src/librustc/ty/util.rs

   1 // Copyright 2012-2015 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 //! misc. type-system utilities too small to deserve their own file
  12
  13 use hir::def_id::{DefId, LOCAL_CRATE};
  14 use hir::map::DefPathData;
  15 use ich::{StableHashingContext, NodeIdHashingMode};
  16 use traits::{self, Reveal};
  17 use ty::{self, Ty, TyCtxt, TypeFoldable};
  18 use ty::fold::TypeVisitor;
  19 use ty::layout::{Layout, LayoutError};
  20 use ty::subst::{Subst, Kind};
  21 use ty::TypeVariants::*;
  22 use util::common::ErrorReported;
  23 use middle::lang_items;
  24
  25 use rustc_const_math::{ConstInt, ConstIsize, ConstUsize};
  26 use rustc_data_structures::stable_hasher::{StableHasher, StableHasherResult,
  27                                            HashStable};
  28 use rustc_data_structures::fx::FxHashMap;
  29 use std::cmp;
  30 use std::iter;
  31 use std::hash::Hash;
  32 use std::intrinsics;
  33 use syntax::ast::{self, Name};
  34 use syntax::attr::{self, SignedInt, UnsignedInt};
  35 use syntax_pos::{Span, DUMMY_SP};
  36
  37 type Disr = ConstInt;
  38
  39 pub trait IntTypeExt {
  40     fn to_ty<'a, 'gcx, 'tcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Ty<'tcx>;
  41     fn disr_incr<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>, val: Option<Disr>)
  42                            -> Option<Disr>;
  43     fn assert_ty_matches(&self, val: Disr);
  44     fn initial_discriminant<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Disr;
  45 }
  46
  47
  48 macro_rules! typed_literal {
  49     ($tcx:expr, $ty:expr, $lit:expr) => {
  50         match $ty {
  51             SignedInt(ast::IntTy::I8)    => ConstInt::I8($lit),
  52             SignedInt(ast::IntTy::I16)   => ConstInt::I16($lit),
  53             SignedInt(ast::IntTy::I32)   => ConstInt::I32($lit),
  54             SignedInt(ast::IntTy::I64)   => ConstInt::I64($lit),
  55             SignedInt(ast::IntTy::I128)   => ConstInt::I128($lit),
  56             SignedInt(ast::IntTy::Is) => match $tcx.sess.target.int_type {
  57                 ast::IntTy::I16 => ConstInt::Isize(ConstIsize::Is16($lit)),
  58                 ast::IntTy::I32 => ConstInt::Isize(ConstIsize::Is32($lit)),
  59                 ast::IntTy::I64 => ConstInt::Isize(ConstIsize::Is64($lit)),
  60                 _ => bug!(),
  61             },
  62             UnsignedInt(ast::UintTy::U8)  => ConstInt::U8($lit),
  63             UnsignedInt(ast::UintTy::U16) => ConstInt::U16($lit),
  64             UnsignedInt(ast::UintTy::U32) => ConstInt::U32($lit),
  65             UnsignedInt(ast::UintTy::U64) => ConstInt::U64($lit),
  66             UnsignedInt(ast::UintTy::U128) => ConstInt::U128($lit),
  67             UnsignedInt(ast::UintTy::Us) => match $tcx.sess.target.uint_type {
  68                 ast::UintTy::U16 => ConstInt::Usize(ConstUsize::Us16($lit)),
  69                 ast::UintTy::U32 => ConstInt::Usize(ConstUsize::Us32($lit)),
  70                 ast::UintTy::U64 => ConstInt::Usize(ConstUsize::Us64($lit)),
  71                 _ => bug!(),
  72             },
  73         }
  74     }
  75 }
  76
  77 impl IntTypeExt for attr::IntType {
  78     fn to_ty<'a, 'gcx, 'tcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Ty<'tcx> {
  79         match *self {
  80             SignedInt(ast::IntTy::I8)      => tcx.types.i8,
  81             SignedInt(ast::IntTy::I16)     => tcx.types.i16,
  82             SignedInt(ast::IntTy::I32)     => tcx.types.i32,
  83             SignedInt(ast::IntTy::I64)     => tcx.types.i64,
  84             SignedInt(ast::IntTy::I128)     => tcx.types.i128,
  85             SignedInt(ast::IntTy::Is)   => tcx.types.isize,
  86             UnsignedInt(ast::UintTy::U8)    => tcx.types.u8,
  87             UnsignedInt(ast::UintTy::U16)   => tcx.types.u16,
  88             UnsignedInt(ast::UintTy::U32)   => tcx.types.u32,
  89             UnsignedInt(ast::UintTy::U64)   => tcx.types.u64,
  90             UnsignedInt(ast::UintTy::U128)   => tcx.types.u128,
  91             UnsignedInt(ast::UintTy::Us) => tcx.types.usize,
  92         }
  93     }
  94
  95     fn initial_discriminant<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Disr {
  96         typed_literal!(tcx, *self, 0)
  97     }
  98
  99     fn assert_ty_matches(&self, val: Disr) {
 100         match (*self, val) {
 101             (SignedInt(ast::IntTy::I8), ConstInt::I8(_)) => {},
 102             (SignedInt(ast::IntTy::I16), ConstInt::I16(_)) => {},
 103             (SignedInt(ast::IntTy::I32), ConstInt::I32(_)) => {},
 104             (SignedInt(ast::IntTy::I64), ConstInt::I64(_)) => {},
 105             (SignedInt(ast::IntTy::I128), ConstInt::I128(_)) => {},
 106             (SignedInt(ast::IntTy::Is), ConstInt::Isize(_)) => {},
 107             (UnsignedInt(ast::UintTy::U8), ConstInt::U8(_)) => {},
 108             (UnsignedInt(ast::UintTy::U16), ConstInt::U16(_)) => {},
 109             (UnsignedInt(ast::UintTy::U32), ConstInt::U32(_)) => {},
 110             (UnsignedInt(ast::UintTy::U64), ConstInt::U64(_)) => {},
 111             (UnsignedInt(ast::UintTy::U128), ConstInt::U128(_)) => {},
 112             (UnsignedInt(ast::UintTy::Us), ConstInt::Usize(_)) => {},
 113             _ => bug!("disr type mismatch: {:?} vs {:?}", self, val),
 114         }
 115     }
 116
 117     fn disr_incr<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>, val: Option<Disr>)
 118                            -> Option<Disr> {
 119         if let Some(val) = val {
 120             self.assert_ty_matches(val);
 121             (val + typed_literal!(tcx, *self, 1)).ok()
 122         } else {
 123             Some(self.initial_discriminant(tcx))
 124         }
 125     }
 126 }
 127
 128
 129 #[derive(Copy, Clone)]
 130 pub enum CopyImplementationError<'tcx> {
 131     InfrigingField(&'tcx ty::FieldDef),
 132     NotAnAdt,
 133     HasDestructor,
 134 }
 135
 136 /// Describes whether a type is representable. For types that are not
 137 /// representable, 'SelfRecursive' and 'ContainsRecursive' are used to
 138 /// distinguish between types that are recursive with themselves and types that
 139 /// contain a different recursive type. These cases can therefore be treated
 140 /// differently when reporting errors.
