         hir::ExprKind::Assign(ref lhs, ref rhs) => {
 315             ExprKind::Assign {
 316                 lhs: lhs.to_ref(),
 317                 rhs: rhs.to_ref(),
 318             }
 319         }
 320
 321         hir::ExprKind::AssignOp(op, ref lhs, ref rhs) => {
 322             if cx.tables().is_method_call(expr) {
 323                 overloaded_operator(cx, expr, vec![lhs.to_ref(), rhs.to_ref()])
 324             } else {
 325                 ExprKind::AssignOp {
 326                     op: bin_op(op.node),
 327                     lhs: lhs.to_ref(),
 328                     rhs: rhs.to_ref(),
 329                 }
 330             }
 331         }
 332
 333         hir::ExprKind::Lit(ref lit) => ExprKind::Literal {
 334             literal: cx.const_eval_literal(&lit.node, expr_ty, lit.span, false),
 335             user_ty: None,
 336         },
 337
 338         hir::ExprKind::Binary(op, ref lhs, ref rhs) => {
 339             if cx.tables().is_method_call(expr) {
 340                 overloaded_operator(cx, expr, vec![lhs.to_ref(), rhs.to_ref()])
 341             } else {
 342                 // FIXME overflow
 343                 match (op.node, cx.constness) {
 344                     // FIXME(eddyb) use logical ops in constants when
 345                     // they can handle that kind of control-flow.
 346                     (hir::BinOpKind::And, hir::Constness::Const) => {
 347                         cx.control_flow_destroyed.push((
 348                             op.span,
 349                             "`&&` operator".into(),
 350                         ));
 351                         ExprKind::Binary {
 352                             op: BinOp::BitAnd,
 353                             lhs: lhs.to_ref(),
 354                             rhs: rhs.to_ref(),
 355                         }
 356                     }
 357                     (hir::BinOpKind::Or, hir::Constness::Const) => {
 358                         cx.control_flow_destroyed.push((
 359                             op.span,
 360                             "`||` operator".into(),
 361                         ));
 362                         ExprKind::Binary {
 363                             op: BinOp::BitOr,
 364                             lhs: lhs.to_ref(),
 365                             rhs: rhs.to_ref(),
 366                         }
 367                     }
 368
 369                     (hir::BinOpKind::And, hir::Constness::NotConst) => {
 370                         ExprKind::LogicalOp {
 371                             op: LogicalOp::And,
 372                             lhs: lhs.to_ref(),
 373                             rhs: rhs.to_ref(),
 374                         }
 375                     }
 376                     (hir::BinOpKind::Or, hir::Constness::NotConst) => {
 377                         ExprKind::LogicalOp {
 378                             op: LogicalOp::Or,
 379                             lhs: lhs.to_ref(),
 380                             rhs: rhs.to_ref(),
 381                         }
 382                     }
 383
 384                     _ => {
 385                         let op = bin_op(op.node);
 386                         ExprKind::Binary {
 387                             op,
 388                             lhs: lhs.to_ref(),
 389                             rhs: rhs.to_ref(),
 390                         }
 391                     }
 392                 }
 393             }
 394         }
 395
 396         hir::ExprKind::Index(ref lhs, ref index) => {
 397             if cx.tables().is_method_call(expr) {
 398                 overloaded_place(cx, expr, expr_ty, None, vec![lhs.to_ref(), index.to_ref()])
 399             } else {
 400                 ExprKind::Index {
 401                     lhs: lhs.to_ref(),
 402                     index: index.to_ref(),
 403                 }
 404             }
 405         }
 406
 407         hir::ExprKind::Unary(hir::UnOp::UnDeref, ref arg) => {
 408             if cx.tables().is_method_call(expr) {
 409                 overloaded_place(cx, expr, expr_ty, None, vec![arg.to_ref()])
 410             } else {
 411                 ExprKind::Deref { arg: arg.to_ref() }
 412             }
 413         }
 414
 415         hir::ExprKind::Unary(hir::UnOp::UnNot, ref arg) => {
 416             if cx.tables().is_method_call(expr) {
 417                 overloaded_operator(cx, expr, vec![arg.to_ref()])
 418             } else {
 419                 ExprKind::Unary {
 420                     op: UnOp::Not,
 421                     arg: arg.to_ref(),
 422                 }
 423             }
 424         }
 425
 426         hir::ExprKind::Unary(hir::UnOp::UnNeg, ref arg) => {
 427             if cx.tables().is_method_call(expr) {
