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::Def;
  14 use hir::def_id::DefId;
  15 use hir::map::{DefPathData, Node};
  16 use hir;
  17 use ich::NodeIdHashingMode;
  18 use middle::const_val::ConstVal;
  19 use traits::{self, Reveal};
  20 use ty::{self, Ty, TyCtxt, TypeFoldable};
  21 use ty::fold::TypeVisitor;
  22 use ty::subst::{Subst, UnpackedKind};
  23 use ty::maps::TyCtxtAt;
  24 use ty::TypeVariants::*;
  25 use util::common::ErrorReported;
  26 use middle::lang_items;
  27 use mir::interpret::{Value, PrimVal};
  28
  29 use rustc_const_math::{ConstInt, ConstIsize, ConstUsize};
  30 use rustc_data_structures::stable_hasher::{StableHasher, StableHasherResult,
  31                                            HashStable};
  32 use rustc_data_structures::fx::FxHashMap;
  33 use std::cmp;
  34 use std::hash::Hash;
  35 use std::intrinsics;
  36 use syntax::ast::{self, Name};
  37 use syntax::attr::{self, SignedInt, UnsignedInt};
  38 use syntax_pos::{Span, DUMMY_SP};
  39
  40 type Disr = ConstInt;
  41
  42 pub trait IntTypeExt {
  43     fn to_ty<'a, 'gcx, 'tcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Ty<'tcx>;
  44     fn disr_incr<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>, val: Option<Disr>)
  45                            -> Option<Disr>;
  46     fn assert_ty_matches(&self, val: Disr);
  47     fn initial_discriminant<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Disr;
  48 }
  49
  50
  51 macro_rules! typed_literal {
  52     ($tcx:expr, $ty:expr, $lit:expr) => {
  53         match $ty {
  54             SignedInt(ast::IntTy::I8)    => ConstInt::I8($lit),
  55             SignedInt(ast::IntTy::I16)   => ConstInt::I16($lit),
  56             SignedInt(ast::IntTy::I32)   => ConstInt::I32($lit),
  57             SignedInt(ast::IntTy::I64)   => ConstInt::I64($lit),
  58             SignedInt(ast::IntTy::I128)   => ConstInt::I128($lit),
  59             SignedInt(ast::IntTy::Isize) => match $tcx.sess.target.isize_ty {
  60                 ast::IntTy::I16 => ConstInt::Isize(ConstIsize::Is16($lit)),
  61                 ast::IntTy::I32 => ConstInt::Isize(ConstIsize::Is32($lit)),
  62                 ast::IntTy::I64 => ConstInt::Isize(ConstIsize::Is64($lit)),
  63                 _ => bug!(),
  64             },
  65             UnsignedInt(ast::UintTy::U8)  => ConstInt::U8($lit),
  66             UnsignedInt(ast::UintTy::U16) => ConstInt::U16($lit),
  67             UnsignedInt(ast::UintTy::U32) => ConstInt::U32($lit),
  68             UnsignedInt(ast::UintTy::U64) => ConstInt::U64($lit),
  69             UnsignedInt(ast::UintTy::U128) => ConstInt::U128($lit),
  70             UnsignedInt(ast::UintTy::Usize) => match $tcx.sess.target.usize_ty {
  71                 ast::UintTy::U16 => ConstInt::Usize(ConstUsize::Us16($lit)),
  72                 ast::UintTy::U32 => ConstInt::Usize(ConstUsize::Us32($lit)),
  73                 ast::UintTy::U64 => ConstInt::Usize(ConstUsize::Us64($lit)),
  74                 _ => bug!(),
  75             },
  76         }
  77     }
  78 }
  79
  80 impl IntTypeExt for attr::IntType {
  81     fn to_ty<'a, 'gcx, 'tcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Ty<'tcx> {
  82         match *self {
  83             SignedInt(ast::IntTy::I8)      => tcx.types.i8,
  84             SignedInt(ast::IntTy::I16)     => tcx.types.i16,
  85             SignedInt(ast::IntTy::I32)     => tcx.types.i32,
  86             SignedInt(ast::IntTy::I64)     => tcx.types.i64,
  87             SignedInt(ast::IntTy::I128)     => tcx.types.i128,
  88             SignedInt(ast::IntTy::Isize)   => tcx.types.isize,
  89             UnsignedInt(ast::UintTy::U8)    => tcx.types.u8,
  90             UnsignedInt(ast::UintTy::U16)   => tcx.types.u16,
  91             UnsignedInt(ast::UintTy::U32)   => tcx.types.u32,
  92             UnsignedInt(ast::UintTy::U64)   => tcx.types.u64,
  93             UnsignedInt(ast::UintTy::U128)   => tcx.types.u128,
  94             UnsignedInt(ast::UintTy::Usize) => tcx.types.usize,
  95         }
  96     }
  97
  98     fn initial_discriminant<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Disr {
  99         typed_literal!(tcx, *self, 0)
 100     }
 101
 102     fn assert_ty_matches(&self, val: Disr) {
 103         match (*self, val) {
 104             (SignedInt(ast::IntTy::I8), ConstInt::I8(_)) => {},
 105             (SignedInt(ast::IntTy::I16), ConstInt::I16(_)) => {},
 106             (SignedInt(ast::IntTy::I32), ConstInt::I32(_)) => {},
 107             (SignedInt(ast::IntTy::I64), ConstInt::I64(_)) => {},
 108             (SignedInt(ast::IntTy::I128), ConstInt::I128(_)) => {},
 109             (SignedInt(ast::IntTy::Isize), ConstInt::Isize(_)) => {},
 110             (UnsignedInt(ast::UintTy::U8), ConstInt::U8(_)) => {},
 111             (UnsignedInt(ast::UintTy::U16), ConstInt::U16(_)) => {},
 112             (UnsignedInt(ast::UintTy::U32), ConstInt::U32(_)) => {},
 113             (UnsignedInt(ast::UintTy::U64), ConstInt::U64(_)) => {},
 114             (UnsignedInt(ast::UintTy::U128), ConstInt::U128(_)) => {},
 115             (UnsignedInt(ast::UintTy::Usize), ConstInt::Usize(_)) => {},
 116             _ => bug!("disr type mismatch: {:?} vs {:?}", self, val),
 117         }
 118     }
 119
 120     fn disr_incr<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>, val: Option<Disr>)
 121                            -> Option<Disr> {
 122         if let Some(val) = val {
 123             self.assert_ty_matches(val);
 124             (val + typed_literal!(tcx, *self, 1)).ok()
 125         } else {
 126             Some(self.initial_discriminant(tcx))
 127         }
 128     }
 129 }
 130
 131
 132 #[derive(Copy, Clone)]
 133 pub enum CopyImplementationError<'tcx> {
 134     InfrigingField(&'tcx ty::FieldDef),
 135     NotAnAdt,
 136     HasDestructor,
 137 }
 138
 139 /// Describes whether a type is representable. For types that are not
 140 /// representable, 'SelfRecursive' and 'ContainsRecursive' are used to
 141 /// distinguish between types that are recursive with themselves and types that
 142 /// contain a different recursive type. These cases can therefore be treated
 143 /// differently when reporting errors.
