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_rptr(r, ref tm) => {
 608             let r = r.fold_with(this);
 609             ty::ty_rptr(this.tcx().mk_region(r), tm.fold_with(this))
 610         }
 611         ty::ty_struct(did, ref substs) => {
 612             let substs = substs.fold_with(this);
 613             ty::ty_struct(did, this.tcx().mk_substs(substs))
 614         }
 615         ty::ty_unboxed_closure(did, ref region, ref substs) => {
 616             let r = region.fold_with(this);
 617             let s = substs.fold_with(this);
 618             ty::ty_unboxed_closure(did, this.tcx().mk_region(r), this.tcx().mk_substs(s))
 619         }
 620         ty::ty_projection(ref data) => {
 621             ty::ty_projection(data.fold_with(this))
 622         }
 623         ty::ty_bool | ty::ty_char | ty::ty_str |
 624         ty::ty_int(_) | ty::ty_uint(_) | ty::ty_float(_) |
 625         ty::ty_err | ty::ty_infer(_) |
 626         ty::ty_param(..) => {
 627             ty.sty.clone()
 628         }
 629     };
 630     ty::mk_t(this.tcx(), sty)
 631 }
 632
 633 pub fn super_fold_substs<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 634                                                     substs: &subst::Substs<'tcx>)
 635                                                     -> subst::Substs<'tcx> {
 636     let regions = match substs.regions {
 637         subst::ErasedRegions => {
 638             subst::ErasedRegions
 639         }
 640         subst::NonerasedRegions(ref regions) => {
 641             subst::NonerasedRegions(regions.fold_with(this))
 642         }
 643     };
 644
 645     subst::Substs { regions: regions,
 646                     types: substs.types.fold_with(this) }
 647 }
 648
 649 pub fn super_fold_fn_sig<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 650                                                     sig: &ty::FnSig<'tcx>)
 651                                                     -> ty::FnSig<'tcx>
 652 {
 653     ty::FnSig { inputs: sig.inputs.fold_with(this),
 654                 output: sig.output.fold_with(this),
 655                 variadic: sig.variadic }
 656 }
 657
 658 pub fn super_fold_output<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 659                                                     output: &ty::FnOutput<'tcx>)
 660                                                     -> ty::FnOutput<'tcx> {
 661     match *output {
 662         ty::FnConverging(ref ty) => ty::FnConverging(ty.fold_with(this)),
 663         ty::FnDiverging => ty::FnDiverging
 664     }
 665 }
 666
 667 pub fn super_fold_bare_fn_ty<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 668                                                         fty: &ty::BareFnTy<'tcx>)
 669                                                         -> ty::BareFnTy<'tcx>
 670 {
 671     ty::BareFnTy { sig: fty.sig.fold_with(this),
 672                    abi: fty.abi,
 673                    unsafety: fty.unsafety }
 674 }
 675
 676 pub fn super_fold_closure_ty<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 677                                                         fty: &ty::ClosureTy<'tcx>)
 678                                                         -> ty::ClosureTy<'tcx>
 679 {
 680     ty::ClosureTy {
 681         store: fty.store.fold_with(this),
 682         sig: fty.sig.fold_with(this),
 683         unsafety: fty.unsafety,
 684         onceness: fty.onceness,
 685         bounds: fty.bounds.fold_with(this),
 686         abi: fty.abi,
 687     }
 688 }
 689
 690 pub fn super_fold_trait_ref<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 691                                                        t: &ty::TraitRef<'tcx>)
 692                                                        -> ty::TraitRef<'tcx>
 693 {
