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()
127 /// Unpack the `Kind` as a type when it is known certainly to be a type.
128 /// This is true in cases where `Substs` is used in places where the kinds are known
129 /// to be limited (e.g. in tuples, where the only parameters are type parameters).
130 pub fn expect_ty(self) -> Ty<'tcx> {
131 match self.unpack() {
132 UnpackedKind::Type(ty) => ty,
133 _ => bug!("expected a type, but found another kind"),
138 impl<'a, 'tcx> Lift<'tcx> for Kind<'a> {
139 type Lifted = Kind<'tcx>;
141 fn lift_to_tcx<'cx, 'gcx>(&self, tcx: TyCtxt<'cx, 'gcx, 'tcx>) -> Option<Self::Lifted> {
142 match self.unpack() {
143 UnpackedKind::Lifetime(lt) => tcx.lift(<).map(|lt| lt.into()),
144 UnpackedKind::Type(ty) => tcx.lift(&ty).map(|ty| ty.into()),
145 UnpackedKind::Const(ct) => tcx.lift(&ct).map(|ct| ct.into()),
150 impl<'tcx> TypeFoldable<'tcx> for Kind<'tcx> {
151 fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
152 match self.unpack() {
153 UnpackedKind::Lifetime(lt) => lt.fold_with(folder).into(),
154 UnpackedKind::Type(ty) => ty.fold_with(folder).into(),
155 UnpackedKind::Const(ct) => ct.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),
163 UnpackedKind::Const(ct) => ct.visit_with(visitor),
168 impl<'tcx> Encodable for Kind<'tcx> {
169 fn encode<E: Encoder>(&self, e: &mut E) -> Result<(), E::Error> {
170 self.unpack().encode(e)
174 impl<'tcx> Decodable for Kind<'tcx> {
175 fn decode<D: Decoder>(d: &mut D) -> Result<Kind<'tcx>, D::Error> {
176 Ok(UnpackedKind::decode(d)?.pack())
180 /// A substitution mapping generic parameters to new values.
181 pub type InternalSubsts<'tcx> = List<Kind<'tcx>>;
183 pub type SubstsRef<'tcx> = &'tcx InternalSubsts<'tcx>;
185 impl<'a, 'gcx, 'tcx> InternalSubsts<'tcx> {
186 /// Creates a `InternalSubsts` that maps each generic parameter to itself.
187 pub fn identity_for_item(tcx: TyCtxt<'a, 'gcx, 'tcx>, def_id: DefId) -> SubstsRef<'tcx> {
188 Self::for_item(tcx, def_id, |param, _| {
189 tcx.mk_param_from_def(param)
193 /// Creates a `InternalSubsts` that maps each generic parameter to a higher-ranked
194 /// var bound at index `0`. For types, we use a `BoundVar` index equal to
195 /// the type parameter index. For regions, we use the `BoundRegion::BrNamed`
196 /// variant (which has a `DefId`).
197 pub fn bound_vars_for_item(
198 tcx: TyCtxt<'a, 'gcx, 'tcx>,
200 ) -> SubstsRef<'tcx> {
201 Self::for_item(tcx, def_id, |param, _| {
203 ty::GenericParamDefKind::Type { .. } => {
205 ty::Bound(ty::INNERMOST, ty::BoundTy {
206 var: ty::BoundVar::from(param.index),
207 kind: ty::BoundTyKind::Param(param.name),
212 ty::GenericParamDefKind::Lifetime => {
213 tcx.mk_region(ty::RegionKind::ReLateBound(
215 ty::BoundRegion::BrNamed(param.def_id, param.name)
219 ty::GenericParamDefKind::Const => {
220 tcx.mk_const(ty::Const {
221 val: ConstValue::Infer(
222 InferConst::Canonical(ty::INNERMOST, ty::BoundVar::from(param.index))
224 ty: tcx.type_of(def_id),
231 /// Creates a `InternalSubsts` for generic parameter definitions,
232 /// by calling closures to obtain each kind.
233 /// The closures get to observe the `InternalSubsts` as they're
234 /// being built, which can be used to correctly
235 /// substitute defaults of generic parameters.