 144 ///
 145 /// The ordering of the cases is significant. They are sorted so that cmp::max
 146 /// will keep the "more erroneous" of two values.
 147 #[derive(Clone, PartialOrd, Ord, Eq, PartialEq, Debug)]
 148 pub enum Representability {
 149     Representable,
 150     ContainsRecursive,
 151     SelfRecursive(Vec<Span>),
 152 }
 153
 154 impl<'tcx> ty::ParamEnv<'tcx> {
 155     /// Construct a trait environment suitable for contexts where
 156     /// there are no where clauses in scope.
 157     pub fn empty(reveal: Reveal) -> Self {
 158         Self::new(ty::Slice::empty(), reveal, ty::UniverseIndex::ROOT)
 159     }
 160
 161     /// Construct a trait environment with the given set of predicates.
 162     pub fn new(caller_bounds: &'tcx ty::Slice<ty::Predicate<'tcx>>,
 163                reveal: Reveal,
 164                universe: ty::UniverseIndex)
 165                -> Self {
 166         ty::ParamEnv { caller_bounds, reveal, universe }
 167     }
 168
 169     /// Returns a new parameter environment with the same clauses, but
 170     /// which "reveals" the true results of projections in all cases
 171     /// (even for associated types that are specializable).  This is
 172     /// the desired behavior during trans and certain other special
 173     /// contexts; normally though we want to use `Reveal::UserFacing`,
 174     /// which is the default.
 175     pub fn reveal_all(self) -> Self {
 176         ty::ParamEnv { reveal: Reveal::All, ..self }
 177     }
 178
 179     pub fn can_type_implement_copy<'a>(self,
 180                                        tcx: TyCtxt<'a, 'tcx, 'tcx>,
 181                                        self_type: Ty<'tcx>, span: Span)
 182                                        -> Result<(), CopyImplementationError<'tcx>> {
 183         // FIXME: (@jroesch) float this code up
 184         tcx.infer_ctxt().enter(|infcx| {
 185             let (adt, substs) = match self_type.sty {
 186                 ty::TyAdt(adt, substs) => (adt, substs),
 187                 _ => return Err(CopyImplementationError::NotAnAdt),
 188             };
 189
 190             let field_implements_copy = |field: &ty::FieldDef| {
 191                 let cause = traits::ObligationCause::dummy();
 192                 match traits::fully_normalize(&infcx, cause, self, &field.ty(tcx, substs)) {
 193                     Ok(ty) => !infcx.type_moves_by_default(self, ty, span),
 194                     Err(..) => false,
 195                 }
 196             };
 197
 198             for variant in &adt.variants {
 199                 for field in &variant.fields {
 200                     if !field_implements_copy(field) {
 201                         return Err(CopyImplementationError::InfrigingField(field));
 202                     }
 203                 }
 204             }
 205
 206             if adt.has_dtor(tcx) {
 207                 return Err(CopyImplementationError::HasDestructor);
 208             }
 209
 210             Ok(())
 211         })
 212     }
 213 }
 214
 215 impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
 216     /// Creates a hash of the type `Ty` which will be the same no matter what crate
 217     /// context it's calculated within. This is used by the `type_id` intrinsic.
 218     pub fn type_id_hash(self, ty: Ty<'tcx>) -> u64 {
 219         let mut hasher = StableHasher::new();
 220         let mut hcx = self.create_stable_hashing_context();
 221
 222         // We want the type_id be independent of the types free regions, so we
 223         // erase them. The erase_regions() call will also anonymize bound
 224         // regions, which is desirable too.
 225         let ty = self.erase_regions(&ty);
 226
 227         hcx.while_hashing_spans(false, |hcx| {
 228             hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
 229                 ty.hash_stable(hcx, &mut hasher);
 230             });
 231         });
 232         hasher.finish()
 233     }
 234 }
 235
 236 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 237     pub fn has_error_field(self, ty: Ty<'tcx>) -> bool {
 238         match ty.sty {
 239             ty::TyAdt(def, substs) => {
 240                 for field in def.all_fields() {
 241                     let field_ty = field.ty(self, substs);
 242                     if let TyError = field_ty.sty {
 243                         return true;
 244                     }
 245                 }
 246             }
 247             _ => (),
 248         }
 249         false
 250     }
 251
 252     /// Returns the type of element at index `i` in tuple or tuple-like type `t`.
 253     /// For an enum `t`, `variant` is None only if `t` is a univariant enum.
 254     pub fn positional_element_ty(self,
 255                                  ty: Ty<'tcx>,
 256                                  i: usize,
 257                                  variant: Option<DefId>) -> Option<Ty<'tcx>> {
 258         match (&ty.sty, variant) {
 259             (&TyAdt(adt, substs), Some(vid)) => {
 260                 adt.variant_with_id(vid).fields.get(i).map(|f| f.ty(self, substs))
 261             }
 262             (&TyAdt(adt, substs), None) => {
 263                 // Don't use `non_enum_variant`, this may be a univariant enum.
 264                 adt.variants[0].fields.get(i).map(|f| f.ty(self, substs))
 265             }
 266             (&TyTuple(ref v, _), None) => v.get(i).cloned(),
 267             _ => None,
 268         }
 269     }
 270
 271     /// Returns the type of element at field `n` in struct or struct-like type `t`.
 272     /// For an enum `t`, `variant` must be some def id.
 273     pub fn named_element_ty(self,
 274                             ty: Ty<'tcx>,
 275                             n: Name,
 276                             variant: Option<DefId>) -> Option<Ty<'tcx>> {
 277         match (&ty.sty, variant) {
 278             (&TyAdt(adt, substs), Some(vid)) => {
 279                 adt.variant_with_id(vid).find_field_named(n).map(|f| f.ty(self, substs))
 280             }
 281             (&TyAdt(adt, substs), None) => {
 282                 adt.non_enum_variant().find_field_named(n).map(|f| f.ty(self, substs))
 283             }
 284             _ => return None
 285         }
 286     }
 287
 288     /// Returns the deeply last field of nested structures, or the same type,
 289     /// if not a structure at all. Corresponds to the only possible unsized
 290     /// field, and its type can be used to determine unsizing strategy.
