src/librustc/traits/util.rs

   1 // Copyright 2014 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 use hir::def_id::DefId;
  12 use ty::subst::{Kind, Subst, Substs};
  13 use ty::{self, Ty, TyCtxt, ToPredicate, ToPolyTraitRef};
  14 use ty::outlives::Component;
  15 use util::nodemap::FxHashSet;
  16 use hir::{self};
  17 use traits::specialize::specialization_graph::NodeItem;
  18
  19 use super::{Obligation, ObligationCause, PredicateObligation, SelectionContext, Normalized};
  20
  21 fn anonymize_predicate<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
  22                                        pred: &ty::Predicate<'tcx>)
  23                                        -> ty::Predicate<'tcx> {
  24     match *pred {
  25         ty::Predicate::Trait(ref data) =>
  26             ty::Predicate::Trait(tcx.anonymize_late_bound_regions(data)),
  27
  28         ty::Predicate::RegionOutlives(ref data) =>
  29             ty::Predicate::RegionOutlives(tcx.anonymize_late_bound_regions(data)),
  30
  31         ty::Predicate::TypeOutlives(ref data) =>
  32             ty::Predicate::TypeOutlives(tcx.anonymize_late_bound_regions(data)),
  33
  34         ty::Predicate::Projection(ref data) =>
  35             ty::Predicate::Projection(tcx.anonymize_late_bound_regions(data)),
  36
  37         ty::Predicate::WellFormed(data) =>
  38             ty::Predicate::WellFormed(data),
  39
  40         ty::Predicate::ObjectSafe(data) =>
  41             ty::Predicate::ObjectSafe(data),
  42
  43         ty::Predicate::ClosureKind(closure_def_id, closure_substs, kind) =>
  44             ty::Predicate::ClosureKind(closure_def_id, closure_substs, kind),
  45
  46         ty::Predicate::Subtype(ref data) =>
  47             ty::Predicate::Subtype(tcx.anonymize_late_bound_regions(data)),
  48
  49         ty::Predicate::ConstEvaluatable(def_id, substs) =>
  50             ty::Predicate::ConstEvaluatable(def_id, substs),
  51     }
  52 }
  53
  54
  55 struct PredicateSet<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
  56     tcx: TyCtxt<'a, 'gcx, 'tcx>,
  57     set: FxHashSet<ty::Predicate<'tcx>>,
  58 }
  59
  60 impl<'a, 'gcx, 'tcx> PredicateSet<'a, 'gcx, 'tcx> {
  61     fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> PredicateSet<'a, 'gcx, 'tcx> {
  62         PredicateSet { tcx: tcx, set: FxHashSet() }
  63     }
  64
  65     fn insert(&mut self, pred: &ty::Predicate<'tcx>) -> bool {
  66         // We have to be careful here because we want
  67         //
  68         //    for<'a> Foo<&'a int>
  69         //
  70         // and
  71         //
  72         //    for<'b> Foo<&'b int>
  73         //
  74         // to be considered equivalent. So normalize all late-bound
  75         // regions before we throw things into the underlying set.
  76         self.set.insert(anonymize_predicate(self.tcx, pred))
  77     }
  78 }
  79
  80 ///////////////////////////////////////////////////////////////////////////
  81 // `Elaboration` iterator
  82 ///////////////////////////////////////////////////////////////////////////
  83
  84 /// "Elaboration" is the process of identifying all the predicates that
  85 /// are implied by a source predicate. Currently this basically means
  86 /// walking the "supertraits" and other similar assumptions. For
  87 /// example, if we know that `T : Ord`, the elaborator would deduce
  88 /// that `T : PartialOrd` holds as well. Similarly, if we have `trait
  89 /// Foo : 'static`, and we know that `T : Foo`, then we know that `T :
  90 /// 'static`.