236 pub fn for_item<F>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
240 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
242 let defs = tcx.generics_of(def_id);
243 let count = defs.count();
244 let mut substs = SmallVec::with_capacity(count);
245 Self::fill_item(&mut substs, tcx, defs, &mut mk_kind);
246 tcx.intern_substs(&substs)
249 pub fn extend_to<F>(&self,
250 tcx: TyCtxt<'a, 'gcx, 'tcx>,
254 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
256 Self::for_item(tcx, def_id, |param, substs| {
257 self.get(param.index as usize)
259 .unwrap_or_else(|| mk_kind(param, substs))
263 fn fill_item<F>(substs: &mut SmallVec<[Kind<'tcx>; 8]>,
264 tcx: TyCtxt<'a, 'gcx, 'tcx>,
267 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
269 if let Some(def_id) = defs.parent {
270 let parent_defs = tcx.generics_of(def_id);
271 Self::fill_item(substs, tcx, parent_defs, mk_kind);
273 Self::fill_single(substs, defs, mk_kind)
276 fn fill_single<F>(substs: &mut SmallVec<[Kind<'tcx>; 8]>,
279 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
281 substs.reserve(defs.params.len());
282 for param in &defs.params {
283 let kind = mk_kind(param, substs);
284 assert_eq!(param.index as usize, substs.len());
289 pub fn is_noop(&self) -> bool {
294 pub fn types(&'a self) -> impl DoubleEndedIterator<Item = Ty<'tcx>> + 'a {
295 self.iter().filter_map(|k| {
296 if let UnpackedKind::Type(ty) = k.unpack() {
305 pub fn regions(&'a self) -> impl DoubleEndedIterator<Item = ty::Region<'tcx>> + 'a {
306 self.iter().filter_map(|k| {
307 if let UnpackedKind::Lifetime(lt) = k.unpack() {
316 pub fn consts(&'a self) -> impl DoubleEndedIterator<Item = &'tcx ty::Const<'tcx>> + 'a {
317 self.iter().filter_map(|k| {
318 if let UnpackedKind::Const(ct) = k.unpack() {
327 pub fn non_erasable_generics(
329 ) -> impl DoubleEndedIterator<Item = UnpackedKind<'tcx>> + 'a {
330 self.iter().filter_map(|k| {
332 UnpackedKind::Lifetime(_) => None,
333 generic => Some(generic),
339 pub fn type_at(&self, i: usize) -> Ty<'tcx> {
340 if let UnpackedKind::Type(ty) = self[i].unpack() {
343 bug!("expected type for param #{} in {:?}", i, self);
348 pub fn region_at(&self, i: usize) -> ty::Region<'tcx> {
349 if let UnpackedKind::Lifetime(lt) = self[i].unpack() {
352 bug!("expected region for param #{} in {:?}", i, self);
357 pub fn const_at(&self, i: usize) -> &'tcx ty::Const<'tcx> {
358 if let UnpackedKind::Const(ct) = self[i].unpack() {
361 bug!("expected const for param #{} in {:?}", i, self);
366 pub fn type_for_def(&self, def: &ty::GenericParamDef) -> Kind<'tcx> {
367 self.type_at(def.index as usize).into()
370 /// Transform from substitutions for a child of `source_ancestor`
371 /// (e.g., a trait or impl) to substitutions for the same child
372 /// in a different item, with `target_substs` as the base for
373 /// the target impl/trait, with the source child-specific
374 /// parameters (e.g., method parameters) on top of that base.
375 pub fn rebase_onto(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
376 source_ancestor: DefId,
377 target_substs: SubstsRef<'tcx>)
379 let defs = tcx.generics_of(source_ancestor);
380 tcx.mk_substs(target_substs.iter().chain(&self[defs.params.len()..]).cloned())
383 pub fn truncate_to(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, generics: &ty::Generics)
385 tcx.mk_substs(self.iter().take(generics.count()).cloned())
389 impl<'tcx> TypeFoldable<'tcx> for SubstsRef<'tcx> {
390 fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
391 let params: SmallVec<[_; 8]> = self.iter().map(|k| k.fold_with(folder)).collect();
393 // If folding doesn't change the substs, it's faster to avoid
394 // calling `mk_substs` and instead reuse the existing substs.
395 if params[..] == self[..] {
398 folder.tcx().intern_substs(¶ms)
402 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
403 self.iter().any(|t| t.visit_with(visitor))
407 impl<'tcx> serialize::UseSpecializedDecodable for SubstsRef<'tcx> {}
409 ///////////////////////////////////////////////////////////////////////////
410 // Public trait `Subst`
412 // Just call `foo.subst(tcx, substs)` to perform a substitution across
413 // `foo`. Or use `foo.subst_spanned(tcx, substs, Some(span))` when
414 // there is more information available (for better errors).
