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, WithStableHash};
10 use rustc_hir::def_id::DefId;
11 use rustc_macros::HashStable;
12 use rustc_serialize::{self, Decodable, Encodable};
13 use smallvec::SmallVec;
16 use std::cmp::Ordering;
18 use std::marker::PhantomData;
20 use std::num::NonZeroUsize;
21 use std::ops::{ControlFlow, Deref};
24 /// An entity in the Rust type system, which can be one of
25 /// several kinds (types, lifetimes, and consts).
26 /// To reduce memory usage, a `GenericArg` is an interned pointer,
27 /// with the lowest 2 bits being reserved for a tag to
28 /// indicate the type (`Ty`, `Region`, or `Const`) it points to.
30 /// Note: the `PartialEq`, `Eq` and `Hash` derives are only valid because `Ty`,
31 /// `Region` and `Const` are all interned.
32 #[derive(Copy, Clone, PartialEq, Eq, Hash)]
33 pub struct GenericArg<'tcx> {
35 marker: PhantomData<(Ty<'tcx>, ty::Region<'tcx>, ty::Const<'tcx>)>,
38 const TAG_MASK: usize = 0b11;
39 const TYPE_TAG: usize = 0b00;
40 const REGION_TAG: usize = 0b01;
41 const CONST_TAG: usize = 0b10;
43 #[derive(Debug, TyEncodable, TyDecodable, PartialEq, Eq, PartialOrd, Ord)]
44 pub enum GenericArgKind<'tcx> {
45 Lifetime(ty::Region<'tcx>),
47 Const(ty::Const<'tcx>),
50 /// This function goes from `&'a [Ty<'tcx>]` to `&'a [GenericArg<'tcx>]`
52 /// This is sound as, for types, `GenericArg` is just
53 /// `NonZeroUsize::new_unchecked(ty as *const _ as usize)` as
54 /// long as we use `0` for the `TYPE_TAG`.
55 pub fn ty_slice_as_generic_args<'a, 'tcx>(ts: &'a [Ty<'tcx>]) -> &'a [GenericArg<'tcx>] {
56 assert_eq!(TYPE_TAG, 0);
57 // SAFETY: the whole slice is valid and immutable.
58 // `Ty` and `GenericArg` is explained above.
59 unsafe { slice::from_raw_parts(ts.as_ptr().cast(), ts.len()) }
62 impl<'tcx> List<Ty<'tcx>> {
63 /// Allows to freely switch between `List<Ty<'tcx>>` and `List<GenericArg<'tcx>>`.
65 /// As lists are interned, `List<Ty<'tcx>>` and `List<GenericArg<'tcx>>` have
66 /// be interned together, see `intern_type_list` for more details.
68 pub fn as_substs(&'tcx self) -> SubstsRef<'tcx> {
69 assert_eq!(TYPE_TAG, 0);
70 // SAFETY: `List<T>` is `#[repr(C)]`. `Ty` and `GenericArg` is explained above.
71 unsafe { &*(self as *const List<Ty<'tcx>> as *const List<GenericArg<'tcx>>) }
75 impl<'tcx> GenericArgKind<'tcx> {
77 fn pack(self) -> GenericArg<'tcx> {
78 let (tag, ptr) = match self {
79 GenericArgKind::Lifetime(lt) => {
80 // Ensure we can use the tag bits.
81 assert_eq!(mem::align_of_val(&*lt.0.0) & TAG_MASK, 0);
82 (REGION_TAG, lt.0.0 as *const ty::RegionKind<'tcx> as usize)
84 GenericArgKind::Type(ty) => {
85 // Ensure we can use the tag bits.
86 assert_eq!(mem::align_of_val(&*ty.0.0) & TAG_MASK, 0);
87 (TYPE_TAG, ty.0.0 as *const WithStableHash<ty::TyS<'tcx>> as usize)
89 GenericArgKind::Const(ct) => {
90 // Ensure we can use the tag bits.
