3 use crate::ty::codec::{TyDecoder, TyEncoder};
4 use crate::ty::fold::{FallibleTypeFolder, TypeFoldable, TypeFolder, TypeSuperFoldable};
5 use crate::ty::sty::{ClosureSubsts, GeneratorSubsts, InlineConstSubsts};
6 use crate::ty::visit::{TypeVisitable, TypeVisitor};
7 use crate::ty::{self, Lift, List, ParamConst, Ty, TyCtxt};
9 use rustc_data_structures::intern::Interned;
10 use rustc_hir::def_id::DefId;
11 use rustc_macros::HashStable;
12 use rustc_serialize::{self, Decodable, Encodable};
13 use rustc_type_ir::WithCachedTypeInfo;
14 use smallvec::SmallVec;
17 use std::cmp::Ordering;
19 use std::marker::PhantomData;
21 use std::num::NonZeroUsize;
22 use std::ops::{ControlFlow, Deref};
25 /// An entity in the Rust type system, which can be one of
26 /// several kinds (types, lifetimes, and consts).
27 /// To reduce memory usage, a `GenericArg` is an interned pointer,
28 /// with the lowest 2 bits being reserved for a tag to
29 /// indicate the type (`Ty`, `Region`, or `Const`) it points to.
31 /// Note: the `PartialEq`, `Eq` and `Hash` derives are only valid because `Ty`,
32 /// `Region` and `Const` are all interned.
33 #[derive(Copy, Clone, PartialEq, Eq, Hash)]
34 pub struct GenericArg<'tcx> {
36 marker: PhantomData<(Ty<'tcx>, ty::Region<'tcx>, ty::Const<'tcx>)>,
39 const TAG_MASK: usize = 0b11;
40 const TYPE_TAG: usize = 0b00;
41 const REGION_TAG: usize = 0b01;
42 const CONST_TAG: usize = 0b10;
44 #[derive(Debug, TyEncodable, TyDecodable, PartialEq, Eq, PartialOrd, Ord)]
45 pub enum GenericArgKind<'tcx> {
46 Lifetime(ty::Region<'tcx>),
48 Const(ty::Const<'tcx>),
51 /// This function goes from `&'a [Ty<'tcx>]` to `&'a [GenericArg<'tcx>]`
53 /// This is sound as, for types, `GenericArg` is just
54 /// `NonZeroUsize::new_unchecked(ty as *const _ as usize)` as
55 /// long as we use `0` for the `TYPE_TAG`.
56 pub fn ty_slice_as_generic_args<'a, 'tcx>(ts: &'a [Ty<'tcx>]) -> &'a [GenericArg<'tcx>] {
57 assert_eq!(TYPE_TAG, 0);
58 // SAFETY: the whole slice is valid and immutable.
59 // `Ty` and `GenericArg` is explained above.
60 unsafe { slice::from_raw_parts(ts.as_ptr().cast(), ts.len()) }
63 impl<'tcx> List<Ty<'tcx>> {
64 /// Allows to freely switch between `List<Ty<'tcx>>` and `List<GenericArg<'tcx>>`.
66 /// As lists are interned, `List<Ty<'tcx>>` and `List<GenericArg<'tcx>>` have
67 /// be interned together, see `intern_type_list` for more details.
69 pub fn as_substs(&'tcx self) -> SubstsRef<'tcx> {
70 assert_eq!(TYPE_TAG, 0);
71 // SAFETY: `List<T>` is `#[repr(C)]`. `Ty` and `GenericArg` is explained above.
72 unsafe { &*(self as *const List<Ty<'tcx>> as *const List<GenericArg<'tcx>>) }
76 impl<'tcx> GenericArgKind<'tcx> {
78 fn pack(self) -> GenericArg<'tcx> {
79 let (tag, ptr) = match self {
80 GenericArgKind::Lifetime(lt) => {
81 // Ensure we can use the tag bits.
82 assert_eq!(mem::align_of_val(&*lt.0.0) & TAG_MASK, 0);
83 (REGION_TAG, lt.0.0 as *const ty::RegionKind<'tcx> as usize)
85 GenericArgKind::Type(ty) => {
86 // Ensure we can use the tag bits.
