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};
  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_binder<T>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T>
  74         where T : TypeFoldable<'tcx> + Repr<'tcx>
  75     {
  76         // FIXME(#20526) this should replace `enter_region_binder`/`exit_region_binder`.
  77         super_fold_binder(self, t)
  78     }
  79
  80     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
  81         super_fold_ty(self, t)
  82     }
  83
  84     fn fold_mt(&mut self, t: &ty::mt<'tcx>) -> ty::mt<'tcx> {
  85         super_fold_mt(self, t)
  86     }
  87
  88     fn fold_trait_ref(&mut self, t: &ty::TraitRef<'tcx>) -> ty::TraitRef<'tcx> {
  89         super_fold_trait_ref(self, t)
  90     }
  91
  92     fn fold_substs(&mut self,
  93                    substs: &subst::Substs<'tcx>)
  94                    -> subst::Substs<'tcx> {
  95         super_fold_substs(self, substs)
  96     }
  97
  98     fn fold_fn_sig(&mut self,
  99                    sig: &ty::FnSig<'tcx>)
 100                    -> ty::FnSig<'tcx> {
 101         super_fold_fn_sig(self, sig)
 102     }
 103
 104     fn fold_output(&mut self,
 105                       output: &ty::FnOutput<'tcx>)
 106                       -> ty::FnOutput<'tcx> {
 107         super_fold_output(self, output)
 108     }
 109
 110     fn fold_bare_fn_ty(&mut self,
 111                        fty: &ty::BareFnTy<'tcx>)
 112                        -> ty::BareFnTy<'tcx>
 113     {
 114         super_fold_bare_fn_ty(self, fty)
 115     }
 116
 117     fn fold_closure_ty(&mut self,
 118                        fty: &ty::ClosureTy<'tcx>)
 119                        -> ty::ClosureTy<'tcx> {
 120         super_fold_closure_ty(self, fty)
 121     }
 122
 123     fn fold_region(&mut self, r: ty::Region) -> ty::Region {
 124         r
 125     }
 126
 127     fn fold_trait_store(&mut self, s: ty::TraitStore) -> ty::TraitStore {
 128         super_fold_trait_store(self, s)
 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 impl<'tcx> TypeFoldable<'tcx> for () {
 157     fn fold_with<F:TypeFolder<'tcx>>(&self, _: &mut F) -> () {
 158         ()
 159     }
 160 }
 161
 162 impl<'tcx, T:TypeFoldable<'tcx>, U:TypeFoldable<'tcx>> TypeFoldable<'tcx> for (T, U) {
 163     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> (T, U) {
 164         (self.0.fold_with(folder), self.1.fold_with(folder))
 165     }
 166 }
 167
 168 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Option<T> {
 169     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Option<T> {
 170         self.as_ref().map(|t| t.fold_with(folder))
 171     }
 172 }
 173
 174 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Rc<T> {
 175     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Rc<T> {
 176         Rc::new((**self).fold_with(folder))
 177     }
 178 }
 179
 180 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Box<T> {
 181     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Box<T> {
 182         let content: T = (**self).fold_with(folder);
 183         box content
 184     }
 185 }
 186
 187 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Vec<T> {
 188     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Vec<T> {
 189         self.iter().map(|t| t.fold_with(folder)).collect()
 190     }
 191 }
 192
 193 impl<'tcx, T:TypeFoldable<'tcx>+Repr<'tcx>> TypeFoldable<'tcx> for ty::Binder<T> {
 194     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::Binder<T> {
 195         folder.fold_binder(self)
 196     }
 197 }
 198
 199 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for OwnedSlice<T> {
 200     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> OwnedSlice<T> {
 201         self.iter().map(|t| t.fold_with(folder)).collect()
 202     }
 203 }
 204
 205 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for VecPerParamSpace<T> {
 206     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> VecPerParamSpace<T> {
 207
 208         // Things in the Fn space take place under an additional level
 209         // of region binding relative to the other spaces. This is
 210         // because those entries are attached to a method, and methods
 211         // always introduce a level of region binding.
