3 use crate::hir::def_id::DefId;
4 use crate::infer::canonical::Canonical;
5 use crate::ty::{self, Lift, List, Ty, TyCtxt, InferConst, ParamConst};
6 use crate::ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
7 use crate::mir::interpret::ConstValue;
9 use serialize::{self, Encodable, Encoder, Decodable, Decoder};
10 use syntax_pos::{Span, DUMMY_SP};
11 use smallvec::SmallVec;
12 use rustc_macros::HashStable;
16 use std::cmp::Ordering;
17 use std::marker::PhantomData;
19 use std::num::NonZeroUsize;
21 /// An entity in the Rust type system, which can be one of
22 /// several kinds (types, lifetimes, and consts).
23 /// To reduce memory usage, a `Kind` is a interned pointer,
24 /// with the lowest 2 bits being reserved for a tag to
25 /// indicate the type (`Ty`, `Region`, or `Const`) it points to.
26 #[derive(Copy, Clone, PartialEq, Eq, Hash)]
27 pub struct Kind<'tcx> {
29 marker: PhantomData<(Ty<'tcx>, ty::Region<'tcx>, &'tcx ty::Const<'tcx>)>
32 const TAG_MASK: usize = 0b11;
33 const TYPE_TAG: usize = 0b00;
34 const REGION_TAG: usize = 0b01;
35 const CONST_TAG: usize = 0b10;
37 #[derive(Debug, RustcEncodable, RustcDecodable, PartialEq, Eq, PartialOrd, Ord, HashStable)]
38 pub enum UnpackedKind<'tcx> {
39 Lifetime(ty::Region<'tcx>),
41 Const(&'tcx ty::Const<'tcx>),
44 impl<'tcx> UnpackedKind<'tcx> {
45 fn pack(self) -> Kind<'tcx> {
46 let (tag, ptr) = match self {
47 UnpackedKind::Lifetime(lt) => {
48 // Ensure we can use the tag bits.
49 assert_eq!(mem::align_of_val(lt) & TAG_MASK, 0);
50 (REGION_TAG, lt as *const _ as usize)
52 UnpackedKind::Type(ty) => {
53 // Ensure we can use the tag bits.
54 assert_eq!(mem::align_of_val(ty) & TAG_MASK, 0);
55 (TYPE_TAG, ty as *const _ as usize)
57 UnpackedKind::Const(ct) => {
58 // Ensure we can use the tag bits.
59 assert_eq!(mem::align_of_val(ct) & TAG_MASK, 0);
60 (CONST_TAG, ct as *const _ as usize)
66 NonZeroUsize::new_unchecked(ptr | tag)
73 impl fmt::Debug for Kind<'tcx> {
74 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
76 UnpackedKind::Lifetime(lt) => lt.fmt(f),
77 UnpackedKind::Type(ty) => ty.fmt(f),
78 UnpackedKind::Const(ct) => ct.fmt(f),
83 impl<'tcx> Ord for Kind<'tcx> {
84 fn cmp(&self, other: &Kind<'_>) -> Ordering {
85 self.unpack().cmp(&other.unpack())
89 impl<'tcx> PartialOrd for Kind<'tcx> {
90 fn partial_cmp(&self, other: &Kind<'_>) -> Option<Ordering> {
91 Some(self.cmp(&other))
95 impl<'tcx> From<ty::Region<'tcx>> for Kind<'tcx> {
96 fn from(r: ty::Region<'tcx>) -> Kind<'tcx> {
97 UnpackedKind::Lifetime(r).pack()
101 impl<'tcx> From<Ty<'tcx>> for Kind<'tcx> {
102 fn from(ty: Ty<'tcx>) -> Kind<'tcx> {
103 UnpackedKind::Type(ty).pack()
107 impl<'tcx> From<&'tcx ty::Const<'tcx>> for Kind<'tcx> {
108 fn from(c: &'tcx ty::Const<'tcx>) -> Kind<'tcx> {
109 UnpackedKind::Const(c).pack()
113 impl<'tcx> Kind<'tcx> {
115 pub fn unpack(self) -> UnpackedKind<'tcx> {
116 let ptr = self.ptr.get();
