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 overriden, 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::{mod, Ty};
  40 use middle::traits;
  41 use std::rc::Rc;
  42 use syntax::owned_slice::OwnedSlice;
  43 use util::ppaux::Repr;
  44
  45 ///////////////////////////////////////////////////////////////////////////
  46 // Two generic traits
  47
  48 /// The TypeFoldable trait is implemented for every type that can be folded.
  49 /// Basically, every type that has a corresponding method in TypeFolder.
  50 pub trait TypeFoldable<'tcx> {
  51     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self;
  52 }
  53
  54 /// The TypeFolder trait defines the actual *folding*. There is a
  55 /// method defined for every foldable type. Each of these has a
  56 /// default implementation that does an "identity" fold. Within each
  57 /// identity fold, it should invoke `foo.fold_with(self)` to fold each
  58 /// sub-item.
  59 pub trait TypeFolder<'tcx> : Sized {
  60     fn tcx<'a>(&'a self) -> &'a ty::ctxt<'tcx>;
  61
  62     /// Invoked by the `super_*` routines when we enter a region
  63     /// binding level (for example, when entering a function
  64     /// signature). This is used by clients that want to track the
  65     /// Debruijn index nesting level.
  66     fn enter_region_binder(&mut self) { }
  67
  68     /// Invoked by the `super_*` routines when we exit a region
  69     /// binding level. This is used by clients that want to
  70     /// track the Debruijn index nesting level.
  71     fn exit_region_binder(&mut self) { }
  72
  73     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
  74         super_fold_ty(self, t)
  75     }
  76
  77     fn fold_mt(&mut self, t: &ty::mt<'tcx>) -> ty::mt<'tcx> {
  78         super_fold_mt(self, t)
  79     }
  80
  81     fn fold_trait_ref(&mut self, t: &ty::TraitRef<'tcx>) -> ty::TraitRef<'tcx> {
  82         super_fold_trait_ref(self, t)
  83     }
  84
  85     fn fold_substs(&mut self,
  86                    substs: &subst::Substs<'tcx>)
  87                    -> subst::Substs<'tcx> {
  88         super_fold_substs(self, substs)
  89     }
  90
  91     fn fold_fn_sig(&mut self,
  92                    sig: &ty::FnSig<'tcx>)
  93                    -> ty::FnSig<'tcx> {
  94         super_fold_fn_sig(self, sig)
  95     }
  96
  97     fn fold_output(&mut self,
  98                       output: &ty::FnOutput<'tcx>)
  99                       -> ty::FnOutput<'tcx> {
 100         super_fold_output(self, output)
 101     }
 102
 103     fn fold_bare_fn_ty(&mut self,
 104                        fty: &ty::BareFnTy<'tcx>)
 105                        -> ty::BareFnTy<'tcx>
 106     {
 107         super_fold_bare_fn_ty(self, fty)
 108     }
 109
 110     fn fold_closure_ty(&mut self,
 111                        fty: &ty::ClosureTy<'tcx>)
 112                        -> ty::ClosureTy<'tcx> {
 113         super_fold_closure_ty(self, fty)
 114     }
 115
 116     fn fold_region(&mut self, r: ty::Region) -> ty::Region {
 117         r
 118     }
 119
 120     fn fold_trait_store(&mut self, s: ty::TraitStore) -> ty::TraitStore {
 121         super_fold_trait_store(self, s)
 122     }
 123
 124     fn fold_existential_bounds(&mut self, s: &ty::ExistentialBounds<'tcx>)
 125                                -> ty::ExistentialBounds<'tcx> {
 126         super_fold_existential_bounds(self, s)
 127     }
 128
 129     fn fold_autoref(&mut self, ar: &ty::AutoRef<'tcx>) -> ty::AutoRef<'tcx> {
 130         super_fold_autoref(self, ar)
 131     }
 132
 133     fn fold_item_substs(&mut self, i: ty::ItemSubsts<'tcx>) -> ty::ItemSubsts<'tcx> {
 134         super_fold_item_substs(self, i)
 135     }
 136 }
 137
 138 ///////////////////////////////////////////////////////////////////////////
 139 // TypeFoldable implementations.
