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 ich::{StableHashingContext, NodeIdHashingMode};
  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                                            HashStable};
  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, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
 191     /// Creates a hash of the type `Ty` which will be the same no matter what crate
 192     /// context it's calculated within. This is used by the `type_id` intrinsic.
 193     pub fn type_id_hash(self, ty: Ty<'tcx>) -> u64 {
 194         let mut hasher = StableHasher::new();
 195         let mut hcx = StableHashingContext::new(self);
 196
 197         hcx.while_hashing_spans(false, |hcx| {
 198             hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
 199                 ty.hash_stable(hcx, &mut hasher);
 200             });
 201         });
 202         hasher.finish()
 203     }
 204 }
 205
 206 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 207     pub fn has_error_field(self, ty: Ty<'tcx>) -> bool {
 208         match ty.sty {
 209             ty::TyAdt(def, substs) => {
 210                 for field in def.all_fields() {
 211                     let field_ty = field.ty(self, substs);
 212                     if let TyError = field_ty.sty {
 213                         return true;
 214                     }
 215                 }
 216             }
 217             _ => (),
 218         }
 219         false
 220     }
 221
 222     /// Returns the type of element at index `i` in tuple or tuple-like type `t`.
 223     /// For an enum `t`, `variant` is None only if `t` is a univariant enum.
 224     pub fn positional_element_ty(self,
 225                                  ty: Ty<'tcx>,
 226                                  i: usize,
 227                                  variant: Option<DefId>) -> Option<Ty<'tcx>> {
 228         match (&ty.sty, variant) {
 229             (&TyAdt(adt, substs), Some(vid)) => {
 230                 adt.variant_with_id(vid).fields.get(i).map(|f| f.ty(self, substs))
 231             }
 232             (&TyAdt(adt, substs), None) => {
 233                 // Don't use `struct_variant`, this may be a univariant enum.
 234                 adt.variants[0].fields.get(i).map(|f| f.ty(self, substs))
 235             }
 236             (&TyTuple(ref v, _), None) => v.get(i).cloned(),
 237             _ => None,
 238         }
 239     }
 240
 241     /// Returns the type of element at field `n` in struct or struct-like type `t`.
 242     /// For an enum `t`, `variant` must be some def id.
 243     pub fn named_element_ty(self,
 244                             ty: Ty<'tcx>,
 245                             n: Name,
 246                             variant: Option<DefId>) -> Option<Ty<'tcx>> {
 247         match (&ty.sty, variant) {
 248             (&TyAdt(adt, substs), Some(vid)) => {
 249                 adt.variant_with_id(vid).find_field_named(n).map(|f| f.ty(self, substs))
 250             }
 251             (&TyAdt(adt, substs), None) => {
 252                 adt.struct_variant().find_field_named(n).map(|f| f.ty(self, substs))
 253             }
 254             _ => return None
 255         }
 256     }
 257
 258     /// Returns the deeply last field of nested structures, or the same type,
 259     /// if not a structure at all. Corresponds to the only possible unsized
 260     /// field, and its type can be used to determine unsizing strategy.
 261     pub fn struct_tail(self, mut ty: Ty<'tcx>) -> Ty<'tcx> {
 262         while let TyAdt(def, substs) = ty.sty {
 263             if !def.is_struct() {
 264                 break;
 265             }
 266             match def.struct_variant().fields.last() {
 267                 Some(f) => ty = f.ty(self, substs),
 268                 None => break,
 269             }
 270         }
 271         ty
 272     }
 273
 274     /// Same as applying struct_tail on `source` and `target`, but only
 275     /// keeps going as long as the two types are instances of the same
 276     /// structure definitions.
 277     /// For `(Foo<Foo<T>>, Foo<Trait>)`, the result will be `(Foo<T>, Trait)`,
 278     /// whereas struct_tail produces `T`, and `Trait`, respectively.
