src/librustc_mir/hair/cx/expr.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use hair::*;
  12 use rustc_data_structures::indexed_vec::Idx;
  13 use hair::cx::Cx;
  14 use hair::cx::block;
  15 use hair::cx::to_ref::ToRef;
  16 use rustc::hir::def::{Def, CtorKind};
  17 use rustc::mir::interpret::GlobalId;
  18 use rustc::ty::{self, AdtKind, Ty};
  19 use rustc::ty::adjustment::{Adjustment, Adjust, AutoBorrow, AutoBorrowMutability};
  20 use rustc::ty::cast::CastKind as TyCastKind;
  21 use rustc::hir;
  22 use rustc::hir::def_id::LocalDefId;
  23 use rustc::mir::{BorrowKind};
  24 use syntax_pos::Span;
  25
  26 impl<'tcx> Mirror<'tcx> for &'tcx hir::Expr {
  27     type Output = Expr<'tcx>;
  28
  29     fn make_mirror<'a, 'gcx>(self, cx: &mut Cx<'a, 'gcx, 'tcx>) -> Expr<'tcx> {
  30         let temp_lifetime = cx.region_scope_tree.temporary_scope(self.hir_id.local_id);
  31         let expr_scope = region::Scope {
  32             id: self.hir_id.local_id,
  33             data: region::ScopeData::Node
  34         };
  35
  36         debug!("Expr::make_mirror(): id={}, span={:?}", self.id, self.span);
  37
  38         let mut expr = make_mirror_unadjusted(cx, self);
  39
  40         // Now apply adjustments, if any.
  41         for adjustment in cx.tables().expr_adjustments(self) {
  42             debug!("make_mirror: expr={:?} applying adjustment={:?}",
  43                    expr,
  44                    adjustment);
  45             expr = apply_adjustment(cx, self, expr, adjustment);
  46         }
  47
  48         // Next, wrap this up in the expr's scope.
  49         expr = Expr {
  50             temp_lifetime,
  51             ty: expr.ty,
  52             span: self.span,
  53             kind: ExprKind::Scope {
  54                 region_scope: expr_scope,
  55                 value: expr.to_ref(),
  56                 lint_level: cx.lint_level_of(self.id),
  57             },
  58         };
  59
  60         // Finally, create a destruction scope, if any.
  61         if let Some(region_scope) =
  62             cx.region_scope_tree.opt_destruction_scope(self.hir_id.local_id) {
  63                 expr = Expr {
  64                     temp_lifetime,
  65                     ty: expr.ty,
  66                     span: self.span,
  67                     kind: ExprKind::Scope {
  68                         region_scope,
  69                         value: expr.to_ref(),
  70                         lint_level: LintLevel::Inherited,
  71                     },
  72                 };
  73             }
  74
  75         // OK, all done!
  76         expr
  77     }
  78 }
  79
  80 fn apply_adjustment<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
  81                                     hir_expr: &'tcx hir::Expr,
  82                                     mut expr: Expr<'tcx>,
  83                                     adjustment: &Adjustment<'tcx>)
  84                                     -> Expr<'tcx> {
  85     let Expr { temp_lifetime, mut span, .. } = expr;
  86     let kind = match adjustment.kind {
  87         Adjust::ReifyFnPointer => {
  88             ExprKind::ReifyFnPointer { source: expr.to_ref() }
  89         }
  90         Adjust::UnsafeFnPointer => {
  91             ExprKind::UnsafeFnPointer { source: expr.to_ref() }
  92         }
  93         Adjust::ClosureFnPointer => {
  94             ExprKind::ClosureFnPointer { source: expr.to_ref() }
  95         }
  96         Adjust::NeverToAny => {
  97             ExprKind::NeverToAny { source: expr.to_ref() }
  98         }
  99         Adjust::MutToConstPointer => {
 100             ExprKind::Cast { source: expr.to_ref() }
 101         }
 102         Adjust::Deref(None) => {
 103             // Adjust the span from the block, to the last expression of the
 104             // block. This is a better span when returning a mutable reference
 105             // with too short a lifetime. The error message will use the span
 106             // from the assignment to the return place, which should only point
 107             // at the returned value, not the entire function body.
 108             //
 109             // fn return_short_lived<'a>(x: &'a mut i32) -> &'static mut i32 {
 110             //      x
 111             //   // ^ error message points at this expression.
 112             // }
 113             //
 114             // We don't need to do this adjustment in the next match arm since
 115             // deref coercions always start with a built-in deref.
 116             if let ExprKind::Block { body } = expr.kind {
 117                 if let Some(ref last_expr) = body.expr {
 118                     span = last_expr.span;
 119                     expr.span = span;
 120                 }
 121             }
 122             ExprKind::Deref { arg: expr.to_ref() }
 123         }
 124         Adjust::Deref(Some(deref)) => {
 125             let call = deref.method_call(cx.tcx(), expr.ty);
 126
 127             expr = Expr {
 128                 temp_lifetime,
 129                 ty: cx.tcx.mk_ref(deref.region,
 130                                   ty::TypeAndMut {
 131                                     ty: expr.ty,
 132                                     mutbl: deref.mutbl,
 133                                   }),
 134                 span,
 135                 kind: ExprKind::Borrow {
 136                     region: deref.region,
 137                     borrow_kind: deref.mutbl.to_borrow_kind(),
 138                     arg: expr.to_ref(),
 139                 },
 140             };
 141
 142             overloaded_place(cx, hir_expr, adjustment.target, Some(call), vec![expr.to_ref()])
 143         }
 144         Adjust::Borrow(AutoBorrow::Ref(r, m)) => {
 145             ExprKind::Borrow {
 146                 region: r,
 147                 borrow_kind: m.to_borrow_kind(),
 148                 arg: expr.to_ref(),
 149             }
 150         }
 151         Adjust::Borrow(AutoBorrow::RawPtr(m)) => {
 152             // Convert this to a suitable `&foo` and
 153             // then an unsafe coercion. Limit the region to be just this
 154             // expression.