 141 ///
 142 /// The ordering of the cases is significant. They are sorted so that cmp::max
 143 /// will keep the "more erroneous" of two values.
 144 #[derive(Clone, PartialOrd, Ord, Eq, PartialEq, Debug)]
 145 pub enum Representability {
 146     Representable,
 147     ContainsRecursive,
 148     SelfRecursive(Vec<Span>),
 149 }
 150
 151 impl<'tcx> ty::ParamEnv<'tcx> {
 152     /// Construct a trait environment suitable for contexts where
 153     /// there are no where clauses in scope.
 154     pub fn empty(reveal: Reveal) -> Self {
 155         Self::new(ty::Slice::empty(), reveal)
 156     }
 157
 158     /// Construct a trait environment with the given set of predicates.
 159     pub fn new(caller_bounds: &'tcx ty::Slice<ty::Predicate<'tcx>>,
 160                reveal: Reveal)
 161                -> Self {
 162         ty::ParamEnv { caller_bounds, reveal }
 163     }
 164
 165     /// Returns a new parameter environment with the same clauses, but
 166     /// which "reveals" the true results of projections in all cases
 167     /// (even for associated types that are specializable).  This is
 168     /// the desired behavior during trans and certain other special
 169     /// contexts; normally though we want to use `Reveal::UserFacing`,
 170     /// which is the default.
 171     pub fn reveal_all(self) -> Self {
 172         ty::ParamEnv { reveal: Reveal::All, ..self }
 173     }
 174
 175     pub fn can_type_implement_copy<'a>(self,
 176                                        tcx: TyCtxt<'a, 'tcx, 'tcx>,
 177                                        self_type: Ty<'tcx>, span: Span)
 178                                        -> Result<(), CopyImplementationError<'tcx>> {
 179         // FIXME: (@jroesch) float this code up
 180         tcx.infer_ctxt().enter(|infcx| {
 181             let (adt, substs) = match self_type.sty {
 182                 ty::TyAdt(adt, substs) => (adt, substs),
 183                 _ => return Err(CopyImplementationError::NotAnAdt),
 184             };
 185
 186             let field_implements_copy = |field: &ty::FieldDef| {
 187                 let cause = traits::ObligationCause::dummy();
 188                 match traits::fully_normalize(&infcx, cause, self, &field.ty(tcx, substs)) {
 189                     Ok(ty) => !infcx.type_moves_by_default(self, ty, span),
 190                     Err(..) => false,
 191                 }
 192             };
 193
 194             for variant in &adt.variants {
 195                 for field in &variant.fields {
 196                     if !field_implements_copy(field) {
 197                         return Err(CopyImplementationError::InfrigingField(field));
 198                     }
 199                 }
 200             }
 201
 202             if adt.has_dtor(tcx) {
 203                 return Err(CopyImplementationError::HasDestructor);
 204             }
 205
 206             Ok(())
 207         })
 208     }
 209 }
 210
 211 impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
 212     /// Creates a hash of the type `Ty` which will be the same no matter what crate
 213     /// context it's calculated within. This is used by the `type_id` intrinsic.
 214     pub fn type_id_hash(self, ty: Ty<'tcx>) -> u64 {
 215         let mut hasher = StableHasher::new();
 216         let mut hcx = StableHashingContext::new(self);
 217
 218         // We want the type_id be independent of the types free regions, so we
 219         // erase them. The erase_regions() call will also anonymize bound
 220         // regions, which is desirable too.
 221         let ty = self.erase_regions(&ty);
 222
 223         hcx.while_hashing_spans(false, |hcx| {
 224             hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
 225                 ty.hash_stable(hcx, &mut hasher);
 226             });
 227         });
 228         hasher.finish()
 229     }
 230 }
 231
 232 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 233     pub fn has_error_field(self, ty: Ty<'tcx>) -> bool {
 234         match ty.sty {
 235             ty::TyAdt(def, substs) => {
 236                 for field in def.all_fields() {
 237                     let field_ty = field.ty(self, substs);
 238                     if let TyError = field_ty.sty {
 239                         return true;
 240                     }
 241                 }
 242             }
 243             _ => (),
 244         }
 245         false
 246     }
 247
 248     /// Returns the type of element at index `i` in tuple or tuple-like type `t`.
 249     /// For an enum `t`, `variant` is None only if `t` is a univariant enum.
 250     pub fn positional_element_ty(self,
 251                                  ty: Ty<'tcx>,
 252                                  i: usize,
 253                                  variant: Option<DefId>) -> Option<Ty<'tcx>> {
 254         match (&ty.sty, variant) {
 255             (&TyAdt(adt, substs), Some(vid)) => {
 256                 adt.variant_with_id(vid).fields.get(i).map(|f| f.ty(self, substs))
 257             }
 258             (&TyAdt(adt, substs), None) => {
 259                 // Don't use `struct_variant`, this may be a univariant enum.
 260                 adt.variants[0].fields.get(i).map(|f| f.ty(self, substs))
 261             }
 262             (&TyTuple(ref v, _), None) => v.get(i).cloned(),
 263             _ => None,
 264         }
 265     }
 266
 267     /// Returns the type of element at field `n` in struct or struct-like type `t`.
