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 infer::InferCtxt;
  16 // use hir::map as hir_map;
  17 use traits::{self, Reveal};
  18 use ty::{self, Ty, TyCtxt, TypeAndMut, TypeFlags, TypeFoldable};
  19 use ty::ParameterEnvironment;
  20 use ty::fold::TypeVisitor;
  21 use ty::layout::{Layout, LayoutError};
  22 use ty::TypeVariants::*;
  23 use util::common::ErrorReported;
  24 use util::nodemap::FxHashMap;
  25 use middle::lang_items;
  26
  27 use rustc_const_math::{ConstInt, ConstIsize, ConstUsize};
  28 use rustc_data_structures::stable_hasher::{StableHasher, StableHasherResult};
  29
  30 use std::cell::RefCell;
  31 use std::cmp;
  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 use hir;
  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::Is) => match $tcx.sess.target.int_type {
  60                 ast::IntTy::I16 => ConstInt::Isize(ConstIsize::Is16($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::Us) => match $tcx.sess.target.uint_type {
  71                 ast::UintTy::U16 => ConstInt::Usize(ConstUsize::Us16($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::Is)   => 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::Us) => 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::Is), 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::Us), 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(Copy, Clone, PartialOrd, Ord, Eq, PartialEq, Debug)]
 148 pub enum Representability {
 149     Representable,
 150     ContainsRecursive,
 151     SelfRecursive,
 152 }
 153
 154 impl<'tcx> ParameterEnvironment<'tcx> {
 155     pub fn can_type_implement_copy<'a>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>,
 156                                        self_type: Ty<'tcx>, span: Span)
 157                                        -> Result<(), CopyImplementationError> {
 158         // FIXME: (@jroesch) float this code up
 159         tcx.infer_ctxt(self.clone(), Reveal::UserFacing).enter(|infcx| {
 160             let (adt, substs) = match self_type.sty {
 161                 ty::TyAdt(adt, substs) => (adt, substs),
 162                 _ => return Err(CopyImplementationError::NotAnAdt),
 163             };
 164
 165             let field_implements_copy = |field: &ty::FieldDef| {
 166                 let cause = traits::ObligationCause::dummy();
 167                 match traits::fully_normalize(&infcx, cause, &field.ty(tcx, substs)) {
 168                     Ok(ty) => !infcx.type_moves_by_default(ty, span),
 169                     Err(..) => false,
 170                 }
 171             };
 172
 173             for variant in &adt.variants {
 174                 for field in &variant.fields {
 175                     if !field_implements_copy(field) {
 176                         return Err(CopyImplementationError::InfrigingField(field));
 177                     }
 178                 }
 179             }
 180
 181             if adt.has_dtor(tcx) {
 182                 return Err(CopyImplementationError::HasDestructor);
 183             }
 184
 185             Ok(())
 186         })
 187     }
 188 }
 189
 190 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 191     pub fn has_error_field(self, ty: Ty<'tcx>) -> bool {
 192         match ty.sty {
 193             ty::TyAdt(def, substs) => {
 194                 for field in def.all_fields() {
 195                     let field_ty = field.ty(self, substs);
 196                     if let TyError = field_ty.sty {
 197                         return true;
 198                     }
 199                 }
 200             }
 201             _ => (),
 202         }
 203         false
 204     }
 205
 206     /// Returns the type of element at index `i` in tuple or tuple-like type `t`.
 207     /// For an enum `t`, `variant` is None only if `t` is a univariant enum.
 208     pub fn positional_element_ty(self,
 209                                  ty: Ty<'tcx>,
 210                                  i: usize,
 211                                  variant: Option<DefId>) -> Option<Ty<'tcx>> {
 212         match (&ty.sty, variant) {
 213             (&TyAdt(adt, substs), Some(vid)) => {
 214                 adt.variant_with_id(vid).fields.get(i).map(|f| f.ty(self, substs))
 215             }
 216             (&TyAdt(adt, substs), None) => {
 217                 // Don't use `struct_variant`, this may be a univariant enum.
 218                 adt.variants[0].fields.get(i).map(|f| f.ty(self, substs))
 219             }
 220             (&TyTuple(ref v, _), None) => v.get(i).cloned(),
 221             _ => None,
 222         }
 223     }
 224
 225     /// Returns the type of element at field `n` in struct or struct-like type `t`.