87 assert_eq!(mem::align_of_val(&*ty.0.0) & TAG_MASK, 0);
88 (TYPE_TAG, ty.0.0 as *const WithCachedTypeInfo<ty::TyKind<'tcx>> as usize)
90 GenericArgKind::Const(ct) => {
91 // Ensure we can use the tag bits.
92 assert_eq!(mem::align_of_val(&*ct.0.0) & TAG_MASK, 0);
93 (CONST_TAG, ct.0.0 as *const ty::ConstData<'tcx> as usize)
97 GenericArg { ptr: unsafe { NonZeroUsize::new_unchecked(ptr | tag) }, marker: PhantomData }
101 impl<'tcx> fmt::Debug for GenericArg<'tcx> {
102 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
103 match self.unpack() {
104 GenericArgKind::Lifetime(lt) => lt.fmt(f),
105 GenericArgKind::Type(ty) => ty.fmt(f),
106 GenericArgKind::Const(ct) => ct.fmt(f),
111 impl<'tcx> Ord for GenericArg<'tcx> {
112 fn cmp(&self, other: &GenericArg<'tcx>) -> Ordering {
113 self.unpack().cmp(&other.unpack())
117 impl<'tcx> PartialOrd for GenericArg<'tcx> {
118 fn partial_cmp(&self, other: &GenericArg<'tcx>) -> Option<Ordering> {
119 Some(self.cmp(&other))
123 impl<'tcx> From<ty::Region<'tcx>> for GenericArg<'tcx> {
125 fn from(r: ty::Region<'tcx>) -> GenericArg<'tcx> {
126 GenericArgKind::Lifetime(r).pack()
130 impl<'tcx> From<Ty<'tcx>> for GenericArg<'tcx> {
132 fn from(ty: Ty<'tcx>) -> GenericArg<'tcx> {
133 GenericArgKind::Type(ty).pack()
137 impl<'tcx> From<ty::Const<'tcx>> for GenericArg<'tcx> {
139 fn from(c: ty::Const<'tcx>) -> GenericArg<'tcx> {
140 GenericArgKind::Const(c).pack()
144 impl<'tcx> From<ty::Term<'tcx>> for GenericArg<'tcx> {
145 fn from(value: ty::Term<'tcx>) -> Self {
146 match value.unpack() {
147 ty::TermKind::Ty(t) => t.into(),
148 ty::TermKind::Const(c) => c.into(),
153 impl<'tcx> GenericArg<'tcx> {
155 pub fn unpack(self) -> GenericArgKind<'tcx> {
156 let ptr = self.ptr.get();
157 // SAFETY: use of `Interned::new_unchecked` here is ok because these
158 // pointers were originally created from `Interned` types in `pack()`,
159 // and this is just going in the other direction.
161 match ptr & TAG_MASK {
162 REGION_TAG => GenericArgKind::Lifetime(ty::Region(Interned::new_unchecked(
163 &*((ptr & !TAG_MASK) as *const ty::RegionKind<'tcx>),
165 TYPE_TAG => GenericArgKind::Type(Ty(Interned::new_unchecked(
166 &*((ptr & !TAG_MASK) as *const WithCachedTypeInfo<ty::TyKind<'tcx>>),
168 CONST_TAG => GenericArgKind::Const(ty::Const(Interned::new_unchecked(
169 &*((ptr & !TAG_MASK) as *const ty::ConstData<'tcx>),
171 _ => intrinsics::unreachable(),
176 /// Unpack the `GenericArg` as a region when it is known certainly to be a region.
177 pub fn expect_region(self) -> ty::Region<'tcx> {
178 match self.unpack() {
179 GenericArgKind::Lifetime(lt) => lt,
180 _ => bug!("expected a region, but found another kind"),
184 /// Unpack the `GenericArg` as a type when it is known certainly to be a type.
185 /// This is true in cases where `Substs` is used in places where the kinds are known
186 /// to be limited (e.g. in tuples, where the only parameters are type parameters).
187 pub fn expect_ty(self) -> Ty<'tcx> {
188 match self.unpack() {
189 GenericArgKind::Type(ty) => ty,
190 _ => bug!("expected a type, but found another kind"),
194 /// Unpack the `GenericArg` as a const when it is known certainly to be a const.