91 assert_eq!(mem::align_of_val(&*ct.0.0) & TAG_MASK, 0);
92 (CONST_TAG, ct.0.0 as *const ty::ConstS<'tcx> as usize)
96 GenericArg { ptr: unsafe { NonZeroUsize::new_unchecked(ptr | tag) }, marker: PhantomData }
100 impl<'tcx> fmt::Debug for GenericArg<'tcx> {
101 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
102 match self.unpack() {
103 GenericArgKind::Lifetime(lt) => lt.fmt(f),
104 GenericArgKind::Type(ty) => ty.fmt(f),
105 GenericArgKind::Const(ct) => ct.fmt(f),
110 impl<'tcx> Ord for GenericArg<'tcx> {
111 fn cmp(&self, other: &GenericArg<'tcx>) -> Ordering {
112 self.unpack().cmp(&other.unpack())
116 impl<'tcx> PartialOrd for GenericArg<'tcx> {
117 fn partial_cmp(&self, other: &GenericArg<'tcx>) -> Option<Ordering> {
118 Some(self.cmp(&other))
122 impl<'tcx> From<ty::Region<'tcx>> for GenericArg<'tcx> {
124 fn from(r: ty::Region<'tcx>) -> GenericArg<'tcx> {
125 GenericArgKind::Lifetime(r).pack()
129 impl<'tcx> From<Ty<'tcx>> for GenericArg<'tcx> {
131 fn from(ty: Ty<'tcx>) -> GenericArg<'tcx> {
132 GenericArgKind::Type(ty).pack()
136 impl<'tcx> From<ty::Const<'tcx>> for GenericArg<'tcx> {
138 fn from(c: ty::Const<'tcx>) -> GenericArg<'tcx> {
139 GenericArgKind::Const(c).pack()
143 impl<'tcx> GenericArg<'tcx> {
145 pub fn unpack(self) -> GenericArgKind<'tcx> {
146 let ptr = self.ptr.get();
147 // SAFETY: use of `Interned::new_unchecked` here is ok because these
148 // pointers were originally created from `Interned` types in `pack()`,
149 // and this is just going in the other direction.
151 match ptr & TAG_MASK {
152 REGION_TAG => GenericArgKind::Lifetime(ty::Region(Interned::new_unchecked(
153 &*((ptr & !TAG_MASK) as *const ty::RegionKind<'tcx>),
155 TYPE_TAG => GenericArgKind::Type(Ty(Interned::new_unchecked(
156 &*((ptr & !TAG_MASK) as *const WithStableHash<ty::TyS<'tcx>>),
158 CONST_TAG => GenericArgKind::Const(ty::Const(Interned::new_unchecked(
159 &*((ptr & !TAG_MASK) as *const ty::ConstS<'tcx>),
161 _ => intrinsics::unreachable(),
166 /// Unpack the `GenericArg` as a region when it is known certainly to be a region.
167 pub fn expect_region(self) -> ty::Region<'tcx> {
168 match self.unpack() {
169 GenericArgKind::Lifetime(lt) => lt,
170 _ => bug!("expected a region, but found another kind"),
174 /// Unpack the `GenericArg` as a type when it is known certainly to be a type.
175 /// This is true in cases where `Substs` is used in places where the kinds are known
176 /// to be limited (e.g. in tuples, where the only parameters are type parameters).
177 pub fn expect_ty(self) -> Ty<'tcx> {
178 match self.unpack() {
179 GenericArgKind::Type(ty) => ty,
180 _ => bug!("expected a type, but found another kind"),
184 /// Unpack the `GenericArg` as a const when it is known certainly to be a const.
185 pub fn expect_const(self) -> ty::Const<'tcx> {
186 match self.unpack() {
187 GenericArgKind::Const(c) => c,
188 _ => bug!("expected a const, but found another kind"),
192 pub fn is_non_region_infer(self) -> bool {
193 match self.unpack() {
194 GenericArgKind::Lifetime(_) => false,
195 GenericArgKind::Type(ty) => ty.is_ty_infer(),
196 GenericArgKind::Const(ct) => ct.is_ct_infer(),
201 impl<'a, 'tcx> Lift<'tcx> for GenericArg<'a> {
202 type Lifted = GenericArg<'tcx>;
204 fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
205 match self.unpack() {
206 GenericArgKind::Lifetime(lt) => tcx.lift(lt).map(|lt| lt.into()),
207 GenericArgKind::Type(ty) => tcx.lift(ty).map(|ty| ty.into()),
208 GenericArgKind::Const(ct) => tcx.lift(ct).map(|ct| ct.into()),
213 impl<'tcx> TypeFoldable<'tcx> for GenericArg<'tcx> {
214 fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
215 match self.unpack() {
216 GenericArgKind::Lifetime(lt) => lt.try_fold_with(folder).map(Into::into),
217 GenericArgKind::Type(ty) => ty.try_fold_with(folder).map(Into::into),
218 GenericArgKind::Const(ct) => ct.try_fold_with(folder).map(Into::into),
223 impl<'tcx> TypeVisitable<'tcx> for GenericArg<'tcx> {
224 fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
225 match self.unpack() {
226 GenericArgKind::Lifetime(lt) => lt.visit_with(visitor),
227 GenericArgKind::Type(ty) => ty.visit_with(visitor),
228 GenericArgKind::Const(ct) => ct.visit_with(visitor),
233 impl<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<E> for GenericArg<'tcx> {
234 fn encode(&self, e: &mut E) {
235 self.unpack().encode(e)
239 impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for GenericArg<'tcx> {
240 fn decode(d: &mut D) -> GenericArg<'tcx> {
241 GenericArgKind::decode(d).pack()
245 /// A substitution mapping generic parameters to new values.