  91 pub struct Elaborator<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
  92     stack: Vec<ty::Predicate<'tcx>>,
  93     visited: PredicateSet<'a, 'gcx, 'tcx>,
  94 }
  95
  96 pub fn elaborate_trait_ref<'cx, 'gcx, 'tcx>(
  97     tcx: TyCtxt<'cx, 'gcx, 'tcx>,
  98     trait_ref: ty::PolyTraitRef<'tcx>)
  99     -> Elaborator<'cx, 'gcx, 'tcx>
 100 {
 101     elaborate_predicates(tcx, vec![trait_ref.to_predicate()])
 102 }
 103
 104 pub fn elaborate_trait_refs<'cx, 'gcx, 'tcx>(
 105     tcx: TyCtxt<'cx, 'gcx, 'tcx>,
 106     trait_refs: &[ty::PolyTraitRef<'tcx>])
 107     -> Elaborator<'cx, 'gcx, 'tcx>
 108 {
 109     let predicates = trait_refs.iter()
 110                                .map(|trait_ref| trait_ref.to_predicate())
 111                                .collect();
 112     elaborate_predicates(tcx, predicates)
 113 }
 114
 115 pub fn elaborate_predicates<'cx, 'gcx, 'tcx>(
 116     tcx: TyCtxt<'cx, 'gcx, 'tcx>,
 117     mut predicates: Vec<ty::Predicate<'tcx>>)
 118     -> Elaborator<'cx, 'gcx, 'tcx>
 119 {
 120     let mut visited = PredicateSet::new(tcx);
 121     predicates.retain(|pred| visited.insert(pred));
 122     Elaborator { stack: predicates, visited: visited }
 123 }
 124
 125 impl<'cx, 'gcx, 'tcx> Elaborator<'cx, 'gcx, 'tcx> {
 126     pub fn filter_to_traits(self) -> FilterToTraits<Self> {
 127         FilterToTraits::new(self)
 128     }
 129
 130     fn push(&mut self, predicate: &ty::Predicate<'tcx>) {
 131         let tcx = self.visited.tcx;
 132         match *predicate {
 133             ty::Predicate::Trait(ref data) => {
 134                 // Predicates declared on the trait.
 135                 let predicates = tcx.super_predicates_of(data.def_id());
 136
 137                 let mut predicates: Vec<_> =
 138                     predicates.predicates
 139                               .iter()
 140                               .map(|p| p.subst_supertrait(tcx, &data.to_poly_trait_ref()))
 141                               .collect();
 142
 143                 debug!("super_predicates: data={:?} predicates={:?}",
 144                        data, predicates);
 145
 146                 // Only keep those bounds that we haven't already
 147                 // seen.  This is necessary to prevent infinite
 148                 // recursion in some cases.  One common case is when
 149                 // people define `trait Sized: Sized { }` rather than `trait
 150                 // Sized { }`.
 151                 predicates.retain(|r| self.visited.insert(r));
 152
 153                 self.stack.extend(predicates);
 154             }
 155             ty::Predicate::WellFormed(..) => {
 156                 // Currently, we do not elaborate WF predicates,
 157                 // although we easily could.
 158             }
 159             ty::Predicate::ObjectSafe(..) => {
 160                 // Currently, we do not elaborate object-safe
 161                 // predicates.
 162             }
 163             ty::Predicate::Subtype(..) => {
 164                 // Currently, we do not "elaborate" predicates like `X
 165                 // <: Y`, though conceivably we might.
 166             }
 167             ty::Predicate::Projection(..) => {
 168                 // Nothing to elaborate in a projection predicate.
 169             }
 170             ty::Predicate::ClosureKind(..) => {
 171                 // Nothing to elaborate when waiting for a closure's kind to be inferred.
 172             }
 173             ty::Predicate::ConstEvaluatable(..) => {
 174                 // Currently, we do not elaborate const-evaluatable
 175                 // predicates.
 176             }
 177
 178             ty::Predicate::RegionOutlives(..) => {
 179                 // Nothing to elaborate from `'a: 'b`.
