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 middle::const_val::ConstVal;
  17 use traits::{self, Reveal};
  18 use ty::{self, Ty, TyCtxt, TypeFoldable};
  19 use ty::fold::TypeVisitor;
  20 use ty::layout::{Layout, LayoutError};
  21 use ty::subst::{Subst, Kind};
  22 use ty::TypeVariants::*;
  23 use util::common::ErrorReported;
  24 use middle::lang_items;
  25
  26 use rustc_const_math::{ConstInt, ConstIsize, ConstUsize};
  27 use rustc_data_structures::stable_hasher::{StableHasher, StableHasherResult,
  28                                            HashStable};
  29 use rustc_data_structures::fx::FxHashMap;
  30 use std::cmp;
  31 use std::iter;
  32 use std::hash::Hash;
  33 use std::intrinsics;
  34 use syntax::ast::{self, Name};
  35 use syntax::attr::{self, SignedInt, UnsignedInt};
  36 use syntax_pos::{Span, DUMMY_SP};
  37
  38 type Disr = ConstInt;
  39
  40 pub trait IntTypeExt {
  41     fn to_ty<'a, 'gcx, 'tcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Ty<'tcx>;
  42     fn disr_incr<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>, val: Option<Disr>)
  43                            -> Option<Disr>;
  44     fn assert_ty_matches(&self, val: Disr);
  45     fn initial_discriminant<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Disr;
  46 }
  47
  48
  49 macro_rules! typed_literal {
  50     ($tcx:expr, $ty:expr, $lit:expr) => {
  51         match $ty {
  52             SignedInt(ast::IntTy::I8)    => ConstInt::I8($lit),
  53             SignedInt(ast::IntTy::I16)   => ConstInt::I16($lit),
  54             SignedInt(ast::IntTy::I32)   => ConstInt::I32($lit),
  55             SignedInt(ast::IntTy::I64)   => ConstInt::I64($lit),
  56             SignedInt(ast::IntTy::I128)   => ConstInt::I128($lit),
  57             SignedInt(ast::IntTy::Is) => match $tcx.sess.target.isize_ty {
  58                 ast::IntTy::I16 => ConstInt::Isize(ConstIsize::Is16($lit)),
  59                 ast::IntTy::I32 => ConstInt::Isize(ConstIsize::Is32($lit)),
  60                 ast::IntTy::I64 => ConstInt::Isize(ConstIsize::Is64($lit)),
  61                 _ => bug!(),
  62             },
  63             UnsignedInt(ast::UintTy::U8)  => ConstInt::U8($lit),
  64             UnsignedInt(ast::UintTy::U16) => ConstInt::U16($lit),
  65             UnsignedInt(ast::UintTy::U32) => ConstInt::U32($lit),
  66             UnsignedInt(ast::UintTy::U64) => ConstInt::U64($lit),
  67             UnsignedInt(ast::UintTy::U128) => ConstInt::U128($lit),
  68             UnsignedInt(ast::UintTy::Us) => match $tcx.sess.target.usize_ty {
  69                 ast::UintTy::U16 => ConstInt::Usize(ConstUsize::Us16($lit)),
  70                 ast::UintTy::U32 => ConstInt::Usize(ConstUsize::Us32($lit)),
  71                 ast::UintTy::U64 => ConstInt::Usize(ConstUsize::Us64($lit)),
  72                 _ => bug!(),
  73             },
  74         }
  75     }
  76 }
  77
  78 impl IntTypeExt for attr::IntType {
  79     fn to_ty<'a, 'gcx, 'tcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Ty<'tcx> {
  80         match *self {
  81             SignedInt(ast::IntTy::I8)      => tcx.types.i8,
  82             SignedInt(ast::IntTy::I16)     => tcx.types.i16,
  83             SignedInt(ast::IntTy::I32)     => tcx.types.i32,
  84             SignedInt(ast::IntTy::I64)     => tcx.types.i64,
  85             SignedInt(ast::IntTy::I128)     => tcx.types.i128,
  86             SignedInt(ast::IntTy::Is)   => tcx.types.isize,
  87             UnsignedInt(ast::UintTy::U8)    => tcx.types.u8,
  88             UnsignedInt(ast::UintTy::U16)   => tcx.types.u16,
  89             UnsignedInt(ast::UintTy::U32)   => tcx.types.u32,
  90             UnsignedInt(ast::UintTy::U64)   => tcx.types.u64,
  91             UnsignedInt(ast::UintTy::U128)   => tcx.types.u128,
  92             UnsignedInt(ast::UintTy::Us) => tcx.types.usize,
  93         }
  94     }
  95
  96     fn initial_discriminant<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Disr {
  97         typed_literal!(tcx, *self, 0)
  98     }
  99
 100     fn assert_ty_matches(&self, val: Disr) {
 101         match (*self, val) {
 102             (SignedInt(ast::IntTy::I8), ConstInt::I8(_)) => {},
 103             (SignedInt(ast::IntTy::I16), ConstInt::I16(_)) => {},
 104             (SignedInt(ast::IntTy::I32), ConstInt::I32(_)) => {},
 105             (SignedInt(ast::IntTy::I64), ConstInt::I64(_)) => {},
 106             (SignedInt(ast::IntTy::I128), ConstInt::I128(_)) => {},
 107             (SignedInt(ast::IntTy::Is), ConstInt::Isize(_)) => {},
 108             (UnsignedInt(ast::UintTy::U8), ConstInt::U8(_)) => {},
 109             (UnsignedInt(ast::UintTy::U16), ConstInt::U16(_)) => {},
 110             (UnsignedInt(ast::UintTy::U32), ConstInt::U32(_)) => {},
 111             (UnsignedInt(ast::UintTy::U64), ConstInt::U64(_)) => {},
 112             (UnsignedInt(ast::UintTy::U128), ConstInt::U128(_)) => {},
 113             (UnsignedInt(ast::UintTy::Us), ConstInt::Usize(_)) => {},
 114             _ => bug!("disr type mismatch: {:?} vs {:?}", self, val),
 115         }
 116     }
 117
 118     fn disr_incr<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>, val: Option<Disr>)
 119                            -> Option<Disr> {
 120         if let Some(val) = val {
 121             self.assert_ty_matches(val);
 122             (val + typed_literal!(tcx, *self, 1)).ok()
 123         } else {
 124             Some(self.initial_discriminant(tcx))
 125         }
 126     }
 127 }
 128
 129
 130 #[derive(Copy, Clone)]
 131 pub enum CopyImplementationError<'tcx> {
 132     InfrigingField(&'tcx ty::FieldDef),
 133     NotAnAdt,
 134     HasDestructor,
 135 }
 136
 137 /// Describes whether a type is representable. For types that are not
 138 /// representable, 'SelfRecursive' and 'ContainsRecursive' are used to
 139 /// distinguish between types that are recursive with themselves and types that
 140 /// contain a different recursive type. These cases can therefore be treated
 141 /// differently when reporting errors.
