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, BoundVar, 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 self.get(param.index as usize)
210 .unwrap_or_else(|| mk_kind(param, substs))
214 fn fill_item<F>(substs: &mut SmallVec<[Kind<'tcx>; 8]>,
215 tcx: TyCtxt<'a, 'gcx, 'tcx>,
218 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
220 if let Some(def_id) = defs.parent {
221 let parent_defs = tcx.generics_of(def_id);
222 Substs::fill_item(substs, tcx, parent_defs, mk_kind);
224 Substs::fill_single(substs, defs, mk_kind)
227 fn fill_single<F>(substs: &mut SmallVec<[Kind<'tcx>; 8]>,
230 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
232 substs.reserve(defs.params.len());
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 impl<'tcx> serialize::UseSpecializedDecodable for &'tcx Substs<'tcx> {}
328 ///////////////////////////////////////////////////////////////////////////
329 // Public trait `Subst`
331 // Just call `foo.subst(tcx, substs)` to perform a substitution across
332 // `foo`. Or use `foo.subst_spanned(tcx, substs, Some(span))` when
333 // there is more information available (for better errors).
335 pub trait Subst<'tcx> : Sized {
336 fn subst<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
337 substs: &[Kind<'tcx>]) -> Self {
338 self.subst_spanned(tcx, substs, None)
341 fn subst_spanned<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
342 substs: &[Kind<'tcx>],
347 impl<'tcx, T:TypeFoldable<'tcx>> Subst<'tcx> for T {
348 fn subst_spanned<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
349 substs: &[Kind<'tcx>],
353 let mut folder = SubstFolder { tcx,
359 (*self).fold_with(&mut folder)
363 ///////////////////////////////////////////////////////////////////////////
364 // The actual substitution engine itself is a type folder.
366 struct SubstFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
367 tcx: TyCtxt<'a, 'gcx, 'tcx>,
368 substs: &'a [Kind<'tcx>],
370 // The location for which the substitution is performed, if available.
373 // The root type that is being substituted, if available.
374 root_ty: Option<Ty<'tcx>>,
376 // Depth of type stack
377 ty_stack_depth: usize,
379 // Number of region binders we have passed through while doing the substitution
383 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for SubstFolder<'a, 'gcx, 'tcx> {
384 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
386 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
387 self.binders_passed += 1;
388 let t = t.super_fold_with(self);
389 self.binders_passed -= 1;
393 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
394 // Note: This routine only handles regions that are bound on
395 // type declarations and other outer declarations, not those
396 // bound in *fn types*. Region substitution of the bound
397 // regions that appear in a function signature is done using
398 // the specialized routine `ty::replace_late_regions()`.
400 ty::ReEarlyBound(data) => {
401 let r = self.substs.get(data.index as usize).map(|k| k.unpack());
403 Some(UnpackedKind::Lifetime(lt)) => {
404 self.shift_region_through_binders(lt)
407 let span = self.span.unwrap_or(DUMMY_SP);
410 "Region parameter out of range \
411 when substituting in region {} (root type={:?}) \
423 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
424 if !t.needs_subst() {
428 // track the root type we were asked to substitute
429 let depth = self.ty_stack_depth;
431 self.root_ty = Some(t);
433 self.ty_stack_depth += 1;
435 let t1 = match t.sty {
437 self.ty_for_param(p, t)
440 t.super_fold_with(self)
444 assert_eq!(depth + 1, self.ty_stack_depth);
445 self.ty_stack_depth -= 1;
454 impl<'a, 'gcx, 'tcx> SubstFolder<'a, 'gcx, 'tcx> {
455 fn ty_for_param(&self, p: ty::ParamTy, source_ty: Ty<'tcx>) -> Ty<'tcx> {
456 // Look up the type in the substitutions. It really should be in there.
457 let opt_ty = self.substs.get(p.idx as usize).map(|k| k.unpack());
458 let ty = match opt_ty {
459 Some(UnpackedKind::Type(ty)) => ty,
461 let span = self.span.unwrap_or(DUMMY_SP);
464 "Type parameter `{:?}` ({:?}/{}) out of range \
465 when substituting (root type={:?}) substs={:?}",
474 self.shift_vars_through_binders(ty)
477 /// It is sometimes necessary to adjust the debruijn indices during substitution. This occurs
478 /// when we are substituting a type with escaping bound vars into a context where we have
479 /// passed through binders. That's quite a mouthful. Let's see an example:
482 /// type Func<A> = fn(A);
483 /// type MetaFunc = for<'a> fn(Func<&'a int>)
486 /// The type `MetaFunc`, when fully expanded, will be
488 /// for<'a> fn(fn(&'a int))
491 /// | | DebruijnIndex of 2
494 /// Here the `'a` lifetime is bound in the outer function, but appears as an argument of the
495 /// inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip
496 /// over the inner binder (remember that we count Debruijn indices from 1). However, in the
497 /// definition of `MetaFunc`, the binder is not visible, so the type `&'a int` will have a
498 /// debruijn index of 1. It's only during the substitution that we can see we must increase the
499 /// depth by 1 to account for the binder that we passed through.
