3 use crate::hir::def_id::DefId;
4 use crate::infer::canonical::Canonical;
5 use crate::ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
6 use crate::ty::sty::{ClosureSubsts, GeneratorSubsts};
7 use crate::ty::{self, Lift, List, ParamConst, Ty, TyCtxt};
9 use rustc_macros::HashStable;
10 use rustc_serialize::{self, Decodable, Decoder, Encodable, Encoder};
11 use smallvec::SmallVec;
12 use syntax_pos::{Span, DUMMY_SP};
15 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 `GenericArg` 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 GenericArg<'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 GenericArgKind<'tcx> {
39 Lifetime(ty::Region<'tcx>),
41 Const(&'tcx ty::Const<'tcx>),
44 impl<'tcx> GenericArgKind<'tcx> {
45 fn pack(self) -> GenericArg<'tcx> {
46 let (tag, ptr) = match self {
47 GenericArgKind::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 GenericArgKind::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 GenericArgKind::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)
64 GenericArg { ptr: unsafe { NonZeroUsize::new_unchecked(ptr | tag) }, marker: PhantomData }
68 impl fmt::Debug for GenericArg<'tcx> {
69 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
71 GenericArgKind::Lifetime(lt) => lt.fmt(f),
72 GenericArgKind::Type(ty) => ty.fmt(f),
73 GenericArgKind::Const(ct) => ct.fmt(f),
78 impl<'tcx> Ord for GenericArg<'tcx> {
79 fn cmp(&self, other: &GenericArg<'_>) -> Ordering {
80 self.unpack().cmp(&other.unpack())
84 impl<'tcx> PartialOrd for GenericArg<'tcx> {
85 fn partial_cmp(&self, other: &GenericArg<'_>) -> Option<Ordering> {
86 Some(self.cmp(&other))
90 impl<'tcx> From<ty::Region<'tcx>> for GenericArg<'tcx> {
91 fn from(r: ty::Region<'tcx>) -> GenericArg<'tcx> {
92 GenericArgKind::Lifetime(r).pack()
96 impl<'tcx> From<Ty<'tcx>> for GenericArg<'tcx> {
97 fn from(ty: Ty<'tcx>) -> GenericArg<'tcx> {
98 GenericArgKind::Type(ty).pack()
102 impl<'tcx> From<&'tcx ty::Const<'tcx>> for GenericArg<'tcx> {
103 fn from(c: &'tcx ty::Const<'tcx>) -> GenericArg<'tcx> {
104 GenericArgKind::Const(c).pack()
108 impl<'tcx> GenericArg<'tcx> {
110 pub fn unpack(self) -> GenericArgKind<'tcx> {
111 let ptr = self.ptr.get();
113 match ptr & TAG_MASK {
114 REGION_TAG => GenericArgKind::Lifetime(&*((ptr & !TAG_MASK) as *const _)),
115 TYPE_TAG => GenericArgKind::Type(&*((ptr & !TAG_MASK) as *const _)),
116 CONST_TAG => GenericArgKind::Const(&*((ptr & !TAG_MASK) as *const _)),
117 _ => intrinsics::unreachable(),
122 /// Unpack the `GenericArg` as a type when it is known certainly to be a type.
123 /// This is true in cases where `Substs` is used in places where the kinds are known
124 /// to be limited (e.g. in tuples, where the only parameters are type parameters).
