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::{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::Equate(ref data) =>
  29             ty::Predicate::Equate(tcx.anonymize_late_bound_regions(data)),
  30
  31         ty::Predicate::RegionOutlives(ref data) =>
  32             ty::Predicate::RegionOutlives(tcx.anonymize_late_bound_regions(data)),
  33
  34         ty::Predicate::TypeOutlives(ref data) =>
  35             ty::Predicate::TypeOutlives(tcx.anonymize_late_bound_regions(data)),
  36
  37         ty::Predicate::Projection(ref data) =>
  38             ty::Predicate::Projection(tcx.anonymize_late_bound_regions(data)),
  39
  40         ty::Predicate::WellFormed(data) =>
  41             ty::Predicate::WellFormed(data),
  42
  43         ty::Predicate::ObjectSafe(data) =>
  44             ty::Predicate::ObjectSafe(data),
  45
  46         ty::Predicate::ClosureKind(closure_def_id, kind) =>
  47             ty::Predicate::ClosureKind(closure_def_id, kind),
  48
  49         ty::Predicate::Subtype(ref data) =>
  50             ty::Predicate::Subtype(tcx.anonymize_late_bound_regions(data)),
  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::Equate(..) => {
 164                 // Currently, we do not "elaborate" predicates like
 165                 // `X == Y`, though conceivably we might. For example,
 166                 // `&X == &Y` implies that `X == Y`.
 167             }
 168             ty::Predicate::Subtype(..) => {
 169                 // Currently, we do not "elaborate" predicates like `X
 170                 // <: Y`, though conceivably we might.
 171             }
 172             ty::Predicate::Projection(..) => {
 173                 // Nothing to elaborate in a projection predicate.
 174             }
 175             ty::Predicate::ClosureKind(..) => {
 176                 // Nothing to elaborate when waiting for a closure's kind to be inferred.
 177             }
 178
 179             ty::Predicate::RegionOutlives(..) => {
 180                 // Nothing to elaborate from `'a: 'b`.
 181             }
 182
 183             ty::Predicate::TypeOutlives(ref data) => {
 184                 // We know that `T: 'a` for some type `T`. We can
 185                 // often elaborate this. For example, if we know that
 186                 // `[U]: 'a`, that implies that `U: 'a`. Similarly, if
 187                 // we know `&'a U: 'b`, then we know that `'a: 'b` and
 188                 // `U: 'b`.
 189                 //
 190                 // We can basically ignore bound regions here. So for
 191                 // example `for<'c> Foo<'a,'c>: 'b` can be elaborated to
 192                 // `'a: 'b`.
 193
 194                 // Ignore `for<'a> T: 'a` -- we might in the future
 195                 // consider this as evidence that `T: 'static`, but
 196                 // I'm a bit wary of such constructions and so for now
 197                 // I want to be conservative. --nmatsakis
 198                 let ty_max = data.skip_binder().0;
 199                 let r_min = data.skip_binder().1;
 200                 if r_min.is_late_bound() {
 201                     return;
 202                 }
 203
 204                 let visited = &mut self.visited;
 205                 self.stack.extend(
 206                     tcx.outlives_components(ty_max)
 207                        .into_iter()
 208                        .filter_map(|component| match component {
 209                            Component::Region(r) => if r.is_late_bound() {
 210                                None
 211                            } else {
 212                                Some(ty::Predicate::RegionOutlives(
 213                                    ty::Binder(ty::OutlivesPredicate(r, r_min))))
 214                            },
 215
 216                            Component::Param(p) => {
 217                                let ty = tcx.mk_param(p.idx, p.name);
 218                                Some(ty::Predicate::TypeOutlives(
 219                                    ty::Binder(ty::OutlivesPredicate(ty, r_min))))
 220                            },
 221
 222                            Component::UnresolvedInferenceVariable(_) => {
 223                                None
 224                            },
 225
 226                            Component::Projection(_) |
 227                            Component::EscapingProjection(_) => {
 228                                // We can probably do more here. This
 229                                // corresponds to a case like `<T as
 230                                // Foo<'a>>::U: 'b`.
