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 hair::util::UserAnnotatedTyHelpers;
  17 use rustc::hir::def::{Def, CtorKind};
  18 use rustc::mir::interpret::{GlobalId, ErrorHandled};
  19 use rustc::ty::{self, AdtKind, Ty};
  20 use rustc::ty::adjustment::{Adjustment, Adjust, AutoBorrow, AutoBorrowMutability};
  21 use rustc::ty::cast::CastKind as TyCastKind;
  22 use rustc::hir;
  23 use rustc::hir::def_id::LocalDefId;
  24 use rustc::mir::{BorrowKind};
  25 use syntax_pos::Span;
  26
  27 impl<'tcx> Mirror<'tcx> for &'tcx hir::Expr {
  28     type Output = Expr<'tcx>;
  29
  30     fn make_mirror<'a, 'gcx>(self, cx: &mut Cx<'a, 'gcx, 'tcx>) -> Expr<'tcx> {
  31         let temp_lifetime = cx.region_scope_tree.temporary_scope(self.hir_id.local_id);
  32         let expr_scope = region::Scope {
  33             id: self.hir_id.local_id,
  34             data: region::ScopeData::Node
  35         };
  36
  37         debug!("Expr::make_mirror(): id={}, span={:?}", self.id, self.span);
  38
  39         let mut expr = make_mirror_unadjusted(cx, self);
  40
  41         // Now apply adjustments, if any.
  42         for adjustment in cx.tables().expr_adjustments(self) {
  43             debug!("make_mirror: expr={:?} applying adjustment={:?}",
  44                    expr,
  45                    adjustment);
  46             expr = apply_adjustment(cx, self, expr, adjustment);
  47         }
  48
  49         // Next, wrap this up in the expr's scope.
  50         expr = Expr {
  51             temp_lifetime,
  52             ty: expr.ty,
  53             span: self.span,
  54             kind: ExprKind::Scope {
  55                 region_scope: expr_scope,
  56                 value: expr.to_ref(),
  57                 lint_level: cx.lint_level_of(self.id),
  58             },
  59         };
  60
  61         // Finally, create a destruction scope, if any.
  62         if let Some(region_scope) =
  63             cx.region_scope_tree.opt_destruction_scope(self.hir_id.local_id) {
  64                 expr = Expr {
  65                     temp_lifetime,
  66                     ty: expr.ty,
  67                     span: self.span,
  68                     kind: ExprKind::Scope {
  69                         region_scope,
  70                         value: expr.to_ref(),
  71                         lint_level: LintLevel::Inherited,
  72                     },
  73                 };
  74             }
  75
  76         // OK, all done!
  77         expr
  78     }
  79 }
  80
  81 fn apply_adjustment<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
  82                                     hir_expr: &'tcx hir::Expr,
  83                                     mut expr: Expr<'tcx>,
  84                                     adjustment: &Adjustment<'tcx>)
  85                                     -> Expr<'tcx> {
  86     let Expr { temp_lifetime, mut span, .. } = expr;
  87     let kind = match adjustment.kind {
  88         Adjust::ReifyFnPointer => {
  89             ExprKind::ReifyFnPointer { source: expr.to_ref() }
  90         }
  91         Adjust::UnsafeFnPointer => {
  92             ExprKind::UnsafeFnPointer { source: expr.to_ref() }
  93         }
  94         Adjust::ClosureFnPointer => {
  95             ExprKind::ClosureFnPointer { source: expr.to_ref() }
  96         }
  97         Adjust::NeverToAny => {
  98             ExprKind::NeverToAny { source: expr.to_ref() }
  99         }
 100         Adjust::MutToConstPointer => {
 101             ExprKind::Cast { source: expr.to_ref() }
 102         }
 103         Adjust::Deref(None) => {
 104             // Adjust the span from the block, to the last expression of the
 105             // block. This is a better span when returning a mutable reference
 106             // with too short a lifetime. The error message will use the span
 107             // from the assignment to the return place, which should only point
 108             // at the returned value, not the entire function body.
 109             //
 110             // fn return_short_lived<'a>(x: &'a mut i32) -> &'static mut i32 {
 111             //      x
 112             //   // ^ error message points at this expression.
 113             // }
 114             //
 115             // We don't need to do this adjustment in the next match arm since
 116             // deref coercions always start with a built-in deref.
 117             if let ExprKind::Block { body } = expr.kind {
 118                 if let Some(ref last_expr) = body.expr {
 119                     span = last_expr.span;
 120                     expr.span = span;
 121                 }
 122             }
 123             ExprKind::Deref { arg: expr.to_ref() }
 124         }
 125         Adjust::Deref(Some(deref)) => {
 126             let call = deref.method_call(cx.tcx(), expr.ty);
 127
 128             expr = Expr {
 129                 temp_lifetime,
 130                 ty: cx.tcx.mk_ref(deref.region,
 131                                   ty::TypeAndMut {
 132                                     ty: expr.ty,
 133                                     mutbl: deref.mutbl,
 134                                   }),
 135                 span,
 136                 kind: ExprKind::Borrow {
 137                     region: deref.region,
 138                     borrow_kind: deref.mutbl.to_borrow_kind(),
 139                     arg: expr.to_ref(),
 140                 },
 141             };
 142
 143             overloaded_place(cx, hir_expr, adjustment.target, Some(call), vec![expr.to_ref()])
 144         }
 145         Adjust::Borrow(AutoBorrow::Ref(r, m)) => {
 146             ExprKind::Borrow {
 147                 region: r,
 148                 borrow_kind: m.to_borrow_kind(),
 149                 arg: expr.to_ref(),
 150             }
 151         }
 152         Adjust::Borrow(AutoBorrow::RawPtr(m)) => {
 153             // Convert this to a suitable `&foo` and
 154             // then an unsafe coercion. Limit the region to be just this
 155             // expression.
