4 use crate::ty::codec::{TyDecoder, TyEncoder};
5 use crate::ty::fold::{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 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 super_fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self {
157 match self.unpack() {
158 GenericArgKind::Lifetime(lt) => lt.fold_with(folder).into(),
159 GenericArgKind::Type(ty) => ty.fold_with(folder).into(),
160 GenericArgKind::Const(ct) => ct.fold_with(folder).into(),
164 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
165 match self.unpack() {
166 GenericArgKind::Lifetime(lt) => lt.visit_with(visitor),
167 GenericArgKind::Type(ty) => ty.visit_with(visitor),
168 GenericArgKind::Const(ct) => ct.visit_with(visitor),
173 impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for GenericArg<'tcx> {
174 fn encode(&self, e: &mut E) -> Result<(), E::Error> {
175 self.unpack().encode(e)
179 impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for GenericArg<'tcx> {
180 fn decode(d: &mut D) -> Result<GenericArg<'tcx>, D::Error> {
181 Ok(GenericArgKind::decode(d)?.pack())
185 /// A substitution mapping generic parameters to new values.
186 pub type InternalSubsts<'tcx> = List<GenericArg<'tcx>>;
188 pub type SubstsRef<'tcx> = &'tcx InternalSubsts<'tcx>;
190 impl<'a, 'tcx> InternalSubsts<'tcx> {
191 /// Interpret these substitutions as the substitutions of a closure type.
192 /// Closure substitutions have a particular structure controlled by the
193 /// compiler that encodes information like the signature and closure kind;
194 /// see `ty::ClosureSubsts` struct for more comments.
195 pub fn as_closure(&'a self) -> ClosureSubsts<'a> {
196 ClosureSubsts { substs: self }
199 /// Interpret these substitutions as the substitutions of a generator type.
200 /// Generator substitutions have a particular structure controlled by the
201 /// compiler that encodes information like the signature and generator kind;
202 /// see `ty::GeneratorSubsts` struct for more comments.
203 pub fn as_generator(&'tcx self) -> GeneratorSubsts<'tcx> {
204 GeneratorSubsts { substs: self }
207 /// Interpret these substitutions as the substitutions of an inline const.
208 /// Inline const substitutions have a particular structure controlled by the
209 /// compiler that encodes information like the inferred type;
210 /// see `ty::InlineConstSubsts` struct for more comments.
211 pub fn as_inline_const(&'tcx self) -> InlineConstSubsts<'tcx> {
212 InlineConstSubsts { substs: self }
215 /// Creates an `InternalSubsts` that maps each generic parameter to itself.
216 pub fn identity_for_item(tcx: TyCtxt<'tcx>, def_id: DefId) -> SubstsRef<'tcx> {
217 Self::for_item(tcx, def_id, |param, _| tcx.mk_param_from_def(param))
220 /// Creates an `InternalSubsts` for generic parameter definitions,
221 /// by calling closures to obtain each kind.
222 /// The closures get to observe the `InternalSubsts` as they're
223 /// being built, which can be used to correctly
224 /// substitute defaults of generic parameters.
