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::{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::Region {
 277     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::Region {
 278         folder.fold_region(*self)
 279     }
 280 }
 281
 282 impl<'tcx> TypeFoldable<'tcx> for subst::Substs<'tcx> {
 283     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> subst::Substs<'tcx> {
 284         folder.fold_substs(self)
 285     }
 286 }
 287
 288 impl<'tcx> TypeFoldable<'tcx> for ty::ItemSubsts<'tcx> {
 289     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ItemSubsts<'tcx> {
 290         ty::ItemSubsts {
 291             substs: self.substs.fold_with(folder),
 292         }
 293     }
 294 }
 295
 296 impl<'tcx> TypeFoldable<'tcx> for ty::AutoRef<'tcx> {
 297     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::AutoRef<'tcx> {
 298         folder.fold_autoref(self)
 299     }
 300 }
 301
 302 impl<'tcx> TypeFoldable<'tcx> for ty::MethodOrigin<'tcx> {
 303     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::MethodOrigin<'tcx> {
 304         match *self {
 305             ty::MethodStatic(def_id) => {
 306                 ty::MethodStatic(def_id)
 307             }
 308             ty::MethodStaticUnboxedClosure(def_id) => {
 309                 ty::MethodStaticUnboxedClosure(def_id)
 310             }
 311             ty::MethodTypeParam(ref param) => {
 312                 ty::MethodTypeParam(ty::MethodParam {
 313                     trait_ref: param.trait_ref.fold_with(folder),
 314                     method_num: param.method_num
 315                 })
 316             }
 317             ty::MethodTraitObject(ref object) => {
 318                 ty::MethodTraitObject(ty::MethodObject {
 319                     trait_ref: object.trait_ref.fold_with(folder),
 320                     object_trait_id: object.object_trait_id,
 321                     method_num: object.method_num,
 322                     real_index: object.real_index
 323                 })
 324             }
 325         }
 326     }
 327 }
 328
 329 impl<'tcx> TypeFoldable<'tcx> for ty::vtable_origin<'tcx> {
 330     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::vtable_origin<'tcx> {
 331         match *self {
 332             ty::vtable_static(def_id, ref substs, ref origins) => {
 333                 let r_substs = substs.fold_with(folder);
 334                 let r_origins = origins.fold_with(folder);
 335                 ty::vtable_static(def_id, r_substs, r_origins)
 336             }
 337             ty::vtable_param(n, b) => {
 338                 ty::vtable_param(n, b)
 339             }
 340             ty::vtable_unboxed_closure(def_id) => {
 341                 ty::vtable_unboxed_closure(def_id)
 342             }
 343             ty::vtable_error => {
 344                 ty::vtable_error
 345             }
 346         }
 347     }
 348 }
 349
 350 impl<'tcx> TypeFoldable<'tcx> for ty::BuiltinBounds {
 351     fn fold_with<F: TypeFolder<'tcx>>(&self, _folder: &mut F) -> ty::BuiltinBounds {
 352         *self
 353     }
 354 }
 355
 356 impl<'tcx> TypeFoldable<'tcx> for ty::ExistentialBounds<'tcx> {
 357     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ExistentialBounds<'tcx> {
 358         folder.fold_existential_bounds(self)
 359     }
 360 }
 361
 362 impl<'tcx> TypeFoldable<'tcx> for ty::ParamBounds<'tcx> {
 363     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ParamBounds<'tcx> {
 364         ty::ParamBounds {
 365             region_bounds: self.region_bounds.fold_with(folder),
 366             builtin_bounds: self.builtin_bounds.fold_with(folder),
 367             trait_bounds: self.trait_bounds.fold_with(folder),
 368             projection_bounds: self.projection_bounds.fold_with(folder),
 369         }
 370     }
 371 }
 372
 373 impl<'tcx> TypeFoldable<'tcx> for ty::TypeParameterDef<'tcx> {
 374     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::TypeParameterDef<'tcx> {
 375         ty::TypeParameterDef {
 376             name: self.name,
 377             def_id: self.def_id,
 378             space: self.space,
 379             index: self.index,
 380             bounds: self.bounds.fold_with(folder),