 156             let region = ty::ReScope(region::Scope {
 157                 id: hir_expr.hir_id.local_id,
 158                 data: region::ScopeData::Node
 159             });
 160             let region = cx.tcx.mk_region(region);
 161             expr = Expr {
 162                 temp_lifetime,
 163                 ty: cx.tcx.mk_ref(region,
 164                                   ty::TypeAndMut {
 165                                     ty: expr.ty,
 166                                     mutbl: m,
 167                                   }),
 168                 span,
 169                 kind: ExprKind::Borrow {
 170                     region,
 171                     borrow_kind: m.to_borrow_kind(),
 172                     arg: expr.to_ref(),
 173                 },
 174             };
 175             let cast_expr = Expr {
 176                 temp_lifetime,
 177                 ty: adjustment.target,
 178                 span,
 179                 kind: ExprKind::Cast { source: expr.to_ref() }
 180             };
 181
 182             // To ensure that both implicit and explicit coercions are
 183             // handled the same way, we insert an extra layer of indirection here.
 184             // For explicit casts (e.g., 'foo as *const T'), the source of the 'Use'
 185             // will be an ExprKind::Hair with the appropriate cast expression. Here,
 186             // we make our Use source the generated Cast from the original coercion.
 187             //
 188             // In both cases, this outer 'Use' ensures that the inner 'Cast' is handled by
 189             // as_operand, not by as_rvalue - causing the cast result to be stored in a temporary.
 190             // Ordinary, this is identical to using the cast directly as an rvalue. However, if the
 191             // source of the cast was previously borrowed as mutable, storing the cast in a
 192             // temporary gives the source a chance to expire before the cast is used. For
 193             // structs with a self-referential *mut ptr, this allows assignment to work as
 194             // expected.
 195             //
 196             // For example, consider the type 'struct Foo { field: *mut Foo }',
 197             // The method 'fn bar(&mut self) { self.field = self }'
 198             // triggers a coercion from '&mut self' to '*mut self'. In order
 199             // for the assignment to be valid, the implicit borrow
 200             // of 'self' involved in the coercion needs to end before the local
 201             // containing the '*mut T' is assigned to 'self.field' - otherwise,
 202             // we end up trying to assign to 'self.field' while we have another mutable borrow
 203             // active.
 204             //
 205             // We only need to worry about this kind of thing for coercions from refs to ptrs,
 206             // since they get rid of a borrow implicitly.
 207             ExprKind::Use { source: cast_expr.to_ref() }
 208         }
 209         Adjust::Unsize => {
 210             // See the above comment for Adjust::Deref
 211             if let ExprKind::Block { body } = expr.kind {
 212                 if let Some(ref last_expr) = body.expr {
 213                     span = last_expr.span;
 214                     expr.span = span;
 215                 }
 216             }
 217             ExprKind::Unsize { source: expr.to_ref() }
 218         }
 219     };
 220
 221     Expr {
 222         temp_lifetime,
 223         ty: adjustment.target,
 224         span,
 225         kind,
 226     }
 227 }
 228
 229 fn make_mirror_unadjusted<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
 230                                           expr: &'tcx hir::Expr)
 231                                           -> Expr<'tcx> {
 232     let expr_ty = cx.tables().expr_ty(expr);
 233     let temp_lifetime = cx.region_scope_tree.temporary_scope(expr.hir_id.local_id);
 234
 235     let kind = match expr.node {
 236         // Here comes the interesting stuff:
 237         hir::ExprKind::MethodCall(_, method_span, ref args) => {
 238             // Rewrite a.b(c) into UFCS form like Trait::b(a, c)
 239             let expr = method_callee(cx, expr, method_span,None);
 240             let args = args.iter()
 241                 .map(|e| e.to_ref())
 242                 .collect();
 243             ExprKind::Call {
 244                 ty: expr.ty,
 245                 fun: expr.to_ref(),
 246                 args,
 247                 from_hir_call: true,
 248             }
 249         }
 250
 251         hir::ExprKind::Call(ref fun, ref args) => {
 252             if cx.tables().is_method_call(expr) {
 253                 // The callee is something implementing Fn, FnMut, or FnOnce.
 254                 // Find the actual method implementation being called and
 255                 // build the appropriate UFCS call expression with the
 256                 // callee-object as expr parameter.
 257
 258                 // rewrite f(u, v) into FnOnce::call_once(f, (u, v))
 259
 260                 let method = method_callee(cx, expr, fun.span,None);
 261
 262                 let arg_tys = args.iter().map(|e| cx.tables().expr_ty_adjusted(e));
 263                 let tupled_args = Expr {
 264                     ty: cx.tcx.mk_tup(arg_tys),
 265                     temp_lifetime,
 266                     span: expr.span,
 267                     kind: ExprKind::Tuple { fields: args.iter().map(ToRef::to_ref).collect() },
 268                 };
 269
 270                 ExprKind::Call {
 271                     ty: method.ty,
 272                     fun: method.to_ref(),
 273                     args: vec![fun.to_ref(), tupled_args.to_ref()],
 274                     from_hir_call: true,
 275                 }
 276             } else {
 277                 let adt_data = if let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) =
 278                     fun.node
 279                 {
 280                     // Tuple-like ADTs are represented as ExprKind::Call. We convert them here.