 279     pub fn struct_lockstep_tails(self,
 280                                  source: Ty<'tcx>,
 281                                  target: Ty<'tcx>)
 282                                  -> (Ty<'tcx>, Ty<'tcx>) {
 283         let (mut a, mut b) = (source, target);
 284         while let (&TyAdt(a_def, a_substs), &TyAdt(b_def, b_substs)) = (&a.sty, &b.sty) {
 285             if a_def != b_def || !a_def.is_struct() {
 286                 break;
 287             }
 288             match a_def.struct_variant().fields.last() {
 289                 Some(f) => {
 290                     a = f.ty(self, a_substs);
 291                     b = f.ty(self, b_substs);
 292                 }
 293                 _ => break,
 294             }
 295         }
 296         (a, b)
 297     }
 298
 299     /// Given a set of predicates that apply to an object type, returns
 300     /// the region bounds that the (erased) `Self` type must
 301     /// outlive. Precisely *because* the `Self` type is erased, the
 302     /// parameter `erased_self_ty` must be supplied to indicate what type
 303     /// has been used to represent `Self` in the predicates
 304     /// themselves. This should really be a unique type; `FreshTy(0)` is a
 305     /// popular choice.
 306     ///
 307     /// NB: in some cases, particularly around higher-ranked bounds,
 308     /// this function returns a kind of conservative approximation.
 309     /// That is, all regions returned by this function are definitely
 310     /// required, but there may be other region bounds that are not
 311     /// returned, as well as requirements like `for<'a> T: 'a`.
 312     ///
 313     /// Requires that trait definitions have been processed so that we can
 314     /// elaborate predicates and walk supertraits.
 315     pub fn required_region_bounds(self,
 316                                   erased_self_ty: Ty<'tcx>,
 317                                   predicates: Vec<ty::Predicate<'tcx>>)
 318                                   -> Vec<&'tcx ty::Region>    {
 319         debug!("required_region_bounds(erased_self_ty={:?}, predicates={:?})",
 320                erased_self_ty,
 321                predicates);
 322
 323         assert!(!erased_self_ty.has_escaping_regions());
 324
 325         traits::elaborate_predicates(self, predicates)
 326             .filter_map(|predicate| {
 327                 match predicate {
 328                     ty::Predicate::Projection(..) |
 329                     ty::Predicate::Trait(..) |
 330                     ty::Predicate::Equate(..) |
 331                     ty::Predicate::Subtype(..) |
 332                     ty::Predicate::WellFormed(..) |
 333                     ty::Predicate::ObjectSafe(..) |
 334                     ty::Predicate::ClosureKind(..) |
 335                     ty::Predicate::RegionOutlives(..) => {
 336                         None
 337                     }
 338                     ty::Predicate::TypeOutlives(ty::Binder(ty::OutlivesPredicate(t, r))) => {
 339                         // Search for a bound of the form `erased_self_ty
 340                         // : 'a`, but be wary of something like `for<'a>
 341                         // erased_self_ty : 'a` (we interpret a
 342                         // higher-ranked bound like that as 'static,
 343                         // though at present the code in `fulfill.rs`
 344                         // considers such bounds to be unsatisfiable, so
 345                         // it's kind of a moot point since you could never
 346                         // construct such an object, but this seems
 347                         // correct even if that code changes).
 348                         if t == erased_self_ty && !r.has_escaping_regions() {
 349                             Some(r)
 350                         } else {
 351                             None
 352                         }
 353                     }
 354                 }
 355             })
 356             .collect()
 357     }
 358
 359     /// Calculate the destructor of a given type.
