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.
13 use hir::def_id::DefId;
14 use ty::{self, Lift, Slice, Ty, TyCtxt};
15 use ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
17 use serialize::{self, Encodable, Encoder, Decodable, Decoder};
18 use syntax_pos::{Span, DUMMY_SP};
19 use rustc_data_structures::accumulate_vec::AccumulateVec;
20 use rustc_data_structures::array_vec::ArrayVec;
23 use std::cmp::Ordering;
25 use std::marker::PhantomData;
27 use std::num::NonZeroUsize;
29 /// An entity in the Rust typesystem, which can be one of
30 /// several kinds (only types and lifetimes for now).
31 /// To reduce memory usage, a `Kind` is a interned pointer,
32 /// with the lowest 2 bits being reserved for a tag to
33 /// indicate the type (`Ty` or `Region`) it points to.
34 #[derive(Copy, Clone, PartialEq, Eq, Hash)]
35 pub struct Kind<'tcx> {
37 marker: PhantomData<(Ty<'tcx>, ty::Region<'tcx>)>
40 const TAG_MASK: usize = 0b11;
41 const TYPE_TAG: usize = 0b00;
42 const REGION_TAG: usize = 0b01;
44 #[derive(Debug, RustcEncodable, RustcDecodable)]
45 pub enum UnpackedKind<'tcx> {
46 Lifetime(ty::Region<'tcx>),
50 impl<'tcx> UnpackedKind<'tcx> {
51 fn pack(self) -> Kind<'tcx> {
52 let (tag, ptr) = match self {
53 UnpackedKind::Lifetime(lt) => {
54 // Ensure we can use the tag bits.
55 assert_eq!(mem::align_of_val(lt) & TAG_MASK, 0);
56 (REGION_TAG, lt as *const _ as usize)
58 UnpackedKind::Type(ty) => {
59 // Ensure we can use the tag bits.
60 assert_eq!(mem::align_of_val(ty) & TAG_MASK, 0);
61 (TYPE_TAG, ty as *const _ as usize)
67 NonZeroUsize::new_unchecked(ptr | tag)
74 impl<'tcx> Ord for Kind<'tcx> {
75 fn cmp(&self, other: &Kind) -> Ordering {
76 match (self.unpack(), other.unpack()) {
77 (UnpackedKind::Type(_), UnpackedKind::Lifetime(_)) => Ordering::Greater,
79 (UnpackedKind::Type(ty1), UnpackedKind::Type(ty2)) => {
83 (UnpackedKind::Lifetime(reg1), UnpackedKind::Lifetime(reg2)) => reg1.cmp(reg2),
85 (UnpackedKind::Lifetime(_), UnpackedKind::Type(_)) => Ordering::Less,
90 impl<'tcx> PartialOrd for Kind<'tcx> {
91 fn partial_cmp(&self, other: &Kind) -> Option<Ordering> {
92 Some(self.cmp(&other))
96 impl<'tcx> From<ty::Region<'tcx>> for Kind<'tcx> {
97 fn from(r: ty::Region<'tcx>) -> Kind<'tcx> {
98 UnpackedKind::Lifetime(r).pack()
102 impl<'tcx> From<Ty<'tcx>> for Kind<'tcx> {
103 fn from(ty: Ty<'tcx>) -> Kind<'tcx> {
104 UnpackedKind::Type(ty).pack()
108 impl<'tcx> Kind<'tcx> {
110 pub fn unpack(self) -> UnpackedKind<'tcx> {
111 let ptr = self.ptr.get();
113 match ptr & TAG_MASK {
114 REGION_TAG => UnpackedKind::Lifetime(&*((ptr & !TAG_MASK) as *const _)),
115 TYPE_TAG => UnpackedKind::Type(&*((ptr & !TAG_MASK) as *const _)),
116 _ => intrinsics::unreachable()
122 impl<'tcx> fmt::Debug for Kind<'tcx> {
123 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
124 match self.unpack() {
125 UnpackedKind::Lifetime(lt) => write!(f, "{:?}", lt),
126 UnpackedKind::Type(ty) => write!(f, "{:?}", ty),
131 impl<'tcx> fmt::Display for Kind<'tcx> {
132 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
133 match self.unpack() {
134 UnpackedKind::Lifetime(lt) => write!(f, "{}", lt),
135 UnpackedKind::Type(ty) => write!(f, "{}", ty),
140 impl<'a, 'tcx> Lift<'tcx> for Kind<'a> {
141 type Lifted = Kind<'tcx>;
143 fn lift_to_tcx<'cx, 'gcx>(&self, tcx: TyCtxt<'cx, 'gcx, 'tcx>) -> Option<Self::Lifted> {
144 match self.unpack() {
145 UnpackedKind::Lifetime(a) => a.lift_to_tcx(tcx).map(|a| a.into()),
146 UnpackedKind::Type(a) => a.lift_to_tcx(tcx).map(|a| a.into()),
151 impl<'tcx> TypeFoldable<'tcx> for Kind<'tcx> {