501 /// As a second example, consider this twist:
504 /// type FuncTuple<A> = (A,fn(A));
505 /// type MetaFuncTuple = for<'a> fn(FuncTuple<&'a int>)
508 /// Here the final type will be:
510 /// for<'a> fn((&'a int, fn(&'a int)))
513 /// DebruijnIndex of 1 |
514 /// DebruijnIndex of 2
516 /// As indicated in the diagram, here the same type `&'a int` is substituted once, but in the
517 /// first case we do not increase the Debruijn index and in the second case we do. The reason
518 /// is that only in the second case have we passed through a fn binder.
519 fn shift_vars_through_binders(&self, ty: Ty<'tcx>) -> Ty<'tcx> {
520 debug!("shift_vars(ty={:?}, binders_passed={:?}, has_escaping_bound_vars={:?})",
521 ty, self.binders_passed, ty.has_escaping_bound_vars());
523 if self.binders_passed == 0 || !ty.has_escaping_bound_vars() {
527 let result = ty::fold::shift_vars(self.tcx(), &ty, self.binders_passed);
528 debug!("shift_vars: shifted result = {:?}", result);
533 fn shift_region_through_binders(&self, region: ty::Region<'tcx>) -> ty::Region<'tcx> {
534 if self.binders_passed == 0 || !region.has_escaping_bound_vars() {
537 ty::fold::shift_region(self.tcx, region, self.binders_passed)
541 pub type CanonicalUserSubsts<'tcx> = Canonical<'tcx, UserSubsts<'tcx>>;
543 impl CanonicalUserSubsts<'tcx> {
544 /// True if this represents a substitution like
550 /// i.e., each thing is mapped to a canonical variable with the same index.
551 pub fn is_identity(&self) -> bool {
552 if self.value.user_self_ty.is_some() {
556 self.value.substs.iter().zip(BoundVar::new(0)..).all(|(kind, cvar)| {
557 match kind.unpack() {
558 UnpackedKind::Type(ty) => match ty.sty {
560 // We only allow a `ty::INNERMOST` index in substitutions.
561 assert_eq!(b.index, ty::INNERMOST);
567 UnpackedKind::Lifetime(r) => match r {
568 ty::ReLateBound(index, br) => {
569 // We only allow a `ty::INNERMOST` index in substitutions.
570 assert_eq!(*index, ty::INNERMOST);
571 cvar == br.as_bound_var()
580 /// Stores the user-given substs to reach some fully qualified path
581 /// (e.g., `<T>::Item` or `<T as Trait>::Item`).
582 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
583 pub struct UserSubsts<'tcx> {
584 /// The substitutions for the item as given by the user.
585 pub substs: &'tcx Substs<'tcx>,
587 /// The self-type, in the case of a `<T>::Item` path (when applied
588 /// to an inherent impl). See `UserSelfTy` below.
589 pub user_self_ty: Option<UserSelfTy<'tcx>>,
592 BraceStructTypeFoldableImpl! {
593 impl<'tcx> TypeFoldable<'tcx> for UserSubsts<'tcx> {
599 BraceStructLiftImpl! {
600 impl<'a, 'tcx> Lift<'tcx> for UserSubsts<'a> {
601 type Lifted = UserSubsts<'tcx>;
607 /// Specifies the user-given self-type. In the case of a path that
608 /// refers to a member in an inherent impl, this self-type is
609 /// sometimes needed to constrain the type parameters on the impl. For
610 /// example, in this code:
613 /// struct Foo<T> { }
614 /// impl<A> Foo<A> { fn method() { } }
617 /// when you then have a path like `<Foo<&'static u32>>::method`,
618 /// this struct would carry the def-id of the impl along with the
619 /// self-type `Foo<u32>`. Then we can instantiate the parameters of
620 /// the impl (with the substs from `UserSubsts`) and apply those to
621 /// the self-type, giving `Foo<?A>`. Finally, we unify that with
622 /// the self-type here, which contains `?A` to be `&'static u32`
623 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
624 pub struct UserSelfTy<'tcx> {
625 pub impl_def_id: DefId,
626 pub self_ty: Ty<'tcx>,
629 BraceStructTypeFoldableImpl! {
630 impl<'tcx> TypeFoldable<'tcx> for UserSelfTy<'tcx> {
636 BraceStructLiftImpl! {
637 impl<'a, 'tcx> Lift<'tcx> for UserSelfTy<'a> {
638 type Lifted = UserSelfTy<'tcx>;