 291     pub fn struct_tail(self, mut ty: Ty<'tcx>) -> Ty<'tcx> {
 292         loop {
 293             match ty.sty {
 294                 ty::TyAdt(def, substs) => {
 295                     if !def.is_struct() {
 296                         break;
 297                     }
 298                     match def.non_enum_variant().fields.last() {
 299                         Some(f) => ty = f.ty(self, substs),
 300                         None => break,
 301                     }
 302                 }
 303
 304                 ty::TyTuple(tys, _) => {
 305                     if let Some((&last_ty, _)) = tys.split_last() {
 306                         ty = last_ty;
 307                     } else {
 308                         break;
 309                     }
 310                 }
 311
 312                 _ => {
 313                     break;
 314                 }
 315             }
 316         }
 317         ty
 318     }
 319
 320     /// Same as applying struct_tail on `source` and `target`, but only
 321     /// keeps going as long as the two types are instances of the same
 322     /// structure definitions.
 323     /// For `(Foo<Foo<T>>, Foo<Trait>)`, the result will be `(Foo<T>, Trait)`,
 324     /// whereas struct_tail produces `T`, and `Trait`, respectively.
 325     pub fn struct_lockstep_tails(self,
 326                                  source: Ty<'tcx>,
 327                                  target: Ty<'tcx>)
 328                                  -> (Ty<'tcx>, Ty<'tcx>) {
 329         let (mut a, mut b) = (source, target);
 330         loop {
 331             match (&a.sty, &b.sty) {
 332                 (&TyAdt(a_def, a_substs), &TyAdt(b_def, b_substs))
 333                         if a_def == b_def && a_def.is_struct() => {
 334                     if let Some(f) = a_def.non_enum_variant().fields.last() {
 335                         a = f.ty(self, a_substs);
 336                         b = f.ty(self, b_substs);
 337                     } else {
 338                         break;
 339                     }
 340                 },
 341                 (&TyTuple(a_tys, _), &TyTuple(b_tys, _))
 342                         if a_tys.len() == b_tys.len() => {
 343                     if let Some(a_last) = a_tys.last() {
 344                         a = a_last;
 345                         b = b_tys.last().unwrap();
 346                     } else {
 347                         break;
 348                     }
 349                 },
 350                 _ => break,
 351             }
 352         }
 353         (a, b)
 354     }
 355
 356     /// Given a set of predicates that apply to an object type, returns
 357     /// the region bounds that the (erased) `Self` type must
 358     /// outlive. Precisely *because* the `Self` type is erased, the
 359     /// parameter `erased_self_ty` must be supplied to indicate what type
 360     /// has been used to represent `Self` in the predicates
 361     /// themselves. This should really be a unique type; `FreshTy(0)` is a
 362     /// popular choice.
 363     ///
 364     /// NB: in some cases, particularly around higher-ranked bounds,
 365     /// this function returns a kind of conservative approximation.
 366     /// That is, all regions returned by this function are definitely
 367     /// required, but there may be other region bounds that are not
 368     /// returned, as well as requirements like `for<'a> T: 'a`.
 369     ///
 370     /// Requires that trait definitions have been processed so that we can
 371     /// elaborate predicates and walk supertraits.
 372     ///
 373     /// FIXME callers may only have a &[Predicate], not a Vec, so that's
 374     /// what this code should accept.
 375     pub fn required_region_bounds(self,
 376                                   erased_self_ty: Ty<'tcx>,
 377                                   predicates: Vec<ty::Predicate<'tcx>>)
 378                                   -> Vec<ty::Region<'tcx>>    {
 379         debug!("required_region_bounds(erased_self_ty={:?}, predicates={:?})",
 380                erased_self_ty,
 381                predicates);
 382
 383         assert!(!erased_self_ty.has_escaping_regions());
 384
 385         traits::elaborate_predicates(self, predicates)
 386             .filter_map(|predicate| {
 387                 match predicate {
 388                     ty::Predicate::Projection(..) |
 389                     ty::Predicate::Trait(..) |
 390                     ty::Predicate::Subtype(..) |
 391                     ty::Predicate::WellFormed(..) |
 392                     ty::Predicate::ObjectSafe(..) |
 393                     ty::Predicate::ClosureKind(..) |
 394                     ty::Predicate::RegionOutlives(..) |
 395                     ty::Predicate::ConstEvaluatable(..) => {
 396                         None
 397                     }
 398                     ty::Predicate::TypeOutlives(ty::Binder(ty::OutlivesPredicate(t, r))) => {
 399                         // Search for a bound of the form `erased_self_ty
 400                         // : 'a`, but be wary of something like `for<'a>
 401                         // erased_self_ty : 'a` (we interpret a
 402                         // higher-ranked bound like that as 'static,
 403                         // though at present the code in `fulfill.rs`
 404                         // considers such bounds to be unsatisfiable, so
 405                         // it's kind of a moot point since you could never
 406                         // construct such an object, but this seems
 407                         // correct even if that code changes).
 408                         if t == erased_self_ty && !r.has_escaping_regions() {
 409                             Some(r)
 410                         } else {
 411                             None
 412                         }
 413                     }
 414                 }
 415             })
 416             .collect()
 417     }
 418
 419     /// Calculate the destructor of a given type.
 420     pub fn calculate_dtor(
 421         self,
 422         adt_did: DefId,
 423         validate: &mut dyn FnMut(Self, DefId) -> Result<(), ErrorReported>
 424     ) -> Option<ty::Destructor> {
 425         let drop_trait = if let Some(def_id) = self.lang_items().drop_trait() {
 426             def_id
 427         } else {
 428             return None;
 429         };
 430
 431         ty::maps::queries::coherent_trait::ensure(self, drop_trait);
 432
 433         let mut dtor_did = None;
 434         let ty = self.type_of(adt_did);
 435         self.for_each_relevant_impl(drop_trait, ty, |impl_did| {
 436             if let Some(item) = self.associated_items(impl_did).next() {
 437                 if let Ok(()) = validate(self, impl_did) {
 438                     dtor_did = Some(item.def_id);
 439                 }
 440             }
 441         });
 442
 443         Some(ty::Destructor { did: dtor_did? })
 444     }
 445
 446     /// Return the set of types that are required to be alive in
 447     /// order to run the destructor of `def` (see RFCs 769 and
 448     /// 1238).
 449     ///
 450     /// Note that this returns only the constraints for the
 451     /// destructor of `def` itself. For the destructors of the
 452     /// contents, you need `adt_dtorck_constraint`.
 453     pub fn destructor_constraints(self, def: &'tcx ty::AdtDef)
 454                                   -> Vec<ty::subst::Kind<'tcx>>
 455     {
 456         let dtor = match def.destructor(self) {
 457             None => {
 458                 debug!("destructor_constraints({:?}) - no dtor", def.did);
 459                 return vec![]
 460             }
 461             Some(dtor) => dtor.did
 462         };
 463
 464         // RFC 1238: if the destructor method is tagged with the
 465         // attribute `unsafe_destructor_blind_to_params`, then the
 466         // compiler is being instructed to *assume* that the
 467         // destructor will not access borrowed data,
 468         // even if such data is otherwise reachable.