195 pub fn expect_const(self) -> ty::Const<'tcx> {
196 match self.unpack() {
197 GenericArgKind::Const(c) => c,
198 _ => bug!("expected a const, but found another kind"),
202 pub fn is_non_region_infer(self) -> bool {
203 match self.unpack() {
204 GenericArgKind::Lifetime(_) => false,
205 GenericArgKind::Type(ty) => ty.is_ty_infer(),
206 GenericArgKind::Const(ct) => ct.is_ct_infer(),
211 impl<'a, 'tcx> Lift<'tcx> for GenericArg<'a> {
212 type Lifted = GenericArg<'tcx>;
214 fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
215 match self.unpack() {
216 GenericArgKind::Lifetime(lt) => tcx.lift(lt).map(|lt| lt.into()),
217 GenericArgKind::Type(ty) => tcx.lift(ty).map(|ty| ty.into()),
218 GenericArgKind::Const(ct) => tcx.lift(ct).map(|ct| ct.into()),
223 impl<'tcx> TypeFoldable<'tcx> for GenericArg<'tcx> {
224 fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
225 match self.unpack() {
226 GenericArgKind::Lifetime(lt) => lt.try_fold_with(folder).map(Into::into),
227 GenericArgKind::Type(ty) => ty.try_fold_with(folder).map(Into::into),
228 GenericArgKind::Const(ct) => ct.try_fold_with(folder).map(Into::into),
233 impl<'tcx> TypeVisitable<'tcx> for GenericArg<'tcx> {
234 fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
235 match self.unpack() {
236 GenericArgKind::Lifetime(lt) => lt.visit_with(visitor),
237 GenericArgKind::Type(ty) => ty.visit_with(visitor),
238 GenericArgKind::Const(ct) => ct.visit_with(visitor),
243 impl<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<E> for GenericArg<'tcx> {
244 fn encode(&self, e: &mut E) {
245 self.unpack().encode(e)
249 impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for GenericArg<'tcx> {
250 fn decode(d: &mut D) -> GenericArg<'tcx> {
251 GenericArgKind::decode(d).pack()
255 /// List of generic arguments that are gonna be used to substitute generic parameters.
256 pub type InternalSubsts<'tcx> = List<GenericArg<'tcx>>;
258 pub type SubstsRef<'tcx> = &'tcx InternalSubsts<'tcx>;
260 impl<'tcx> InternalSubsts<'tcx> {
261 /// Checks whether all elements of this list are types, if so, transmute.
262 pub fn try_as_type_list(&'tcx self) -> Option<&'tcx List<Ty<'tcx>>> {
263 if self.iter().all(|arg| matches!(arg.unpack(), GenericArgKind::Type(_))) {
264 assert_eq!(TYPE_TAG, 0);
265 // SAFETY: All elements are types, see `List<Ty<'tcx>>::as_substs`.
266 Some(unsafe { &*(self as *const List<GenericArg<'tcx>> as *const List<Ty<'tcx>>) })
272 /// Interpret these substitutions as the substitutions of a closure type.
273 /// Closure substitutions have a particular structure controlled by the
274 /// compiler that encodes information like the signature and closure kind;
275 /// see `ty::ClosureSubsts` struct for more comments.
276 pub fn as_closure(&'tcx self) -> ClosureSubsts<'tcx> {
277 ClosureSubsts { substs: self }
280 /// Interpret these substitutions as the substitutions of a generator type.
281 /// Generator substitutions have a particular structure controlled by the
282 /// compiler that encodes information like the signature and generator kind;
283 /// see `ty::GeneratorSubsts` struct for more comments.
284 pub fn as_generator(&'tcx self) -> GeneratorSubsts<'tcx> {
285 GeneratorSubsts { substs: self }
288 /// Interpret these substitutions as the substitutions of an inline const.
289 /// Inline const substitutions have a particular structure controlled by the
290 /// compiler that encodes information like the inferred type;
291 /// see `ty::InlineConstSubsts` struct for more comments.
292 pub fn as_inline_const(&'tcx self) -> InlineConstSubsts<'tcx> {
293 InlineConstSubsts { substs: self }
296 /// Creates an `InternalSubsts` that maps each generic parameter to itself.