 360     pub fn calculate_dtor(
 361         self,
 362         adt_did: DefId,
 363         validate: &mut FnMut(Self, DefId) -> Result<(), ErrorReported>
 364     ) -> Option<ty::Destructor> {
 365         let drop_trait = if let Some(def_id) = self.lang_items.drop_trait() {
 366             def_id
 367         } else {
 368             return None;
 369         };
 370
 371         ty::queries::coherent_trait::get(self, DUMMY_SP, (LOCAL_CRATE, drop_trait));
 372
 373         let mut dtor_did = None;
 374         let ty = self.item_type(adt_did);
 375         self.lookup_trait_def(drop_trait).for_each_relevant_impl(self, ty, |impl_did| {
 376             if let Some(item) = self.associated_items(impl_did).next() {
 377                 if let Ok(()) = validate(self, impl_did) {
 378                     dtor_did = Some(item.def_id);
 379                 }
 380             }
 381         });
 382
 383         let dtor_did = match dtor_did {
 384             Some(dtor) => dtor,
 385             None => return None,
 386         };
 387
 388         // RFC 1238: if the destructor method is tagged with the
 389         // attribute `unsafe_destructor_blind_to_params`, then the
 390         // compiler is being instructed to *assume* that the
 391         // destructor will not access borrowed data,
 392         // even if such data is otherwise reachable.
 393         //
 394         // Such access can be in plain sight (e.g. dereferencing
 395         // `*foo.0` of `Foo<'a>(&'a u32)`) or indirectly hidden
 396         // (e.g. calling `foo.0.clone()` of `Foo<T:Clone>`).
 397         let is_dtorck = !self.has_attr(dtor_did, "unsafe_destructor_blind_to_params");
 398         Some(ty::Destructor { did: dtor_did, is_dtorck: is_dtorck })
 399     }
 400
 401     pub fn closure_base_def_id(&self, def_id: DefId) -> DefId {
 402         let mut def_id = def_id;
 403         while self.def_key(def_id).disambiguated_data.data == DefPathData::ClosureExpr {
 404             def_id = self.parent_def_id(def_id).unwrap_or_else(|| {
 405                 bug!("closure {:?} has no parent", def_id);
 406             });
 407         }
 408         def_id
 409     }
 410
 411     /// Given the def-id of some item that has no type parameters, make
 412     /// a suitable "empty substs" for it.
 413     pub fn empty_substs_for_def_id(self, item_def_id: DefId) -> &'tcx ty::Substs<'tcx> {
 414         ty::Substs::for_item(self, item_def_id,
 415                              |_, _| self.mk_region(ty::ReErased),
 416                              |_, _| {
 417             bug!("empty_substs_for_def_id: {:?} has type parameters", item_def_id)
 418         })
 419     }
 420 }
 421
 422 pub struct TypeIdHasher<'a, 'gcx: 'a+'tcx, 'tcx: 'a, W> {
 423     tcx: TyCtxt<'a, 'gcx, 'tcx>,
 424     state: StableHasher<W>,
 425 }
 426
 427 impl<'a, 'gcx, 'tcx, W> TypeIdHasher<'a, 'gcx, 'tcx, W>
 428     where W: StableHasherResult
 429 {
 430     pub fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Self {
 431         TypeIdHasher { tcx: tcx, state: StableHasher::new() }
 432     }
 433
 434     pub fn finish(self) -> W {
 435         self.state.finish()
 436     }
 437
 438     pub fn hash<T: Hash>(&mut self, x: T) {
 439         x.hash(&mut self.state);
 440     }
 441
 442     fn hash_discriminant_u8<T>(&mut self, x: &T) {
 443         let v = unsafe {
 444             intrinsics::discriminant_value(x)
 445         };
 446         let b = v as u8;
 447         assert_eq!(v, b as u64);
 448         self.hash(b)
 449     }
 450
 451     fn def_id(&mut self, did: DefId) {
 452         // Hash the DefPath corresponding to the DefId, which is independent
 453         // of compiler internal state. We already have a stable hash value of
 454         // all DefPaths available via tcx.def_path_hash(), so we just feed that
 455         // into the hasher.