 694     let substs = t.substs.fold_with(this);
 695     ty::TraitRef {
 696         def_id: t.def_id,
 697         substs: this.tcx().mk_substs(substs),
 698     }
 699 }
 700
 701 pub fn super_fold_mt<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 702                                                 mt: &ty::mt<'tcx>)
 703                                                 -> ty::mt<'tcx> {
 704     ty::mt {ty: mt.ty.fold_with(this),
 705             mutbl: mt.mutbl}
 706 }
 707
 708 pub fn super_fold_trait_store<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 709                                                          trait_store: ty::TraitStore)
 710                                                          -> ty::TraitStore {
 711     match trait_store {
 712         ty::UniqTraitStore => ty::UniqTraitStore,
 713         ty::RegionTraitStore(r, m) => {
 714             ty::RegionTraitStore(r.fold_with(this), m)
 715         }
 716     }
 717 }
 718
 719 pub fn super_fold_existential_bounds<'tcx, T: TypeFolder<'tcx>>(
 720     this: &mut T,
 721     bounds: &ty::ExistentialBounds<'tcx>)
 722     -> ty::ExistentialBounds<'tcx>
 723 {
 724     ty::ExistentialBounds {
 725         region_bound: bounds.region_bound.fold_with(this),
 726         builtin_bounds: bounds.builtin_bounds,
 727         projection_bounds: bounds.projection_bounds.fold_with(this),
 728     }
 729 }
 730
 731 pub fn super_fold_autoref<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 732                                                      autoref: &ty::AutoRef<'tcx>)
 733                                                      -> ty::AutoRef<'tcx>
 734 {
 735     match *autoref {
 736         ty::AutoPtr(r, m, None) => ty::AutoPtr(this.fold_region(r), m, None),
 737         ty::AutoPtr(r, m, Some(ref a)) => {
 738             ty::AutoPtr(this.fold_region(r), m, Some(box super_fold_autoref(this, &**a)))
 739         }
 740         ty::AutoUnsafe(m, None) => ty::AutoUnsafe(m, None),
 741         ty::AutoUnsafe(m, Some(ref a)) => {
 742             ty::AutoUnsafe(m, Some(box super_fold_autoref(this, &**a)))
 743         }
 744         ty::AutoUnsize(ref k) => ty::AutoUnsize(k.fold_with(this)),
 745         ty::AutoUnsizeUniq(ref k) => ty::AutoUnsizeUniq(k.fold_with(this)),
 746     }
 747 }
 748
 749 pub fn super_fold_item_substs<'tcx, T: TypeFolder<'tcx>>(this: &mut T,
 750                                                          substs: ty::ItemSubsts<'tcx>)
 751                                                          -> ty::ItemSubsts<'tcx>
 752 {
 753     ty::ItemSubsts {
 754         substs: substs.substs.fold_with(this),
 755     }
 756 }
 757
 758 ///////////////////////////////////////////////////////////////////////////
 759 // Some sample folders
 760
 761 pub struct BottomUpFolder<'a, 'tcx: 'a, F> where F: FnMut(Ty<'tcx>) -> Ty<'tcx> {
 762     pub tcx: &'a ty::ctxt<'tcx>,
 763     pub fldop: F,
 764 }
 765
 766 impl<'a, 'tcx, F> TypeFolder<'tcx> for BottomUpFolder<'a, 'tcx, F> where
 767     F: FnMut(Ty<'tcx>) -> Ty<'tcx>,
 768 {
 769     fn tcx(&self) -> &ty::ctxt<'tcx> { self.tcx }
 770
 771     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
 772         let t1 = super_fold_ty(self, ty);
 773         (self.fldop)(t1)
 774     }
 775 }
 776
 777 ///////////////////////////////////////////////////////////////////////////
 778 // Region folder
 779
 780 /// Folds over the substructure of a type, visiting its component
 781 /// types and all regions that occur *free* within it.
 782 ///
 783 /// That is, `Ty` can contain function or method types that bind
 784 /// regions at the call site (`ReLateBound`), and occurrences of
 785 /// regions (aka "lifetimes") that are bound within a type are not
 786 /// visited by this folder; only regions that occur free will be
 787 /// visited by `fld_r`.