 226     /// For an enum `t`, `variant` must be some def id.
 227     pub fn named_element_ty(self,
 228                             ty: Ty<'tcx>,
 229                             n: Name,
 230                             variant: Option<DefId>) -> Option<Ty<'tcx>> {
 231         match (&ty.sty, variant) {
 232             (&TyAdt(adt, substs), Some(vid)) => {
 233                 adt.variant_with_id(vid).find_field_named(n).map(|f| f.ty(self, substs))
 234             }
 235             (&TyAdt(adt, substs), None) => {
 236                 adt.struct_variant().find_field_named(n).map(|f| f.ty(self, substs))
 237             }
 238             _ => return None
 239         }
 240     }
 241
 242     /// Returns the deeply last field of nested structures, or the same type,
 243     /// if not a structure at all. Corresponds to the only possible unsized
 244     /// field, and its type can be used to determine unsizing strategy.
 245     pub fn struct_tail(self, mut ty: Ty<'tcx>) -> Ty<'tcx> {
 246         while let TyAdt(def, substs) = ty.sty {
 247             if !def.is_struct() {
 248                 break;
 249             }
 250             match def.struct_variant().fields.last() {
 251                 Some(f) => ty = f.ty(self, substs),
 252                 None => break,
 253             }
 254         }
 255         ty
 256     }
 257
 258     /// Same as applying struct_tail on `source` and `target`, but only
 259     /// keeps going as long as the two types are instances of the same
 260     /// structure definitions.
 261     /// For `(Foo<Foo<T>>, Foo<Trait>)`, the result will be `(Foo<T>, Trait)`,
 262     /// whereas struct_tail produces `T`, and `Trait`, respectively.
 263     pub fn struct_lockstep_tails(self,
 264                                  source: Ty<'tcx>,
 265                                  target: Ty<'tcx>)
 266                                  -> (Ty<'tcx>, Ty<'tcx>) {
 267         let (mut a, mut b) = (source, target);
 268         while let (&TyAdt(a_def, a_substs), &TyAdt(b_def, b_substs)) = (&a.sty, &b.sty) {
 269             if a_def != b_def || !a_def.is_struct() {
 270                 break;
 271             }
 272             match a_def.struct_variant().fields.last() {
 273                 Some(f) => {
 274                     a = f.ty(self, a_substs);
 275                     b = f.ty(self, b_substs);
 276                 }
 277                 _ => break,
 278             }
 279         }
 280         (a, b)
 281     }
 282
 283     /// Given a set of predicates that apply to an object type, returns
 284     /// the region bounds that the (erased) `Self` type must
 285     /// outlive. Precisely *because* the `Self` type is erased, the
 286     /// parameter `erased_self_ty` must be supplied to indicate what type
 287     /// has been used to represent `Self` in the predicates
 288     /// themselves. This should really be a unique type; `FreshTy(0)` is a
 289     /// popular choice.
 290     ///
 291     /// NB: in some cases, particularly around higher-ranked bounds,
 292     /// this function returns a kind of conservative approximation.
 293     /// That is, all regions returned by this function are definitely
 294     /// required, but there may be other region bounds that are not
 295     /// returned, as well as requirements like `for<'a> T: 'a`.
 296     ///
 297     /// Requires that trait definitions have been processed so that we can
 298     /// elaborate predicates and walk supertraits.
 299     pub fn required_region_bounds(self,
 300                                   erased_self_ty: Ty<'tcx>,
 301                                   predicates: Vec<ty::Predicate<'tcx>>)
 302                                   -> Vec<&'tcx ty::Region>    {
 303         debug!("required_region_bounds(erased_self_ty={:?}, predicates={:?})",
 304                erased_self_ty,
 305                predicates);
 306
 307         assert!(!erased_self_ty.has_escaping_regions());
 308
 309         traits::elaborate_predicates(self, predicates)
 310             .filter_map(|predicate| {
 311                 match predicate {
 312                     ty::Predicate::Projection(..) |
 313                     ty::Predicate::Trait(..) |
 314                     ty::Predicate::Equate(..) |
 315                     ty::Predicate::WellFormed(..) |
 316                     ty::Predicate::ObjectSafe(..) |
 317                     ty::Predicate::ClosureKind(..) |
 318                     ty::Predicate::RegionOutlives(..) => {
 319                         None
 320                     }
 321                     ty::Predicate::TypeOutlives(ty::Binder(ty::OutlivesPredicate(t, r))) => {
 322                         // Search for a bound of the form `erased_self_ty
 323                         // : 'a`, but be wary of something like `for<'a>
 324                         // erased_self_ty : 'a` (we interpret a
 325                         // higher-ranked bound like that as 'static,
 326                         // though at present the code in `fulfill.rs`
 327                         // considers such bounds to be unsatisfiable, so
 328                         // it's kind of a moot point since you could never
 329                         // construct such an object, but this seems
 330                         // correct even if that code changes).