225 pub fn for_item<F>(tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx>
227 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
229 let defs = tcx.generics_of(def_id);
230 let count = defs.count();
231 let mut substs = SmallVec::with_capacity(count);
232 Self::fill_item(&mut substs, tcx, defs, &mut mk_kind);
233 tcx.intern_substs(&substs)
236 pub fn extend_to<F>(&self, tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx>
238 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
240 Self::for_item(tcx, def_id, |param, substs| {
241 self.get(param.index as usize).cloned().unwrap_or_else(|| mk_kind(param, substs))
246 substs: &mut SmallVec<[GenericArg<'tcx>; 8]>,
251 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
253 if let Some(def_id) = defs.parent {
254 let parent_defs = tcx.generics_of(def_id);
255 Self::fill_item(substs, tcx, parent_defs, mk_kind);
257 Self::fill_single(substs, defs, mk_kind)
260 pub fn fill_single<F>(
261 substs: &mut SmallVec<[GenericArg<'tcx>; 8]>,
265 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
267 substs.reserve(defs.params.len());
268 for param in &defs.params {
269 let kind = mk_kind(param, substs);
270 assert_eq!(param.index as usize, substs.len());
275 pub fn is_noop(&self) -> bool {
280 pub fn types(&'a self) -> impl DoubleEndedIterator<Item = Ty<'tcx>> + 'a {
282 .filter_map(|k| if let GenericArgKind::Type(ty) = k.unpack() { Some(ty) } else { None })
286 pub fn regions(&'a self) -> impl DoubleEndedIterator<Item = ty::Region<'tcx>> + 'a {
287 self.iter().filter_map(|k| {
288 if let GenericArgKind::Lifetime(lt) = k.unpack() { Some(lt) } else { None }
293 pub fn consts(&'a self) -> impl DoubleEndedIterator<Item = &'tcx ty::Const<'tcx>> + 'a {
294 self.iter().filter_map(|k| {
295 if let GenericArgKind::Const(ct) = k.unpack() { Some(ct) } else { None }
300 pub fn non_erasable_generics(
302 ) -> impl DoubleEndedIterator<Item = GenericArgKind<'tcx>> + 'a {
303 self.iter().filter_map(|k| match k.unpack() {
304 GenericArgKind::Lifetime(_) => None,
305 generic => Some(generic),
310 pub fn type_at(&self, i: usize) -> Ty<'tcx> {
311 if let GenericArgKind::Type(ty) = self[i].unpack() {
314 bug!("expected type for param #{} in {:?}", i, self);
319 pub fn region_at(&self, i: usize) -> ty::Region<'tcx> {
320 if let GenericArgKind::Lifetime(lt) = self[i].unpack() {
323 bug!("expected region for param #{} in {:?}", i, self);
328 pub fn const_at(&self, i: usize) -> &'tcx ty::Const<'tcx> {
329 if let GenericArgKind::Const(ct) = self[i].unpack() {
332 bug!("expected const for param #{} in {:?}", i, self);
337 pub fn type_for_def(&self, def: &ty::GenericParamDef) -> GenericArg<'tcx> {
338 self.type_at(def.index as usize).into()
341 /// Transform from substitutions for a child of `source_ancestor`
342 /// (e.g., a trait or impl) to substitutions for the same child
343 /// in a different item, with `target_substs` as the base for
344 /// the target impl/trait, with the source child-specific
345 /// parameters (e.g., method parameters) on top of that base.
347 /// For example given:
350 /// trait X<S> { fn f<T>(); }
351 /// impl<U> X<U> for U { fn f<V>() {} }
354 /// * If `self` is `[Self, S, T]`: the identity substs of `f` in the trait.
355 /// * If `source_ancestor` is the def_id of the trait.
356 /// * If `target_substs` is `[U]`, the substs for the impl.
357 /// * Then we will return `[U, T]`, the subst for `f` in the impl that
358 /// are needed for it to match the trait.
362 source_ancestor: DefId,
363 target_substs: SubstsRef<'tcx>,
364 ) -> SubstsRef<'tcx> {
365 let defs = tcx.generics_of(source_ancestor);
366 tcx.mk_substs(target_substs.iter().chain(self.iter().skip(defs.params.len())))
369 pub fn truncate_to(&self, tcx: TyCtxt<'tcx>, generics: &ty::Generics) -> SubstsRef<'tcx> {
370 tcx.mk_substs(self.iter().take(generics.count()))
374 impl<'tcx> TypeFoldable<'tcx> for SubstsRef<'tcx> {
375 fn super_fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self {
376 // This code is hot enough that it's worth specializing for the most
377 // common length lists, to avoid the overhead of `SmallVec` creation.
378 // The match arms are in order of frequency. The 1, 2, and 0 cases are
379 // typically hit in 90--99.99% of cases. When folding doesn't change
380 // the substs, it's faster to reuse the existing substs rather than
381 // calling `intern_substs`.