 155             let region = ty::ReScope(region::Scope {
 156                 id: hir_expr.hir_id.local_id,
 157                 data: region::ScopeData::Node
 158             });
 159             let region = cx.tcx.mk_region(region);
 160             expr = Expr {
 161                 temp_lifetime,
 162                 ty: cx.tcx.mk_ref(region,
 163                                   ty::TypeAndMut {
 164                                     ty: expr.ty,
 165                                     mutbl: m,
 166                                   }),
 167                 span,
 168                 kind: ExprKind::Borrow {
 169                     region,
 170                     borrow_kind: m.to_borrow_kind(),
 171                     arg: expr.to_ref(),
 172                 },
 173             };
 174             let cast_expr = Expr {
 175                 temp_lifetime,
 176                 ty: adjustment.target,
 177                 span,
 178                 kind: ExprKind::Cast { source: expr.to_ref() }
 179             };
 180
 181             // To ensure that both implicit and explicit coercions are
 182             // handled the same way, we insert an extra layer of indirection here.
 183             // For explicit casts (e.g. 'foo as *const T'), the source of the 'Use'
 184             // will be an ExprKind::Hair with the appropriate cast expression. Here,
 185             // we make our Use source the generated Cast from the original coercion.
 186             //
 187             // In both cases, this outer 'Use' ensures that the inner 'Cast' is handled by
 188             // as_operand, not by as_rvalue - causing the cast result to be stored in a temporary.
 189             // Ordinary, this is identical to using the cast directly as an rvalue. However, if the
 190             // source of the cast was previously borrowed as mutable, storing the cast in a
 191             // temporary gives the source a chance to expire before the cast is used. For
 192             // structs with a self-referential *mut ptr, this allows assignment to work as
 193             // expected.
 194             //
 195             // For example, consider the type 'struct Foo { field: *mut Foo }',
 196             // The method 'fn bar(&mut self) { self.field = self }'
 197             // triggers a coercion from '&mut self' to '*mut self'. In order
 198             // for the assignment to be valid, the implicit borrow
 199             // of 'self' involved in the coercion needs to end before the local
 200             // containing the '*mut T' is assigned to 'self.field' - otherwise,
 201             // we end up trying to assign to 'self.field' while we have another mutable borrow
 202             // active.
 203             //
 204             // We only need to worry about this kind of thing for coercions from refs to ptrs,
 205             // since they get rid of a borrow implicitly.
 206             ExprKind::Use { source: cast_expr.to_ref() }
 207         }
 208         Adjust::Unsize => {
 209             // See the above comment for Adjust::Deref
 210             if let ExprKind::Block { body } = expr.kind {
 211                 if let Some(ref last_expr) = body.expr {
 212                     span = last_expr.span;
 213                     expr.span = span;
 214                 }
 215             }
 216             ExprKind::Unsize { source: expr.to_ref() }
 217         }
 218     };
 219
 220     Expr {
 221         temp_lifetime,
 222         ty: adjustment.target,
 223         span,
 224         kind,
 225     }
 226 }
 227
 228 fn make_mirror_unadjusted<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
 229                                           expr: &'tcx hir::Expr)
 230                                           -> Expr<'tcx> {
 231     let expr_ty = cx.tables().expr_ty(expr);
 232     let temp_lifetime = cx.region_scope_tree.temporary_scope(expr.hir_id.local_id);
 233
 234     let kind = match expr.node {
 235         // Here comes the interesting stuff:
 236         hir::ExprKind::MethodCall(_, method_span, ref args) => {
 237             // Rewrite a.b(c) into UFCS form like Trait::b(a, c)
 238             let expr = method_callee(cx, expr, method_span,None);
 239             let args = args.iter()
 240                 .map(|e| e.to_ref())
 241                 .collect();
 242             ExprKind::Call {
 243                 ty: expr.ty,
 244                 fun: expr.to_ref(),
 245                 args,
 246                 from_hir_call: true,
 247             }
 248         }
 249
 250         hir::ExprKind::Call(ref fun, ref args) => {
 251             if cx.tables().is_method_call(expr) {
 252                 // The callee is something implementing Fn, FnMut, or FnOnce.
 253                 // Find the actual method implementation being called and
 254                 // build the appropriate UFCS call expression with the
 255                 // callee-object as expr parameter.
 256
 257                 // rewrite f(u, v) into FnOnce::call_once(f, (u, v))
 258
 259                 let method = method_callee(cx, expr, fun.span,None);
 260
 261                 let arg_tys = args.iter().map(|e| cx.tables().expr_ty_adjusted(e));
 262                 let tupled_args = Expr {
 263                     ty: cx.tcx.mk_tup(arg_tys),
 264                     temp_lifetime,
 265                     span: expr.span,
 266                     kind: ExprKind::Tuple { fields: args.iter().map(ToRef::to_ref).collect() },
 267                 };
 268
 269                 ExprKind::Call {
 270                     ty: method.ty,
 271                     fun: method.to_ref(),
 272                     args: vec![fun.to_ref(), tupled_args.to_ref()],
 273                     from_hir_call: true,
 274                 }
 275             } else {
 276                 let adt_data = if let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) =
 277                     fun.node
 278                 {
 279                     // Tuple-like ADTs are represented as ExprKind::Call. We convert them here.
 280                     expr_ty.ty_adt_def().and_then(|adt_def| {
 281                         match path.def {
 282                             Def::VariantCtor(variant_id, CtorKind::Fn) => {
 283                                 Some((adt_def, adt_def.variant_index_with_id(variant_id)))
 284                             }
 285                             Def::StructCtor(_, CtorKind::Fn) |
 286                             Def::SelfCtor(..) => Some((adt_def, 0)),
 287                             _ => None,
 288                         }
 289                     })
 290                 } else {
 291                     None
 292                 };
 293                 if let Some((adt_def, index)) = adt_data {
 294                     let substs = cx.tables().node_substs(fun.hir_id);
 295
 296                     let user_ty = cx.tables().user_substs(fun.hir_id)
 297                         .map(|user_substs| {
 298                             user_substs.unchecked_map(|user_substs| {
 299                                 // Here, we just pair an `AdtDef` with the
 300                                 // `user_substs`, so no new types etc are introduced.