 281                     expr_ty.ty_adt_def().and_then(|adt_def| {
 282                         match path.def {
 283                             Def::VariantCtor(variant_id, CtorKind::Fn) => {
 284                                 Some((adt_def, adt_def.variant_index_with_id(variant_id)))
 285                             }
 286                             Def::StructCtor(_, CtorKind::Fn) |
 287                             Def::SelfCtor(..) => Some((adt_def, VariantIdx::new(0))),
 288                             _ => None,
 289                         }
 290                     })
 291                 } else {
 292                     None
 293                 };
 294                 if let Some((adt_def, index)) = adt_data {
 295                     let substs = cx.tables().node_substs(fun.hir_id);
 296
 297                     let user_ty = cx.tables().user_substs(fun.hir_id)
 298                         .map(|user_substs| UserTypeAnnotation::TypeOf(adt_def.did, user_substs));
 299
 300                     let field_refs = args.iter()
 301                         .enumerate()
 302                         .map(|(idx, e)| {
 303                             FieldExprRef {
 304                                 name: Field::new(idx),
 305                                 expr: e.to_ref(),
 306                             }
 307                         })
 308                         .collect();
 309                     ExprKind::Adt {
 310                         adt_def,
 311                         substs,
 312                         variant_index: index,
 313                         fields: field_refs,
 314                         user_ty,
 315                         base: None,
 316                     }
 317                 } else {
 318                     ExprKind::Call {
 319                         ty: cx.tables().node_id_to_type(fun.hir_id),
 320                         fun: fun.to_ref(),
 321                         args: args.to_ref(),
 322                         from_hir_call: true,
 323                     }
 324                 }
 325             }
 326         }
 327
 328         hir::ExprKind::AddrOf(mutbl, ref expr) => {
 329             let region = match expr_ty.sty {
 330                 ty::Ref(r, _, _) => r,
 331                 _ => span_bug!(expr.span, "type of & not region"),
 332             };
 333             ExprKind::Borrow {
 334                 region,
 335                 borrow_kind: mutbl.to_borrow_kind(),
 336                 arg: expr.to_ref(),
 337             }
 338         }
 339
 340         hir::ExprKind::Block(ref blk, _) => ExprKind::Block { body: &blk },
 341
 342         hir::ExprKind::Assign(ref lhs, ref rhs) => {
 343             ExprKind::Assign {
 344                 lhs: lhs.to_ref(),
 345                 rhs: rhs.to_ref(),
 346             }
 347         }
 348
 349         hir::ExprKind::AssignOp(op, ref lhs, ref rhs) => {
 350             if cx.tables().is_method_call(expr) {
 351                 overloaded_operator(cx, expr, vec![lhs.to_ref(), rhs.to_ref()])
 352             } else {
 353                 ExprKind::AssignOp {
 354                     op: bin_op(op.node),
 355                     lhs: lhs.to_ref(),
 356                     rhs: rhs.to_ref(),
 357                 }
 358             }
 359         }
 360
 361         hir::ExprKind::Lit(ref lit) => ExprKind::Literal {
 362             literal: cx.const_eval_literal(&lit.node, expr_ty, lit.span, false),
 363             user_ty: None,
 364         },
 365
 366         hir::ExprKind::Binary(op, ref lhs, ref rhs) => {
 367             if cx.tables().is_method_call(expr) {
 368                 overloaded_operator(cx, expr, vec![lhs.to_ref(), rhs.to_ref()])
 369             } else {
 370                 // FIXME overflow
 371                 match (op.node, cx.constness) {
 372                     // FIXME(eddyb) use logical ops in constants when
 373                     // they can handle that kind of control-flow.
 374                     (hir::BinOpKind::And, hir::Constness::Const) => {
 375                         cx.control_flow_destroyed.push((
 376                             op.span,
 377                             "`&&` operator".into(),
 378                         ));
 379                         ExprKind::Binary {
 380                             op: BinOp::BitAnd,
 381                             lhs: lhs.to_ref(),
 382                             rhs: rhs.to_ref(),
 383                         }
 384                     }
 385                     (hir::BinOpKind::Or, hir::Constness::Const) => {
 386                         cx.control_flow_destroyed.push((
 387                             op.span,
 388                             "`||` operator".into(),
 389                         ));
 390                         ExprKind::Binary {
 391                             op: BinOp::BitOr,
 392                             lhs: lhs.to_ref(),
 393                             rhs: rhs.to_ref(),
 394                         }
 395                     }
 396
 397                     (hir::BinOpKind::And, hir::Constness::NotConst) => {
 398                         ExprKind::LogicalOp {
 399                             op: LogicalOp::And,
 400                             lhs: lhs.to_ref(),
 401                             rhs: rhs.to_ref(),
 402                         }
 403                     }
 404                     (hir::BinOpKind::Or, hir::Constness::NotConst) => {
 405                         ExprKind::LogicalOp {
 406                             op: LogicalOp::Or,
 407                             lhs: lhs.to_ref(),
 408                             rhs: rhs.to_ref(),
 409                         }
 410                     }
 411
 412                     _ => {
 413                         let op = bin_op(op.node);
 414                         ExprKind::Binary {
 415                             op,
 416                             lhs: lhs.to_ref(),
 417                             rhs: rhs.to_ref(),
 418                         }
 419                     }
 420                 }
 421             }
 422         }
 423
 424         hir::ExprKind::Index(ref lhs, ref index) => {
 425             if cx.tables().is_method_call(expr) {
 426                 overloaded_place(cx, expr, expr_ty, None, vec![lhs.to_ref(), index.to_ref()])
 427             } else {
 428                 ExprKind::Index {
 429                     lhs: lhs.to_ref(),
 430                     index: index.to_ref(),
 431                 }
 432             }
 433         }
 434
 435         hir::ExprKind::Unary(hir::UnOp::UnDeref, ref arg) => {
 436             if cx.tables().is_method_call(expr) {
 437                 overloaded_place(cx, expr, expr_ty, None, vec![arg.to_ref()])
 438             } else {
 439                 ExprKind::Deref { arg: arg.to_ref() }
 440             }
 441         }
 442
 443         hir::ExprKind::Unary(hir::UnOp::UnNot, ref arg) => {
 444             if cx.tables().is_method_call(expr) {
 445                 overloaded_operator(cx, expr, vec![arg.to_ref()])
 446             } else {
 447                 ExprKind::Unary {
 448                     op: UnOp::Not,
 449                     arg: arg.to_ref(),
 450                 }
 451             }
 452         }
 453
 454         hir::ExprKind::Unary(hir::UnOp::UnNeg, ref arg) => {
 455             if cx.tables().is_method_call(expr) {
 456                 overloaded_operator(cx, expr, vec![arg.to_ref()])
 457             } else {
 458                 if let hir::ExprKind::Lit(ref lit) = arg.node {
 459                     ExprKind::Literal {
 460                         literal: cx.const_eval_literal(&lit.node, expr_ty, lit.span, true),
 461                         user_ty: None,
 462                     }
 463                 } else {
 464                     ExprKind::Unary {
 465                         op: UnOp::Neg,
 466                         arg: arg.to_ref(),
 467                     }
 468                 }
 469             }
 470         }
 471
 472         hir::ExprKind::Struct(ref qpath, ref fields, ref base) => {
 473             match expr_ty.sty {
 474                 ty::Adt(adt, substs) => {
 475                     match adt.adt_kind() {
 476                         AdtKind::Struct | AdtKind::Union => {
 477                             ExprKind::Adt {
 478                                 adt_def: adt,