 469         //
 470         // Such access can be in plain sight (e.g. dereferencing
 471         // `*foo.0` of `Foo<'a>(&'a u32)`) or indirectly hidden
 472         // (e.g. calling `foo.0.clone()` of `Foo<T:Clone>`).
 473         if self.has_attr(dtor, "unsafe_destructor_blind_to_params") {
 474             debug!("destructor_constraint({:?}) - blind", def.did);
 475             return vec![];
 476         }
 477
 478         let impl_def_id = self.associated_item(dtor).container.id();
 479         let impl_generics = self.generics_of(impl_def_id);
 480
 481         // We have a destructor - all the parameters that are not
 482         // pure_wrt_drop (i.e, don't have a #[may_dangle] attribute)
 483         // must be live.
 484
 485         // We need to return the list of parameters from the ADTs
 486         // generics/substs that correspond to impure parameters on the
 487         // impl's generics. This is a bit ugly, but conceptually simple:
 488         //
 489         // Suppose our ADT looks like the following
 490         //
 491         //     struct S<X, Y, Z>(X, Y, Z);
 492         //
 493         // and the impl is
 494         //
 495         //     impl<#[may_dangle] P0, P1, P2> Drop for S<P1, P2, P0>
 496         //
 497         // We want to return the parameters (X, Y). For that, we match
 498         // up the item-substs <X, Y, Z> with the substs on the impl ADT,
 499         // <P1, P2, P0>, and then look up which of the impl substs refer to
 500         // parameters marked as pure.
 501
 502         let impl_substs = match self.type_of(impl_def_id).sty {
 503             ty::TyAdt(def_, substs) if def_ == def => substs,
 504             _ => bug!()
 505         };
 506
 507         let item_substs = match self.type_of(def.did).sty {
 508             ty::TyAdt(def_, substs) if def_ == def => substs,
 509             _ => bug!()
 510         };
 511
 512         let result = item_substs.iter().zip(impl_substs.iter())
 513             .filter(|&(_, &k)| {
 514                 match k.unpack() {
 515                     UnpackedKind::Lifetime(&ty::RegionKind::ReEarlyBound(ref ebr)) => {
 516                         !impl_generics.region_param(ebr, self).pure_wrt_drop
 517                     }
 518                     UnpackedKind::Type(&ty::TyS {
 519                         sty: ty::TypeVariants::TyParam(ref pt), ..
 520                     }) => {
 521                         !impl_generics.type_param(pt, self).pure_wrt_drop
 522                     }
 523                     UnpackedKind::Lifetime(_) | UnpackedKind::Type(_) => {
 524                         // not a type or region param - this should be reported
 525                         // as an error.
 526                         false
 527                     }
 528                 }
 529             }).map(|(&item_param, _)| item_param).collect();
 530         debug!("destructor_constraint({:?}) = {:?}", def.did, result);
 531         result
 532     }
 533
 534     /// Return a set of constraints that needs to be satisfied in
 535     /// order for `ty` to be valid for destruction.
 536     pub fn dtorck_constraint_for_ty(self,
 537                                     span: Span,
 538                                     for_ty: Ty<'tcx>,
 539                                     depth: usize,
 540                                     ty: Ty<'tcx>)
 541                                     -> Result<ty::DtorckConstraint<'tcx>, ErrorReported>
 542     {
 543         debug!("dtorck_constraint_for_ty({:?}, {:?}, {:?}, {:?})",
 544                span, for_ty, depth, ty);
 545
 546         if depth >= self.sess.recursion_limit.get() {
 547             let mut err = struct_span_err!(
 548                 self.sess, span, E0320,
 549                 "overflow while adding drop-check rules for {}", for_ty);
 550             err.note(&format!("overflowed on {}", ty));
 551             err.emit();
 552             return Err(ErrorReported);
 553         }
 554
 555         let result = match ty.sty {
 556             ty::TyBool | ty::TyChar | ty::TyInt(_) | ty::TyUint(_) |
 557             ty::TyFloat(_) | ty::TyStr | ty::TyNever | ty::TyForeign(..) |
 558             ty::TyRawPtr(..) | ty::TyRef(..) | ty::TyFnDef(..) | ty::TyFnPtr(_) |
 559             ty::TyGeneratorWitness(..) => {
 560                 // these types never have a destructor
 561                 Ok(ty::DtorckConstraint::empty())
 562             }
 563
 564             ty::TyArray(ety, _) | ty::TySlice(ety) => {
 565                 // single-element containers, behave like their element
 566                 self.dtorck_constraint_for_ty(span, for_ty, depth+1, ety)
 567             }
 568
 569             ty::TyTuple(tys, _) => {
 570                 tys.iter().map(|ty| {
 571                     self.dtorck_constraint_for_ty(span, for_ty, depth+1, ty)
 572                 }).collect()
 573             }
 574
 575             ty::TyClosure(def_id, substs) => {
 576                 substs.upvar_tys(def_id, self).map(|ty| {
 577                     self.dtorck_constraint_for_ty(span, for_ty, depth+1, ty)
 578                 }).collect()
 579             }
 580
 581             ty::TyGenerator(def_id, substs, _) => {
 582                 // Note that the interior types are ignored here.
 583                 // Any type reachable inside the interior must also be reachable
 584                 // through the upvars.
 585                 substs.upvar_tys(def_id, self).map(|ty| {
 586                     self.dtorck_constraint_for_ty(span, for_ty, depth+1, ty)
 587                 }).collect()
 588             }
 589
 590             ty::TyAdt(def, substs) => {
 591                 let ty::DtorckConstraint {
 592                     dtorck_types, outlives
 593                 } = self.at(span).adt_dtorck_constraint(def.did);
 594                 Ok(ty::DtorckConstraint {
 595                     // FIXME: we can try to recursively `dtorck_constraint_on_ty`
 596                     // there, but that needs some way to handle cycles.
 597                     dtorck_types: dtorck_types.subst(self, substs),
 598                     outlives: outlives.subst(self, substs)
 599                 })
 600             }
 601
 602             // Objects must be alive in order for their destructor
 603             // to be called.
 604             ty::TyDynamic(..) => Ok(ty::DtorckConstraint {
 605                 outlives: vec![ty.into()],
 606                 dtorck_types: vec![],
 607             }),
 608
 609             // Types that can't be resolved. Pass them forward.
 610             ty::TyProjection(..) | ty::TyAnon(..) | ty::TyParam(..) => {
 611                 Ok(ty::DtorckConstraint {
 612                     outlives: vec![],
 613                     dtorck_types: vec![ty],
 614                 })
 615             }
 616
 617             ty::TyInfer(..) | ty::TyError => {
 618                 self.sess.delay_span_bug(span, "unresolved type in dtorck");
 619                 Err(ErrorReported)
 620             }
 621         };
 622
 623         debug!("dtorck_constraint_for_ty({:?}) = {:?}", ty, result);
 624         result
 625     }
 626
 627     pub fn is_closure(self, def_id: DefId) -> bool {
 628         self.def_key(def_id).disambiguated_data.data == DefPathData::ClosureExpr
 629     }
 630
 631     /// Given the `DefId` of a fn or closure, returns the `DefId` of
 632     /// the innermost fn item that the closure is contained within.