152 fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
153 match self.unpack() {
154 UnpackedKind::Lifetime(lt) => lt.fold_with(folder).into(),
155 UnpackedKind::Type(ty) => ty.fold_with(folder).into(),
159 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
160 match self.unpack() {
161 UnpackedKind::Lifetime(lt) => lt.visit_with(visitor),
162 UnpackedKind::Type(ty) => ty.visit_with(visitor),
167 impl<'tcx> Encodable for Kind<'tcx> {
168 fn encode<E: Encoder>(&self, e: &mut E) -> Result<(), E::Error> {
169 self.unpack().encode(e)
173 impl<'tcx> Decodable for Kind<'tcx> {
174 fn decode<D: Decoder>(d: &mut D) -> Result<Kind<'tcx>, D::Error> {
175 Ok(UnpackedKind::decode(d)?.pack())
179 /// A substitution mapping generic parameters to new values.
180 pub type Substs<'tcx> = Slice<Kind<'tcx>>;
182 impl<'a, 'gcx, 'tcx> Substs<'tcx> {
183 /// Creates a Substs that maps each generic parameter to itself.
184 pub fn identity_for_item(tcx: TyCtxt<'a, 'gcx, 'tcx>, def_id: DefId)
185 -> &'tcx Substs<'tcx> {
186 Substs::for_item(tcx, def_id, |param, _| {
187 tcx.mk_param_from_def(param)
191 /// Creates a Substs for generic parameter definitions,
192 /// by calling closures to obtain each kind.
193 /// The closures get to observe the Substs as they're
194 /// being built, which can be used to correctly
195 /// substitute defaults of generic parameters.
196 pub fn for_item<F>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
199 -> &'tcx Substs<'tcx>
200 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
202 let defs = tcx.generics_of(def_id);
203 let count = defs.count();
204 let mut substs = if count <= 8 {
205 AccumulateVec::Array(ArrayVec::new())
207 AccumulateVec::Heap(Vec::with_capacity(count))
209 Substs::fill_item(&mut substs, tcx, defs, &mut mk_kind);
210 tcx.intern_substs(&substs)
213 pub fn extend_to<F>(&self,
214 tcx: TyCtxt<'a, 'gcx, 'tcx>,
217 -> &'tcx Substs<'tcx>
218 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
220 Substs::for_item(tcx, def_id, |param, substs| {
221 match self.get(param.index as usize) {
223 None => mk_kind(param, substs),
228 fn fill_item<F>(substs: &mut AccumulateVec<[Kind<'tcx>; 8]>,
229 tcx: TyCtxt<'a, 'gcx, 'tcx>,
232 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
234 if let Some(def_id) = defs.parent {
235 let parent_defs = tcx.generics_of(def_id);
236 Substs::fill_item(substs, tcx, parent_defs, mk_kind);
238 Substs::fill_single(substs, defs, mk_kind)
241 fn fill_single<F>(substs: &mut AccumulateVec<[Kind<'tcx>; 8]>,
244 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
246 for param in &defs.params {
247 let kind = mk_kind(param, substs);
248 assert_eq!(param.index as usize, substs.len());
250 AccumulateVec::Array(ref mut arr) => arr.push(kind),
251 AccumulateVec::Heap(ref mut vec) => vec.push(kind),
256 pub fn is_noop(&self) -> bool {
261 pub fn types(&'a self) -> impl DoubleEndedIterator<Item=Ty<'tcx>> + 'a {
262 self.iter().filter_map(|k| {
263 if let UnpackedKind::Type(ty) = k.unpack() {
272 pub fn regions(&'a self) -> impl DoubleEndedIterator<Item=ty::Region<'tcx>> + 'a {
273 self.iter().filter_map(|k| {
274 if let UnpackedKind::Lifetime(lt) = k.unpack() {
283 pub fn type_at(&self, i: usize) -> Ty<'tcx> {
284 if let UnpackedKind::Type(ty) = self[i].unpack() {
287 bug!("expected type for param #{} in {:?}", i, self);
292 pub fn region_at(&self, i: usize) -> ty::Region<'tcx> {
293 if let UnpackedKind::Lifetime(lt) = self[i].unpack() {
296 bug!("expected region for param #{} in {:?}", i, self);
301 pub fn type_for_def(&self, def: &ty::GenericParamDef) -> Kind<'tcx> {
302 self.type_at(def.index as usize).into()
