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 rustc_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(&self, tcx: TyCtxt<'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<F: TypeFolder<'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, 'tcx> InternalSubsts<'tcx> {
186 /// Creates a `InternalSubsts` that maps each generic parameter to itself.
187 pub fn identity_for_item(tcx: TyCtxt<'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(tcx: TyCtxt<'tcx>, def_id: DefId) -> SubstsRef<'tcx> {
198 Self::for_item(tcx, def_id, |param, _| {
200 ty::GenericParamDefKind::Type { .. } => {
202 ty::Bound(ty::INNERMOST, ty::BoundTy {
203 var: ty::BoundVar::from(param.index),
204 kind: ty::BoundTyKind::Param(param.name),
209 ty::GenericParamDefKind::Lifetime => {
210 tcx.mk_region(ty::RegionKind::ReLateBound(
212 ty::BoundRegion::BrNamed(param.def_id, param.name)
216 ty::GenericParamDefKind::Const => {
217 tcx.mk_const(ty::Const {
218 val: ConstValue::Infer(
219 InferConst::Canonical(ty::INNERMOST, ty::BoundVar::from(param.index))
221 ty: tcx.type_of(def_id),
228 /// Creates a `InternalSubsts` for generic parameter definitions,
229 /// by calling closures to obtain each kind.
230 /// The closures get to observe the `InternalSubsts` as they're
231 /// being built, which can be used to correctly
232 /// substitute defaults of generic parameters.
233 pub fn for_item<F>(tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx>
235 F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>,
237 let defs = tcx.generics_of(def_id);
238 let count = defs.count();
239 let mut substs = SmallVec::with_capacity(count);
240 Self::fill_item(&mut substs, tcx, defs, &mut mk_kind);
241 tcx.intern_substs(&substs)
244 pub fn extend_to<F>(&self, tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx>
246 F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>,
248 Self::for_item(tcx, def_id, |param, substs| {
249 self.get(param.index as usize)
251 .unwrap_or_else(|| mk_kind(param, substs))
256 substs: &mut SmallVec<[Kind<'tcx>; 8]>,
261 F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>,
263 if let Some(def_id) = defs.parent {
264 let parent_defs = tcx.generics_of(def_id);
265 Self::fill_item(substs, tcx, parent_defs, mk_kind);
267 Self::fill_single(substs, defs, mk_kind)
270 fn fill_single<F>(substs: &mut SmallVec<[Kind<'tcx>; 8]>,
273 where F: FnMut(&ty::GenericParamDef, &[Kind<'tcx>]) -> Kind<'tcx>
275 substs.reserve(defs.params.len());
276 for param in &defs.params {
277 let kind = mk_kind(param, substs);
278 assert_eq!(param.index as usize, substs.len());
283 pub fn is_noop(&self) -> bool {
288 pub fn types(&'a self) -> impl DoubleEndedIterator<Item = Ty<'tcx>> + 'a {
289 self.iter().filter_map(|k| {
290 if let UnpackedKind::Type(ty) = k.unpack() {
299 pub fn regions(&'a self) -> impl DoubleEndedIterator<Item = ty::Region<'tcx>> + 'a {
300 self.iter().filter_map(|k| {
301 if let UnpackedKind::Lifetime(lt) = k.unpack() {
310 pub fn consts(&'a self) -> impl DoubleEndedIterator<Item = &'tcx ty::Const<'tcx>> + 'a {
311 self.iter().filter_map(|k| {
312 if let UnpackedKind::Const(ct) = k.unpack() {
321 pub fn non_erasable_generics(
323 ) -> impl DoubleEndedIterator<Item = UnpackedKind<'tcx>> + 'a {
324 self.iter().filter_map(|k| {
326 UnpackedKind::Lifetime(_) => None,
327 generic => Some(generic),
333 pub fn type_at(&self, i: usize) -> Ty<'tcx> {
334 if let UnpackedKind::Type(ty) = self[i].unpack() {
337 bug!("expected type for param #{} in {:?}", i, self);
342 pub fn region_at(&self, i: usize) -> ty::Region<'tcx> {
343 if let UnpackedKind::Lifetime(lt) = self[i].unpack() {
346 bug!("expected region for param #{} in {:?}", i, self);
351 pub fn const_at(&self, i: usize) -> &'tcx ty::Const<'tcx> {
352 if let UnpackedKind::Const(ct) = self[i].unpack() {
355 bug!("expected const for param #{} in {:?}", i, self);
360 pub fn type_for_def(&self, def: &ty::GenericParamDef) -> Kind<'tcx> {
361 self.type_at(def.index as usize).into()
364 /// Transform from substitutions for a child of `source_ancestor`
365 /// (e.g., a trait or impl) to substitutions for the same child
366 /// in a different item, with `target_substs` as the base for
367 /// the target impl/trait, with the source child-specific
368 /// parameters (e.g., method parameters) on top of that base.
