src/librustc/middle/ty/fold.rs

   1 // Copyright 2012-2013 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 //! Generalized type folding mechanism. The setup is a bit convoluted
  12 //! but allows for convenient usage. Let T be an instance of some
  13 //! "foldable type" (one which implements `TypeFoldable`) and F be an
  14 //! instance of a "folder" (a type which implements `TypeFolder`). Then
  15 //! the setup is intended to be:
  16 //!
  17 //!     T.fold_with(F) --calls--> F.fold_T(T) --calls--> super_fold_T(F, T)
  18 //!
  19 //! This way, when you define a new folder F, you can override
  20 //! `fold_T()` to customize the behavior, and invoke `super_fold_T()`
  21 //! to get the original behavior. Meanwhile, to actually fold
  22 //! something, you can just write `T.fold_with(F)`, which is
  23 //! convenient. (Note that `fold_with` will also transparently handle
  24 //! things like a `Vec<T>` where T is foldable and so on.)
  25 //!
  26 //! In this ideal setup, the only function that actually *does*
  27 //! anything is `super_fold_T`, which traverses the type `T`. Moreover,
  28 //! `super_fold_T` should only ever call `T.fold_with()`.
  29 //!
  30 //! In some cases, we follow a degenerate pattern where we do not have
  31 //! a `fold_T` nor `super_fold_T` method. Instead, `T.fold_with`
  32 //! traverses the structure directly. This is suboptimal because the
  33 //! behavior cannot be overridden, but it's much less work to implement.
  34 //! If you ever *do* need an override that doesn't exist, it's not hard
  35 //! to convert the degenerate pattern into the proper thing.
  36
  37 use middle::subst;
  38 use middle::subst::VecPerParamSpace;
  39 use middle::ty::{self, Ty, HasTypeFlags, RegionEscape};
  40 use middle::traits;
  41
  42 use std::fmt;
  43 use std::rc::Rc;
  44 use syntax::abi;
  45 use rustc_front::hir;
  46 use syntax::owned_slice::OwnedSlice;
  47 use util::nodemap::{FnvHashMap, FnvHashSet};
  48
  49 ///////////////////////////////////////////////////////////////////////////
  50 // Two generic traits
  51
  52 /// The TypeFoldable trait is implemented for every type that can be folded.
  53 /// Basically, every type that has a corresponding method in TypeFolder.
  54 pub trait TypeFoldable<'tcx>: fmt::Debug + Clone {
  55     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self;
  56 }
  57
  58 /// The TypeFolder trait defines the actual *folding*. There is a
  59 /// method defined for every foldable type. Each of these has a
  60 /// default implementation that does an "identity" fold. Within each
  61 /// identity fold, it should invoke `foo.fold_with(self)` to fold each
  62 /// sub-item.
  63 pub trait TypeFolder<'tcx> : Sized {
  64     fn tcx<'a>(&'a self) -> &'a ty::ctxt<'tcx>;
  65
  66     /// Invoked by the `super_*` routines when we enter a region
  67     /// binding level (for example, when entering a function
  68     /// signature). This is used by clients that want to track the
  69     /// Debruijn index nesting level.
  70     fn enter_region_binder(&mut self) { }
  71
  72     /// Invoked by the `super_*` routines when we exit a region
  73     /// binding level. This is used by clients that want to
  74     /// track the Debruijn index nesting level.
  75     fn exit_region_binder(&mut self) { }
  76
  77     fn fold_binder<T>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T>
  78         where T : TypeFoldable<'tcx>
  79     {
  80         // FIXME(#20526) this should replace `enter_region_binder`/`exit_region_binder`.
  81         super_fold_binder(self, t)
  82     }
  83
  84     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
  85         super_fold_ty(self, t)
  86     }
  87
  88     fn fold_mt(&mut self, t: &ty::TypeAndMut<'tcx>) -> ty::TypeAndMut<'tcx> {
  89         super_fold_mt(self, t)
  90     }
  91
  92     fn fold_trait_ref(&mut self, t: &ty::TraitRef<'tcx>) -> ty::TraitRef<'tcx> {
  93         super_fold_trait_ref(self, t)
  94     }
  95
  96     fn fold_substs(&mut self,
  97                    substs: &subst::Substs<'tcx>)
  98                    -> subst::Substs<'tcx> {
  99         super_fold_substs(self, substs)
 100     }
 101
 102     fn fold_fn_sig(&mut self,
 103                    sig: &ty::FnSig<'tcx>)
 104                    -> ty::FnSig<'tcx> {
 105         super_fold_fn_sig(self, sig)
 106     }
 107
 108     fn fold_output(&mut self,
 109                       output: &ty::FnOutput<'tcx>)
 110                       -> ty::FnOutput<'tcx> {
 111         super_fold_output(self, output)
 112     }
 113
 114     fn fold_bare_fn_ty(&mut self,
 115                        fty: &ty::BareFnTy<'tcx>)
 116                        -> ty::BareFnTy<'tcx>
 117     {
 118         super_fold_bare_fn_ty(self, fty)
 119     }
 120
 121     fn fold_closure_ty(&mut self,
 122                        fty: &ty::ClosureTy<'tcx>)
 123                        -> ty::ClosureTy<'tcx> {
 124         super_fold_closure_ty(self, fty)
 125     }
 126
 127     fn fold_region(&mut self, r: ty::Region) -> ty::Region {
 128         r
 129     }
 130
 131     fn fold_existential_bounds(&mut self, s: &ty::ExistentialBounds<'tcx>)
 132                                -> ty::ExistentialBounds<'tcx> {
 133         super_fold_existential_bounds(self, s)
 134     }
 135
 136     fn fold_autoref(&mut self, ar: &ty::AutoRef<'tcx>) -> ty::AutoRef<'tcx> {
 137         super_fold_autoref(self, ar)
 138     }
 139
 140     fn fold_item_substs(&mut self, i: ty::ItemSubsts<'tcx>) -> ty::ItemSubsts<'tcx> {
 141         super_fold_item_substs(self, i)
 142     }
 143 }
 144
 145 ///////////////////////////////////////////////////////////////////////////
 146 // TypeFoldable implementations.