 212
 213         let result = self.map_enumerated(|(space, index, elem)| {
 214             if space == subst::FnSpace && index == 0 {
 215                 // enter new level when/if we reach the first thing in fn space
 216                 folder.enter_region_binder();
 217             }
 218             elem.fold_with(folder)
 219         });
 220         if result.len(subst::FnSpace) > 0 {
 221             // if there was anything in fn space, exit the region binding level
 222             folder.exit_region_binder();
 223         }
 224         result
 225     }
 226 }
 227
 228 impl<'tcx> TypeFoldable<'tcx> for ty::TraitStore {
 229     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::TraitStore {
 230         folder.fold_trait_store(*self)
 231     }
 232 }
 233
 234 impl<'tcx> TypeFoldable<'tcx> for Ty<'tcx> {
 235     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Ty<'tcx> {
 236         folder.fold_ty(*self)
 237     }
 238 }
 239
 240 impl<'tcx> TypeFoldable<'tcx> for ty::BareFnTy<'tcx> {
 241     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::BareFnTy<'tcx> {
 242         folder.fold_bare_fn_ty(self)
 243     }
 244 }
 245
 246 impl<'tcx> TypeFoldable<'tcx> for ty::ClosureTy<'tcx> {
 247     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ClosureTy<'tcx> {
 248         folder.fold_closure_ty(self)
 249     }
 250 }
 251
 252 impl<'tcx> TypeFoldable<'tcx> for ty::mt<'tcx> {
 253     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::mt<'tcx> {
 254         folder.fold_mt(self)
 255     }
 256 }
 257
 258 impl<'tcx> TypeFoldable<'tcx> for ty::FnOutput<'tcx> {
 259     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::FnOutput<'tcx> {
 260         folder.fold_output(self)
 261     }
 262 }
 263
 264 impl<'tcx> TypeFoldable<'tcx> for ty::FnSig<'tcx> {
 265     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::FnSig<'tcx> {
 266         folder.fold_fn_sig(self)
 267     }
 268 }
 269
 270 impl<'tcx> TypeFoldable<'tcx> for ty::TraitRef<'tcx> {
 271     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::TraitRef<'tcx> {
 272         folder.fold_trait_ref(self)
 273     }
 274 }
 275
 276 impl<'tcx> TypeFoldable<'tcx> for ty::field<'tcx> {
 277     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::field<'tcx> {
 278         ty::field {
 279             name: self.name,
 280             mt: self.mt.fold_with(folder),
 281         }
 282     }
 283 }
 284
 285 impl<'tcx> TypeFoldable<'tcx> for ty::Region {
 286     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::Region {
 287         folder.fold_region(*self)
 288     }
 289 }
 290
 291 impl<'tcx> TypeFoldable<'tcx> for subst::Substs<'tcx> {
 292     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> subst::Substs<'tcx> {
 293         folder.fold_substs(self)
 294     }
 295 }
 296
 297 impl<'tcx> TypeFoldable<'tcx> for ty::ItemSubsts<'tcx> {
 298     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ItemSubsts<'tcx> {
 299         ty::ItemSubsts {
 300             substs: self.substs.fold_with(folder),
 301         }
 302     }
 303 }
 304
 305 impl<'tcx> TypeFoldable<'tcx> for ty::AutoRef<'tcx> {
 306     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::AutoRef<'tcx> {
 307         folder.fold_autoref(self)
 308     }
 309 }
 310
 311 impl<'tcx> TypeFoldable<'tcx> for ty::MethodOrigin<'tcx> {
 312     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::MethodOrigin<'tcx> {
 313         match *self {
 314             ty::MethodStatic(def_id) => {
 315                 ty::MethodStatic(def_id)
 316             }
 317             ty::MethodStaticUnboxedClosure(def_id) => {
 318                 ty::MethodStaticUnboxedClosure(def_id)
 319             }
 320             ty::MethodTypeParam(ref param) => {
 321                 ty::MethodTypeParam(ty::MethodParam {
 322                     trait_ref: param.trait_ref.fold_with(folder),
 323                     method_num: param.method_num
 324                 })