 428                 overloaded_operator(cx, expr, vec![arg.to_ref()])
 429             } else {
 430                 if let hir::ExprKind::Lit(ref lit) = arg.kind {
 431                     ExprKind::Literal {
 432                         literal: cx.const_eval_literal(&lit.node, expr_ty, lit.span, true),
 433                         user_ty: None,
 434                     }
 435                 } else {
 436                     ExprKind::Unary {
 437                         op: UnOp::Neg,
 438                         arg: arg.to_ref(),
 439                     }
 440                 }
 441             }
 442         }
 443
 444         hir::ExprKind::Struct(ref qpath, ref fields, ref base) => {
 445             match expr_ty.kind {
 446                 ty::Adt(adt, substs) => {
 447                     match adt.adt_kind() {
 448                         AdtKind::Struct | AdtKind::Union => {
 449                             let user_provided_types = cx.tables().user_provided_types();
 450                             let user_ty = user_provided_types.get(expr.hir_id).map(|u_ty| *u_ty);
 451                             debug!("make_mirror_unadjusted: (struct/union) user_ty={:?}", user_ty);
 452                             ExprKind::Adt {
 453                                 adt_def: adt,
 454                                 variant_index: VariantIdx::new(0),
 455                                 substs,
 456                                 user_ty,
 457                                 fields: field_refs(cx, fields),
 458                                 base: base.as_ref().map(|base| {
 459                                     FruInfo {
 460                                         base: base.to_ref(),
 461                                         field_types: cx.tables()
 462                                                        .fru_field_types()[expr.hir_id]
 463                                                        .clone(),
 464                                     }
 465                                 }),
 466                             }
 467                         }
 468                         AdtKind::Enum => {
 469                             let res = cx.tables().qpath_res(qpath, expr.hir_id);
 470                             match res {
 471                                 Res::Def(DefKind::Variant, variant_id) => {
 472                                     assert!(base.is_none());
 473
 474                                     let index = adt.variant_index_with_id(variant_id);
 475                                     let user_provided_types = cx.tables().user_provided_types();
 476                                     let user_ty = user_provided_types.get(expr.hir_id)
 477                                         .map(|u_ty| *u_ty);
 478                                     debug!(
 479                                         "make_mirror_unadjusted: (variant) user_ty={:?}",
 480                                         user_ty
 481                                     );
 482                                     ExprKind::Adt {
 483                                         adt_def: adt,
 484                                         variant_index: index,
 485                                         substs,
 486                                         user_ty,
 487                                         fields: field_refs(cx, fields),
 488                                         base: None,
 489                                     }
 490                                 }
 491                                 _ => {
 492                                     span_bug!(expr.span, "unexpected res: {:?}", res);
 493                                 }
 494                             }
 495                         }
 496                     }
 497                 }
 498                 _ => {
 499                     span_bug!(expr.span,
 500                               "unexpected type for struct literal: {:?}",
 501                               expr_ty);
 502                 }
 503             }
 504         }
 505
 506         hir::ExprKind::Closure(..) => {
 507             let closure_ty = cx.tables().expr_ty(expr);
 508             let (def_id, substs, movability) = match closure_ty.kind {
 509                 ty::Closure(def_id, substs) => (def_id,
 510                     UpvarSubsts::Closure(substs), None),
 511                 ty::Generator(def_id, substs, movability) => {
 512                     (def_id, UpvarSubsts::Generator(substs), Some(movability))
 513                 }
 514                 _ => {
 515                     span_bug!(expr.span, "closure expr w/o closure type: {:?}", closure_ty);
 516                 }
 517             };
