1 // Copyright 2012 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.
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.
11 // Type substitutions.
14 use hir::def_id::DefId;
15 use ty::{self, Ty, TyCtxt};
16 use ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
18 use serialize::{Encodable, Encoder, Decodable, Decoder};
19 use syntax_pos::{Span, DUMMY_SP};
21 use core::nonzero::NonZero;
24 use std::marker::PhantomData;
27 /// An entity in the Rust typesystem, which can be one of
28 /// several kinds (only types and lifetimes for now).
29 /// To reduce memory usage, a `Kind` is a interned pointer,
30 /// with the lowest 2 bits being reserved for a tag to
31 /// indicate the type (`Ty` or `Region`) it points to.
32 #[derive(Copy, Clone, PartialEq, Eq, Hash)]
33 pub struct Kind<'tcx> {
35 marker: PhantomData<(Ty<'tcx>, &'tcx ty::Region)>
38 const TAG_MASK: usize = 0b11;
39 const TYPE_TAG: usize = 0b00;
40 const REGION_TAG: usize = 0b01;
42 impl<'tcx> From<Ty<'tcx>> for Kind<'tcx> {
43 fn from(ty: Ty<'tcx>) -> Kind<'tcx> {
44 // Ensure we can use the tag bits.
45 assert_eq!(mem::align_of_val(ty) & TAG_MASK, 0);
47 let ptr = ty as *const _ as usize;
50 NonZero::new(ptr | TYPE_TAG)
57 impl<'tcx> From<&'tcx ty::Region> for Kind<'tcx> {
58 fn from(r: &'tcx ty::Region) -> Kind<'tcx> {
59 // Ensure we can use the tag bits.
60 assert_eq!(mem::align_of_val(r) & TAG_MASK, 0);
62 let ptr = r as *const _ as usize;
65 NonZero::new(ptr | REGION_TAG)
72 impl<'tcx> Kind<'tcx> {
74 unsafe fn downcast<T>(self, tag: usize) -> Option<&'tcx T> {
76 if ptr & TAG_MASK == tag {
77 Some(&*((ptr & !TAG_MASK) as *const _))
84 pub fn as_type(self) -> Option<Ty<'tcx>> {
86 self.downcast(TYPE_TAG)
91 pub fn as_region(self) -> Option<&'tcx ty::Region> {
93 self.downcast(REGION_TAG)
98 impl<'tcx> fmt::Debug for Kind<'tcx> {
99 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
100 if let Some(ty) = self.as_type() {
101 write!(f, "{:?}", ty)
102 } else if let Some(r) = self.as_region() {
105 write!(f, "<unknwon @ {:p}>", *self.ptr as *const ())
110 impl<'tcx> TypeFoldable<'tcx> for Kind<'tcx> {
111 fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
112 if let Some(ty) = self.as_type() {
113 Kind::from(ty.fold_with(folder))
114 } else if let Some(r) = self.as_region() {
115 Kind::from(r.fold_with(folder))
121 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
122 if let Some(ty) = self.as_type() {
123 ty.visit_with(visitor)
124 } else if let Some(r) = self.as_region() {
125 r.visit_with(visitor)
132 /// A substitution mapping type/region parameters to new values.
133 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
134 pub struct Substs<'tcx> {
135 params: Vec<Kind<'tcx>>
138 impl<'a, 'gcx, 'tcx> Substs<'tcx> {
139 pub fn new<I>(tcx: TyCtxt<'a, 'gcx, 'tcx>, params: I)
140 -> &'tcx Substs<'tcx>
141 where I: IntoIterator<Item=Kind<'tcx>> {
142 tcx.mk_substs(Substs {
143 params: params.into_iter().collect()
147 pub fn maybe_new<I, E>(tcx: TyCtxt<'a, 'gcx, 'tcx>, params: I)
148 -> Result<&'tcx Substs<'tcx>, E>
149 where I: IntoIterator<Item=Result<Kind<'tcx>, E>> {
150 Ok(tcx.mk_substs(Substs {
151 params: params.into_iter().collect::<Result<_, _>>()?