297 pub fn identity_for_item(tcx: TyCtxt<'tcx>, def_id: DefId) -> SubstsRef<'tcx> {
298 Self::for_item(tcx, def_id, |param, _| tcx.mk_param_from_def(param))
301 /// Creates an `InternalSubsts` for generic parameter definitions,
302 /// by calling closures to obtain each kind.
303 /// The closures get to observe the `InternalSubsts` as they're
304 /// being built, which can be used to correctly
305 /// substitute defaults of generic parameters.
306 pub fn for_item<F>(tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx>
308 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
310 let defs = tcx.generics_of(def_id);
311 let count = defs.count();
312 let mut substs = SmallVec::with_capacity(count);
313 Self::fill_item(&mut substs, tcx, defs, &mut mk_kind);
314 tcx.intern_substs(&substs)
317 pub fn extend_to<F>(&self, tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx>
319 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
321 Self::for_item(tcx, def_id, |param, substs| {
322 self.get(param.index as usize).cloned().unwrap_or_else(|| mk_kind(param, substs))
327 substs: &mut SmallVec<[GenericArg<'tcx>; 8]>,
332 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
334 if let Some(def_id) = defs.parent {
335 let parent_defs = tcx.generics_of(def_id);
336 Self::fill_item(substs, tcx, parent_defs, mk_kind);
338 Self::fill_single(substs, defs, mk_kind)
341 pub fn fill_single<F>(
342 substs: &mut SmallVec<[GenericArg<'tcx>; 8]>,
346 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
348 substs.reserve(defs.params.len());
349 for param in &defs.params {
350 let kind = mk_kind(param, substs);
351 assert_eq!(param.index as usize, substs.len());
356 // Extend an `original_substs` list to the full number of substs expected by `def_id`,
357 // filling in the missing parameters with error ty/ct or 'static regions.
358 pub fn extend_with_error(
361 original_substs: &[GenericArg<'tcx>],
362 ) -> SubstsRef<'tcx> {
363 ty::InternalSubsts::for_item(tcx, def_id, |def, substs| {
364 if let Some(subst) = original_substs.get(def.index as usize) {
367 def.to_error(tcx, substs)
373 pub fn types(&'tcx self) -> impl DoubleEndedIterator<Item = Ty<'tcx>> + 'tcx {
375 .filter_map(|k| if let GenericArgKind::Type(ty) = k.unpack() { Some(ty) } else { None })
379 pub fn regions(&'tcx self) -> impl DoubleEndedIterator<Item = ty::Region<'tcx>> + 'tcx {
380 self.iter().filter_map(|k| {
381 if let GenericArgKind::Lifetime(lt) = k.unpack() { Some(lt) } else { None }
386 pub fn consts(&'tcx self) -> impl DoubleEndedIterator<Item = ty::Const<'tcx>> + 'tcx {
387 self.iter().filter_map(|k| {
388 if let GenericArgKind::Const(ct) = k.unpack() { Some(ct) } else { None }
393 pub fn non_erasable_generics(
395 ) -> impl DoubleEndedIterator<Item = GenericArgKind<'tcx>> + 'tcx {
396 self.iter().filter_map(|k| match k.unpack() {
397 GenericArgKind::Lifetime(_) => None,
398 generic => Some(generic),
403 pub fn type_at(&self, i: usize) -> Ty<'tcx> {
404 if let GenericArgKind::Type(ty) = self[i].unpack() {
407 bug!("expected type for param #{} in {:?}", i, self);
412 pub fn region_at(&self, i: usize) -> ty::Region<'tcx> {
413 if let GenericArgKind::Lifetime(lt) = self[i].unpack() {
416 bug!("expected region for param #{} in {:?}", i, self);
421 pub fn const_at(&self, i: usize) -> ty::Const<'tcx> {
422 if let GenericArgKind::Const(ct) = self[i].unpack() {
425 bug!("expected const for param #{} in {:?}", i, self);
430 pub fn type_for_def(&self, def: &ty::GenericParamDef) -> GenericArg<'tcx> {
431 self.type_at(def.index as usize).into()
434 /// Transform from substitutions for a child of `source_ancestor`
435 /// (e.g., a trait or impl) to substitutions for the same child
436 /// in a different item, with `target_substs` as the base for
437 /// the target impl/trait, with the source child-specific
438 /// parameters (e.g., method parameters) on top of that base.