 147 //
 148 // Ideally, each type should invoke `folder.fold_foo(self)` and
 149 // nothing else. In some cases, though, we haven't gotten around to
 150 // adding methods on the `folder` yet, and thus the folding is
 151 // hard-coded here. This is less-flexible, because folders cannot
 152 // override the behavior, but there are a lot of random types and one
 153 // can easily refactor the folding into the TypeFolder trait as
 154 // needed.
 155
 156 macro_rules! CopyImpls {
 157     ($($ty:ty),+) => {
 158         $(
 159             impl<'tcx> TypeFoldable<'tcx> for $ty {
 160                 fn fold_with<F:TypeFolder<'tcx>>(&self, _: &mut F) -> $ty {
 161                     *self
 162                 }
 163             }
 164         )+
 165     }
 166 }
 167
 168 CopyImpls! { (), hir::Unsafety, abi::Abi }
 169
 170 impl<'tcx, T:TypeFoldable<'tcx>, U:TypeFoldable<'tcx>> TypeFoldable<'tcx> for (T, U) {
 171     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> (T, U) {
 172         (self.0.fold_with(folder), self.1.fold_with(folder))
 173     }
 174 }
 175
 176 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Option<T> {
 177     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Option<T> {
 178         self.as_ref().map(|t| t.fold_with(folder))
 179     }
 180 }
 181
 182 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Rc<T> {
 183     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Rc<T> {
 184         Rc::new((**self).fold_with(folder))
 185     }
 186 }
 187
 188 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Box<T> {
 189     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Box<T> {
 190         let content: T = (**self).fold_with(folder);
 191         box content
 192     }
 193 }
 194
 195 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Vec<T> {
 196     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Vec<T> {
 197         self.iter().map(|t| t.fold_with(folder)).collect()
 198     }
 199 }
 200
 201 impl<'tcx, T:TypeFoldable<'tcx>> TypeFoldable<'tcx> for ty::Binder<T> {
 202     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::Binder<T> {
 203         folder.fold_binder(self)
 204     }
 205 }
 206
 207 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for OwnedSlice<T> {
 208     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> OwnedSlice<T> {
 209         self.iter().map(|t| t.fold_with(folder)).collect()
 210     }
 211 }
 212
 213 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for VecPerParamSpace<T> {
 214     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> VecPerParamSpace<T> {
 215
 216         // Things in the Fn space take place under an additional level
 217         // of region binding relative to the other spaces. This is
 218         // because those entries are attached to a method, and methods
 219         // always introduce a level of region binding.