155 pub fn new_trait(tcx: TyCtxt<'a, 'gcx, 'tcx>,
158 -> &'tcx Substs<'tcx>
160 let t = iter::once(s).chain(t.iter().cloned());
161 Substs::new(tcx, t.map(Kind::from))
164 pub fn empty(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> &'tcx Substs<'tcx> {
165 Substs::new(tcx, vec![])
168 /// Creates a Substs for generic parameter definitions,
169 /// by calling closures to obtain each region and type.
170 /// The closures get to observe the Substs as they're
171 /// being built, which can be used to correctly
172 /// substitute defaults of type parameters.
173 pub fn for_item<FR, FT>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
177 -> &'tcx Substs<'tcx>
178 where FR: FnMut(&ty::RegionParameterDef, &Substs<'tcx>) -> &'tcx ty::Region,
179 FT: FnMut(&ty::TypeParameterDef<'tcx>, &Substs<'tcx>) -> Ty<'tcx> {
180 let defs = tcx.lookup_generics(def_id);
181 let mut substs = Substs {
182 params: Vec::with_capacity(defs.count())
185 substs.fill_item(tcx, defs, &mut mk_region, &mut mk_type);
187 tcx.mk_substs(substs)
190 fn fill_item<FR, FT>(&mut self,
191 tcx: TyCtxt<'a, 'gcx, 'tcx>,
192 defs: &ty::Generics<'tcx>,
195 where FR: FnMut(&ty::RegionParameterDef, &Substs<'tcx>) -> &'tcx ty::Region,
196 FT: FnMut(&ty::TypeParameterDef<'tcx>, &Substs<'tcx>) -> Ty<'tcx> {
197 if let Some(def_id) = defs.parent {
198 let parent_defs = tcx.lookup_generics(def_id);
199 self.fill_item(tcx, parent_defs, mk_region, mk_type);
202 // Handle Self first, before all regions.
203 let mut types = defs.types.iter();
204 if defs.parent.is_none() && defs.has_self {
205 let def = types.next().unwrap();
206 let ty = mk_type(def, self);
207 assert_eq!(def.index as usize, self.params.len());
208 self.params.push(Kind::from(ty));
211 for def in &defs.regions {
212 let region = mk_region(def, self);
213 assert_eq!(def.index as usize, self.params.len());
214 self.params.push(Kind::from(region));
218 let ty = mk_type(def, self);
219 assert_eq!(def.index as usize, self.params.len());
220 self.params.push(Kind::from(ty));
224 pub fn is_noop(&self) -> bool {
225 self.params.is_empty()
229 pub fn params(&self) -> &[Kind<'tcx>] {
234 pub fn types(&'a self) -> impl DoubleEndedIterator<Item=Ty<'tcx>> + 'a {
235 self.params.iter().filter_map(|k| k.as_type())
239 pub fn regions(&'a self) -> impl DoubleEndedIterator<Item=&'tcx ty::Region> + 'a {
240 self.params.iter().filter_map(|k| k.as_region())
244 pub fn type_at(&self, i: usize) -> Ty<'tcx> {
245 self.params[i].as_type().unwrap_or_else(|| {
246 bug!("expected type for param #{} in {:?}", i, self.params);
251 pub fn region_at(&self, i: usize) -> &'tcx ty::Region {
252 self.params[i].as_region().unwrap_or_else(|| {
253 bug!("expected region for param #{} in {:?}", i, self.params);
258 pub fn type_for_def(&self, ty_param_def: &ty::TypeParameterDef) -> Ty<'tcx> {
259 self.type_at(ty_param_def.index as usize)
263 pub fn region_for_def(&self, def: &ty::RegionParameterDef) -> &'tcx ty::Region {
264 self.region_at(def.index as usize)
267 /// Transform from substitutions for a child of `source_ancestor`
268 /// (e.g. a trait or impl) to substitutions for the same child
269 /// in a different item, with `target_substs` as the base for
270 /// the target impl/trait, with the source child-specific
271 /// parameters (e.g. method parameters) on top of that base.
