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 infer::canonical::Canonical;
15 use ty::{self, CanonicalVar, Lift, List, Ty, TyCtxt};
16 use ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
18 use serialize::{self, Encodable, Encoder, Decodable, Decoder};
19 use syntax_pos::{Span, DUMMY_SP};
20 use rustc_data_structures::indexed_vec::Idx;
21 use smallvec::SmallVec;
24 use std::cmp::Ordering;
26 use std::marker::PhantomData;
28 use std::num::NonZeroUsize;
30 /// An entity in the Rust typesystem, which can be one of
31 /// several kinds (only types and lifetimes for now).
32 /// To reduce memory usage, a `Kind` is a interned pointer,
33 /// with the lowest 2 bits being reserved for a tag to
34 /// indicate the type (`Ty` or `Region`) it points to.
35 #[derive(Copy, Clone, PartialEq, Eq, Hash)]
36 pub struct Kind<'tcx> {
38 marker: PhantomData<(Ty<'tcx>, ty::Region<'tcx>)>
41 const TAG_MASK: usize = 0b11;
42 const TYPE_TAG: usize = 0b00;
43 const REGION_TAG: usize = 0b01;
45 #[derive(Debug, RustcEncodable, RustcDecodable, PartialEq, Eq, PartialOrd, Ord)]
46 pub enum UnpackedKind<'tcx> {
47 Lifetime(ty::Region<'tcx>),
51 impl<'tcx> UnpackedKind<'tcx> {
52 fn pack(self) -> Kind<'tcx> {
53 let (tag, ptr) = match self {
54 UnpackedKind::Lifetime(lt) => {
55 // Ensure we can use the tag bits.
56 assert_eq!(mem::align_of_val(lt) & TAG_MASK, 0);
57 (REGION_TAG, lt as *const _ as usize)
59 UnpackedKind::Type(ty) => {
60 // Ensure we can use the tag bits.
61 assert_eq!(mem::align_of_val(ty) & TAG_MASK, 0);
62 (TYPE_TAG, ty as *const _ as usize)
68 NonZeroUsize::new_unchecked(ptr | tag)
75 impl<'tcx> Ord for Kind<'tcx> {
76 fn cmp(&self, other: &Kind) -> Ordering {
77 self.unpack().cmp(&other.unpack())
81 impl<'tcx> PartialOrd for Kind<'tcx> {
82 fn partial_cmp(&self, other: &Kind) -> Option<Ordering> {
83 Some(self.cmp(&other))
87 impl<'tcx> From<ty::Region<'tcx>> for Kind<'tcx> {
88 fn from(r: ty::Region<'tcx>) -> Kind<'tcx> {
89 UnpackedKind::Lifetime(r).pack()
93 impl<'tcx> From<Ty<'tcx>> for Kind<'tcx> {
94 fn from(ty: Ty<'tcx>) -> Kind<'tcx> {
95 UnpackedKind::Type(ty).pack()
99 impl<'tcx> Kind<'tcx> {
101 pub fn unpack(self) -> UnpackedKind<'tcx> {
102 let ptr = self.ptr.get();
104 match ptr & TAG_MASK {
105 REGION_TAG => UnpackedKind::Lifetime(&*((ptr & !TAG_MASK) as *const _)),
106 TYPE_TAG => UnpackedKind::Type(&*((ptr & !TAG_MASK) as *const _)),
107 _ => intrinsics::unreachable()
113 impl<'tcx> fmt::Debug for Kind<'tcx> {
114 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
115 match self.unpack() {
116 UnpackedKind::Lifetime(lt) => write!(f, "{:?}", lt),
117 UnpackedKind::Type(ty) => write!(f, "{:?}", ty),
122 impl<'tcx> fmt::Display 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<'a, 'tcx> Lift<'tcx> for Kind<'a> {
132 type Lifted = Kind<'tcx>;
134 fn lift_to_tcx<'cx, 'gcx>(&self, tcx: TyCtxt<'cx, 'gcx, 'tcx>) -> Option<Self::Lifted> {
135 match self.unpack() {
136 UnpackedKind::Lifetime(a) => a.lift_to_tcx(tcx).map(|a| a.into()),
137 UnpackedKind::Type(a) => a.lift_to_tcx(tcx).map(|a| a.into()),
142 impl<'tcx> TypeFoldable<'tcx> for Kind<'tcx> {
143 fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
144 match self.unpack() {
145 UnpackedKind::Lifetime(lt) => lt.fold_with(folder).into(),
146 UnpackedKind::Type(ty) => ty.fold_with(folder).into(),
150 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
151 match self.unpack() {
152 UnpackedKind::Lifetime(lt) => lt.visit_with(visitor),
153 UnpackedKind::Type(ty) => ty.visit_with(visitor),
158 impl<'tcx> Encodable for Kind<'tcx> {
159 fn encode<E: Encoder>(&self, e: &mut E) -> Result<(), E::Error> {
160 self.unpack().encode(e)
164 impl<'tcx> Decodable for Kind<'tcx> {
165 fn decode<D: Decoder>(d: &mut D) -> Result<Kind<'tcx>, D::Error> {
166 Ok(UnpackedKind::decode(d)?.pack())
170 /// A substitution mapping generic parameters to new values.