 268     /// For an enum `t`, `variant` must be some def id.
 269     pub fn named_element_ty(self,
 270                             ty: Ty<'tcx>,
 271                             n: Name,
 272                             variant: Option<DefId>) -> Option<Ty<'tcx>> {
 273         match (&ty.sty, variant) {
 274             (&TyAdt(adt, substs), Some(vid)) => {
 275                 adt.variant_with_id(vid).find_field_named(n).map(|f| f.ty(self, substs))
 276             }
 277             (&TyAdt(adt, substs), None) => {
 278                 adt.struct_variant().find_field_named(n).map(|f| f.ty(self, substs))
 279             }
 280             _ => return None
 281         }
 282     }
 283
 284     /// Returns the deeply last field of nested structures, or the same type,
 285     /// if not a structure at all. Corresponds to the only possible unsized
 286     /// field, and its type can be used to determine unsizing strategy.
 287     pub fn struct_tail(self, mut ty: Ty<'tcx>) -> Ty<'tcx> {
 288         loop {
 289             match ty.sty {
 290                 ty::TyAdt(def, substs) => {
 291                     if !def.is_struct() {
 292                         break;
 293                     }
 294                     match def.struct_variant().fields.last() {
 295                         Some(f) => ty = f.ty(self, substs),
 296                         None => break,
 297                     }
 298                 }
 299
 300                 ty::TyTuple(tys, _) => {
 301                     if let Some((&last_ty, _)) = tys.split_last() {
 302                         ty = last_ty;
 303                     } else {
 304                         break;
 305                     }
 306                 }
 307
 308                 _ => {
 309                     break;
 310                 }
 311             }
 312         }
 313         ty
 314     }
 315
 316     /// Same as applying struct_tail on `source` and `target`, but only
 317     /// keeps going as long as the two types are instances of the same
 318     /// structure definitions.
 319     /// For `(Foo<Foo<T>>, Foo<Trait>)`, the result will be `(Foo<T>, Trait)`,
 320     /// whereas struct_tail produces `T`, and `Trait`, respectively.
 321     pub fn struct_lockstep_tails(self,
 322                                  source: Ty<'tcx>,
 323                                  target: Ty<'tcx>)
 324                                  -> (Ty<'tcx>, Ty<'tcx>) {
 325         let (mut a, mut b) = (source, target);
 326         loop {
 327             match (&a.sty, &b.sty) {
 328                 (&TyAdt(a_def, a_substs), &TyAdt(b_def, b_substs))
 329                         if a_def == b_def && a_def.is_struct() => {
 330                     if let Some(f) = a_def.struct_variant().fields.last() {
 331                         a = f.ty(self, a_substs);
 332                         b = f.ty(self, b_substs);
 333                     } else {
 334                         break;
 335                     }
 336                 },
 337                 (&TyTuple(a_tys, _), &TyTuple(b_tys, _))
 338                         if a_tys.len() == b_tys.len() => {
 339                     if let Some(a_last) = a_tys.last() {
 340                         a = a_last;
 341                         b = b_tys.last().unwrap();
 342                     } else {
 343                         break;
 344                     }
 345                 },
 346                 _ => break,
 347             }
 348         }
 349         (a, b)
 350     }
 351
 352     /// Given a set of predicates that apply to an object type, returns
 353     /// the region bounds that the (erased) `Self` type must
 354     /// outlive. Precisely *because* the `Self` type is erased, the
 355     /// parameter `erased_self_ty` must be supplied to indicate what type
 356     /// has been used to represent `Self` in the predicates
 357     /// themselves. This should really be a unique type; `FreshTy(0)` is a
 358     /// popular choice.
 359     ///
 360     /// NB: in some cases, particularly around higher-ranked bounds,
 361     /// this function returns a kind of conservative approximation.
 362     /// That is, all regions returned by this function are definitely
 363     /// required, but there may be other region bounds that are not
 364     /// returned, as well as requirements like `for<'a> T: 'a`.
 365     ///
 366     /// Requires that trait definitions have been processed so that we can
 367     /// elaborate predicates and walk supertraits.
 368     ///
 369     /// FIXME callers may only have a &[Predicate], not a Vec, so that's
 370     /// what this code should accept.
 371     pub fn required_region_bounds(self,
 372                                   erased_self_ty: Ty<'tcx>,
 373                                   predicates: Vec<ty::Predicate<'tcx>>)
 374                                   -> Vec<ty::Region<'tcx>>    {
 375         debug!("required_region_bounds(erased_self_ty={:?}, predicates={:?})",
 376                erased_self_ty,
 377                predicates);
 378
 379         assert!(!erased_self_ty.has_escaping_regions());
 380
 381         traits::elaborate_predicates(self, predicates)
 382             .filter_map(|predicate| {
 383                 match predicate {
 384                     ty::Predicate::Projection(..) |
 385                     ty::Predicate::Trait(..) |
 386                     ty::Predicate::Equate(..) |
 387                     ty::Predicate::Subtype(..) |
 388                     ty::Predicate::WellFormed(..) |
 389                     ty::Predicate::ObjectSafe(..) |
 390                     ty::Predicate::ClosureKind(..) |
 391                     ty::Predicate::RegionOutlives(..) => {
 392                         None
 393                     }
 394                     ty::Predicate::TypeOutlives(ty::Binder(ty::OutlivesPredicate(t, r))) => {
 395                         // Search for a bound of the form `erased_self_ty
 396                         // : 'a`, but be wary of something like `for<'a>
 397                         // erased_self_ty : 'a` (we interpret a
 398                         // higher-ranked bound like that as 'static,
 399                         // though at present the code in `fulfill.rs`
 400                         // considers such bounds to be unsatisfiable, so
 401                         // it's kind of a moot point since you could never
 402                         // construct such an object, but this seems
 403                         // correct even if that code changes).
 404                         if t == erased_self_ty && !r.has_escaping_regions() {
 405                             Some(r)
 406                         } else {
 407                             None
 408                         }
 409                     }
 410                 }
 411             })
 412             .collect()
 413     }
 414
 415     /// Calculate the destructor of a given type.