440 /// For example given:
443 /// trait X<S> { fn f<T>(); }
444 /// impl<U> X<U> for U { fn f<V>() {} }
447 /// * If `self` is `[Self, S, T]`: the identity substs of `f` in the trait.
448 /// * If `source_ancestor` is the def_id of the trait.
449 /// * If `target_substs` is `[U]`, the substs for the impl.
450 /// * Then we will return `[U, T]`, the subst for `f` in the impl that
451 /// are needed for it to match the trait.
455 source_ancestor: DefId,
456 target_substs: SubstsRef<'tcx>,
457 ) -> SubstsRef<'tcx> {
458 let defs = tcx.generics_of(source_ancestor);
459 tcx.mk_substs(target_substs.iter().chain(self.iter().skip(defs.params.len())))
462 pub fn truncate_to(&self, tcx: TyCtxt<'tcx>, generics: &ty::Generics) -> SubstsRef<'tcx> {
463 tcx.mk_substs(self.iter().take(generics.count()))
467 impl<'tcx> TypeFoldable<'tcx> for SubstsRef<'tcx> {
468 fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
469 // This code is hot enough that it's worth specializing for the most
470 // common length lists, to avoid the overhead of `SmallVec` creation.
471 // The match arms are in order of frequency. The 1, 2, and 0 cases are
472 // typically hit in 90--99.99% of cases. When folding doesn't change
473 // the substs, it's faster to reuse the existing substs rather than
474 // calling `intern_substs`.
477 let param0 = self[0].try_fold_with(folder)?;
478 if param0 == self[0] { Ok(self) } else { Ok(folder.tcx().intern_substs(&[param0])) }
481 let param0 = self[0].try_fold_with(folder)?;
482 let param1 = self[1].try_fold_with(folder)?;
483 if param0 == self[0] && param1 == self[1] {
486 Ok(folder.tcx().intern_substs(&[param0, param1]))
490 _ => ty::util::fold_list(self, folder, |tcx, v| tcx.intern_substs(v)),
495 impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<Ty<'tcx>> {
496 fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
497 // This code is fairly hot, though not as hot as `SubstsRef`.
499 // When compiling stage 2, I get the following results:
502 // --- | --------- | -----
503 // 2 | 15083590 | 48.1
504 // 3 | 7540067 | 24.0
505 // 1 | 5300377 | 16.9
509 // I've tried it with some private repositories and got
510 // close to the same result, with 4 and 0 swapping places
514 let param0 = self[0].try_fold_with(folder)?;
515 let param1 = self[1].try_fold_with(folder)?;
516 if param0 == self[0] && param1 == self[1] {
519 Ok(folder.tcx().intern_type_list(&[param0, param1]))
522 _ => ty::util::fold_list(self, folder, |tcx, v| tcx.intern_type_list(v)),
527 impl<'tcx, T: TypeVisitable<'tcx>> TypeVisitable<'tcx> for &'tcx ty::List<T> {
529 fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
530 self.iter().try_for_each(|t| t.visit_with(visitor))
534 /// Similar to [`super::Binder`] except that it tracks early bound generics, i.e. `struct Foo<T>(T)`
535 /// needs `T` substituted immediately. This type primarily exists to avoid forgetting to call
537 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
538 #[derive(Encodable, Decodable, HashStable)]
539 pub struct EarlyBinder<T>(pub T);
541 /// For early binders, you should first call `subst` before using any visitors.