125 pub fn expect_ty(self) -> Ty<'tcx> {
126 match self.unpack() {
127 GenericArgKind::Type(ty) => ty,
128 _ => bug!("expected a type, but found another kind"),
133 impl<'a, 'tcx> Lift<'tcx> for GenericArg<'a> {
134 type Lifted = GenericArg<'tcx>;
136 fn lift_to_tcx(&self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
137 match self.unpack() {
138 GenericArgKind::Lifetime(lt) => tcx.lift(<).map(|lt| lt.into()),
139 GenericArgKind::Type(ty) => tcx.lift(&ty).map(|ty| ty.into()),
140 GenericArgKind::Const(ct) => tcx.lift(&ct).map(|ct| ct.into()),
145 impl<'tcx> TypeFoldable<'tcx> for GenericArg<'tcx> {
146 fn super_fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self {
147 match self.unpack() {
148 GenericArgKind::Lifetime(lt) => lt.fold_with(folder).into(),
149 GenericArgKind::Type(ty) => ty.fold_with(folder).into(),
150 GenericArgKind::Const(ct) => ct.fold_with(folder).into(),
154 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
155 match self.unpack() {
156 GenericArgKind::Lifetime(lt) => lt.visit_with(visitor),
157 GenericArgKind::Type(ty) => ty.visit_with(visitor),
158 GenericArgKind::Const(ct) => ct.visit_with(visitor),
163 impl<'tcx> Encodable for GenericArg<'tcx> {
164 fn encode<E: Encoder>(&self, e: &mut E) -> Result<(), E::Error> {
165 self.unpack().encode(e)
169 impl<'tcx> Decodable for GenericArg<'tcx> {
170 fn decode<D: Decoder>(d: &mut D) -> Result<GenericArg<'tcx>, D::Error> {
171 Ok(GenericArgKind::decode(d)?.pack())
175 /// A substitution mapping generic parameters to new values.
176 pub type InternalSubsts<'tcx> = List<GenericArg<'tcx>>;
178 pub type SubstsRef<'tcx> = &'tcx InternalSubsts<'tcx>;
180 impl<'a, 'tcx> InternalSubsts<'tcx> {
181 /// Interpret these substitutions as the substitutions of a closure type.
182 /// Closure substitutions have a particular structure controlled by the
183 /// compiler that encodes information like the signature and closure kind;
184 /// see `ty::ClosureSubsts` struct for more comments.
185 pub fn as_closure(&'a self) -> ClosureSubsts<'a> {
186 ClosureSubsts { substs: self }
189 /// Interpret these substitutions as the substitutions of a generator type.
190 /// Closure substitutions have a particular structure controlled by the
191 /// compiler that encodes information like the signature and generator kind;
192 /// see `ty::GeneratorSubsts` struct for more comments.
193 pub fn as_generator(&'tcx self) -> GeneratorSubsts<'tcx> {
194 GeneratorSubsts { substs: self }
197 /// Creates a `InternalSubsts` that maps each generic parameter to itself.
198 pub fn identity_for_item(tcx: TyCtxt<'tcx>, def_id: DefId) -> SubstsRef<'tcx> {
199 Self::for_item(tcx, def_id, |param, _| tcx.mk_param_from_def(param))
202 /// Creates a `InternalSubsts` that maps each generic parameter to a higher-ranked
203 /// var bound at index `0`. For types, we use a `BoundVar` index equal to
204 /// the type parameter index. For regions, we use the `BoundRegion::BrNamed`
205 /// variant (which has a `DefId`).
206 pub fn bound_vars_for_item(tcx: TyCtxt<'tcx>, def_id: DefId) -> SubstsRef<'tcx> {
207 Self::for_item(tcx, def_id, |param, _| match param.kind {
208 ty::GenericParamDefKind::Type { .. } => tcx
212 var: ty::BoundVar::from(param.index),
213 kind: ty::BoundTyKind::Param(param.name),
218 ty::GenericParamDefKind::Lifetime => tcx
219 .mk_region(ty::RegionKind::ReLateBound(
221 ty::BoundRegion::BrNamed(param.def_id, param.name),
225 ty::GenericParamDefKind::Const => tcx
226 .mk_const(ty::Const {
227 val: ty::ConstKind::Bound(ty::INNERMOST, ty::BoundVar::from(param.index)),
228 ty: tcx.type_of(param.def_id),
234 /// Creates a `InternalSubsts` for generic parameter definitions,
235 /// by calling closures to obtain each kind.
236 /// The closures get to observe the `InternalSubsts` as they're
237 /// being built, which can be used to correctly
238 /// substitute defaults of generic parameters.