 142 ///
 143 /// The ordering of the cases is significant. They are sorted so that cmp::max
 144 /// will keep the "more erroneous" of two values.
 145 #[derive(Clone, PartialOrd, Ord, Eq, PartialEq, Debug)]
 146 pub enum Representability {
 147     Representable,
 148     ContainsRecursive,
 149     SelfRecursive(Vec<Span>),
 150 }
 151
 152 impl<'tcx> ty::ParamEnv<'tcx> {
 153     /// Construct a trait environment suitable for contexts where
 154     /// there are no where clauses in scope.
 155     pub fn empty(reveal: Reveal) -> Self {
 156         Self::new(ty::Slice::empty(), reveal)
 157     }
 158
 159     /// Construct a trait environment with the given set of predicates.
 160     pub fn new(caller_bounds: &'tcx ty::Slice<ty::Predicate<'tcx>>,
 161                reveal: Reveal)
 162                -> Self {
 163         ty::ParamEnv { caller_bounds, reveal }
 164     }
 165
 166     /// Returns a new parameter environment with the same clauses, but
 167     /// which "reveals" the true results of projections in all cases
 168     /// (even for associated types that are specializable).  This is
 169     /// the desired behavior during trans and certain other special
 170     /// contexts; normally though we want to use `Reveal::UserFacing`,
 171     /// which is the default.
 172     pub fn reveal_all(self) -> Self {
 173         ty::ParamEnv { reveal: Reveal::All, ..self }
 174     }
 175
 176     pub fn can_type_implement_copy<'a>(self,
 177                                        tcx: TyCtxt<'a, 'tcx, 'tcx>,
 178                                        self_type: Ty<'tcx>, span: Span)
 179                                        -> Result<(), CopyImplementationError<'tcx>> {
 180         // FIXME: (@jroesch) float this code up
 181         tcx.infer_ctxt().enter(|infcx| {
 182             let (adt, substs) = match self_type.sty {
 183                 ty::TyAdt(adt, substs) => (adt, substs),
 184                 _ => return Err(CopyImplementationError::NotAnAdt),
 185             };
 186
 187             let field_implements_copy = |field: &ty::FieldDef| {
 188                 let cause = traits::ObligationCause::dummy();
 189                 match traits::fully_normalize(&infcx, cause, self, &field.ty(tcx, substs)) {
 190                     Ok(ty) => !infcx.type_moves_by_default(self, ty, span),
 191                     Err(..) => false,
 192                 }
 193             };
 194
 195             for variant in &adt.variants {
 196                 for field in &variant.fields {
 197                     if !field_implements_copy(field) {
 198                         return Err(CopyImplementationError::InfrigingField(field));
 199                     }
 200                 }
 201             }
 202
 203             if adt.has_dtor(tcx) {
 204                 return Err(CopyImplementationError::HasDestructor);
 205             }
 206
 207             Ok(())
 208         })
 209     }
 210 }
 211
 212 impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
 213     /// Creates a hash of the type `Ty` which will be the same no matter what crate
 214     /// context it's calculated within. This is used by the `type_id` intrinsic.
 215     pub fn type_id_hash(self, ty: Ty<'tcx>) -> u64 {
 216         let mut hasher = StableHasher::new();
 217         let mut hcx = StableHashingContext::new(self);
 218
 219         // We want the type_id be independent of the types free regions, so we
 220         // erase them. The erase_regions() call will also anonymize bound
 221         // regions, which is desirable too.
 222         let ty = self.erase_regions(&ty);
 223
 224         hcx.while_hashing_spans(false, |hcx| {
 225             hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
 226                 ty.hash_stable(hcx, &mut hasher);
 227             });
 228         });
 229         hasher.finish()
 230     }
 231 }
 232
 233 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 234     pub fn has_error_field(self, ty: Ty<'tcx>) -> bool {
 235         match ty.sty {
 236             ty::TyAdt(def, substs) => {
 237                 for field in def.all_fields() {
 238                     let field_ty = field.ty(self, substs);
 239                     if let TyError = field_ty.sty {
 240                         return true;
 241                     }
 242                 }
 243             }
 244             _ => (),
 245         }
 246         false
 247     }
 248
 249     /// Returns the type of element at index `i` in tuple or tuple-like type `t`.
 250     /// For an enum `t`, `variant` is None only if `t` is a univariant enum.
 251     pub fn positional_element_ty(self,
 252                                  ty: Ty<'tcx>,
 253                                  i: usize,
 254                                  variant: Option<DefId>) -> Option<Ty<'tcx>> {
 255         match (&ty.sty, variant) {
 256             (&TyAdt(adt, substs), Some(vid)) => {
 257                 adt.variant_with_id(vid).fields.get(i).map(|f| f.ty(self, substs))
 258             }
 259             (&TyAdt(adt, substs), None) => {
 260                 // Don't use `struct_variant`, this may be a univariant enum.
 261                 adt.variants[0].fields.get(i).map(|f| f.ty(self, substs))
 262             }
 263             (&TyTuple(ref v, _), None) => v.get(i).cloned(),
 264             _ => None,
 265         }
 266     }
 267
 268     /// Returns the type of element at field `n` in struct or struct-like type `t`.
 269     /// For an enum `t`, `variant` must be some def id.