 301                                 cx.tcx().mk_adt(adt_def, user_substs)
 302                             })
 303                         });
 304
 305                     let field_refs = args.iter()
 306                         .enumerate()
 307                         .map(|(idx, e)| {
 308                             FieldExprRef {
 309                                 name: Field::new(idx),
 310                                 expr: e.to_ref(),
 311                             }
 312                         })
 313                         .collect();
 314                     ExprKind::Adt {
 315                         adt_def,
 316                         substs,
 317                         variant_index: index,
 318                         fields: field_refs,
 319                         user_ty,
 320                         base: None,
 321                     }
 322                 } else {
 323                     ExprKind::Call {
 324                         ty: cx.tables().node_id_to_type(fun.hir_id),
 325                         fun: fun.to_ref(),
 326                         args: args.to_ref(),
 327                         from_hir_call: true,
 328                     }
 329                 }
 330             }
 331         }
 332
 333         hir::ExprKind::AddrOf(mutbl, ref expr) => {
 334             let region = match expr_ty.sty {
 335                 ty::Ref(r, _, _) => r,
 336                 _ => span_bug!(expr.span, "type of & not region"),
 337             };
 338             ExprKind::Borrow {
 339                 region,
 340                 borrow_kind: mutbl.to_borrow_kind(),
 341                 arg: expr.to_ref(),
 342             }
 343         }
 344
 345         hir::ExprKind::Block(ref blk, _) => ExprKind::Block { body: &blk },
 346
 347         hir::ExprKind::Assign(ref lhs, ref rhs) => {
 348             ExprKind::Assign {
 349                 lhs: lhs.to_ref(),
 350                 rhs: rhs.to_ref(),
 351             }
 352         }
 353
 354         hir::ExprKind::AssignOp(op, ref lhs, ref rhs) => {
 355             if cx.tables().is_method_call(expr) {
 356                 overloaded_operator(cx, expr, vec![lhs.to_ref(), rhs.to_ref()])
 357             } else {
 358                 ExprKind::AssignOp {
 359                     op: bin_op(op.node),
 360                     lhs: lhs.to_ref(),
 361                     rhs: rhs.to_ref(),
 362                 }
 363             }
 364         }
 365
 366         hir::ExprKind::Lit(ref lit) => ExprKind::Literal {
 367             literal: cx.const_eval_literal(&lit.node, expr_ty, lit.span, false),
 368             user_ty: None,
 369         },
 370
 371         hir::ExprKind::Binary(op, ref lhs, ref rhs) => {
 372             if cx.tables().is_method_call(expr) {
 373                 overloaded_operator(cx, expr, vec![lhs.to_ref(), rhs.to_ref()])
 374             } else {
 375                 // FIXME overflow
 376                 match (op.node, cx.constness) {
 377                     // FIXME(eddyb) use logical ops in constants when
 378                     // they can handle that kind of control-flow.
 379                     (hir::BinOpKind::And, hir::Constness::Const) => {
 380                         ExprKind::Binary {
 381                             op: BinOp::BitAnd,
 382                             lhs: lhs.to_ref(),
 383                             rhs: rhs.to_ref(),
 384                         }
 385                     }
 386                     (hir::BinOpKind::Or, hir::Constness::Const) => {
 387                         ExprKind::Binary {
 388                             op: BinOp::BitOr,
 389                             lhs: lhs.to_ref(),
 390                             rhs: rhs.to_ref(),
 391                         }
 392                     }
 393
 394                     (hir::BinOpKind::And, hir::Constness::NotConst) => {
 395                         ExprKind::LogicalOp {
 396                             op: LogicalOp::And,
 397                             lhs: lhs.to_ref(),
 398                             rhs: rhs.to_ref(),
 399                         }
 400                     }
 401                     (hir::BinOpKind::Or, hir::Constness::NotConst) => {
 402                         ExprKind::LogicalOp {
 403                             op: LogicalOp::Or,
 404                             lhs: lhs.to_ref(),
 405                             rhs: rhs.to_ref(),
 406                         }
 407                     }
 408
 409                     _ => {
 410                         let op = bin_op(op.node);
 411                         ExprKind::Binary {
 412                             op,
 413                             lhs: lhs.to_ref(),
 414                             rhs: rhs.to_ref(),
 415                         }
 416                     }
 417                 }
 418             }
 419         }
 420
 421         hir::ExprKind::Index(ref lhs, ref index) => {
 422             if cx.tables().is_method_call(expr) {
 423                 overloaded_place(cx, expr, expr_ty, None, vec![lhs.to_ref(), index.to_ref()])
 424             } else {
 425                 ExprKind::Index {
 426                     lhs: lhs.to_ref(),
 427                     index: index.to_ref(),
 428                 }
 429             }
 430         }
 431
 432         hir::ExprKind::Unary(hir::UnOp::UnDeref, ref arg) => {
 433             if cx.tables().is_method_call(expr) {
 434                 overloaded_place(cx, expr, expr_ty, None, vec![arg.to_ref()])
 435             } else {
 436                 ExprKind::Deref { arg: arg.to_ref() }
 437             }
 438         }
 439
 440         hir::ExprKind::Unary(hir::UnOp::UnNot, ref arg) => {
 441             if cx.tables().is_method_call(expr) {
 442                 overloaded_operator(cx, expr, vec![arg.to_ref()])
 443             } else {
 444                 ExprKind::Unary {
 445                     op: UnOp::Not,
 446                     arg: arg.to_ref(),
 447                 }
 448             }
 449         }
 450
 451         hir::ExprKind::Unary(hir::UnOp::UnNeg, ref arg) => {
 452             if cx.tables().is_method_call(expr) {
 453                 overloaded_operator(cx, expr, vec![arg.to_ref()])
 454             } else {
 455                 if let hir::ExprKind::Lit(ref lit) = arg.node {
 456                     ExprKind::Literal {
 457                         literal: cx.const_eval_literal(&lit.node, expr_ty, lit.span, true),
 458                         user_ty: None,
 459                     }
 460                 } else {
 461                     ExprKind::Unary {
 462                         op: UnOp::Neg,
 463                         arg: arg.to_ref(),
 464                     }
 465                 }
 466             }
 467         }
 468
 469         hir::ExprKind::Struct(ref qpath, ref fields, ref base) => {
 470             match expr_ty.sty {
 471                 ty::Adt(adt, substs) => {
 472                     match adt.adt_kind() {
 473                         AdtKind::Struct | AdtKind::Union => {
 474                             ExprKind::Adt {
 475                                 adt_def: adt,
 476                                 variant_index: 0,
 477                                 substs,
 478                                 user_ty: user_annotated_ty_for_adt(cx, expr.hir_id, adt),
 479                                 fields: field_refs(cx, fields),
 480                                 base: base.as_ref().map(|base| {