118 match ptr & TAG_MASK {
119 REGION_TAG => UnpackedKind::Lifetime(&*((ptr & !TAG_MASK) as *const _)),
120 TYPE_TAG => UnpackedKind::Type(&*((ptr & !TAG_MASK) as *const _)),
121 CONST_TAG => UnpackedKind::Const(&*((ptr & !TAG_MASK) as *const _)),
122 _ => intrinsics::unreachable()
128 impl<'a, 'tcx> Lift<'tcx> for Kind<'a> {
129 type Lifted = Kind<'tcx>;
131 fn lift_to_tcx<'cx, 'gcx>(&self, tcx: TyCtxt<'cx, 'gcx, 'tcx>) -> Option<Self::Lifted> {
132 match self.unpack() {
133 UnpackedKind::Lifetime(lt) => tcx.lift(<).map(|lt| lt.into()),
134 UnpackedKind::Type(ty) => tcx.lift(&ty).map(|ty| ty.into()),
135 UnpackedKind::Const(ct) => tcx.lift(&ct).map(|ct| ct.into()),
140 impl<'tcx> TypeFoldable<'tcx> for Kind<'tcx> {
141 fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
142 match self.unpack() {
143 UnpackedKind::Lifetime(lt) => lt.fold_with(folder).into(),
144 UnpackedKind::Type(ty) => ty.fold_with(folder).into(),
145 UnpackedKind::Const(ct) => ct.fold_with(folder).into(),
149 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
150 match self.unpack() {
151 UnpackedKind::Lifetime(lt) => lt.visit_with(visitor),
152 UnpackedKind::Type(ty) => ty.visit_with(visitor),
153 UnpackedKind::Const(ct) => ct.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 InternalSubsts<'tcx> = List<Kind<'tcx>>;
173 pub type SubstsRef<'tcx> = &'tcx InternalSubsts<'tcx>;
175 impl<'a, 'gcx, 'tcx> InternalSubsts<'tcx> {
176 /// Creates a `InternalSubsts` that maps each generic parameter to itself.
177 pub fn identity_for_item(tcx: TyCtxt<'a, 'gcx, 'tcx>, def_id: DefId)
179 Self::for_item(tcx, def_id, |param, _| {
180 tcx.mk_param_from_def(param)
184 /// Creates a `InternalSubsts` that maps each generic parameter to a higher-ranked
185 /// var bound at index `0`. For types, we use a `BoundVar` index equal to
186 /// the type parameter index. For regions, we use the `BoundRegion::BrNamed`
187 /// variant (which has a `DefId`).
188 pub fn bound_vars_for_item(
189 tcx: TyCtxt<'a, 'gcx, 'tcx>,
191 ) -> SubstsRef<'tcx> {
192 Self::for_item(tcx, def_id, |param, _| {
194 ty::GenericParamDefKind::Type { .. } => {
196 ty::Bound(ty::INNERMOST, ty::BoundTy {
197 var: ty::BoundVar::from(param.index),
198 kind: ty::BoundTyKind::Param(param.name),
203 ty::GenericParamDefKind::Lifetime => {
204 tcx.mk_region(ty::RegionKind::ReLateBound(
206 ty::BoundRegion::BrNamed(param.def_id, param.name)
210 ty::GenericParamDefKind::Const => {
211 tcx.mk_const(ty::Const {
212 val: ConstValue::Infer(
213 InferConst::Canonical(ty::INNERMOST, ty::BoundVar::from(param.index))
215 ty: tcx.type_of(def_id),
222 /// Creates a `InternalSubsts` for generic parameter definitions,
223 /// by calling closures to obtain each kind.
224 /// The closures get to observe the `InternalSubsts` as they're
225 /// being built, which can be used to correctly
226 /// substitute defaults of generic parameters.