372 source_ancestor: DefId,
373 target_substs: SubstsRef<'tcx>,
374 ) -> SubstsRef<'tcx> {
375 let defs = tcx.generics_of(source_ancestor);
376 tcx.mk_substs(target_substs.iter().chain(&self[defs.params.len()..]).cloned())
379 pub fn truncate_to(&self, tcx: TyCtxt<'tcx>, generics: &ty::Generics) -> SubstsRef<'tcx> {
380 tcx.mk_substs(self.iter().take(generics.count()).cloned())
384 impl<'tcx> TypeFoldable<'tcx> for SubstsRef<'tcx> {
385 fn super_fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self {
386 let params: SmallVec<[_; 8]> = self.iter().map(|k| k.fold_with(folder)).collect();
388 // If folding doesn't change the substs, it's faster to avoid
389 // calling `mk_substs` and instead reuse the existing substs.
390 if params[..] == self[..] {
393 folder.tcx().intern_substs(¶ms)
397 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
398 self.iter().any(|t| t.visit_with(visitor))
402 impl<'tcx> rustc_serialize::UseSpecializedDecodable for SubstsRef<'tcx> {}
404 ///////////////////////////////////////////////////////////////////////////
405 // Public trait `Subst`
407 // Just call `foo.subst(tcx, substs)` to perform a substitution across
408 // `foo`. Or use `foo.subst_spanned(tcx, substs, Some(span))` when
409 // there is more information available (for better errors).
411 pub trait Subst<'tcx>: Sized {
412 fn subst(&self, tcx: TyCtxt<'tcx>, substs: &[Kind<'tcx>]) -> Self {
413 self.subst_spanned(tcx, substs, None)
416 fn subst_spanned(&self, tcx: TyCtxt<'tcx>, substs: &[Kind<'tcx>], span: Option<Span>) -> Self;
419 impl<'tcx, T: TypeFoldable<'tcx>> Subst<'tcx> for T {
420 fn subst_spanned(&self, tcx: TyCtxt<'tcx>, substs: &[Kind<'tcx>], span: Option<Span>) -> T {
421 let mut folder = SubstFolder { tcx,
427 (*self).fold_with(&mut folder)
431 ///////////////////////////////////////////////////////////////////////////
432 // The actual substitution engine itself is a type folder.
434 struct SubstFolder<'a, 'tcx> {
436 substs: &'a [Kind<'tcx>],
438 /// The location for which the substitution is performed, if available.
441 /// The root type that is being substituted, if available.
442 root_ty: Option<Ty<'tcx>>,
444 /// Depth of type stack
445 ty_stack_depth: usize,
447 /// Number of region binders we have passed through while doing the substitution
451 impl<'a, 'tcx> TypeFolder<'tcx> for SubstFolder<'a, 'tcx> {
452 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> { self.tcx }
454 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
455 self.binders_passed += 1;
456 let t = t.super_fold_with(self);
457 self.binders_passed -= 1;
461 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
462 // Note: This routine only handles regions that are bound on
463 // type declarations and other outer declarations, not those
464 // bound in *fn types*. Region substitution of the bound
465 // regions that appear in a function signature is done using
466 // the specialized routine `ty::replace_late_regions()`.
468 ty::ReEarlyBound(data) => {
469 let rk = self.substs.get(data.index as usize).map(|k| k.unpack());
471 Some(UnpackedKind::Lifetime(lt)) => {
472 self.shift_region_through_binders(lt)
475 let span = self.span.unwrap_or(DUMMY_SP);
477 "Region parameter out of range \
478 when substituting in region {} (root type={:?}) \
483 self.tcx.sess.delay_span_bug(span, &msg);
492 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
493 if !t.needs_subst() {
497 // track the root type we were asked to substitute
498 let depth = self.ty_stack_depth;
500 self.root_ty = Some(t);
502 self.ty_stack_depth += 1;
504 let t1 = match t.sty {
506 self.ty_for_param(p, t)
509 t.super_fold_with(self)
513 assert_eq!(depth + 1, self.ty_stack_depth);
514 self.ty_stack_depth -= 1;
522 fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
523 if !c.needs_subst() {
527 if let ConstValue::Param(p) = c.val {
528 self.const_for_param(p, c)
530 c.super_fold_with(self)
535 impl<'a, 'tcx> SubstFolder<'a, 'tcx> {
536 fn ty_for_param(&self, p: ty::ParamTy, source_ty: Ty<'tcx>) -> Ty<'tcx> {
537 // Look up the type in the substitutions. It really should be in there.
538 let opt_ty = self.substs.get(p.index as usize).map(|k| k.unpack());
539 let ty = match opt_ty {
540 Some(UnpackedKind::Type(ty)) => ty,
542 let span = self.span.unwrap_or(DUMMY_SP);
545 "expected type for `{:?}` ({:?}/{}) but found {:?} \
546 when substituting (root type={:?}) substs={:?}",
556 let span = self.span.unwrap_or(DUMMY_SP);
559 "type parameter `{:?}` ({:?}/{}) out of range \
560 when substituting (root type={:?}) substs={:?}",
570 self.shift_vars_through_binders(ty)
576 source_ct: &'tcx ty::Const<'tcx>
577 ) -> &'tcx ty::Const<'tcx> {
578 // Look up the const in the substitutions. It really should be in there.