 481                                     FruInfo {
 482                                         base: base.to_ref(),
 483                                         field_types: cx.tables()
 484                                                        .fru_field_types()[expr.hir_id]
 485                                                        .clone(),
 486                                     }
 487                                 }),
 488                             }
 489                         }
 490                         AdtKind::Enum => {
 491                             let def = match *qpath {
 492                                 hir::QPath::Resolved(_, ref path) => path.def,
 493                                 hir::QPath::TypeRelative(..) => Def::Err,
 494                             };
 495                             match def {
 496                                 Def::Variant(variant_id) => {
 497                                     assert!(base.is_none());
 498
 499                                     let index = adt.variant_index_with_id(variant_id);
 500                                     ExprKind::Adt {
 501                                         adt_def: adt,
 502                                         variant_index: index,
 503                                         substs,
 504                                         user_ty: user_annotated_ty_for_adt(cx, expr.hir_id, adt),
 505                                         fields: field_refs(cx, fields),
 506                                         base: None,
 507                                     }
 508                                 }
 509                                 _ => {
 510                                     span_bug!(expr.span, "unexpected def: {:?}", def);
 511                                 }
 512                             }
 513                         }
 514                     }
 515                 }
 516                 _ => {
 517                     span_bug!(expr.span,
 518                               "unexpected type for struct literal: {:?}",
 519                               expr_ty);
 520                 }
 521             }
 522         }
 523
 524         hir::ExprKind::Closure(..) => {
 525             let closure_ty = cx.tables().expr_ty(expr);
 526             let (def_id, substs, movability) = match closure_ty.sty {
 527                 ty::Closure(def_id, substs) => (def_id, UpvarSubsts::Closure(substs), None),
 528                 ty::Generator(def_id, substs, movability) => {
 529                     (def_id, UpvarSubsts::Generator(substs), Some(movability))
 530                 }
 531                 _ => {
 532                     span_bug!(expr.span, "closure expr w/o closure type: {:?}", closure_ty);
 533                 }
 534             };
 535             let upvars = cx.tcx.with_freevars(expr.id, |freevars| {
 536                 freevars.iter()
 537                     .zip(substs.upvar_tys(def_id, cx.tcx))
 538                     .map(|(fv, ty)| capture_freevar(cx, expr, fv, ty))
 539                     .collect()
 540             });
 541             ExprKind::Closure {
 542                 closure_id: def_id,
 543                 substs,
 544                 upvars,
 545                 movability,
 546             }
 547         }
 548
 549         hir::ExprKind::Path(ref qpath) => {
 550             let def = cx.tables().qpath_def(qpath, expr.hir_id);
 551             convert_path_expr(cx, expr, def)
 552         }
 553
 554         hir::ExprKind::InlineAsm(ref asm, ref outputs, ref inputs) => {
 555             ExprKind::InlineAsm {
 556                 asm,
 557                 outputs: outputs.to_ref(),
 558                 inputs: inputs.to_ref(),
 559             }
 560         }
 561
 562         // Now comes the rote stuff:
 563         hir::ExprKind::Repeat(ref v, ref count) => {
 564             let def_id = cx.tcx.hir.local_def_id(count.id);
 565             let substs = Substs::identity_for_item(cx.tcx.global_tcx(), def_id);
 566             let instance = ty::Instance::resolve(
 567                 cx.tcx.global_tcx(),
 568                 cx.param_env,
 569                 def_id,
 570                 substs,
 571             ).unwrap();
 572             let global_id = GlobalId {
 573                 instance,
 574                 promoted: None
 575             };
 576             let span = cx.tcx.def_span(def_id);
 577             let count = match cx.tcx.at(span).const_eval(cx.param_env.and(global_id)) {
 578                 Ok(cv) => cv.unwrap_usize(cx.tcx),
 579                 Err(e) => {
 580                     e.report_as_error(cx.tcx.at(span), "could not evaluate array length");
 581                     0
 582                 },
 583             };
 584
 585             ExprKind::Repeat {
 586                 value: v.to_ref(),
 587                 count,
 588             }
 589         }
 590         hir::ExprKind::Ret(ref v) => ExprKind::Return { value: v.to_ref() },
 591         hir::ExprKind::Break(dest, ref value) => {
 592             match dest.target_id {
 593                 Ok(target_id) => ExprKind::Break {
 594                     label: region::Scope {
 595                         id: cx.tcx.hir.node_to_hir_id(target_id).local_id,
 596                         data: region::ScopeData::Node
 597                     },
 598                     value: value.to_ref(),
 599                 },
 600                 Err(err) => bug!("invalid loop id for break: {}", err)
 601             }
 602         }
 603         hir::ExprKind::Continue(dest) => {
 604             match dest.target_id {
 605                 Ok(loop_id) => ExprKind::Continue {
 606                     label: region::Scope {
 607                         id: cx.tcx.hir.node_to_hir_id(loop_id).local_id,
 608                         data: region::ScopeData::Node
 609                     },
 610                 },
 611                 Err(err) => bug!("invalid loop id for continue: {}", err)
 612             }
 613         }
 614         hir::ExprKind::Match(ref discr, ref arms, _) => {
 615             ExprKind::Match {
 616                 discriminant: discr.to_ref(),
 617                 arms: arms.iter().map(|a| convert_arm(cx, a)).collect(),
 618             }
 619         }
 620         hir::ExprKind::If(ref cond, ref then, ref otherwise) => {
 621             ExprKind::If {
 622                 condition: cond.to_ref(),
 623                 then: then.to_ref(),
 624                 otherwise: otherwise.to_ref(),
 625             }
 626         }
 627         hir::ExprKind::While(ref cond, ref body, _) => {
 628             ExprKind::Loop {
 629                 condition: Some(cond.to_ref()),
 630                 body: block::to_expr_ref(cx, body),
 631             }
 632         }
 633         hir::ExprKind::Loop(ref body, _, _) => {
 634             ExprKind::Loop {
 635                 condition: None,
 636                 body: block::to_expr_ref(cx, body),
 637             }
 638         }
 639         hir::ExprKind::Field(ref source, ..) => {
 640             ExprKind::Field {
 641                 lhs: source.to_ref(),
 642                 name: Field::new(cx.tcx.field_index(expr.id, cx.tables)),
 643             }
 644         }
 645         hir::ExprKind::Cast(ref source, _) => {
 646             // Check to see if this cast is a "coercion cast", where the cast is actually done
 647             // using a coercion (or is a no-op).