227 pub fn for_item<F>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
231 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
233 let defs = tcx.generics_of(def_id);
234 let count = defs.count();
235 let mut substs = SmallVec::with_capacity(count);
236 Self::fill_item(&mut substs, tcx, defs, &mut mk_kind);
237 tcx.intern_substs(&substs)
240 pub fn extend_to<F>(&self,
241 tcx: TyCtxt<'a, 'gcx, 'tcx>,
245 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
247 Self::for_item(tcx, def_id, |param, substs| {
248 self.get(param.index as usize)
250 .unwrap_or_else(|| mk_kind(param, substs))
254 fn fill_item<F>(substs: &mut SmallVec<[Kind<'tcx>; 8]>,
255 tcx: TyCtxt<'a, 'gcx, 'tcx>,
258 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
260 if let Some(def_id) = defs.parent {
261 let parent_defs = tcx.generics_of(def_id);
262 Self::fill_item(substs, tcx, parent_defs, mk_kind);
264 Self::fill_single(substs, defs, mk_kind)
267 fn fill_single<F>(substs: &mut SmallVec<[Kind<'tcx>; 8]>,
270 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
272 substs.reserve(defs.params.len());
273 for param in &defs.params {
274 let kind = mk_kind(param, substs);
275 assert_eq!(param.index as usize, substs.len());
280 pub fn is_noop(&self) -> bool {
285 pub fn types(&'a self) -> impl DoubleEndedIterator<Item = Ty<'tcx>> + 'a {
286 self.iter().filter_map(|k| {
287 if let UnpackedKind::Type(ty) = k.unpack() {
296 pub fn regions(&'a self) -> impl DoubleEndedIterator<Item = ty::Region<'tcx>> + 'a {
297 self.iter().filter_map(|k| {
298 if let UnpackedKind::Lifetime(lt) = k.unpack() {
307 pub fn consts(&'a self) -> impl DoubleEndedIterator<Item = &'tcx ty::Const<'tcx>> + 'a {
308 self.iter().filter_map(|k| {
309 if let UnpackedKind::Const(ct) = k.unpack() {
318 pub fn non_erasable_generics(
320 ) -> impl DoubleEndedIterator<Item = UnpackedKind<'tcx>> + 'a {
321 self.iter().filter_map(|k| {
323 UnpackedKind::Lifetime(_) => None,
324 generic => Some(generic),
330 pub fn type_at(&self, i: usize) -> Ty<'tcx> {
331 if let UnpackedKind::Type(ty) = self[i].unpack() {
334 bug!("expected type for param #{} in {:?}", i, self);
339 pub fn region_at(&self, i: usize) -> ty::Region<'tcx> {
340 if let UnpackedKind::Lifetime(lt) = self[i].unpack() {
343 bug!("expected region for param #{} in {:?}", i, self);
348 pub fn const_at(&self, i: usize) -> &'tcx ty::Const<'tcx> {
349 if let UnpackedKind::Const(ct) = self[i].unpack() {
352 bug!("expected const for param #{} in {:?}", i, self);
357 pub fn type_for_def(&self, def: &ty::GenericParamDef) -> Kind<'tcx> {
358 self.type_at(def.index as usize).into()
361 /// Transform from substitutions for a child of `source_ancestor`
362 /// (e.g., a trait or impl) to substitutions for the same child
363 /// in a different item, with `target_substs` as the base for
364 /// the target impl/trait, with the source child-specific
365 /// parameters (e.g., method parameters) on top of that base.
366 pub fn rebase_onto(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
367 source_ancestor: DefId,
368 target_substs: SubstsRef<'tcx>)
370 let defs = tcx.generics_of(source_ancestor);
371 tcx.mk_substs(target_substs.iter().chain(&self[defs.params.len()..]).cloned())
374 pub fn truncate_to(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, generics: &ty::Generics)
376 tcx.mk_substs(self.iter().take(generics.count()).cloned())
380 impl<'tcx> TypeFoldable<'tcx> for SubstsRef<'tcx> {
381 fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
382 let params: SmallVec<[_; 8]> = self.iter().map(|k| k.fold_with(folder)).collect();
384 // If folding doesn't change the substs, it's faster to avoid
385 // calling `mk_substs` and instead reuse the existing substs.
386 if params[..] == self[..] {
389 folder.tcx().intern_substs(¶ms)
393 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
394 self.iter().any(|t| t.visit_with(visitor))
398 impl<'tcx> serialize::UseSpecializedDecodable for SubstsRef<'tcx> {}
400 ///////////////////////////////////////////////////////////////////////////
401 // Public trait `Subst`
403 // Just call `foo.subst(tcx, substs)` to perform a substitution across
404 // `foo`. Or use `foo.subst_spanned(tcx, substs, Some(span))` when
405 // there is more information available (for better errors).