 325             }
 326             ty::MethodTraitObject(ref object) => {
 327                 ty::MethodTraitObject(ty::MethodObject {
 328                     trait_ref: object.trait_ref.fold_with(folder),
 329                     object_trait_id: object.object_trait_id,
 330                     method_num: object.method_num,
 331                     real_index: object.real_index
 332                 })
 333             }
 334         }
 335     }
 336 }
 337
 338 impl<'tcx> TypeFoldable<'tcx> for ty::vtable_origin<'tcx> {
 339     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::vtable_origin<'tcx> {
 340         match *self {
 341             ty::vtable_static(def_id, ref substs, ref origins) => {
 342                 let r_substs = substs.fold_with(folder);
 343                 let r_origins = origins.fold_with(folder);
 344                 ty::vtable_static(def_id, r_substs, r_origins)
 345             }
 346             ty::vtable_param(n, b) => {
 347                 ty::vtable_param(n, b)
 348             }
 349             ty::vtable_unboxed_closure(def_id) => {
 350                 ty::vtable_unboxed_closure(def_id)
 351             }
 352             ty::vtable_error => {
 353                 ty::vtable_error
 354             }
 355         }
 356     }
 357 }
 358
 359 impl<'tcx> TypeFoldable<'tcx> for ty::BuiltinBounds {
 360     fn fold_with<F: TypeFolder<'tcx>>(&self, _folder: &mut F) -> ty::BuiltinBounds {
 361         *self
 362     }
 363 }
 364
 365 impl<'tcx> TypeFoldable<'tcx> for ty::ExistentialBounds<'tcx> {
 366     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ExistentialBounds<'tcx> {
 367         folder.fold_existential_bounds(self)
 368     }
 369 }
 370
 371 impl<'tcx> TypeFoldable<'tcx> for ty::ParamBounds<'tcx> {
 372     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ParamBounds<'tcx> {
 373         ty::ParamBounds {
 374             region_bounds: self.region_bounds.fold_with(folder),
 375             builtin_bounds: self.builtin_bounds.fold_with(folder),
 376             trait_bounds: self.trait_bounds.fold_with(folder),
 377             projection_bounds: self.projection_bounds.fold_with(folder),
 378         }
 379     }
 380 }
 381
 382 impl<'tcx> TypeFoldable<'tcx> for ty::TypeParameterDef<'tcx> {
 383     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::TypeParameterDef<'tcx> {
 384         ty::TypeParameterDef {
 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             default: self.default.fold_with(folder),
 391         }
 392     }
 393 }
 394
 395 impl<'tcx> TypeFoldable<'tcx> for ty::RegionParameterDef {
 396     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::RegionParameterDef {
 397         ty::RegionParameterDef {
 398             name: self.name,
 399             def_id: self.def_id,
 400             space: self.space,
 401             index: self.index,
 402             bounds: self.bounds.fold_with(folder)
 403         }
 404     }
 405 }
 406
 407 impl<'tcx> TypeFoldable<'tcx> for ty::Generics<'tcx> {
 408     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::Generics<'tcx> {
 409         ty::Generics {
 410             types: self.types.fold_with(folder),
 411             regions: self.regions.fold_with(folder),
 412             predicates: self.predicates.fold_with(folder),
 413         }
 414     }
 415 }
 416
 417 impl<'tcx> TypeFoldable<'tcx> for ty::Predicate<'tcx> {
 418     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::Predicate<'tcx> {
 419         match *self {
 420             ty::Predicate::Trait(ref a) =>
 421                 ty::Predicate::Trait(a.fold_with(folder)),
 422             ty::Predicate::Equate(ref binder) =>
 423                 ty::Predicate::Equate(binder.fold_with(folder)),
 424             ty::Predicate::RegionOutlives(ref binder) =>
 425                 ty::Predicate::RegionOutlives(binder.fold_with(folder)),
 426             ty::Predicate::TypeOutlives(ref binder) =>
