4 use crate::ty::codec::{TyDecoder, TyEncoder};
5 use crate::ty::fold::{FallibleTypeFolder, TypeFoldable, TypeFolder, TypeVisitor};
6 use crate::ty::sty::{ClosureSubsts, GeneratorSubsts, InlineConstSubsts};
7 use crate::ty::{self, Lift, List, ParamConst, Ty, TyCtxt};
9 use rustc_hir::def_id::DefId;
10 use rustc_macros::HashStable;
11 use rustc_serialize::{self, Decodable, Encodable};
12 use rustc_span::{Span, DUMMY_SP};
13 use smallvec::SmallVec;
16 use std::cmp::Ordering;
18 use std::marker::PhantomData;
20 use std::num::NonZeroUsize;
21 use std::ops::ControlFlow;
23 /// An entity in the Rust type system, which can be one of
24 /// several kinds (types, lifetimes, and consts).
25 /// To reduce memory usage, a `GenericArg` is an interned pointer,
26 /// with the lowest 2 bits being reserved for a tag to
27 /// indicate the type (`Ty`, `Region`, or `Const`) it points to.
28 #[derive(Copy, Clone, PartialEq, Eq, Hash)]
29 pub struct GenericArg<'tcx> {
31 marker: PhantomData<(Ty<'tcx>, ty::Region<'tcx>, &'tcx ty::Const<'tcx>)>,
34 const TAG_MASK: usize = 0b11;
35 const TYPE_TAG: usize = 0b00;
36 const REGION_TAG: usize = 0b01;
37 const CONST_TAG: usize = 0b10;
39 #[derive(Debug, TyEncodable, TyDecodable, PartialEq, Eq, PartialOrd, Ord, HashStable)]
40 pub enum GenericArgKind<'tcx> {
41 Lifetime(ty::Region<'tcx>),
43 Const(&'tcx ty::Const<'tcx>),
46 impl<'tcx> GenericArgKind<'tcx> {
47 fn pack(self) -> GenericArg<'tcx> {
48 let (tag, ptr) = match self {
49 GenericArgKind::Lifetime(lt) => {
50 // Ensure we can use the tag bits.
51 assert_eq!(mem::align_of_val(lt) & TAG_MASK, 0);
52 (REGION_TAG, lt as *const _ as usize)
54 GenericArgKind::Type(ty) => {
55 // Ensure we can use the tag bits.
56 assert_eq!(mem::align_of_val(ty) & TAG_MASK, 0);
57 (TYPE_TAG, ty as *const _ as usize)
59 GenericArgKind::Const(ct) => {
60 // Ensure we can use the tag bits.
61 assert_eq!(mem::align_of_val(ct) & TAG_MASK, 0);
62 (CONST_TAG, ct as *const _ as usize)
66 GenericArg { ptr: unsafe { NonZeroUsize::new_unchecked(ptr | tag) }, marker: PhantomData }
70 impl<'tcx> fmt::Debug for GenericArg<'tcx> {
71 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
73 GenericArgKind::Lifetime(lt) => lt.fmt(f),
74 GenericArgKind::Type(ty) => ty.fmt(f),
75 GenericArgKind::Const(ct) => ct.fmt(f),
80 impl<'tcx> Ord for GenericArg<'tcx> {
81 fn cmp(&self, other: &GenericArg<'_>) -> Ordering {
82 self.unpack().cmp(&other.unpack())
86 impl<'tcx> PartialOrd for GenericArg<'tcx> {
87 fn partial_cmp(&self, other: &GenericArg<'_>) -> Option<Ordering> {
88 Some(self.cmp(&other))
92 impl<'tcx> From<ty::Region<'tcx>> for GenericArg<'tcx> {
93 fn from(r: ty::Region<'tcx>) -> GenericArg<'tcx> {
94 GenericArgKind::Lifetime(r).pack()
98 impl<'tcx> From<Ty<'tcx>> for GenericArg<'tcx> {
99 fn from(ty: Ty<'tcx>) -> GenericArg<'tcx> {
100 GenericArgKind::Type(ty).pack()
104 impl<'tcx> From<&'tcx ty::Const<'tcx>> for GenericArg<'tcx> {
105 fn from(c: &'tcx ty::Const<'tcx>) -> GenericArg<'tcx> {
106 GenericArgKind::Const(c).pack()
110 impl<'tcx> GenericArg<'tcx> {
112 pub fn unpack(self) -> GenericArgKind<'tcx> {
113 let ptr = self.ptr.get();
115 match ptr & TAG_MASK {
116 REGION_TAG => GenericArgKind::Lifetime(&*((ptr & !TAG_MASK) as *const _)),
117 TYPE_TAG => GenericArgKind::Type(&*((ptr & !TAG_MASK) as *const _)),
118 CONST_TAG => GenericArgKind::Const(&*((ptr & !TAG_MASK) as *const _)),
119 _ => intrinsics::unreachable(),
124 /// Unpack the `GenericArg` as a type when it is known certainly to be a type.