 331                         if t == erased_self_ty && !r.has_escaping_regions() {
 332                             Some(r)
 333                         } else {
 334                             None
 335                         }
 336                     }
 337                 }
 338             })
 339             .collect()
 340     }
 341
 342     /// Creates a hash of the type `Ty` which will be the same no matter what crate
 343     /// context it's calculated within. This is used by the `type_id` intrinsic.
 344     pub fn type_id_hash(self, ty: Ty<'tcx>) -> u64 {
 345         let mut hasher = TypeIdHasher::new(self);
 346         hasher.visit_ty(ty);
 347         hasher.finish()
 348     }
 349
 350     /// Calculate the destructor of a given type.
 351     pub fn calculate_dtor(
 352         self,
 353         adt_did: DefId,
 354         validate: &mut FnMut(Self, DefId) -> Result<(), ErrorReported>
 355     ) -> Option<ty::Destructor> {
 356         let drop_trait = if let Some(def_id) = self.lang_items.drop_trait() {
 357             def_id
 358         } else {
 359             return None;
 360         };
 361
 362         ty::queries::coherent_trait::get(self, DUMMY_SP, (LOCAL_CRATE, drop_trait));
 363
 364         let mut dtor_did = None;
 365         let ty = self.item_type(adt_did);
 366         self.lookup_trait_def(drop_trait).for_each_relevant_impl(self, ty, |impl_did| {
 367             if let Some(item) = self.associated_items(impl_did).next() {
 368                 if let Ok(()) = validate(self, impl_did) {
 369                     dtor_did = Some(item.def_id);
 370                 }
 371             }
 372         });
 373
 374         let dtor_did = match dtor_did {
 375             Some(dtor) => dtor,
 376             None => return None,
 377         };
 378
 379         // RFC 1238: if the destructor method is tagged with the
 380         // attribute `unsafe_destructor_blind_to_params`, then the
 381         // compiler is being instructed to *assume* that the
 382         // destructor will not access borrowed data,
 383         // even if such data is otherwise reachable.
 384         //
 385         // Such access can be in plain sight (e.g. dereferencing
 386         // `*foo.0` of `Foo<'a>(&'a u32)`) or indirectly hidden
 387         // (e.g. calling `foo.0.clone()` of `Foo<T:Clone>`).
 388         let is_dtorck = !self.has_attr(dtor_did, "unsafe_destructor_blind_to_params");
 389         Some(ty::Destructor { did: dtor_did, is_dtorck: is_dtorck })
 390     }
 391
 392     pub fn closure_base_def_id(&self, def_id: DefId) -> DefId {
 393         let mut def_id = def_id;
 394         while self.def_key(def_id).disambiguated_data.data == DefPathData::ClosureExpr {
 395             def_id = self.parent_def_id(def_id).unwrap_or_else(|| {
 396                 bug!("closure {:?} has no parent", def_id);
 397             });
 398         }
 399         def_id
 400     }
 401
 402     /// Given the def-id of some item that has no type parameters, make
 403     /// a suitable "empty substs" for it.