 427                 ty::Predicate::TypeOutlives(binder.fold_with(folder)),
 428             ty::Predicate::Projection(ref binder) =>
 429                 ty::Predicate::Projection(binder.fold_with(folder)),
 430         }
 431     }
 432 }
 433
 434 impl<'tcx> TypeFoldable<'tcx> for ty::ProjectionPredicate<'tcx> {
 435     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ProjectionPredicate<'tcx> {
 436         ty::ProjectionPredicate {
 437             projection_ty: self.projection_ty.fold_with(folder),
 438             ty: self.ty.fold_with(folder),
 439         }
 440     }
 441 }
 442
 443 impl<'tcx> TypeFoldable<'tcx> for ty::ProjectionTy<'tcx> {
 444     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ProjectionTy<'tcx> {
 445         ty::ProjectionTy {
 446             trait_ref: self.trait_ref.fold_with(folder),
 447             item_name: self.item_name,
 448         }
 449     }
 450 }
 451
 452 impl<'tcx> TypeFoldable<'tcx> for ty::GenericBounds<'tcx> {
 453     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::GenericBounds<'tcx> {
 454         ty::GenericBounds {
 455             predicates: self.predicates.fold_with(folder),
 456         }
 457     }
 458 }
 459
 460 impl<'tcx> TypeFoldable<'tcx> for ty::UnsizeKind<'tcx> {
 461     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::UnsizeKind<'tcx> {
 462         match *self {
 463             ty::UnsizeLength(len) => ty::UnsizeLength(len),
 464             ty::UnsizeStruct(box ref k, n) => ty::UnsizeStruct(box k.fold_with(folder), n),
 465             ty::UnsizeVtable(ty::TyTrait{ref principal, ref bounds}, self_ty) => {
 466                 ty::UnsizeVtable(
 467                     ty::TyTrait {
 468                         principal: principal.fold_with(folder),
 469                         bounds: bounds.fold_with(folder),
 470                     },
 471                     self_ty.fold_with(folder))
 472             }
 473         }
 474     }
 475 }
 476
 477 impl<'tcx,O> TypeFoldable<'tcx> for traits::Obligation<'tcx,O>
 478     where O : TypeFoldable<'tcx>
 479 {
 480     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::Obligation<'tcx, O> {
 481         traits::Obligation {
 482             cause: self.cause.clone(),
 483             recursion_depth: self.recursion_depth,
 484             predicate: self.predicate.fold_with(folder),
 485         }
 486     }
 487 }
 488
 489 impl<'tcx, N: TypeFoldable<'tcx>> TypeFoldable<'tcx> for traits::VtableImplData<'tcx, N> {
 490     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::VtableImplData<'tcx, N> {
 491         traits::VtableImplData {
 492             impl_def_id: self.impl_def_id,
 493             substs: self.substs.fold_with(folder),
 494             nested: self.nested.fold_with(folder),
 495         }
 496     }
 497 }
 498
 499 impl<'tcx, N: TypeFoldable<'tcx>> TypeFoldable<'tcx> for traits::VtableBuiltinData<N> {
 500     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::VtableBuiltinData<N> {
 501         traits::VtableBuiltinData {
 502             nested: self.nested.fold_with(folder),
 503         }
 504     }
 505 }
 506
 507 impl<'tcx, N: TypeFoldable<'tcx>> TypeFoldable<'tcx> for traits::Vtable<'tcx, N> {
 508     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::Vtable<'tcx, N> {
 509         match *self {
 510             traits::VtableImpl(ref v) => traits::VtableImpl(v.fold_with(folder)),
 511             traits::VtableUnboxedClosure(d, ref s) => {
 512                 traits::VtableUnboxedClosure(d, s.fold_with(folder))
 513             }
 514             traits::VtableFnPointer(ref d) => {
 515                 traits::VtableFnPointer(d.fold_with(folder))
 516             }
 517             traits::VtableParam(ref n) => traits::VtableParam(n.fold_with(folder)),
 518             traits::VtableBuiltin(ref d) => traits::VtableBuiltin(d.fold_with(folder)),
 519             traits::VtableObject(ref d) => traits::VtableObject(d.fold_with(folder)),