 416     pub fn calculate_dtor(
 417         self,
 418         adt_did: DefId,
 419         validate: &mut FnMut(Self, DefId) -> Result<(), ErrorReported>
 420     ) -> Option<ty::Destructor> {
 421         let drop_trait = if let Some(def_id) = self.lang_items.drop_trait() {
 422             def_id
 423         } else {
 424             return None;
 425         };
 426
 427         self.coherent_trait((LOCAL_CRATE, drop_trait));
 428
 429         let mut dtor_did = None;
 430         let ty = self.type_of(adt_did);
 431         self.for_each_relevant_impl(drop_trait, ty, |impl_did| {
 432             if let Some(item) = self.associated_items(impl_did).next() {
 433                 if let Ok(()) = validate(self, impl_did) {
 434                     dtor_did = Some(item.def_id);
 435                 }
 436             }
 437         });
 438
 439         let dtor_did = match dtor_did {
 440             Some(dtor) => dtor,
 441             None => return None,
 442         };
 443
 444         Some(ty::Destructor { did: dtor_did })
 445     }
 446
 447     /// Return the set of types that are required to be alive in
 448     /// order to run the destructor of `def` (see RFCs 769 and
 449     /// 1238).
 450     ///
 451     /// Note that this returns only the constraints for the
 452     /// destructor of `def` itself. For the destructors of the
 453     /// contents, you need `adt_dtorck_constraint`.
 454     pub fn destructor_constraints(self, def: &'tcx ty::AdtDef)
 455                                   -> Vec<ty::subst::Kind<'tcx>>
 456     {
 457         let dtor = match def.destructor(self) {
 458             None => {
 459                 debug!("destructor_constraints({:?}) - no dtor", def.did);
 460                 return vec![]
 461             }
 462             Some(dtor) => dtor.did
 463         };
 464
 465         // RFC 1238: if the destructor method is tagged with the
 466         // attribute `unsafe_destructor_blind_to_params`, then the
 467         // compiler is being instructed to *assume* that the
 468         // destructor will not access borrowed data,
 469         // even if such data is otherwise reachable.
 470         //
 471         // Such access can be in plain sight (e.g. dereferencing
 472         // `*foo.0` of `Foo<'a>(&'a u32)`) or indirectly hidden
 473         // (e.g. calling `foo.0.clone()` of `Foo<T:Clone>`).
 474         if self.has_attr(dtor, "unsafe_destructor_blind_to_params") {
 475             debug!("destructor_constraint({:?}) - blind", def.did);
 476             return vec![];
 477         }
 478
 479         let impl_def_id = self.associated_item(dtor).container.id();
 480         let impl_generics = self.generics_of(impl_def_id);
 481
 482         // We have a destructor - all the parameters that are not
 483         // pure_wrt_drop (i.e, don't have a #[may_dangle] attribute)
 484         // must be live.
 485
 486         // We need to return the list of parameters from the ADTs
 487         // generics/substs that correspond to impure parameters on the
 488         // impl's generics. This is a bit ugly, but conceptually simple:
 489         //
 490         // Suppose our ADT looks like the following
 491         //
 492         //     struct S<X, Y, Z>(X, Y, Z);
 493         //
 494         // and the impl is
 495         //
 496         //     impl<#[may_dangle] P0, P1, P2> Drop for S<P1, P2, P0>
 497         //
 498         // We want to return the parameters (X, Y). For that, we match
 499         // up the item-substs <X, Y, Z> with the substs on the impl ADT,
 500         // <P1, P2, P0>, and then look up which of the impl substs refer to
 501         // parameters marked as pure.
 502
 503         let impl_substs = match self.type_of(impl_def_id).sty {
 504             ty::TyAdt(def_, substs) if def_ == def => substs,
 505             _ => bug!()
 506         };
 507
 508         let item_substs = match self.type_of(def.did).sty {
 509             ty::TyAdt(def_, substs) if def_ == def => substs,
 510             _ => bug!()
 511         };
 512
 513         let result = item_substs.iter().zip(impl_substs.iter())
 514             .filter(|&(_, &k)| {
 515                 if let Some(&ty::RegionKind::ReEarlyBound(ref ebr)) = k.as_region() {
 516                     !impl_generics.region_param(ebr).pure_wrt_drop
 517                 } else if let Some(&ty::TyS {
 518                     sty: ty::TypeVariants::TyParam(ref pt), ..
 519                 }) = k.as_type() {
 520                     !impl_generics.type_param(pt).pure_wrt_drop
 521                 } else {
 522                     // not a type or region param - this should be reported
 523                     // as an error.
 524                     false
 525                 }
 526             }).map(|(&item_param, _)| item_param).collect();
 527         debug!("destructor_constraint({:?}) = {:?}", def.did, result);
 528         result
 529     }
 530
 531     /// Return a set of constraints that needs to be satisfied in
 532     /// order for `ty` to be valid for destruction.
 533     pub fn dtorck_constraint_for_ty(self,
 534                                     span: Span,
 535                                     for_ty: Ty<'tcx>,
 536                                     depth: usize,
 537                                     ty: Ty<'tcx>)
 538                                     -> Result<ty::DtorckConstraint<'tcx>, ErrorReported>
 539     {
 540         debug!("dtorck_constraint_for_ty({:?}, {:?}, {:?}, {:?})",
 541                span, for_ty, depth, ty);
 542
 543         if depth >= self.sess.recursion_limit.get() {
 544             let mut err = struct_span_err!(
 545                 self.sess, span, E0320,
 546                 "overflow while adding drop-check rules for {}", for_ty);
 547             err.note(&format!("overflowed on {}", ty));
 548             err.emit();
 549             return Err(ErrorReported);
 550         }
 551
 552         let result = match ty.sty {
 553             ty::TyBool | ty::TyChar | ty::TyInt(_) | ty::TyUint(_) |
 554             ty::TyFloat(_) | ty::TyStr | ty::TyNever |
 555             ty::TyRawPtr(..) | ty::TyRef(..) | ty::TyFnDef(..) | ty::TyFnPtr(_) => {
 556                 // these types never have a destructor
 557                 Ok(ty::DtorckConstraint::empty())
 558             }
 559
 560             ty::TyArray(ety, _) | ty::TySlice(ety) => {
 561                 // single-element containers, behave like their element
 562                 self.dtorck_constraint_for_ty(span, for_ty, depth+1, ety)
 563             }
 564
 565             ty::TyTuple(tys, _) => {
 566                 tys.iter().map(|ty| {
 567                     self.dtorck_constraint_for_ty(span, for_ty, depth+1, ty)
 568                 }).collect()
 569             }
 570
 571             ty::TyClosure(def_id, substs) => {
 572                 substs.upvar_tys(def_id, self).map(|ty| {
 573                     self.dtorck_constraint_for_ty(span, for_ty, depth+1, ty)
 574                 }).collect()
 575             }
 576
 577             ty::TyGenerator(def_id, substs, interior) => {
 578                 substs.upvar_tys(def_id, self).chain(iter::once(interior.witness)).map(|ty| {
 579                     self.dtorck_constraint_for_ty(span, for_ty, depth+1, ty)
 580                 }).collect()
 581             }
 582
 583             ty::TyAdt(def, substs) => {
 584                 let ty::DtorckConstraint {
 585                     dtorck_types, outlives
 586                 } = self.at(span).adt_dtorck_constraint(def.did);
 587                 Ok(ty::DtorckConstraint {
 588                     // FIXME: we can try to recursively `dtorck_constraint_on_ty`
 589                     // there, but that needs some way to handle cycles.