 404     pub fn empty_substs_for_def_id(self, item_def_id: DefId) -> &'tcx ty::Substs<'tcx> {
 405         ty::Substs::for_item(self, item_def_id,
 406                              |_, _| self.mk_region(ty::ReErased),
 407                              |_, _| {
 408             bug!("empty_substs_for_def_id: {:?} has type parameters", item_def_id)
 409         })
 410     }
 411 }
 412
 413 pub struct TypeIdHasher<'a, 'gcx: 'a+'tcx, 'tcx: 'a, W> {
 414     tcx: TyCtxt<'a, 'gcx, 'tcx>,
 415     state: StableHasher<W>,
 416 }
 417
 418 impl<'a, 'gcx, 'tcx, W> TypeIdHasher<'a, 'gcx, 'tcx, W>
 419     where W: StableHasherResult
 420 {
 421     pub fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Self {
 422         TypeIdHasher { tcx: tcx, state: StableHasher::new() }
 423     }
 424
 425     pub fn finish(self) -> W {
 426         self.state.finish()
 427     }
 428
 429     pub fn hash<T: Hash>(&mut self, x: T) {
 430         x.hash(&mut self.state);
 431     }
 432
 433     fn hash_discriminant_u8<T>(&mut self, x: &T) {
 434         let v = unsafe {
 435             intrinsics::discriminant_value(x)
 436         };
 437         let b = v as u8;
 438         assert_eq!(v, b as u64);
 439         self.hash(b)
 440     }
 441
 442     fn def_id(&mut self, did: DefId) {
 443         // Hash the DefPath corresponding to the DefId, which is independent
 444         // of compiler internal state. We already have a stable hash value of
 445         // all DefPaths available via tcx.def_path_hash(), so we just feed that
 446         // into the hasher.
 447         let hash = self.tcx.def_path_hash(did);
 448         self.hash(hash);
 449     }
 450 }
 451
 452 impl<'a, 'gcx, 'tcx, W> TypeVisitor<'tcx> for TypeIdHasher<'a, 'gcx, 'tcx, W>
 453     where W: StableHasherResult
 454 {
 455     fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
 456         // Distinguish between the Ty variants uniformly.
 457         self.hash_discriminant_u8(&ty.sty);
 458
 459         match ty.sty {
 460             TyInt(i) => self.hash(i),
 461             TyUint(u) => self.hash(u),
 462             TyFloat(f) => self.hash(f),
 463             TyArray(_, n) => self.hash(n),
 464             TyRawPtr(m) |
 465             TyRef(_, m) => self.hash(m.mutbl),
 466             TyClosure(def_id, _) |
 467             TyAnon(def_id, _) |
 468             TyFnDef(def_id, ..) => self.def_id(def_id),
 469             TyAdt(d, _) => self.def_id(d.did),
 470             TyFnPtr(f) => {
 471                 self.hash(f.unsafety());
 472                 self.hash(f.abi());
 473                 self.hash(f.variadic());
 474                 self.hash(f.inputs().skip_binder().len());
 475             }
 476             TyDynamic(ref data, ..) => {
 477                 if let Some(p) = data.principal() {
 478                     self.def_id(p.def_id());
 479                 }
 480                 for d in data.auto_traits() {
 481                     self.def_id(d);
 482                 }
 483             }
 484             TyTuple(tys, defaulted) => {
 485                 self.hash(tys.len());
 486                 self.hash(defaulted);
 487             }
 488             TyParam(p) => {
 489                 self.hash(p.idx);
 490                 self.hash(p.name.as_str());
 491             }
 492             TyProjection(ref data) => {
 493                 self.def_id(data.trait_ref.def_id);
 494                 self.hash(data.item_name.as_str());
 495             }
 496             TyNever |
 497             TyBool |
 498             TyChar |
 499             TyStr |
 500             TySlice(_) => {}
 501
 502             TyError |
 503             TyInfer(_) => bug!("TypeIdHasher: unexpected type {}", ty)
 504         }
 505
 506         ty.super_visit_with(self)
 507     }
 508
 509     fn visit_region(&mut self, r: &'tcx ty::Region) -> bool {
 510         self.hash_discriminant_u8(r);
 511         match *r {
 512             ty::ReErased |
 513             ty::ReStatic |
 514             ty::ReEmpty => {
 515                 // No variant fields to hash for these ...