 180             }
 181
 182             ty::Predicate::TypeOutlives(ref data) => {
 183                 // We know that `T: 'a` for some type `T`. We can
 184                 // often elaborate this. For example, if we know that
 185                 // `[U]: 'a`, that implies that `U: 'a`. Similarly, if
 186                 // we know `&'a U: 'b`, then we know that `'a: 'b` and
 187                 // `U: 'b`.
 188                 //
 189                 // We can basically ignore bound regions here. So for
 190                 // example `for<'c> Foo<'a,'c>: 'b` can be elaborated to
 191                 // `'a: 'b`.
 192
 193                 // Ignore `for<'a> T: 'a` -- we might in the future
 194                 // consider this as evidence that `T: 'static`, but
 195                 // I'm a bit wary of such constructions and so for now
 196                 // I want to be conservative. --nmatsakis
 197                 let ty_max = data.skip_binder().0;
 198                 let r_min = data.skip_binder().1;
 199                 if r_min.is_late_bound() {
 200                     return;
 201                 }
 202
 203                 let visited = &mut self.visited;
 204                 self.stack.extend(
 205                     tcx.outlives_components(ty_max)
 206                        .into_iter()
 207                        .filter_map(|component| match component {
 208                            Component::Region(r) => if r.is_late_bound() {
 209                                None
 210                            } else {
 211                                Some(ty::Predicate::RegionOutlives(
 212                                    ty::Binder::dummy(ty::OutlivesPredicate(r, r_min))))
 213                            },
 214
 215                            Component::Param(p) => {
 216                                let ty = tcx.mk_ty_param(p.idx, p.name);
 217                                Some(ty::Predicate::TypeOutlives(
 218                                    ty::Binder::dummy(ty::OutlivesPredicate(ty, r_min))))
 219                            },
 220
 221                            Component::UnresolvedInferenceVariable(_) => {
 222                                None
 223                            },
 224
 225                            Component::Projection(_) |
 226                            Component::EscapingProjection(_) => {
 227                                // We can probably do more here. This
 228                                // corresponds to a case like `<T as
 229                                // Foo<'a>>::U: 'b`.
 230                                None
 231                            },
 232                        })
 233                        .filter(|p| visited.insert(p)));
 234             }
 235         }
 236     }
 237 }
 238
 239 impl<'cx, 'gcx, 'tcx> Iterator for Elaborator<'cx, 'gcx, 'tcx> {
 240     type Item = ty::Predicate<'tcx>;
 241
 242     fn next(&mut self) -> Option<ty::Predicate<'tcx>> {
 243         // Extract next item from top-most stack frame, if any.
 244         let next_predicate = match self.stack.pop() {
 245             Some(predicate) => predicate,
 246             None => {
 247                 // No more stack frames. Done.
 248                 return None;
 249             }
 250         };
 251         self.push(&next_predicate);
 252         return Some(next_predicate);
 253     }
 254 }
 255
 256 ///////////////////////////////////////////////////////////////////////////
 257 // Supertrait iterator
 258 ///////////////////////////////////////////////////////////////////////////
 259
 260 pub type Supertraits<'cx, 'gcx, 'tcx> = FilterToTraits<Elaborator<'cx, 'gcx, 'tcx>>;
 261
 262 pub fn supertraits<'cx, 'gcx, 'tcx>(tcx: TyCtxt<'cx, 'gcx, 'tcx>,