 381             default: self.default.fold_with(folder),
 382         }
 383     }
 384 }
 385
 386 impl<'tcx> TypeFoldable<'tcx> for ty::RegionParameterDef {
 387     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::RegionParameterDef {
 388         ty::RegionParameterDef {
 389             name: self.name,
 390             def_id: self.def_id,
 391             space: self.space,
 392             index: self.index,
 393             bounds: self.bounds.fold_with(folder)
 394         }
 395     }
 396 }
 397
 398 impl<'tcx> TypeFoldable<'tcx> for ty::Generics<'tcx> {
 399     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::Generics<'tcx> {
 400         ty::Generics {
 401             types: self.types.fold_with(folder),
 402             regions: self.regions.fold_with(folder),
 403             predicates: self.predicates.fold_with(folder),
 404         }
 405     }
 406 }
 407
 408 impl<'tcx> TypeFoldable<'tcx> for ty::Predicate<'tcx> {
 409     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::Predicate<'tcx> {
 410         match *self {
 411             ty::Predicate::Trait(ref a) =>
 412                 ty::Predicate::Trait(a.fold_with(folder)),
 413             ty::Predicate::Equate(ref binder) =>
 414                 ty::Predicate::Equate(binder.fold_with(folder)),
 415             ty::Predicate::RegionOutlives(ref binder) =>
 416                 ty::Predicate::RegionOutlives(binder.fold_with(folder)),
 417             ty::Predicate::TypeOutlives(ref binder) =>
 418                 ty::Predicate::TypeOutlives(binder.fold_with(folder)),
 419             ty::Predicate::Projection(ref binder) =>
 420                 ty::Predicate::Projection(binder.fold_with(folder)),
 421         }
 422     }
 423 }
 424
 425 impl<'tcx> TypeFoldable<'tcx> for ty::ProjectionPredicate<'tcx> {
 426     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ProjectionPredicate<'tcx> {
 427         ty::ProjectionPredicate {
 428             projection_ty: self.projection_ty.fold_with(folder),
 429             ty: self.ty.fold_with(folder),
 430         }
 431     }
 432 }
 433
 434 impl<'tcx> TypeFoldable<'tcx> for ty::ProjectionTy<'tcx> {
 435     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::ProjectionTy<'tcx> {
 436         ty::ProjectionTy {
 437             trait_ref: self.trait_ref.fold_with(folder),
 438             item_name: self.item_name,
 439         }
 440     }
 441 }
 442
 443 impl<'tcx> TypeFoldable<'tcx> for ty::GenericBounds<'tcx> {
 444     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::GenericBounds<'tcx> {
 445         ty::GenericBounds {
 446             predicates: self.predicates.fold_with(folder),
 447         }
 448     }
 449 }
 450
 451 impl<'tcx> TypeFoldable<'tcx> for ty::UnsizeKind<'tcx> {
 452     fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::UnsizeKind<'tcx> {
 453         match *self {
 454             ty::UnsizeLength(len) => ty::UnsizeLength(len),
 455             ty::UnsizeStruct(box ref k, n) => ty::UnsizeStruct(box k.fold_with(folder), n),
 456             ty::UnsizeVtable(ty::TyTrait{ref principal, ref bounds}, self_ty) => {
 457                 ty::UnsizeVtable(
 458                     ty::TyTrait {
 459                         principal: principal.fold_with(folder),
 460                         bounds: bounds.fold_with(folder),
 461                     },
 462                     self_ty.fold_with(folder))
 463             }
 464         }
 465     }
 466 }
 467
 468 impl<'tcx,O> TypeFoldable<'tcx> for traits::Obligation<'tcx,O>
 469     where O : TypeFoldable<'tcx>
 470 {
 471     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::Obligation<'tcx, O> {
 472         traits::Obligation {
 473             cause: self.cause.clone(),
 474             recursion_depth: self.recursion_depth,
 475             predicate: self.predicate.fold_with(folder),
 476         }
 477     }
 478 }
 479
 480 impl<'tcx, N: TypeFoldable<'tcx>> TypeFoldable<'tcx> for traits::VtableImplData<'tcx, N> {
 481     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::VtableImplData<'tcx, N> {
 482         traits::VtableImplData {
 483             impl_def_id: self.impl_def_id,
 484             substs: self.substs.fold_with(folder),