579 let opt_ct = self.substs.get(p.index as usize).map(|k| k.unpack());
580 let ct = match opt_ct {
581 Some(UnpackedKind::Const(ct)) => ct,
583 let span = self.span.unwrap_or(DUMMY_SP);
586 "expected const for `{:?}` ({:?}/{}) but found {:?} \
587 when substituting substs={:?}",
596 let span = self.span.unwrap_or(DUMMY_SP);
599 "const parameter `{:?}` ({:?}/{}) out of range \
600 when substituting substs={:?}",
609 self.shift_vars_through_binders(ct)
612 /// It is sometimes necessary to adjust the De Bruijn indices during substitution. This occurs
613 /// when we are substituting a type with escaping bound vars into a context where we have
614 /// passed through binders. That's quite a mouthful. Let's see an example:
617 /// type Func<A> = fn(A);
618 /// type MetaFunc = for<'a> fn(Func<&'a int>)
621 /// The type `MetaFunc`, when fully expanded, will be
623 /// for<'a> fn(fn(&'a int))
626 /// | | DebruijnIndex of 2
629 /// Here the `'a` lifetime is bound in the outer function, but appears as an argument of the
630 /// inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip
631 /// over the inner binder (remember that we count De Bruijn indices from 1). However, in the
632 /// definition of `MetaFunc`, the binder is not visible, so the type `&'a int` will have a
633 /// De Bruijn index of 1. It's only during the substitution that we can see we must increase the
634 /// depth by 1 to account for the binder that we passed through.
636 /// As a second example, consider this twist:
639 /// type FuncTuple<A> = (A,fn(A));
640 /// type MetaFuncTuple = for<'a> fn(FuncTuple<&'a int>)
643 /// Here the final type will be:
645 /// for<'a> fn((&'a int, fn(&'a int)))
648 /// DebruijnIndex of 1 |
649 /// DebruijnIndex of 2
651 /// As indicated in the diagram, here the same type `&'a int` is substituted once, but in the
652 /// first case we do not increase the De Bruijn index and in the second case we do. The reason
653 /// is that only in the second case have we passed through a fn binder.
654 fn shift_vars_through_binders<T: TypeFoldable<'tcx>>(&self, val: T) -> T {
655 debug!("shift_vars(val={:?}, binders_passed={:?}, has_escaping_bound_vars={:?})",
656 val, self.binders_passed, val.has_escaping_bound_vars());
658 if self.binders_passed == 0 || !val.has_escaping_bound_vars() {
662 let result = ty::fold::shift_vars(self.tcx(), &val, self.binders_passed);
663 debug!("shift_vars: shifted result = {:?}", result);
668 fn shift_region_through_binders(&self, region: ty::Region<'tcx>) -> ty::Region<'tcx> {
669 if self.binders_passed == 0 || !region.has_escaping_bound_vars() {
672 ty::fold::shift_region(self.tcx, region, self.binders_passed)
676 pub type CanonicalUserSubsts<'tcx> = Canonical<'tcx, UserSubsts<'tcx>>;
678 /// Stores the user-given substs to reach some fully qualified path
679 /// (e.g., `<T>::Item` or `<T as Trait>::Item`).
680 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, HashStable)]
681 pub struct UserSubsts<'tcx> {
682 /// The substitutions for the item as given by the user.
683 pub substs: SubstsRef<'tcx>,
685 /// The self type, in the case of a `<T>::Item` path (when applied
686 /// to an inherent impl). See `UserSelfTy` below.
687 pub user_self_ty: Option<UserSelfTy<'tcx>>,
690 BraceStructTypeFoldableImpl! {
691 impl<'tcx> TypeFoldable<'tcx> for UserSubsts<'tcx> {
697 BraceStructLiftImpl! {
698 impl<'a, 'tcx> Lift<'tcx> for UserSubsts<'a> {
699 type Lifted = UserSubsts<'tcx>;
705 /// Specifies the user-given self type. In the case of a path that
706 /// refers to a member in an inherent impl, this self type is
707 /// sometimes needed to constrain the type parameters on the impl. For
708 /// example, in this code:
711 /// struct Foo<T> { }
712 /// impl<A> Foo<A> { fn method() { } }
715 /// when you then have a path like `<Foo<&'static u32>>::method`,
716 /// this struct would carry the `DefId` of the impl along with the
717 /// self type `Foo<u32>`. Then we can instantiate the parameters of
718 /// the impl (with the substs from `UserSubsts`) and apply those to
719 /// the self type, giving `Foo<?A>`. Finally, we unify that with
720 /// the self type here, which contains `?A` to be `&'static u32`
721 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, HashStable)]
722 pub struct UserSelfTy<'tcx> {
723 pub impl_def_id: DefId,
724 pub self_ty: Ty<'tcx>,
727 BraceStructTypeFoldableImpl! {
728 impl<'tcx> TypeFoldable<'tcx> for UserSelfTy<'tcx> {
734 BraceStructLiftImpl! {
735 impl<'a, 'tcx> Lift<'tcx> for UserSelfTy<'a> {
736 type Lifted = UserSelfTy<'tcx>;