 520         }
 521     }
 522 }
 523
 524 impl<'tcx> TypeFoldable<'tcx> for traits::VtableObjectData<'tcx> {
 525     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::VtableObjectData<'tcx> {
 526         traits::VtableObjectData {
 527             object_ty: self.object_ty.fold_with(folder)
 528         }
 529     }
 530 }
 531
 532 impl<'tcx> TypeFoldable<'tcx> for ty::EquatePredicate<'tcx> {
 533     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::EquatePredicate<'tcx> {
 534         ty::EquatePredicate(self.0.fold_with(folder),
 535                             self.1.fold_with(folder))
 536     }
 537 }
 538
 539 impl<'tcx> TypeFoldable<'tcx> for ty::TraitPredicate<'tcx> {
 540     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::TraitPredicate<'tcx> {
 541         ty::TraitPredicate {
 542             trait_ref: self.trait_ref.fold_with(folder)
 543         }
 544     }
 545 }
 546
 547 impl<'tcx,T,U> TypeFoldable<'tcx> for ty::OutlivesPredicate<T,U>
 548     where T : TypeFoldable<'tcx>,
 549           U : TypeFoldable<'tcx>,
 550 {
 551     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::OutlivesPredicate<T,U> {
 552         ty::OutlivesPredicate(self.0.fold_with(folder),
 553                               self.1.fold_with(folder))
 554     }
 555 }
 556
 557 impl<'tcx> TypeFoldable<'tcx> for ty::UnboxedClosureUpvar<'tcx> {
 558     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::UnboxedClosureUpvar<'tcx> {
 559         ty::UnboxedClosureUpvar {
 560             def: self.def,
 561             span: self.span,
 562             ty: self.ty.fold_with(folder),
 563         }
 564     }
 565 }
 566
 567 impl<'a, 'tcx> TypeFoldable<'tcx> for ty::ParameterEnvironment<'a, 'tcx> where 'tcx: 'a {
 568     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ParameterEnvironment<'a, 'tcx> {
 569         ty::ParameterEnvironment {
 570             tcx: self.tcx,
 571             free_substs: self.free_substs.fold_with(folder),
 572             implicit_region_bound: self.implicit_region_bound.fold_with(folder),
 573             caller_bounds: self.caller_bounds.fold_with(folder),
 574             selection_cache: traits::SelectionCache::new(),
 575         }
 576     }
 577 }
 578
 579 ///////////////////////////////////////////////////////////////////////////
 580 // "super" routines: these are the default implementations for TypeFolder.
 581 //
 582 // They should invoke `foo.fold_with()` to do recursive folding.
 583
 584 pub fn super_fold_binder<'tcx, T, U>(this: &mut T,
 585                                      binder: &ty::Binder<U>)
 586                                      -> ty::Binder<U>
 587     where T : TypeFolder<'tcx>, U : TypeFoldable<'tcx>
 588 {
 589     this.enter_region_binder();
 590     let result = ty::Binder(binder.0.fold_with(this));
 591     this.exit_region_binder();
 592     result
 593 }
 594
 595 pub fn super_fold_ty<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 596                                                 ty: Ty<'tcx>)
 597                                                 -> Ty<'tcx> {
 598     let sty = match ty.sty {
 599         ty::ty_uniq(typ) => {
 600             ty::ty_uniq(typ.fold_with(this))
 601         }
 602         ty::ty_ptr(ref tm) => {
 603             ty::ty_ptr(tm.fold_with(this))
 604         }
 605         ty::ty_vec(typ, sz) => {
 606             ty::ty_vec(typ.fold_with(this), sz)
 607         }
 608         ty::ty_open(typ) => {
 609             ty::ty_open(typ.fold_with(this))
 610         }
 611         ty::ty_enum(tid, ref substs) => {
 612             let substs = substs.fold_with(this);
 613             ty::ty_enum(tid, this.tcx().mk_substs(substs))
 614         }
 615         ty::ty_trait(box ty::TyTrait { ref principal, ref bounds }) => {
 616             ty::ty_trait(box ty::TyTrait {
 617                 principal: principal.fold_with(this),
 618                 bounds: bounds.fold_with(this),
 619             })