 270     pub fn named_element_ty(self,
 271                             ty: Ty<'tcx>,
 272                             n: Name,
 273                             variant: Option<DefId>) -> Option<Ty<'tcx>> {
 274         match (&ty.sty, variant) {
 275             (&TyAdt(adt, substs), Some(vid)) => {
 276                 adt.variant_with_id(vid).find_field_named(n).map(|f| f.ty(self, substs))
 277             }
 278             (&TyAdt(adt, substs), None) => {
 279                 adt.struct_variant().find_field_named(n).map(|f| f.ty(self, substs))
 280             }
 281             _ => return None
 282         }
 283     }
 284
 285     /// Returns the deeply last field of nested structures, or the same type,
 286     /// if not a structure at all. Corresponds to the only possible unsized
 287     /// field, and its type can be used to determine unsizing strategy.
 288     pub fn struct_tail(self, mut ty: Ty<'tcx>) -> Ty<'tcx> {
 289         loop {
 290             match ty.sty {
 291                 ty::TyAdt(def, substs) => {
 292                     if !def.is_struct() {
 293                         break;
 294                     }
 295                     match def.struct_variant().fields.last() {
 296                         Some(f) => ty = f.ty(self, substs),
 297                         None => break,
 298                     }
 299                 }
 300
 301                 ty::TyTuple(tys, _) => {
 302                     if let Some((&last_ty, _)) = tys.split_last() {
 303                         ty = last_ty;
 304                     } else {
 305                         break;
 306                     }
 307                 }
 308
 309                 _ => {
 310                     break;
 311                 }
 312             }
 313         }
 314         ty
 315     }
 316
 317     /// Same as applying struct_tail on `source` and `target`, but only
 318     /// keeps going as long as the two types are instances of the same
 319     /// structure definitions.
 320     /// For `(Foo<Foo<T>>, Foo<Trait>)`, the result will be `(Foo<T>, Trait)`,
 321     /// whereas struct_tail produces `T`, and `Trait`, respectively.
 322     pub fn struct_lockstep_tails(self,
 323                                  source: Ty<'tcx>,
 324                                  target: Ty<'tcx>)
 325                                  -> (Ty<'tcx>, Ty<'tcx>) {
 326         let (mut a, mut b) = (source, target);
 327         loop {
 328             match (&a.sty, &b.sty) {
 329                 (&TyAdt(a_def, a_substs), &TyAdt(b_def, b_substs))
 330                         if a_def == b_def && a_def.is_struct() => {
 331                     if let Some(f) = a_def.struct_variant().fields.last() {
 332                         a = f.ty(self, a_substs);
 333                         b = f.ty(self, b_substs);
 334                     } else {
 335                         break;
 336                     }
 337                 },
 338                 (&TyTuple(a_tys, _), &TyTuple(b_tys, _))
 339                         if a_tys.len() == b_tys.len() => {
 340                     if let Some(a_last) = a_tys.last() {
 341                         a = a_last;
 342                         b = b_tys.last().unwrap();
 343                     } else {
 344                         break;
 345                     }
 346                 },
 347                 _ => break,
 348             }
 349         }
 350         (a, b)
 351     }
 352
 353     /// Given a set of predicates that apply to an object type, returns
 354     /// the region bounds that the (erased) `Self` type must
 355     /// outlive. Precisely *because* the `Self` type is erased, the
 356     /// parameter `erased_self_ty` must be supplied to indicate what type
 357     /// has been used to represent `Self` in the predicates
 358     /// themselves. This should really be a unique type; `FreshTy(0)` is a
 359     /// popular choice.
 360     ///
 361     /// NB: in some cases, particularly around higher-ranked bounds,
 362     /// this function returns a kind of conservative approximation.
 363     /// That is, all regions returned by this function are definitely
 364     /// required, but there may be other region bounds that are not
 365     /// returned, as well as requirements like `for<'a> T: 'a`.
 366     ///
 367     /// Requires that trait definitions have been processed so that we can
 368     /// elaborate predicates and walk supertraits.
 369     ///
 370     /// FIXME callers may only have a &[Predicate], not a Vec, so that's
 371     /// what this code should accept.
 372     pub fn required_region_bounds(self,
 373                                   erased_self_ty: Ty<'tcx>,
 374                                   predicates: Vec<ty::Predicate<'tcx>>)
 375                                   -> Vec<ty::Region<'tcx>>    {
 376         debug!("required_region_bounds(erased_self_ty={:?}, predicates={:?})",
 377                erased_self_ty,
 378                predicates);
 379
 380         assert!(!erased_self_ty.has_escaping_regions());
 381
 382         traits::elaborate_predicates(self, predicates)
 383             .filter_map(|predicate| {
 384                 match predicate {
 385                     ty::Predicate::Projection(..) |
 386                     ty::Predicate::Trait(..) |
 387                     ty::Predicate::Equate(..) |
 388                     ty::Predicate::Subtype(..) |
 389                     ty::Predicate::WellFormed(..) |
 390                     ty::Predicate::ObjectSafe(..) |
 391                     ty::Predicate::ClosureKind(..) |
 392                     ty::Predicate::RegionOutlives(..) |
 393                     ty::Predicate::ConstEvaluatable(..) => {
 394                         None
 395                     }
 396                     ty::Predicate::TypeOutlives(ty::Binder(ty::OutlivesPredicate(t, r))) => {
 397                         // Search for a bound of the form `erased_self_ty
 398                         // : 'a`, but be wary of something like `for<'a>
 399                         // erased_self_ty : 'a` (we interpret a
 400                         // higher-ranked bound like that as 'static,
 401                         // though at present the code in `fulfill.rs`
 402                         // considers such bounds to be unsatisfiable, so
 403                         // it's kind of a moot point since you could never
 404                         // construct such an object, but this seems
 405                         // correct even if that code changes).
 406                         if t == erased_self_ty && !r.has_escaping_regions() {
 407                             Some(r)
 408                         } else {
 409                             None
 410                         }
 411                     }
 412                 }
 413             })
 414             .collect()
 415     }
 416
 417     /// Calculate the destructor of a given type.