 788
 789 pub struct RegionFolder<'a, 'tcx: 'a> {
 790     tcx: &'a ty::ctxt<'tcx>,
 791     current_depth: u32,
 792     fld_r: &'a mut (FnMut(ty::Region, u32) -> ty::Region + 'a),
 793 }
 794
 795 impl<'a, 'tcx> RegionFolder<'a, 'tcx> {
 796     pub fn new<F>(tcx: &'a ty::ctxt<'tcx>, fld_r: &'a mut F) -> RegionFolder<'a, 'tcx>
 797         where F : FnMut(ty::Region, u32) -> ty::Region
 798     {
 799         RegionFolder {
 800             tcx: tcx,
 801             current_depth: 1,
 802             fld_r: fld_r,
 803         }
 804     }
 805 }
 806
 807 pub fn collect_regions<'tcx,T>(tcx: &ty::ctxt<'tcx>, value: &T) -> Vec<ty::Region>
 808     where T : TypeFoldable<'tcx>
 809 {
 810     let mut vec = Vec::new();
 811     fold_regions(tcx, value, |r, _| { vec.push(r); r });
 812     vec
 813 }
 814
 815 pub fn fold_regions<'tcx,T,F>(tcx: &ty::ctxt<'tcx>,
 816                               value: &T,
 817                               mut f: F)
 818                               -> T
 819     where F : FnMut(ty::Region, u32) -> ty::Region,
 820           T : TypeFoldable<'tcx>,
 821 {
 822     value.fold_with(&mut RegionFolder::new(tcx, &mut f))
 823 }
 824
 825 impl<'a, 'tcx> TypeFolder<'tcx> for RegionFolder<'a, 'tcx>
 826 {
 827     fn tcx(&self) -> &ty::ctxt<'tcx> { self.tcx }
 828
 829     fn enter_region_binder(&mut self) {
 830         self.current_depth += 1;
 831     }
 832
 833     fn exit_region_binder(&mut self) {
 834         self.current_depth -= 1;
 835     }
 836
 837     fn fold_region(&mut self, r: ty::Region) -> ty::Region {
 838         match r {
 839             ty::ReLateBound(debruijn, _) if debruijn.depth < self.current_depth => {
 840                 debug!("RegionFolder.fold_region({}) skipped bound region (current depth={})",
 841                        r.repr(self.tcx()), self.current_depth);
 842                 r
 843             }
 844             _ => {
 845                 debug!("RegionFolder.fold_region({}) folding free region (current_depth={})",
 846                        r.repr(self.tcx()), self.current_depth);
 847                 self.fld_r.call_mut((r, self.current_depth))
 848             }
 849         }
 850     }
 851 }
 852
 853 ///////////////////////////////////////////////////////////////////////////
 854 // Region eraser
 855 //
 856 // Replaces all free regions with 'static. Useful in trans.
 857
 858 pub struct RegionEraser<'a, 'tcx: 'a> {
 859     tcx: &'a ty::ctxt<'tcx>,
 860 }
 861
 862 pub fn erase_regions<'tcx, T: TypeFoldable<'tcx>>(tcx: &ty::ctxt<'tcx>, t: T) -> T {
 863     let mut eraser = RegionEraser { tcx: tcx };
 864     t.fold_with(&mut eraser)
 865 }
 866
 867 impl<'a, 'tcx> TypeFolder<'tcx> for RegionEraser<'a, 'tcx> {
 868     fn tcx(&self) -> &ty::ctxt<'tcx> { self.tcx }
 869
 870     fn fold_region(&mut self, r: ty::Region) -> ty::Region {
 871         match r {
 872             ty::ReLateBound(..) | ty::ReEarlyBound(..) => r,
 873             _ => ty::ReStatic
 874         }
 875     }
 876 }
 877
 878 ///////////////////////////////////////////////////////////////////////////
 879 // Region shifter
 880 //
 881 // Shifts the De Bruijn indices on all escaping bound regions by a
 882 // fixed amount. Useful in substitution or when otherwise introducing
 883 // a binding level that is not intended to capture the existing bound
 884 // regions. See comment on `shift_regions_through_binders` method in
 885 // `subst.rs` for more details.
 886
 887 pub fn shift_region(region: ty::Region, amount: u32) -> ty::Region {
 888     match region {
 889         ty::ReLateBound(debruijn, br) => {
 890             ty::ReLateBound(debruijn.shifted(amount), br)
 891         }
 892         _ => {
 893             region
 894         }
 895     }
 896 }
 897
 898 pub fn shift_regions<'tcx, T:TypeFoldable<'tcx>+Repr<'tcx>>(tcx: &ty::ctxt<'tcx>,
 899                                                             amount: u32, value: &T) -> T {
 900     debug!("shift_regions(value={}, amount={})",
 901            value.repr(tcx), amount);
 902
 903     value.fold_with(&mut RegionFolder::new(tcx, &mut |region, _current_depth| {
 904         shift_region(region, amount)
 905     }))
 906 }