239 pub fn for_item<F>(tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx>
241 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
243 let defs = tcx.generics_of(def_id);
244 let count = defs.count();
245 let mut substs = SmallVec::with_capacity(count);
246 Self::fill_item(&mut substs, tcx, defs, &mut mk_kind);
247 tcx.intern_substs(&substs)
250 pub fn extend_to<F>(&self, tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx>
252 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
254 Self::for_item(tcx, def_id, |param, substs| {
255 self.get(param.index as usize).cloned().unwrap_or_else(|| mk_kind(param, substs))
260 substs: &mut SmallVec<[GenericArg<'tcx>; 8]>,
265 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
267 if let Some(def_id) = defs.parent {
268 let parent_defs = tcx.generics_of(def_id);
269 Self::fill_item(substs, tcx, parent_defs, mk_kind);
271 Self::fill_single(substs, defs, mk_kind)
275 substs: &mut SmallVec<[GenericArg<'tcx>; 8]>,
279 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'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 {
296 .filter_map(|k| if let GenericArgKind::Type(ty) = k.unpack() { Some(ty) } else { None })
300 pub fn regions(&'a self) -> impl DoubleEndedIterator<Item = ty::Region<'tcx>> + 'a {
301 self.iter().filter_map(|k| {
302 if let GenericArgKind::Lifetime(lt) = k.unpack() { Some(lt) } else { None }
307 pub fn consts(&'a self) -> impl DoubleEndedIterator<Item = &'tcx ty::Const<'tcx>> + 'a {
308 self.iter().filter_map(|k| {
309 if let GenericArgKind::Const(ct) = k.unpack() { Some(ct) } else { None }
314 pub fn non_erasable_generics(
316 ) -> impl DoubleEndedIterator<Item = GenericArgKind<'tcx>> + 'a {
317 self.iter().filter_map(|k| match k.unpack() {
318 GenericArgKind::Lifetime(_) => None,
319 generic => Some(generic),
324 pub fn type_at(&self, i: usize) -> Ty<'tcx> {
325 if let GenericArgKind::Type(ty) = self[i].unpack() {
328 bug!("expected type for param #{} in {:?}", i, self);
333 pub fn region_at(&self, i: usize) -> ty::Region<'tcx> {
334 if let GenericArgKind::Lifetime(lt) = self[i].unpack() {
337 bug!("expected region for param #{} in {:?}", i, self);
342 pub fn const_at(&self, i: usize) -> &'tcx ty::Const<'tcx> {
343 if let GenericArgKind::Const(ct) = self[i].unpack() {
346 bug!("expected const for param #{} in {:?}", i, self);
351 pub fn type_for_def(&self, def: &ty::GenericParamDef) -> GenericArg<'tcx> {
352 self.type_at(def.index as usize).into()
355 /// Transform from substitutions for a child of `source_ancestor`
356 /// (e.g., a trait or impl) to substitutions for the same child
357 /// in a different item, with `target_substs` as the base for
358 /// the target impl/trait, with the source child-specific
359 /// parameters (e.g., method parameters) on top of that base.
363 source_ancestor: DefId,
364 target_substs: SubstsRef<'tcx>,
365 ) -> SubstsRef<'tcx> {
366 let defs = tcx.generics_of(source_ancestor);
367 tcx.mk_substs(target_substs.iter().chain(&self[defs.params.len()..]).cloned())
370 pub fn truncate_to(&self, tcx: TyCtxt<'tcx>, generics: &ty::Generics) -> SubstsRef<'tcx> {
371 tcx.mk_substs(self.iter().take(generics.count()).cloned())
375 impl<'tcx> TypeFoldable<'tcx> for SubstsRef<'tcx> {
376 fn super_fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self {
377 // This code is hot enough that it's worth specializing for the most
378 // common length lists, to avoid the overhead of `SmallVec` creation.
379 // The match arms are in order of frequency. The 1, 2, and 0 cases are
380 // typically hit in 90--99.99% of cases. When folding doesn't change
381 // the substs, it's faster to reuse the existing substs rather than
382 // calling `intern_substs`.
385 let param0 = self[0].fold_with(folder);
386 if param0 == self[0] { self } else { folder.tcx().intern_substs(&[param0]) }
389 let param0 = self[0].fold_with(folder);
390 let param1 = self[1].fold_with(folder);
391 if param0 == self[0] && param1 == self[1] {
394 folder.tcx().intern_substs(&[param0, param1])
399 let params: SmallVec<[_; 8]> = self.iter().map(|k| k.fold_with(folder)).collect();
400 if params[..] == self[..] { self } else { folder.tcx().intern_substs(¶ms) }
405 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
406 self.iter().any(|t| t.visit_with(visitor))
410 impl<'tcx> rustc_serialize::UseSpecializedDecodable for SubstsRef<'tcx> {}
412 ///////////////////////////////////////////////////////////////////////////
413 // Public trait `Subst`
415 // Just call `foo.subst(tcx, substs)` to perform a substitution across
416 // `foo`. Or use `foo.subst_spanned(tcx, substs, Some(span))` when
417 // there is more information available (for better errors).