 418     pub fn calculate_dtor(
 419         self,
 420         adt_did: DefId,
 421         validate: &mut FnMut(Self, DefId) -> Result<(), ErrorReported>
 422     ) -> Option<ty::Destructor> {
 423         let drop_trait = if let Some(def_id) = self.lang_items().drop_trait() {
 424             def_id
 425         } else {
 426             return None;
 427         };
 428
 429         self.coherent_trait((LOCAL_CRATE, drop_trait));
 430
 431         let mut dtor_did = None;
 432         let ty = self.type_of(adt_did);
 433         self.for_each_relevant_impl(drop_trait, ty, |impl_did| {
 434             if let Some(item) = self.associated_items(impl_did).next() {
 435                 if let Ok(()) = validate(self, impl_did) {
 436                     dtor_did = Some(item.def_id);
 437                 }
 438             }
 439         });
 440
 441         let dtor_did = match dtor_did {
 442             Some(dtor) => dtor,
 443             None => return None,
 444         };
 445
 446         Some(ty::Destructor { did: dtor_did })
 447     }
 448
 449     /// Return the set of types that are required to be alive in
 450     /// order to run the destructor of `def` (see RFCs 769 and
 451     /// 1238).
 452     ///
 453     /// Note that this returns only the constraints for the
 454     /// destructor of `def` itself. For the destructors of the
 455     /// contents, you need `adt_dtorck_constraint`.
 456     pub fn destructor_constraints(self, def: &'tcx ty::AdtDef)
 457                                   -> Vec<ty::subst::Kind<'tcx>>
 458     {
 459         let dtor = match def.destructor(self) {
 460             None => {
 461                 debug!("destructor_constraints({:?}) - no dtor", def.did);
 462                 return vec![]
 463             }
 464             Some(dtor) => dtor.did
 465         };
 466
 467         // RFC 1238: if the destructor method is tagged with the
 468         // attribute `unsafe_destructor_blind_to_params`, then the
 469         // compiler is being instructed to *assume* that the
 470         // destructor will not access borrowed data,
 471         // even if such data is otherwise reachable.
 472         //
 473         // Such access can be in plain sight (e.g. dereferencing
 474         // `*foo.0` of `Foo<'a>(&'a u32)`) or indirectly hidden
 475         // (e.g. calling `foo.0.clone()` of `Foo<T:Clone>`).
 476         if self.has_attr(dtor, "unsafe_destructor_blind_to_params") {
 477             debug!("destructor_constraint({:?}) - blind", def.did);
 478             return vec![];
 479         }
 480
 481         let impl_def_id = self.associated_item(dtor).container.id();
 482         let impl_generics = self.generics_of(impl_def_id);
 483
 484         // We have a destructor - all the parameters that are not
 485         // pure_wrt_drop (i.e, don't have a #[may_dangle] attribute)
 486         // must be live.
 487
 488         // We need to return the list of parameters from the ADTs
 489         // generics/substs that correspond to impure parameters on the
 490         // impl's generics. This is a bit ugly, but conceptually simple:
 491         //
 492         // Suppose our ADT looks like the following
 493         //
 494         //     struct S<X, Y, Z>(X, Y, Z);
 495         //
 496         // and the impl is
 497         //
 498         //     impl<#[may_dangle] P0, P1, P2> Drop for S<P1, P2, P0>
 499         //
 500         // We want to return the parameters (X, Y). For that, we match
 501         // up the item-substs <X, Y, Z> with the substs on the impl ADT,
 502         // <P1, P2, P0>, and then look up which of the impl substs refer to
 503         // parameters marked as pure.
 504
 505         let impl_substs = match self.type_of(impl_def_id).sty {
 506             ty::TyAdt(def_, substs) if def_ == def => substs,
 507             _ => bug!()
 508         };
 509
 510         let item_substs = match self.type_of(def.did).sty {
 511             ty::TyAdt(def_, substs) if def_ == def => substs,
 512             _ => bug!()
 513         };
 514
 515         let result = item_substs.iter().zip(impl_substs.iter())
 516             .filter(|&(_, &k)| {
 517                 if let Some(&ty::RegionKind::ReEarlyBound(ref ebr)) = k.as_region() {
 518                     !impl_generics.region_param(ebr).pure_wrt_drop
 519                 } else if let Some(&ty::TyS {
 520                     sty: ty::TypeVariants::TyParam(ref pt), ..
 521                 }) = k.as_type() {
 522                     !impl_generics.type_param(pt).pure_wrt_drop
 523                 } else {
 524                     // not a type or region param - this should be reported
 525                     // as an error.
 526                     false
 527                 }
 528             }).map(|(&item_param, _)| item_param).collect();
 529         debug!("destructor_constraint({:?}) = {:?}", def.did, result);
 530         result
 531     }
 532
 533     /// Return a set of constraints that needs to be satisfied in
 534     /// order for `ty` to be valid for destruction.
 535     pub fn dtorck_constraint_for_ty(self,
 536                                     span: Span,
 537                                     for_ty: Ty<'tcx>,
 538                                     depth: usize,
 539                                     ty: Ty<'tcx>)
 540                                     -> Result<ty::DtorckConstraint<'tcx>, ErrorReported>
 541     {
 542         debug!("dtorck_constraint_for_ty({:?}, {:?}, {:?}, {:?})",
 543                span, for_ty, depth, ty);
 544
 545         if depth >= self.sess.recursion_limit.get() {
 546             let mut err = struct_span_err!(
 547                 self.sess, span, E0320,
 548                 "overflow while adding drop-check rules for {}", for_ty);
 549             err.note(&format!("overflowed on {}", ty));
 550             err.emit();
 551             return Err(ErrorReported);
 552         }
 553
 554         let result = match ty.sty {
 555             ty::TyBool | ty::TyChar | ty::TyInt(_) | ty::TyUint(_) |
 556             ty::TyFloat(_) | ty::TyStr | ty::TyNever |
 557             ty::TyRawPtr(..) | ty::TyRef(..) | ty::TyFnDef(..) | ty::TyFnPtr(_) => {
 558                 // these types never have a destructor
 559                 Ok(ty::DtorckConstraint::empty())
 560             }
 561
 562             ty::TyArray(ety, _) | ty::TySlice(ety) => {
 563                 // single-element containers, behave like their element
 564                 self.dtorck_constraint_for_ty(span, for_ty, depth+1, ety)
 565             }
 566
 567             ty::TyTuple(tys, _) => {
 568                 tys.iter().map(|ty| {
 569                     self.dtorck_constraint_for_ty(span, for_ty, depth+1, ty)
 570                 }).collect()
 571             }
 572
 573             ty::TyClosure(def_id, substs) => {
 574                 substs.upvar_tys(def_id, self).map(|ty| {
 575                     self.dtorck_constraint_for_ty(span, for_ty, depth+1, ty)
 576                 }).collect()
 577             }
 578
 579             ty::TyGenerator(def_id, substs, interior) => {
 580                 substs.upvar_tys(def_id, self).chain(iter::once(interior.witness)).map(|ty| {
 581                     self.dtorck_constraint_for_ty(span, for_ty, depth+1, ty)
 582                 }).collect()
 583             }
 584
 585             ty::TyAdt(def, substs) => {
 586                 let ty::DtorckConstraint {
 587                     dtorck_types, outlives
 588                 } = self.at(span).adt_dtorck_constraint(def.did);
 589                 Ok(ty::DtorckConstraint {
 590                     // FIXME: we can try to recursively `dtorck_constraint_on_ty`
 591                     // there, but that needs some way to handle cycles.