 263                                     trait_ref: ty::PolyTraitRef<'tcx>)
 264                                     -> Supertraits<'cx, 'gcx, 'tcx>
 265 {
 266     elaborate_trait_ref(tcx, trait_ref).filter_to_traits()
 267 }
 268
 269 pub fn transitive_bounds<'cx, 'gcx, 'tcx>(tcx: TyCtxt<'cx, 'gcx, 'tcx>,
 270                                           bounds: &[ty::PolyTraitRef<'tcx>])
 271                                           -> Supertraits<'cx, 'gcx, 'tcx>
 272 {
 273     elaborate_trait_refs(tcx, bounds).filter_to_traits()
 274 }
 275
 276 ///////////////////////////////////////////////////////////////////////////
 277 // Iterator over def-ids of supertraits
 278
 279 pub struct SupertraitDefIds<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
 280     tcx: TyCtxt<'a, 'gcx, 'tcx>,
 281     stack: Vec<DefId>,
 282     visited: FxHashSet<DefId>,
 283 }
 284
 285 pub fn supertrait_def_ids<'cx, 'gcx, 'tcx>(tcx: TyCtxt<'cx, 'gcx, 'tcx>,
 286                                            trait_def_id: DefId)
 287                                            -> SupertraitDefIds<'cx, 'gcx, 'tcx>
 288 {
 289     SupertraitDefIds {
 290         tcx,
 291         stack: vec![trait_def_id],
 292         visited: Some(trait_def_id).into_iter().collect(),
 293     }
 294 }
 295
 296 impl<'cx, 'gcx, 'tcx> Iterator for SupertraitDefIds<'cx, 'gcx, 'tcx> {
 297     type Item = DefId;
 298
 299     fn next(&mut self) -> Option<DefId> {
 300         let def_id = match self.stack.pop() {
 301             Some(def_id) => def_id,
 302             None => { return None; }
 303         };
 304
 305         let predicates = self.tcx.super_predicates_of(def_id);
 306         let visited = &mut self.visited;
 307         self.stack.extend(
 308             predicates.predicates
 309                       .iter()
 310                       .filter_map(|p| p.to_opt_poly_trait_ref())
 311                       .map(|t| t.def_id())
 312                       .filter(|&super_def_id| visited.insert(super_def_id)));
 313         Some(def_id)
 314     }
 315 }
 316
 317 ///////////////////////////////////////////////////////////////////////////
 318 // Other
 319 ///////////////////////////////////////////////////////////////////////////
 320
 321 /// A filter around an iterator of predicates that makes it yield up
 322 /// just trait references.
 323 pub struct FilterToTraits<I> {
 324     base_iterator: I
 325 }
 326
 327 impl<I> FilterToTraits<I> {
 328     fn new(base: I) -> FilterToTraits<I> {
 329         FilterToTraits { base_iterator: base }
 330     }
 331 }
 332
 333 impl<'tcx,I:Iterator<Item=ty::Predicate<'tcx>>> Iterator for FilterToTraits<I> {
 334     type Item = ty::PolyTraitRef<'tcx>;
 335
 336     fn next(&mut self) -> Option<ty::PolyTraitRef<'tcx>> {
 337         loop {
 338             match self.base_iterator.next() {
 339                 None => {
 340                     return None;
 341                 }
 342                 Some(ty::Predicate::Trait(data)) => {
 343                     return Some(data.to_poly_trait_ref());
 344                 }
 345                 Some(_) => {
 346                 }
 347             }
 348         }
 349     }
 350
 351     fn size_hint(&self) -> (usize, Option<usize>) {
 352         let (_, upper) = self.base_iterator.size_hint();
 353         (0, upper)
 354     }
 355 }
 356
 357 ///////////////////////////////////////////////////////////////////////////
 358 // Other
 359 ///////////////////////////////////////////////////////////////////////////
 360
 361 /// Instantiate all bound parameters of the impl with the given substs,
 362 /// returning the resulting trait ref and all obligations that arise.
 363 /// The obligations are closed under normalization.