 140 //
 141 // Ideally, each type should invoke `folder.fold_foo(self)` and
 142 // nothing else. In some cases, though, we haven't gotten around to
 143 // adding methods on the `folder` yet, and thus the folding is
 144 // hard-coded here. This is less-flexible, because folders cannot
 145 // override the behavior, but there are a lot of random types and one
 146 // can easily refactor the folding into the TypeFolder trait as
 147 // needed.
 148
 149 impl<'tcx> TypeFoldable<'tcx> for () {
 150     fn fold_with<F:TypeFolder<'tcx>>(&self, _: &mut F) -> () {
 151         ()
 152     }
 153 }
 154
 155 impl<'tcx, T:TypeFoldable<'tcx>, U:TypeFoldable<'tcx>> TypeFoldable<'tcx> for (T, U) {
 156     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> (T, U) {
 157         (self.0.fold_with(folder), self.1.fold_with(folder))
 158     }
 159 }
 160
 161 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Option<T> {
 162     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Option<T> {
 163         self.as_ref().map(|t| t.fold_with(folder))
 164     }
 165 }
 166
 167 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Rc<T> {
 168     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Rc<T> {
 169         Rc::new((**self).fold_with(folder))
 170     }
 171 }
 172
 173 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Box<T> {
 174     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Box<T> {
 175         let content: T = (**self).fold_with(folder);
 176         box content
 177     }
 178 }
 179
 180 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Vec<T> {
 181     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Vec<T> {
 182         self.iter().map(|t| t.fold_with(folder)).collect()
 183     }
 184 }
 185
 186 impl<'tcx, T:TypeFoldable<'tcx>> TypeFoldable<'tcx> for ty::Binder<T> {
 187     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::Binder<T> {
 188         folder.enter_region_binder();
 189         let result = ty::Binder(self.0.fold_with(folder));
 190         folder.exit_region_binder();
 191         result
 192     }
 193 }
 194
 195 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for OwnedSlice<T> {
 196     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> OwnedSlice<T> {
 197         self.iter().map(|t| t.fold_with(folder)).collect()
 198     }
 199 }
 200
 201 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for VecPerParamSpace<T> {
 202     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> VecPerParamSpace<T> {
 203
 204         // Things in the Fn space take place under an additional level
 205         // of region binding relative to the other spaces. This is
 206         // because those entries are attached to a method, and methods
 207         // always introduce a level of region binding.
 208
 209         let result = self.map_enumerated(|(space, index, elem)| {
 210             if space == subst::FnSpace && index == 0 {
 211                 // enter new level when/if we reach the first thing in fn space
 212                 folder.enter_region_binder();
 213             }
 214             elem.fold_with(folder)
 215         });
 216         if result.len(subst::FnSpace) > 0 {
 217             // if there was anything in fn space, exit the region binding level
 218             folder.exit_region_binder();
 219         }
 220         result
 221     }
 222 }
 223
 224 impl<'tcx> TypeFoldable<'tcx> for ty::TraitStore {
 225     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::TraitStore {
 226         folder.fold_trait_store(*self)
 227     }
 228 }
 229
 230 impl<'tcx> TypeFoldable<'tcx> for Ty<'tcx> {
 231     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Ty<'tcx> {
 232         folder.fold_ty(*self)
 233     }
 234 }
 235
 236 impl<'tcx> TypeFoldable<'tcx> for ty::BareFnTy<'tcx> {
 237     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::BareFnTy<'tcx> {
 238         folder.fold_bare_fn_ty(self)
 239     }
 240 }
 241
 242 impl<'tcx> TypeFoldable<'tcx> for ty::ClosureTy<'tcx> {
 243     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ClosureTy<'tcx> {