171 pub type Substs<'tcx> = List<Kind<'tcx>>;
173 impl<'a, 'gcx, 'tcx> Substs<'tcx> {
174 /// Creates a Substs that maps each generic parameter to itself.
175 pub fn identity_for_item(tcx: TyCtxt<'a, 'gcx, 'tcx>, def_id: DefId)
176 -> &'tcx Substs<'tcx> {
177 Substs::for_item(tcx, def_id, |param, _| {
178 tcx.mk_param_from_def(param)
182 /// Creates a Substs for generic parameter definitions,
183 /// by calling closures to obtain each kind.
184 /// The closures get to observe the Substs as they're
185 /// being built, which can be used to correctly
186 /// substitute defaults of generic parameters.
187 pub fn for_item<F>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
190 -> &'tcx Substs<'tcx>
191 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
193 let defs = tcx.generics_of(def_id);
194 let count = defs.count();
195 let mut substs = SmallVec::with_capacity(count);
196 Substs::fill_item(&mut substs, tcx, defs, &mut mk_kind);
197 tcx.intern_substs(&substs)
200 pub fn extend_to<F>(&self,
201 tcx: TyCtxt<'a, 'gcx, 'tcx>,
204 -> &'tcx Substs<'tcx>
205 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
207 Substs::for_item(tcx, def_id, |param, substs| {
208 match self.get(param.index as usize) {
210 None => mk_kind(param, substs),
215 fn fill_item<F>(substs: &mut SmallVec<[Kind<'tcx>; 8]>,
216 tcx: TyCtxt<'a, 'gcx, 'tcx>,
219 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
221 if let Some(def_id) = defs.parent {
222 let parent_defs = tcx.generics_of(def_id);
223 Substs::fill_item(substs, tcx, parent_defs, mk_kind);
225 Substs::fill_single(substs, defs, mk_kind)
228 fn fill_single<F>(substs: &mut SmallVec<[Kind<'tcx>; 8]>,
231 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
233 for param in &defs.params {
234 let kind = mk_kind(param, substs);
235 assert_eq!(param.index as usize, substs.len());
240 pub fn is_noop(&self) -> bool {
245 pub fn types(&'a self) -> impl DoubleEndedIterator<Item=Ty<'tcx>> + 'a {
246 self.iter().filter_map(|k| {
247 if let UnpackedKind::Type(ty) = k.unpack() {
256 pub fn regions(&'a self) -> impl DoubleEndedIterator<Item=ty::Region<'tcx>> + 'a {
257 self.iter().filter_map(|k| {
258 if let UnpackedKind::Lifetime(lt) = k.unpack() {
267 pub fn type_at(&self, i: usize) -> Ty<'tcx> {
268 if let UnpackedKind::Type(ty) = self[i].unpack() {
271 bug!("expected type for param #{} in {:?}", i, self);
276 pub fn region_at(&self, i: usize) -> ty::Region<'tcx> {
277 if let UnpackedKind::Lifetime(lt) = self[i].unpack() {
280 bug!("expected region for param #{} in {:?}", i, self);
285 pub fn type_for_def(&self, def: &ty::GenericParamDef) -> Kind<'tcx> {
286 self.type_at(def.index as usize).into()
289 /// Transform from substitutions for a child of `source_ancestor`
290 /// (e.g. a trait or impl) to substitutions for the same child
291 /// in a different item, with `target_substs` as the base for
292 /// the target impl/trait, with the source child-specific
293 /// parameters (e.g. method parameters) on top of that base.