125 /// This is true in cases where `Substs` is used in places where the kinds are known
126 /// to be limited (e.g. in tuples, where the only parameters are type parameters).
127 pub fn expect_ty(self) -> Ty<'tcx> {
128 match self.unpack() {
129 GenericArgKind::Type(ty) => ty,
130 _ => bug!("expected a type, but found another kind"),
134 /// Unpack the `GenericArg` as a const when it is known certainly to be a const.
135 pub fn expect_const(self) -> &'tcx ty::Const<'tcx> {
136 match self.unpack() {
137 GenericArgKind::Const(c) => c,
138 _ => bug!("expected a const, but found another kind"),
143 impl<'a, 'tcx> Lift<'tcx> for GenericArg<'a> {
144 type Lifted = GenericArg<'tcx>;
146 fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
147 match self.unpack() {
148 GenericArgKind::Lifetime(lt) => tcx.lift(lt).map(|lt| lt.into()),
149 GenericArgKind::Type(ty) => tcx.lift(ty).map(|ty| ty.into()),
150 GenericArgKind::Const(ct) => tcx.lift(ct).map(|ct| ct.into()),
155 impl<'tcx> TypeFoldable<'tcx> for GenericArg<'tcx> {
156 fn try_super_fold_with<F: FallibleTypeFolder<'tcx>>(
159 ) -> Result<Self, F::Error> {
160 match self.unpack() {
161 GenericArgKind::Lifetime(lt) => lt.try_fold_with(folder).map(Into::into),
162 GenericArgKind::Type(ty) => ty.try_fold_with(folder).map(Into::into),
163 GenericArgKind::Const(ct) => ct.try_fold_with(folder).map(Into::into),
167 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
168 match self.unpack() {
169 GenericArgKind::Lifetime(lt) => lt.visit_with(visitor),
170 GenericArgKind::Type(ty) => ty.visit_with(visitor),
171 GenericArgKind::Const(ct) => ct.visit_with(visitor),
176 impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for GenericArg<'tcx> {
177 fn encode(&self, e: &mut E) -> Result<(), E::Error> {
178 self.unpack().encode(e)
182 impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for GenericArg<'tcx> {
183 fn decode(d: &mut D) -> GenericArg<'tcx> {
184 GenericArgKind::decode(d).pack()
188 /// A substitution mapping generic parameters to new values.
189 pub type InternalSubsts<'tcx> = List<GenericArg<'tcx>>;
191 pub type SubstsRef<'tcx> = &'tcx InternalSubsts<'tcx>;
193 impl<'a, 'tcx> InternalSubsts<'tcx> {
194 /// Interpret these substitutions as the substitutions of a closure type.
195 /// Closure substitutions have a particular structure controlled by the
196 /// compiler that encodes information like the signature and closure kind;
197 /// see `ty::ClosureSubsts` struct for more comments.
198 pub fn as_closure(&'a self) -> ClosureSubsts<'a> {
199 ClosureSubsts { substs: self }
202 /// Interpret these substitutions as the substitutions of a generator type.
203 /// Generator substitutions have a particular structure controlled by the
204 /// compiler that encodes information like the signature and generator kind;
205 /// see `ty::GeneratorSubsts` struct for more comments.
206 pub fn as_generator(&'tcx self) -> GeneratorSubsts<'tcx> {
207 GeneratorSubsts { substs: self }
210 /// Interpret these substitutions as the substitutions of an inline const.
211 /// Inline const substitutions have a particular structure controlled by the
212 /// compiler that encodes information like the inferred type;
213 /// see `ty::InlineConstSubsts` struct for more comments.
214 pub fn as_inline_const(&'tcx self) -> InlineConstSubsts<'tcx> {
215 InlineConstSubsts { substs: self }
218 /// Creates an `InternalSubsts` that maps each generic parameter to itself.