 244         folder.fold_closure_ty(self)
 245     }
 246 }
 247
 248 impl<'tcx> TypeFoldable<'tcx> for ty::mt<'tcx> {
 249     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::mt<'tcx> {
 250         folder.fold_mt(self)
 251     }
 252 }
 253
 254 impl<'tcx> TypeFoldable<'tcx> for ty::FnOutput<'tcx> {
 255     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::FnOutput<'tcx> {
 256         folder.fold_output(self)
 257     }
 258 }
 259
 260 impl<'tcx> TypeFoldable<'tcx> for ty::FnSig<'tcx> {
 261     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::FnSig<'tcx> {
 262         folder.fold_fn_sig(self)
 263     }
 264 }
 265
 266 impl<'tcx> TypeFoldable<'tcx> for ty::TraitRef<'tcx> {
 267     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::TraitRef<'tcx> {
 268         folder.fold_trait_ref(self)
 269     }
 270 }
 271
 272 impl<'tcx> TypeFoldable<'tcx> for ty::Region {
 273     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::Region {
 274         folder.fold_region(*self)
 275     }
 276 }
 277
 278 impl<'tcx> TypeFoldable<'tcx> for subst::Substs<'tcx> {
 279     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> subst::Substs<'tcx> {
 280         folder.fold_substs(self)
 281     }
 282 }
 283
 284 impl<'tcx> TypeFoldable<'tcx> for ty::ItemSubsts<'tcx> {
 285     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ItemSubsts<'tcx> {
 286         ty::ItemSubsts {
 287             substs: self.substs.fold_with(folder),
 288         }
 289     }
 290 }
 291
 292 impl<'tcx> TypeFoldable<'tcx> for ty::AutoRef<'tcx> {
 293     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::AutoRef<'tcx> {
 294         folder.fold_autoref(self)
 295     }
 296 }
 297
 298 impl<'tcx> TypeFoldable<'tcx> for ty::MethodOrigin<'tcx> {
 299     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::MethodOrigin<'tcx> {
 300         match *self {
 301             ty::MethodStatic(def_id) => {
 302                 ty::MethodStatic(def_id)
 303             }
 304             ty::MethodStaticUnboxedClosure(def_id) => {
 305                 ty::MethodStaticUnboxedClosure(def_id)
 306             }
 307             ty::MethodTypeParam(ref param) => {
 308                 ty::MethodTypeParam(ty::MethodParam {
 309                     trait_ref: param.trait_ref.fold_with(folder),
 310                     method_num: param.method_num
 311                 })
 312             }
 313             ty::MethodTraitObject(ref object) => {
 314                 ty::MethodTraitObject(ty::MethodObject {
 315                     trait_ref: object.trait_ref.fold_with(folder),
 316                     object_trait_id: object.object_trait_id,
 317                     method_num: object.method_num,
 318                     real_index: object.real_index
 319                 })
 320             }
 321         }
 322     }
 323 }
 324
 325 impl<'tcx> TypeFoldable<'tcx> for ty::vtable_origin<'tcx> {
 326     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::vtable_origin<'tcx> {
 327         match *self {
 328             ty::vtable_static(def_id, ref substs, ref origins) => {
 329                 let r_substs = substs.fold_with(folder);
 330                 let r_origins = origins.fold_with(folder);
 331                 ty::vtable_static(def_id, r_substs, r_origins)
 332             }
 333             ty::vtable_param(n, b) => {
 334                 ty::vtable_param(n, b)
 335             }
 336             ty::vtable_unboxed_closure(def_id) => {
 337                 ty::vtable_unboxed_closure(def_id)
 338             }
 339             ty::vtable_error => {
 340                 ty::vtable_error
 341             }
 342         }
 343     }
 344 }
 345
 346 impl<'tcx> TypeFoldable<'tcx> for ty::BuiltinBounds {
 347     fn fold_with<F: TypeFolder<'tcx>>(&self, _folder: &mut F) -> ty::BuiltinBounds {
 348         *self
 349     }
 350 }
 351
 352 impl<'tcx> TypeFoldable<'tcx> for ty::ExistentialBounds<'tcx> {
 353     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ExistentialBounds<'tcx> {
 354         folder.fold_existential_bounds(self)
 355     }
 356 }
 357