416 pub trait Subst<'tcx>: Sized {
417 fn subst<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
418 substs: &[Kind<'tcx>]) -> Self {
419 self.subst_spanned(tcx, substs, None)
422 fn subst_spanned<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
423 substs: &[Kind<'tcx>],
428 impl<'tcx, T:TypeFoldable<'tcx>> Subst<'tcx> for T {
429 fn subst_spanned<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
430 substs: &[Kind<'tcx>],
434 let mut folder = SubstFolder { tcx,
440 (*self).fold_with(&mut folder)
444 ///////////////////////////////////////////////////////////////////////////
445 // The actual substitution engine itself is a type folder.
447 struct SubstFolder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
448 tcx: TyCtxt<'a, 'gcx, 'tcx>,
449 substs: &'a [Kind<'tcx>],
451 /// The location for which the substitution is performed, if available.
454 /// The root type that is being substituted, if available.
455 root_ty: Option<Ty<'tcx>>,
457 /// Depth of type stack
458 ty_stack_depth: usize,
460 /// Number of region binders we have passed through while doing the substitution
464 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for SubstFolder<'a, 'gcx, 'tcx> {
465 fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
467 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
468 self.binders_passed += 1;
469 let t = t.super_fold_with(self);
470 self.binders_passed -= 1;
474 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
475 // Note: This routine only handles regions that are bound on
476 // type declarations and other outer declarations, not those
477 // bound in *fn types*. Region substitution of the bound
478 // regions that appear in a function signature is done using
479 // the specialized routine `ty::replace_late_regions()`.
481 ty::ReEarlyBound(data) => {
482 let rk = self.substs.get(data.index as usize).map(|k| k.unpack());
484 Some(UnpackedKind::Lifetime(lt)) => {
485 self.shift_region_through_binders(lt)
488 let span = self.span.unwrap_or(DUMMY_SP);
490 "Region parameter out of range \
491 when substituting in region {} (root type={:?}) \
496 self.tcx.sess.delay_span_bug(span, &msg);
505 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
506 if !t.needs_subst() {
510 // track the root type we were asked to substitute
511 let depth = self.ty_stack_depth;
513 self.root_ty = Some(t);
515 self.ty_stack_depth += 1;
517 let t1 = match t.sty {
519 self.ty_for_param(p, t)
522 t.super_fold_with(self)
526 assert_eq!(depth + 1, self.ty_stack_depth);
527 self.ty_stack_depth -= 1;
535 fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
536 if !c.needs_subst() {
540 if let ConstValue::Param(p) = c.val {
541 self.const_for_param(p, c)
543 c.super_fold_with(self)
548 impl<'a, 'gcx, 'tcx> SubstFolder<'a, 'gcx, 'tcx> {
549 fn ty_for_param(&self, p: ty::ParamTy, source_ty: Ty<'tcx>) -> Ty<'tcx> {
550 // Look up the type in the substitutions. It really should be in there.
551 let opt_ty = self.substs.get(p.index as usize).map(|k| k.unpack());
552 let ty = match opt_ty {
553 Some(UnpackedKind::Type(ty)) => ty,
555 let span = self.span.unwrap_or(DUMMY_SP);
558 "expected type for `{:?}` ({:?}/{}) but found {:?} \
559 when substituting (root type={:?}) substs={:?}",
569 let span = self.span.unwrap_or(DUMMY_SP);
572 "type parameter `{:?}` ({:?}/{}) out of range \
573 when substituting (root type={:?}) substs={:?}",
583 self.shift_vars_through_binders(ty)
589 source_ct: &'tcx ty::Const<'tcx>
590 ) -> &'tcx ty::Const<'tcx> {
591 // Look up the const in the substitutions. It really should be in there.