 479                                 variant_index: VariantIdx::new(0),
 480                                 substs,
 481                                 user_ty: cx.user_substs_applied_to_adt(expr.hir_id, adt),
 482                                 fields: field_refs(cx, fields),
 483                                 base: base.as_ref().map(|base| {
 484                                     FruInfo {
 485                                         base: base.to_ref(),
 486                                         field_types: cx.tables()
 487                                                        .fru_field_types()[expr.hir_id]
 488                                                        .clone(),
 489                                     }
 490                                 }),
 491                             }
 492                         }
 493                         AdtKind::Enum => {
 494                             let def = match *qpath {
 495                                 hir::QPath::Resolved(_, ref path) => path.def,
 496                                 hir::QPath::TypeRelative(..) => Def::Err,
 497                             };
 498                             match def {
 499                                 Def::Variant(variant_id) => {
 500                                     assert!(base.is_none());
 501
 502                                     let index = adt.variant_index_with_id(variant_id);
 503                                     ExprKind::Adt {
 504                                         adt_def: adt,
 505                                         variant_index: index,
 506                                         substs,
 507                                         user_ty: cx.user_substs_applied_to_adt(expr.hir_id, adt),
 508                                         fields: field_refs(cx, fields),
 509                                         base: None,
 510                                     }
 511                                 }
 512                                 _ => {
 513                                     span_bug!(expr.span, "unexpected def: {:?}", def);
 514                                 }
 515                             }
 516                         }
 517                     }
 518                 }
 519                 _ => {
 520                     span_bug!(expr.span,
 521                               "unexpected type for struct literal: {:?}",
 522                               expr_ty);
 523                 }
 524             }
 525         }
 526
 527         hir::ExprKind::Closure(..) => {
 528             let closure_ty = cx.tables().expr_ty(expr);
 529             let (def_id, substs, movability) = match closure_ty.sty {
 530                 ty::Closure(def_id, substs) => (def_id, UpvarSubsts::Closure(substs), None),
 531                 ty::Generator(def_id, substs, movability) => {
 532                     (def_id, UpvarSubsts::Generator(substs), Some(movability))
 533                 }
 534                 _ => {
 535                     span_bug!(expr.span, "closure expr w/o closure type: {:?}", closure_ty);
 536                 }
 537             };
 538             let upvars = cx.tcx.with_freevars(expr.id, |freevars| {
 539                 freevars.iter()
 540                     .zip(substs.upvar_tys(def_id, cx.tcx))
 541                     .map(|(fv, ty)| capture_freevar(cx, expr, fv, ty))
 542                     .collect()
 543             });
 544             ExprKind::Closure {
 545                 closure_id: def_id,
 546                 substs,
 547                 upvars,
 548                 movability,
 549             }
 550         }
 551
 552         hir::ExprKind::Path(ref qpath) => {
 553             let def = cx.tables().qpath_def(qpath, expr.hir_id);
 554             convert_path_expr(cx, expr, def)
 555         }
 556
 557         hir::ExprKind::InlineAsm(ref asm, ref outputs, ref inputs) => {
 558             ExprKind::InlineAsm {
 559                 asm,
 560                 outputs: outputs.to_ref(),
 561                 inputs: inputs.to_ref(),
 562             }
 563         }
 564
 565         // Now comes the rote stuff:
 566         hir::ExprKind::Repeat(ref v, ref count) => {
 567             let def_id = cx.tcx.hir().local_def_id(count.id);
 568             let substs = Substs::identity_for_item(cx.tcx.global_tcx(), def_id);
 569             let instance = ty::Instance::resolve(
 570                 cx.tcx.global_tcx(),
 571                 cx.param_env,
 572                 def_id,
 573                 substs,
 574             ).unwrap();
 575             let global_id = GlobalId {
 576                 instance,
 577                 promoted: None
 578             };
 579             let span = cx.tcx.def_span(def_id);
 580             let count = match cx.tcx.at(span).const_eval(cx.param_env.and(global_id)) {
 581                 Ok(cv) => cv.unwrap_usize(cx.tcx),
 582                 Err(ErrorHandled::Reported) => 0,
 583                 Err(ErrorHandled::TooGeneric) => {
 584                     cx.tcx.sess.span_err(span, "array lengths can't depend on generic parameters");
 585                     0
 586                 },
 587             };
 588
 589             ExprKind::Repeat {
 590                 value: v.to_ref(),
 591                 count,
 592             }
 593         }
 594         hir::ExprKind::Ret(ref v) => ExprKind::Return { value: v.to_ref() },
 595         hir::ExprKind::Break(dest, ref value) => {
 596             match dest.target_id {
 597                 Ok(target_id) => ExprKind::Break {
 598                     label: region::Scope {
 599                         id: cx.tcx.hir().node_to_hir_id(target_id).local_id,
 600                         data: region::ScopeData::Node
 601                     },
 602                     value: value.to_ref(),
 603                 },
 604                 Err(err) => bug!("invalid loop id for break: {}", err)
 605             }
 606         }
 607         hir::ExprKind::Continue(dest) => {
 608             match dest.target_id {
 609                 Ok(loop_id) => ExprKind::Continue {
 610                     label: region::Scope {
 611                         id: cx.tcx.hir().node_to_hir_id(loop_id).local_id,
 612                         data: region::ScopeData::Node
 613                     },
 614                 },
 615                 Err(err) => bug!("invalid loop id for continue: {}", err)
 616             }
 617         }
 618         hir::ExprKind::Match(ref discr, ref arms, _) => {
 619             ExprKind::Match {
 620                 discriminant: discr.to_ref(),
 621                 arms: arms.iter().map(|a| convert_arm(cx, a)).collect(),
 622             }
 623         }
 624         hir::ExprKind::If(ref cond, ref then, ref otherwise) => {
 625             ExprKind::If {
 626                 condition: cond.to_ref(),
 627                 then: then.to_ref(),
 628                 otherwise: otherwise.to_ref(),
 629             }
 630         }
 631         hir::ExprKind::While(ref cond, ref body, _) => {
 632             ExprKind::Loop {
 633                 condition: Some(cond.to_ref()),
 634                 body: block::to_expr_ref(cx, body),
 635             }
 636         }
 637         hir::ExprKind::Loop(ref body, _, _) => {
 638             ExprKind::Loop {
 639                 condition: None,
 640                 body: block::to_expr_ref(cx, body),
 641             }
 642         }
 643         hir::ExprKind::Field(ref source, ..) => {
 644             ExprKind::Field {
 645                 lhs: source.to_ref(),
 646                 name: Field::new(cx.tcx.field_index(expr.id, cx.tables)),
 647             }
 648         }
 649         hir::ExprKind::Cast(ref source, ref cast_ty) => {
 650             // Check for a user-given type annotation on this `cast`
 651             let user_ty = cx.tables.user_provided_tys().get(cast_ty.hir_id)
 652                 .map(|&t| UserTypeAnnotation::Ty(t));
 653
 654             debug!(
 655                 "cast({:?}) has ty w/ hir_id {:?} and user provided ty {:?}",
 656                 expr,
 657                 cast_ty.hir_id,
 658                 user_ty,
 659             );
 660
 661             // Check to see if this cast is a "coercion cast", where the cast is actually done
 662             // using a coercion (or is a no-op).