 358 impl<'tcx> TypeFoldable<'tcx> for ty::ParamBounds<'tcx> {
 359     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ParamBounds<'tcx> {
 360         ty::ParamBounds {
 361             region_bounds: self.region_bounds.fold_with(folder),
 362             builtin_bounds: self.builtin_bounds.fold_with(folder),
 363             trait_bounds: self.trait_bounds.fold_with(folder),
 364             projection_bounds: self.projection_bounds.fold_with(folder),
 365         }
 366     }
 367 }
 368
 369 impl<'tcx> TypeFoldable<'tcx> for ty::TypeParameterDef<'tcx> {
 370     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::TypeParameterDef<'tcx> {
 371         ty::TypeParameterDef {
 372             name: self.name,
 373             def_id: self.def_id,
 374             space: self.space,
 375             index: self.index,
 376             bounds: self.bounds.fold_with(folder),
 377             default: self.default.fold_with(folder),
 378         }
 379     }
 380 }
 381
 382 impl<'tcx> TypeFoldable<'tcx> for ty::RegionParameterDef {
 383     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::RegionParameterDef {
 384         ty::RegionParameterDef {
 385             name: self.name,
 386             def_id: self.def_id,
 387             space: self.space,
 388             index: self.index,
 389             bounds: self.bounds.fold_with(folder)
 390         }
 391     }
 392 }
 393
 394 impl<'tcx> TypeFoldable<'tcx> for ty::Generics<'tcx> {
 395     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::Generics<'tcx> {
 396         ty::Generics {
 397             types: self.types.fold_with(folder),
 398             regions: self.regions.fold_with(folder),
 399             predicates: self.predicates.fold_with(folder),
 400         }
 401     }
 402 }
 403
 404 impl<'tcx> TypeFoldable<'tcx> for ty::Predicate<'tcx> {
 405     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::Predicate<'tcx> {
 406         match *self {
 407             ty::Predicate::Trait(ref a) =>
 408                 ty::Predicate::Trait(a.fold_with(folder)),
 409             ty::Predicate::Equate(ref binder) =>
 410                 ty::Predicate::Equate(binder.fold_with(folder)),
 411             ty::Predicate::RegionOutlives(ref binder) =>
 412                 ty::Predicate::RegionOutlives(binder.fold_with(folder)),
 413             ty::Predicate::TypeOutlives(ref binder) =>
 414                 ty::Predicate::TypeOutlives(binder.fold_with(folder)),
 415             ty::Predicate::Projection(ref binder) =>
 416                 ty::Predicate::Projection(binder.fold_with(folder)),
 417         }
 418     }
 419 }
 420
 421 impl<'tcx> TypeFoldable<'tcx> for ty::ProjectionPredicate<'tcx> {
 422     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ProjectionPredicate<'tcx> {
 423         ty::ProjectionPredicate {
 424             projection_ty: self.projection_ty.fold_with(folder),
 425             ty: self.ty.fold_with(folder),
 426         }
 427     }
 428 }
 429
 430 impl<'tcx> TypeFoldable<'tcx> for ty::ProjectionTy<'tcx> {
 431     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ProjectionTy<'tcx> {
 432         ty::ProjectionTy {
 433             trait_ref: self.trait_ref.fold_with(folder),
 434             item_name: self.item_name,
 435         }
 436     }
 437 }
 438
 439 impl<'tcx> TypeFoldable<'tcx> for ty::GenericBounds<'tcx> {
 440     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::GenericBounds<'tcx> {
 441         ty::GenericBounds {
 442             predicates: self.predicates.fold_with(folder),
 443         }
 444     }
 445 }
 446
 447 impl<'tcx> TypeFoldable<'tcx> for ty::UnsizeKind<'tcx> {
 448     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::UnsizeKind<'tcx> {
 449         match *self {
 450             ty::UnsizeLength(len) => ty::UnsizeLength(len),
 451             ty::UnsizeStruct(box ref k, n) => ty::UnsizeStruct(box k.fold_with(folder), n),
 452             ty::UnsizeVtable(ty::TyTrait{ref principal, ref bounds}, self_ty) => {
 453                 ty::UnsizeVtable(
 454                     ty::TyTrait {