 648             if let Some(&TyCastKind::CoercionCast) = cx.tables()
 649                                                     .cast_kinds()
 650                                                     .get(source.hir_id) {
 651                 // Convert the lexpr to a vexpr.
 652                 ExprKind::Use { source: source.to_ref() }
 653             } else {
 654                 // check whether this is casting an enum variant discriminant
 655                 // to prevent cycles, we refer to the discriminant initializer
 656                 // which is always an integer and thus doesn't need to know the
 657                 // enum's layout (or its tag type) to compute it during const eval
 658                 // Example:
 659                 // enum Foo {
 660                 //     A,
 661                 //     B = A as isize + 4,
 662                 // }
 663                 // The correct solution would be to add symbolic computations to miri,
 664                 // so we wouldn't have to compute and store the actual value
 665                 let var = if let hir::ExprKind::Path(ref qpath) = source.node {
 666                     let def = cx.tables().qpath_def(qpath, source.hir_id);
 667                     cx
 668                         .tables()
 669                         .node_id_to_type(source.hir_id)
 670                         .ty_adt_def()
 671                         .and_then(|adt_def| {
 672                         match def {
 673                             Def::VariantCtor(variant_id, CtorKind::Const) => {
 674                                 let idx = adt_def.variant_index_with_id(variant_id);
 675                                 let (d, o) = adt_def.discriminant_def_for_variant(idx);
 676                                 use rustc::ty::util::IntTypeExt;
 677                                 let ty = adt_def.repr.discr_type();
 678                                 let ty = ty.to_ty(cx.tcx());
 679                                 Some((d, o, ty))
 680                             }
 681                             _ => None,
 682                         }
 683                     })
 684                 } else {
 685                     None
 686                 };
 687                 let source = if let Some((did, offset, ty)) = var {
 688                     let mk_const = |literal| Expr {
 689                         temp_lifetime,
 690                         ty,
 691                         span: expr.span,
 692                         kind: ExprKind::Literal { literal, user_ty: None },
 693                     }.to_ref();
 694                     let offset = mk_const(ty::Const::from_bits(
 695                         cx.tcx,
 696                         offset as u128,
 697                         cx.param_env.and(ty),
 698                     ));
 699                     match did {
 700                         Some(did) => {
 701                             // in case we are offsetting from a computed discriminant
 702                             // and not the beginning of discriminants (which is always `0`)
 703                             let substs = Substs::identity_for_item(cx.tcx(), did);
 704                             let lhs = mk_const(ty::Const::unevaluated(cx.tcx(), did, substs, ty));
 705                             let bin = ExprKind::Binary {
 706                                 op: BinOp::Add,
 707                                 lhs,
 708                                 rhs: offset,
 709                             };
 710                             Expr {
 711                                 temp_lifetime,
 712                                 ty,
 713                                 span: expr.span,
 714                                 kind: bin,
 715                             }.to_ref()
 716                         },
 717                         None => offset,
 718                     }
 719                 } else {
 720                     source.to_ref()
 721                 };
 722                 ExprKind::Cast { source }
 723             }
 724         }
 725         hir::ExprKind::Type(ref source, ref ty) => {
 726             let user_provided_tys = cx.tables.user_provided_tys();
 727             let user_ty = *user_provided_tys
 728                 .get(ty.hir_id)
 729                 .expect(&format!("{:?} not found in user_provided_tys, source: {:?}", ty, source));
 730             if source.is_place_expr() {
 731                 ExprKind::PlaceTypeAscription {
 732                     source: source.to_ref(),
 733                     user_ty,
 734                 }
 735             } else {
 736                 ExprKind::ValueTypeAscription {
 737                     source: source.to_ref(),
 738                     user_ty,
 739                 }
 740             }
 741         }
 742         hir::ExprKind::Box(ref value) => {
 743             ExprKind::Box {
 744                 value: value.to_ref(),
 745             }
 746         }
 747         hir::ExprKind::Array(ref fields) => ExprKind::Array { fields: fields.to_ref() },
 748         hir::ExprKind::Tup(ref fields) => ExprKind::Tuple { fields: fields.to_ref() },
 749
 750         hir::ExprKind::Yield(ref v) => ExprKind::Yield { value: v.to_ref() },
 751     };
 752
 753     Expr {
 754         temp_lifetime,
 755         ty: expr_ty,
 756         span: expr.span,
 757         kind,
 758     }
 759 }
 760
 761 fn user_annotated_ty_for_def(
 762     cx: &mut Cx<'a, 'gcx, 'tcx>,
 763     hir_id: hir::HirId,
 764     def: &Def,
 765 ) -> Option<CanonicalTy<'tcx>> {
 766     match def {
 767         // A reference to something callable -- e.g., a fn, method, or
 768         // a tuple-struct or tuple-variant. This has the type of a
 769         // `Fn` but with the user-given substitutions.
 770         Def::Fn(_) |
 771         Def::Method(_) |
 772         Def::StructCtor(_, CtorKind::Fn) |
 773         Def::VariantCtor(_, CtorKind::Fn) =>
 774             Some(cx.tables().user_substs(hir_id)?.unchecked_map(|user_substs| {
 775                 // Here, we just pair a `DefId` with the
 776                 // `user_substs`, so no new types etc are introduced.