 364 pub fn impl_trait_ref_and_oblig<'a, 'gcx, 'tcx>(selcx: &mut SelectionContext<'a, 'gcx, 'tcx>,
 365                                                 param_env: ty::ParamEnv<'tcx>,
 366                                                 impl_def_id: DefId,
 367                                                 impl_substs: &Substs<'tcx>)
 368                                                 -> (ty::TraitRef<'tcx>,
 369                                                     Vec<PredicateObligation<'tcx>>)
 370 {
 371     let impl_trait_ref =
 372         selcx.tcx().impl_trait_ref(impl_def_id).unwrap();
 373     let impl_trait_ref =
 374         impl_trait_ref.subst(selcx.tcx(), impl_substs);
 375     let Normalized { value: impl_trait_ref, obligations: normalization_obligations1 } =
 376         super::normalize(selcx, param_env, ObligationCause::dummy(), &impl_trait_ref);
 377
 378     let predicates = selcx.tcx().predicates_of(impl_def_id);
 379     let predicates = predicates.instantiate(selcx.tcx(), impl_substs);
 380     let Normalized { value: predicates, obligations: normalization_obligations2 } =
 381         super::normalize(selcx, param_env, ObligationCause::dummy(), &predicates);
 382     let impl_obligations =
 383         predicates_for_generics(ObligationCause::dummy(), 0, param_env, &predicates);
 384
 385     let impl_obligations: Vec<_> =
 386         impl_obligations.into_iter()
 387         .chain(normalization_obligations1)
 388         .chain(normalization_obligations2)
 389         .collect();
 390
 391     (impl_trait_ref, impl_obligations)
 392 }
 393
 394 /// See `super::obligations_for_generics`
 395 pub fn predicates_for_generics<'tcx>(cause: ObligationCause<'tcx>,
 396                                      recursion_depth: usize,
 397                                      param_env: ty::ParamEnv<'tcx>,
 398                                      generic_bounds: &ty::InstantiatedPredicates<'tcx>)
 399                                      -> Vec<PredicateObligation<'tcx>>
 400 {
 401     debug!("predicates_for_generics(generic_bounds={:?})",
 402            generic_bounds);
 403
 404     generic_bounds.predicates.iter().map(|predicate| {
 405         Obligation { cause: cause.clone(),
 406                      recursion_depth,
 407                      param_env,
 408                      predicate: predicate.clone() }
 409     }).collect()
 410 }
 411
 412 pub fn predicate_for_trait_ref<'tcx>(
 413     cause: ObligationCause<'tcx>,
 414     param_env: ty::ParamEnv<'tcx>,
 415     trait_ref: ty::TraitRef<'tcx>,
 416     recursion_depth: usize)
 417     -> PredicateObligation<'tcx>
 418 {
 419     Obligation {
 420         cause,
 421         param_env,
 422         recursion_depth,
 423         predicate: trait_ref.to_predicate(),
 424     }
 425 }
 426
 427 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 428     pub fn predicate_for_trait_def(self,
 429                                    param_env: ty::ParamEnv<'tcx>,
 430                                    cause: ObligationCause<'tcx>,
 431                                    trait_def_id: DefId,
 432                                    recursion_depth: usize,
 433                                    self_ty: Ty<'tcx>,
 434                                    params: &[Kind<'tcx>])
 435         -> PredicateObligation<'tcx>
 436     {
 437         let trait_ref = ty::TraitRef {
 438             def_id: trait_def_id,
 439             substs: self.mk_substs_trait(self_ty, params)
 440         };
 441         predicate_for_trait_ref(cause, param_env, trait_ref, recursion_depth)
 442     }
 443
 444     /// Cast a trait reference into a reference to one of its super
 445     /// traits; returns `None` if `target_trait_def_id` is not a
 446     /// supertrait.
 447     pub fn upcast_choices(self,
 448                           source_trait_ref: ty::PolyTraitRef<'tcx>,
 449                           target_trait_def_id: DefId)
 450                           -> Vec<ty::PolyTraitRef<'tcx>>
 451     {
 452         if source_trait_ref.def_id() == target_trait_def_id {
 453             return vec![source_trait_ref]; // shorcut the most common case
 454         }
 455
 456         supertraits(self, source_trait_ref)
 457             .filter(|r| r.def_id() == target_trait_def_id)
 458             .collect()
 459     }
 460
 461     /// Given a trait `trait_ref`, returns the number of vtable entries
 462     /// that come from `trait_ref`, excluding its supertraits. Used in
 463     /// computing the vtable base for an upcast trait of a trait object.
 464     pub fn count_own_vtable_entries(self, trait_ref: ty::PolyTraitRef<'tcx>) -> usize {
 465         let mut entries = 0;
 466         // Count number of methods and add them to the total offset.