 518             let upvars = cx.tcx.upvars(def_id).iter()
 519                 .flat_map(|upvars| upvars.iter())
 520                 .zip(substs.upvar_tys(def_id, cx.tcx))
 521                 .map(|((&var_hir_id, _), ty)| capture_upvar(cx, expr, var_hir_id, ty))
 522                 .collect();
 523             ExprKind::Closure {
 524                 closure_id: def_id,
 525                 substs,
 526                 upvars,
 527                 movability,
 528             }
 529         }
 530
 531         hir::ExprKind::Path(ref qpath) => {
 532             let res = cx.tables().qpath_res(qpath, expr.hir_id);
 533             convert_path_expr(cx, expr, res)
 534         }
 535
 536         hir::ExprKind::InlineAsm(ref asm, ref outputs, ref inputs) => {
 537             ExprKind::InlineAsm {
 538                 asm,
 539                 outputs: outputs.to_ref(),
 540                 inputs: inputs.to_ref(),
 541             }
 542         }
 543
 544         // Now comes the rote stuff:
 545         hir::ExprKind::Repeat(ref v, ref count) => {
 546             let def_id = cx.tcx.hir().local_def_id(count.hir_id);
 547             let substs = InternalSubsts::identity_for_item(cx.tcx, def_id);
 548             let instance = ty::Instance::resolve(
 549                 cx.tcx,
 550                 cx.param_env,
 551                 def_id,
 552                 substs,
 553             ).unwrap();
 554             let global_id = GlobalId {
 555                 instance,
 556                 promoted: None
 557             };
 558             let span = cx.tcx.def_span(def_id);
 559             let count = match cx.tcx.at(span).const_eval(cx.param_env.and(global_id)) {
 560                 Ok(cv) => cv.eval_usize(cx.tcx, cx.param_env),
 561                 Err(ErrorHandled::Reported) => 0,
 562                 Err(ErrorHandled::TooGeneric) => {
 563                     cx.tcx.sess.span_err(span, "array lengths can't depend on generic parameters");
 564                     0
 565                 },
 566             };
 567
 568             ExprKind::Repeat {
 569                 value: v.to_ref(),
 570                 count,
 571             }
 572         }
 573         hir::ExprKind::Ret(ref v) => ExprKind::Return { value: v.to_ref() },
 574         hir::ExprKind::Break(dest, ref value) => {
 575             match dest.target_id {
 576                 Ok(target_id) => ExprKind::Break {
 577                     label: region::Scope {
 578                         id: target_id.local_id,
 579                         data: region::ScopeData::Node
 580                     },
 581                     value: value.to_ref(),
 582                 },
 583                 Err(err) => bug!("invalid loop id for break: {}", err)
 584             }
 585         }
 586         hir::ExprKind::Continue(dest) => {
 587             match dest.target_id {
 588                 Ok(loop_id) => ExprKind::Continue {
 589                     label: region::Scope {
 590                         id: loop_id.local_id,
 591                         data: region::ScopeData::Node
 592                     },
 593                 },
 594                 Err(err) => bug!("invalid loop id for continue: {}", err)
 595             }
 596         }
 597         hir::ExprKind::Match(ref discr, ref arms, _) => {
 598             ExprKind::Match {
 599                 scrutinee: discr.to_ref(),
 600                 arms: arms.iter().map(|a| convert_arm(cx, a)).collect(),
 601             }
 602         }
 603         hir::ExprKind::Loop(ref body, _, _) => {
 604             ExprKind::Loop {
 605                 body: block::to_expr_ref(cx, body),
 606             }
 607         }
 608         hir::ExprKind::Field(ref source, ..) => {
 609             ExprKind::Field {
 610                 lhs: source.to_ref(),
 611                 name: Field::new(cx.tcx.field_index(expr.hir_id, cx.tables)),
 612             }
 613         }
 614         hir::ExprKind::Cast(ref source, ref cast_ty) => {
 615             // Check for a user-given type annotation on this `cast`
 616             let user_provided_types = cx.tables.user_provided_types();
 617             let user_ty = user_provided_types.get(cast_ty.hir_id);
 618
 619             debug!(
 620                 "cast({:?}) has ty w/ hir_id {:?} and user provided ty {:?}",
 621                 expr,
 622                 cast_ty.hir_id,
 623                 user_ty,
 624             );
 625
 626             // Check to see if this cast is a "coercion cast", where the cast is actually done
 627             // using a coercion (or is a no-op).
 628             let cast = if cx.tables().is_coercion_cast(source.hir_id) {
 629                 // Convert the lexpr to a vexpr.