 633     /// This is a significant def-id because, when we do
 634     /// type-checking, we type-check this fn item and all of its
 635     /// (transitive) closures together.  Therefore, when we fetch the
 636     /// `typeck_tables_of` the closure, for example, we really wind up
 637     /// fetching the `typeck_tables_of` the enclosing fn item.
 638     pub fn closure_base_def_id(self, def_id: DefId) -> DefId {
 639         let mut def_id = def_id;
 640         while self.is_closure(def_id) {
 641             def_id = self.parent_def_id(def_id).unwrap_or_else(|| {
 642                 bug!("closure {:?} has no parent", def_id);
 643             });
 644         }
 645         def_id
 646     }
 647
 648     /// Given the def-id and substs a closure, creates the type of
 649     /// `self` argument that the closure expects. For example, for a
 650     /// `Fn` closure, this would return a reference type `&T` where
 651     /// `T=closure_ty`.
 652     ///
 653     /// Returns `None` if this closure's kind has not yet been inferred.
 654     /// This should only be possible during type checking.
 655     ///
 656     /// Note that the return value is a late-bound region and hence
 657     /// wrapped in a binder.
 658     pub fn closure_env_ty(self,
 659                           closure_def_id: DefId,
 660                           closure_substs: ty::ClosureSubsts<'tcx>)
 661                           -> Option<ty::Binder<Ty<'tcx>>>
 662     {
 663         let closure_ty = self.mk_closure(closure_def_id, closure_substs);
 664         let env_region = ty::ReLateBound(ty::DebruijnIndex::new(1), ty::BrEnv);
 665         let closure_kind_ty = closure_substs.closure_kind_ty(closure_def_id, self);
 666         let closure_kind = closure_kind_ty.to_opt_closure_kind()?;
 667         let env_ty = match closure_kind {
 668             ty::ClosureKind::Fn => self.mk_imm_ref(self.mk_region(env_region), closure_ty),
 669             ty::ClosureKind::FnMut => self.mk_mut_ref(self.mk_region(env_region), closure_ty),
 670             ty::ClosureKind::FnOnce => closure_ty,
 671         };
 672         Some(ty::Binder(env_ty))
 673     }
 674
 675     /// Given the def-id of some item that has no type parameters, make
 676     /// a suitable "empty substs" for it.
 677     pub fn empty_substs_for_def_id(self, item_def_id: DefId) -> &'tcx ty::Substs<'tcx> {
 678         ty::Substs::for_item(self, item_def_id,
 679                              |_, _| self.types.re_erased,
 680                              |_, _| {
 681             bug!("empty_substs_for_def_id: {:?} has type parameters", item_def_id)
 682         })
 683     }
 684
 685     pub fn const_usize(&self, val: u16) -> ConstInt {
 686         match self.sess.target.usize_ty {
 687             ast::UintTy::U16 => ConstInt::Usize(ConstUsize::Us16(val as u16)),
 688             ast::UintTy::U32 => ConstInt::Usize(ConstUsize::Us32(val as u32)),
 689             ast::UintTy::U64 => ConstInt::Usize(ConstUsize::Us64(val as u64)),
 690             _ => bug!(),
 691         }
 692     }
 693
 694     /// Return whether the node pointed to by def_id is a static item, and its mutability
 695     pub fn is_static(&self, def_id: DefId) -> Option<hir::Mutability> {
 696         if let Some(node) = self.hir.get_if_local(def_id) {
 697             match node {
 698                 Node::NodeItem(&hir::Item {
 699                     node: hir::ItemStatic(_, mutbl, _), ..
 700                 }) => Some(mutbl),
 701                 Node::NodeForeignItem(&hir::ForeignItem {
 702                     node: hir::ForeignItemStatic(_, is_mutbl), ..
 703                 }) =>
 704                     Some(if is_mutbl {
 705                         hir::Mutability::MutMutable
 706                     } else {
 707                         hir::Mutability::MutImmutable
 708                     }),
 709                 _ => None
 710             }
 711         } else {
 712             match self.describe_def(def_id) {
 713                 Some(Def::Static(_, is_mutbl)) =>
 714                     Some(if is_mutbl {
 715                         hir::Mutability::MutMutable
 716                     } else {
 717                         hir::Mutability::MutImmutable
 718                     }),
 719                 _ => None
 720             }
 721         }
 722     }
 723 }
 724
 725 pub struct TypeIdHasher<'a, 'gcx: 'a+'tcx, 'tcx: 'a, W> {
 726     tcx: TyCtxt<'a, 'gcx, 'tcx>,
 727     state: StableHasher<W>,
 728 }
 729
 730 impl<'a, 'gcx, 'tcx, W> TypeIdHasher<'a, 'gcx, 'tcx, W>
 731     where W: StableHasherResult
 732 {
 733     pub fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Self {
 734         TypeIdHasher { tcx: tcx, state: StableHasher::new() }
 735     }
 736
 737     pub fn finish(self) -> W {
 738         self.state.finish()
 739     }
 740
 741     pub fn hash<T: Hash>(&mut self, x: T) {
 742         x.hash(&mut self.state);
 743     }
 744
 745     fn hash_discriminant_u8<T>(&mut self, x: &T) {
 746         let v = unsafe {
 747             intrinsics::discriminant_value(x)
 748         };
 749         let b = v as u8;
 750         assert_eq!(v, b as u64);
 751         self.hash(b)
 752     }
 753
 754     fn def_id(&mut self, did: DefId) {
 755         // Hash the DefPath corresponding to the DefId, which is independent
 756         // of compiler internal state. We already have a stable hash value of
 757         // all DefPaths available via tcx.def_path_hash(), so we just feed that
 758         // into the hasher.
 759         let hash = self.tcx.def_path_hash(did);
 760         self.hash(hash);
 761     }
 762 }
 763
 764 impl<'a, 'gcx, 'tcx, W> TypeVisitor<'tcx> for TypeIdHasher<'a, 'gcx, 'tcx, W>
 765     where W: StableHasherResult
 766 {
 767     fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
 768         // Distinguish between the Ty variants uniformly.