272 pub fn rebase_onto(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
273 source_ancestor: DefId,
274 target_substs: &Substs<'tcx>)
275 -> &'tcx Substs<'tcx> {
276 let defs = tcx.lookup_generics(source_ancestor);
277 tcx.mk_substs(Substs {
278 params: target_substs.params.iter()
279 .chain(&self.params[defs.own_count()..]).cloned().collect()
284 impl<'tcx> TypeFoldable<'tcx> for &'tcx Substs<'tcx> {
285 fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
286 let params = self.params.iter().map(|k| k.fold_with(folder)).collect();
287 folder.tcx().mk_substs(Substs {
292 fn fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
293 folder.fold_substs(self)
296 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
297 self.params.visit_with(visitor)
301 impl<'tcx> Encodable for &'tcx Substs<'tcx> {
302 fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
303 cstore::tls::with_encoding_context(s, |ecx, rbml_w| {
304 ecx.encode_substs(rbml_w, self);
310 impl<'tcx> Decodable for &'tcx Substs<'tcx> {
311 fn decode<D: Decoder>(d: &mut D) -> Result<&'tcx Substs<'tcx>, D::Error> {
312 let substs = cstore::tls::with_decoding_context(d, |dcx, rbml_r| {
313 dcx.decode_substs(rbml_r)
321 ///////////////////////////////////////////////////////////////////////////
322 // Public trait `Subst`
324 // Just call `foo.subst(tcx, substs)` to perform a substitution across
325 // `foo`. Or use `foo.subst_spanned(tcx, substs, Some(span))` when
326 // there is more information available (for better errors).
328 pub trait Subst<'tcx> : Sized {
329 fn subst<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
330 substs: &Substs<'tcx>) -> Self {
331 self.subst_spanned(tcx, substs, None)
334 fn subst_spanned<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
335 substs: &Substs<'tcx>,
340 impl<'tcx, T:TypeFoldable<'tcx>> Subst<'tcx> for T {
341 fn subst_spanned<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
342 substs: &Substs<'tcx>,
346 let mut folder = SubstFolder { tcx: tcx,
351 region_binders_passed: 0 };
352 (*self).fold_with(&mut folder)
356 ///////////////////////////////////////////////////////////////////////////
357 // The actual substitution engine itself is a type folder.
359 struct SubstFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
360 tcx: TyCtxt<'a, 'gcx, 'tcx>,
361 substs: &'a Substs<'tcx>,
363 // The location for which the substitution is performed, if available.
366 // The root type that is being substituted, if available.
367 root_ty: Option<Ty<'tcx>>,
369 // Depth of type stack
370 ty_stack_depth: usize,
372 // Number of region binders we have passed through while doing the substitution
373 region_binders_passed: u32,
376 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for SubstFolder<'a, 'gcx, 'tcx> {
377 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
379 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
380 self.region_binders_passed += 1;
381 let t = t.super_fold_with(self);
382 self.region_binders_passed -= 1;
386 fn fold_region(&mut self, r: &'tcx ty::Region) -> &'tcx ty::Region {
387 // Note: This routine only handles regions that are bound on
388 // type declarations and other outer declarations, not those
389 // bound in *fn types*. Region substitution of the bound
390 // regions that appear in a function signature is done using
391 // the specialized routine `ty::replace_late_regions()`.
393 ty::ReEarlyBound(data) => {
394 let r = self.substs.params.get(data.index as usize)
395 .and_then(|k| k.as_region());
398 self.shift_region_through_binders(r)
401 let span = self.span.unwrap_or(DUMMY_SP);
404 "Region parameter out of range \
405 when substituting in region {} (root type={:?}) \
417 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
418 if !t.needs_subst() {
422 // track the root type we were asked to substitute
423 let depth = self.ty_stack_depth;
425 self.root_ty = Some(t);
427 self.ty_stack_depth += 1;
429 let t1 = match t.sty {
431 self.ty_for_param(p, t)
434 t.super_fold_with(self)
438 assert_eq!(depth + 1, self.ty_stack_depth);
439 self.ty_stack_depth -= 1;
448 impl<'a, 'gcx, 'tcx> SubstFolder<'a, 'gcx, 'tcx> {
449 fn ty_for_param(&self, p: ty::ParamTy, source_ty: Ty<'tcx>) -> Ty<'tcx> {
450 // Look up the type in the substitutions. It really should be in there.