 620         }
 621         ty::ty_tup(ref ts) => {
 622             ty::ty_tup(ts.fold_with(this))
 623         }
 624         ty::ty_bare_fn(opt_def_id, ref f) => {
 625             let bfn = f.fold_with(this);
 626             ty::ty_bare_fn(opt_def_id, this.tcx().mk_bare_fn(bfn))
 627         }
 628         ty::ty_rptr(r, ref tm) => {
 629             let r = r.fold_with(this);
 630             ty::ty_rptr(this.tcx().mk_region(r), tm.fold_with(this))
 631         }
 632         ty::ty_struct(did, ref substs) => {
 633             let substs = substs.fold_with(this);
 634             ty::ty_struct(did, this.tcx().mk_substs(substs))
 635         }
 636         ty::ty_unboxed_closure(did, ref region, ref substs) => {
 637             let r = region.fold_with(this);
 638             let s = substs.fold_with(this);
 639             ty::ty_unboxed_closure(did, this.tcx().mk_region(r), this.tcx().mk_substs(s))
 640         }
 641         ty::ty_projection(ref data) => {
 642             ty::ty_projection(data.fold_with(this))
 643         }
 644         ty::ty_bool | ty::ty_char | ty::ty_str |
 645         ty::ty_int(_) | ty::ty_uint(_) | ty::ty_float(_) |
 646         ty::ty_err | ty::ty_infer(_) |
 647         ty::ty_param(..) => {
 648             ty.sty.clone()
 649         }
 650     };
 651     ty::mk_t(this.tcx(), sty)
 652 }
 653
 654 pub fn super_fold_substs<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 655                                                     substs: &subst::Substs<'tcx>)
 656                                                     -> subst::Substs<'tcx> {
 657     let regions = match substs.regions {
 658         subst::ErasedRegions => {
 659             subst::ErasedRegions
 660         }
 661         subst::NonerasedRegions(ref regions) => {
 662             subst::NonerasedRegions(regions.fold_with(this))
 663         }
 664     };
 665
 666     subst::Substs { regions: regions,
 667                     types: substs.types.fold_with(this) }
 668 }
 669
 670 pub fn super_fold_fn_sig<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 671                                                     sig: &ty::FnSig<'tcx>)
 672                                                     -> ty::FnSig<'tcx>
 673 {
 674     ty::FnSig { inputs: sig.inputs.fold_with(this),
 675                 output: sig.output.fold_with(this),
 676                 variadic: sig.variadic }
 677 }
 678
 679 pub fn super_fold_output<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 680                                                     output: &ty::FnOutput<'tcx>)
 681                                                     -> ty::FnOutput<'tcx> {
 682     match *output {
 683         ty::FnConverging(ref ty) => ty::FnConverging(ty.fold_with(this)),
 684         ty::FnDiverging => ty::FnDiverging
 685     }
 686 }
 687
 688 pub fn super_fold_bare_fn_ty<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 689                                                         fty: &ty::BareFnTy<'tcx>)
 690                                                         -> ty::BareFnTy<'tcx>
 691 {
 692     ty::BareFnTy { sig: fty.sig.fold_with(this),
 693                    abi: fty.abi,
 694                    unsafety: fty.unsafety }
 695 }
 696
 697 pub fn super_fold_closure_ty<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 698                                                         fty: &ty::ClosureTy<'tcx>)
 699                                                         -> ty::ClosureTy<'tcx>
 700 {
 701     ty::ClosureTy {
 702         store: fty.store.fold_with(this),
 703         sig: fty.sig.fold_with(this),
 704         unsafety: fty.unsafety,
 705         onceness: fty.onceness,
 706         bounds: fty.bounds.fold_with(this),
 707         abi: fty.abi,
 708     }
 709 }
 710
 711 pub fn super_fold_trait_ref<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 712                                                        t: &ty::TraitRef<'tcx>)