 456         let hash = self.tcx.def_path_hash(did);
 457         self.hash(hash);
 458     }
 459 }
 460
 461 impl<'a, 'gcx, 'tcx, W> TypeVisitor<'tcx> for TypeIdHasher<'a, 'gcx, 'tcx, W>
 462     where W: StableHasherResult
 463 {
 464     fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
 465         // Distinguish between the Ty variants uniformly.
 466         self.hash_discriminant_u8(&ty.sty);
 467
 468         match ty.sty {
 469             TyInt(i) => self.hash(i),
 470             TyUint(u) => self.hash(u),
 471             TyFloat(f) => self.hash(f),
 472             TyArray(_, n) => self.hash(n),
 473             TyRawPtr(m) |
 474             TyRef(_, m) => self.hash(m.mutbl),
 475             TyClosure(def_id, _) |
 476             TyAnon(def_id, _) |
 477             TyFnDef(def_id, ..) => self.def_id(def_id),
 478             TyAdt(d, _) => self.def_id(d.did),
 479             TyFnPtr(f) => {
 480                 self.hash(f.unsafety());
 481                 self.hash(f.abi());
 482                 self.hash(f.variadic());
 483                 self.hash(f.inputs().skip_binder().len());
 484             }
 485             TyDynamic(ref data, ..) => {
 486                 if let Some(p) = data.principal() {
 487                     self.def_id(p.def_id());
 488                 }
 489                 for d in data.auto_traits() {
 490                     self.def_id(d);
 491                 }
 492             }
 493             TyTuple(tys, defaulted) => {
 494                 self.hash(tys.len());
 495                 self.hash(defaulted);
 496             }
 497             TyParam(p) => {
 498                 self.hash(p.idx);
 499                 self.hash(p.name.as_str());
 500             }
 501             TyProjection(ref data) => {
 502                 self.def_id(data.trait_ref.def_id);
 503                 self.hash(data.item_name.as_str());
 504             }
 505             TyNever |
 506             TyBool |
 507             TyChar |
 508             TyStr |
 509             TySlice(_) => {}
 510
 511             TyError |
 512             TyInfer(_) => bug!("TypeIdHasher: unexpected type {}", ty)
 513         }
 514
 515         ty.super_visit_with(self)
 516     }
 517
 518     fn visit_region(&mut self, r: &'tcx ty::Region) -> bool {
 519         self.hash_discriminant_u8(r);
 520         match *r {
 521             ty::ReErased |
 522             ty::ReStatic |
 523             ty::ReEmpty => {
 524                 // No variant fields to hash for these ...
 525             }
 526             ty::ReLateBound(db, ty::BrAnon(i)) => {
 527                 self.hash(db.depth);
 528                 self.hash(i);
 529             }
 530             ty::ReEarlyBound(ty::EarlyBoundRegion { index, name }) => {
 531                 self.hash(index);
 532                 self.hash(name.as_str());
 533             }
 534             ty::ReLateBound(..) |
 535             ty::ReFree(..) |
 536             ty::ReScope(..) |
 537             ty::ReVar(..) |
 538             ty::ReSkolemized(..) => {
 539                 bug!("TypeIdHasher: unexpected region {:?}", r)
 540             }
 541         }
 542         false
 543     }
 544
 545     fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, x: &ty::Binder<T>) -> bool {
 546         // Anonymize late-bound regions so that, for example:
 547         // `for<'a, b> fn(&'a &'b T)` and `for<'a, b> fn(&'b &'a T)`
 548         // result in the same TypeId (the two types are equivalent).