 592                     dtorck_types: dtorck_types.subst(self, substs),
 593                     outlives: outlives.subst(self, substs)
 594                 })
 595             }
 596
 597             // Objects must be alive in order for their destructor
 598             // to be called.
 599             ty::TyDynamic(..) => Ok(ty::DtorckConstraint {
 600                 outlives: vec![Kind::from(ty)],
 601                 dtorck_types: vec![],
 602             }),
 603
 604             // Types that can't be resolved. Pass them forward.
 605             ty::TyProjection(..) | ty::TyAnon(..) | ty::TyParam(..) => {
 606                 Ok(ty::DtorckConstraint {
 607                     outlives: vec![],
 608                     dtorck_types: vec![ty],
 609                 })
 610             }
 611
 612             ty::TyInfer(..) | ty::TyError => {
 613                 self.sess.delay_span_bug(span, "unresolved type in dtorck");
 614                 Err(ErrorReported)
 615             }
 616         };
 617
 618         debug!("dtorck_constraint_for_ty({:?}) = {:?}", ty, result);
 619         result
 620     }
 621
 622     pub fn closure_base_def_id(self, def_id: DefId) -> DefId {
 623         let mut def_id = def_id;
 624         while self.def_key(def_id).disambiguated_data.data == DefPathData::ClosureExpr {
 625             def_id = self.parent_def_id(def_id).unwrap_or_else(|| {
 626                 bug!("closure {:?} has no parent", def_id);
 627             });
 628         }
 629         def_id
 630     }
 631
 632     /// Given the def-id of some item that has no type parameters, make
 633     /// a suitable "empty substs" for it.
 634     pub fn empty_substs_for_def_id(self, item_def_id: DefId) -> &'tcx ty::Substs<'tcx> {
 635         ty::Substs::for_item(self, item_def_id,
 636                              |_, _| self.types.re_erased,
 637                              |_, _| {
 638             bug!("empty_substs_for_def_id: {:?} has type parameters", item_def_id)
 639         })
 640     }
 641
 642     pub fn const_usize(&self, val: u16) -> ConstInt {
 643         match self.sess.target.usize_ty {
 644             ast::UintTy::U16 => ConstInt::Usize(ConstUsize::Us16(val as u16)),
 645             ast::UintTy::U32 => ConstInt::Usize(ConstUsize::Us32(val as u32)),
 646             ast::UintTy::U64 => ConstInt::Usize(ConstUsize::Us64(val as u64)),
 647             _ => bug!(),
 648         }
 649     }
 650 }
 651
 652 pub struct TypeIdHasher<'a, 'gcx: 'a+'tcx, 'tcx: 'a, W> {
 653     tcx: TyCtxt<'a, 'gcx, 'tcx>,
 654     state: StableHasher<W>,
 655 }
 656
 657 impl<'a, 'gcx, 'tcx, W> TypeIdHasher<'a, 'gcx, 'tcx, W>
 658     where W: StableHasherResult
 659 {
 660     pub fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Self {
 661         TypeIdHasher { tcx: tcx, state: StableHasher::new() }
 662     }
 663
 664     pub fn finish(self) -> W {
 665         self.state.finish()
 666     }
 667
 668     pub fn hash<T: Hash>(&mut self, x: T) {
 669         x.hash(&mut self.state);
 670     }
 671
 672     fn hash_discriminant_u8<T>(&mut self, x: &T) {
 673         let v = unsafe {
 674             intrinsics::discriminant_value(x)
 675         };
 676         let b = v as u8;
 677         assert_eq!(v, b as u64);
 678         self.hash(b)
 679     }
 680
 681     fn def_id(&mut self, did: DefId) {
 682         // Hash the DefPath corresponding to the DefId, which is independent
 683         // of compiler internal state. We already have a stable hash value of
 684         // all DefPaths available via tcx.def_path_hash(), so we just feed that
 685         // into the hasher.
 686         let hash = self.tcx.def_path_hash(did);
 687         self.hash(hash);
 688     }
 689 }
 690
 691 impl<'a, 'gcx, 'tcx, W> TypeVisitor<'tcx> for TypeIdHasher<'a, 'gcx, 'tcx, W>
 692     where W: StableHasherResult
 693 {
 694     fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
 695         // Distinguish between the Ty variants uniformly.