 713                                                        -> ty::TraitRef<'tcx>
 714 {
 715     let substs = t.substs.fold_with(this);
 716     ty::TraitRef {
 717         def_id: t.def_id,
 718         substs: this.tcx().mk_substs(substs),
 719     }
 720 }
 721
 722 pub fn super_fold_mt<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 723                                                 mt: &ty::mt<'tcx>)
 724                                                 -> ty::mt<'tcx> {
 725     ty::mt {ty: mt.ty.fold_with(this),
 726             mutbl: mt.mutbl}
 727 }
 728
 729 pub fn super_fold_trait_store<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 730                                                          trait_store: ty::TraitStore)
 731                                                          -> ty::TraitStore {
 732     match trait_store {
 733         ty::UniqTraitStore => ty::UniqTraitStore,
 734         ty::RegionTraitStore(r, m) => {
 735             ty::RegionTraitStore(r.fold_with(this), m)
 736         }
 737     }
 738 }
 739
 740 pub fn super_fold_existential_bounds<'tcx, T: TypeFolder<'tcx>>(
 741     this: &mut T,
 742     bounds: &ty::ExistentialBounds<'tcx>)
 743     -> ty::ExistentialBounds<'tcx>
 744 {
 745     ty::ExistentialBounds {
 746         region_bound: bounds.region_bound.fold_with(this),
 747         builtin_bounds: bounds.builtin_bounds,
 748         projection_bounds: bounds.projection_bounds.fold_with(this),
 749     }
 750 }
 751
 752 pub fn super_fold_autoref<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 753                                                      autoref: &ty::AutoRef<'tcx>)
 754                                                      -> ty::AutoRef<'tcx>
 755 {
 756     match *autoref {
 757         ty::AutoPtr(r, m, None) => ty::AutoPtr(this.fold_region(r), m, None),
 758         ty::AutoPtr(r, m, Some(ref a)) => {
 759             ty::AutoPtr(this.fold_region(r), m, Some(box super_fold_autoref(this, &**a)))
 760         }
 761         ty::AutoUnsafe(m, None) => ty::AutoUnsafe(m, None),
 762         ty::AutoUnsafe(m, Some(ref a)) => {
 763             ty::AutoUnsafe(m, Some(box super_fold_autoref(this, &**a)))
 764         }
 765         ty::AutoUnsize(ref k) => ty::AutoUnsize(k.fold_with(this)),
 766         ty::AutoUnsizeUniq(ref k) => ty::AutoUnsizeUniq(k.fold_with(this)),
 767     }
 768 }
 769
 770 pub fn super_fold_item_substs<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 771                                                          substs: ty::ItemSubsts<'tcx>)
 772                                                          -> ty::ItemSubsts<'tcx>
 773 {
 774     ty::ItemSubsts {
 775         substs: substs.substs.fold_with(this),
 776     }
 777 }
 778
 779 ///////////////////////////////////////////////////////////////////////////
 780 // Some sample folders
 781
 782 pub struct BottomUpFolder<'a, 'tcx: 'a, F> where F: FnMut(Ty<'tcx>) -> Ty<'tcx> {
 783     pub tcx: &'a ty::ctxt<'tcx>,
 784     pub fldop: F,
 785 }
 786
 787 impl<'a, 'tcx, F> TypeFolder<'tcx> for BottomUpFolder<'a, 'tcx, F> where
 788     F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
 789 {
 790     fn tcx(&self) -> &ty::ctxt<'tcx> { self.tcx }
 791
 792     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
 793         let t1 = super_fold_ty(self, ty);
 794         (self.fldop)(t1)
 795     }
 796 }
 797
 798 ///////////////////////////////////////////////////////////////////////////
 799 // Region folder
 800
 801 /// Folds over the substructure of a type, visiting its component
 802 /// types and all regions that occur *free* within it.
 803 ///
 804 /// That is, `Ty` can contain function or method types that bind
 805 /// regions at the call site (`ReLateBound`), and occurrences of
 806 /// regions (aka "lifetimes") that are bound within a type are not
 807 /// visited by this folder; only regions that occur free will be
 808 /// visited by `fld_r`.