 549         self.tcx.anonymize_late_bound_regions(x).super_visit_with(self)
 550     }
 551 }
 552
 553 impl<'a, 'tcx> ty::TyS<'tcx> {
 554     fn impls_bound(&'tcx self, tcx: TyCtxt<'a, 'tcx, 'tcx>,
 555                    param_env: &ParameterEnvironment<'tcx>,
 556                    def_id: DefId,
 557                    cache: &RefCell<FxHashMap<Ty<'tcx>, bool>>,
 558                    span: Span) -> bool
 559     {
 560         if self.has_param_types() || self.has_self_ty() {
 561             if let Some(result) = cache.borrow().get(self) {
 562                 return *result;
 563             }
 564         }
 565         let result =
 566             tcx.infer_ctxt(param_env.clone(), Reveal::UserFacing)
 567             .enter(|infcx| {
 568                 traits::type_known_to_meet_bound(&infcx, self, def_id, span)
 569             });
 570         if self.has_param_types() || self.has_self_ty() {
 571             cache.borrow_mut().insert(self, result);
 572         }
 573         return result;
 574     }
 575
 576     // FIXME (@jroesch): I made this public to use it, not sure if should be private
 577     pub fn moves_by_default(&'tcx self, tcx: TyCtxt<'a, 'tcx, 'tcx>,
 578                             param_env: &ParameterEnvironment<'tcx>,
 579                             span: Span) -> bool {
 580         if self.flags.get().intersects(TypeFlags::MOVENESS_CACHED) {
 581             return self.flags.get().intersects(TypeFlags::MOVES_BY_DEFAULT);
 582         }
 583
 584         assert!(!self.needs_infer());
 585
 586         // Fast-path for primitive types
 587         let result = match self.sty {
 588             TyBool | TyChar | TyInt(..) | TyUint(..) | TyFloat(..) | TyNever |
 589             TyRawPtr(..) | TyFnDef(..) | TyFnPtr(_) | TyRef(_, TypeAndMut {
 590                 mutbl: hir::MutImmutable, ..
 591             }) => Some(false),
 592
 593             TyStr | TyRef(_, TypeAndMut {
 594                 mutbl: hir::MutMutable, ..
 595             }) => Some(true),
 596
 597             TyArray(..) | TySlice(..) | TyDynamic(..) | TyTuple(..) |
 598             TyClosure(..) | TyAdt(..) | TyAnon(..) |
 599             TyProjection(..) | TyParam(..) | TyInfer(..) | TyError => None
 600         }.unwrap_or_else(|| {
 601             !self.impls_bound(tcx, param_env,
 602                               tcx.require_lang_item(lang_items::CopyTraitLangItem),
 603                               &param_env.is_copy_cache, span) });
 604
 605         if !self.has_param_types() && !self.has_self_ty() {
 606             self.flags.set(self.flags.get() | if result {
 607                 TypeFlags::MOVENESS_CACHED | TypeFlags::MOVES_BY_DEFAULT
 608             } else {
 609                 TypeFlags::MOVENESS_CACHED
 610             });
 611         }
 612
 613         result
 614     }
 615
 616     #[inline]
 617     pub fn is_sized(&'tcx self, tcx: TyCtxt<'a, 'tcx, 'tcx>,
 618                     param_env: &ParameterEnvironment<'tcx>,
 619                     span: Span) -> bool
 620     {
 621         if self.flags.get().intersects(TypeFlags::SIZEDNESS_CACHED) {
 622             return self.flags.get().intersects(TypeFlags::IS_SIZED);
 623         }
 624
 625         self.is_sized_uncached(tcx, param_env, span)
 626     }
 627
 628     fn is_sized_uncached(&'tcx self, tcx: TyCtxt<'a, 'tcx, 'tcx>,
 629                          param_env: &ParameterEnvironment<'tcx>,
 630                          span: Span) -> bool {
 631         assert!(!self.needs_infer());
 632
 633         // Fast-path for primitive types
 634         let result = match self.sty {