407 pub trait Subst<'tcx>: Sized {
408 fn subst<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
409 substs: &[Kind<'tcx>]) -> Self {
410 self.subst_spanned(tcx, substs, None)
413 fn subst_spanned<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
414 substs: &[Kind<'tcx>],
419 impl<'tcx, T:TypeFoldable<'tcx>> Subst<'tcx> for T {
420 fn subst_spanned<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
421 substs: &[Kind<'tcx>],
425 let mut folder = SubstFolder { tcx,
431 (*self).fold_with(&mut folder)
435 ///////////////////////////////////////////////////////////////////////////
436 // The actual substitution engine itself is a type folder.
438 struct SubstFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
439 tcx: TyCtxt<'a, 'gcx, 'tcx>,
440 substs: &'a [Kind<'tcx>],
442 /// The location for which the substitution is performed, if available.
445 /// The root type that is being substituted, if available.
446 root_ty: Option<Ty<'tcx>>,
448 /// Depth of type stack
449 ty_stack_depth: usize,
451 /// Number of region binders we have passed through while doing the substitution
455 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for SubstFolder<'a, 'gcx, 'tcx> {
456 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
458 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
459 self.binders_passed += 1;
460 let t = t.super_fold_with(self);
461 self.binders_passed -= 1;
465 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
466 // Note: This routine only handles regions that are bound on
467 // type declarations and other outer declarations, not those
468 // bound in *fn types*. Region substitution of the bound
469 // regions that appear in a function signature is done using
470 // the specialized routine `ty::replace_late_regions()`.
472 ty::ReEarlyBound(data) => {
473 let r = self.substs.get(data.index as usize).map(|k| k.unpack());
475 Some(UnpackedKind::Lifetime(lt)) => {
476 self.shift_region_through_binders(lt)
479 let span = self.span.unwrap_or(DUMMY_SP);
482 "Region parameter out of range \
483 when substituting in region {} (root type={:?}) \
495 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
496 if !t.needs_subst() {
500 // track the root type we were asked to substitute
501 let depth = self.ty_stack_depth;
503 self.root_ty = Some(t);
505 self.ty_stack_depth += 1;
507 let t1 = match t.sty {
509 self.ty_for_param(p, t)
512 t.super_fold_with(self)
516 assert_eq!(depth + 1, self.ty_stack_depth);
517 self.ty_stack_depth -= 1;
525 fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
526 if !c.needs_subst() {
530 if let ConstValue::Param(p) = c.val {
531 self.const_for_param(p, c)
533 c.super_fold_with(self)
538 impl<'a, 'gcx, 'tcx> SubstFolder<'a, 'gcx, 'tcx> {
539 fn ty_for_param(&self, p: ty::ParamTy, source_ty: Ty<'tcx>) -> Ty<'tcx> {
540 // Look up the type in the substitutions. It really should be in there.
541 let opt_ty = self.substs.get(p.idx as usize).map(|k| k.unpack());
542 let ty = match opt_ty {
543 Some(UnpackedKind::Type(ty)) => ty,
545 let span = self.span.unwrap_or(DUMMY_SP);
548 "Type parameter `{:?}` ({:?}/{}) out of range \
549 when substituting (root type={:?}) substs={:?}",
558 self.shift_vars_through_binders(ty)
564 source_cn: &'tcx ty::Const<'tcx>
565 ) -> &'tcx ty::Const<'tcx> {
566 // Look up the const in the substitutions. It really should be in there.
567 let opt_cn = self.substs.get(p.index as usize).map(|k| k.unpack());
568 let cn = match opt_cn {
569 Some(UnpackedKind::Const(cn)) => cn,
571 let span = self.span.unwrap_or(DUMMY_SP);
574 "Const parameter `{:?}` ({:?}/{}) out of range \
575 when substituting (root type={:?}) substs={:?}",
585 // FIXME(const_generics): shift const through binders
589 /// It is sometimes necessary to adjust the De Bruijn indices during substitution. This occurs
590 /// when we are substituting a type with escaping bound vars into a context where we have
591 /// passed through binders. That's quite a mouthful. Let's see an example:
594 /// type Func<A> = fn(A);
595 /// type MetaFunc = for<'a> fn(Func<&'a int>)
598 /// The type `MetaFunc`, when fully expanded, will be
600 /// for<'a> fn(fn(&'a int))
603 /// | | DebruijnIndex of 2
606 /// Here the `'a` lifetime is bound in the outer function, but appears as an argument of the
607 /// inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip
608 /// over the inner binder (remember that we count De Bruijn indices from 1). However, in the
609 /// definition of `MetaFunc`, the binder is not visible, so the type `&'a int` will have a
610 /// De Bruijn index of 1. It's only during the substitution that we can see we must increase the
611 /// depth by 1 to account for the binder that we passed through.