 455                         principal: principal.fold_with(folder),
 456                         bounds: bounds.fold_with(folder),
 457                     },
 458                     self_ty.fold_with(folder))
 459             }
 460         }
 461     }
 462 }
 463
 464 impl<'tcx,O> TypeFoldable<'tcx> for traits::Obligation<'tcx,O>
 465     where O : TypeFoldable<'tcx>
 466 {
 467     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::Obligation<'tcx, O> {
 468         traits::Obligation {
 469             cause: self.cause.clone(),
 470             recursion_depth: self.recursion_depth,
 471             predicate: self.predicate.fold_with(folder),
 472         }
 473     }
 474 }
 475
 476 impl<'tcx, N: TypeFoldable<'tcx>> TypeFoldable<'tcx> for traits::VtableImplData<'tcx, N> {
 477     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::VtableImplData<'tcx, N> {
 478         traits::VtableImplData {
 479             impl_def_id: self.impl_def_id,
 480             substs: self.substs.fold_with(folder),
 481             nested: self.nested.fold_with(folder),
 482         }
 483     }
 484 }
 485
 486 impl<'tcx, N: TypeFoldable<'tcx>> TypeFoldable<'tcx> for traits::VtableBuiltinData<N> {
 487     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::VtableBuiltinData<N> {
 488         traits::VtableBuiltinData {
 489             nested: self.nested.fold_with(folder),
 490         }
 491     }
 492 }
 493
 494 impl<'tcx, N: TypeFoldable<'tcx>> TypeFoldable<'tcx> for traits::Vtable<'tcx, N> {
 495     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::Vtable<'tcx, N> {
 496         match *self {
 497             traits::VtableImpl(ref v) => traits::VtableImpl(v.fold_with(folder)),
 498             traits::VtableUnboxedClosure(d, ref s) => {
 499                 traits::VtableUnboxedClosure(d, s.fold_with(folder))
 500             }
 501             traits::VtableFnPointer(ref d) => {
 502                 traits::VtableFnPointer(d.fold_with(folder))
 503             }
 504             traits::VtableParam => traits::VtableParam,
 505             traits::VtableBuiltin(ref d) => traits::VtableBuiltin(d.fold_with(folder)),
 506             traits::VtableObject(ref d) => traits::VtableObject(d.fold_with(folder)),
 507         }
 508     }
 509 }
 510
 511 impl<'tcx> TypeFoldable<'tcx> for traits::VtableObjectData<'tcx> {
 512     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::VtableObjectData<'tcx> {
 513         traits::VtableObjectData {
 514             object_ty: self.object_ty.fold_with(folder)
 515         }
 516     }
 517 }
 518
 519 impl<'tcx> TypeFoldable<'tcx> for ty::EquatePredicate<'tcx> {
 520     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::EquatePredicate<'tcx> {
 521         ty::EquatePredicate(self.0.fold_with(folder),
 522                             self.1.fold_with(folder))
 523     }
 524 }
 525
 526 impl<'tcx> TypeFoldable<'tcx> for ty::TraitPredicate<'tcx> {
 527     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::TraitPredicate<'tcx> {
 528         ty::TraitPredicate {
 529             trait_ref: self.trait_ref.fold_with(folder)
 530         }
 531     }
 532 }
 533
 534 impl<'tcx,T,U> TypeFoldable<'tcx> for ty::OutlivesPredicate<T,U>
 535     where T : TypeFoldable<'tcx>,
 536           U : TypeFoldable<'tcx>,
 537 {
 538     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::OutlivesPredicate<T,U> {
 539         ty::OutlivesPredicate(self.0.fold_with(folder),
 540                               self.1.fold_with(folder))
 541     }
 542 }
 543
 544 impl<'tcx> TypeFoldable<'tcx> for ty::UnboxedClosureUpvar<'tcx> {
 545     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::UnboxedClosureUpvar<'tcx> {
 546         ty::UnboxedClosureUpvar {
 547             def: self.def,
 548             span: self.span,
 549             ty: self.ty.fold_with(folder),
 550         }
 551     }
 552 }
 553
 554 ///////////////////////////////////////////////////////////////////////////
 555 // "super" routines: these are the default implementations for TypeFolder.
 556 //
 557 // They should invoke `foo.fold_with()` to do recursive folding.