419 pub trait Subst<'tcx>: Sized {
420 fn subst(&self, tcx: TyCtxt<'tcx>, substs: &[GenericArg<'tcx>]) -> Self {
421 self.subst_spanned(tcx, substs, None)
427 substs: &[GenericArg<'tcx>],
432 impl<'tcx, T: TypeFoldable<'tcx>> Subst<'tcx> for T {
436 substs: &[GenericArg<'tcx>],
440 SubstFolder { tcx, substs, span, root_ty: None, ty_stack_depth: 0, binders_passed: 0 };
441 (*self).fold_with(&mut folder)
445 ///////////////////////////////////////////////////////////////////////////
446 // The actual substitution engine itself is a type folder.
448 struct SubstFolder<'a, 'tcx> {
450 substs: &'a [GenericArg<'tcx>],
452 /// The location for which the substitution is performed, if available.
455 /// The root type that is being substituted, if available.
456 root_ty: Option<Ty<'tcx>>,
458 /// Depth of type stack
459 ty_stack_depth: usize,
461 /// Number of region binders we have passed through while doing the substitution
465 impl<'a, 'tcx> TypeFolder<'tcx> for SubstFolder<'a, 'tcx> {
466 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
470 fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> {
471 self.binders_passed += 1;
472 let t = t.super_fold_with(self);
473 self.binders_passed -= 1;
477 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
478 // Note: This routine only handles regions that are bound on
479 // type declarations and other outer declarations, not those
480 // bound in *fn types*. Region substitution of the bound
481 // regions that appear in a function signature is done using
482 // the specialized routine `ty::replace_late_regions()`.
484 ty::ReEarlyBound(data) => {
485 let rk = self.substs.get(data.index as usize).map(|k| k.unpack());
487 Some(GenericArgKind::Lifetime(lt)) => self.shift_region_through_binders(lt),
489 let span = self.span.unwrap_or(DUMMY_SP);
491 "Region parameter out of range \
492 when substituting in region {} (root type={:?}) \
494 data.name, self.root_ty, data.index
496 span_bug!(span, "{}", msg);
504 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
505 if !t.needs_subst() {
509 // track the root type we were asked to substitute
510 let depth = self.ty_stack_depth;
512 self.root_ty = Some(t);
514 self.ty_stack_depth += 1;
516 let t1 = match t.kind {
517 ty::Param(p) => self.ty_for_param(p, t),
518 _ => t.super_fold_with(self),
521 assert_eq!(depth + 1, self.ty_stack_depth);
522 self.ty_stack_depth -= 1;
530 fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
531 if !c.needs_subst() {
535 if let ty::ConstKind::Param(p) = c.val {
536 self.const_for_param(p, c)
538 c.super_fold_with(self)
543 impl<'a, 'tcx> SubstFolder<'a, 'tcx> {
544 fn ty_for_param(&self, p: ty::ParamTy, source_ty: Ty<'tcx>) -> Ty<'tcx> {
545 // Look up the type in the substitutions. It really should be in there.
546 let opt_ty = self.substs.get(p.index as usize).map(|k| k.unpack());
547 let ty = match opt_ty {
548 Some(GenericArgKind::Type(ty)) => ty,
550 let span = self.span.unwrap_or(DUMMY_SP);
553 "expected type for `{:?}` ({:?}/{}) but found {:?} \
554 when substituting (root type={:?}) substs={:?}",
564 let span = self.span.unwrap_or(DUMMY_SP);
567 "type parameter `{:?}` ({:?}/{}) out of range \
568 when substituting (root type={:?}) substs={:?}",
578 self.shift_vars_through_binders(ty)
584 source_ct: &'tcx ty::Const<'tcx>,
585 ) -> &'tcx ty::Const<'tcx> {
586 // Look up the const in the substitutions. It really should be in there.