 590                     dtorck_types: dtorck_types.subst(self, substs),
 591                     outlives: outlives.subst(self, substs)
 592                 })
 593             }
 594
 595             // Objects must be alive in order for their destructor
 596             // to be called.
 597             ty::TyDynamic(..) => Ok(ty::DtorckConstraint {
 598                 outlives: vec![Kind::from(ty)],
 599                 dtorck_types: vec![],
 600             }),
 601
 602             // Types that can't be resolved. Pass them forward.
 603             ty::TyProjection(..) | ty::TyAnon(..) | ty::TyParam(..) => {
 604                 Ok(ty::DtorckConstraint {
 605                     outlives: vec![],
 606                     dtorck_types: vec![ty],
 607                 })
 608             }
 609
 610             ty::TyInfer(..) | ty::TyError => {
 611                 self.sess.delay_span_bug(span, "unresolved type in dtorck");
 612                 Err(ErrorReported)
 613             }
 614         };
 615
 616         debug!("dtorck_constraint_for_ty({:?}) = {:?}", ty, result);
 617         result
 618     }
 619
 620     pub fn closure_base_def_id(self, def_id: DefId) -> DefId {
 621         let mut def_id = def_id;
 622         while self.def_key(def_id).disambiguated_data.data == DefPathData::ClosureExpr {
 623             def_id = self.parent_def_id(def_id).unwrap_or_else(|| {
 624                 bug!("closure {:?} has no parent", def_id);
 625             });
 626         }
 627         def_id
 628     }
 629
 630     /// Given the def-id of some item that has no type parameters, make
 631     /// a suitable "empty substs" for it.
 632     pub fn empty_substs_for_def_id(self, item_def_id: DefId) -> &'tcx ty::Substs<'tcx> {
 633         ty::Substs::for_item(self, item_def_id,
 634                              |_, _| self.types.re_erased,
 635                              |_, _| {
 636             bug!("empty_substs_for_def_id: {:?} has type parameters", item_def_id)
 637         })
 638     }
 639
 640     pub fn const_usize(&self, val: u16) -> ConstInt {
 641         match self.sess.target.uint_type {
 642             ast::UintTy::U16 => ConstInt::Usize(ConstUsize::Us16(val as u16)),
 643             ast::UintTy::U32 => ConstInt::Usize(ConstUsize::Us32(val as u32)),
 644             ast::UintTy::U64 => ConstInt::Usize(ConstUsize::Us64(val as u64)),
 645             _ => bug!(),
 646         }
 647     }
 648 }
 649
 650 pub struct TypeIdHasher<'a, 'gcx: 'a+'tcx, 'tcx: 'a, W> {
 651     tcx: TyCtxt<'a, 'gcx, 'tcx>,
 652     state: StableHasher<W>,
 653 }
 654
 655 impl<'a, 'gcx, 'tcx, W> TypeIdHasher<'a, 'gcx, 'tcx, W>
 656     where W: StableHasherResult
 657 {
 658     pub fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Self {
 659         TypeIdHasher { tcx: tcx, state: StableHasher::new() }
 660     }
 661
 662     pub fn finish(self) -> W {
 663         self.state.finish()
 664     }
 665
 666     pub fn hash<T: Hash>(&mut self, x: T) {
 667         x.hash(&mut self.state);
 668     }
 669
 670     fn hash_discriminant_u8<T>(&mut self, x: &T) {
 671         let v = unsafe {
 672             intrinsics::discriminant_value(x)
 673         };
 674         let b = v as u8;
 675         assert_eq!(v, b as u64);
 676         self.hash(b)
 677     }
 678
 679     fn def_id(&mut self, did: DefId) {
 680         // Hash the DefPath corresponding to the DefId, which is independent
 681         // of compiler internal state. We already have a stable hash value of
 682         // all DefPaths available via tcx.def_path_hash(), so we just feed that
 683         // into the hasher.
 684         let hash = self.tcx.def_path_hash(did);
 685         self.hash(hash);
 686     }
 687 }
 688
 689 impl<'a, 'gcx, 'tcx, W> TypeVisitor<'tcx> for TypeIdHasher<'a, 'gcx, 'tcx, W>
 690     where W: StableHasherResult
 691 {
 692     fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
 693         // Distinguish between the Ty variants uniformly.