 696         self.hash_discriminant_u8(&ty.sty);
 697
 698         match ty.sty {
 699             TyInt(i) => self.hash(i),
 700             TyUint(u) => self.hash(u),
 701             TyFloat(f) => self.hash(f),
 702             TyArray(_, n) => {
 703                 self.hash_discriminant_u8(&n.val);
 704                 match n.val {
 705                     ConstVal::Integral(x) => self.hash(x.to_u64().unwrap()),
 706                     ConstVal::Unevaluated(def_id, _) => self.def_id(def_id),
 707                     _ => bug!("arrays should not have {:?} as length", n)
 708                 }
 709             }
 710             TyRawPtr(m) |
 711             TyRef(_, m) => self.hash(m.mutbl),
 712             TyClosure(def_id, _) |
 713             TyGenerator(def_id, _, _) |
 714             TyAnon(def_id, _) |
 715             TyFnDef(def_id, _) => self.def_id(def_id),
 716             TyAdt(d, _) => self.def_id(d.did),
 717             TyFnPtr(f) => {
 718                 self.hash(f.unsafety());
 719                 self.hash(f.abi());
 720                 self.hash(f.variadic());
 721                 self.hash(f.inputs().skip_binder().len());
 722             }
 723             TyDynamic(ref data, ..) => {
 724                 if let Some(p) = data.principal() {
 725                     self.def_id(p.def_id());
 726                 }
 727                 for d in data.auto_traits() {
 728                     self.def_id(d);
 729                 }
 730             }
 731             TyTuple(tys, defaulted) => {
 732                 self.hash(tys.len());
 733                 self.hash(defaulted);
 734             }
 735             TyParam(p) => {
 736                 self.hash(p.idx);
 737                 self.hash(p.name.as_str());
 738             }
 739             TyProjection(ref data) => {
 740                 self.def_id(data.item_def_id);
 741             }
 742             TyNever |
 743             TyBool |
 744             TyChar |
 745             TyStr |
 746             TySlice(_) => {}
 747
 748             TyError |
 749             TyInfer(_) => bug!("TypeIdHasher: unexpected type {}", ty)
 750         }
 751
 752         ty.super_visit_with(self)
 753     }
 754
 755     fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
 756         self.hash_discriminant_u8(r);
 757         match *r {
 758             ty::ReErased |
 759             ty::ReStatic |
 760             ty::ReEmpty => {
 761                 // No variant fields to hash for these ...
 762             }
 763             ty::ReLateBound(db, ty::BrAnon(i)) => {
 764                 self.hash(db.depth);
 765                 self.hash(i);
 766             }
 767             ty::ReEarlyBound(ty::EarlyBoundRegion { def_id, .. }) => {
 768                 self.def_id(def_id);
 769             }
 770             ty::ReLateBound(..) |
 771             ty::ReFree(..) |
 772             ty::ReScope(..) |
 773             ty::ReVar(..) |
 774             ty::ReSkolemized(..) => {
 775                 bug!("TypeIdHasher: unexpected region {:?}", r)
 776             }
 777         }
 778         false
 779     }
 780
 781     fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, x: &ty::Binder<T>) -> bool {
 782         // Anonymize late-bound regions so that, for example:
 783         // `for<'a, b> fn(&'a &'b T)` and `for<'a, b> fn(&'b &'a T)`
 784         // result in the same TypeId (the two types are equivalent).
 785         self.tcx.anonymize_late_bound_regions(x).super_visit_with(self)
 786     }
 787 }
 788
 789 impl<'a, 'tcx> ty::TyS<'tcx> {
 790     pub fn moves_by_default(&'tcx self,
 791                             tcx: TyCtxt<'a, 'tcx, 'tcx>,
 792                             param_env: ty::ParamEnv<'tcx>,
 793                             span: Span)
 794                             -> bool {
 795         !tcx.at(span).is_copy_raw(param_env.and(self))
 796     }
 797
 798     pub fn is_sized(&'tcx self,
 799                     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 800                     param_env: ty::ParamEnv<'tcx>,
 801                     span: Span)-> bool
 802     {
 803         tcx.at(span).is_sized_raw(param_env.and(self))
 804     }
 805
 806     pub fn is_freeze(&'tcx self,
 807                      tcx: TyCtxt<'a, 'tcx, 'tcx>,
 808                      param_env: ty::ParamEnv<'tcx>,
 809                      span: Span)-> bool
 810     {
 811         tcx.at(span).is_freeze_raw(param_env.and(self))
 812     }
 813
 814     /// If `ty.needs_drop(...)` returns `true`, then `ty` is definitely
 815     /// non-copy and *might* have a destructor attached; if it returns
 816     /// `false`, then `ty` definitely has no destructor (i.e. no drop glue).
 817     ///
 818     /// (Note that this implies that if `ty` has a destructor attached,
 819     /// then `needs_drop` will definitely return `true` for `ty`.)
 820     #[inline]
 821     pub fn needs_drop(&'tcx self,
 822                       tcx: TyCtxt<'a, 'tcx, 'tcx>,
 823                       param_env: ty::ParamEnv<'tcx>)
 824                       -> bool {
 825         tcx.needs_drop_raw(param_env.and(self))
 826     }
 827
 828     /// Computes the layout of a type. Note that this implicitly
 829     /// executes in "reveal all" mode.
 830     #[inline]
 831     pub fn layout<'lcx>(&'tcx self,
 832                         tcx: TyCtxt<'a, 'tcx, 'tcx>,
 833                         param_env: ty::ParamEnv<'tcx>)
 834                         -> Result<&'tcx Layout, LayoutError<'tcx>> {
 835         let ty = tcx.erase_regions(&self);
 836         let layout = tcx.layout_raw(param_env.reveal_all().and(ty));
 837
 838         // NB: This recording is normally disabled; when enabled, it
 839         // can however trigger recursive invocations of `layout()`.
 840         // Therefore, we execute it *after* the main query has
 841         // completed, to avoid problems around recursive structures
 842         // and the like. (Admitedly, I wasn't able to reproduce a problem
 843         // here, but it seems like the right thing to do. -nmatsakis)
 844         if let Ok(l) = layout {
 845             Layout::record_layout_for_printing(tcx, ty, param_env, l);
 846         }
 847
 848         layout
 849     }
 850
 851
 852     /// Check whether a type is representable. This means it cannot contain unboxed
 853     /// structural recursion. This check is needed for structs and enums.
 854     pub fn is_representable(&'tcx self,
 855                             tcx: TyCtxt<'a, 'tcx, 'tcx>,
 856                             sp: Span)
 857                             -> Representability {
 858
 859         // Iterate until something non-representable is found
 860         fn fold_repr<It: Iterator<Item=Representability>>(iter: It) -> Representability {
 861             iter.fold(Representability::Representable, |r1, r2| {
 862                 match (r1, r2) {
 863                     (Representability::SelfRecursive(v1),
 864                      Representability::SelfRecursive(v2)) => {
 865                         Representability::SelfRecursive(v1.iter().map(|s| *s).chain(v2).collect())
 866                     }
 867                     (r1, r2) => cmp::max(r1, r2)
 868                 }
 869             })
 870         }
 871
 872         fn are_inner_types_recursive<'a, 'tcx>(
 873             tcx: TyCtxt<'a, 'tcx, 'tcx>, sp: Span,
 874             seen: &mut Vec<Ty<'tcx>>,
 875             representable_cache: &mut FxHashMap<Ty<'tcx>, Representability>,
 876             ty: Ty<'tcx>)
 877             -> Representability
 878         {
 879             match ty.sty {
 880                 TyTuple(ref ts, _) => {
 881                     // Find non representable
 882                     fold_repr(ts.iter().map(|ty| {
 883                         is_type_structurally_recursive(tcx, sp, seen, representable_cache, ty)
 884                     }))
 885                 }
 886                 // Fixed-length vectors.