294 pub fn rebase_onto(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
295 source_ancestor: DefId,
296 target_substs: &Substs<'tcx>)
297 -> &'tcx Substs<'tcx> {
298 let defs = tcx.generics_of(source_ancestor);
299 tcx.mk_substs(target_substs.iter().chain(&self[defs.params.len()..]).cloned())
302 pub fn truncate_to(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, generics: &ty::Generics)
303 -> &'tcx Substs<'tcx> {
304 tcx.mk_substs(self.iter().take(generics.count()).cloned())
308 impl<'tcx> TypeFoldable<'tcx> for &'tcx Substs<'tcx> {
309 fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
310 let params: SmallVec<[_; 8]> = self.iter().map(|k| k.fold_with(folder)).collect();
312 // If folding doesn't change the substs, it's faster to avoid
313 // calling `mk_substs` and instead reuse the existing substs.
314 if params[..] == self[..] {
317 folder.tcx().intern_substs(¶ms)
321 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
322 self.iter().any(|t| t.visit_with(visitor))
326 pub type CanonicalSubsts<'gcx> = Canonical<'gcx, &'gcx Substs<'gcx>>;
328 impl<'gcx> CanonicalSubsts<'gcx> {
329 /// True if this represents a substitution like
335 /// i.e., each thing is mapped to a canonical variable with the same index.
336 pub fn is_identity(&self) -> bool {
337 self.value.iter().zip(CanonicalVar::new(0)..).all(|(kind, cvar)| {
338 match kind.unpack() {
339 UnpackedKind::Type(ty) => match ty.sty {
340 ty::Infer(ty::CanonicalTy(cvar1)) => cvar == cvar1,
344 UnpackedKind::Lifetime(r) => match r {
345 ty::ReCanonical(cvar1) => cvar == *cvar1,
353 impl<'tcx> serialize::UseSpecializedDecodable for &'tcx Substs<'tcx> {}
355 ///////////////////////////////////////////////////////////////////////////
356 // Public trait `Subst`
358 // Just call `foo.subst(tcx, substs)` to perform a substitution across
359 // `foo`. Or use `foo.subst_spanned(tcx, substs, Some(span))` when
360 // there is more information available (for better errors).
362 pub trait Subst<'tcx> : Sized {
363 fn subst<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
364 substs: &[Kind<'tcx>]) -> Self {
365 self.subst_spanned(tcx, substs, None)
368 fn subst_spanned<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
369 substs: &[Kind<'tcx>],
374 impl<'tcx, T:TypeFoldable<'tcx>> Subst<'tcx> for T {
375 fn subst_spanned<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
376 substs: &[Kind<'tcx>],
380 let mut folder = SubstFolder { tcx,
385 region_binders_passed: 0 };
386 (*self).fold_with(&mut folder)
390 ///////////////////////////////////////////////////////////////////////////
391 // The actual substitution engine itself is a type folder.
393 struct SubstFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
394 tcx: TyCtxt<'a, 'gcx, 'tcx>,
395 substs: &'a [Kind<'tcx>],
397 // The location for which the substitution is performed, if available.
400 // The root type that is being substituted, if available.
401 root_ty: Option<Ty<'tcx>>,
403 // Depth of type stack
404 ty_stack_depth: usize,
406 // Number of region binders we have passed through while doing the substitution
407 region_binders_passed: u32,
410 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for SubstFolder<'a, 'gcx, 'tcx> {
411 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
413 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
414 self.region_binders_passed += 1;
415 let t = t.super_fold_with(self);
416 self.region_binders_passed -= 1;
420 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
421 // Note: This routine only handles regions that are bound on
422 // type declarations and other outer declarations, not those
423 // bound in *fn types*. Region substitution of the bound
424 // regions that appear in a function signature is done using
425 // the specialized routine `ty::replace_late_regions()`.