 558
 559 pub fn super_fold_ty<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 560                                                 ty: Ty<'tcx>)
 561                                                 -> Ty<'tcx> {
 562     let sty = match ty.sty {
 563         ty::ty_uniq(typ) => {
 564             ty::ty_uniq(typ.fold_with(this))
 565         }
 566         ty::ty_ptr(ref tm) => {
 567             ty::ty_ptr(tm.fold_with(this))
 568         }
 569         ty::ty_vec(typ, sz) => {
 570             ty::ty_vec(typ.fold_with(this), sz)
 571         }
 572         ty::ty_open(typ) => {
 573             ty::ty_open(typ.fold_with(this))
 574         }
 575         ty::ty_enum(tid, ref substs) => {
 576             let substs = substs.fold_with(this);
 577             ty::ty_enum(tid, this.tcx().mk_substs(substs))
 578         }
 579         ty::ty_trait(box ty::TyTrait { ref principal, ref bounds }) => {
 580             ty::ty_trait(box ty::TyTrait {
 581                 principal: principal.fold_with(this),
 582                 bounds: bounds.fold_with(this),
 583             })
 584         }
 585         ty::ty_tup(ref ts) => {
 586             ty::ty_tup(ts.fold_with(this))
 587         }
 588         ty::ty_bare_fn(opt_def_id, ref f) => {
 589             let bfn = f.fold_with(this);
 590             ty::ty_bare_fn(opt_def_id, this.tcx().mk_bare_fn(bfn))
 591         }
 592         ty::ty_closure(ref f) => {
 593             ty::ty_closure(f.fold_with(this))
 594         }
 595         ty::ty_rptr(r, ref tm) => {
 596             let r = r.fold_with(this);
 597             ty::ty_rptr(this.tcx().mk_region(r), tm.fold_with(this))
 598         }
 599         ty::ty_struct(did, ref substs) => {
 600             let substs = substs.fold_with(this);
 601             ty::ty_struct(did, this.tcx().mk_substs(substs))
 602         }
 603         ty::ty_unboxed_closure(did, ref region, ref substs) => {
 604             let r = region.fold_with(this);
 605             let s = substs.fold_with(this);
 606             ty::ty_unboxed_closure(did, this.tcx().mk_region(r), this.tcx().mk_substs(s))
 607         }
 608         ty::ty_projection(ref data) => {
 609             ty::ty_projection(data.fold_with(this))
 610         }
 611         ty::ty_bool | ty::ty_char | ty::ty_str |
 612         ty::ty_int(_) | ty::ty_uint(_) | ty::ty_float(_) |
 613         ty::ty_err | ty::ty_infer(_) |
 614         ty::ty_param(..) => {
 615             ty.sty.clone()
 616         }
 617     };
 618     ty::mk_t(this.tcx(), sty)
 619 }
 620
 621 pub fn super_fold_substs<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 622                                                     substs: &subst::Substs<'tcx>)
 623                                                     -> subst::Substs<'tcx> {
 624     let regions = match substs.regions {
 625         subst::ErasedRegions => {
 626             subst::ErasedRegions
 627         }
 628         subst::NonerasedRegions(ref regions) => {
 629             subst::NonerasedRegions(regions.fold_with(this))
 630         }
 631     };
 632
 633     subst::Substs { regions: regions,
 634                     types: substs.types.fold_with(this) }
 635 }
 636
 637 pub fn super_fold_fn_sig<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 638                                                     sig: &ty::FnSig<'tcx>)
 639                                                     -> ty::FnSig<'tcx>
 640 {
 641     ty::FnSig { inputs: sig.inputs.fold_with(this),
 642                 output: sig.output.fold_with(this),
 643                 variadic: sig.variadic }
 644 }
 645
 646 pub fn super_fold_output<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 647                                                     output: &ty::FnOutput<'tcx>)
 648                                                     -> ty::FnOutput<'tcx> {
 649     match *output {
 650         ty::FnConverging(ref ty) => ty::FnConverging(ty.fold_with(this)),
 651         ty::FnDiverging => ty::FnDiverging
 652     }
 653 }
 654
 655 pub fn super_fold_bare_fn_ty<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 656                                                         fty: &ty::BareFnTy<'tcx>)
 657                                                         -> ty::BareFnTy<'tcx>
 658 {
 659     ty::BareFnTy { sig: fty.sig.fold_with(this),
 660                    abi: fty.abi,
 661                    unsafety: fty.unsafety }
 662 }
 663
 664 pub fn super_fold_closure_ty<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 665                                                         fty: &ty::ClosureTy<'tcx>)