246 pub type InternalSubsts<'tcx> = List<GenericArg<'tcx>>;
248 pub type SubstsRef<'tcx> = &'tcx InternalSubsts<'tcx>;
250 impl<'tcx> InternalSubsts<'tcx> {
251 /// Checks whether all elements of this list are types, if so, transmute.
252 pub fn try_as_type_list(&'tcx self) -> Option<&'tcx List<Ty<'tcx>>> {
253 if self.iter().all(|arg| matches!(arg.unpack(), GenericArgKind::Type(_))) {
254 assert_eq!(TYPE_TAG, 0);
255 // SAFETY: All elements are types, see `List<Ty<'tcx>>::as_substs`.
256 Some(unsafe { &*(self as *const List<GenericArg<'tcx>> as *const List<Ty<'tcx>>) })
262 /// Interpret these substitutions as the substitutions of a closure type.
263 /// Closure substitutions have a particular structure controlled by the
264 /// compiler that encodes information like the signature and closure kind;
265 /// see `ty::ClosureSubsts` struct for more comments.
266 pub fn as_closure(&'tcx self) -> ClosureSubsts<'tcx> {
267 ClosureSubsts { substs: self }
270 /// Interpret these substitutions as the substitutions of a generator type.
271 /// Generator substitutions have a particular structure controlled by the
272 /// compiler that encodes information like the signature and generator kind;
273 /// see `ty::GeneratorSubsts` struct for more comments.
274 pub fn as_generator(&'tcx self) -> GeneratorSubsts<'tcx> {
275 GeneratorSubsts { substs: self }
278 /// Interpret these substitutions as the substitutions of an inline const.
279 /// Inline const substitutions have a particular structure controlled by the
280 /// compiler that encodes information like the inferred type;
281 /// see `ty::InlineConstSubsts` struct for more comments.
282 pub fn as_inline_const(&'tcx self) -> InlineConstSubsts<'tcx> {
283 InlineConstSubsts { substs: self }
286 /// Creates an `InternalSubsts` that maps each generic parameter to itself.
287 pub fn identity_for_item(tcx: TyCtxt<'tcx>, def_id: DefId) -> SubstsRef<'tcx> {
288 Self::for_item(tcx, def_id, |param, _| tcx.mk_param_from_def(param))
291 /// Creates an `InternalSubsts` for generic parameter definitions,
292 /// by calling closures to obtain each kind.
293 /// The closures get to observe the `InternalSubsts` as they're
294 /// being built, which can be used to correctly
295 /// substitute defaults of generic parameters.
