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