 220
 221         let result = self.map_enumerated(|(space, index, elem)| {
 222             if space == subst::FnSpace && index == 0 {
 223                 // enter new level when/if we reach the first thing in fn space
 224                 folder.enter_region_binder();
 225             }
 226             elem.fold_with(folder)
 227         });
 228         if result.len(subst::FnSpace) > 0 {
 229             // if there was anything in fn space, exit the region binding level
 230             folder.exit_region_binder();
 231         }
 232         result
 233     }
 234 }
 235
 236 impl<'tcx> TypeFoldable<'tcx> for Ty<'tcx> {
 237     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Ty<'tcx> {
 238         folder.fold_ty(*self)
 239     }
 240 }
 241
 242 impl<'tcx> TypeFoldable<'tcx> for ty::BareFnTy<'tcx> {
 243     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::BareFnTy<'tcx> {
 244         folder.fold_bare_fn_ty(self)
 245     }
 246 }
 247
 248 impl<'tcx> TypeFoldable<'tcx> for ty::ClosureTy<'tcx> {
 249     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ClosureTy<'tcx> {
 250         folder.fold_closure_ty(self)
 251     }
 252 }
 253
 254 impl<'tcx> TypeFoldable<'tcx> for ty::TypeAndMut<'tcx> {
 255     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::TypeAndMut<'tcx> {
 256         folder.fold_mt(self)
 257     }
 258 }
 259
 260 impl<'tcx> TypeFoldable<'tcx> for ty::FnOutput<'tcx> {
 261     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::FnOutput<'tcx> {
 262         folder.fold_output(self)
 263     }
 264 }
 265
 266 impl<'tcx> TypeFoldable<'tcx> for ty::FnSig<'tcx> {
 267     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::FnSig<'tcx> {
 268         folder.fold_fn_sig(self)
 269     }
 270 }
 271
 272 impl<'tcx> TypeFoldable<'tcx> for ty::TraitRef<'tcx> {
 273     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::TraitRef<'tcx> {
 274         folder.fold_trait_ref(self)
 275     }
 276 }
 277
 278 impl<'tcx> TypeFoldable<'tcx> for ty::Region {
 279     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::Region {
 280         folder.fold_region(*self)
 281     }
 282 }
 283
 284 impl<'tcx> TypeFoldable<'tcx> for subst::Substs<'tcx> {
 285     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> subst::Substs<'tcx> {
 286         folder.fold_substs(self)
 287     }
 288 }
 289
 290 impl<'tcx> TypeFoldable<'tcx> for ty::ClosureSubsts<'tcx> {
 291     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ClosureSubsts<'tcx> {
 292         let func_substs = self.func_substs.fold_with(folder);
 293         ty::ClosureSubsts {
 294             func_substs: folder.tcx().mk_substs(func_substs),
 295             upvar_tys: self.upvar_tys.fold_with(folder),
 296         }
 297     }
 298 }
 299
 300 impl<'tcx> TypeFoldable<'tcx> for ty::ItemSubsts<'tcx> {
 301     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ItemSubsts<'tcx> {
 302         ty::ItemSubsts {
 303             substs: self.substs.fold_with(folder),
 304         }
 305     }
 306 }
 307
 308 impl<'tcx> TypeFoldable<'tcx> for ty::AutoRef<'tcx> {
 309     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::AutoRef<'tcx> {
 310         folder.fold_autoref(self)
 311     }
 312 }
 313
 314 impl<'tcx> TypeFoldable<'tcx> for ty::BuiltinBounds {
 315     fn fold_with<F: TypeFolder<'tcx>>(&self, _folder: &mut F) -> ty::BuiltinBounds {
 316         *self
 317     }
 318 }
 319
 320 impl<'tcx> TypeFoldable<'tcx> for ty::ExistentialBounds<'tcx> {
 321     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ExistentialBounds<'tcx> {
 322         folder.fold_existential_bounds(self)
 323     }
 324 }
 325
 326 impl<'tcx> TypeFoldable<'tcx> for ty::TypeParameterDef<'tcx> {
 327     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::TypeParameterDef<'tcx> {
 328         ty::TypeParameterDef {
 329             name: self.name,
 330             def_id: self.def_id,
 331             space: self.space,
 332             index: self.index,
 333             default: self.default.fold_with(folder),
 334             default_def_id: self.default_def_id,
 335             object_lifetime_default: self.object_lifetime_default.fold_with(folder),
 336         }
 337     }
 338 }
 339
 340 impl<'tcx> TypeFoldable<'tcx> for ty::ObjectLifetimeDefault {
 341     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ObjectLifetimeDefault {
 342         match *self {
 343             ty::ObjectLifetimeDefault::Ambiguous =>
 344                 ty::ObjectLifetimeDefault::Ambiguous,
 345
 346             ty::ObjectLifetimeDefault::BaseDefault =>
 347                 ty::ObjectLifetimeDefault::BaseDefault,
 348
 349             ty::ObjectLifetimeDefault::Specific(r) =>
 350                 ty::ObjectLifetimeDefault::Specific(r.fold_with(folder)),
 351         }
 352     }
 353 }
 354
 355 impl<'tcx> TypeFoldable<'tcx> for ty::RegionParameterDef {
 356     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::RegionParameterDef {
 357         ty::RegionParameterDef {
 358             name: self.name,
 359             def_id: self.def_id,
 360             space: self.space,
 361             index: self.index,
 362             bounds: self.bounds.fold_with(folder)
 363         }
 364     }
 365 }
 366
 367 impl<'tcx> TypeFoldable<'tcx> for ty::Generics<'tcx> {