 635             TyBool | TyChar | TyInt(..) | TyUint(..) | TyFloat(..) |
 636             TyRawPtr(..) | TyRef(..) | TyFnDef(..) | TyFnPtr(_) |
 637             TyArray(..) | TyTuple(..) | TyClosure(..) | TyNever => Some(true),
 638
 639             TyStr | TyDynamic(..) | TySlice(_) => Some(false),
 640
 641             TyAdt(..) | TyProjection(..) | TyParam(..) |
 642             TyInfer(..) | TyAnon(..) | TyError => None
 643         }.unwrap_or_else(|| {
 644             self.impls_bound(tcx, param_env, tcx.require_lang_item(lang_items::SizedTraitLangItem),
 645                               &param_env.is_sized_cache, span) });
 646
 647         if !self.has_param_types() && !self.has_self_ty() {
 648             self.flags.set(self.flags.get() | if result {
 649                 TypeFlags::SIZEDNESS_CACHED | TypeFlags::IS_SIZED
 650             } else {
 651                 TypeFlags::SIZEDNESS_CACHED
 652             });
 653         }
 654
 655         result
 656     }
 657
 658     #[inline]
 659     pub fn layout<'lcx>(&'tcx self, infcx: &InferCtxt<'a, 'tcx, 'lcx>)
 660                         -> Result<&'tcx Layout, LayoutError<'tcx>> {
 661         let tcx = infcx.tcx.global_tcx();
 662         let can_cache = !self.has_param_types() && !self.has_self_ty();
 663         if can_cache {
 664             if let Some(&cached) = tcx.layout_cache.borrow().get(&self) {
 665                 return Ok(cached);
 666             }
 667         }
 668
 669         let rec_limit = tcx.sess.recursion_limit.get();
 670         let depth = tcx.layout_depth.get();
 671         if depth > rec_limit {
 672             tcx.sess.fatal(
 673                 &format!("overflow representing the type `{}`", self));
 674         }
 675
 676         tcx.layout_depth.set(depth+1);
 677         let layout = Layout::compute_uncached(self, infcx);
 678         tcx.layout_depth.set(depth);
 679         let layout = layout?;
 680         if can_cache {
 681             tcx.layout_cache.borrow_mut().insert(self, layout);
 682         }
 683         Ok(layout)
 684     }
 685
 686
 687     /// Check whether a type is representable. This means it cannot contain unboxed
 688     /// structural recursion. This check is needed for structs and enums.
 689     pub fn is_representable(&'tcx self, tcx: TyCtxt<'a, 'tcx, 'tcx>, sp: Span)
 690                             -> Representability {
 691
 692         // Iterate until something non-representable is found
 693         fn find_nonrepresentable<'a, 'tcx, It>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 694                                                sp: Span,
 695                                                seen: &mut Vec<Ty<'tcx>>,
 696                                                iter: It)
 697                                                -> Representability
 698         where It: Iterator<Item=Ty<'tcx>> {
 699             iter.fold(Representability::Representable,
 700                       |r, ty| cmp::max(r, is_type_structurally_recursive(tcx, sp, seen, ty)))
 701         }
 702
 703         fn are_inner_types_recursive<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, sp: Span,
 704                                                seen: &mut Vec<Ty<'tcx>>, ty: Ty<'tcx>)
 705                                                -> Representability {
 706             match ty.sty {
 707                 TyTuple(ref ts, _) => {
 708                     find_nonrepresentable(tcx, sp, seen, ts.iter().cloned())
 709                 }
 710                 // Fixed-length vectors.
 711                 // FIXME(#11924) Behavior undecided for zero-length vectors.