 887                 // FIXME(#11924) Behavior undecided for zero-length vectors.
 888                 TyArray(ty, _) => {
 889                     is_type_structurally_recursive(tcx, sp, seen, representable_cache, ty)
 890                 }
 891                 TyAdt(def, substs) => {
 892                     // Find non representable fields with their spans
 893                     fold_repr(def.all_fields().map(|field| {
 894                         let ty = field.ty(tcx, substs);
 895                         let span = tcx.hir.span_if_local(field.did).unwrap_or(sp);
 896                         match is_type_structurally_recursive(tcx, span, seen,
 897                                                              representable_cache, ty)
 898                         {
 899                             Representability::SelfRecursive(_) => {
 900                                 Representability::SelfRecursive(vec![span])
 901                             }
 902                             x => x,
 903                         }
 904                     }))
 905                 }
 906                 TyClosure(..) => {
 907                     // this check is run on type definitions, so we don't expect
 908                     // to see closure types
 909                     bug!("requires check invoked on inapplicable type: {:?}", ty)
 910                 }
 911                 _ => Representability::Representable,
 912             }
 913         }
 914
 915         fn same_struct_or_enum<'tcx>(ty: Ty<'tcx>, def: &'tcx ty::AdtDef) -> bool {
 916             match ty.sty {
 917                 TyAdt(ty_def, _) => {
 918                      ty_def == def
 919                 }
 920                 _ => false
 921             }
 922         }
 923
 924         fn same_type<'tcx>(a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
 925             match (&a.sty, &b.sty) {
 926                 (&TyAdt(did_a, substs_a), &TyAdt(did_b, substs_b)) => {
 927                     if did_a != did_b {
 928                         return false;
 929                     }
 930
 931                     substs_a.types().zip(substs_b.types()).all(|(a, b)| same_type(a, b))
 932                 }
 933                 _ => a == b,
 934             }
 935         }
 936
 937         // Does the type `ty` directly (without indirection through a pointer)
 938         // contain any types on stack `seen`?
 939         fn is_type_structurally_recursive<'a, 'tcx>(
 940             tcx: TyCtxt<'a, 'tcx, 'tcx>,
 941             sp: Span,
 942             seen: &mut Vec<Ty<'tcx>>,
 943             representable_cache: &mut FxHashMap<Ty<'tcx>, Representability>,
 944             ty: Ty<'tcx>) -> Representability
 945         {
 946             debug!("is_type_structurally_recursive: {:?} {:?}", ty, sp);
 947             if let Some(representability) = representable_cache.get(ty) {
 948                 debug!("is_type_structurally_recursive: {:?} {:?} - (cached) {:?}",
 949                        ty, sp, representability);
 950                 return representability.clone();
 951             }
 952
 953             let representability = is_type_structurally_recursive_inner(
 954                 tcx, sp, seen, representable_cache, ty);
 955
 956             representable_cache.insert(ty, representability.clone());
 957             representability
 958         }
 959
 960         fn is_type_structurally_recursive_inner<'a, 'tcx>(
 961             tcx: TyCtxt<'a, 'tcx, 'tcx>,
 962             sp: Span,
 963             seen: &mut Vec<Ty<'tcx>>,
 964             representable_cache: &mut FxHashMap<Ty<'tcx>, Representability>,
 965             ty: Ty<'tcx>) -> Representability
 966         {
 967             match ty.sty {
 968                 TyAdt(def, _) => {
 969                     {
 970                         // Iterate through stack of previously seen types.
 971                         let mut iter = seen.iter();
 972
 973                         // The first item in `seen` is the type we are actually curious about.
 974                         // We want to return SelfRecursive if this type contains itself.
 975                         // It is important that we DON'T take generic parameters into account
 976                         // for this check, so that Bar<T> in this example counts as SelfRecursive:
 977                         //
 978                         // struct Foo;
 979                         // struct Bar<T> { x: Bar<Foo> }
 980
 981                         if let Some(&seen_type) = iter.next() {
 982                             if same_struct_or_enum(seen_type, def) {
 983                                 debug!("SelfRecursive: {:?} contains {:?}",
 984                                        seen_type,
 985                                        ty);
 986                                 return Representability::SelfRecursive(vec![sp]);
 987                             }
 988                         }
 989
 990                         // We also need to know whether the first item contains other types
 991                         // that are structurally recursive. If we don't catch this case, we
 992                         // will recurse infinitely for some inputs.
 993                         //
 994                         // It is important that we DO take generic parameters into account
 995                         // here, so that code like this is considered SelfRecursive, not
 996                         // ContainsRecursive:
 997                         //
 998                         // struct Foo { Option<Option<Foo>> }
 999
1000                         for &seen_type in iter {
1001                             if same_type(ty, seen_type) {
1002                                 debug!("ContainsRecursive: {:?} contains {:?}",
1003                                        seen_type,
1004                                        ty);
1005                                 return Representability::ContainsRecursive;
1006                             }
1007                         }
1008                     }
1009
1010                     // For structs and enums, track all previously seen types by pushing them
1011                     // onto the 'seen' stack.
1012                     seen.push(ty);
1013                     let out = are_inner_types_recursive(tcx, sp, seen, representable_cache, ty);
1014                     seen.pop();
1015                     out
1016                 }
1017                 _ => {
1018                     // No need to push in other cases.
1019                     are_inner_types_recursive(tcx, sp, seen, representable_cache, ty)
1020                 }
1021             }
1022         }
1023
1024         debug!("is_type_representable: {:?}", self);
1025
1026         // To avoid a stack overflow when checking an enum variant or struct that
1027         // contains a different, structurally recursive type, maintain a stack
1028         // of seen types and check recursion for each of them (issues #3008, #3779).