 630                 ExprKind::Use { source: source.to_ref() }
 631             } else {
 632                 // check whether this is casting an enum variant discriminant
 633                 // to prevent cycles, we refer to the discriminant initializer
 634                 // which is always an integer and thus doesn't need to know the
 635                 // enum's layout (or its tag type) to compute it during const eval
 636                 // Example:
 637                 // enum Foo {
 638                 //     A,
 639                 //     B = A as isize + 4,
 640                 // }
 641                 // The correct solution would be to add symbolic computations to miri,
 642                 // so we wouldn't have to compute and store the actual value
 643                 let var = if let hir::ExprKind::Path(ref qpath) = source.kind {
 644                     let res = cx.tables().qpath_res(qpath, source.hir_id);
 645                     cx
 646                         .tables()
 647                         .node_type(source.hir_id)
 648                         .ty_adt_def()
 649                         .and_then(|adt_def| {
 650                         match res {
 651                             Res::Def(
 652                                 DefKind::Ctor(CtorOf::Variant, CtorKind::Const),
 653                                 variant_ctor_id,
 654                             ) => {
 655                                 let idx = adt_def.variant_index_with_ctor_id(variant_ctor_id);
 656                                 let (d, o) = adt_def.discriminant_def_for_variant(idx);
 657                                 use rustc::ty::util::IntTypeExt;
 658                                 let ty = adt_def.repr.discr_type();
 659                                 let ty = ty.to_ty(cx.tcx());
 660                                 Some((d, o, ty))
 661                             }
 662                             _ => None,
 663                         }
 664                     })
 665                 } else {
 666                     None
 667                 };
 668
 669                 let source = if let Some((did, offset, var_ty)) = var {
 670                     let mk_const = |literal| Expr {
 671                         temp_lifetime,
 672                         ty: var_ty,
 673                         span: expr.span,
 674                         kind: ExprKind::Literal {
 675                             literal,
 676                             user_ty: None
 677                         },
 678                     }.to_ref();
 679                     let offset = mk_const(ty::Const::from_bits(
 680                         cx.tcx,
 681                         offset as u128,
 682                         cx.param_env.and(var_ty),
 683                     ));
 684                     match did {
 685                         Some(did) => {
 686                             // in case we are offsetting from a computed discriminant
 687                             // and not the beginning of discriminants (which is always `0`)
 688                             let substs = InternalSubsts::identity_for_item(cx.tcx(), did);
 689                             let lhs = mk_const(cx.tcx().mk_const(ty::Const {
 690                                 val: ConstValue::Unevaluated(did, substs),
 691                                 ty: var_ty,
 692                             }));
 693                             let bin = ExprKind::Binary {
 694                                 op: BinOp::Add,
 695                                 lhs,
 696                                 rhs: offset,
 697                             };
 698                             Expr {
 699                                 temp_lifetime,
 700                                 ty: var_ty,
 701                                 span: expr.span,
 702                                 kind: bin,
 703                             }.to_ref()
 704                         },
 705                         None => offset,
 706                     }
 707                 } else {
 708                     source.to_ref()
 709                 };
 710
 711                 ExprKind::Cast { source }
 712             };
 713
 714             if let Some(user_ty) = user_ty {
 715                 // NOTE: Creating a new Expr and wrapping a Cast inside of it may be
 716                 //       inefficient, revisit this when performance becomes an issue.
 717                 let cast_expr = Expr {
 718                     temp_lifetime,
 719                     ty: expr_ty,
 720                     span: expr.span,
 721                     kind: cast,
 722                 };
 723                 debug!("make_mirror_unadjusted: (cast) user_ty={:?}", user_ty);
 724
 725                 ExprKind::ValueTypeAscription {
 726                     source: cast_expr.to_ref(),
 727                     user_ty: Some(*user_ty),
 728                 }
 729             } else {
 730                 cast
 731             }
 732         }
 733         hir::ExprKind::Type(ref source, ref ty) => {
 734             let user_provided_types = cx.tables.user_provided_types();
 735             let user_ty = user_provided_types.get(ty.hir_id).map(|u_ty| *u_ty);
 736             debug!("make_mirror_unadjusted: (type) user_ty={:?}", user_ty);
 737             if source.is_place_expr() {
 738                 ExprKind::PlaceTypeAscription {
 739                     source: source.to_ref(),
 740                     user_ty,
 741                 }
 742             } else {
 743                 ExprKind::ValueTypeAscription {
 744                     source: source.to_ref(),
 745                     user_ty,
 746                 }
 747             }
 748         }
 749         hir::ExprKind::DropTemps(ref source) => {
 750             ExprKind::Use { source: source.to_ref() }
 751         }
 752         hir::ExprKind::Box(ref value) => {
 753             ExprKind::Box {
 754                 value: value.to_ref(),
 755             }
 756         }
 757         hir::ExprKind::Array(ref fields) => ExprKind::Array { fields: fields.to_ref() },
 758         hir::ExprKind::Tup(ref fields) => ExprKind::Tuple { fields: fields.to_ref() },
 759
 760         hir::ExprKind::Yield(ref v, _) => ExprKind::Yield { value: v.to_ref() },
 761         hir::ExprKind::Err => unreachable!(),
 762     };
 763
 764     Expr {
 765         temp_lifetime,
 766         ty: expr_ty,
 767         span: expr.span,
 768         kind,
 769     }
 770 }
 771
 772 fn user_substs_applied_to_res(
 773     cx: &mut Cx<'a, 'tcx>,
 774     hir_id: hir::HirId,
 775     res: Res,
 776 ) -> Option<ty::CanonicalUserType<'tcx>> {
 777     debug!("user_substs_applied_to_res: res={:?}", res);
 778     let user_provided_type = match res {
 779         // A reference to something callable -- e.g., a fn, method, or
 780         // a tuple-struct or tuple-variant. This has the type of a
 781         // `Fn` but with the user-given substitutions.