305 /// Transform from substitutions for a child of `source_ancestor`
306 /// (e.g. a trait or impl) to substitutions for the same child
307 /// in a different item, with `target_substs` as the base for
308 /// the target impl/trait, with the source child-specific
309 /// parameters (e.g. method parameters) on top of that base.
310 pub fn rebase_onto(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
311 source_ancestor: DefId,
312 target_substs: &Substs<'tcx>)
313 -> &'tcx Substs<'tcx> {
314 let defs = tcx.generics_of(source_ancestor);
315 tcx.mk_substs(target_substs.iter().chain(&self[defs.params.len()..]).cloned())
318 pub fn truncate_to(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, generics: &ty::Generics)
319 -> &'tcx Substs<'tcx> {
320 tcx.mk_substs(self.iter().take(generics.count()).cloned())
324 impl<'tcx> TypeFoldable<'tcx> for &'tcx Substs<'tcx> {
325 fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
326 let params: AccumulateVec<[_; 8]> = self.iter().map(|k| k.fold_with(folder)).collect();
328 // If folding doesn't change the substs, it's faster to avoid
329 // calling `mk_substs` and instead reuse the existing substs.
330 if params[..] == self[..] {
333 folder.tcx().intern_substs(¶ms)
337 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
338 self.iter().any(|t| t.visit_with(visitor))
342 impl<'tcx> serialize::UseSpecializedDecodable for &'tcx Substs<'tcx> {}
344 ///////////////////////////////////////////////////////////////////////////
345 // Public trait `Subst`
347 // Just call `foo.subst(tcx, substs)` to perform a substitution across
348 // `foo`. Or use `foo.subst_spanned(tcx, substs, Some(span))` when
349 // there is more information available (for better errors).
351 pub trait Subst<'tcx> : Sized {
352 fn subst<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
353 substs: &[Kind<'tcx>]) -> Self {
354 self.subst_spanned(tcx, substs, None)
357 fn subst_spanned<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
358 substs: &[Kind<'tcx>],
363 impl<'tcx, T:TypeFoldable<'tcx>> Subst<'tcx> for T {
364 fn subst_spanned<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
365 substs: &[Kind<'tcx>],
369 let mut folder = SubstFolder { tcx,
374 region_binders_passed: 0 };
375 (*self).fold_with(&mut folder)
379 ///////////////////////////////////////////////////////////////////////////
380 // The actual substitution engine itself is a type folder.
382 struct SubstFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
383 tcx: TyCtxt<'a, 'gcx, 'tcx>,
384 substs: &'a [Kind<'tcx>],
386 // The location for which the substitution is performed, if available.
389 // The root type that is being substituted, if available.
390 root_ty: Option<Ty<'tcx>>,
392 // Depth of type stack
393 ty_stack_depth: usize,
395 // Number of region binders we have passed through while doing the substitution
396 region_binders_passed: u32,
399 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for SubstFolder<'a, 'gcx, 'tcx> {
400 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
402 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
403 self.region_binders_passed += 1;
404 let t = t.super_fold_with(self);
405 self.region_binders_passed -= 1;
409 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
410 // Note: This routine only handles regions that are bound on
411 // type declarations and other outer declarations, not those
412 // bound in *fn types*. Region substitution of the bound
413 // regions that appear in a function signature is done using
414 // the specialized routine `ty::replace_late_regions()`.