 368     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::Generics<'tcx> {
 369         ty::Generics {
 370             types: self.types.fold_with(folder),
 371             regions: self.regions.fold_with(folder),
 372         }
 373     }
 374 }
 375
 376 impl<'tcx> TypeFoldable<'tcx> for ty::GenericPredicates<'tcx> {
 377     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::GenericPredicates<'tcx> {
 378         ty::GenericPredicates {
 379             predicates: self.predicates.fold_with(folder),
 380         }
 381     }
 382 }
 383
 384 impl<'tcx> TypeFoldable<'tcx> for ty::Predicate<'tcx> {
 385     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::Predicate<'tcx> {
 386         match *self {
 387             ty::Predicate::Trait(ref a) =>
 388                 ty::Predicate::Trait(a.fold_with(folder)),
 389             ty::Predicate::Equate(ref binder) =>
 390                 ty::Predicate::Equate(binder.fold_with(folder)),
 391             ty::Predicate::RegionOutlives(ref binder) =>
 392                 ty::Predicate::RegionOutlives(binder.fold_with(folder)),
 393             ty::Predicate::TypeOutlives(ref binder) =>
 394                 ty::Predicate::TypeOutlives(binder.fold_with(folder)),
 395             ty::Predicate::Projection(ref binder) =>
 396                 ty::Predicate::Projection(binder.fold_with(folder)),
 397             ty::Predicate::WellFormed(data) =>
 398                 ty::Predicate::WellFormed(data.fold_with(folder)),
 399             ty::Predicate::ObjectSafe(trait_def_id) =>
 400                 ty::Predicate::ObjectSafe(trait_def_id),
 401         }
 402     }
 403 }
 404
 405 impl<'tcx> TypeFoldable<'tcx> for ty::ProjectionPredicate<'tcx> {
 406     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ProjectionPredicate<'tcx> {
 407         ty::ProjectionPredicate {
 408             projection_ty: self.projection_ty.fold_with(folder),
 409             ty: self.ty.fold_with(folder),
 410         }
 411     }
 412 }
 413
 414 impl<'tcx> TypeFoldable<'tcx> for ty::ProjectionTy<'tcx> {
 415     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ProjectionTy<'tcx> {
 416         ty::ProjectionTy {
 417             trait_ref: self.trait_ref.fold_with(folder),
 418             item_name: self.item_name,
 419         }
 420     }
 421 }
 422
 423 impl<'tcx> TypeFoldable<'tcx> for ty::InstantiatedPredicates<'tcx> {
 424     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::InstantiatedPredicates<'tcx> {
 425         ty::InstantiatedPredicates {
 426             predicates: self.predicates.fold_with(folder),
 427         }
 428     }
 429 }
 430
 431 impl<'tcx,O> TypeFoldable<'tcx> for traits::Obligation<'tcx,O>
 432     where O : TypeFoldable<'tcx>
 433 {
 434     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::Obligation<'tcx, O> {
 435         traits::Obligation {
 436             cause: self.cause.clone(),
 437             recursion_depth: self.recursion_depth,
 438             predicate: self.predicate.fold_with(folder),
 439         }
 440     }
 441 }
 442
 443 impl<'tcx, N: TypeFoldable<'tcx>> TypeFoldable<'tcx> for traits::VtableImplData<'tcx, N> {
 444     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::VtableImplData<'tcx, N> {
 445         traits::VtableImplData {
 446             impl_def_id: self.impl_def_id,
 447             substs: self.substs.fold_with(folder),
 448             nested: self.nested.fold_with(folder),
 449         }
 450     }
 451 }
 452
 453 impl<'tcx, N: TypeFoldable<'tcx>> TypeFoldable<'tcx> for traits::VtableClosureData<'tcx, N> {
 454     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::VtableClosureData<'tcx, N> {
 455         traits::VtableClosureData {
 456             closure_def_id: self.closure_def_id,
 457             substs: self.substs.fold_with(folder),
 458             nested: self.nested.fold_with(folder),
 459         }
 460     }
 461 }
 462
 463 impl<'tcx, N: TypeFoldable<'tcx>> TypeFoldable<'tcx> for traits::VtableDefaultImplData<N> {
 464     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::VtableDefaultImplData<N> {
 465         traits::VtableDefaultImplData {
 466             trait_def_id: self.trait_def_id,
 467             nested: self.nested.fold_with(folder),
 468         }
 469     }
 470 }
 471
 472 impl<'tcx, N: TypeFoldable<'tcx>> TypeFoldable<'tcx> for traits::VtableBuiltinData<N> {
 473     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::VtableBuiltinData<N> {
 474         traits::VtableBuiltinData {
 475             nested: self.nested.fold_with(folder),
 476         }
 477     }
 478 }
 479
 480 impl<'tcx, N: TypeFoldable<'tcx>> TypeFoldable<'tcx> for traits::Vtable<'tcx, N> {
 481     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::Vtable<'tcx, N> {
 482         match *self {
 483             traits::VtableImpl(ref v) => traits::VtableImpl(v.fold_with(folder)),
 484             traits::VtableDefaultImpl(ref t) => traits::VtableDefaultImpl(t.fold_with(folder)),
 485             traits::VtableClosure(ref d) => {
 486                 traits::VtableClosure(d.fold_with(folder))
 487             }
 488             traits::VtableFnPointer(ref d) => {
 489                 traits::VtableFnPointer(d.fold_with(folder))
 490             }
 491             traits::VtableParam(ref n) => traits::VtableParam(n.fold_with(folder)),