 231                                None
 232                            },
 233                        })
 234                        .filter(|p| visited.insert(p)));
 235             }
 236         }
 237     }
 238 }
 239
 240 impl<'cx, 'gcx, 'tcx> Iterator for Elaborator<'cx, 'gcx, 'tcx> {
 241     type Item = ty::Predicate<'tcx>;
 242
 243     fn next(&mut self) -> Option<ty::Predicate<'tcx>> {
 244         // Extract next item from top-most stack frame, if any.
 245         let next_predicate = match self.stack.pop() {
 246             Some(predicate) => predicate,
 247             None => {
 248                 // No more stack frames. Done.
 249                 return None;
 250             }
 251         };
 252         self.push(&next_predicate);
 253         return Some(next_predicate);
 254     }
 255 }
 256
 257 ///////////////////////////////////////////////////////////////////////////
 258 // Supertrait iterator
 259 ///////////////////////////////////////////////////////////////////////////
 260
 261 pub type Supertraits<'cx, 'gcx, 'tcx> = FilterToTraits<Elaborator<'cx, 'gcx, 'tcx>>;
 262
 263 pub fn supertraits<'cx, 'gcx, 'tcx>(tcx: TyCtxt<'cx, 'gcx, 'tcx>,
 264                                     trait_ref: ty::PolyTraitRef<'tcx>)
 265                                     -> Supertraits<'cx, 'gcx, 'tcx>
 266 {
 267     elaborate_trait_ref(tcx, trait_ref).filter_to_traits()
 268 }
 269
 270 pub fn transitive_bounds<'cx, 'gcx, 'tcx>(tcx: TyCtxt<'cx, 'gcx, 'tcx>,
 271                                           bounds: &[ty::PolyTraitRef<'tcx>])
 272                                           -> Supertraits<'cx, 'gcx, 'tcx>
 273 {
 274     elaborate_trait_refs(tcx, bounds).filter_to_traits()
 275 }
 276
 277 ///////////////////////////////////////////////////////////////////////////
 278 // Iterator over def-ids of supertraits
 279
 280 pub struct SupertraitDefIds<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
 281     tcx: TyCtxt<'a, 'gcx, 'tcx>,
 282     stack: Vec<DefId>,
 283     visited: FxHashSet<DefId>,
 284 }
 285
 286 pub fn supertrait_def_ids<'cx, 'gcx, 'tcx>(tcx: TyCtxt<'cx, 'gcx, 'tcx>,
 287                                            trait_def_id: DefId)
 288                                            -> SupertraitDefIds<'cx, 'gcx, 'tcx>
 289 {
 290     SupertraitDefIds {
 291         tcx: tcx,
 292         stack: vec![trait_def_id],
 293         visited: Some(trait_def_id).into_iter().collect(),
 294     }
 295 }
 296
 297 impl<'cx, 'gcx, 'tcx> Iterator for SupertraitDefIds<'cx, 'gcx, 'tcx> {
 298     type Item = DefId;
 299
 300     fn next(&mut self) -> Option<DefId> {
 301         let def_id = match self.stack.pop() {
 302             Some(def_id) => def_id,
 303             None => { return None; }
 304         };
 305
 306         let predicates = self.tcx.super_predicates_of(def_id);
 307         let visited = &mut self.visited;
 308         self.stack.extend(
 309             predicates.predicates
 310                       .iter()
 311                       .filter_map(|p| p.to_opt_poly_trait_ref())
 312                       .map(|t| t.def_id())
 313                       .filter(|&super_def_id| visited.insert(super_def_id)));
 314         Some(def_id)
 315     }
 316 }
 317
 318 ///////////////////////////////////////////////////////////////////////////
 319 // Other
 320 ///////////////////////////////////////////////////////////////////////////
 321
 322 /// A filter around an iterator of predicates that makes it yield up
 323 /// just trait references.