 782         Res::Def(DefKind::Fn, _) |
 783         Res::Def(DefKind::Method, _) |
 784         Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) |
 785         Res::Def(DefKind::Const, _) |
 786         Res::Def(DefKind::AssocConst, _) =>
 787             cx.tables().user_provided_types().get(hir_id).map(|u_ty| *u_ty),
 788
 789         // A unit struct/variant which is used as a value (e.g.,
 790         // `None`). This has the type of the enum/struct that defines
 791         // this variant -- but with the substitutions given by the
 792         // user.
 793         Res::Def(DefKind::Ctor(_, CtorKind::Const), _) =>
 794             cx.user_substs_applied_to_ty_of_hir_id(hir_id),
 795
 796         // `Self` is used in expression as a tuple struct constructor or an unit struct constructor
 797         Res::SelfCtor(_) =>
 798             cx.user_substs_applied_to_ty_of_hir_id(hir_id),
 799
 800         _ =>
 801             bug!("user_substs_applied_to_res: unexpected res {:?} at {:?}", res, hir_id)
 802     };
 803     debug!("user_substs_applied_to_res: user_provided_type={:?}", user_provided_type);
 804     user_provided_type
 805 }
 806
 807 fn method_callee<'a, 'tcx>(
 808     cx: &mut Cx<'a, 'tcx>,
 809     expr: &hir::Expr,
 810     span: Span,
 811     overloaded_callee: Option<(DefId, SubstsRef<'tcx>)>,
 812 ) -> Expr<'tcx> {
 813     let temp_lifetime = cx.region_scope_tree.temporary_scope(expr.hir_id.local_id);
 814     let (def_id, substs, user_ty) = match overloaded_callee {
 815         Some((def_id, substs)) => (def_id, substs, None),
 816         None => {
 817             let (kind, def_id) = cx.tables().type_dependent_def(expr.hir_id)
 818                 .unwrap_or_else(|| {
 819                     span_bug!(expr.span, "no type-dependent def for method callee")
 820                 });
 821             let user_ty = user_substs_applied_to_res(cx, expr.hir_id, Res::Def(kind, def_id));
 822             debug!("method_callee: user_ty={:?}", user_ty);
 823             (def_id, cx.tables().node_substs(expr.hir_id), user_ty)
 824         }
 825     };
 826     let ty = cx.tcx().mk_fn_def(def_id, substs);
 827     Expr {
 828         temp_lifetime,
 829         ty,
 830         span,
 831         kind: ExprKind::Literal {
 832             literal: ty::Const::zero_sized(cx.tcx(), ty),
 833             user_ty,
 834         },
 835     }
 836 }
 837
 838 trait ToBorrowKind { fn to_borrow_kind(&self) -> BorrowKind; }
 839
 840 impl ToBorrowKind for AutoBorrowMutability {
 841     fn to_borrow_kind(&self) -> BorrowKind {
 842         use rustc::ty::adjustment::AllowTwoPhase;
 843         match *self {
 844             AutoBorrowMutability::Mutable { allow_two_phase_borrow } =>
 845                 BorrowKind::Mut { allow_two_phase_borrow: match allow_two_phase_borrow {
 846                     AllowTwoPhase::Yes => true,
 847                     AllowTwoPhase::No => false
 848                 }},
 849             AutoBorrowMutability::Immutable =>
 850                 BorrowKind::Shared,
 851         }
 852     }
 853 }
 854
 855 impl ToBorrowKind for hir::Mutability {
 856     fn to_borrow_kind(&self) -> BorrowKind {
 857         match *self {
 858             hir::MutMutable => BorrowKind::Mut { allow_two_phase_borrow: false },
 859             hir::MutImmutable => BorrowKind::Shared,
 860         }
 861     }
 862 }
 863
 864 fn convert_arm<'tcx>(cx: &mut Cx<'_, 'tcx>, arm: &'tcx hir::Arm) -> Arm<'tcx> {
 865     Arm {
 866         pattern: cx.pattern_from_hir(&arm.pat),
 867         guard: match arm.guard {
 868                 Some(hir::Guard::If(ref e)) => Some(Guard::If(e.to_ref())),
 869                 _ => None,
 870             },
 871         body: arm.body.to_ref(),
 872         lint_level: LintLevel::Explicit(arm.hir_id),
 873         scope: region::Scope {
 874             id: arm.hir_id.local_id,
 875             data: region::ScopeData::Node
 876         },
 877         span: arm.span,
 878     }
 879 }
 880
 881 fn convert_path_expr<'a, 'tcx>(
 882     cx: &mut Cx<'a, 'tcx>,
 883     expr: &'tcx hir::Expr,
 884     res: Res,
 885 ) -> ExprKind<'tcx> {
 886     let substs = cx.tables().node_substs(expr.hir_id);
 887     match res {
 888         // A regular function, constructor function or a constant.