 694         self.hash_discriminant_u8(&ty.sty);
 695
 696         match ty.sty {
 697             TyInt(i) => self.hash(i),
 698             TyUint(u) => self.hash(u),
 699             TyFloat(f) => self.hash(f),
 700             TyArray(_, n) => self.hash(n),
 701             TyRawPtr(m) |
 702             TyRef(_, m) => self.hash(m.mutbl),
 703             TyClosure(def_id, _) |
 704             TyGenerator(def_id, _, _) |
 705             TyAnon(def_id, _) |
 706             TyFnDef(def_id, _) => self.def_id(def_id),
 707             TyAdt(d, _) => self.def_id(d.did),
 708             TyFnPtr(f) => {
 709                 self.hash(f.unsafety());
 710                 self.hash(f.abi());
 711                 self.hash(f.variadic());
 712                 self.hash(f.inputs().skip_binder().len());
 713             }
 714             TyDynamic(ref data, ..) => {
 715                 if let Some(p) = data.principal() {
 716                     self.def_id(p.def_id());
 717                 }
 718                 for d in data.auto_traits() {
 719                     self.def_id(d);
 720                 }
 721             }
 722             TyTuple(tys, defaulted) => {
 723                 self.hash(tys.len());
 724                 self.hash(defaulted);
 725             }
 726             TyParam(p) => {
 727                 self.hash(p.idx);
 728                 self.hash(p.name.as_str());
 729             }
 730             TyProjection(ref data) => {
 731                 self.def_id(data.item_def_id);
 732             }
 733             TyNever |
 734             TyBool |
 735             TyChar |
 736             TyStr |
 737             TySlice(_) => {}
 738
 739             TyError |
 740             TyInfer(_) => bug!("TypeIdHasher: unexpected type {}", ty)
 741         }
 742
 743         ty.super_visit_with(self)
 744     }
 745
 746     fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
 747         self.hash_discriminant_u8(r);
 748         match *r {
 749             ty::ReErased |
 750             ty::ReStatic |
 751             ty::ReEmpty => {
 752                 // No variant fields to hash for these ...
 753             }
 754             ty::ReLateBound(db, ty::BrAnon(i)) => {
 755                 self.hash(db.depth);
 756                 self.hash(i);
 757             }
 758             ty::ReEarlyBound(ty::EarlyBoundRegion { def_id, .. }) => {
 759                 self.def_id(def_id);
 760             }
 761             ty::ReLateBound(..) |
 762             ty::ReFree(..) |
 763             ty::ReScope(..) |
 764             ty::ReVar(..) |
 765             ty::ReSkolemized(..) => {
 766                 bug!("TypeIdHasher: unexpected region {:?}", r)
 767             }
 768         }
 769         false
 770     }
 771
 772     fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, x: &ty::Binder<T>) -> bool {
 773         // Anonymize late-bound regions so that, for example:
 774         // `for<'a, b> fn(&'a &'b T)` and `for<'a, b> fn(&'b &'a T)`
 775         // result in the same TypeId (the two types are equivalent).
 776         self.tcx.anonymize_late_bound_regions(x).super_visit_with(self)
 777     }
 778 }
 779
 780 impl<'a, 'tcx> ty::TyS<'tcx> {
 781     pub fn moves_by_default(&'tcx self,
 782                             tcx: TyCtxt<'a, 'tcx, 'tcx>,
 783                             param_env: ty::ParamEnv<'tcx>,
 784                             span: Span)
 785                             -> bool {
 786         !tcx.at(span).is_copy_raw(param_env.and(self))
 787     }
 788
 789     pub fn is_sized(&'tcx self,
 790                     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 791                     param_env: ty::ParamEnv<'tcx>,
 792                     span: Span)-> bool
 793     {
 794         tcx.at(span).is_sized_raw(param_env.and(self))
 795     }
 796
 797     pub fn is_freeze(&'tcx self,
 798                      tcx: TyCtxt<'a, 'tcx, 'tcx>,
 799                      param_env: ty::ParamEnv<'tcx>,
 800                      span: Span)-> bool
 801     {
 802         tcx.at(span).is_freeze_raw(param_env.and(self))
 803     }
 804
 805     /// If `ty.needs_drop(...)` returns `true`, then `ty` is definitely
 806     /// non-copy and *might* have a destructor attached; if it returns
 807     /// `false`, then `ty` definitely has no destructor (i.e. no drop glue).
 808     ///
 809     /// (Note that this implies that if `ty` has a destructor attached,
 810     /// then `needs_drop` will definitely return `true` for `ty`.)
 811     #[inline]
 812     pub fn needs_drop(&'tcx self,
 813                       tcx: TyCtxt<'a, 'tcx, 'tcx>,
 814                       param_env: ty::ParamEnv<'tcx>)
 815                       -> bool {
 816         tcx.needs_drop_raw(param_env.and(self))
 817     }
 818
 819     /// Computes the layout of a type. Note that this implicitly
 820     /// executes in "reveal all" mode.
 821     #[inline]
 822     pub fn layout<'lcx>(&'tcx self,
 823                         tcx: TyCtxt<'a, 'tcx, 'tcx>,
 824                         param_env: ty::ParamEnv<'tcx>)
 825                         -> Result<&'tcx Layout, LayoutError<'tcx>> {
 826         let ty = tcx.erase_regions(&self);
 827         let layout = tcx.layout_raw(param_env.reveal_all().and(ty));
 828
 829         // NB: This recording is normally disabled; when enabled, it
 830         // can however trigger recursive invocations of `layout()`.
 831         // Therefore, we execute it *after* the main query has
 832         // completed, to avoid problems around recursive structures
 833         // and the like. (Admitedly, I wasn't able to reproduce a problem
 834         // here, but it seems like the right thing to do. -nmatsakis)
 835         if let Ok(l) = layout {
 836             Layout::record_layout_for_printing(tcx, ty, param_env, l);
 837         }
 838
 839         layout
 840     }
 841
 842
 843     /// Check whether a type is representable. This means it cannot contain unboxed
 844     /// structural recursion. This check is needed for structs and enums.
 845     pub fn is_representable(&'tcx self,
 846                             tcx: TyCtxt<'a, 'tcx, 'tcx>,
 847                             sp: Span)
 848                             -> Representability {
 849
 850         // Iterate until something non-representable is found
 851         fn fold_repr<It: Iterator<Item=Representability>>(iter: It) -> Representability {
 852             iter.fold(Representability::Representable, |r1, r2| {
 853                 match (r1, r2) {
 854                     (Representability::SelfRecursive(v1),
 855                      Representability::SelfRecursive(v2)) => {
 856                         Representability::SelfRecursive(v1.iter().map(|s| *s).chain(v2).collect())
 857                     }
 858                     (r1, r2) => cmp::max(r1, r2)
 859                 }
 860             })
 861         }
 862
 863         fn are_inner_types_recursive<'a, 'tcx>(
 864             tcx: TyCtxt<'a, 'tcx, 'tcx>, sp: Span,
 865             seen: &mut Vec<Ty<'tcx>>,
 866             representable_cache: &mut FxHashMap<Ty<'tcx>, Representability>,
 867             ty: Ty<'tcx>)
 868             -> Representability
 869         {
 870             match ty.sty {
 871                 TyTuple(ref ts, _) => {
 872                     // Find non representable
 873                     fold_repr(ts.iter().map(|ty| {
 874                         is_type_structurally_recursive(tcx, sp, seen, representable_cache, ty)
 875                     }))
 876                 }
 877                 // Fixed-length vectors.
