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