542 impl<'tcx, T> !TypeFoldable<'tcx> for ty::EarlyBinder<T> {}
543 impl<'tcx, T> !TypeVisitable<'tcx> for ty::EarlyBinder<T> {}
545 impl<T> EarlyBinder<T> {
546 pub fn as_ref(&self) -> EarlyBinder<&T> {
550 pub fn map_bound_ref<F, U>(&self, f: F) -> EarlyBinder<U>
554 self.as_ref().map_bound(f)
557 pub fn map_bound<F, U>(self, f: F) -> EarlyBinder<U>
561 let value = f(self.0);
565 pub fn try_map_bound<F, U, E>(self, f: F) -> Result<EarlyBinder<U>, E>
567 F: FnOnce(T) -> Result<U, E>,
569 let value = f(self.0)?;
570 Ok(EarlyBinder(value))
573 pub fn rebind<U>(&self, value: U) -> EarlyBinder<U> {
578 impl<T> EarlyBinder<Option<T>> {
579 pub fn transpose(self) -> Option<EarlyBinder<T>> {
580 self.0.map(|v| EarlyBinder(v))
584 impl<T, U> EarlyBinder<(T, U)> {
585 pub fn transpose_tuple2(self) -> (EarlyBinder<T>, EarlyBinder<U>) {
586 (EarlyBinder(self.0.0), EarlyBinder(self.0.1))
590 impl<'tcx, 's, I: IntoIterator> EarlyBinder<I>
592 I::Item: TypeFoldable<'tcx>,
597 substs: &'s [GenericArg<'tcx>],
598 ) -> SubstIter<'s, 'tcx, I> {
599 SubstIter { it: self.0.into_iter(), tcx, substs }
603 pub struct SubstIter<'s, 'tcx, I: IntoIterator> {
606 substs: &'s [GenericArg<'tcx>],
609 impl<'tcx, I: IntoIterator> Iterator for SubstIter<'_, 'tcx, I>
611 I::Item: TypeFoldable<'tcx>,
615 fn next(&mut self) -> Option<Self::Item> {
616 Some(EarlyBinder(self.it.next()?).subst(self.tcx, self.substs))
619 fn size_hint(&self) -> (usize, Option<usize>) {
624 impl<'tcx, I: IntoIterator> DoubleEndedIterator for SubstIter<'_, 'tcx, I>
626 I::IntoIter: DoubleEndedIterator,
627 I::Item: TypeFoldable<'tcx>,
629 fn next_back(&mut self) -> Option<Self::Item> {
630 Some(EarlyBinder(self.it.next_back()?).subst(self.tcx, self.substs))
634 impl<'tcx, 's, I: IntoIterator> EarlyBinder<I>
637 <I::Item as Deref>::Target: Copy + TypeFoldable<'tcx>,
639 pub fn subst_iter_copied(
642 substs: &'s [GenericArg<'tcx>],
643 ) -> SubstIterCopied<'s, 'tcx, I> {
644 SubstIterCopied { it: self.0.into_iter(), tcx, substs }
648 pub struct SubstIterCopied<'a, 'tcx, I: IntoIterator> {
651 substs: &'a [GenericArg<'tcx>],
654 impl<'tcx, I: IntoIterator> Iterator for SubstIterCopied<'_, 'tcx, I>
657 <I::Item as Deref>::Target: Copy + TypeFoldable<'tcx>,
659 type Item = <I::Item as Deref>::Target;
661 fn next(&mut self) -> Option<Self::Item> {
662 Some(EarlyBinder(*self.it.next()?).subst(self.tcx, self.substs))
665 fn size_hint(&self) -> (usize, Option<usize>) {
670 impl<'tcx, I: IntoIterator> DoubleEndedIterator for SubstIterCopied<'_, 'tcx, I>
672 I::IntoIter: DoubleEndedIterator,
674 <I::Item as Deref>::Target: Copy + TypeFoldable<'tcx>,
676 fn next_back(&mut self) -> Option<Self::Item> {
677 Some(EarlyBinder(*self.it.next_back()?).subst(self.tcx, self.substs))
681 pub struct EarlyBinderIter<T> {
685 impl<T: IntoIterator> EarlyBinder<T> {
686 pub fn transpose_iter(self) -> EarlyBinderIter<T::IntoIter> {
687 EarlyBinderIter { t: self.0.into_iter() }
691 impl<T: Iterator> Iterator for EarlyBinderIter<T> {
692 type Item = EarlyBinder<T::Item>;
694 fn next(&mut self) -> Option<Self::Item> {
695 self.t.next().map(|i| EarlyBinder(i))
698 fn size_hint(&self) -> (usize, Option<usize>) {
703 impl<'tcx, T: TypeFoldable<'tcx>> ty::EarlyBinder<T> {
704 pub fn subst(self, tcx: TyCtxt<'tcx>, substs: &[GenericArg<'tcx>]) -> T {
705 let mut folder = SubstFolder { tcx, substs, binders_passed: 0 };
706 self.0.fold_with(&mut folder)
710 ///////////////////////////////////////////////////////////////////////////
711 // The actual substitution engine itself is a type folder.