384 let param0 = self[0].fold_with(folder);
385 if param0 == self[0] { self } else { folder.tcx().intern_substs(&[param0]) }
388 let param0 = self[0].fold_with(folder);
389 let param1 = self[1].fold_with(folder);
390 if param0 == self[0] && param1 == self[1] {
393 folder.tcx().intern_substs(&[param0, param1])
398 let params: SmallVec<[_; 8]> = self.iter().map(|k| k.fold_with(folder)).collect();
399 if params[..] == self[..] { self } else { folder.tcx().intern_substs(¶ms) }
404 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
405 self.iter().try_for_each(|t| t.visit_with(visitor))
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(self, tcx: TyCtxt<'tcx>, substs: &[GenericArg<'tcx>]) -> Self {
418 self.subst_spanned(tcx, substs, None)
424 substs: &[GenericArg<'tcx>],
429 impl<'tcx, T: TypeFoldable<'tcx>> Subst<'tcx> for T {
433 substs: &[GenericArg<'tcx>],
436 let mut folder = SubstFolder { tcx, substs, span, binders_passed: 0 };
437 self.fold_with(&mut folder)
441 ///////////////////////////////////////////////////////////////////////////
442 // The actual substitution engine itself is a type folder.
444 struct SubstFolder<'a, 'tcx> {
446 substs: &'a [GenericArg<'tcx>],
448 /// The location for which the substitution is performed, if available.
451 /// Number of region binders we have passed through while doing the substitution
455 impl<'a, 'tcx> TypeFolder<'tcx> for SubstFolder<'a, 'tcx> {
456 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
460 fn fold_binder<T: TypeFoldable<'tcx>>(
462 t: ty::Binder<'tcx, T>,
463 ) -> ty::Binder<'tcx, T> {
464 self.binders_passed += 1;
465 let t = t.super_fold_with(self);
466 self.binders_passed -= 1;
470 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
471 // Note: This routine only handles regions that are bound on
472 // type declarations and other outer declarations, not those
473 // bound in *fn types*. Region substitution of the bound
474 // regions that appear in a function signature is done using
475 // the specialized routine `ty::replace_late_regions()`.
477 ty::ReEarlyBound(data) => {
478 let rk = self.substs.get(data.index as usize).map(|k| k.unpack());
480 Some(GenericArgKind::Lifetime(lt)) => self.shift_region_through_binders(lt),
482 let span = self.span.unwrap_or(DUMMY_SP);
484 "Region parameter out of range \
485 when substituting in region {} (index={})",
486 data.name, data.index
488 span_bug!(span, "{}", msg);
496 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
497 if !t.potentially_needs_subst() {
502 ty::Param(p) => self.ty_for_param(p, t),
503 _ => t.super_fold_with(self),
507 fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
508 if let ty::ConstKind::Param(p) = c.val {
509 self.const_for_param(p, c)
511 c.super_fold_with(self)
516 fn fold_mir_const(&mut self, c: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
517 c.super_fold_with(self)
521 impl<'a, 'tcx> SubstFolder<'a, 'tcx> {
522 fn ty_for_param(&self, p: ty::ParamTy, source_ty: Ty<'tcx>) -> Ty<'tcx> {
523 // Look up the type in the substitutions. It really should be in there.
524 let opt_ty = self.substs.get(p.index as usize).map(|k| k.unpack());
525 let ty = match opt_ty {
526 Some(GenericArgKind::Type(ty)) => ty,
528 let span = self.span.unwrap_or(DUMMY_SP);
531 "expected type for `{:?}` ({:?}/{}) but found {:?} \
532 when substituting, substs={:?}",
541 let span = self.span.unwrap_or(DUMMY_SP);
544 "type parameter `{:?}` ({:?}/{}) out of range \
545 when substituting, substs={:?}",
554 self.shift_vars_through_binders(ty)
560 source_ct: &'tcx ty::Const<'tcx>,
561 ) -> &'tcx ty::Const<'tcx> {
562 // Look up the const in the substitutions. It really should be in there.