 777                 cx.tcx().mk_fn_def(def.def_id(), user_substs)
 778             })),
 779
 780         Def::Const(_def_id) |
 781         Def::AssociatedConst(_def_id) =>
 782             bug!("unimplemented"),
 783
 784         // A unit struct/variant which is used as a value (e.g.,
 785         // `None`). This has the type of the enum/struct that defines
 786         // this variant -- but with the substitutions given by the
 787         // user.
 788         Def::StructCtor(_def_id, CtorKind::Const) |
 789         Def::VariantCtor(_def_id, CtorKind::Const) =>
 790             match &cx.tables().node_id_to_type(hir_id).sty {
 791                 ty::Adt(adt_def, _) => user_annotated_ty_for_adt(cx, hir_id, adt_def),
 792                 sty => bug!("unexpected sty: {:?}", sty),
 793             },
 794
 795         // `Self` is used in expression as a tuple struct constructor or an unit struct constructor
 796         Def::SelfCtor(_) => {
 797             let sty = &cx.tables().node_id_to_type(hir_id).sty;
 798             match sty {
 799                 ty::FnDef(ref def_id, _) => {
 800                     Some(cx.tables().user_substs(hir_id)?.unchecked_map(|user_substs| {
 801                         // Here, we just pair a `DefId` with the
 802                         // `user_substs`, so no new types etc are introduced.
 803                         cx.tcx().mk_fn_def(*def_id, user_substs)
 804                     }))
 805                 }
 806                 ty::Adt(ref adt_def, _) => {
 807                     user_annotated_ty_for_adt(cx, hir_id, adt_def)
 808                 }
 809                 _ => {
 810                     bug!("unexpected sty: {:?}", sty)
 811                 }
 812             }
 813         }
 814         _ =>
 815             bug!("user_annotated_ty_for_def: unexpected def {:?} at {:?}", def, hir_id)
 816     }
 817 }
 818
 819 fn user_annotated_ty_for_adt(
 820     cx: &mut Cx<'a, 'gcx, 'tcx>,
 821     hir_id: hir::HirId,
 822     adt_def: &'tcx AdtDef,
 823 ) -> Option<CanonicalTy<'tcx>> {
 824     let user_substs = cx.tables().user_substs(hir_id)?;
 825     Some(user_substs.unchecked_map(|user_substs| {
 826         // Here, we just pair an `AdtDef` with the
 827         // `user_substs`, so no new types etc are introduced.
 828         cx.tcx().mk_adt(adt_def, user_substs)
 829     }))
 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_annotated_ty_for_def(cx, expr.hir_id, def);
 849             (def.def_id(), cx.tables().node_substs(expr.hir_id), user_ty)
 850         }
 851     };
 852     let ty = cx.tcx().mk_fn_def(def_id, substs);
 853     Expr {
 854         temp_lifetime,
 855         ty,
 856         span,
 857         kind: ExprKind::Literal {
 858             literal: ty::Const::zero_sized(cx.tcx(), ty),
 859             user_ty,
 860         },
 861     }
 862 }
 863
 864 trait ToBorrowKind { fn to_borrow_kind(&self) -> BorrowKind; }
 865
 866 impl ToBorrowKind for AutoBorrowMutability {
 867     fn to_borrow_kind(&self) -> BorrowKind {
 868         use rustc::ty::adjustment::AllowTwoPhase;
 869         match *self {
 870             AutoBorrowMutability::Mutable { allow_two_phase_borrow } =>
 871                 BorrowKind::Mut { allow_two_phase_borrow: match allow_two_phase_borrow {
 872                     AllowTwoPhase::Yes => true,
 873                     AllowTwoPhase::No => false
 874                 }},
 875             AutoBorrowMutability::Immutable =>
 876                 BorrowKind::Shared,
 877         }
 878     }
 879 }
 880
 881 impl ToBorrowKind for hir::Mutability {
 882     fn to_borrow_kind(&self) -> BorrowKind {
 883         match *self {
 884             hir::MutMutable => BorrowKind::Mut { allow_two_phase_borrow: false },
 885             hir::MutImmutable => BorrowKind::Shared,
 886         }
 887     }
 888 }
 889
 890 fn convert_arm<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>, arm: &'tcx hir::Arm) -> Arm<'tcx> {
 891     Arm {
 892         patterns: arm.pats.iter().map(|p| cx.pattern_from_hir(p)).collect(),
 893         guard: match arm.guard {
 894                 Some(hir::Guard::If(ref e)) => Some(Guard::If(e.to_ref())),
 895                 _ => None,
 896             },
 897         body: arm.body.to_ref(),
 898         // BUG: fix this
 899         lint_level: LintLevel::Inherited,
 900     }
 901 }
 902
 903 fn convert_path_expr<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
 904                                      expr: &'tcx hir::Expr,
 905                                      def: Def)
 906                                      -> ExprKind<'tcx> {
 907     let substs = cx.tables().node_substs(expr.hir_id);
 908     match def {
 909         // A regular function, constructor function or a constant.
 910         Def::Fn(_) |
 911         Def::Method(_) |
 912         Def::StructCtor(_, CtorKind::Fn) |
 913         Def::VariantCtor(_, CtorKind::Fn) |
 914         Def::SelfCtor(..) => {
 915             let user_ty = user_annotated_ty_for_def(cx, expr.hir_id, &def);
 916             ExprKind::Literal {
 917                 literal: ty::Const::zero_sized(
 918                     cx.tcx,
 919                     cx.tables().node_id_to_type(expr.hir_id),
 920                 ),
 921                 user_ty,
 922             }
 923         },
 924
 925         Def::Const(def_id) |
 926         Def::AssociatedConst(def_id) => ExprKind::Literal {
 927             literal: ty::Const::unevaluated(
 928                 cx.tcx,
 929                 def_id,
 930                 substs,
 931                 cx.tables().node_id_to_type(expr.hir_id),
 932             ),
 933             user_ty: None, // FIXME(#47184) -- user given type annot on constants
 934         },
 935
 936         Def::StructCtor(def_id, CtorKind::Const) |
 937         Def::VariantCtor(def_id, CtorKind::Const) => {
 938             match cx.tables().node_id_to_type(expr.hir_id).sty {
 939                 // A unit struct/variant which is used as a value.