 467         // Skip over associated types and constants.
 468         for trait_item in self.associated_items(trait_ref.def_id()) {
 469             if trait_item.kind == ty::AssociatedKind::Method {
 470                 entries += 1;
 471             }
 472         }
 473         entries
 474     }
 475
 476     /// Given an upcast trait object described by `object`, returns the
 477     /// index of the method `method_def_id` (which should be part of
 478     /// `object.upcast_trait_ref`) within the vtable for `object`.
 479     pub fn get_vtable_index_of_object_method<N>(self,
 480                                                 object: &super::VtableObjectData<'tcx, N>,
 481                                                 method_def_id: DefId) -> usize {
 482         // Count number of methods preceding the one we are selecting and
 483         // add them to the total offset.
 484         // Skip over associated types and constants.
 485         let mut entries = object.vtable_base;
 486         for trait_item in self.associated_items(object.upcast_trait_ref.def_id()) {
 487             if trait_item.def_id == method_def_id {
 488                 // The item with the ID we were given really ought to be a method.
 489                 assert_eq!(trait_item.kind, ty::AssociatedKind::Method);
 490                 return entries;
 491             }
 492             if trait_item.kind == ty::AssociatedKind::Method {
 493                 entries += 1;
 494             }
 495         }
 496
 497         bug!("get_vtable_index_of_object_method: {:?} was not found",
 498              method_def_id);
 499     }
 500
 501     pub fn closure_trait_ref_and_return_type(self,
 502         fn_trait_def_id: DefId,
 503         self_ty: Ty<'tcx>,
 504         sig: ty::PolyFnSig<'tcx>,
 505         tuple_arguments: TupleArgumentsFlag)
 506         -> ty::Binder<(ty::TraitRef<'tcx>, Ty<'tcx>)>
 507     {
 508         let arguments_tuple = match tuple_arguments {
 509             TupleArgumentsFlag::No => sig.skip_binder().inputs()[0],
 510             TupleArgumentsFlag::Yes =>
 511                 self.intern_tup(sig.skip_binder().inputs()),
 512         };
 513         let trait_ref = ty::TraitRef {
 514             def_id: fn_trait_def_id,
 515             substs: self.mk_substs_trait(self_ty, &[arguments_tuple.into()]),
 516         };
 517         ty::Binder::bind((trait_ref, sig.skip_binder().output()))
 518     }
 519
 520     pub fn generator_trait_ref_and_outputs(self,
 521         fn_trait_def_id: DefId,
 522         self_ty: Ty<'tcx>,
 523         sig: ty::PolyGenSig<'tcx>)
 524         -> ty::Binder<(ty::TraitRef<'tcx>, Ty<'tcx>, Ty<'tcx>)>
 525     {
 526         let trait_ref = ty::TraitRef {
 527             def_id: fn_trait_def_id,
 528             substs: self.mk_substs_trait(self_ty, &[]),
 529         };
 530         ty::Binder::bind((trait_ref, sig.skip_binder().yield_ty, sig.skip_binder().return_ty))
 531     }
 532
 533     pub fn impl_is_default(self, node_item_def_id: DefId) -> bool {
 534         match self.hir.as_local_node_id(node_item_def_id) {
 535             Some(node_id) => {
 536                 let item = self.hir.expect_item(node_id);
 537                 if let hir::ItemKind::Impl(_, _, defaultness, ..) = item.node {
 538                     defaultness.is_default()
 539                 } else {
 540                     false
 541                 }
 542             }
 543             None => {
 544                 self.global_tcx()
 545                     .impl_defaultness(node_item_def_id)
 546                     .is_default()
 547             }
 548         }
 549     }
 550
 551     pub fn impl_item_is_final(self, node_item: &NodeItem<hir::Defaultness>) -> bool {
 552         node_item.item.is_final() && !self.impl_is_default(node_item.node.def_id())
 553     }
 554 }
 555
 556 pub enum TupleArgumentsFlag { Yes, No }