 663             let cast = if let Some(&TyCastKind::CoercionCast) =
 664                 cx.tables()
 665                 .cast_kinds()
 666                 .get(source.hir_id)
 667             {
 668                 // Convert the lexpr to a vexpr.
 669                 ExprKind::Use { source: source.to_ref() }
 670             } else {
 671                 // check whether this is casting an enum variant discriminant
 672                 // to prevent cycles, we refer to the discriminant initializer
 673                 // which is always an integer and thus doesn't need to know the
 674                 // enum's layout (or its tag type) to compute it during const eval
 675                 // Example:
 676                 // enum Foo {
 677                 //     A,
 678                 //     B = A as isize + 4,
 679                 // }
 680                 // The correct solution would be to add symbolic computations to miri,
 681                 // so we wouldn't have to compute and store the actual value
 682                 let var = if let hir::ExprKind::Path(ref qpath) = source.node {
 683                     let def = cx.tables().qpath_def(qpath, source.hir_id);
 684                     cx
 685                         .tables()
 686                         .node_id_to_type(source.hir_id)
 687                         .ty_adt_def()
 688                         .and_then(|adt_def| {
 689                         match def {
 690                             Def::VariantCtor(variant_id, CtorKind::Const) => {
 691                                 let idx = adt_def.variant_index_with_id(variant_id);
 692                                 let (d, o) = adt_def.discriminant_def_for_variant(idx);
 693                                 use rustc::ty::util::IntTypeExt;
 694                                 let ty = adt_def.repr.discr_type();
 695                                 let ty = ty.to_ty(cx.tcx());
 696                                 Some((d, o, ty))
 697                             }
 698                             _ => None,
 699                         }
 700                     })
 701                 } else {
 702                     None
 703                 };
 704
 705                 let source = if let Some((did, offset, var_ty)) = var {
 706                     let mk_const = |literal| Expr {
 707                         temp_lifetime,
 708                         ty: var_ty,
 709                         span: expr.span,
 710                         kind: ExprKind::Literal { literal, user_ty: None },
 711                     }.to_ref();
 712                     let offset = mk_const(ty::Const::from_bits(
 713                         cx.tcx,
 714                         offset as u128,
 715                         cx.param_env.and(var_ty),
 716                     ));
 717                     match did {
 718                         Some(did) => {
 719                             // in case we are offsetting from a computed discriminant
 720                             // and not the beginning of discriminants (which is always `0`)
 721                             let substs = Substs::identity_for_item(cx.tcx(), did);
 722                             let lhs = mk_const(ty::Const::unevaluated(
 723                                 cx.tcx(),
 724                                 did,
 725                                 substs,
 726                                 var_ty,
 727                             ));
 728                             let bin = ExprKind::Binary {
 729                                 op: BinOp::Add,
 730                                 lhs,
 731                                 rhs: offset,
 732                             };
 733                             Expr {
 734                                 temp_lifetime,
 735                                 ty: var_ty,
 736                                 span: expr.span,
 737                                 kind: bin,
 738                             }.to_ref()
 739                         },
 740                         None => offset,
 741                     }
 742                 } else {
 743                     source.to_ref()
 744                 };
 745
 746                 ExprKind::Cast { source }
 747             };
 748
 749             if let Some(user_ty) = user_ty {
 750                 // NOTE: Creating a new Expr and wrapping a Cast inside of it may be
 751                 //       inefficient, revisit this when performance becomes an issue.
 752                 let cast_expr = Expr {
 753                     temp_lifetime,
 754                     ty: expr_ty,
 755                     span: expr.span,
 756                     kind: cast,
 757                 };
 758
 759                 ExprKind::ValueTypeAscription {
 760                     source: cast_expr.to_ref(),
 761                     user_ty: Some(user_ty),
 762                 }
 763             } else {
 764                 cast
 765             }
 766         }
 767         hir::ExprKind::Type(ref source, ref ty) => {
 768             let user_provided_tys = cx.tables.user_provided_tys();
 769             let user_ty = user_provided_tys
 770                 .get(ty.hir_id)
 771                 .map(|&c_ty| UserTypeAnnotation::Ty(c_ty));
 772             if source.is_place_expr() {
 773                 ExprKind::PlaceTypeAscription {
 774                     source: source.to_ref(),
 775                     user_ty,
 776                 }
 777             } else {
 778                 ExprKind::ValueTypeAscription {
 779                     source: source.to_ref(),
 780                     user_ty,
 781                 }
 782             }
 783         }
 784         hir::ExprKind::Box(ref value) => {
 785             ExprKind::Box {
 786                 value: value.to_ref(),
 787             }
 788         }
 789         hir::ExprKind::Array(ref fields) => ExprKind::Array { fields: fields.to_ref() },
 790         hir::ExprKind::Tup(ref fields) => ExprKind::Tuple { fields: fields.to_ref() },
 791
 792         hir::ExprKind::Yield(ref v) => ExprKind::Yield { value: v.to_ref() },
 793     };
 794
 795     Expr {
 796         temp_lifetime,
 797         ty: expr_ty,
 798         span: expr.span,
 799         kind,
 800     }
 801 }
 802
 803 fn user_substs_applied_to_def(
 804     cx: &mut Cx<'a, 'gcx, 'tcx>,
 805     hir_id: hir::HirId,
 806     def: &Def,
 807 ) -> Option<UserTypeAnnotation<'tcx>> {
 808     match def {
 809         // A reference to something callable -- e.g., a fn, method, or
 810         // a tuple-struct or tuple-variant. This has the type of a
 811         // `Fn` but with the user-given substitutions.