 516             }
 517             ty::ReLateBound(db, ty::BrAnon(i)) => {
 518                 self.hash(db.depth);
 519                 self.hash(i);
 520             }
 521             ty::ReEarlyBound(ty::EarlyBoundRegion { index, name }) => {
 522                 self.hash(index);
 523                 self.hash(name.as_str());
 524             }
 525             ty::ReLateBound(..) |
 526             ty::ReFree(..) |
 527             ty::ReScope(..) |
 528             ty::ReVar(..) |
 529             ty::ReSkolemized(..) => {
 530                 bug!("TypeIdHasher: unexpected region {:?}", r)
 531             }
 532         }
 533         false
 534     }
 535
 536     fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, x: &ty::Binder<T>) -> bool {
 537         // Anonymize late-bound regions so that, for example:
 538         // `for<'a, b> fn(&'a &'b T)` and `for<'a, b> fn(&'b &'a T)`
 539         // result in the same TypeId (the two types are equivalent).
 540         self.tcx.anonymize_late_bound_regions(x).super_visit_with(self)
 541     }
 542 }
 543
 544 impl<'a, 'tcx> ty::TyS<'tcx> {
 545     fn impls_bound(&'tcx self, tcx: TyCtxt<'a, 'tcx, 'tcx>,
 546                    param_env: &ParameterEnvironment<'tcx>,
 547                    def_id: DefId,
 548                    cache: &RefCell<FxHashMap<Ty<'tcx>, bool>>,
 549                    span: Span) -> bool
 550     {
 551         if self.has_param_types() || self.has_self_ty() {
 552             if let Some(result) = cache.borrow().get(self) {
 553                 return *result;
 554             }
 555         }
 556         let result =
 557             tcx.infer_ctxt(param_env.clone(), Reveal::UserFacing)
 558             .enter(|infcx| {
 559                 traits::type_known_to_meet_bound(&infcx, self, def_id, span)
 560             });
 561         if self.has_param_types() || self.has_self_ty() {
 562             cache.borrow_mut().insert(self, result);
 563         }
 564         return result;
 565     }
 566
 567     // FIXME (@jroesch): I made this public to use it, not sure if should be private
 568     pub fn moves_by_default(&'tcx self, tcx: TyCtxt<'a, 'tcx, 'tcx>,
 569                             param_env: &ParameterEnvironment<'tcx>,
 570                             span: Span) -> bool {
 571         if self.flags.get().intersects(TypeFlags::MOVENESS_CACHED) {
 572             return self.flags.get().intersects(TypeFlags::MOVES_BY_DEFAULT);
 573         }
 574
 575         assert!(!self.needs_infer());
 576
 577         // Fast-path for primitive types
 578         let result = match self.sty {
 579             TyBool | TyChar | TyInt(..) | TyUint(..) | TyFloat(..) | TyNever |
 580             TyRawPtr(..) | TyFnDef(..) | TyFnPtr(_) | TyRef(_, TypeAndMut {
 581                 mutbl: hir::MutImmutable, ..
 582             }) => Some(false),
 583
 584             TyStr | TyRef(_, TypeAndMut {
 585                 mutbl: hir::MutMutable, ..
 586             }) => Some(true),
 587
 588             TyArray(..) | TySlice(..) | TyDynamic(..) | TyTuple(..) |
 589             TyClosure(..) | TyAdt(..) | TyAnon(..) |
 590             TyProjection(..) | TyParam(..) | TyInfer(..) | TyError => None
 591         }.unwrap_or_else(|| {
 592             !self.impls_bound(tcx, param_env,
 593                               tcx.require_lang_item(lang_items::CopyTraitLangItem),
 594                               &param_env.is_copy_cache, span) });
 595
 596         if !self.has_param_types() && !self.has_self_ty() {
 597             self.flags.set(self.flags.get() | if result {
 598                 TypeFlags::MOVENESS_CACHED | TypeFlags::MOVES_BY_DEFAULT
 599             } else {
 600                 TypeFlags::MOVENESS_CACHED
 601             });
 602         }
 603
 604         result
 605     }
 606
 607     #[inline]
 608     pub fn is_sized(&'tcx self, tcx: TyCtxt<'a, 'tcx, 'tcx>,
 609                     param_env: &ParameterEnvironment<'tcx>,
 610                     span: Span) -> bool
 611     {
 612         if self.flags.get().intersects(TypeFlags::SIZEDNESS_CACHED) {