 666                                                         -> ty::ClosureTy<'tcx>
 667 {
 668     ty::ClosureTy {
 669         store: fty.store.fold_with(this),
 670         sig: fty.sig.fold_with(this),
 671         unsafety: fty.unsafety,
 672         onceness: fty.onceness,
 673         bounds: fty.bounds.fold_with(this),
 674         abi: fty.abi,
 675     }
 676 }
 677
 678 pub fn super_fold_trait_ref<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 679                                                        t: &ty::TraitRef<'tcx>)
 680                                                        -> ty::TraitRef<'tcx>
 681 {
 682     let substs = t.substs.fold_with(this);
 683     ty::TraitRef {
 684         def_id: t.def_id,
 685         substs: this.tcx().mk_substs(substs),
 686     }
 687 }
 688
 689 pub fn super_fold_mt<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 690                                                 mt: &ty::mt<'tcx>)
 691                                                 -> ty::mt<'tcx> {
 692     ty::mt {ty: mt.ty.fold_with(this),
 693             mutbl: mt.mutbl}
 694 }
 695
 696 pub fn super_fold_trait_store<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 697                                                          trait_store: ty::TraitStore)
 698                                                          -> ty::TraitStore {
 699     match trait_store {
 700         ty::UniqTraitStore => ty::UniqTraitStore,
 701         ty::RegionTraitStore(r, m) => {
 702             ty::RegionTraitStore(r.fold_with(this), m)
 703         }
 704     }
 705 }
 706
 707 pub fn super_fold_existential_bounds<'tcx, T: TypeFolder<'tcx>>(
 708     this: &mut T,
 709     bounds: &ty::ExistentialBounds<'tcx>)
 710     -> ty::ExistentialBounds<'tcx>
 711 {
 712     ty::ExistentialBounds {
 713         region_bound: bounds.region_bound.fold_with(this),
 714         builtin_bounds: bounds.builtin_bounds,
 715         projection_bounds: bounds.projection_bounds.fold_with(this),
 716     }
 717 }
 718
 719 pub fn super_fold_autoref<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 720                                                      autoref: &ty::AutoRef<'tcx>)
 721                                                      -> ty::AutoRef<'tcx>
 722 {
 723     match *autoref {
 724         ty::AutoPtr(r, m, None) => ty::AutoPtr(this.fold_region(r), m, None),
 725         ty::AutoPtr(r, m, Some(ref a)) => {
 726             ty::AutoPtr(this.fold_region(r), m, Some(box super_fold_autoref(this, &**a)))
 727         }
 728         ty::AutoUnsafe(m, None) => ty::AutoUnsafe(m, None),
 729         ty::AutoUnsafe(m, Some(ref a)) => {
 730             ty::AutoUnsafe(m, Some(box super_fold_autoref(this, &**a)))
 731         }
 732         ty::AutoUnsize(ref k) => ty::AutoUnsize(k.fold_with(this)),
 733         ty::AutoUnsizeUniq(ref k) => ty::AutoUnsizeUniq(k.fold_with(this)),
 734     }
 735 }
 736
 737 pub fn super_fold_item_substs<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 738                                                          substs: ty::ItemSubsts<'tcx>)
 739                                                          -> ty::ItemSubsts<'tcx>
 740 {
 741     ty::ItemSubsts {
 742         substs: substs.substs.fold_with(this),
 743     }
 744 }
 745
 746 ///////////////////////////////////////////////////////////////////////////
 747 // Some sample folders
 748
 749 pub struct BottomUpFolder<'a, 'tcx: 'a, F> where F: FnMut(Ty<'tcx>) -> Ty<'tcx> {
 750     pub tcx: &'a ty::ctxt<'tcx>,
 751     pub fldop: F,
 752 }
 753
 754 impl<'a, 'tcx, F> TypeFolder<'tcx> for BottomUpFolder<'a, 'tcx, F> where
 755     F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
 756 {
 757     fn tcx(&self) -> &ty::ctxt<'tcx> { self.tcx }
 758
 759     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
 760         let t1 = super_fold_ty(self, ty);
 761         (self.fldop)(t1)
 762     }
 763 }
 764
 765 ///////////////////////////////////////////////////////////////////////////
 766 // Region folder
 767
 768 /// Folds over the substructure of a type, visiting its component
 769 /// types and all regions that occur *free* within it.
 770 ///
 771 /// That is, `Ty` can contain function or method types that bind
 772 /// regions at the call site (`ReLateBound`), and occurrences of
 773 /// regions (aka "lifetimes") that are bound within a type are not
 774 /// visited by this folder; only regions that occur free will be
 775 /// visited by `fld_r`.