 492             traits::VtableBuiltin(ref d) => traits::VtableBuiltin(d.fold_with(folder)),
 493             traits::VtableObject(ref d) => traits::VtableObject(d.fold_with(folder)),
 494         }
 495     }
 496 }
 497
 498 impl<'tcx> TypeFoldable<'tcx> for traits::VtableObjectData<'tcx> {
 499     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::VtableObjectData<'tcx> {
 500         traits::VtableObjectData {
 501             upcast_trait_ref: self.upcast_trait_ref.fold_with(folder),
 502             vtable_base: self.vtable_base
 503         }
 504     }
 505 }
 506
 507 impl<'tcx> TypeFoldable<'tcx> for ty::EquatePredicate<'tcx> {
 508     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::EquatePredicate<'tcx> {
 509         ty::EquatePredicate(self.0.fold_with(folder),
 510                             self.1.fold_with(folder))
 511     }
 512 }
 513
 514 impl<'tcx> TypeFoldable<'tcx> for ty::TraitPredicate<'tcx> {
 515     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::TraitPredicate<'tcx> {
 516         ty::TraitPredicate {
 517             trait_ref: self.trait_ref.fold_with(folder)
 518         }
 519     }
 520 }
 521
 522 impl<'tcx,T,U> TypeFoldable<'tcx> for ty::OutlivesPredicate<T,U>
 523     where T : TypeFoldable<'tcx>,
 524           U : TypeFoldable<'tcx>,
 525 {
 526     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::OutlivesPredicate<T,U> {
 527         ty::OutlivesPredicate(self.0.fold_with(folder),
 528                               self.1.fold_with(folder))
 529     }
 530 }
 531
 532 impl<'tcx> TypeFoldable<'tcx> for ty::ClosureUpvar<'tcx> {
 533     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ClosureUpvar<'tcx> {
 534         ty::ClosureUpvar {
 535             def: self.def,
 536             span: self.span,
 537             ty: self.ty.fold_with(folder),
 538         }
 539     }
 540 }
 541
 542 impl<'a, 'tcx> TypeFoldable<'tcx> for ty::ParameterEnvironment<'a, 'tcx> where 'tcx: 'a {
 543     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ParameterEnvironment<'a, 'tcx> {
 544         ty::ParameterEnvironment {
 545             tcx: self.tcx,
 546             free_substs: self.free_substs.fold_with(folder),
 547             implicit_region_bound: self.implicit_region_bound.fold_with(folder),
 548             caller_bounds: self.caller_bounds.fold_with(folder),
 549             selection_cache: traits::SelectionCache::new(),
 550             free_id: self.free_id,
 551         }
 552     }
 553 }
 554
 555 ///////////////////////////////////////////////////////////////////////////
 556 // "super" routines: these are the default implementations for TypeFolder.
 557 //
 558 // They should invoke `foo.fold_with()` to do recursive folding.
 559
 560 pub fn super_fold_binder<'tcx, T, U>(this: &mut T,
 561                                      binder: &ty::Binder<U>)
 562                                      -> ty::Binder<U>
 563     where T : TypeFolder<'tcx>, U : TypeFoldable<'tcx>
 564 {
 565     this.enter_region_binder();
 566     let result = ty::Binder(binder.0.fold_with(this));
 567     this.exit_region_binder();
 568     result
 569 }
 570
 571 pub fn super_fold_ty<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 572                                                 ty: Ty<'tcx>)
 573                                                 -> Ty<'tcx> {
 574     let sty = match ty.sty {
 575         ty::TyBox(typ) => {
 576             ty::TyBox(typ.fold_with(this))
 577         }
 578         ty::TyRawPtr(ref tm) => {
 579             ty::TyRawPtr(tm.fold_with(this))
 580         }
 581         ty::TyArray(typ, sz) => {
 582             ty::TyArray(typ.fold_with(this), sz)
 583         }
 584         ty::TySlice(typ) => {
 585             ty::TySlice(typ.fold_with(this))
 586         }
 587         ty::TyEnum(tid, ref substs) => {
 588             let substs = substs.fold_with(this);
 589             ty::TyEnum(tid, this.tcx().mk_substs(substs))
 590         }
 591         ty::TyTrait(box ty::TraitTy { ref principal, ref bounds }) => {
 592             ty::TyTrait(box ty::TraitTy {
 593                 principal: principal.fold_with(this),
 594                 bounds: bounds.fold_with(this),
 595             })
 596         }
 597         ty::TyTuple(ref ts) => {
 598             ty::TyTuple(ts.fold_with(this))
 599         }
 600         ty::TyBareFn(opt_def_id, ref f) => {
 601             let bfn = f.fold_with(this);
 602             ty::TyBareFn(opt_def_id, this.tcx().mk_bare_fn(bfn))
 603         }
 604         ty::TyRef(r, ref tm) => {
 605             let r = r.fold_with(this);
 606             ty::TyRef(this.tcx().mk_region(r), tm.fold_with(this))
 607         }
 608         ty::TyStruct(did, ref substs) => {
 609             let substs = substs.fold_with(this);
 610             ty::TyStruct(did, this.tcx().mk_substs(substs))
 611         }
 612         ty::TyClosure(did, ref substs) => {
 613             let s = substs.fold_with(this);
 614             ty::TyClosure(did, s)
 615         }
 616         ty::TyProjection(ref data) => {
 617             ty::TyProjection(data.fold_with(this))
 618         }
 619         ty::TyBool | ty::TyChar | ty::TyStr |
 620         ty::TyInt(_) | ty::TyUint(_) | ty::TyFloat(_) |
 621         ty::TyError | ty::TyInfer(_) |
 622         ty::TyParam(..) => {
 623             ty.sty.clone()
 624         }