451 let opt_ty = self.substs.params.get(p.idx as usize)
452 .and_then(|k| k.as_type());
453 let ty = match opt_ty {
456 let span = self.span.unwrap_or(DUMMY_SP);
459 "Type parameter `{:?}` ({:?}/{}) out of range \
460 when substituting (root type={:?}) substs={:?}",
469 self.shift_regions_through_binders(ty)
472 /// It is sometimes necessary to adjust the debruijn indices during substitution. This occurs
473 /// when we are substituting a type with escaping regions into a context where we have passed
474 /// through region binders. That's quite a mouthful. Let's see an example:
477 /// type Func<A> = fn(A);
478 /// type MetaFunc = for<'a> fn(Func<&'a int>)
481 /// The type `MetaFunc`, when fully expanded, will be
483 /// for<'a> fn(fn(&'a int))
486 /// | | DebruijnIndex of 2
489 /// Here the `'a` lifetime is bound in the outer function, but appears as an argument of the
490 /// inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip
491 /// over the inner binder (remember that we count Debruijn indices from 1). However, in the
492 /// definition of `MetaFunc`, the binder is not visible, so the type `&'a int` will have a
493 /// debruijn index of 1. It's only during the substitution that we can see we must increase the
494 /// depth by 1 to account for the binder that we passed through.
496 /// As a second example, consider this twist:
499 /// type FuncTuple<A> = (A,fn(A));
500 /// type MetaFuncTuple = for<'a> fn(FuncTuple<&'a int>)
503 /// Here the final type will be:
505 /// for<'a> fn((&'a int, fn(&'a int)))
508 /// DebruijnIndex of 1 |
509 /// DebruijnIndex of 2
511 /// As indicated in the diagram, here the same type `&'a int` is substituted once, but in the
512 /// first case we do not increase the Debruijn index and in the second case we do. The reason
513 /// is that only in the second case have we passed through a fn binder.
514 fn shift_regions_through_binders(&self, ty: Ty<'tcx>) -> Ty<'tcx> {
515 debug!("shift_regions(ty={:?}, region_binders_passed={:?}, has_escaping_regions={:?})",
516 ty, self.region_binders_passed, ty.has_escaping_regions());
518 if self.region_binders_passed == 0 || !ty.has_escaping_regions() {
522 let result = ty::fold::shift_regions(self.tcx(), self.region_binders_passed, &ty);
523 debug!("shift_regions: shifted result = {:?}", result);
528 fn shift_region_through_binders(&self, region: &'tcx ty::Region) -> &'tcx ty::Region {
529 self.tcx().mk_region(ty::fold::shift_region(*region, self.region_binders_passed))
533 // Helper methods that modify substitutions.
535 impl<'a, 'gcx, 'tcx> ty::TraitRef<'tcx> {
536 pub fn from_method(tcx: TyCtxt<'a, 'gcx, 'tcx>,
538 substs: &Substs<'tcx>)
539 -> ty::TraitRef<'tcx> {
540 let defs = tcx.lookup_generics(trait_id);
542 let params = substs.params[..defs.own_count()].iter().cloned();
545 substs: Substs::new(tcx, params)
550 impl<'a, 'gcx, 'tcx> ty::ExistentialTraitRef<'tcx> {
551 pub fn erase_self_ty(tcx: TyCtxt<'a, 'gcx, 'tcx>,
552 trait_ref: ty::TraitRef<'tcx>)
553 -> ty::ExistentialTraitRef<'tcx> {
554 // Assert there is a Self.
555 trait_ref.substs.type_at(0);
557 let params = trait_ref.substs.params[1..].iter().cloned();
558 ty::ExistentialTraitRef {
559 def_id: trait_ref.def_id,
560 substs: Substs::new(tcx, params)
565 impl<'a, 'gcx, 'tcx> ty::PolyExistentialTraitRef<'tcx> {
566 /// Object types don't have a self-type specified. Therefore, when
567 /// we convert the principal trait-ref into a normal trait-ref,
568 /// you must give *some* self-type. A common choice is `mk_err()`
569 /// or some skolemized type.
570 pub fn with_self_ty(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
572 -> ty::PolyTraitRef<'tcx> {
573 // otherwise the escaping regions would be captured by the binder
574 assert!(!self_ty.has_escaping_regions());
576 self.map_bound(|trait_ref| {
577 let params = trait_ref.substs.params.iter().cloned();
578 let params = iter::once(Kind::from(self_ty)).chain(params);
580 def_id: trait_ref.def_id,
581 substs: Substs::new(tcx, params)