 485             nested: self.nested.fold_with(folder),
 486         }
 487     }
 488 }
 489
 490 impl<'tcx, N: TypeFoldable<'tcx>> TypeFoldable<'tcx> for traits::VtableBuiltinData<N> {
 491     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::VtableBuiltinData<N> {
 492         traits::VtableBuiltinData {
 493             nested: self.nested.fold_with(folder),
 494         }
 495     }
 496 }
 497
 498 impl<'tcx, N: TypeFoldable<'tcx>> TypeFoldable<'tcx> for traits::Vtable<'tcx, N> {
 499     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::Vtable<'tcx, N> {
 500         match *self {
 501             traits::VtableImpl(ref v) => traits::VtableImpl(v.fold_with(folder)),
 502             traits::VtableUnboxedClosure(d, ref s) => {
 503                 traits::VtableUnboxedClosure(d, s.fold_with(folder))
 504             }
 505             traits::VtableFnPointer(ref d) => {
 506                 traits::VtableFnPointer(d.fold_with(folder))
 507             }
 508             traits::VtableParam => traits::VtableParam,
 509             traits::VtableBuiltin(ref d) => traits::VtableBuiltin(d.fold_with(folder)),
 510             traits::VtableObject(ref d) => traits::VtableObject(d.fold_with(folder)),
 511         }
 512     }
 513 }
 514
 515 impl<'tcx> TypeFoldable<'tcx> for traits::VtableObjectData<'tcx> {
 516     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::VtableObjectData<'tcx> {
 517         traits::VtableObjectData {
 518             object_ty: self.object_ty.fold_with(folder)
 519         }
 520     }
 521 }
 522
 523 impl<'tcx> TypeFoldable<'tcx> for ty::EquatePredicate<'tcx> {
 524     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::EquatePredicate<'tcx> {
 525         ty::EquatePredicate(self.0.fold_with(folder),
 526                             self.1.fold_with(folder))
 527     }
 528 }
 529
 530 impl<'tcx> TypeFoldable<'tcx> for ty::TraitPredicate<'tcx> {
 531     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::TraitPredicate<'tcx> {
 532         ty::TraitPredicate {
 533             trait_ref: self.trait_ref.fold_with(folder)
 534         }
 535     }
 536 }
 537
 538 impl<'tcx,T,U> TypeFoldable<'tcx> for ty::OutlivesPredicate<T,U>
 539     where T : TypeFoldable<'tcx>,
 540           U : TypeFoldable<'tcx>,
 541 {
 542     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::OutlivesPredicate<T,U> {
 543         ty::OutlivesPredicate(self.0.fold_with(folder),
 544                               self.1.fold_with(folder))
 545     }
 546 }
 547
 548 impl<'tcx> TypeFoldable<'tcx> for ty::UnboxedClosureUpvar<'tcx> {
 549     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> ty::UnboxedClosureUpvar<'tcx> {
 550         ty::UnboxedClosureUpvar {
 551             def: self.def,
 552             span: self.span,
 553             ty: self.ty.fold_with(folder),
 554         }
 555     }
 556 }
 557
 558 ///////////////////////////////////////////////////////////////////////////
 559 // "super" routines: these are the default implementations for TypeFolder.
 560 //
 561 // They should invoke `foo.fold_with()` to do recursive folding.
 562
 563 pub fn super_fold_binder<'tcx, T, U>(this: &mut T,
 564                                      binder: &ty::Binder<U>)
 565                                      -> ty::Binder<U>
 566     where T : TypeFolder<'tcx>, U : TypeFoldable<'tcx>
 567 {
 568     this.enter_region_binder();
 569     let result = ty::Binder(binder.0.fold_with(this));
 570     this.exit_region_binder();
 571     result
 572 }
 573
 574 pub fn super_fold_ty<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 575                                                 ty: Ty<'tcx>)
 576                                                 -> Ty<'tcx> {
 577     let sty = match ty.sty {
 578         ty::ty_uniq(typ) => {
 579             ty::ty_uniq(typ.fold_with(this))
 580         }
 581         ty::ty_ptr(ref tm) => {
 582             ty::ty_ptr(tm.fold_with(this))
 583         }
 584         ty::ty_vec(typ, sz) => {
 585             ty::ty_vec(typ.fold_with(this), sz)
 586         }
 587         ty::ty_open(typ) => {
 588             ty::ty_open(typ.fold_with(this))
 589         }
 590         ty::ty_enum(tid, ref substs) => {