 940                 // We return a completely different ExprKind here to account for this special case.
 941                 ty::Adt(adt_def, substs) => {
 942                     ExprKind::Adt {
 943                         adt_def,
 944                         variant_index: adt_def.variant_index_with_id(def_id),
 945                         substs,
 946                         user_ty: user_annotated_ty_for_adt(cx, expr.hir_id, adt_def),
 947                         fields: vec![],
 948                         base: None,
 949                     }
 950                 }
 951                 ref sty => bug!("unexpected sty: {:?}", sty),
 952             }
 953         }
 954
 955         Def::Static(node_id, _) => ExprKind::StaticRef { id: node_id },
 956
 957         Def::Local(..) | Def::Upvar(..) => convert_var(cx, expr, def),
 958
 959         _ => span_bug!(expr.span, "def `{:?}` not yet implemented", def),
 960     }
 961 }
 962
 963 fn convert_var<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
 964                                expr: &'tcx hir::Expr,
 965                                def: Def)
 966                                -> ExprKind<'tcx> {
 967     let temp_lifetime = cx.region_scope_tree.temporary_scope(expr.hir_id.local_id);
 968
 969     match def {
 970         Def::Local(id) => ExprKind::VarRef { id },
 971
 972         Def::Upvar(var_id, index, closure_expr_id) => {
 973             debug!("convert_var(upvar({:?}, {:?}, {:?}))",
 974                    var_id,
 975                    index,
 976                    closure_expr_id);
 977             let var_hir_id = cx.tcx.hir.node_to_hir_id(var_id);
 978             let var_ty = cx.tables().node_id_to_type(var_hir_id);
 979
 980             // FIXME free regions in closures are not right
 981             let closure_ty = cx.tables()
 982                                .node_id_to_type(cx.tcx.hir.node_to_hir_id(closure_expr_id));
 983
 984             // FIXME we're just hard-coding the idea that the
 985             // signature will be &self or &mut self and hence will
 986             // have a bound region with number 0
 987             let closure_def_id = cx.tcx.hir.local_def_id(closure_expr_id);
 988             let region = ty::ReFree(ty::FreeRegion {
 989                 scope: closure_def_id,
 990                 bound_region: ty::BoundRegion::BrAnon(0),
 991             });
 992             let region = cx.tcx.mk_region(region);
 993
 994             let self_expr = if let ty::Closure(_, closure_substs) = closure_ty.sty {
 995                 match cx.infcx.closure_kind(closure_def_id, closure_substs).unwrap() {
 996                     ty::ClosureKind::Fn => {
 997                         let ref_closure_ty = cx.tcx.mk_ref(region,
 998                                                            ty::TypeAndMut {
 999                                                                ty: closure_ty,
1000                                                                mutbl: hir::MutImmutable,
1001                                                            });
1002                         Expr {
1003                             ty: closure_ty,
1004                             temp_lifetime: temp_lifetime,
1005                             span: expr.span,
1006                             kind: ExprKind::Deref {
1007                                 arg: Expr {
1008                                     ty: ref_closure_ty,
1009                                     temp_lifetime,
1010                                     span: expr.span,
1011                                     kind: ExprKind::SelfRef,
1012                                 }
1013                                 .to_ref(),
1014                             },
1015                         }
1016                     }
1017                     ty::ClosureKind::FnMut => {
1018                         let ref_closure_ty = cx.tcx.mk_ref(region,
1019                                                            ty::TypeAndMut {
1020                                                                ty: closure_ty,
1021                                                                mutbl: hir::MutMutable,
1022                                                            });
1023                         Expr {
1024                             ty: closure_ty,
1025                             temp_lifetime,
1026                             span: expr.span,
1027                             kind: ExprKind::Deref {
1028                                 arg: Expr {
1029                                     ty: ref_closure_ty,
1030                                     temp_lifetime,
1031                                     span: expr.span,
1032                                     kind: ExprKind::SelfRef,
1033                                 }.to_ref(),
1034                             },
1035                         }
1036                     }
1037                     ty::ClosureKind::FnOnce => {
1038                         Expr {
1039                             ty: closure_ty,
1040                             temp_lifetime,
1041                             span: expr.span,
1042                             kind: ExprKind::SelfRef,
1043                         }
1044                     }
1045                 }
1046             } else {
1047                 Expr {
1048                     ty: closure_ty,
1049                     temp_lifetime,
1050                     span: expr.span,
1051                     kind: ExprKind::SelfRef,
1052                 }
1053             };
1054
1055             // at this point we have `self.n`, which loads up the upvar
1056             let field_kind = ExprKind::Field {
1057                 lhs: self_expr.to_ref(),
1058                 name: Field::new(index),
1059             };
1060
1061             // ...but the upvar might be an `&T` or `&mut T` capture, at which
1062             // point we need an implicit deref
1063             let upvar_id = ty::UpvarId {
1064                 var_id: var_hir_id,
1065                 closure_expr_id: LocalDefId::from_def_id(closure_def_id),
1066             };
1067             match cx.tables().upvar_capture(upvar_id) {
1068                 ty::UpvarCapture::ByValue => field_kind,
1069                 ty::UpvarCapture::ByRef(borrow) => {
1070                     ExprKind::Deref {
1071                         arg: Expr {
1072                             temp_lifetime,