 769         self.hash_discriminant_u8(&ty.sty);
 770
 771         match ty.sty {
 772             TyInt(i) => self.hash(i),
 773             TyUint(u) => self.hash(u),
 774             TyFloat(f) => self.hash(f),
 775             TyArray(_, n) => {
 776                 self.hash_discriminant_u8(&n.val);
 777                 match n.val {
 778                     ConstVal::Value(Value::ByVal(PrimVal::Bytes(b))) => self.hash(b),
 779                     ConstVal::Unevaluated(def_id, _) => self.def_id(def_id),
 780                     _ => bug!("arrays should not have {:?} as length", n)
 781                 }
 782             }
 783             TyRawPtr(m) |
 784             TyRef(_, m) => self.hash(m.mutbl),
 785             TyClosure(def_id, _) |
 786             TyGenerator(def_id, _, _) |
 787             TyAnon(def_id, _) |
 788             TyFnDef(def_id, _) => self.def_id(def_id),
 789             TyAdt(d, _) => self.def_id(d.did),
 790             TyForeign(def_id) => self.def_id(def_id),
 791             TyFnPtr(f) => {
 792                 self.hash(f.unsafety());
 793                 self.hash(f.abi());
 794                 self.hash(f.variadic());
 795                 self.hash(f.inputs().skip_binder().len());
 796             }
 797             TyDynamic(ref data, ..) => {
 798                 if let Some(p) = data.principal() {
 799                     self.def_id(p.def_id());
 800                 }
 801                 for d in data.auto_traits() {
 802                     self.def_id(d);
 803                 }
 804             }
 805             TyGeneratorWitness(tys) => {
 806                 self.hash(tys.skip_binder().len());
 807             }
 808             TyTuple(tys, defaulted) => {
 809                 self.hash(tys.len());
 810                 self.hash(defaulted);
 811             }
 812             TyParam(p) => {
 813                 self.hash(p.idx);
 814                 self.hash(p.name.as_str());
 815             }
 816             TyProjection(ref data) => {
 817                 self.def_id(data.item_def_id);
 818             }
 819             TyNever |
 820             TyBool |
 821             TyChar |
 822             TyStr |
 823             TySlice(_) => {}
 824
 825             TyError |
 826             TyInfer(_) => bug!("TypeIdHasher: unexpected type {}", ty)
 827         }
 828
 829         ty.super_visit_with(self)
 830     }
 831
 832     fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
 833         self.hash_discriminant_u8(r);
 834         match *r {
 835             ty::ReErased |
 836             ty::ReStatic |
 837             ty::ReEmpty => {
 838                 // No variant fields to hash for these ...
 839             }
 840             ty::ReLateBound(db, ty::BrAnon(i)) => {
 841                 self.hash(db.depth);
 842                 self.hash(i);
 843             }
 844             ty::ReEarlyBound(ty::EarlyBoundRegion { def_id, .. }) => {
 845                 self.def_id(def_id);
 846             }
 847
 848             ty::ReClosureBound(..) |
 849             ty::ReLateBound(..) |
 850             ty::ReFree(..) |
 851             ty::ReScope(..) |
 852             ty::ReVar(..) |
 853             ty::ReSkolemized(..) => {
 854                 bug!("TypeIdHasher: unexpected region {:?}", r)
 855             }
 856         }
 857         false
 858     }
 859
 860     fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, x: &ty::Binder<T>) -> bool {
 861         // Anonymize late-bound regions so that, for example:
 862         // `for<'a, b> fn(&'a &'b T)` and `for<'a, b> fn(&'b &'a T)`
 863         // result in the same TypeId (the two types are equivalent).
 864         self.tcx.anonymize_late_bound_regions(x).super_visit_with(self)
 865     }
 866 }
 867
 868 impl<'a, 'tcx> ty::TyS<'tcx> {
 869     pub fn moves_by_default(&'tcx self,
 870                             tcx: TyCtxt<'a, 'tcx, 'tcx>,
 871                             param_env: ty::ParamEnv<'tcx>,
 872                             span: Span)
 873                             -> bool {
 874         !tcx.at(span).is_copy_raw(param_env.and(self))
 875     }
 876
 877     pub fn is_sized(&'tcx self,
 878                     tcx_at: TyCtxtAt<'a, 'tcx, 'tcx>,
 879                     param_env: ty::ParamEnv<'tcx>)-> bool
 880     {
 881         tcx_at.is_sized_raw(param_env.and(self))
 882     }
 883
 884     pub fn is_freeze(&'tcx self,
 885                      tcx: TyCtxt<'a, 'tcx, 'tcx>,
 886                      param_env: ty::ParamEnv<'tcx>,
 887                      span: Span)-> bool
 888     {
 889         tcx.at(span).is_freeze_raw(param_env.and(self))
 890     }
 891
 892     /// If `ty.needs_drop(...)` returns `true`, then `ty` is definitely
 893     /// non-copy and *might* have a destructor attached; if it returns
 894     /// `false`, then `ty` definitely has no destructor (i.e. no drop glue).
 895     ///
 896     /// (Note that this implies that if `ty` has a destructor attached,
 897     /// then `needs_drop` will definitely return `true` for `ty`.)
 898     #[inline]
 899     pub fn needs_drop(&'tcx self,
 900                       tcx: TyCtxt<'a, 'tcx, 'tcx>,
 901                       param_env: ty::ParamEnv<'tcx>)
 902                       -> bool {
 903         tcx.needs_drop_raw(param_env.and(self))
 904     }
 905
 906     /// Check whether a type is representable. This means it cannot contain unboxed
 907     /// structural recursion. This check is needed for structs and enums.
 908     pub fn is_representable(&'tcx self,
 909                             tcx: TyCtxt<'a, 'tcx, 'tcx>,
 910                             sp: Span)
 911                             -> Representability {
 912
 913         // Iterate until something non-representable is found
 914         fn fold_repr<It: Iterator<Item=Representability>>(iter: It) -> Representability {
 915             iter.fold(Representability::Representable, |r1, r2| {
 916                 match (r1, r2) {
 917                     (Representability::SelfRecursive(v1),
 918                      Representability::SelfRecursive(v2)) => {
 919                         Representability::SelfRecursive(v1.iter().map(|s| *s).chain(v2).collect())
 920                     }
 921                     (r1, r2) => cmp::max(r1, r2)
 922                 }
 923             })
 924         }
 925
 926         fn are_inner_types_recursive<'a, 'tcx>(
 927             tcx: TyCtxt<'a, 'tcx, 'tcx>, sp: Span,
 928             seen: &mut Vec<Ty<'tcx>>,
 929             representable_cache: &mut FxHashMap<Ty<'tcx>, Representability>,
 930             ty: Ty<'tcx>)
 931             -> Representability
 932         {
 933             match ty.sty {
 934                 TyTuple(ref ts, _) => {
 935                     // Find non representable
 936                     fold_repr(ts.iter().map(|ty| {
 937                         is_type_structurally_recursive(tcx, sp, seen, representable_cache, ty)
 938                     }))
 939                 }
 940                 // Fixed-length vectors.
 941                 // FIXME(#11924) Behavior undecided for zero-length vectors.