563 let opt_ct = self.substs.get(p.index as usize).map(|k| k.unpack());
564 let ct = match opt_ct {
565 Some(GenericArgKind::Const(ct)) => ct,
567 let span = self.span.unwrap_or(DUMMY_SP);
570 "expected const for `{:?}` ({:?}/{}) but found {:?} \
571 when substituting substs={:?}",
580 let span = self.span.unwrap_or(DUMMY_SP);
583 "const parameter `{:?}` ({:?}/{}) out of range \
584 when substituting substs={:?}",
593 self.shift_vars_through_binders(ct)
596 /// It is sometimes necessary to adjust the De Bruijn indices during substitution. This occurs
597 /// when we are substituting a type with escaping bound vars into a context where we have
598 /// passed through binders. That's quite a mouthful. Let's see an example:
601 /// type Func<A> = fn(A);
602 /// type MetaFunc = for<'a> fn(Func<&'a i32>)
605 /// The type `MetaFunc`, when fully expanded, will be
607 /// for<'a> fn(fn(&'a i32))
610 /// | | DebruijnIndex of 2
613 /// Here the `'a` lifetime is bound in the outer function, but appears as an argument of the
614 /// inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip
615 /// over the inner binder (remember that we count De Bruijn indices from 1). However, in the
616 /// definition of `MetaFunc`, the binder is not visible, so the type `&'a i32` will have a
617 /// De Bruijn index of 1. It's only during the substitution that we can see we must increase the
618 /// depth by 1 to account for the binder that we passed through.
620 /// As a second example, consider this twist:
623 /// type FuncTuple<A> = (A,fn(A));
624 /// type MetaFuncTuple = for<'a> fn(FuncTuple<&'a i32>)
627 /// Here the final type will be:
629 /// for<'a> fn((&'a i32, fn(&'a i32)))
632 /// DebruijnIndex of 1 |
633 /// DebruijnIndex of 2
635 /// As indicated in the diagram, here the same type `&'a i32` is substituted once, but in the
636 /// first case we do not increase the De Bruijn index and in the second case we do. The reason
637 /// is that only in the second case have we passed through a fn binder.
638 fn shift_vars_through_binders<T: TypeFoldable<'tcx>>(&self, val: T) -> T {
640 "shift_vars(val={:?}, binders_passed={:?}, has_escaping_bound_vars={:?})",
643 val.has_escaping_bound_vars()
646 if self.binders_passed == 0 || !val.has_escaping_bound_vars() {
650 let result = ty::fold::shift_vars(self.tcx(), val, self.binders_passed);
651 debug!("shift_vars: shifted result = {:?}", result);
656 fn shift_region_through_binders(&self, region: ty::Region<'tcx>) -> ty::Region<'tcx> {
657 if self.binders_passed == 0 || !region.has_escaping_bound_vars() {
660 ty::fold::shift_region(self.tcx, region, self.binders_passed)
664 /// Stores the user-given substs to reach some fully qualified path
665 /// (e.g., `<T>::Item` or `<T as Trait>::Item`).
666 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable)]
667 #[derive(HashStable, TypeFoldable, Lift)]
668 pub struct UserSubsts<'tcx> {
669 /// The substitutions for the item as given by the user.
670 pub substs: SubstsRef<'tcx>,
672 /// The self type, in the case of a `<T>::Item` path (when applied
673 /// to an inherent impl). See `UserSelfTy` below.
674 pub user_self_ty: Option<UserSelfTy<'tcx>>,
677 /// Specifies the user-given self type. In the case of a path that
678 /// refers to a member in an inherent impl, this self type is
679 /// sometimes needed to constrain the type parameters on the impl. For
680 /// example, in this code:
683 /// struct Foo<T> { }
684 /// impl<A> Foo<A> { fn method() { } }
687 /// when you then have a path like `<Foo<&'static u32>>::method`,
688 /// this struct would carry the `DefId` of the impl along with the
689 /// self type `Foo<u32>`. Then we can instantiate the parameters of
690 /// the impl (with the substs from `UserSubsts`) and apply those to
691 /// the self type, giving `Foo<?A>`. Finally, we unify that with
692 /// the self type here, which contains `?A` to be `&'static u32`
693 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable)]
694 #[derive(HashStable, TypeFoldable, Lift)]
695 pub struct UserSelfTy<'tcx> {
696 pub impl_def_id: DefId,
697 pub self_ty: Ty<'tcx>,