 812         Def::Fn(_) |
 813         Def::Method(_) |
 814         Def::StructCtor(_, CtorKind::Fn) |
 815         Def::VariantCtor(_, CtorKind::Fn) |
 816         Def::Const(_) |
 817         Def::AssociatedConst(_) =>
 818             Some(UserTypeAnnotation::TypeOf(def.def_id(), cx.tables().user_substs(hir_id)?)),
 819
 820         // A unit struct/variant which is used as a value (e.g.,
 821         // `None`). This has the type of the enum/struct that defines
 822         // this variant -- but with the substitutions given by the
 823         // user.
 824         Def::StructCtor(_def_id, CtorKind::Const) |
 825         Def::VariantCtor(_def_id, CtorKind::Const) =>
 826             cx.user_substs_applied_to_ty_of_hir_id(hir_id),
 827
 828         // `Self` is used in expression as a tuple struct constructor or an unit struct constructor
 829         Def::SelfCtor(_) =>
 830             cx.user_substs_applied_to_ty_of_hir_id(hir_id),
 831
 832         _ =>
 833             bug!("user_substs_applied_to_def: unexpected def {:?} at {:?}", def, hir_id)
 834     }
 835 }
 836
 837 fn method_callee<'a, 'gcx, 'tcx>(
 838     cx: &mut Cx<'a, 'gcx, 'tcx>,
 839     expr: &hir::Expr,
 840     span: Span,
 841     overloaded_callee: Option<(DefId, &'tcx Substs<'tcx>)>,
 842 ) -> Expr<'tcx> {
 843     let temp_lifetime = cx.region_scope_tree.temporary_scope(expr.hir_id.local_id);
 844     let (def_id, substs, user_ty) = match overloaded_callee {
 845         Some((def_id, substs)) => (def_id, substs, None),
 846         None => {
 847             let type_dependent_defs = cx.tables().type_dependent_defs();
 848             let def = type_dependent_defs
 849                 .get(expr.hir_id)
 850                 .unwrap_or_else(|| {
 851                     span_bug!(expr.span, "no type-dependent def for method callee")
 852                 });
 853             let user_ty = user_substs_applied_to_def(cx, expr.hir_id, def);
 854             (def.def_id(), cx.tables().node_substs(expr.hir_id), user_ty)
 855         }
 856     };
 857     let ty = cx.tcx().mk_fn_def(def_id, substs);
 858     Expr {
 859         temp_lifetime,
 860         ty,
 861         span,
 862         kind: ExprKind::Literal {
 863             literal: ty::Const::zero_sized(cx.tcx(), ty),
 864             user_ty,
 865         },
 866     }
 867 }
 868
 869 trait ToBorrowKind { fn to_borrow_kind(&self) -> BorrowKind; }
 870
 871 impl ToBorrowKind for AutoBorrowMutability {
 872     fn to_borrow_kind(&self) -> BorrowKind {
 873         use rustc::ty::adjustment::AllowTwoPhase;
 874         match *self {
 875             AutoBorrowMutability::Mutable { allow_two_phase_borrow } =>
 876                 BorrowKind::Mut { allow_two_phase_borrow: match allow_two_phase_borrow {
 877                     AllowTwoPhase::Yes => true,
 878                     AllowTwoPhase::No => false
 879                 }},
 880             AutoBorrowMutability::Immutable =>
 881                 BorrowKind::Shared,
 882         }
 883     }
 884 }
 885
 886 impl ToBorrowKind for hir::Mutability {
 887     fn to_borrow_kind(&self) -> BorrowKind {
 888         match *self {
 889             hir::MutMutable => BorrowKind::Mut { allow_two_phase_borrow: false },
 890             hir::MutImmutable => BorrowKind::Shared,
 891         }
 892     }
 893 }
 894
 895 fn convert_arm<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>, arm: &'tcx hir::Arm) -> Arm<'tcx> {
 896     Arm {
 897         patterns: arm.pats.iter().map(|p| cx.pattern_from_hir(p)).collect(),
 898         guard: match arm.guard {
 899                 Some(hir::Guard::If(ref e)) => Some(Guard::If(e.to_ref())),
 900                 _ => None,
 901             },
 902         body: arm.body.to_ref(),
 903         // BUG: fix this
 904         lint_level: LintLevel::Inherited,
 905     }
 906 }
 907
 908 fn convert_path_expr<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
 909                                      expr: &'tcx hir::Expr,
 910                                      def: Def)
 911                                      -> ExprKind<'tcx> {
 912     let substs = cx.tables().node_substs(expr.hir_id);
 913     match def {
 914         // A regular function, constructor function or a constant.
 915         Def::Fn(_) |
 916         Def::Method(_) |
 917         Def::StructCtor(_, CtorKind::Fn) |
 918         Def::VariantCtor(_, CtorKind::Fn) |
 919         Def::SelfCtor(..) => {
 920             let user_ty = user_substs_applied_to_def(cx, expr.hir_id, &def);
 921             ExprKind::Literal {
 922                 literal: ty::Const::zero_sized(
 923                     cx.tcx,
 924                     cx.tables().node_id_to_type(expr.hir_id),
 925                 ),
 926                 user_ty,
 927             }
 928         },
 929
 930         Def::Const(def_id) |
 931         Def::AssociatedConst(def_id) => {
 932             let user_ty = user_substs_applied_to_def(cx, expr.hir_id, &def);
 933             ExprKind::Literal {
 934                 literal: ty::Const::unevaluated(
 935                     cx.tcx,
 936                     def_id,
 937                     substs,
 938                     cx.tables().node_id_to_type(expr.hir_id),
 939                 ),
 940                 user_ty,
 941             }
 942         },
 943
 944         Def::StructCtor(def_id, CtorKind::Const) |
 945         Def::VariantCtor(def_id, CtorKind::Const) => {
 946             match cx.tables().node_id_to_type(expr.hir_id).sty {
 947                 // A unit struct/variant which is used as a value.