613 /// As a second example, consider this twist:
616 /// type FuncTuple<A> = (A,fn(A));
617 /// type MetaFuncTuple = for<'a> fn(FuncTuple<&'a int>)
620 /// Here the final type will be:
622 /// for<'a> fn((&'a int, fn(&'a int)))
625 /// DebruijnIndex of 1 |
626 /// DebruijnIndex of 2
628 /// As indicated in the diagram, here the same type `&'a int` is substituted once, but in the
629 /// first case we do not increase the De Bruijn index and in the second case we do. The reason
630 /// is that only in the second case have we passed through a fn binder.
631 fn shift_vars_through_binders(&self, ty: Ty<'tcx>) -> Ty<'tcx> {
632 debug!("shift_vars(ty={:?}, binders_passed={:?}, has_escaping_bound_vars={:?})",
633 ty, self.binders_passed, ty.has_escaping_bound_vars());
635 if self.binders_passed == 0 || !ty.has_escaping_bound_vars() {
639 let result = ty::fold::shift_vars(self.tcx(), &ty, self.binders_passed);
640 debug!("shift_vars: shifted result = {:?}", result);
645 fn shift_region_through_binders(&self, region: ty::Region<'tcx>) -> ty::Region<'tcx> {
646 if self.binders_passed == 0 || !region.has_escaping_bound_vars() {
649 ty::fold::shift_region(self.tcx, region, self.binders_passed)
653 pub type CanonicalUserSubsts<'tcx> = Canonical<'tcx, UserSubsts<'tcx>>;
655 /// Stores the user-given substs to reach some fully qualified path
656 /// (e.g., `<T>::Item` or `<T as Trait>::Item`).
657 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, HashStable)]
658 pub struct UserSubsts<'tcx> {
659 /// The substitutions for the item as given by the user.
660 pub substs: SubstsRef<'tcx>,
662 /// The self type, in the case of a `<T>::Item` path (when applied
663 /// to an inherent impl). See `UserSelfTy` below.
664 pub user_self_ty: Option<UserSelfTy<'tcx>>,
667 BraceStructTypeFoldableImpl! {
668 impl<'tcx> TypeFoldable<'tcx> for UserSubsts<'tcx> {
674 BraceStructLiftImpl! {
675 impl<'a, 'tcx> Lift<'tcx> for UserSubsts<'a> {
676 type Lifted = UserSubsts<'tcx>;
682 /// Specifies the user-given self type. In the case of a path that
683 /// refers to a member in an inherent impl, this self type is
684 /// sometimes needed to constrain the type parameters on the impl. For
685 /// example, in this code:
688 /// struct Foo<T> { }
689 /// impl<A> Foo<A> { fn method() { } }
692 /// when you then have a path like `<Foo<&'static u32>>::method`,
693 /// this struct would carry the `DefId` of the impl along with the
694 /// self type `Foo<u32>`. Then we can instantiate the parameters of
695 /// the impl (with the substs from `UserSubsts`) and apply those to
696 /// the self type, giving `Foo<?A>`. Finally, we unify that with
697 /// the self type here, which contains `?A` to be `&'static u32`
698 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, HashStable)]
699 pub struct UserSelfTy<'tcx> {
700 pub impl_def_id: DefId,
701 pub self_ty: Ty<'tcx>,
704 BraceStructTypeFoldableImpl! {
705 impl<'tcx> TypeFoldable<'tcx> for UserSelfTy<'tcx> {
711 BraceStructLiftImpl! {
712 impl<'a, 'tcx> Lift<'tcx> for UserSelfTy<'a> {
713 type Lifted = UserSelfTy<'tcx>;