 324 pub struct FilterToTraits<I> {
 325     base_iterator: I
 326 }
 327
 328 impl<I> FilterToTraits<I> {
 329     fn new(base: I) -> FilterToTraits<I> {
 330         FilterToTraits { base_iterator: base }
 331     }
 332 }
 333
 334 impl<'tcx,I:Iterator<Item=ty::Predicate<'tcx>>> Iterator for FilterToTraits<I> {
 335     type Item = ty::PolyTraitRef<'tcx>;
 336
 337     fn next(&mut self) -> Option<ty::PolyTraitRef<'tcx>> {
 338         loop {
 339             match self.base_iterator.next() {
 340                 None => {
 341                     return None;
 342                 }
 343                 Some(ty::Predicate::Trait(data)) => {
 344                     return Some(data.to_poly_trait_ref());
 345                 }
 346                 Some(_) => {
 347                 }
 348             }
 349         }
 350     }
 351 }
 352
 353 ///////////////////////////////////////////////////////////////////////////
 354 // Other
 355 ///////////////////////////////////////////////////////////////////////////
 356
 357 /// Instantiate all bound parameters of the impl with the given substs,
 358 /// returning the resulting trait ref and all obligations that arise.
 359 /// The obligations are closed under normalization.
 360 pub fn impl_trait_ref_and_oblig<'a, 'gcx, 'tcx>(selcx: &mut SelectionContext<'a, 'gcx, 'tcx>,
 361                                                 impl_def_id: DefId,
 362                                                 impl_substs: &Substs<'tcx>)
 363                                                 -> (ty::TraitRef<'tcx>,
 364                                                     Vec<PredicateObligation<'tcx>>)
 365 {
 366     let impl_trait_ref =
 367         selcx.tcx().impl_trait_ref(impl_def_id).unwrap();
 368     let impl_trait_ref =
 369         impl_trait_ref.subst(selcx.tcx(), impl_substs);
 370     let Normalized { value: impl_trait_ref, obligations: normalization_obligations1 } =
 371         super::normalize(selcx, ObligationCause::dummy(), &impl_trait_ref);
 372
 373     let predicates = selcx.tcx().predicates_of(impl_def_id);
 374     let predicates = predicates.instantiate(selcx.tcx(), impl_substs);
 375     let Normalized { value: predicates, obligations: normalization_obligations2 } =
 376         super::normalize(selcx, ObligationCause::dummy(), &predicates);
 377     let impl_obligations =
 378         predicates_for_generics(ObligationCause::dummy(), 0, &predicates);
 379
 380     let impl_obligations: Vec<_> =
 381         impl_obligations.into_iter()
 382         .chain(normalization_obligations1)
 383         .chain(normalization_obligations2)
 384         .collect();
 385
 386     (impl_trait_ref, impl_obligations)
 387 }
 388
 389 /// See `super::obligations_for_generics`
 390 pub fn predicates_for_generics<'tcx>(cause: ObligationCause<'tcx>,
 391                                      recursion_depth: usize,
 392                                      generic_bounds: &ty::InstantiatedPredicates<'tcx>)
 393                                      -> Vec<PredicateObligation<'tcx>>
 394 {
 395     debug!("predicates_for_generics(generic_bounds={:?})",
 396            generic_bounds);
 397
 398     generic_bounds.predicates.iter().map(|predicate| {
 399         Obligation { cause: cause.clone(),
 400                      recursion_depth: recursion_depth,
 401                      predicate: predicate.clone() }
 402     }).collect()
 403 }
 404
 405 pub fn predicate_for_trait_ref<'tcx>(
 406     cause: ObligationCause<'tcx>,
 407     trait_ref: ty::TraitRef<'tcx>,
 408     recursion_depth: usize)
 409     -> PredicateObligation<'tcx>
 410 {
 411     Obligation {
 412         cause: cause,
 413         recursion_depth: recursion_depth,
 414         predicate: trait_ref.to_predicate(),
 415     }
 416 }
 417
 418 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 419     pub fn predicate_for_trait_def(self,
 420         cause: ObligationCause<'tcx>,
 421         trait_def_id: DefId,
 422         recursion_depth: usize,
 423         param_ty: Ty<'tcx>,
 424         ty_params: &[Ty<'tcx>])
 425         -> PredicateObligation<'tcx>
 426     {
 427         let trait_ref = ty::TraitRef {
 428             def_id: trait_def_id,
 429             substs: self.mk_substs_trait(param_ty, ty_params)
 430         };
 431         predicate_for_trait_ref(cause, trait_ref, recursion_depth)
 432     }
 433
 434     /// Cast a trait reference into a reference to one of its super
 435     /// traits; returns `None` if `target_trait_def_id` is not a
 436     /// supertrait.