 625     };
 626     this.tcx().mk_ty(sty)
 627 }
 628
 629 pub fn super_fold_substs<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 630                                                     substs: &subst::Substs<'tcx>)
 631                                                     -> subst::Substs<'tcx> {
 632     let regions = match substs.regions {
 633         subst::ErasedRegions => {
 634             subst::ErasedRegions
 635         }
 636         subst::NonerasedRegions(ref regions) => {
 637             subst::NonerasedRegions(regions.fold_with(this))
 638         }
 639     };
 640
 641     subst::Substs { regions: regions,
 642                     types: substs.types.fold_with(this) }
 643 }
 644
 645 pub fn super_fold_fn_sig<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 646                                                     sig: &ty::FnSig<'tcx>)
 647                                                     -> ty::FnSig<'tcx>
 648 {
 649     ty::FnSig { inputs: sig.inputs.fold_with(this),
 650                 output: sig.output.fold_with(this),
 651                 variadic: sig.variadic }
 652 }
 653
 654 pub fn super_fold_output<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 655                                                     output: &ty::FnOutput<'tcx>)
 656                                                     -> ty::FnOutput<'tcx> {
 657     match *output {
 658         ty::FnConverging(ref ty) => ty::FnConverging(ty.fold_with(this)),
 659         ty::FnDiverging => ty::FnDiverging
 660     }
 661 }
 662
 663 pub fn super_fold_bare_fn_ty<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 664                                                         fty: &ty::BareFnTy<'tcx>)
 665                                                         -> ty::BareFnTy<'tcx>
 666 {
 667     ty::BareFnTy { sig: fty.sig.fold_with(this),
 668                    abi: fty.abi,
 669                    unsafety: fty.unsafety }
 670 }
 671
 672 pub fn super_fold_closure_ty<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 673                                                         fty: &ty::ClosureTy<'tcx>)
 674                                                         -> ty::ClosureTy<'tcx>
 675 {
 676     ty::ClosureTy {
 677         sig: fty.sig.fold_with(this),
 678         unsafety: fty.unsafety,
 679         abi: fty.abi,
 680     }
 681 }
 682
 683 pub fn super_fold_trait_ref<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 684                                                        t: &ty::TraitRef<'tcx>)
 685                                                        -> ty::TraitRef<'tcx>
 686 {
 687     let substs = t.substs.fold_with(this);
 688     ty::TraitRef {
 689         def_id: t.def_id,
 690         substs: this.tcx().mk_substs(substs),
 691     }
 692 }
 693
 694 pub fn super_fold_mt<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 695                                                 mt: &ty::TypeAndMut<'tcx>)
 696                                                 -> ty::TypeAndMut<'tcx> {
 697     ty::TypeAndMut {ty: mt.ty.fold_with(this),
 698             mutbl: mt.mutbl}
 699 }
 700
 701 pub fn super_fold_existential_bounds<'tcx, T: TypeFolder<'tcx>>(
 702     this: &mut T,
 703     bounds: &ty::ExistentialBounds<'tcx>)
 704     -> ty::ExistentialBounds<'tcx>
 705 {
 706     ty::ExistentialBounds {
 707         region_bound: bounds.region_bound.fold_with(this),
 708         builtin_bounds: bounds.builtin_bounds,
 709         projection_bounds: bounds.projection_bounds.fold_with(this),
 710     }
 711 }
 712
 713 pub fn super_fold_autoref<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 714                                                      autoref: &ty::AutoRef<'tcx>)
 715                                                      -> ty::AutoRef<'tcx>
 716 {
 717     match *autoref {
 718         ty::AutoPtr(r, m) => {
 719             let r = r.fold_with(this);
 720             ty::AutoPtr(this.tcx().mk_region(r), m)
 721         }
 722         ty::AutoUnsafe(m) => ty::AutoUnsafe(m)
 723     }
 724 }
 725
 726 pub fn super_fold_item_substs<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 727                                                          substs: ty::ItemSubsts<'tcx>)
 728                                                          -> ty::ItemSubsts<'tcx>
 729 {
 730     ty::ItemSubsts {
 731         substs: substs.substs.fold_with(this),
 732     }
 733 }
 734
 735 ///////////////////////////////////////////////////////////////////////////
 736 // Some sample folders
 737
 738 pub struct BottomUpFolder<'a, 'tcx: 'a, F> where F: FnMut(Ty<'tcx>) -> Ty<'tcx> {
 739     pub tcx: &'a ty::ctxt<'tcx>,
 740     pub fldop: F,
 741 }
 742
 743 impl<'a, 'tcx, F> TypeFolder<'tcx> for BottomUpFolder<'a, 'tcx, F> where
 744     F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
 745 {
 746     fn tcx(&self) -> &ty::ctxt<'tcx> { self.tcx }
 747
 748     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
 749         let t1 = super_fold_ty(self, ty);
 750         (self.fldop)(t1)
 751     }
 752 }
 753
 754 ///////////////////////////////////////////////////////////////////////////
 755 // Region folder
 756
 757 /// Folds over the substructure of a type, visiting its component
 758 /// types and all regions that occur *free* within it.