592 let opt_ct = self.substs.get(p.index as usize).map(|k| k.unpack());
593 let ct = match opt_ct {
594 Some(UnpackedKind::Const(ct)) => ct,
596 let span = self.span.unwrap_or(DUMMY_SP);
599 "expected const for `{:?}` ({:?}/{}) but found {:?} \
600 when substituting substs={:?}",
609 let span = self.span.unwrap_or(DUMMY_SP);
612 "const parameter `{:?}` ({:?}/{}) out of range \
613 when substituting substs={:?}",
622 self.shift_vars_through_binders(ct)
625 /// It is sometimes necessary to adjust the De Bruijn indices during substitution. This occurs
626 /// when we are substituting a type with escaping bound vars into a context where we have
627 /// passed through binders. That's quite a mouthful. Let's see an example:
630 /// type Func<A> = fn(A);
631 /// type MetaFunc = for<'a> fn(Func<&'a int>)
634 /// The type `MetaFunc`, when fully expanded, will be
636 /// for<'a> fn(fn(&'a int))
639 /// | | DebruijnIndex of 2
642 /// Here the `'a` lifetime is bound in the outer function, but appears as an argument of the
643 /// inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip
644 /// over the inner binder (remember that we count De Bruijn indices from 1). However, in the
645 /// definition of `MetaFunc`, the binder is not visible, so the type `&'a int` will have a
646 /// De Bruijn index of 1. It's only during the substitution that we can see we must increase the
647 /// depth by 1 to account for the binder that we passed through.
649 /// As a second example, consider this twist:
652 /// type FuncTuple<A> = (A,fn(A));
653 /// type MetaFuncTuple = for<'a> fn(FuncTuple<&'a int>)
656 /// Here the final type will be:
658 /// for<'a> fn((&'a int, fn(&'a int)))
661 /// DebruijnIndex of 1 |
662 /// DebruijnIndex of 2
664 /// As indicated in the diagram, here the same type `&'a int` is substituted once, but in the
665 /// first case we do not increase the De Bruijn index and in the second case we do. The reason
666 /// is that only in the second case have we passed through a fn binder.
667 fn shift_vars_through_binders<T: TypeFoldable<'tcx>>(&self, val: T) -> T {
668 debug!("shift_vars(val={:?}, binders_passed={:?}, has_escaping_bound_vars={:?})",
669 val, self.binders_passed, val.has_escaping_bound_vars());
671 if self.binders_passed == 0 || !val.has_escaping_bound_vars() {
675 let result = ty::fold::shift_vars(self.tcx(), &val, self.binders_passed);
676 debug!("shift_vars: shifted result = {:?}", result);
681 fn shift_region_through_binders(&self, region: ty::Region<'tcx>) -> ty::Region<'tcx> {
682 if self.binders_passed == 0 || !region.has_escaping_bound_vars() {
685 ty::fold::shift_region(self.tcx, region, self.binders_passed)
689 pub type CanonicalUserSubsts<'tcx> = Canonical<'tcx, UserSubsts<'tcx>>;
691 /// Stores the user-given substs to reach some fully qualified path
692 /// (e.g., `<T>::Item` or `<T as Trait>::Item`).
693 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, HashStable)]
694 pub struct UserSubsts<'tcx> {
695 /// The substitutions for the item as given by the user.
696 pub substs: SubstsRef<'tcx>,
698 /// The self type, in the case of a `<T>::Item` path (when applied
699 /// to an inherent impl). See `UserSelfTy` below.
700 pub user_self_ty: Option<UserSelfTy<'tcx>>,
703 BraceStructTypeFoldableImpl! {
704 impl<'tcx> TypeFoldable<'tcx> for UserSubsts<'tcx> {
710 BraceStructLiftImpl! {
711 impl<'a, 'tcx> Lift<'tcx> for UserSubsts<'a> {
712 type Lifted = UserSubsts<'tcx>;
718 /// Specifies the user-given self type. In the case of a path that
719 /// refers to a member in an inherent impl, this self type is
720 /// sometimes needed to constrain the type parameters on the impl. For
721 /// example, in this code:
724 /// struct Foo<T> { }
725 /// impl<A> Foo<A> { fn method() { } }
728 /// when you then have a path like `<Foo<&'static u32>>::method`,
729 /// this struct would carry the `DefId` of the impl along with the
730 /// self type `Foo<u32>`. Then we can instantiate the parameters of
731 /// the impl (with the substs from `UserSubsts`) and apply those to
732 /// the self type, giving `Foo<?A>`. Finally, we unify that with
733 /// the self type here, which contains `?A` to be `&'static u32`
734 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, HashStable)]
735 pub struct UserSelfTy<'tcx> {
736 pub impl_def_id: DefId,
737 pub self_ty: Ty<'tcx>,
740 BraceStructTypeFoldableImpl! {
741 impl<'tcx> TypeFoldable<'tcx> for UserSelfTy<'tcx> {
747 BraceStructLiftImpl! {
748 impl<'a, 'tcx> Lift<'tcx> for UserSelfTy<'a> {
749 type Lifted = UserSelfTy<'tcx>;