219 pub fn identity_for_item(tcx: TyCtxt<'tcx>, def_id: DefId) -> SubstsRef<'tcx> {
220 Self::for_item(tcx, def_id, |param, _| tcx.mk_param_from_def(param))
223 /// Creates an `InternalSubsts` for generic parameter definitions,
224 /// by calling closures to obtain each kind.
225 /// The closures get to observe the `InternalSubsts` as they're
226 /// being built, which can be used to correctly
227 /// substitute defaults of generic parameters.
228 pub fn for_item<F>(tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx>
230 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
232 let defs = tcx.generics_of(def_id);
233 let count = defs.count();
234 let mut substs = SmallVec::with_capacity(count);
235 Self::fill_item(&mut substs, tcx, defs, &mut mk_kind);
236 tcx.intern_substs(&substs)
239 pub fn extend_to<F>(&self, tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx>
241 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
243 Self::for_item(tcx, def_id, |param, substs| {
244 self.get(param.index as usize).cloned().unwrap_or_else(|| mk_kind(param, substs))
249 substs: &mut SmallVec<[GenericArg<'tcx>; 8]>,
254 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
256 if let Some(def_id) = defs.parent {
257 let parent_defs = tcx.generics_of(def_id);
258 Self::fill_item(substs, tcx, parent_defs, mk_kind);
260 Self::fill_single(substs, defs, mk_kind)
263 pub fn fill_single<F>(
264 substs: &mut SmallVec<[GenericArg<'tcx>; 8]>,
268 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
270 substs.reserve(defs.params.len());
271 for param in &defs.params {
272 let kind = mk_kind(param, substs);
273 assert_eq!(param.index as usize, substs.len());
279 pub fn types(&'a self) -> impl DoubleEndedIterator<Item = Ty<'tcx>> + 'a {
281 .filter_map(|k| if let GenericArgKind::Type(ty) = k.unpack() { Some(ty) } else { None })
285 pub fn regions(&'a self) -> impl DoubleEndedIterator<Item = ty::Region<'tcx>> + 'a {
286 self.iter().filter_map(|k| {
287 if let GenericArgKind::Lifetime(lt) = k.unpack() { Some(lt) } else { None }
292 pub fn consts(&'a self) -> impl DoubleEndedIterator<Item = &'tcx ty::Const<'tcx>> + 'a {
293 self.iter().filter_map(|k| {
294 if let GenericArgKind::Const(ct) = k.unpack() { Some(ct) } else { None }
299 pub fn non_erasable_generics(
301 ) -> impl DoubleEndedIterator<Item = GenericArgKind<'tcx>> + 'a {
302 self.iter().filter_map(|k| match k.unpack() {
303 GenericArgKind::Lifetime(_) => None,
304 generic => Some(generic),
309 pub fn type_at(&self, i: usize) -> Ty<'tcx> {
310 if let GenericArgKind::Type(ty) = self[i].unpack() {
313 bug!("expected type for param #{} in {:?}", i, self);
318 pub fn region_at(&self, i: usize) -> ty::Region<'tcx> {
319 if let GenericArgKind::Lifetime(lt) = self[i].unpack() {
322 bug!("expected region for param #{} in {:?}", i, self);
327 pub fn const_at(&self, i: usize) -> &'tcx ty::Const<'tcx> {
328 if let GenericArgKind::Const(ct) = self[i].unpack() {
331 bug!("expected const for param #{} in {:?}", i, self);
336 pub fn type_for_def(&self, def: &ty::GenericParamDef) -> GenericArg<'tcx> {
337 self.type_at(def.index as usize).into()
340 /// Transform from substitutions for a child of `source_ancestor`
341 /// (e.g., a trait or impl) to substitutions for the same child
342 /// in a different item, with `target_substs` as the base for
343 /// the target impl/trait, with the source child-specific
344 /// parameters (e.g., method parameters) on top of that base.
346 /// For example given:
349 /// trait X<S> { fn f<T>(); }
350 /// impl<U> X<U> for U { fn f<V>() {} }
353 /// * If `self` is `[Self, S, T]`: the identity substs of `f` in the trait.
354 /// * If `source_ancestor` is the def_id of the trait.
355 /// * If `target_substs` is `[U]`, the substs for the impl.
356 /// * Then we will return `[U, T]`, the subst for `f` in the impl that
357 /// are needed for it to match the trait.