 591             let substs = substs.fold_with(this);
 592             ty::ty_enum(tid, this.tcx().mk_substs(substs))
 593         }
 594         ty::ty_trait(box ty::TyTrait { ref principal, ref bounds }) => {
 595             ty::ty_trait(box ty::TyTrait {
 596                 principal: principal.fold_with(this),
 597                 bounds: bounds.fold_with(this),
 598             })
 599         }
 600         ty::ty_tup(ref ts) => {
 601             ty::ty_tup(ts.fold_with(this))
 602         }
 603         ty::ty_bare_fn(opt_def_id, ref f) => {
 604             let bfn = f.fold_with(this);
 605             ty::ty_bare_fn(opt_def_id, this.tcx().mk_bare_fn(bfn))
 606         }
 607         ty::ty_closure(ref f) => {
 608             ty::ty_closure(f.fold_with(this))
 609         }
 610         ty::ty_rptr(r, ref tm) => {
 611             let r = r.fold_with(this);
 612             ty::ty_rptr(this.tcx().mk_region(r), tm.fold_with(this))
 613         }
 614         ty::ty_struct(did, ref substs) => {
 615             let substs = substs.fold_with(this);
 616             ty::ty_struct(did, this.tcx().mk_substs(substs))
 617         }
 618         ty::ty_unboxed_closure(did, ref region, ref substs) => {
 619             let r = region.fold_with(this);
 620             let s = substs.fold_with(this);
 621             ty::ty_unboxed_closure(did, this.tcx().mk_region(r), this.tcx().mk_substs(s))
 622         }
 623         ty::ty_projection(ref data) => {
 624             ty::ty_projection(data.fold_with(this))
 625         }
 626         ty::ty_bool | ty::ty_char | ty::ty_str |
 627         ty::ty_int(_) | ty::ty_uint(_) | ty::ty_float(_) |
 628         ty::ty_err | ty::ty_infer(_) |
 629         ty::ty_param(..) => {
 630             ty.sty.clone()
 631         }
 632     };
 633     ty::mk_t(this.tcx(), sty)
 634 }
 635
 636 pub fn super_fold_substs<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 637                                                     substs: &subst::Substs<'tcx>)
 638                                                     -> subst::Substs<'tcx> {
 639     let regions = match substs.regions {
 640         subst::ErasedRegions => {
 641             subst::ErasedRegions
 642         }
 643         subst::NonerasedRegions(ref regions) => {
 644             subst::NonerasedRegions(regions.fold_with(this))
 645         }
 646     };
 647
 648     subst::Substs { regions: regions,
 649                     types: substs.types.fold_with(this) }
 650 }
 651
 652 pub fn super_fold_fn_sig<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 653                                                     sig: &ty::FnSig<'tcx>)
 654                                                     -> ty::FnSig<'tcx>
 655 {
 656     ty::FnSig { inputs: sig.inputs.fold_with(this),
 657                 output: sig.output.fold_with(this),
 658                 variadic: sig.variadic }
 659 }
 660
 661 pub fn super_fold_output<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 662                                                     output: &ty::FnOutput<'tcx>)
 663                                                     -> ty::FnOutput<'tcx> {
 664     match *output {
 665         ty::FnConverging(ref ty) => ty::FnConverging(ty.fold_with(this)),
 666         ty::FnDiverging => ty::FnDiverging
 667     }
 668 }
 669
 670 pub fn super_fold_bare_fn_ty<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 671                                                         fty: &ty::BareFnTy<'tcx>)
 672                                                         -> ty::BareFnTy<'tcx>
 673 {
 674     ty::BareFnTy { sig: fty.sig.fold_with(this),
 675                    abi: fty.abi,
 676                    unsafety: fty.unsafety }
 677 }
 678
 679 pub fn super_fold_closure_ty<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 680                                                         fty: &ty::ClosureTy<'tcx>)
 681                                                         -> ty::ClosureTy<'tcx>
 682 {
 683     ty::ClosureTy {
 684         store: fty.store.fold_with(this),
 685         sig: fty.sig.fold_with(this),
 686         unsafety: fty.unsafety,
 687         onceness: fty.onceness,