 759 ///
 760 /// That is, `Ty` can contain function or method types that bind
 761 /// regions at the call site (`ReLateBound`), and occurrences of
 762 /// regions (aka "lifetimes") that are bound within a type are not
 763 /// visited by this folder; only regions that occur free will be
 764 /// visited by `fld_r`.
 765
 766 pub struct RegionFolder<'a, 'tcx: 'a> {
 767     tcx: &'a ty::ctxt<'tcx>,
 768     skipped_regions: &'a mut bool,
 769     current_depth: u32,
 770     fld_r: &'a mut (FnMut(ty::Region, u32) -> ty::Region + 'a),
 771 }
 772
 773 impl<'a, 'tcx> RegionFolder<'a, 'tcx> {
 774     pub fn new<F>(tcx: &'a ty::ctxt<'tcx>,
 775                   skipped_regions: &'a mut bool,
 776                   fld_r: &'a mut F) -> RegionFolder<'a, 'tcx>
 777         where F : FnMut(ty::Region, u32) -> ty::Region
 778     {
 779         RegionFolder {
 780             tcx: tcx,
 781             skipped_regions: skipped_regions,
 782             current_depth: 1,
 783             fld_r: fld_r,
 784         }
 785     }
 786 }
 787
 788 /// Collects the free and escaping regions in `value` into `region_set`. Returns
 789 /// whether any late-bound regions were skipped
 790 pub fn collect_regions<'tcx,T>(tcx: &ty::ctxt<'tcx>,
 791                                value: &T,
 792                                region_set: &mut FnvHashSet<ty::Region>) -> bool
 793     where T : TypeFoldable<'tcx>
 794 {
 795     let mut have_bound_regions = false;
 796     fold_regions(tcx, value, &mut have_bound_regions,
 797                  |r, d| { region_set.insert(r.from_depth(d)); r });
 798     have_bound_regions
 799 }
 800
 801 /// Folds the escaping and free regions in `value` using `f`, and
 802 /// sets `skipped_regions` to true if any late-bound region was found
 803 /// and skipped.
 804 pub fn fold_regions<'tcx,T,F>(tcx: &ty::ctxt<'tcx>,
 805                               value: &T,
 806                               skipped_regions: &mut bool,
 807                               mut f: F)
 808                               -> T
 809     where F : FnMut(ty::Region, u32) -> ty::Region,
 810           T : TypeFoldable<'tcx>,
 811 {
 812     value.fold_with(&mut RegionFolder::new(tcx, skipped_regions, &mut f))
 813 }
 814
 815 impl<'a, 'tcx> TypeFolder<'tcx> for RegionFolder<'a, 'tcx>
 816 {
 817     fn tcx(&self) -> &ty::ctxt<'tcx> { self.tcx }
 818
 819     fn enter_region_binder(&mut self) {
 820         self.current_depth += 1;
 821     }
 822
 823     fn exit_region_binder(&mut self) {
 824         self.current_depth -= 1;
 825     }
 826
 827     fn fold_region(&mut self, r: ty::Region) -> ty::Region {
 828         match r {
 829             ty::ReLateBound(debruijn, _) if debruijn.depth < self.current_depth => {
 830                 debug!("RegionFolder.fold_region({:?}) skipped bound region (current depth={})",
 831                        r, self.current_depth);
 832                 *self.skipped_regions = true;
 833                 r
 834             }
 835             _ => {
 836                 debug!("RegionFolder.fold_region({:?}) folding free region (current_depth={})",
 837                        r, self.current_depth);
 838                 (self.fld_r)(r, self.current_depth)
 839             }
 840         }
 841     }
 842 }
 843
 844 ///////////////////////////////////////////////////////////////////////////
 845 // Late-bound region replacer
 846
 847 // Replaces the escaping regions in a type.