 889         Res::Def(DefKind::Fn, _) |
 890         Res::Def(DefKind::Method, _) |
 891         Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) |
 892         Res::SelfCtor(..) => {
 893             let user_ty = user_substs_applied_to_res(cx, expr.hir_id, res);
 894             debug!("convert_path_expr: user_ty={:?}", user_ty);
 895             ExprKind::Literal {
 896                 literal: ty::Const::zero_sized(
 897                     cx.tcx,
 898                     cx.tables().node_type(expr.hir_id),
 899                 ),
 900                 user_ty,
 901             }
 902         }
 903
 904         Res::Def(DefKind::ConstParam, def_id) => {
 905             let hir_id = cx.tcx.hir().as_local_hir_id(def_id).unwrap();
 906             let item_id = cx.tcx.hir().get_parent_node(hir_id);
 907             let item_def_id = cx.tcx.hir().local_def_id(item_id);
 908             let generics = cx.tcx.generics_of(item_def_id);
 909             let local_def_id = cx.tcx.hir().local_def_id(hir_id);
 910             let index = generics.param_def_id_to_index[&local_def_id];
 911             let name = cx.tcx.hir().name(hir_id);
 912             let val = ConstValue::Param(ty::ParamConst::new(index, name));
 913             ExprKind::Literal {
 914                 literal: cx.tcx.mk_const(
 915                     ty::Const {
 916                         val,
 917                         ty: cx.tables().node_type(expr.hir_id),
 918                     }
 919                 ),
 920                 user_ty: None,
 921             }
 922         }
 923
 924         Res::Def(DefKind::Const, def_id) |
 925         Res::Def(DefKind::AssocConst, def_id) => {
 926             let user_ty = user_substs_applied_to_res(cx, expr.hir_id, res);
 927             debug!("convert_path_expr: (const) user_ty={:?}", user_ty);
 928             ExprKind::Literal {
 929                 literal: cx.tcx.mk_const(ty::Const {
 930                     val: ConstValue::Unevaluated(def_id, substs),
 931                     ty: cx.tables().node_type(expr.hir_id),
 932                 }),
 933                 user_ty,
 934             }
 935         },
 936
 937         Res::Def(DefKind::Ctor(_, CtorKind::Const), def_id) => {
 938             let user_provided_types = cx.tables.user_provided_types();
 939             let user_provided_type = user_provided_types.get(expr.hir_id).map(|u_ty| *u_ty);
 940             debug!("convert_path_expr: user_provided_type={:?}", user_provided_type);
 941             let ty = cx.tables().node_type(expr.hir_id);
 942             match ty.kind {
 943                 // A unit struct/variant which is used as a value.
 944                 // We return a completely different ExprKind here to account for this special case.
 945                 ty::Adt(adt_def, substs) => {
 946                     ExprKind::Adt {
 947                         adt_def,
 948                         variant_index: adt_def.variant_index_with_ctor_id(def_id),
 949                         substs,
 950                         user_ty: user_provided_type,
 951                         fields: vec![],
 952                         base: None,
 953                     }
 954                 }
 955                 _ => bug!("unexpected ty: {:?}", ty),
 956             }
 957         }
 958
 959         Res::Def(DefKind::Static, id) => ExprKind::StaticRef { id },
 960
 961         Res::Local(var_hir_id) => convert_var(cx, expr, var_hir_id),
 962
 963         _ => span_bug!(expr.span, "res `{:?}` not yet implemented", res),
 964     }
 965 }
 966
 967 fn convert_var(
 968     cx: &mut Cx<'_, 'tcx>,
 969     expr: &'tcx hir::Expr,
 970     var_hir_id: hir::HirId,
 971 ) -> ExprKind<'tcx> {
 972     let upvar_index = cx.tables().upvar_list.get(&cx.body_owner)
 973         .and_then(|upvars| upvars.get_full(&var_hir_id).map(|(i, _, _)| i));
 974
 975     debug!("convert_var({:?}): upvar_index={:?}, body_owner={:?}",
 976            var_hir_id, upvar_index, cx.body_owner);
 977
 978     let temp_lifetime = cx.region_scope_tree.temporary_scope(expr.hir_id.local_id);
 979
 980     match upvar_index {
 981         None => ExprKind::VarRef { id: var_hir_id },
 982
 983         Some(upvar_index) => {
 984             let closure_def_id = cx.body_owner;
 985             let upvar_id = ty::UpvarId {
 986                 var_path: ty::UpvarPath {hir_id: var_hir_id},
 987                 closure_expr_id: LocalDefId::from_def_id(closure_def_id),
 988             };
 989             let var_ty = cx.tables().node_type(var_hir_id);
 990
 991             // FIXME free regions in closures are not right
 992             let closure_ty = cx.tables().node_type(
 993                 cx.tcx.hir().local_def_id_to_hir_id(upvar_id.closure_expr_id),
 994             );
 995
 996             // FIXME we're just hard-coding the idea that the
 997             // signature will be &self or &mut self and hence will
 998             // have a bound region with number 0
 999             let region = ty::ReFree(ty::FreeRegion {
1000                 scope: closure_def_id,
1001                 bound_region: ty::BoundRegion::BrAnon(0),
1002             });
1003             let region = cx.tcx.mk_region(region);
1004
1005             let self_expr = if let ty::Closure(_, closure_substs) = closure_ty.kind {
1006                 match cx.infcx.closure_kind(closure_def_id, closure_substs).unwrap() {