 948                 // We return a completely different ExprKind here to account for this special case.
 949                 ty::Adt(adt_def, substs) => {
 950                     ExprKind::Adt {
 951                         adt_def,
 952                         variant_index: adt_def.variant_index_with_id(def_id),
 953                         substs,
 954                         user_ty: cx.user_substs_applied_to_adt(expr.hir_id, adt_def),
 955                         fields: vec![],
 956                         base: None,
 957                     }
 958                 }
 959                 ref sty => bug!("unexpected sty: {:?}", sty),
 960             }
 961         }
 962
 963         Def::Static(node_id, _) => ExprKind::StaticRef { id: node_id },
 964
 965         Def::Local(..) | Def::Upvar(..) => convert_var(cx, expr, def),
 966
 967         _ => span_bug!(expr.span, "def `{:?}` not yet implemented", def),
 968     }
 969 }
 970
 971 fn convert_var<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
 972                                expr: &'tcx hir::Expr,
 973                                def: Def)
 974                                -> ExprKind<'tcx> {
 975     let temp_lifetime = cx.region_scope_tree.temporary_scope(expr.hir_id.local_id);
 976
 977     match def {
 978         Def::Local(id) => ExprKind::VarRef { id },
 979
 980         Def::Upvar(var_id, index, closure_expr_id) => {
 981             debug!("convert_var(upvar({:?}, {:?}, {:?}))",
 982                    var_id,
 983                    index,
 984                    closure_expr_id);
 985             let var_hir_id = cx.tcx.hir().node_to_hir_id(var_id);
 986             let var_ty = cx.tables().node_id_to_type(var_hir_id);
 987
 988             // FIXME free regions in closures are not right
 989             let closure_ty = cx.tables()
 990                                .node_id_to_type(cx.tcx.hir().node_to_hir_id(closure_expr_id));
 991
 992             // FIXME we're just hard-coding the idea that the
 993             // signature will be &self or &mut self and hence will
 994             // have a bound region with number 0
 995             let closure_def_id = cx.tcx.hir().local_def_id(closure_expr_id);
 996             let region = ty::ReFree(ty::FreeRegion {
 997                 scope: closure_def_id,
 998                 bound_region: ty::BoundRegion::BrAnon(0),
 999             });
1000             let region = cx.tcx.mk_region(region);
1001
1002             let self_expr = if let ty::Closure(_, closure_substs) = closure_ty.sty {
1003                 match cx.infcx.closure_kind(closure_def_id, closure_substs).unwrap() {
1004                     ty::ClosureKind::Fn => {
1005                         let ref_closure_ty = cx.tcx.mk_ref(region,
1006                                                            ty::TypeAndMut {
1007                                                                ty: closure_ty,
1008                                                                mutbl: hir::MutImmutable,
1009                                                            });
1010                         Expr {
1011                             ty: closure_ty,
1012                             temp_lifetime: temp_lifetime,
1013                             span: expr.span,
1014                             kind: ExprKind::Deref {
1015                                 arg: Expr {
1016                                     ty: ref_closure_ty,
1017                                     temp_lifetime,
1018                                     span: expr.span,
1019                                     kind: ExprKind::SelfRef,
1020                                 }
1021                                 .to_ref(),
1022                             },
1023                         }
1024                     }
1025                     ty::ClosureKind::FnMut => {
1026                         let ref_closure_ty = cx.tcx.mk_ref(region,
1027                                                            ty::TypeAndMut {
1028                                                                ty: closure_ty,
1029                                                                mutbl: hir::MutMutable,
1030                                                            });
1031                         Expr {
1032                             ty: closure_ty,
1033                             temp_lifetime,
1034                             span: expr.span,
1035                             kind: ExprKind::Deref {
1036                                 arg: Expr {
1037                                     ty: ref_closure_ty,
1038                                     temp_lifetime,
1039                                     span: expr.span,
1040                                     kind: ExprKind::SelfRef,
1041                                 }.to_ref(),
1042                             },
1043                         }
1044                     }
1045                     ty::ClosureKind::FnOnce => {
1046                         Expr {
1047                             ty: closure_ty,
1048                             temp_lifetime,
1049                             span: expr.span,
1050                             kind: ExprKind::SelfRef,
1051                         }
1052                     }
1053                 }
1054             } else {
1055                 Expr {
1056                     ty: closure_ty,
1057                     temp_lifetime,
1058                     span: expr.span,
1059                     kind: ExprKind::SelfRef,
1060                 }
1061             };
1062
1063             // at this point we have `self.n`, which loads up the upvar
1064             let field_kind = ExprKind::Field {
1065                 lhs: self_expr.to_ref(),
1066                 name: Field::new(index),
1067             };
1068
1069             // ...but the upvar might be an `&T` or `&mut T` capture, at which
1070             // point we need an implicit deref
1071             let upvar_id = ty::UpvarId {
1072                 var_path: ty::UpvarPath {hir_id: var_hir_id},
1073                 closure_expr_id: LocalDefId::from_def_id(closure_def_id),
1074             };
1075             match cx.tables().upvar_capture(upvar_id) {
1076                 ty::UpvarCapture::ByValue => field_kind,
1077                 ty::UpvarCapture::ByRef(borrow) => {
1078                     ExprKind::Deref {
1079                         arg: Expr {
1080                             temp_lifetime,
