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