 809
 810 pub struct RegionFolder<'a, 'tcx: 'a> {
 811     tcx: &'a ty::ctxt<'tcx>,
 812     current_depth: u32,
 813     fld_r: &'a mut (FnMut(ty::Region, u32) -> ty::Region + 'a),
 814 }
 815
 816 impl<'a, 'tcx> RegionFolder<'a, 'tcx> {
 817     pub fn new<F>(tcx: &'a ty::ctxt<'tcx>, fld_r: &'a mut F) -> RegionFolder<'a, 'tcx>
 818         where F : FnMut(ty::Region, u32) -> ty::Region
 819     {
 820         RegionFolder {
 821             tcx: tcx,
 822             current_depth: 1,
 823             fld_r: fld_r,
 824         }
 825     }
 826 }
 827
 828 pub fn collect_regions<'tcx,T>(tcx: &ty::ctxt<'tcx>, value: &T) -> Vec<ty::Region>
 829     where T : TypeFoldable<'tcx>
 830 {
 831     let mut vec = Vec::new();
 832     fold_regions(tcx, value, |r, _| { vec.push(r); r });
 833     vec
 834 }
 835
 836 pub fn fold_regions<'tcx,T,F>(tcx: &ty::ctxt<'tcx>,
 837                               value: &T,
 838                               mut f: F)
 839                               -> T
 840     where F : FnMut(ty::Region, u32) -> ty::Region,
 841           T : TypeFoldable<'tcx>,
 842 {
 843     value.fold_with(&mut RegionFolder::new(tcx, &mut f))
 844 }
 845
 846 impl<'a, 'tcx> TypeFolder<'tcx> for RegionFolder<'a, 'tcx>
 847 {
 848     fn tcx(&self) -> &ty::ctxt<'tcx> { self.tcx }
 849
 850     fn enter_region_binder(&mut self) {
 851         self.current_depth += 1;
 852     }
 853
 854     fn exit_region_binder(&mut self) {
 855         self.current_depth -= 1;
 856     }
 857
 858     fn fold_region(&mut self, r: ty::Region) -> ty::Region {
 859         match r {
 860             ty::ReLateBound(debruijn, _) if debruijn.depth < self.current_depth => {
 861                 debug!("RegionFolder.fold_region({}) skipped bound region (current depth={})",
 862                        r.repr(self.tcx()), self.current_depth);
 863                 r
 864             }
 865             _ => {
 866                 debug!("RegionFolder.fold_region({}) folding free region (current_depth={})",
 867                        r.repr(self.tcx()), self.current_depth);
 868                 (self.fld_r)(r, self.current_depth)
 869             }
 870         }
 871     }
 872 }
 873
 874 ///////////////////////////////////////////////////////////////////////////
 875 // Region eraser
 876 //
 877 // Replaces all free regions with 'static. Useful in contexts, such as
 878 // method probing, where precise region relationships are not
 879 // important. Note that in trans you should use
 880 // `common::erase_regions` instead.
 881
 882 pub struct RegionEraser<'a, 'tcx: 'a> {
 883     tcx: &'a ty::ctxt<'tcx>,
 884 }
 885
 886 pub fn erase_regions<'tcx, T: TypeFoldable<'tcx>>(tcx: &ty::ctxt<'tcx>, t: T) -> T {
 887     let mut eraser = RegionEraser { tcx: tcx };
 888     t.fold_with(&mut eraser)
 889 }
 890
 891 impl<'a, 'tcx> TypeFolder<'tcx> for RegionEraser<'a, 'tcx> {
 892     fn tcx(&self) -> &ty::ctxt<'tcx> { self.tcx }
 893
 894     fn fold_region(&mut self, r: ty::Region) -> ty::Region {
 895         // because whether or not a region is bound affects subtyping,
 896         // we can't erase the bound/free distinction, but we can
 897         // replace all free regions with 'static
 898         match r {
 899             ty::ReLateBound(..) | ty::ReEarlyBound(..) => r,
 900             _ => ty::ReStatic
 901         }
 902     }
 903 }
 904
 905 ///////////////////////////////////////////////////////////////////////////
 906 // Region shifter
 907 //
 908 // Shifts the De Bruijn indices on all escaping bound regions by a
 909 // fixed amount. Useful in substitution or when otherwise introducing
 910 // a binding level that is not intended to capture the existing bound
 911 // regions. See comment on `shift_regions_through_binders` method in
 912 // `subst.rs` for more details.
 913
 914 pub fn shift_region(region: ty::Region, amount: u32) -> ty::Region {
 915     match region {
 916         ty::ReLateBound(debruijn, br) => {
 917             ty::ReLateBound(debruijn.shifted(amount), br)
 918         }
 919         _ => {
 920             region
 921         }
 922     }
 923 }
 924
 925 pub fn shift_regions<'tcx, T:TypeFoldable<'tcx>+Repr<'tcx>>(tcx: &ty::ctxt<'tcx>,
 926                                                             amount: u32, value: &T) -> T {
 927     debug!("shift_regions(value={}, amount={})",
 928            value.repr(tcx), amount);
 929
 930     value.fold_with(&mut RegionFolder::new(tcx, &mut |region, _current_depth| {
 931         shift_region(region, amount)
 932     }))
 933 }