1073                             ty: cx.tcx.mk_ref(borrow.region,
1074                                               ty::TypeAndMut {
1075                                                   ty: var_ty,
1076                                                   mutbl: borrow.kind.to_mutbl_lossy(),
1077                                               }),
1078                             span: expr.span,
1079                             kind: field_kind,
1080                         }.to_ref(),
1081                     }
1082                 }
1083             }
1084         }
1085
1086         _ => span_bug!(expr.span, "type of & not region"),
1087     }
1088 }
1089
1090
1091 fn bin_op(op: hir::BinOpKind) -> BinOp {
1092     match op {
1093         hir::BinOpKind::Add => BinOp::Add,
1094         hir::BinOpKind::Sub => BinOp::Sub,
1095         hir::BinOpKind::Mul => BinOp::Mul,
1096         hir::BinOpKind::Div => BinOp::Div,
1097         hir::BinOpKind::Rem => BinOp::Rem,
1098         hir::BinOpKind::BitXor => BinOp::BitXor,
1099         hir::BinOpKind::BitAnd => BinOp::BitAnd,
1100         hir::BinOpKind::BitOr => BinOp::BitOr,
1101         hir::BinOpKind::Shl => BinOp::Shl,
1102         hir::BinOpKind::Shr => BinOp::Shr,
1103         hir::BinOpKind::Eq => BinOp::Eq,
1104         hir::BinOpKind::Lt => BinOp::Lt,
1105         hir::BinOpKind::Le => BinOp::Le,
1106         hir::BinOpKind::Ne => BinOp::Ne,
1107         hir::BinOpKind::Ge => BinOp::Ge,
1108         hir::BinOpKind::Gt => BinOp::Gt,
1109         _ => bug!("no equivalent for ast binop {:?}", op),
1110     }
1111 }
1112
1113 fn overloaded_operator<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
1114                                        expr: &'tcx hir::Expr,
1115                                        args: Vec<ExprRef<'tcx>>)
1116                                        -> ExprKind<'tcx> {
1117     let fun = method_callee(cx, expr, expr.span, None);
1118     ExprKind::Call {
1119         ty: fun.ty,
1120         fun: fun.to_ref(),
1121         args,
1122         from_hir_call: false,
1123     }
1124 }
1125
1126 fn overloaded_place<'a, 'gcx, 'tcx>(
1127     cx: &mut Cx<'a, 'gcx, 'tcx>,
1128     expr: &'tcx hir::Expr,
1129     place_ty: Ty<'tcx>,
1130     overloaded_callee: Option<(DefId, &'tcx Substs<'tcx>)>,
1131     args: Vec<ExprRef<'tcx>>,
1132 ) -> ExprKind<'tcx> {
1133     // For an overloaded *x or x[y] expression of type T, the method
1134     // call returns an &T and we must add the deref so that the types
1135     // line up (this is because `*x` and `x[y]` represent places):
1136
1137     let recv_ty = match args[0] {
1138         ExprRef::Hair(e) => cx.tables().expr_ty_adjusted(e),
1139         ExprRef::Mirror(ref e) => e.ty
1140     };
1141
1142     // Reconstruct the output assuming it's a reference with the
1143     // same region and mutability as the receiver. This holds for
1144     // `Deref(Mut)::Deref(_mut)` and `Index(Mut)::index(_mut)`.
1145     let (region, mutbl) = match recv_ty.sty {
1146         ty::Ref(region, _, mutbl) => (region, mutbl),
1147         _ => span_bug!(expr.span, "overloaded_place: receiver is not a reference"),
1148     };
1149     let ref_ty = cx.tcx.mk_ref(region, ty::TypeAndMut {
1150         ty: place_ty,
1151         mutbl,
1152     });
1153
1154     // construct the complete expression `foo()` for the overloaded call,
1155     // which will yield the &T type
1156     let temp_lifetime = cx.region_scope_tree.temporary_scope(expr.hir_id.local_id);
1157     let fun = method_callee(cx, expr, expr.span, overloaded_callee);
1158     let ref_expr = Expr {
1159         temp_lifetime,
1160         ty: ref_ty,
1161         span: expr.span,
1162         kind: ExprKind::Call {
1163             ty: fun.ty,
1164             fun: fun.to_ref(),
1165             args,
1166             from_hir_call: false,
1167         },
1168     };
1169
1170     // construct and return a deref wrapper `*foo()`
1171     ExprKind::Deref { arg: ref_expr.to_ref() }
1172 }
1173
1174 fn capture_freevar<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
1175                                    closure_expr: &'tcx hir::Expr,
1176                                    freevar: &hir::Freevar,
1177                                    freevar_ty: Ty<'tcx>)
1178                                    -> ExprRef<'tcx> {
1179     let var_hir_id = cx.tcx.hir.node_to_hir_id(freevar.var_id());
1180     let upvar_id = ty::UpvarId {
1181         var_id: var_hir_id,
1182         closure_expr_id: cx.tcx.hir.local_def_id(closure_expr.id).to_local(),
1183     };
1184     let upvar_capture = cx.tables().upvar_capture(upvar_id);
1185     let temp_lifetime = cx.region_scope_tree.temporary_scope(closure_expr.hir_id.local_id);
1186     let var_ty = cx.tables().node_id_to_type(var_hir_id);
1187     let captured_var = Expr {
1188         temp_lifetime,
1189         ty: var_ty,
1190         span: closure_expr.span,
1191         kind: convert_var(cx, closure_expr, freevar.def),
1192     };
1193     match upvar_capture {
1194         ty::UpvarCapture::ByValue => captured_var.to_ref(),
1195         ty::UpvarCapture::ByRef(upvar_borrow) => {
1196             let borrow_kind = match upvar_borrow.kind {
1197                 ty::BorrowKind::ImmBorrow => BorrowKind::Shared,
1198                 ty::BorrowKind::UniqueImmBorrow => BorrowKind::Unique,
1199                 ty::BorrowKind::MutBorrow => BorrowKind::Mut { allow_two_phase_borrow: false }
1200             };
1201             Expr {
1202                 temp_lifetime,
1203                 ty: freevar_ty,
1204                 span: closure_expr.span,
1205                 kind: ExprKind::Borrow {
1206                     region: upvar_borrow.region,
1207                     borrow_kind,
1208                     arg: captured_var.to_ref(),
1209                 },
1210             }.to_ref()
1211         }
1212     }
1213 }
1214
1215 /// Converts a list of named fields (i.e. for struct-like struct/enum ADTs) into FieldExprRef.
1216 fn field_refs<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
1217                               fields: &'tcx [hir::Field])
1218                               -> Vec<FieldExprRef<'tcx>> {
1219     fields.iter()
1220         .map(|field| {
1221             FieldExprRef {
1222                 name: Field::new(cx.tcx.field_index(field.id, cx.tables)),
1223                 expr: field.expr.to_ref(),
1224             }
1225         })
1226         .collect()
1227 }