 613             return self.flags.get().intersects(TypeFlags::IS_SIZED);
 614         }
 615
 616         self.is_sized_uncached(tcx, param_env, span)
 617     }
 618
 619     fn is_sized_uncached(&'tcx self, tcx: TyCtxt<'a, 'tcx, 'tcx>,
 620                          param_env: &ParameterEnvironment<'tcx>,
 621                          span: Span) -> bool {
 622         assert!(!self.needs_infer());
 623
 624         // Fast-path for primitive types
 625         let result = match self.sty {
 626             TyBool | TyChar | TyInt(..) | TyUint(..) | TyFloat(..) |
 627             TyRawPtr(..) | TyRef(..) | TyFnDef(..) | TyFnPtr(_) |
 628             TyArray(..) | TyTuple(..) | TyClosure(..) | TyNever => Some(true),
 629
 630             TyStr | TyDynamic(..) | TySlice(_) => Some(false),
 631
 632             TyAdt(..) | TyProjection(..) | TyParam(..) |
 633             TyInfer(..) | TyAnon(..) | TyError => None
 634         }.unwrap_or_else(|| {
 635             self.impls_bound(tcx, param_env, tcx.require_lang_item(lang_items::SizedTraitLangItem),
 636                               &param_env.is_sized_cache, span) });
 637
 638         if !self.has_param_types() && !self.has_self_ty() {
 639             self.flags.set(self.flags.get() | if result {
 640                 TypeFlags::SIZEDNESS_CACHED | TypeFlags::IS_SIZED
 641             } else {
 642                 TypeFlags::SIZEDNESS_CACHED
 643             });
 644         }
 645
 646         result
 647     }
 648
 649     #[inline]
 650     pub fn layout<'lcx>(&'tcx self, infcx: &InferCtxt<'a, 'tcx, 'lcx>)
 651                         -> Result<&'tcx Layout, LayoutError<'tcx>> {
 652         let tcx = infcx.tcx.global_tcx();
 653         let can_cache = !self.has_param_types() && !self.has_self_ty();
 654         if can_cache {
 655             if let Some(&cached) = tcx.layout_cache.borrow().get(&self) {
 656                 return Ok(cached);
 657             }
 658         }
 659
 660         let rec_limit = tcx.sess.recursion_limit.get();
 661         let depth = tcx.layout_depth.get();
 662         if depth > rec_limit {
 663             tcx.sess.fatal(
 664                 &format!("overflow representing the type `{}`", self));
 665         }
 666
 667         tcx.layout_depth.set(depth+1);
 668         let layout = Layout::compute_uncached(self, infcx);
 669         tcx.layout_depth.set(depth);
 670         let layout = layout?;
 671         if can_cache {
 672             tcx.layout_cache.borrow_mut().insert(self, layout);
 673         }
 674         Ok(layout)
 675     }
 676
 677
 678     /// Check whether a type is representable. This means it cannot contain unboxed
 679     /// structural recursion. This check is needed for structs and enums.
 680     pub fn is_representable(&'tcx self, tcx: TyCtxt<'a, 'tcx, 'tcx>, sp: Span)
 681                             -> Representability {
 682
 683         // Iterate until something non-representable is found
 684         fn find_nonrepresentable<'a, 'tcx, It>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 685                                                sp: Span,
 686                                                seen: &mut Vec<Ty<'tcx>>,
 687                                                iter: It)
 688                                                -> Representability
 689         where It: Iterator<Item=Ty<'tcx>> {
 690             iter.fold(Representability::Representable,
 691                       |r, ty| cmp::max(r, is_type_structurally_recursive(tcx, sp, seen, ty)))
 692         }
 693
 694         fn are_inner_types_recursive<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, sp: Span,
 695                                                seen: &mut Vec<Ty<'tcx>>, ty: Ty<'tcx>)
 696                                                -> Representability {
 697             match ty.sty {
 698                 TyTuple(ref ts, _) => {
 699                     find_nonrepresentable(tcx, sp, seen, ts.iter().cloned())
 700                 }
 701                 // Fixed-length vectors.
 702                 // FIXME(#11924) Behavior undecided for zero-length vectors.