 878                 // FIXME(#11924) Behavior undecided for zero-length vectors.
 879                 TyArray(ty, _) => {
 880                     is_type_structurally_recursive(tcx, sp, seen, representable_cache, ty)
 881                 }
 882                 TyAdt(def, substs) => {
 883                     // Find non representable fields with their spans
 884                     fold_repr(def.all_fields().map(|field| {
 885                         let ty = field.ty(tcx, substs);
 886                         let span = tcx.hir.span_if_local(field.did).unwrap_or(sp);
 887                         match is_type_structurally_recursive(tcx, span, seen,
 888                                                              representable_cache, ty)
 889                         {
 890                             Representability::SelfRecursive(_) => {
 891                                 Representability::SelfRecursive(vec![span])
 892                             }
 893                             x => x,
 894                         }
 895                     }))
 896                 }
 897                 TyClosure(..) => {
 898                     // this check is run on type definitions, so we don't expect
 899                     // to see closure types
 900                     bug!("requires check invoked on inapplicable type: {:?}", ty)
 901                 }
 902                 _ => Representability::Representable,
 903             }
 904         }
 905
 906         fn same_struct_or_enum<'tcx>(ty: Ty<'tcx>, def: &'tcx ty::AdtDef) -> bool {
 907             match ty.sty {
 908                 TyAdt(ty_def, _) => {
 909                      ty_def == def
 910                 }
 911                 _ => false
 912             }
 913         }
 914
 915         fn same_type<'tcx>(a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
 916             match (&a.sty, &b.sty) {
 917                 (&TyAdt(did_a, substs_a), &TyAdt(did_b, substs_b)) => {
 918                     if did_a != did_b {
 919                         return false;
 920                     }
 921
 922                     substs_a.types().zip(substs_b.types()).all(|(a, b)| same_type(a, b))
 923                 }
 924                 _ => a == b,
 925             }
 926         }
 927
 928         // Does the type `ty` directly (without indirection through a pointer)
 929         // contain any types on stack `seen`?
 930         fn is_type_structurally_recursive<'a, 'tcx>(
 931             tcx: TyCtxt<'a, 'tcx, 'tcx>,
 932             sp: Span,
 933             seen: &mut Vec<Ty<'tcx>>,
 934             representable_cache: &mut FxHashMap<Ty<'tcx>, Representability>,
 935             ty: Ty<'tcx>) -> Representability
 936         {
 937             debug!("is_type_structurally_recursive: {:?} {:?}", ty, sp);
 938             if let Some(representability) = representable_cache.get(ty) {
 939                 debug!("is_type_structurally_recursive: {:?} {:?} - (cached) {:?}",
 940                        ty, sp, representability);
 941                 return representability.clone();
 942             }
 943
 944             let representability = is_type_structurally_recursive_inner(
 945                 tcx, sp, seen, representable_cache, ty);
 946
 947             representable_cache.insert(ty, representability.clone());
 948             representability
 949         }
 950
 951         fn is_type_structurally_recursive_inner<'a, 'tcx>(
 952             tcx: TyCtxt<'a, 'tcx, 'tcx>,
 953             sp: Span,
 954             seen: &mut Vec<Ty<'tcx>>,
 955             representable_cache: &mut FxHashMap<Ty<'tcx>, Representability>,
 956             ty: Ty<'tcx>) -> Representability
 957         {
 958             match ty.sty {
 959                 TyAdt(def, _) => {
 960                     {
 961                         // Iterate through stack of previously seen types.
 962                         let mut iter = seen.iter();
 963
 964                         // The first item in `seen` is the type we are actually curious about.
 965                         // We want to return SelfRecursive if this type contains itself.
 966                         // It is important that we DON'T take generic parameters into account
 967                         // for this check, so that Bar<T> in this example counts as SelfRecursive:
 968                         //
 969                         // struct Foo;
 970                         // struct Bar<T> { x: Bar<Foo> }
 971
 972                         if let Some(&seen_type) = iter.next() {
 973                             if same_struct_or_enum(seen_type, def) {
 974                                 debug!("SelfRecursive: {:?} contains {:?}",
 975                                        seen_type,
 976                                        ty);
 977                                 return Representability::SelfRecursive(vec![sp]);
 978                             }
 979                         }
 980
 981                         // We also need to know whether the first item contains other types
 982                         // that are structurally recursive. If we don't catch this case, we
 983                         // will recurse infinitely for some inputs.
 984                         //
 985                         // It is important that we DO take generic parameters into account
 986                         // here, so that code like this is considered SelfRecursive, not
 987                         // ContainsRecursive:
 988                         //
 989                         // struct Foo { Option<Option<Foo>> }
 990
 991                         for &seen_type in iter {
 992                             if same_type(ty, seen_type) {
 993                                 debug!("ContainsRecursive: {:?} contains {:?}",
 994                                        seen_type,
 995                                        ty);
 996                                 return Representability::ContainsRecursive;
 997                             }
 998                         }
 999                     }
1000
1001                     // For structs and enums, track all previously seen types by pushing them
1002                     // onto the 'seen' stack.
1003                     seen.push(ty);
1004                     let out = are_inner_types_recursive(tcx, sp, seen, representable_cache, ty);
1005                     seen.pop();
1006                     out
1007                 }
1008                 _ => {
1009                     // No need to push in other cases.
1010                     are_inner_types_recursive(tcx, sp, seen, representable_cache, ty)
1011                 }
1012             }
1013         }
1014
1015         debug!("is_type_representable: {:?}", self);
1016
1017         // To avoid a stack overflow when checking an enum variant or struct that
1018         // contains a different, structurally recursive type, maintain a stack
1019         // of seen types and check recursion for each of them (issues #3008, #3779).