1007                     ty::ClosureKind::Fn => {
1008                         let ref_closure_ty = cx.tcx.mk_ref(region,
1009                                                            ty::TypeAndMut {
1010                                                                ty: closure_ty,
1011                                                                mutbl: hir::MutImmutable,
1012                                                            });
1013                         Expr {
1014                             ty: closure_ty,
1015                             temp_lifetime,
1016                             span: expr.span,
1017                             kind: ExprKind::Deref {
1018                                 arg: Expr {
1019                                     ty: ref_closure_ty,
1020                                     temp_lifetime,
1021                                     span: expr.span,
1022                                     kind: ExprKind::SelfRef,
1023                                 }
1024                                 .to_ref(),
1025                             },
1026                         }
1027                     }
1028                     ty::ClosureKind::FnMut => {
1029                         let ref_closure_ty = cx.tcx.mk_ref(region,
1030                                                            ty::TypeAndMut {
1031                                                                ty: closure_ty,
1032                                                                mutbl: hir::MutMutable,
1033                                                            });
1034                         Expr {
1035                             ty: closure_ty,
1036                             temp_lifetime,
1037                             span: expr.span,
1038                             kind: ExprKind::Deref {
1039                                 arg: Expr {
1040                                     ty: ref_closure_ty,
1041                                     temp_lifetime,
1042                                     span: expr.span,
1043                                     kind: ExprKind::SelfRef,
1044                                 }.to_ref(),
1045                             },
1046                         }
1047                     }
1048                     ty::ClosureKind::FnOnce => {
1049                         Expr {
1050                             ty: closure_ty,
1051                             temp_lifetime,
1052                             span: expr.span,
1053                             kind: ExprKind::SelfRef,
1054                         }
1055                     }
1056                 }
1057             } else {
1058                 Expr {
1059                     ty: closure_ty,
1060                     temp_lifetime,
1061                     span: expr.span,
1062                     kind: ExprKind::SelfRef,
1063                 }
1064             };
1065
1066             // at this point we have `self.n`, which loads up the upvar
1067             let field_kind = ExprKind::Field {
1068                 lhs: self_expr.to_ref(),
1069                 name: Field::new(upvar_index),
1070             };
1071
1072             // ...but the upvar might be an `&T` or `&mut T` capture, at which
1073             // point we need an implicit deref
1074             match cx.tables().upvar_capture(upvar_id) {
1075                 ty::UpvarCapture::ByValue => field_kind,
1076                 ty::UpvarCapture::ByRef(borrow) => {
1077                     ExprKind::Deref {
1078                         arg: Expr {
1079                             temp_lifetime,
1080                             ty: cx.tcx.mk_ref(borrow.region,
1081                                               ty::TypeAndMut {
1082                                                   ty: var_ty,
1083                                                   mutbl: borrow.kind.to_mutbl_lossy(),
1084                                               }),
1085                             span: expr.span,
1086                             kind: field_kind,
1087                         }.to_ref(),
1088                     }
1089                 }
1090             }
1091         }
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, 'tcx>(
1119     cx: &mut Cx<'a, 'tcx>,
1120     expr: &'tcx hir::Expr,
1121     args: Vec<ExprRef<'tcx>>
1122 ) -> ExprKind<'tcx> {
1123     let fun = method_callee(cx, expr, expr.span, None);
1124     ExprKind::Call {
1125         ty: fun.ty,
1126         fun: fun.to_ref(),
1127         args,
1128         from_hir_call: false,
1129     }
1130 }
1131
1132 fn overloaded_place<'a, 'tcx>(
1133     cx: &mut Cx<'a, 'tcx>,
1134     expr: &'tcx hir::Expr,
1135     place_ty: Ty<'tcx>,
1136     overloaded_callee: Option<(DefId, SubstsRef<'tcx>)>,
1137     args: Vec<ExprRef<'tcx>>,
1138 ) -> ExprKind<'tcx> {
1139     // For an overloaded *x or x[y] expression of type T, the method
1140     // call returns an &T and we must add the deref so that the types
1141     // line up (this is because `*x` and `x[y]` represent places):
1142
1143     let recv_ty = match args[0] {
1144         ExprRef::Hair(e) => cx.tables().expr_ty_adjusted(e),
1145         ExprRef::Mirror(ref e) => e.ty
1146     };
1147
1148     // Reconstruct the output assuming it's a reference with the
1149     // same region and mutability as the receiver. This holds for
1150     // `Deref(Mut)::Deref(_mut)` and `Index(Mut)::index(_mut)`.