 437     pub fn upcast_choices(self,
 438                           source_trait_ref: ty::PolyTraitRef<'tcx>,
 439                           target_trait_def_id: DefId)
 440                           -> Vec<ty::PolyTraitRef<'tcx>>
 441     {
 442         if source_trait_ref.def_id() == target_trait_def_id {
 443             return vec![source_trait_ref]; // shorcut the most common case
 444         }
 445
 446         supertraits(self, source_trait_ref)
 447             .filter(|r| r.def_id() == target_trait_def_id)
 448             .collect()
 449     }
 450
 451     /// Given a trait `trait_ref`, returns the number of vtable entries
 452     /// that come from `trait_ref`, excluding its supertraits. Used in
 453     /// computing the vtable base for an upcast trait of a trait object.
 454     pub fn count_own_vtable_entries(self, trait_ref: ty::PolyTraitRef<'tcx>) -> usize {
 455         let mut entries = 0;
 456         // Count number of methods and add them to the total offset.
 457         // Skip over associated types and constants.
 458         for trait_item in self.associated_items(trait_ref.def_id()) {
 459             if trait_item.kind == ty::AssociatedKind::Method {
 460                 entries += 1;
 461             }
 462         }
 463         entries
 464     }
 465
 466     /// Given an upcast trait object described by `object`, returns the
 467     /// index of the method `method_def_id` (which should be part of
 468     /// `object.upcast_trait_ref`) within the vtable for `object`.
 469     pub fn get_vtable_index_of_object_method<N>(self,
 470                                                 object: &super::VtableObjectData<'tcx, N>,
 471                                                 method_def_id: DefId) -> usize {
 472         // Count number of methods preceding the one we are selecting and
 473         // add them to the total offset.
 474         // Skip over associated types and constants.
 475         let mut entries = object.vtable_base;
 476         for trait_item in self.associated_items(object.upcast_trait_ref.def_id()) {
 477             if trait_item.def_id == method_def_id {
 478                 // The item with the ID we were given really ought to be a method.
 479                 assert_eq!(trait_item.kind, ty::AssociatedKind::Method);
 480                 return entries;
 481             }
 482             if trait_item.kind == ty::AssociatedKind::Method {
 483                 entries += 1;
 484             }
 485         }
 486
 487         bug!("get_vtable_index_of_object_method: {:?} was not found",
 488              method_def_id);
 489     }
 490
 491     pub fn closure_trait_ref_and_return_type(self,
 492         fn_trait_def_id: DefId,
 493         self_ty: Ty<'tcx>,
 494         sig: ty::PolyFnSig<'tcx>,
 495         tuple_arguments: TupleArgumentsFlag)
 496         -> ty::Binder<(ty::TraitRef<'tcx>, Ty<'tcx>)>
 497     {
 498         let arguments_tuple = match tuple_arguments {
 499             TupleArgumentsFlag::No => sig.skip_binder().inputs()[0],
 500             TupleArgumentsFlag::Yes =>
 501                 self.intern_tup(sig.skip_binder().inputs(), false),
 502         };
 503         let trait_ref = ty::TraitRef {
 504             def_id: fn_trait_def_id,
 505             substs: self.mk_substs_trait(self_ty, &[arguments_tuple]),
 506         };
 507         ty::Binder((trait_ref, sig.skip_binder().output()))
 508     }
 509
 510     pub fn impl_is_default(self, node_item_def_id: DefId) -> bool {
 511         match self.hir.as_local_node_id(node_item_def_id) {
 512             Some(node_id) => {
 513                 let item = self.hir.expect_item(node_id);
 514                 if let hir::ItemImpl(_, _, defaultness, ..) = item.node {
 515                     defaultness.is_default()
 516                 } else {
 517                     false
 518                 }
 519             }
 520             None => {
 521                 self.global_tcx()
 522                     .sess
 523                     .cstore
 524                     .impl_defaultness(node_item_def_id)
 525                     .is_default()
 526             }
 527         }
 528     }
 529
 530     pub fn impl_item_is_final(self, node_item: &NodeItem<hir::Defaultness>) -> bool {
 531         node_item.item.is_final() && !self.impl_is_default(node_item.node.def_id())
 532     }
 533 }
 534
 535 pub enum TupleArgumentsFlag { Yes, No }