 776
 777 pub struct RegionFolder<'a, 'tcx: 'a> {
 778     tcx: &'a ty::ctxt<'tcx>,
 779     current_depth: u32,
 780     fld_r: &'a mut (FnMut(ty::Region, u32) -> ty::Region + 'a),
 781 }
 782
 783 impl<'a, 'tcx> RegionFolder<'a, 'tcx> {
 784     pub fn new<F>(tcx: &'a ty::ctxt<'tcx>, fld_r: &'a mut F) -> RegionFolder<'a, 'tcx>
 785         where F : FnMut(ty::Region, u32) -> ty::Region
 786     {
 787         RegionFolder {
 788             tcx: tcx,
 789             current_depth: 1,
 790             fld_r: fld_r,
 791         }
 792     }
 793 }
 794
 795 pub fn collect_regions<'tcx,T>(tcx: &ty::ctxt<'tcx>, value: &T) -> Vec<ty::Region>
 796     where T : TypeFoldable<'tcx>
 797 {
 798     let mut vec = Vec::new();
 799     fold_regions(tcx, value, |r, _| { vec.push(r); r });
 800     vec
 801 }
 802
 803 pub fn fold_regions<'tcx,T,F>(tcx: &ty::ctxt<'tcx>,
 804                               value: &T,
 805                               mut f: F)
 806                               -> T
 807     where F : FnMut(ty::Region, u32) -> ty::Region,
 808           T : TypeFoldable<'tcx>,
 809 {
 810     value.fold_with(&mut RegionFolder::new(tcx, &mut f))
 811 }
 812
 813 impl<'a, 'tcx> TypeFolder<'tcx> for RegionFolder<'a, 'tcx>
 814 {
 815     fn tcx(&self) -> &ty::ctxt<'tcx> { self.tcx }
 816
 817     fn enter_region_binder(&mut self) {
 818         self.current_depth += 1;
 819     }
 820
 821     fn exit_region_binder(&mut self) {
 822         self.current_depth -= 1;
 823     }
 824
 825     fn fold_region(&mut self, r: ty::Region) -> ty::Region {
 826         match r {
 827             ty::ReLateBound(debruijn, _) if debruijn.depth < self.current_depth => {
 828                 debug!("RegionFolder.fold_region({}) skipped bound region (current depth={})",
 829                        r.repr(self.tcx()), self.current_depth);
 830                 r
 831             }
 832             _ => {
 833                 debug!("RegionFolder.fold_region({}) folding free region (current_depth={})",
 834                        r.repr(self.tcx()), self.current_depth);
 835                 self.fld_r.call_mut((r, self.current_depth))
 836             }
 837         }
 838     }
 839 }
 840
 841 ///////////////////////////////////////////////////////////////////////////
 842 // Region eraser
 843 //
 844 // Replaces all free regions with 'static. Useful in trans.
 845
 846 pub struct RegionEraser<'a, 'tcx: 'a> {
 847     tcx: &'a ty::ctxt<'tcx>,
 848 }
 849
 850 pub fn erase_regions<'tcx, T: TypeFoldable<'tcx>>(tcx: &ty::ctxt<'tcx>, t: T) -> T {
 851     let mut eraser = RegionEraser { tcx: tcx };
 852     t.fold_with(&mut eraser)
 853 }
 854
 855 impl<'a, 'tcx> TypeFolder<'tcx> for RegionEraser<'a, 'tcx> {
 856     fn tcx(&self) -> &ty::ctxt<'tcx> { self.tcx }
 857
 858     fn fold_region(&mut self, r: ty::Region) -> ty::Region {
 859         match r {
 860             ty::ReLateBound(..) | ty::ReEarlyBound(..) => r,
 861             _ => ty::ReStatic
 862         }
 863     }
 864 }
 865
 866 ///////////////////////////////////////////////////////////////////////////
 867 // Region shifter
 868 //
 869 // Shifts the De Bruijn indices on all escaping bound regions by a
 870 // fixed amount. Useful in substitution or when otherwise introducing
 871 // a binding level that is not intended to capture the existing bound
 872 // regions. See comment on `shift_regions_through_binders` method in
 873 // `subst.rs` for more details.
 874
 875 pub fn shift_region(region: ty::Region, amount: u32) -> ty::Region {
 876     match region {
 877         ty::ReLateBound(debruijn, br) => {
 878             ty::ReLateBound(debruijn.shifted(amount), br)
 879         }
 880         _ => {
 881             region
 882         }
 883     }
 884 }
 885
 886 pub fn shift_regions<'tcx, T:TypeFoldable<'tcx>+Repr<'tcx>>(tcx: &ty::ctxt<'tcx>,
 887                                                             amount: u32, value: &T) -> T {
 888     debug!("shift_regions(value={}, amount={})",
 889            value.repr(tcx), amount);
 890
 891     value.fold_with(&mut RegionFolder::new(tcx, &mut |region, _current_depth| {
 892         shift_region(region, amount)
 893     }))
 894 }