 712                 TyArray(ty, _) => {
 713                     is_type_structurally_recursive(tcx, sp, seen, ty)
 714                 }
 715                 TyAdt(def, substs) => {
 716                     find_nonrepresentable(tcx,
 717                                           sp,
 718                                           seen,
 719                                           def.all_fields().map(|f| f.ty(tcx, substs)))
 720                 }
 721                 TyClosure(..) => {
 722                     // this check is run on type definitions, so we don't expect
 723                     // to see closure types
 724                     bug!("requires check invoked on inapplicable type: {:?}", ty)
 725                 }
 726                 _ => Representability::Representable,
 727             }
 728         }
 729
 730         fn same_struct_or_enum<'tcx>(ty: Ty<'tcx>, def: &'tcx ty::AdtDef) -> bool {
 731             match ty.sty {
 732                 TyAdt(ty_def, _) => {
 733                      ty_def == def
 734                 }
 735                 _ => false
 736             }
 737         }
 738
 739         fn same_type<'tcx>(a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
 740             match (&a.sty, &b.sty) {
 741                 (&TyAdt(did_a, substs_a), &TyAdt(did_b, substs_b)) => {
 742                     if did_a != did_b {
 743                         return false;
 744                     }
 745
 746                     substs_a.types().zip(substs_b.types()).all(|(a, b)| same_type(a, b))
 747                 }
 748                 _ => a == b,
 749             }
 750         }
 751
 752         // Does the type `ty` directly (without indirection through a pointer)
 753         // contain any types on stack `seen`?
 754         fn is_type_structurally_recursive<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 755                                                     sp: Span,
 756                                                     seen: &mut Vec<Ty<'tcx>>,
 757                                                     ty: Ty<'tcx>) -> Representability {
 758             debug!("is_type_structurally_recursive: {:?}", ty);
 759
 760             match ty.sty {
 761                 TyAdt(def, _) => {
 762                     {
 763                         // Iterate through stack of previously seen types.
 764                         let mut iter = seen.iter();
 765
 766                         // The first item in `seen` is the type we are actually curious about.
 767                         // We want to return SelfRecursive if this type contains itself.
 768                         // It is important that we DON'T take generic parameters into account
 769                         // for this check, so that Bar<T> in this example counts as SelfRecursive:
 770                         //
 771                         // struct Foo;
 772                         // struct Bar<T> { x: Bar<Foo> }
 773
 774                         if let Some(&seen_type) = iter.next() {
 775                             if same_struct_or_enum(seen_type, def) {
 776                                 debug!("SelfRecursive: {:?} contains {:?}",
 777                                        seen_type,
 778                                        ty);
 779                                 return Representability::SelfRecursive;
 780                             }
 781                         }
 782
 783                         // We also need to know whether the first item contains other types
 784                         // that are structurally recursive. If we don't catch this case, we
 785                         // will recurse infinitely for some inputs.
 786                         //
 787                         // It is important that we DO take generic parameters into account
 788                         // here, so that code like this is considered SelfRecursive, not
 789                         // ContainsRecursive:
 790                         //
 791                         // struct Foo { Option<Option<Foo>> }
 792
 793                         for &seen_type in iter {
 794                             if same_type(ty, seen_type) {
 795                                 debug!("ContainsRecursive: {:?} contains {:?}",
 796                                        seen_type,
 797                                        ty);
 798                                 return Representability::ContainsRecursive;
 799                             }
 800                         }
 801                     }
 802
 803                     // For structs and enums, track all previously seen types by pushing them
 804                     // onto the 'seen' stack.
 805                     seen.push(ty);
 806                     let out = are_inner_types_recursive(tcx, sp, seen, ty);
 807                     seen.pop();
 808                     out
 809                 }
 810                 _ => {
 811                     // No need to push in other cases.
 812                     are_inner_types_recursive(tcx, sp, seen, ty)
 813                 }
 814             }
 815         }
 816
 817         debug!("is_type_representable: {:?}", self);
 818
 819         // To avoid a stack overflow when checking an enum variant or struct that
 820         // contains a different, structurally recursive type, maintain a stack
 821         // of seen types and check recursion for each of them (issues #3008, #3779).
 822         let mut seen: Vec<Ty> = Vec::new();
 823         let r = is_type_structurally_recursive(tcx, sp, &mut seen, self);
 824         debug!("is_type_representable: {:?} is {:?}", self, r);
 825         r
 826     }
 827 }