1020         let mut seen: Vec<Ty> = Vec::new();
1021         let mut representable_cache = FxHashMap();
1022         let r = is_type_structurally_recursive(
1023             tcx, sp, &mut seen, &mut representable_cache, self);
1024         debug!("is_type_representable: {:?} is {:?}", self, r);
1025         r
1026     }
1027 }
1028
1029 fn is_copy_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1030                          query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
1031                          -> bool
1032 {
1033     let (param_env, ty) = query.into_parts();
1034     let trait_def_id = tcx.require_lang_item(lang_items::CopyTraitLangItem);
1035     tcx.infer_ctxt()
1036        .enter(|infcx| traits::type_known_to_meet_bound(&infcx,
1037                                                        param_env,
1038                                                        ty,
1039                                                        trait_def_id,
1040                                                        DUMMY_SP))
1041 }
1042
1043 fn is_sized_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1044                           query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
1045                           -> bool
1046 {
1047     let (param_env, ty) = query.into_parts();
1048     let trait_def_id = tcx.require_lang_item(lang_items::SizedTraitLangItem);
1049     tcx.infer_ctxt()
1050        .enter(|infcx| traits::type_known_to_meet_bound(&infcx,
1051                                                        param_env,
1052                                                        ty,
1053                                                        trait_def_id,
1054                                                        DUMMY_SP))
1055 }
1056
1057 fn is_freeze_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1058                            query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
1059                            -> bool
1060 {
1061     let (param_env, ty) = query.into_parts();
1062     let trait_def_id = tcx.require_lang_item(lang_items::FreezeTraitLangItem);
1063     tcx.infer_ctxt()
1064        .enter(|infcx| traits::type_known_to_meet_bound(&infcx,
1065                                                        param_env,
1066                                                        ty,
1067                                                        trait_def_id,
1068                                                        DUMMY_SP))
1069 }
1070
1071 fn needs_drop_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1072                             query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
1073                             -> bool
1074 {
1075     let (param_env, ty) = query.into_parts();
1076
1077     let needs_drop = |ty: Ty<'tcx>| -> bool {
1078         match ty::queries::needs_drop_raw::try_get(tcx, DUMMY_SP, param_env.and(ty)) {
1079             Ok(v) => v,
1080             Err(_) => {
1081                 // Cycles should be reported as an error by `check_representable`.
1082                 //
1083                 // Consider the type as not needing drop in the meanwhile to avoid
1084                 // further errors.
1085                 false
1086             }
1087         }
1088     };
1089
1090     assert!(!ty.needs_infer());
1091
1092     match ty.sty {
1093         // Fast-path for primitive types
1094         ty::TyInfer(ty::FreshIntTy(_)) | ty::TyInfer(ty::FreshFloatTy(_)) |
1095         ty::TyBool | ty::TyInt(_) | ty::TyUint(_) | ty::TyFloat(_) | ty::TyNever |
1096         ty::TyFnDef(..) | ty::TyFnPtr(_) | ty::TyChar |
1097         ty::TyRawPtr(_) | ty::TyRef(..) | ty::TyStr => false,
1098
1099         // Issue #22536: We first query type_moves_by_default.  It sees a
1100         // normalized version of the type, and therefore will definitely
1101         // know whether the type implements Copy (and thus needs no
1102         // cleanup/drop/zeroing) ...
1103         _ if !ty.moves_by_default(tcx, param_env, DUMMY_SP) => false,
1104
1105         // ... (issue #22536 continued) but as an optimization, still use
1106         // prior logic of asking for the structural "may drop".
1107
1108         // FIXME(#22815): Note that this is a conservative heuristic;
1109         // it may report that the type "may drop" when actual type does
1110         // not actually have a destructor associated with it. But since
1111         // the type absolutely did not have the `Copy` bound attached
1112         // (see above), it is sound to treat it as having a destructor.
1113
1114         // User destructors are the only way to have concrete drop types.
1115         ty::TyAdt(def, _) if def.has_dtor(tcx) => true,
1116
1117         // Can refer to a type which may drop.
1118         // FIXME(eddyb) check this against a ParamEnv.
1119         ty::TyDynamic(..) | ty::TyProjection(..) | ty::TyParam(_) |
1120         ty::TyAnon(..) | ty::TyInfer(_) | ty::TyError => true,
1121
1122         // Structural recursion.
1123         ty::TyArray(ty, _) | ty::TySlice(ty) => needs_drop(ty),
1124
1125         ty::TyClosure(def_id, ref substs) => substs.upvar_tys(def_id, tcx).any(needs_drop),
1126
1127         ty::TyGenerator(..) => true,
1128
1129         ty::TyTuple(ref tys, _) => tys.iter().cloned().any(needs_drop),
1130
1131         // unions don't have destructors regardless of the child types
1132         ty::TyAdt(def, _) if def.is_union() => false,
1133
1134         ty::TyAdt(def, substs) =>
1135             def.variants.iter().any(
1136                 |variant| variant.fields.iter().any(
1137                     |field| needs_drop(field.ty(tcx, substs)))),
1138     }
1139 }
1140
1141 fn layout_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1142                         query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
1143                         -> Result<&'tcx Layout, LayoutError<'tcx>>
1144 {
1145     let (param_env, ty) = query.into_parts();
1146
1147     let rec_limit = tcx.sess.recursion_limit.get();
1148     let depth = tcx.layout_depth.get();
1149     if depth > rec_limit {
1150         tcx.sess.fatal(
1151             &format!("overflow representing the type `{}`", ty));
1152     }
1153
1154     tcx.layout_depth.set(depth+1);
1155     let layout = Layout::compute_uncached(tcx, param_env, ty);
1156     tcx.layout_depth.set(depth);
1157
1158     layout
1159 }
1160
1161 pub fn provide(providers: &mut ty::maps::Providers) {
1162     *providers = ty::maps::Providers {
1163         is_copy_raw,
1164         is_sized_raw,
1165         is_freeze_raw,
1166         needs_drop_raw,
1167         layout_raw,
1168         ..*providers
1169     };
1170 }