 942                 TyArray(ty, _) => {
 943                     is_type_structurally_recursive(tcx, sp, seen, representable_cache, ty)
 944                 }
 945                 TyAdt(def, substs) => {
 946                     // Find non representable fields with their spans
 947                     fold_repr(def.all_fields().map(|field| {
 948                         let ty = field.ty(tcx, substs);
 949                         let span = tcx.hir.span_if_local(field.did).unwrap_or(sp);
 950                         match is_type_structurally_recursive(tcx, span, seen,
 951                                                              representable_cache, ty)
 952                         {
 953                             Representability::SelfRecursive(_) => {
 954                                 Representability::SelfRecursive(vec![span])
 955                             }
 956                             x => x,
 957                         }
 958                     }))
 959                 }
 960                 TyClosure(..) => {
 961                     // this check is run on type definitions, so we don't expect
 962                     // to see closure types
 963                     bug!("requires check invoked on inapplicable type: {:?}", ty)
 964                 }
 965                 _ => Representability::Representable,
 966             }
 967         }
 968
 969         fn same_struct_or_enum<'tcx>(ty: Ty<'tcx>, def: &'tcx ty::AdtDef) -> bool {
 970             match ty.sty {
 971                 TyAdt(ty_def, _) => {
 972                      ty_def == def
 973                 }
 974                 _ => false
 975             }
 976         }
 977
 978         fn same_type<'tcx>(a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
 979             match (&a.sty, &b.sty) {
 980                 (&TyAdt(did_a, substs_a), &TyAdt(did_b, substs_b)) => {
 981                     if did_a != did_b {
 982                         return false;
 983                     }
 984
 985                     substs_a.types().zip(substs_b.types()).all(|(a, b)| same_type(a, b))
 986                 }
 987                 _ => a == b,
 988             }
 989         }
 990
 991         // Does the type `ty` directly (without indirection through a pointer)
 992         // contain any types on stack `seen`?
 993         fn is_type_structurally_recursive<'a, 'tcx>(
 994             tcx: TyCtxt<'a, 'tcx, 'tcx>,
 995             sp: Span,
 996             seen: &mut Vec<Ty<'tcx>>,
 997             representable_cache: &mut FxHashMap<Ty<'tcx>, Representability>,
 998             ty: Ty<'tcx>) -> Representability
 999         {
1000             debug!("is_type_structurally_recursive: {:?} {:?}", ty, sp);
1001             if let Some(representability) = representable_cache.get(ty) {
1002                 debug!("is_type_structurally_recursive: {:?} {:?} - (cached) {:?}",
1003                        ty, sp, representability);
1004                 return representability.clone();
1005             }
1006
1007             let representability = is_type_structurally_recursive_inner(
1008                 tcx, sp, seen, representable_cache, ty);
1009
1010             representable_cache.insert(ty, representability.clone());
1011             representability
1012         }
1013
1014         fn is_type_structurally_recursive_inner<'a, 'tcx>(
1015             tcx: TyCtxt<'a, 'tcx, 'tcx>,
1016             sp: Span,
1017             seen: &mut Vec<Ty<'tcx>>,
1018             representable_cache: &mut FxHashMap<Ty<'tcx>, Representability>,
1019             ty: Ty<'tcx>) -> Representability
1020         {
1021             match ty.sty {
1022                 TyAdt(def, _) => {
1023                     {
1024                         // Iterate through stack of previously seen types.
1025                         let mut iter = seen.iter();
1026
1027                         // The first item in `seen` is the type we are actually curious about.
1028                         // We want to return SelfRecursive if this type contains itself.
1029                         // It is important that we DON'T take generic parameters into account
1030                         // for this check, so that Bar<T> in this example counts as SelfRecursive:
1031                         //
1032                         // struct Foo;
1033                         // struct Bar<T> { x: Bar<Foo> }
1034
1035                         if let Some(&seen_type) = iter.next() {
1036                             if same_struct_or_enum(seen_type, def) {
1037                                 debug!("SelfRecursive: {:?} contains {:?}",
1038                                        seen_type,
1039                                        ty);
1040                                 return Representability::SelfRecursive(vec![sp]);
1041                             }
1042                         }
1043
1044                         // We also need to know whether the first item contains other types
1045                         // that are structurally recursive. If we don't catch this case, we
1046                         // will recurse infinitely for some inputs.
1047                         //
1048                         // It is important that we DO take generic parameters into account
1049                         // here, so that code like this is considered SelfRecursive, not
1050                         // ContainsRecursive:
1051                         //
1052                         // struct Foo { Option<Option<Foo>> }
1053
1054                         for &seen_type in iter {
1055                             if same_type(ty, seen_type) {
1056                                 debug!("ContainsRecursive: {:?} contains {:?}",
1057                                        seen_type,
1058                                        ty);
1059                                 return Representability::ContainsRecursive;
1060                             }
1061                         }
1062                     }
1063
1064                     // For structs and enums, track all previously seen types by pushing them
1065                     // onto the 'seen' stack.
1066                     seen.push(ty);
1067                     let out = are_inner_types_recursive(tcx, sp, seen, representable_cache, ty);
1068                     seen.pop();
1069                     out
1070                 }
1071                 _ => {
1072                     // No need to push in other cases.
1073                     are_inner_types_recursive(tcx, sp, seen, representable_cache, ty)
1074                 }
1075             }
1076         }
1077
1078         debug!("is_type_representable: {:?}", self);
1079
1080         // To avoid a stack overflow when checking an enum variant or struct that
1081         // contains a different, structurally recursive type, maintain a stack
1082         // of seen types and check recursion for each of them (issues #3008, #3779).
1083         let mut seen: Vec<Ty> = Vec::new();
1084         let mut representable_cache = FxHashMap();
1085         let r = is_type_structurally_recursive(
1086             tcx, sp, &mut seen, &mut representable_cache, self);
1087         debug!("is_type_representable: {:?} is {:?}", self, r);
1088         r
1089     }
1090 }
1091
1092 fn is_copy_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1093                          query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
1094                          -> bool
1095 {
1096     let (param_env, ty) = query.into_parts();
1097     let trait_def_id = tcx.require_lang_item(lang_items::CopyTraitLangItem);
1098     tcx.infer_ctxt()
1099        .enter(|infcx| traits::type_known_to_meet_bound(&infcx,
1100                                                        param_env,
1101                                                        ty,
1102                                                        trait_def_id,
1103                                                        DUMMY_SP))
1104 }
1105
1106 fn is_sized_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1107                           query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
1108                           -> bool
1109 {
1110     let (param_env, ty) = query.into_parts();
1111     let trait_def_id = tcx.require_lang_item(lang_items::SizedTraitLangItem);
1112     tcx.infer_ctxt()
1113        .enter(|infcx| traits::type_known_to_meet_bound(&infcx,
1114                                                        param_env,
1115                                                        ty,
1116                                                        trait_def_id,
1117                                                        DUMMY_SP))
1118 }
1119
1120 fn is_freeze_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1121                            query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
1122                            -> bool
1123 {
1124     let (param_env, ty) = query.into_parts();
1125     let trait_def_id = tcx.require_lang_item(lang_items::FreezeTraitLangItem);
1126     tcx.infer_ctxt()
1127        .enter(|infcx| traits::type_known_to_meet_bound(&infcx,
1128                                                        param_env,
1129                                                        ty,
1130                                                        trait_def_id,
1131                                                        DUMMY_SP))
1132 }
1133
1134 fn needs_drop_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1135                             query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
1136                             -> bool
1137 {
1138     let (param_env, ty) = query.into_parts();
1139
1140     let needs_drop = |ty: Ty<'tcx>| -> bool {
1141         match ty::queries::needs_drop_raw::try_get(tcx, DUMMY_SP, param_env.and(ty)) {
1142             Ok(v) => v,
1143             Err(mut bug) => {
1144                 // Cycles should be reported as an error by `check_representable`.