 848
 849 struct RegionReplacer<'a, 'tcx: 'a> {
 850     tcx: &'a ty::ctxt<'tcx>,
 851     current_depth: u32,
 852     fld_r: &'a mut (FnMut(ty::BoundRegion) -> ty::Region + 'a),
 853     map: FnvHashMap<ty::BoundRegion, ty::Region>
 854 }
 855
 856 impl<'a, 'tcx> RegionReplacer<'a, 'tcx> {
 857     fn new<F>(tcx: &'a ty::ctxt<'tcx>, fld_r: &'a mut F) -> RegionReplacer<'a, 'tcx>
 858         where F : FnMut(ty::BoundRegion) -> ty::Region
 859     {
 860         RegionReplacer {
 861             tcx: tcx,
 862             current_depth: 1,
 863             fld_r: fld_r,
 864             map: FnvHashMap()
 865         }
 866     }
 867 }
 868
 869 pub fn replace_late_bound_regions<'tcx,T,F>(tcx: &ty::ctxt<'tcx>,
 870                                             value: &ty::Binder<T>,
 871                                             mut f: F)
 872                                             -> (T, FnvHashMap<ty::BoundRegion, ty::Region>)
 873     where F : FnMut(ty::BoundRegion) -> ty::Region,
 874           T : TypeFoldable<'tcx>,
 875 {
 876     debug!("replace_late_bound_regions({:?})", value);
 877     let mut replacer = RegionReplacer::new(tcx, &mut f);
 878     let result = value.skip_binder().fold_with(&mut replacer);
 879     (result, replacer.map)
 880 }
 881
 882 impl<'a, 'tcx> TypeFolder<'tcx> for RegionReplacer<'a, 'tcx>
 883 {
 884     fn tcx(&self) -> &ty::ctxt<'tcx> { self.tcx }
 885
 886     fn enter_region_binder(&mut self) {
 887         self.current_depth += 1;
 888     }
 889
 890     fn exit_region_binder(&mut self) {
 891         self.current_depth -= 1;
 892     }
 893
 894     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
 895         if !t.has_regions_escaping_depth(self.current_depth-1) {
 896             return t;
 897         }
 898
 899         super_fold_ty(self, t)
 900     }
 901
 902     fn fold_region(&mut self, r: ty::Region) -> ty::Region {
 903         match r {
 904             ty::ReLateBound(debruijn, br) if debruijn.depth == self.current_depth => {
 905                 debug!("RegionReplacer.fold_region({:?}) folding region (current_depth={})",
 906                        r, self.current_depth);
 907                 let fld_r = &mut self.fld_r;
 908                 let region = *self.map.entry(br).or_insert_with(|| fld_r(br));
 909                 if let ty::ReLateBound(debruijn1, br) = region {
 910                     // If the callback returns a late-bound region,
 911                     // that region should always use depth 1. Then we
 912                     // adjust it to the correct depth.
 913                     assert_eq!(debruijn1.depth, 1);
 914                     ty::ReLateBound(debruijn, br)
 915                 } else {
 916                     region
 917                 }
 918             }
 919             r => r
 920         }
 921     }
 922 }
 923
 924 ///////////////////////////////////////////////////////////////////////////
 925 // Region eraser
 926 //
 927 // Replaces all free regions with 'static. Useful in contexts, such as
 928 // method probing, where precise region relationships are not
 929 // important. Note that in trans you should use
 930 // `common::erase_regions` instead.
 931
 932 pub struct RegionEraser<'a, 'tcx: 'a> {
 933     tcx: &'a ty::ctxt<'tcx>,
 934 }
 935
 936 pub fn erase_regions<'tcx, T: TypeFoldable<'tcx>>(tcx: &ty::ctxt<'tcx>, t: T) -> T {
 937     let mut eraser = RegionEraser { tcx: tcx };
 938     t.fold_with(&mut eraser)
 939 }
 940
 941 impl<'a, 'tcx> TypeFolder<'tcx> for RegionEraser<'a, 'tcx> {
 942     fn tcx(&self) -> &ty::ctxt<'tcx> { self.tcx }
 943
 944     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
 945         if !t.has_erasable_regions() {
 946             return t;
 947         }
 948
 949         super_fold_ty(self, t)
 950     }
 951
 952     fn fold_region(&mut self, r: ty::Region) -> ty::Region {
 953         // because whether or not a region is bound affects subtyping,
 954         // we can't erase the bound/free distinction, but we can
 955         // replace all free regions with 'static
 956         match r {
 957             ty::ReLateBound(..) | ty::ReEarlyBound(..) => r,
 958             _ => ty::ReStatic
 959         }
 960     }
 961 }
 962
 963 ///////////////////////////////////////////////////////////////////////////
 964 // Region shifter
 965 //
 966 // Shifts the De Bruijn indices on all escaping bound regions by a
 967 // fixed amount. Useful in substitution or when otherwise introducing
 968 // a binding level that is not intended to capture the existing bound
 969 // regions. See comment on `shift_regions_through_binders` method in
 970 // `subst.rs` for more details.
 971
 972 pub fn shift_region(region: ty::Region, amount: u32) -> ty::Region {
 973     match region {
 974         ty::ReLateBound(debruijn, br) => {
 975             ty::ReLateBound(debruijn.shifted(amount), br)
 976         }
 977         _ => {
 978             region
 979         }
 980     }
 981 }
 982
 983 pub fn shift_regions<'tcx, T:TypeFoldable<'tcx>>(tcx: &ty::ctxt<'tcx>,
 984                                                  amount: u32, value: &T) -> T {
 985     debug!("shift_regions(value={:?}, amount={})",
 986            value, amount);
 987
 988     value.fold_with(&mut RegionFolder::new(tcx, &mut false, &mut |region, _current_depth| {
 989         shift_region(region, amount)
 990     }))
 991 }