 688         bounds: fty.bounds.fold_with(this),
 689         abi: fty.abi,
 690     }
 691 }
 692
 693 pub fn super_fold_trait_ref<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 694                                                        t: &ty::TraitRef<'tcx>)
 695                                                        -> ty::TraitRef<'tcx>
 696 {
 697     let substs = t.substs.fold_with(this);
 698     ty::TraitRef {
 699         def_id: t.def_id,
 700         substs: this.tcx().mk_substs(substs),
 701     }
 702 }
 703
 704 pub fn super_fold_mt<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 705                                                 mt: &ty::mt<'tcx>)
 706                                                 -> ty::mt<'tcx> {
 707     ty::mt {ty: mt.ty.fold_with(this),
 708             mutbl: mt.mutbl}
 709 }
 710
 711 pub fn super_fold_trait_store<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 712                                                          trait_store: ty::TraitStore)
 713                                                          -> ty::TraitStore {
 714     match trait_store {
 715         ty::UniqTraitStore => ty::UniqTraitStore,
 716         ty::RegionTraitStore(r, m) => {
 717             ty::RegionTraitStore(r.fold_with(this), m)
 718         }
 719     }
 720 }
 721
 722 pub fn super_fold_existential_bounds<'tcx, T: TypeFolder<'tcx>>(
 723     this: &mut T,
 724     bounds: &ty::ExistentialBounds<'tcx>)
 725     -> ty::ExistentialBounds<'tcx>
 726 {
 727     ty::ExistentialBounds {
 728         region_bound: bounds.region_bound.fold_with(this),
 729         builtin_bounds: bounds.builtin_bounds,
 730         projection_bounds: bounds.projection_bounds.fold_with(this),
 731     }
 732 }
 733
 734 pub fn super_fold_autoref<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 735                                                      autoref: &ty::AutoRef<'tcx>)
 736                                                      -> ty::AutoRef<'tcx>
 737 {
 738     match *autoref {
 739         ty::AutoPtr(r, m, None) => ty::AutoPtr(this.fold_region(r), m, None),
 740         ty::AutoPtr(r, m, Some(ref a)) => {
 741             ty::AutoPtr(this.fold_region(r), m, Some(box super_fold_autoref(this, &**a)))
 742         }
 743         ty::AutoUnsafe(m, None) => ty::AutoUnsafe(m, None),
 744         ty::AutoUnsafe(m, Some(ref a)) => {
 745             ty::AutoUnsafe(m, Some(box super_fold_autoref(this, &**a)))
 746         }
 747         ty::AutoUnsize(ref k) => ty::AutoUnsize(k.fold_with(this)),
 748         ty::AutoUnsizeUniq(ref k) => ty::AutoUnsizeUniq(k.fold_with(this)),
 749     }
 750 }
 751
 752 pub fn super_fold_item_substs<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 753                                                          substs: ty::ItemSubsts<'tcx>)
 754                                                          -> ty::ItemSubsts<'tcx>
 755 {
 756     ty::ItemSubsts {
 757         substs: substs.substs.fold_with(this),
 758     }
 759 }
 760
 761 ///////////////////////////////////////////////////////////////////////////
 762 // Some sample folders
 763
 764 pub struct BottomUpFolder<'a, 'tcx: 'a, F> where F: FnMut(Ty<'tcx>) -> Ty<'tcx> {
 765     pub tcx: &'a ty::ctxt<'tcx>,
 766     pub fldop: F,
 767 }
 768
 769 impl<'a, 'tcx, F> TypeFolder<'tcx> for BottomUpFolder<'a, 'tcx, F> where
 770     F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
 771 {
 772     fn tcx(&self) -> &ty::ctxt<'tcx> { self.tcx }
 773
 774     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
 775         let t1 = super_fold_ty(self, ty);
 776         (self.fldop)(t1)
 777     }
 778 }
 779
 780 ///////////////////////////////////////////////////////////////////////////
 781 // Region folder
 782
 783 /// Folds over the substructure of a type, visiting its component
 784 /// types and all regions that occur *free* within it.
 785 ///
 786 /// That is, `Ty` can contain function or method types that bind
 787 /// regions at the call site (`ReLateBound`), and occurrences of
 788 /// regions (aka "lifetimes") that are bound within a type are not
 789 /// visited by this folder; only regions that occur free will be
 790 /// visited by `fld_r`.