361 source_ancestor: DefId,
362 target_substs: SubstsRef<'tcx>,
363 ) -> SubstsRef<'tcx> {
364 let defs = tcx.generics_of(source_ancestor);
365 tcx.mk_substs(target_substs.iter().chain(self.iter().skip(defs.params.len())))
368 pub fn truncate_to(&self, tcx: TyCtxt<'tcx>, generics: &ty::Generics) -> SubstsRef<'tcx> {
369 tcx.mk_substs(self.iter().take(generics.count()))
373 impl<'tcx> TypeFoldable<'tcx> for SubstsRef<'tcx> {
374 fn try_super_fold_with<F: FallibleTypeFolder<'tcx>>(
377 ) -> Result<Self, F::Error> {
378 // This code is hot enough that it's worth specializing for the most
379 // common length lists, to avoid the overhead of `SmallVec` creation.
380 // The match arms are in order of frequency. The 1, 2, and 0 cases are
381 // typically hit in 90--99.99% of cases. When folding doesn't change
382 // the substs, it's faster to reuse the existing substs rather than
383 // calling `intern_substs`.
386 let param0 = self[0].try_fold_with(folder)?;
387 if param0 == self[0] { Ok(self) } else { Ok(folder.tcx().intern_substs(&[param0])) }
390 let param0 = self[0].try_fold_with(folder)?;
391 let param1 = self[1].try_fold_with(folder)?;
392 if param0 == self[0] && param1 == self[1] {
395 Ok(folder.tcx().intern_substs(&[param0, param1]))
400 let params: SmallVec<[_; 8]> =
401 self.iter().map(|k| k.try_fold_with(folder)).collect::<Result<_, _>>()?;
402 if params[..] == self[..] {
405 Ok(folder.tcx().intern_substs(¶ms))
411 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
412 self.iter().try_for_each(|t| t.visit_with(visitor))
416 ///////////////////////////////////////////////////////////////////////////
417 // Public trait `Subst`
419 // Just call `foo.subst(tcx, substs)` to perform a substitution across
420 // `foo`. Or use `foo.subst_spanned(tcx, substs, Some(span))` when
421 // there is more information available (for better errors).
423 pub trait Subst<'tcx>: Sized {
424 fn subst(self, tcx: TyCtxt<'tcx>, substs: &[GenericArg<'tcx>]) -> Self {
425 self.subst_spanned(tcx, substs, None)
431 substs: &[GenericArg<'tcx>],
436 impl<'tcx, T: TypeFoldable<'tcx>> Subst<'tcx> for T {
440 substs: &[GenericArg<'tcx>],
443 let mut folder = SubstFolder { tcx, substs, span, binders_passed: 0 };
444 self.fold_with(&mut folder)
448 ///////////////////////////////////////////////////////////////////////////
449 // The actual substitution engine itself is a type folder.
451 struct SubstFolder<'a, 'tcx> {
453 substs: &'a [GenericArg<'tcx>],
455 /// The location for which the substitution is performed, if available.
458 /// Number of region binders we have passed through while doing the substitution
462 impl<'a, 'tcx> TypeFolder<'tcx> for SubstFolder<'a, 'tcx> {
463 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
467 fn fold_binder<T: TypeFoldable<'tcx>>(
469 t: ty::Binder<'tcx, T>,
470 ) -> ty::Binder<'tcx, 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 {} (index={})",
493 data.name, data.index
495 span_bug!(span, "{}", msg);
503 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
504 if !t.needs_subst() {
509 ty::Param(p) => self.ty_for_param(p, t),
510 _ => t.super_fold_with(self),
514 fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
515 if let ty::ConstKind::Param(p) = c.val {
516 self.const_for_param(p, c)
518 c.super_fold_with(self)
523 fn fold_mir_const(&mut self, c: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
524 c.super_fold_with(self)
528 impl<'a, 'tcx> SubstFolder<'a, 'tcx> {
529 fn ty_for_param(&self, p: ty::ParamTy, source_ty: Ty<'tcx>) -> Ty<'tcx> {
530 // Look up the type in the substitutions. It really should be in there.
531 let opt_ty = self.substs.get(p.index as usize).map(|k| k.unpack());
532 let ty = match opt_ty {
533 Some(GenericArgKind::Type(ty)) => ty,
535 let span = self.span.unwrap_or(DUMMY_SP);
538 "expected type for `{:?}` ({:?}/{}) but found {:?} \
539 when substituting, substs={:?}",
548 let span = self.span.unwrap_or(DUMMY_SP);
551 "type parameter `{:?}` ({:?}/{}) out of range \
552 when substituting, substs={:?}",
561 self.shift_vars_through_binders(ty)
567 source_ct: &'tcx ty::Const<'tcx>,
568 ) -> &'tcx ty::Const<'tcx> {
569 // Look up the const in the substitutions. It really should be in there.