1081                             ty: cx.tcx.mk_ref(borrow.region,
1082                                               ty::TypeAndMut {
1083                                                   ty: var_ty,
1084                                                   mutbl: borrow.kind.to_mutbl_lossy(),
1085                                               }),
1086                             span: expr.span,
1087                             kind: field_kind,
1088                         }.to_ref(),
1089                     }
1090                 }
1091             }
1092         }
1093
1094         _ => span_bug!(expr.span, "type of & not region"),
1095     }
1096 }
1097
1098
1099 fn bin_op(op: hir::BinOpKind) -> BinOp {
1100     match op {
1101         hir::BinOpKind::Add => BinOp::Add,
1102         hir::BinOpKind::Sub => BinOp::Sub,
1103         hir::BinOpKind::Mul => BinOp::Mul,
1104         hir::BinOpKind::Div => BinOp::Div,
1105         hir::BinOpKind::Rem => BinOp::Rem,
1106         hir::BinOpKind::BitXor => BinOp::BitXor,
1107         hir::BinOpKind::BitAnd => BinOp::BitAnd,
1108         hir::BinOpKind::BitOr => BinOp::BitOr,
1109         hir::BinOpKind::Shl => BinOp::Shl,
1110         hir::BinOpKind::Shr => BinOp::Shr,
1111         hir::BinOpKind::Eq => BinOp::Eq,
1112         hir::BinOpKind::Lt => BinOp::Lt,
1113         hir::BinOpKind::Le => BinOp::Le,
1114         hir::BinOpKind::Ne => BinOp::Ne,
1115         hir::BinOpKind::Ge => BinOp::Ge,
1116         hir::BinOpKind::Gt => BinOp::Gt,
1117         _ => bug!("no equivalent for ast binop {:?}", op),
1118     }
1119 }
1120
1121 fn overloaded_operator<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
1122                                        expr: &'tcx hir::Expr,
1123                                        args: Vec<ExprRef<'tcx>>)
1124                                        -> ExprKind<'tcx> {
1125     let fun = method_callee(cx, expr, expr.span, None);
1126     ExprKind::Call {
1127         ty: fun.ty,
1128         fun: fun.to_ref(),
1129         args,
1130         from_hir_call: false,
1131     }
1132 }
1133
1134 fn overloaded_place<'a, 'gcx, 'tcx>(
1135     cx: &mut Cx<'a, 'gcx, 'tcx>,
1136     expr: &'tcx hir::Expr,
1137     place_ty: Ty<'tcx>,
1138     overloaded_callee: Option<(DefId, &'tcx Substs<'tcx>)>,
1139     args: Vec<ExprRef<'tcx>>,
1140 ) -> ExprKind<'tcx> {
1141     // For an overloaded *x or x[y] expression of type T, the method
1142     // call returns an &T and we must add the deref so that the types
1143     // line up (this is because `*x` and `x[y]` represent places):
1144
1145     let recv_ty = match args[0] {
1146         ExprRef::Hair(e) => cx.tables().expr_ty_adjusted(e),
1147         ExprRef::Mirror(ref e) => e.ty
1148     };
1149
1150     // Reconstruct the output assuming it's a reference with the
1151     // same region and mutability as the receiver. This holds for
1152     // `Deref(Mut)::Deref(_mut)` and `Index(Mut)::index(_mut)`.
1153     let (region, mutbl) = match recv_ty.sty {
1154         ty::Ref(region, _, mutbl) => (region, mutbl),
1155         _ => span_bug!(expr.span, "overloaded_place: receiver is not a reference"),
1156     };
1157     let ref_ty = cx.tcx.mk_ref(region, ty::TypeAndMut {
1158         ty: place_ty,
1159         mutbl,
1160     });
1161
1162     // construct the complete expression `foo()` for the overloaded call,
1163     // which will yield the &T type
1164     let temp_lifetime = cx.region_scope_tree.temporary_scope(expr.hir_id.local_id);
1165     let fun = method_callee(cx, expr, expr.span, overloaded_callee);
1166     let ref_expr = Expr {
1167         temp_lifetime,
1168         ty: ref_ty,
1169         span: expr.span,
1170         kind: ExprKind::Call {
1171             ty: fun.ty,
1172             fun: fun.to_ref(),
1173             args,
1174             from_hir_call: false,
1175         },
1176     };
1177
1178     // construct and return a deref wrapper `*foo()`
1179     ExprKind::Deref { arg: ref_expr.to_ref() }
1180 }
1181
1182 fn capture_freevar<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
1183                                    closure_expr: &'tcx hir::Expr,
1184                                    freevar: &hir::Freevar,
1185                                    freevar_ty: Ty<'tcx>)
1186                                    -> ExprRef<'tcx> {
1187     let var_hir_id = cx.tcx.hir().node_to_hir_id(freevar.var_id());
1188     let upvar_id = ty::UpvarId {
1189         var_path: ty::UpvarPath { hir_id: var_hir_id },
1190         closure_expr_id: cx.tcx.hir().local_def_id(closure_expr.id).to_local(),
1191     };
1192     let upvar_capture = cx.tables().upvar_capture(upvar_id);
1193     let temp_lifetime = cx.region_scope_tree.temporary_scope(closure_expr.hir_id.local_id);
1194     let var_ty = cx.tables().node_id_to_type(var_hir_id);
1195     let captured_var = Expr {
1196         temp_lifetime,
1197         ty: var_ty,
1198         span: closure_expr.span,
1199         kind: convert_var(cx, closure_expr, freevar.def),
1200     };
1201     match upvar_capture {
1202         ty::UpvarCapture::ByValue => captured_var.to_ref(),
1203         ty::UpvarCapture::ByRef(upvar_borrow) => {
1204             let borrow_kind = match upvar_borrow.kind {
1205                 ty::BorrowKind::ImmBorrow => BorrowKind::Shared,
1206                 ty::BorrowKind::UniqueImmBorrow => BorrowKind::Unique,
1207                 ty::BorrowKind::MutBorrow => BorrowKind::Mut { allow_two_phase_borrow: false }
1208             };
1209             Expr {
1210                 temp_lifetime,
1211                 ty: freevar_ty,
1212                 span: closure_expr.span,
1213                 kind: ExprKind::Borrow {
1214                     region: upvar_borrow.region,
1215                     borrow_kind,
1216                     arg: captured_var.to_ref(),
1217                 },
1218             }.to_ref()
1219         }
1220     }
1221 }
1222
1223 /// Converts a list of named fields (i.e., for struct-like struct/enum ADTs) into FieldExprRef.
1224 fn field_refs<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
1225                               fields: &'tcx [hir::Field])
1226                               -> Vec<FieldExprRef<'tcx>> {
1227     fields.iter()
1228         .map(|field| {
1229             FieldExprRef {
1230                 name: Field::new(cx.tcx.field_index(field.id, cx.tables)),
1231                 expr: field.expr.to_ref(),
1232             }
1233         })
1234         .collect()
1235 }