1145                 //
1146                 // Consider the type as not needing drop in the meanwhile to
1147                 // avoid further errors.
1148                 //
1149                 // In case we forgot to emit a bug elsewhere, delay our
1150                 // diagnostic to get emitted as a compiler bug.
1151                 bug.delay_as_bug();
1152                 false
1153             }
1154         }
1155     };
1156
1157     assert!(!ty.needs_infer());
1158
1159     match ty.sty {
1160         // Fast-path for primitive types
1161         ty::TyInfer(ty::FreshIntTy(_)) | ty::TyInfer(ty::FreshFloatTy(_)) |
1162         ty::TyBool | ty::TyInt(_) | ty::TyUint(_) | ty::TyFloat(_) | ty::TyNever |
1163         ty::TyFnDef(..) | ty::TyFnPtr(_) | ty::TyChar | ty::TyGeneratorWitness(..) |
1164         ty::TyRawPtr(_) | ty::TyRef(..) | ty::TyStr => false,
1165
1166         // Foreign types can never have destructors
1167         ty::TyForeign(..) => false,
1168
1169         // Issue #22536: We first query type_moves_by_default.  It sees a
1170         // normalized version of the type, and therefore will definitely
1171         // know whether the type implements Copy (and thus needs no
1172         // cleanup/drop/zeroing) ...
1173         _ if !ty.moves_by_default(tcx, param_env, DUMMY_SP) => false,
1174
1175         // ... (issue #22536 continued) but as an optimization, still use
1176         // prior logic of asking for the structural "may drop".
1177
1178         // FIXME(#22815): Note that this is a conservative heuristic;
1179         // it may report that the type "may drop" when actual type does
1180         // not actually have a destructor associated with it. But since
1181         // the type absolutely did not have the `Copy` bound attached
1182         // (see above), it is sound to treat it as having a destructor.
1183
1184         // User destructors are the only way to have concrete drop types.
1185         ty::TyAdt(def, _) if def.has_dtor(tcx) => true,
1186
1187         // Can refer to a type which may drop.
1188         // FIXME(eddyb) check this against a ParamEnv.
1189         ty::TyDynamic(..) | ty::TyProjection(..) | ty::TyParam(_) |
1190         ty::TyAnon(..) | ty::TyInfer(_) | ty::TyError => true,
1191
1192         // Structural recursion.
1193         ty::TyArray(ty, _) | ty::TySlice(ty) => needs_drop(ty),
1194
1195         ty::TyClosure(def_id, ref substs) => substs.upvar_tys(def_id, tcx).any(needs_drop),
1196
1197         // Pessimistically assume that all generators will require destructors
1198         // as we don't know if a destructor is a noop or not until after the MIR
1199         // state transformation pass
1200         ty::TyGenerator(..) => true,
1201
1202         ty::TyTuple(ref tys, _) => tys.iter().cloned().any(needs_drop),
1203
1204         // unions don't have destructors regardless of the child types
1205         ty::TyAdt(def, _) if def.is_union() => false,
1206
1207         ty::TyAdt(def, substs) =>
1208             def.variants.iter().any(
1209                 |variant| variant.fields.iter().any(
1210                     |field| needs_drop(field.ty(tcx, substs)))),
1211     }
1212 }
1213
1214 pub enum ExplicitSelf<'tcx> {
1215     ByValue,
1216     ByReference(ty::Region<'tcx>, hir::Mutability),
1217     ByRawPointer(hir::Mutability),
1218     ByBox,
1219     Other
1220 }
1221
1222 impl<'tcx> ExplicitSelf<'tcx> {
1223     /// Categorizes an explicit self declaration like `self: SomeType`
1224     /// into either `self`, `&self`, `&mut self`, `Box<self>`, or
1225     /// `Other`.
1226     /// This is mainly used to require the arbitrary_self_types feature
1227     /// in the case of `Other`, to improve error messages in the common cases,
1228     /// and to make `Other` non-object-safe.
1229     ///
1230     /// Examples:
1231     ///
1232     /// ```
1233     /// impl<'a> Foo for &'a T {
1234     ///     // Legal declarations:
1235     ///     fn method1(self: &&'a T); // ExplicitSelf::ByReference
1236     ///     fn method2(self: &'a T); // ExplicitSelf::ByValue
1237     ///     fn method3(self: Box<&'a T>); // ExplicitSelf::ByBox
1238     ///     fn method4(self: Rc<&'a T>); // ExplicitSelf::Other
1239     ///
1240     ///     // Invalid cases will be caught by `check_method_receiver`:
1241     ///     fn method_err1(self: &'a mut T); // ExplicitSelf::Other
1242     ///     fn method_err2(self: &'static T) // ExplicitSelf::ByValue
1243     ///     fn method_err3(self: &&T) // ExplicitSelf::ByReference
1244     /// }
1245     /// ```
1246     ///
1247     pub fn determine<P>(
1248         self_arg_ty: Ty<'tcx>,
1249         is_self_ty: P
1250     ) -> ExplicitSelf<'tcx>
1251     where
1252         P: Fn(Ty<'tcx>) -> bool
1253     {
1254         use self::ExplicitSelf::*;
1255
1256         match self_arg_ty.sty {
1257             _ if is_self_ty(self_arg_ty) => ByValue,
1258             ty::TyRef(region, ty::TypeAndMut { ty, mutbl }) if is_self_ty(ty) => {
1259                 ByReference(region, mutbl)
1260             }
1261             ty::TyRawPtr(ty::TypeAndMut { ty, mutbl }) if is_self_ty(ty) => {
1262                 ByRawPointer(mutbl)
1263             }
1264             ty::TyAdt(def, _) if def.is_box() && is_self_ty(self_arg_ty.boxed_ty()) => {
1265                 ByBox
1266             }
1267             _ => Other
1268         }
1269     }
1270 }
1271
1272 pub fn provide(providers: &mut ty::maps::Providers) {
1273     *providers = ty::maps::Providers {
1274         is_copy_raw,
1275         is_sized_raw,
1276         is_freeze_raw,
1277         needs_drop_raw,
1278         ..*providers
1279     };
1280 }