713 struct SubstFolder<'a, 'tcx> {
715 substs: &'a [GenericArg<'tcx>],
717 /// Number of region binders we have passed through while doing the substitution
721 impl<'a, 'tcx> TypeFolder<'tcx> for SubstFolder<'a, 'tcx> {
723 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
727 fn fold_binder<T: TypeFoldable<'tcx>>(
729 t: ty::Binder<'tcx, T>,
730 ) -> ty::Binder<'tcx, T> {
731 self.binders_passed += 1;
732 let t = t.super_fold_with(self);
733 self.binders_passed -= 1;
737 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
740 fn region_param_out_of_range(data: ty::EarlyBoundRegion, substs: &[GenericArg<'_>]) -> ! {
742 "Region parameter out of range when substituting in region {} (index={}, substs = {:?})",
751 fn region_param_invalid(data: ty::EarlyBoundRegion, other: GenericArgKind<'_>) -> ! {
753 "Unexpected parameter {:?} when substituting in region {} (index={})",
760 // Note: This routine only handles regions that are bound on
761 // type declarations and other outer declarations, not those
762 // bound in *fn types*. Region substitution of the bound
763 // regions that appear in a function signature is done using
764 // the specialized routine `ty::replace_late_regions()`.
766 ty::ReEarlyBound(data) => {
767 let rk = self.substs.get(data.index as usize).map(|k| k.unpack());
769 Some(GenericArgKind::Lifetime(lt)) => self.shift_region_through_binders(lt),
770 Some(other) => region_param_invalid(data, other),
771 None => region_param_out_of_range(data, self.substs),
778 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
779 if !t.needs_subst() {
784 ty::Param(p) => self.ty_for_param(p, t),
785 _ => t.super_fold_with(self),
789 fn fold_const(&mut self, c: ty::Const<'tcx>) -> ty::Const<'tcx> {
790 if let ty::ConstKind::Param(p) = c.kind() {
791 self.const_for_param(p, c)
793 c.super_fold_with(self)
798 impl<'a, 'tcx> SubstFolder<'a, 'tcx> {
799 fn ty_for_param(&self, p: ty::ParamTy, source_ty: Ty<'tcx>) -> Ty<'tcx> {
800 // Look up the type in the substitutions. It really should be in there.
801 let opt_ty = self.substs.get(p.index as usize).map(|k| k.unpack());
802 let ty = match opt_ty {
803 Some(GenericArgKind::Type(ty)) => ty,
804 Some(kind) => self.type_param_expected(p, source_ty, kind),
805 None => self.type_param_out_of_range(p, source_ty),
808 self.shift_vars_through_binders(ty)
813 fn type_param_expected(&self, p: ty::ParamTy, ty: Ty<'tcx>, kind: GenericArgKind<'tcx>) -> ! {
815 "expected type for `{:?}` ({:?}/{}) but found {:?} when substituting, substs={:?}",
826 fn type_param_out_of_range(&self, p: ty::ParamTy, ty: Ty<'tcx>) -> ! {
828 "type parameter `{:?}` ({:?}/{}) out of range when substituting, substs={:?}",
836 fn const_for_param(&self, p: ParamConst, source_ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
837 // Look up the const in the substitutions. It really should be in there.