587 let opt_ct = self.substs.get(p.index as usize).map(|k| k.unpack());
588 let ct = match opt_ct {
589 Some(GenericArgKind::Const(ct)) => ct,
591 let span = self.span.unwrap_or(DUMMY_SP);
594 "expected const for `{:?}` ({:?}/{}) but found {:?} \
595 when substituting substs={:?}",
604 let span = self.span.unwrap_or(DUMMY_SP);
607 "const parameter `{:?}` ({:?}/{}) out of range \
608 when substituting substs={:?}",
617 self.shift_vars_through_binders(ct)
620 /// It is sometimes necessary to adjust the De Bruijn indices during substitution. This occurs
621 /// when we are substituting a type with escaping bound vars into a context where we have
622 /// passed through binders. That's quite a mouthful. Let's see an example:
625 /// type Func<A> = fn(A);
626 /// type MetaFunc = for<'a> fn(Func<&'a int>)
629 /// The type `MetaFunc`, when fully expanded, will be
631 /// for<'a> fn(fn(&'a int))
634 /// | | DebruijnIndex of 2
637 /// Here the `'a` lifetime is bound in the outer function, but appears as an argument of the
638 /// inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip
639 /// over the inner binder (remember that we count De Bruijn indices from 1). However, in the
640 /// definition of `MetaFunc`, the binder is not visible, so the type `&'a int` will have a
641 /// De Bruijn index of 1. It's only during the substitution that we can see we must increase the
642 /// depth by 1 to account for the binder that we passed through.
644 /// As a second example, consider this twist:
647 /// type FuncTuple<A> = (A,fn(A));
648 /// type MetaFuncTuple = for<'a> fn(FuncTuple<&'a int>)
651 /// Here the final type will be:
653 /// for<'a> fn((&'a int, fn(&'a int)))
656 /// DebruijnIndex of 1 |
657 /// DebruijnIndex of 2
659 /// As indicated in the diagram, here the same type `&'a int` is substituted once, but in the
660 /// first case we do not increase the De Bruijn index and in the second case we do. The reason
661 /// is that only in the second case have we passed through a fn binder.
662 fn shift_vars_through_binders<T: TypeFoldable<'tcx>>(&self, val: T) -> T {
664 "shift_vars(val={:?}, binders_passed={:?}, has_escaping_bound_vars={:?})",
667 val.has_escaping_bound_vars()
670 if self.binders_passed == 0 || !val.has_escaping_bound_vars() {
674 let result = ty::fold::shift_vars(self.tcx(), &val, self.binders_passed);
675 debug!("shift_vars: shifted result = {:?}", result);
680 fn shift_region_through_binders(&self, region: ty::Region<'tcx>) -> ty::Region<'tcx> {
681 if self.binders_passed == 0 || !region.has_escaping_bound_vars() {
684 ty::fold::shift_region(self.tcx, region, self.binders_passed)
688 pub type CanonicalUserSubsts<'tcx> = Canonical<'tcx, UserSubsts<'tcx>>;
690 /// Stores the user-given substs to reach some fully qualified path
691 /// (e.g., `<T>::Item` or `<T as Trait>::Item`).
692 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
693 #[derive(HashStable, TypeFoldable, Lift)]
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 /// Specifies the user-given self type. In the case of a path that
704 /// refers to a member in an inherent impl, this self type is
705 /// sometimes needed to constrain the type parameters on the impl. For
706 /// example, in this code:
709 /// struct Foo<T> { }
710 /// impl<A> Foo<A> { fn method() { } }
713 /// when you then have a path like `<Foo<&'static u32>>::method`,
714 /// this struct would carry the `DefId` of the impl along with the
715 /// self type `Foo<u32>`. Then we can instantiate the parameters of
716 /// the impl (with the substs from `UserSubsts`) and apply those to
717 /// the self type, giving `Foo<?A>`. Finally, we unify that with
718 /// the self type here, which contains `?A` to be `&'static u32`
719 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
720 #[derive(HashStable, TypeFoldable, Lift)]
721 pub struct UserSelfTy<'tcx> {
722 pub impl_def_id: DefId,
723 pub self_ty: Ty<'tcx>,