416 ty::ReEarlyBound(data) => {
417 let r = self.substs.get(data.index as usize).map(|k| k.unpack());
419 Some(UnpackedKind::Lifetime(lt)) => {
420 self.shift_region_through_binders(lt)
423 let span = self.span.unwrap_or(DUMMY_SP);
426 "Region parameter out of range \
427 when substituting in region {} (root type={:?}) \
439 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
440 if !t.needs_subst() {
444 // track the root type we were asked to substitute
445 let depth = self.ty_stack_depth;
447 self.root_ty = Some(t);
449 self.ty_stack_depth += 1;
451 let t1 = match t.sty {
453 self.ty_for_param(p, t)
456 t.super_fold_with(self)
460 assert_eq!(depth + 1, self.ty_stack_depth);
461 self.ty_stack_depth -= 1;
470 impl<'a, 'gcx, 'tcx> SubstFolder<'a, 'gcx, 'tcx> {
471 fn ty_for_param(&self, p: ty::ParamTy, source_ty: Ty<'tcx>) -> Ty<'tcx> {
472 // Look up the type in the substitutions. It really should be in there.
473 let opt_ty = self.substs.get(p.idx as usize).map(|k| k.unpack());
474 let ty = match opt_ty {
475 Some(UnpackedKind::Type(ty)) => ty,
477 let span = self.span.unwrap_or(DUMMY_SP);
480 "Type parameter `{:?}` ({:?}/{}) out of range \
481 when substituting (root type={:?}) substs={:?}",
490 self.shift_regions_through_binders(ty)
493 /// It is sometimes necessary to adjust the debruijn indices during substitution. This occurs
494 /// when we are substituting a type with escaping regions into a context where we have passed
495 /// through region binders. That's quite a mouthful. Let's see an example:
498 /// type Func<A> = fn(A);
499 /// type MetaFunc = for<'a> fn(Func<&'a int>)
502 /// The type `MetaFunc`, when fully expanded, will be
504 /// for<'a> fn(fn(&'a int))
507 /// | | DebruijnIndex of 2
510 /// Here the `'a` lifetime is bound in the outer function, but appears as an argument of the
511 /// inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip
512 /// over the inner binder (remember that we count Debruijn indices from 1). However, in the
513 /// definition of `MetaFunc`, the binder is not visible, so the type `&'a int` will have a
514 /// debruijn index of 1. It's only during the substitution that we can see we must increase the
515 /// depth by 1 to account for the binder that we passed through.
517 /// As a second example, consider this twist:
520 /// type FuncTuple<A> = (A,fn(A));
521 /// type MetaFuncTuple = for<'a> fn(FuncTuple<&'a int>)
524 /// Here the final type will be:
526 /// for<'a> fn((&'a int, fn(&'a int)))
529 /// DebruijnIndex of 1 |
530 /// DebruijnIndex of 2
532 /// As indicated in the diagram, here the same type `&'a int` is substituted once, but in the
533 /// first case we do not increase the Debruijn index and in the second case we do. The reason
534 /// is that only in the second case have we passed through a fn binder.
535 fn shift_regions_through_binders(&self, ty: Ty<'tcx>) -> Ty<'tcx> {
536 debug!("shift_regions(ty={:?}, region_binders_passed={:?}, has_escaping_regions={:?})",
537 ty, self.region_binders_passed, ty.has_escaping_regions());
539 if self.region_binders_passed == 0 || !ty.has_escaping_regions() {
543 let result = ty::fold::shift_regions(self.tcx(), self.region_binders_passed, &ty);
544 debug!("shift_regions: shifted result = {:?}", result);
549 fn shift_region_through_binders(&self, region: ty::Region<'tcx>) -> ty::Region<'tcx> {
550 if self.region_binders_passed == 0 || !region.has_escaping_regions() {
553 self.tcx().mk_region(ty::fold::shift_region(*region, self.region_binders_passed))