 703                 TyArray(ty, _) => {
 704                     is_type_structurally_recursive(tcx, sp, seen, ty)
 705                 }
 706                 TyAdt(def, substs) => {
 707                     find_nonrepresentable(tcx,
 708                                           sp,
 709                                           seen,
 710                                           def.all_fields().map(|f| f.ty(tcx, substs)))
 711                 }
 712                 TyClosure(..) => {
 713                     // this check is run on type definitions, so we don't expect
 714                     // to see closure types
 715                     bug!("requires check invoked on inapplicable type: {:?}", ty)
 716                 }
 717                 _ => Representability::Representable,
 718             }
 719         }
 720
 721         fn same_struct_or_enum<'tcx>(ty: Ty<'tcx>, def: &'tcx ty::AdtDef) -> bool {
 722             match ty.sty {
 723                 TyAdt(ty_def, _) => {
 724                      ty_def == def
 725                 }
 726                 _ => false
 727             }
 728         }
 729
 730         fn same_type<'tcx>(a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
 731             match (&a.sty, &b.sty) {
 732                 (&TyAdt(did_a, substs_a), &TyAdt(did_b, substs_b)) => {
 733                     if did_a != did_b {
 734                         return false;
 735                     }
 736
 737                     substs_a.types().zip(substs_b.types()).all(|(a, b)| same_type(a, b))
 738                 }
 739                 _ => a == b,
 740             }
 741         }
 742
 743         // Does the type `ty` directly (without indirection through a pointer)
 744         // contain any types on stack `seen`?
 745         fn is_type_structurally_recursive<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 746                                                     sp: Span,
 747                                                     seen: &mut Vec<Ty<'tcx>>,
 748                                                     ty: Ty<'tcx>) -> Representability {
 749             debug!("is_type_structurally_recursive: {:?}", ty);
 750
 751             match ty.sty {
 752                 TyAdt(def, _) => {
 753                     {
 754                         // Iterate through stack of previously seen types.
 755                         let mut iter = seen.iter();
 756
 757                         // The first item in `seen` is the type we are actually curious about.
 758                         // We want to return SelfRecursive if this type contains itself.
 759                         // It is important that we DON'T take generic parameters into account
 760                         // for this check, so that Bar<T> in this example counts as SelfRecursive:
 761                         //
 762                         // struct Foo;
 763                         // struct Bar<T> { x: Bar<Foo> }
 764
 765                         if let Some(&seen_type) = iter.next() {
 766                             if same_struct_or_enum(seen_type, def) {
 767                                 debug!("SelfRecursive: {:?} contains {:?}",
 768                                        seen_type,
 769                                        ty);
 770                                 return Representability::SelfRecursive;
 771                             }
 772                         }
 773
 774                         // We also need to know whether the first item contains other types
 775                         // that are structurally recursive. If we don't catch this case, we
 776                         // will recurse infinitely for some inputs.
 777                         //
 778                         // It is important that we DO take generic parameters into account
 779                         // here, so that code like this is considered SelfRecursive, not
 780                         // ContainsRecursive:
 781                         //
 782                         // struct Foo { Option<Option<Foo>> }
 783
 784                         for &seen_type in iter {
 785                             if same_type(ty, seen_type) {
 786                                 debug!("ContainsRecursive: {:?} contains {:?}",
 787                                        seen_type,
 788                                        ty);
 789                                 return Representability::ContainsRecursive;
 790                             }
 791                         }
 792                     }
 793
 794                     // For structs and enums, track all previously seen types by pushing them
 795                     // onto the 'seen' stack.
 796                     seen.push(ty);
 797                     let out = are_inner_types_recursive(tcx, sp, seen, ty);
 798                     seen.pop();
 799                     out
 800                 }
 801                 _ => {
 802                     // No need to push in other cases.
 803                     are_inner_types_recursive(tcx, sp, seen, ty)
 804                 }
 805             }
 806         }
 807
 808         debug!("is_type_representable: {:?}", self);
 809
 810         // To avoid a stack overflow when checking an enum variant or struct that
 811         // contains a different, structurally recursive type, maintain a stack
 812         // of seen types and check recursion for each of them (issues #3008, #3779).
 813         let mut seen: Vec<Ty> = Vec::new();
 814         let r = is_type_structurally_recursive(tcx, sp, &mut seen, self);
 815         debug!("is_type_representable: {:?} is {:?}", self, r);
 816         r
 817     }
 818 }