838 let opt_ct = self.substs.get(p.index as usize).map(|k| k.unpack());
839 let ct = match opt_ct {
840 Some(GenericArgKind::Const(ct)) => ct,
841 Some(kind) => self.const_param_expected(p, source_ct, kind),
842 None => self.const_param_out_of_range(p, source_ct),
845 self.shift_vars_through_binders(ct)
850 fn const_param_expected(
854 kind: GenericArgKind<'tcx>,
857 "expected const for `{:?}` ({:?}/{}) but found {:?} when substituting substs={:?}",
868 fn const_param_out_of_range(&self, p: ty::ParamConst, ct: ty::Const<'tcx>) -> ! {
870 "const parameter `{:?}` ({:?}/{}) out of range when substituting substs={:?}",
878 /// It is sometimes necessary to adjust the De Bruijn indices during substitution. This occurs
879 /// when we are substituting a type with escaping bound vars into a context where we have
880 /// passed through binders. That's quite a mouthful. Let's see an example:
883 /// type Func<A> = fn(A);
884 /// type MetaFunc = for<'a> fn(Func<&'a i32>);
887 /// The type `MetaFunc`, when fully expanded, will be
888 /// ```ignore (illustrative)
889 /// for<'a> fn(fn(&'a i32))
892 /// // | | DebruijnIndex of 2
895 /// Here the `'a` lifetime is bound in the outer function, but appears as an argument of the
896 /// inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip
897 /// over the inner binder (remember that we count De Bruijn indices from 1). However, in the
898 /// definition of `MetaFunc`, the binder is not visible, so the type `&'a i32` will have a
899 /// De Bruijn index of 1. It's only during the substitution that we can see we must increase the
900 /// depth by 1 to account for the binder that we passed through.
902 /// As a second example, consider this twist:
905 /// type FuncTuple<A> = (A,fn(A));
906 /// type MetaFuncTuple = for<'a> fn(FuncTuple<&'a i32>);
909 /// Here the final type will be:
910 /// ```ignore (illustrative)
911 /// for<'a> fn((&'a i32, fn(&'a i32)))
914 /// // DebruijnIndex of 1 |
915 /// // DebruijnIndex of 2
917 /// As indicated in the diagram, here the same type `&'a i32` is substituted once, but in the
918 /// first case we do not increase the De Bruijn index and in the second case we do. The reason
919 /// is that only in the second case have we passed through a fn binder.
920 fn shift_vars_through_binders<T: TypeFoldable<'tcx>>(&self, val: T) -> T {
922 "shift_vars(val={:?}, binders_passed={:?}, has_escaping_bound_vars={:?})",
925 val.has_escaping_bound_vars()
928 if self.binders_passed == 0 || !val.has_escaping_bound_vars() {
932 let result = ty::fold::shift_vars(TypeFolder::tcx(self), val, self.binders_passed);
933 debug!("shift_vars: shifted result = {:?}", result);
938 fn shift_region_through_binders(&self, region: ty::Region<'tcx>) -> ty::Region<'tcx> {
939 if self.binders_passed == 0 || !region.has_escaping_bound_vars() {
942 ty::fold::shift_region(self.tcx, region, self.binders_passed)
946 /// Stores the user-given substs to reach some fully qualified path
947 /// (e.g., `<T>::Item` or `<T as Trait>::Item`).
948 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable)]
949 #[derive(HashStable, TypeFoldable, TypeVisitable, Lift)]
950 pub struct UserSubsts<'tcx> {
951 /// The substitutions for the item as given by the user.
952 pub substs: SubstsRef<'tcx>,
954 /// The self type, in the case of a `<T>::Item` path (when applied
955 /// to an inherent impl). See `UserSelfTy` below.
956 pub user_self_ty: Option<UserSelfTy<'tcx>>,
959 /// Specifies the user-given self type. In the case of a path that
960 /// refers to a member in an inherent impl, this self type is
961 /// sometimes needed to constrain the type parameters on the impl. For
962 /// example, in this code:
964 /// ```ignore (illustrative)
965 /// struct Foo<T> { }
966 /// impl<A> Foo<A> { fn method() { } }
969 /// when you then have a path like `<Foo<&'static u32>>::method`,
970 /// this struct would carry the `DefId` of the impl along with the
971 /// self type `Foo<u32>`. Then we can instantiate the parameters of
972 /// the impl (with the substs from `UserSubsts`) and apply those to
973 /// the self type, giving `Foo<?A>`. Finally, we unify that with
974 /// the self type here, which contains `?A` to be `&'static u32`
975 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable)]
976 #[derive(HashStable, TypeFoldable, TypeVisitable, Lift)]
977 pub struct UserSelfTy<'tcx> {
978 pub impl_def_id: DefId,
979 pub self_ty: Ty<'tcx>,