570 let opt_ct = self.substs.get(p.index as usize).map(|k| k.unpack());
571 let ct = match opt_ct {
572 Some(GenericArgKind::Const(ct)) => ct,
574 let span = self.span.unwrap_or(DUMMY_SP);
577 "expected const for `{:?}` ({:?}/{}) but found {:?} \
578 when substituting substs={:?}",
587 let span = self.span.unwrap_or(DUMMY_SP);
590 "const parameter `{:?}` ({:?}/{}) out of range \
591 when substituting substs={:?}",
600 self.shift_vars_through_binders(ct)
603 /// It is sometimes necessary to adjust the De Bruijn indices during substitution. This occurs
604 /// when we are substituting a type with escaping bound vars into a context where we have
605 /// passed through binders. That's quite a mouthful. Let's see an example:
608 /// type Func<A> = fn(A);
609 /// type MetaFunc = for<'a> fn(Func<&'a i32>)
612 /// The type `MetaFunc`, when fully expanded, will be
614 /// for<'a> fn(fn(&'a i32))
617 /// | | DebruijnIndex of 2
620 /// Here the `'a` lifetime is bound in the outer function, but appears as an argument of the
621 /// inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip
622 /// over the inner binder (remember that we count De Bruijn indices from 1). However, in the
623 /// definition of `MetaFunc`, the binder is not visible, so the type `&'a i32` will have a
624 /// De Bruijn index of 1. It's only during the substitution that we can see we must increase the
625 /// depth by 1 to account for the binder that we passed through.
627 /// As a second example, consider this twist:
630 /// type FuncTuple<A> = (A,fn(A));
631 /// type MetaFuncTuple = for<'a> fn(FuncTuple<&'a i32>)
634 /// Here the final type will be:
636 /// for<'a> fn((&'a i32, fn(&'a i32)))
639 /// DebruijnIndex of 1 |
640 /// DebruijnIndex of 2
642 /// As indicated in the diagram, here the same type `&'a i32` is substituted once, but in the
643 /// first case we do not increase the De Bruijn index and in the second case we do. The reason
644 /// is that only in the second case have we passed through a fn binder.
645 fn shift_vars_through_binders<T: TypeFoldable<'tcx>>(&self, val: T) -> T {
647 "shift_vars(val={:?}, binders_passed={:?}, has_escaping_bound_vars={:?})",
650 val.has_escaping_bound_vars()
653 if self.binders_passed == 0 || !val.has_escaping_bound_vars() {
657 let result = ty::fold::shift_vars(self.tcx(), val, self.binders_passed);
658 debug!("shift_vars: shifted result = {:?}", result);
663 fn shift_region_through_binders(&self, region: ty::Region<'tcx>) -> ty::Region<'tcx> {
664 if self.binders_passed == 0 || !region.has_escaping_bound_vars() {
667 ty::fold::shift_region(self.tcx, region, self.binders_passed)
671 /// Stores the user-given substs to reach some fully qualified path
672 /// (e.g., `<T>::Item` or `<T as Trait>::Item`).
673 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable)]
674 #[derive(HashStable, TypeFoldable, Lift)]
675 pub struct UserSubsts<'tcx> {
676 /// The substitutions for the item as given by the user.
677 pub substs: SubstsRef<'tcx>,
679 /// The self type, in the case of a `<T>::Item` path (when applied
680 /// to an inherent impl). See `UserSelfTy` below.
681 pub user_self_ty: Option<UserSelfTy<'tcx>>,
684 /// Specifies the user-given self type. In the case of a path that
685 /// refers to a member in an inherent impl, this self type is
686 /// sometimes needed to constrain the type parameters on the impl. For
687 /// example, in this code:
690 /// struct Foo<T> { }
691 /// impl<A> Foo<A> { fn method() { } }
694 /// when you then have a path like `<Foo<&'static u32>>::method`,
695 /// this struct would carry the `DefId` of the impl along with the
696 /// self type `Foo<u32>`. Then we can instantiate the parameters of
697 /// the impl (with the substs from `UserSubsts`) and apply those to
698 /// the self type, giving `Foo<?A>`. Finally, we unify that with
699 /// the self type here, which contains `?A` to be `&'static u32`
700 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable)]
701 #[derive(HashStable, TypeFoldable, Lift)]
702 pub struct UserSelfTy<'tcx> {
703 pub impl_def_id: DefId,
704 pub self_ty: Ty<'tcx>,