1151     let (region, mutbl) = match recv_ty.kind {
1152         ty::Ref(region, _, mutbl) => (region, mutbl),
1153         _ => span_bug!(expr.span, "overloaded_place: receiver is not a reference"),
1154     };
1155     let ref_ty = cx.tcx.mk_ref(region, ty::TypeAndMut {
1156         ty: place_ty,
1157         mutbl,
1158     });
1159
1160     // construct the complete expression `foo()` for the overloaded call,
1161     // which will yield the &T type
1162     let temp_lifetime = cx.region_scope_tree.temporary_scope(expr.hir_id.local_id);
1163     let fun = method_callee(cx, expr, expr.span, overloaded_callee);
1164     let ref_expr = Expr {
1165         temp_lifetime,
1166         ty: ref_ty,
1167         span: expr.span,
1168         kind: ExprKind::Call {
1169             ty: fun.ty,
1170             fun: fun.to_ref(),
1171             args,
1172             from_hir_call: false,
1173         },
1174     };
1175
1176     // construct and return a deref wrapper `*foo()`
1177     ExprKind::Deref { arg: ref_expr.to_ref() }
1178 }
1179
1180 fn capture_upvar<'tcx>(
1181     cx: &mut Cx<'_, 'tcx>,
1182     closure_expr: &'tcx hir::Expr,
1183     var_hir_id: hir::HirId,
1184     upvar_ty: Ty<'tcx>
1185 ) -> ExprRef<'tcx> {
1186     let upvar_id = ty::UpvarId {
1187         var_path: ty::UpvarPath { hir_id: var_hir_id },
1188         closure_expr_id: cx.tcx.hir().local_def_id(closure_expr.hir_id).to_local(),
1189     };
1190     let upvar_capture = cx.tables().upvar_capture(upvar_id);
1191     let temp_lifetime = cx.region_scope_tree.temporary_scope(closure_expr.hir_id.local_id);
1192     let var_ty = cx.tables().node_type(var_hir_id);
1193     let captured_var = Expr {
1194         temp_lifetime,
1195         ty: var_ty,
1196         span: closure_expr.span,
1197         kind: convert_var(cx, closure_expr, var_hir_id),
1198     };
1199     match upvar_capture {
1200         ty::UpvarCapture::ByValue => captured_var.to_ref(),
1201         ty::UpvarCapture::ByRef(upvar_borrow) => {
1202             let borrow_kind = match upvar_borrow.kind {
1203                 ty::BorrowKind::ImmBorrow => BorrowKind::Shared,
1204                 ty::BorrowKind::UniqueImmBorrow => BorrowKind::Unique,
1205                 ty::BorrowKind::MutBorrow => BorrowKind::Mut { allow_two_phase_borrow: false }
1206             };
1207             Expr {
1208                 temp_lifetime,
1209                 ty: upvar_ty,
1210                 span: closure_expr.span,
1211                 kind: ExprKind::Borrow {
1212                     borrow_kind,
1213                     arg: captured_var.to_ref(),
1214                 },
1215             }.to_ref()
1216         }
1217     }
1218 }
1219
1220 /// Converts a list of named fields (i.e., for struct-like struct/enum ADTs) into FieldExprRef.
1221 fn field_refs<'a, 'tcx>(
1222     cx: &mut Cx<'a, 'tcx>,
1223     fields: &'tcx [hir::Field]
1224 ) -> Vec<FieldExprRef<'tcx>> {
1225     fields.iter()
1226         .map(|field| {
1227             FieldExprRef {
1228                 name: Field::new(cx.tcx.field_index(field.hir_id, cx.tables)),
1229                 expr: field.expr.to_ref(),
1230             }
1231         })
1232         .collect()
1233 }