427 ty::ReEarlyBound(data) => {
428 let r = self.substs.get(data.index as usize).map(|k| k.unpack());
430 Some(UnpackedKind::Lifetime(lt)) => {
431 self.shift_region_through_binders(lt)
434 let span = self.span.unwrap_or(DUMMY_SP);
437 "Region parameter out of range \
438 when substituting in region {} (root type={:?}) \
450 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
451 if !t.needs_subst() {
455 // track the root type we were asked to substitute
456 let depth = self.ty_stack_depth;
458 self.root_ty = Some(t);
460 self.ty_stack_depth += 1;
462 let t1 = match t.sty {
464 self.ty_for_param(p, t)
467 t.super_fold_with(self)
471 assert_eq!(depth + 1, self.ty_stack_depth);
472 self.ty_stack_depth -= 1;
481 impl<'a, 'gcx, 'tcx> SubstFolder<'a, 'gcx, 'tcx> {
482 fn ty_for_param(&self, p: ty::ParamTy, source_ty: Ty<'tcx>) -> Ty<'tcx> {
483 // Look up the type in the substitutions. It really should be in there.
484 let opt_ty = self.substs.get(p.idx as usize).map(|k| k.unpack());
485 let ty = match opt_ty {
486 Some(UnpackedKind::Type(ty)) => ty,
488 let span = self.span.unwrap_or(DUMMY_SP);
491 "Type parameter `{:?}` ({:?}/{}) out of range \
492 when substituting (root type={:?}) substs={:?}",
501 self.shift_regions_through_binders(ty)
504 /// It is sometimes necessary to adjust the debruijn indices during substitution. This occurs
505 /// when we are substituting a type with escaping regions into a context where we have passed
506 /// through region binders. That's quite a mouthful. Let's see an example:
509 /// type Func<A> = fn(A);
510 /// type MetaFunc = for<'a> fn(Func<&'a int>)
513 /// The type `MetaFunc`, when fully expanded, will be
515 /// for<'a> fn(fn(&'a int))
518 /// | | DebruijnIndex of 2
521 /// Here the `'a` lifetime is bound in the outer function, but appears as an argument of the
522 /// inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip
523 /// over the inner binder (remember that we count Debruijn indices from 1). However, in the
524 /// definition of `MetaFunc`, the binder is not visible, so the type `&'a int` will have a
525 /// debruijn index of 1. It's only during the substitution that we can see we must increase the
526 /// depth by 1 to account for the binder that we passed through.
528 /// As a second example, consider this twist:
531 /// type FuncTuple<A> = (A,fn(A));
532 /// type MetaFuncTuple = for<'a> fn(FuncTuple<&'a int>)
535 /// Here the final type will be:
537 /// for<'a> fn((&'a int, fn(&'a int)))
540 /// DebruijnIndex of 1 |
541 /// DebruijnIndex of 2
543 /// As indicated in the diagram, here the same type `&'a int` is substituted once, but in the
544 /// first case we do not increase the Debruijn index and in the second case we do. The reason
545 /// is that only in the second case have we passed through a fn binder.
546 fn shift_regions_through_binders(&self, ty: Ty<'tcx>) -> Ty<'tcx> {
547 debug!("shift_regions(ty={:?}, region_binders_passed={:?}, has_escaping_regions={:?})",
548 ty, self.region_binders_passed, ty.has_escaping_regions());
550 if self.region_binders_passed == 0 || !ty.has_escaping_regions() {
554 let result = ty::fold::shift_regions(self.tcx(), self.region_binders_passed, &ty);
555 debug!("shift_regions: shifted result = {:?}", result);
560 fn shift_region_through_binders(&self, region: ty::Region<'tcx>) -> ty::Region<'tcx> {
561 if self.region_binders_passed == 0 || !region.has_escaping_regions() {
564 self.tcx().mk_region(ty::fold::shift_region(*region, self.region_binders_passed))