 791
 792 pub struct RegionFolder<'a, 'tcx: 'a> {
 793     tcx: &'a ty::ctxt<'tcx>,
 794     current_depth: u32,
 795     fld_r: &'a mut (FnMut(ty::Region, u32) -> ty::Region + 'a),
 796 }
 797
 798 impl<'a, 'tcx> RegionFolder<'a, 'tcx> {
 799     pub fn new<F>(tcx: &'a ty::ctxt<'tcx>, fld_r: &'a mut F) -> RegionFolder<'a, 'tcx>
 800         where F : FnMut(ty::Region, u32) -> ty::Region
 801     {
 802         RegionFolder {
 803             tcx: tcx,
 804             current_depth: 1,
 805             fld_r: fld_r,
 806         }
 807     }
 808 }
 809
 810 pub fn collect_regions<'tcx,T>(tcx: &ty::ctxt<'tcx>, value: &T) -> Vec<ty::Region>
 811     where T : TypeFoldable<'tcx>
 812 {
 813     let mut vec = Vec::new();
 814     fold_regions(tcx, value, |r, _| { vec.push(r); r });
 815     vec
 816 }
 817
 818 pub fn fold_regions<'tcx,T,F>(tcx: &ty::ctxt<'tcx>,
 819                               value: &T,
 820                               mut f: F)
 821                               -> T
 822     where F : FnMut(ty::Region, u32) -> ty::Region,
 823           T : TypeFoldable<'tcx>,
 824 {
 825     value.fold_with(&mut RegionFolder::new(tcx, &mut f))
 826 }
 827
 828 impl<'a, 'tcx> TypeFolder<'tcx> for RegionFolder<'a, 'tcx>
 829 {
 830     fn tcx(&self) -> &ty::ctxt<'tcx> { self.tcx }
 831
 832     fn enter_region_binder(&mut self) {
 833         self.current_depth += 1;
 834     }
 835
 836     fn exit_region_binder(&mut self) {
 837         self.current_depth -= 1;
 838     }
 839
 840     fn fold_region(&mut self, r: ty::Region) -> ty::Region {
 841         match r {
 842             ty::ReLateBound(debruijn, _) if debruijn.depth < self.current_depth => {
 843                 debug!("RegionFolder.fold_region({}) skipped bound region (current depth={})",
 844                        r.repr(self.tcx()), self.current_depth);
 845                 r
 846             }
 847             _ => {
 848                 debug!("RegionFolder.fold_region({}) folding free region (current_depth={})",
 849                        r.repr(self.tcx()), self.current_depth);
 850                 self.fld_r.call_mut((r, self.current_depth))
 851             }
 852         }
 853     }
 854 }
 855
 856 ///////////////////////////////////////////////////////////////////////////
 857 // Region eraser
 858 //
 859 // Replaces all free regions with 'static. Useful in trans.
 860
 861 pub struct RegionEraser<'a, 'tcx: 'a> {
 862     tcx: &'a ty::ctxt<'tcx>,
 863 }
 864
 865 pub fn erase_regions<'tcx, T: TypeFoldable<'tcx>>(tcx: &ty::ctxt<'tcx>, t: T) -> T {
 866     let mut eraser = RegionEraser { tcx: tcx };
 867     t.fold_with(&mut eraser)
 868 }
 869
 870 impl<'a, 'tcx> TypeFolder<'tcx> for RegionEraser<'a, 'tcx> {
 871     fn tcx(&self) -> &ty::ctxt<'tcx> { self.tcx }
 872
 873     fn fold_region(&mut self, r: ty::Region) -> ty::Region {
 874         match r {
 875             ty::ReLateBound(..) | ty::ReEarlyBound(..) => r,
 876             _ => ty::ReStatic
 877         }
 878     }
 879 }
 880
 881 ///////////////////////////////////////////////////////////////////////////
 882 // Region shifter
 883 //
 884 // Shifts the De Bruijn indices on all escaping bound regions by a
 885 // fixed amount. Useful in substitution or when otherwise introducing
 886 // a binding level that is not intended to capture the existing bound
 887 // regions. See comment on `shift_regions_through_binders` method in
 888 // `subst.rs` for more details.
 889
 890 pub fn shift_region(region: ty::Region, amount: u32) -> ty::Region {
 891     match region {
 892         ty::ReLateBound(debruijn, br) => {
 893             ty::ReLateBound(debruijn.shifted(amount), br)
 894         }
 895         _ => {
 896             region
 897         }
 898     }
 899 }
 900
 901 pub fn shift_regions<'tcx, T:TypeFoldable<'tcx>+Repr<'tcx>>(tcx: &ty::ctxt<'tcx>,
 902                                                             amount: u32, value: &T) -> T {
 903     debug!("shift_regions(value={}, amount={})",
 904            value.repr(tcx), amount);
 905
 906     value.fold_with(&mut RegionFolder::new(tcx, &mut |region, _current_depth| {
 907         shift_region(region, amount)
 908     }))
 909 }