1029         let mut seen: Vec<Ty> = Vec::new();
1030         let mut representable_cache = FxHashMap();
1031         let r = is_type_structurally_recursive(
1032             tcx, sp, &mut seen, &mut representable_cache, self);
1033         debug!("is_type_representable: {:?} is {:?}", self, r);
1034         r
1035     }
1036 }
1037
1038 fn is_copy_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1039                          query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
1040                          -> bool
1041 {
1042     let (param_env, ty) = query.into_parts();
1043     let trait_def_id = tcx.require_lang_item(lang_items::CopyTraitLangItem);
1044     tcx.infer_ctxt()
1045        .enter(|infcx| traits::type_known_to_meet_bound(&infcx,
1046                                                        param_env,
1047                                                        ty,
1048                                                        trait_def_id,
1049                                                        DUMMY_SP))
1050 }
1051
1052 fn is_sized_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1053                           query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
1054                           -> bool
1055 {
1056     let (param_env, ty) = query.into_parts();
1057     let trait_def_id = tcx.require_lang_item(lang_items::SizedTraitLangItem);
1058     tcx.infer_ctxt()
1059        .enter(|infcx| traits::type_known_to_meet_bound(&infcx,
1060                                                        param_env,
1061                                                        ty,
1062                                                        trait_def_id,
1063                                                        DUMMY_SP))
1064 }
1065
1066 fn is_freeze_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1067                            query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
1068                            -> bool
1069 {
1070     let (param_env, ty) = query.into_parts();
1071     let trait_def_id = tcx.require_lang_item(lang_items::FreezeTraitLangItem);
1072     tcx.infer_ctxt()
1073        .enter(|infcx| traits::type_known_to_meet_bound(&infcx,
1074                                                        param_env,
1075                                                        ty,
1076                                                        trait_def_id,
1077                                                        DUMMY_SP))
1078 }
1079
1080 fn needs_drop_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1081                             query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
1082                             -> bool
1083 {
1084     let (param_env, ty) = query.into_parts();
1085
1086     let needs_drop = |ty: Ty<'tcx>| -> bool {
1087         match ty::queries::needs_drop_raw::try_get(tcx, DUMMY_SP, param_env.and(ty)) {
1088             Ok(v) => v,
1089             Err(mut bug) => {
1090                 // Cycles should be reported as an error by `check_representable`.
1091                 //
1092                 // Consider the type as not needing drop in the meanwhile to
1093                 // avoid further errors.
1094                 //
1095                 // In case we forgot to emit a bug elsewhere, delay our
1096                 // diagnostic to get emitted as a compiler bug.
1097                 bug.delay_as_bug();
1098                 false
1099             }
1100         }
1101     };
1102
1103     assert!(!ty.needs_infer());
1104
1105     match ty.sty {
1106         // Fast-path for primitive types
1107         ty::TyInfer(ty::FreshIntTy(_)) | ty::TyInfer(ty::FreshFloatTy(_)) |
1108         ty::TyBool | ty::TyInt(_) | ty::TyUint(_) | ty::TyFloat(_) | ty::TyNever |
1109         ty::TyFnDef(..) | ty::TyFnPtr(_) | ty::TyChar |
1110         ty::TyRawPtr(_) | ty::TyRef(..) | ty::TyStr => false,
1111
1112         // Issue #22536: We first query type_moves_by_default.  It sees a
1113         // normalized version of the type, and therefore will definitely
1114         // know whether the type implements Copy (and thus needs no
1115         // cleanup/drop/zeroing) ...
1116         _ if !ty.moves_by_default(tcx, param_env, DUMMY_SP) => false,
1117
1118         // ... (issue #22536 continued) but as an optimization, still use
1119         // prior logic of asking for the structural "may drop".
1120
1121         // FIXME(#22815): Note that this is a conservative heuristic;
1122         // it may report that the type "may drop" when actual type does
1123         // not actually have a destructor associated with it. But since
1124         // the type absolutely did not have the `Copy` bound attached
1125         // (see above), it is sound to treat it as having a destructor.
1126
1127         // User destructors are the only way to have concrete drop types.
1128         ty::TyAdt(def, _) if def.has_dtor(tcx) => true,
1129
1130         // Can refer to a type which may drop.
1131         // FIXME(eddyb) check this against a ParamEnv.
1132         ty::TyDynamic(..) | ty::TyProjection(..) | ty::TyParam(_) |
1133         ty::TyAnon(..) | ty::TyInfer(_) | ty::TyError => true,
1134
1135         // Structural recursion.
1136         ty::TyArray(ty, _) | ty::TySlice(ty) => needs_drop(ty),
1137
1138         ty::TyClosure(def_id, ref substs) => substs.upvar_tys(def_id, tcx).any(needs_drop),
1139
1140         // Pessimistically assume that all generators will require destructors
1141         // as we don't know if a destructor is a noop or not until after the MIR
1142         // state transformation pass
1143         ty::TyGenerator(..) => true,
1144
1145         ty::TyTuple(ref tys, _) => tys.iter().cloned().any(needs_drop),
1146
1147         // unions don't have destructors regardless of the child types
1148         ty::TyAdt(def, _) if def.is_union() => false,
1149
1150         ty::TyAdt(def, substs) =>
1151             def.variants.iter().any(
1152                 |variant| variant.fields.iter().any(
1153                     |field| needs_drop(field.ty(tcx, substs)))),
1154     }
1155 }
1156
1157 fn layout_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1158                         query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
1159                         -> Result<&'tcx Layout, LayoutError<'tcx>>
1160 {
1161     let (param_env, ty) = query.into_parts();
1162
1163     let rec_limit = tcx.sess.recursion_limit.get();
1164     let depth = tcx.layout_depth.get();
1165     if depth > rec_limit {
1166         tcx.sess.fatal(
1167             &format!("overflow representing the type `{}`", ty));
1168     }
1169
1170     tcx.layout_depth.set(depth+1);
1171     let layout = Layout::compute_uncached(tcx, param_env, ty);
1172     tcx.layout_depth.set(depth);
1173
1174     layout
1175 }
1176
1177 pub fn provide(providers: &mut ty::maps::Providers) {
1178     *providers = ty::maps::Providers {
1179         is_copy_raw,
1180         is_sized_raw,
1181         is_freeze_raw,
1182         needs_drop_raw,
1183         layout_raw,
1184         ..*providers
1185     };
1186 }