296 pub fn for_item<F>(tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx>
298 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
300 let defs = tcx.generics_of(def_id);
301 let count = defs.count();
302 let mut substs = SmallVec::with_capacity(count);
303 Self::fill_item(&mut substs, tcx, defs, &mut mk_kind);
304 tcx.intern_substs(&substs)
307 pub fn extend_to<F>(&self, tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx>
309 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
311 Self::for_item(tcx, def_id, |param, substs| {
312 self.get(param.index as usize).cloned().unwrap_or_else(|| mk_kind(param, substs))
317 substs: &mut SmallVec<[GenericArg<'tcx>; 8]>,
322 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
324 if let Some(def_id) = defs.parent {
325 let parent_defs = tcx.generics_of(def_id);
326 Self::fill_item(substs, tcx, parent_defs, mk_kind);
328 Self::fill_single(substs, defs, mk_kind)
331 pub fn fill_single<F>(
332 substs: &mut SmallVec<[GenericArg<'tcx>; 8]>,
336 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
338 substs.reserve(defs.params.len());
339 for param in &defs.params {
340 let kind = mk_kind(param, substs);
341 assert_eq!(param.index as usize, substs.len());
347 pub fn types(&'tcx self) -> impl DoubleEndedIterator<Item = Ty<'tcx>> + 'tcx {
349 .filter_map(|k| if let GenericArgKind::Type(ty) = k.unpack() { Some(ty) } else { None })
353 pub fn regions(&'tcx self) -> impl DoubleEndedIterator<Item = ty::Region<'tcx>> + 'tcx {
354 self.iter().filter_map(|k| {
355 if let GenericArgKind::Lifetime(lt) = k.unpack() { Some(lt) } else { None }
360 pub fn consts(&'tcx self) -> impl DoubleEndedIterator<Item = ty::Const<'tcx>> + 'tcx {
361 self.iter().filter_map(|k| {
362 if let GenericArgKind::Const(ct) = k.unpack() { Some(ct) } else { None }
367 pub fn non_erasable_generics(
369 ) -> impl DoubleEndedIterator<Item = GenericArgKind<'tcx>> + 'tcx {
370 self.iter().filter_map(|k| match k.unpack() {
371 GenericArgKind::Lifetime(_) => None,
372 generic => Some(generic),
377 pub fn type_at(&self, i: usize) -> Ty<'tcx> {
378 if let GenericArgKind::Type(ty) = self[i].unpack() {
381 bug!("expected type for param #{} in {:?}", i, self);
386 pub fn region_at(&self, i: usize) -> ty::Region<'tcx> {
387 if let GenericArgKind::Lifetime(lt) = self[i].unpack() {
390 bug!("expected region for param #{} in {:?}", i, self);
395 pub fn const_at(&self, i: usize) -> ty::Const<'tcx> {
396 if let GenericArgKind::Const(ct) = self[i].unpack() {
399 bug!("expected const for param #{} in {:?}", i, self);
404 pub fn type_for_def(&self, def: &ty::GenericParamDef) -> GenericArg<'tcx> {
405 self.type_at(def.index as usize).into()
408 /// Transform from substitutions for a child of `source_ancestor`
409 /// (e.g., a trait or impl) to substitutions for the same child
410 /// in a different item, with `target_substs` as the base for
411 /// the target impl/trait, with the source child-specific
412 /// parameters (e.g., method parameters) on top of that base.
414 /// For example given:
417 /// trait X<S> { fn f<T>(); }
418 /// impl<U> X<U> for U { fn f<V>() {} }
421 /// * If `self` is `[Self, S, T]`: the identity substs of `f` in the trait.
422 /// * If `source_ancestor` is the def_id of the trait.
423 /// * If `target_substs` is `[U]`, the substs for the impl.
424 /// * Then we will return `[U, T]`, the subst for `f` in the impl that
425 /// are needed for it to match the trait.
429 source_ancestor: DefId,
430 target_substs: SubstsRef<'tcx>,
431 ) -> SubstsRef<'tcx> {
432 let defs = tcx.generics_of(source_ancestor);
433 tcx.mk_substs(target_substs.iter().chain(self.iter().skip(defs.params.len())))
436 pub fn truncate_to(&self, tcx: TyCtxt<'tcx>, generics: &ty::Generics) -> SubstsRef<'tcx> {
437 tcx.mk_substs(self.iter().take(generics.count()))
441 impl<'tcx> TypeFoldable<'tcx> for SubstsRef<'tcx> {
442 fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
443 // This code is hot enough that it's worth specializing for the most
444 // common length lists, to avoid the overhead of `SmallVec` creation.
445 // The match arms are in order of frequency. The 1, 2, and 0 cases are
446 // typically hit in 90--99.99% of cases. When folding doesn't change
447 // the substs, it's faster to reuse the existing substs rather than
448 // calling `intern_substs`.
451 let param0 = self[0].try_fold_with(folder)?;
452 if param0 == self[0] { Ok(self) } else { Ok(folder.tcx().intern_substs(&[param0])) }
455 let param0 = self[0].try_fold_with(folder)?;
456 let param1 = self[1].try_fold_with(folder)?;
457 if param0 == self[0] && param1 == self[1] {
460 Ok(folder.tcx().intern_substs(&[param0, param1]))
464 _ => ty::util::fold_list(self, folder, |tcx, v| tcx.intern_substs(v)),
469 impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<Ty<'tcx>> {
470 fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
471 // This code is fairly hot, though not as hot as `SubstsRef`.
473 // When compiling stage 2, I get the following results:
476 // --- | --------- | -----
477 // 2 | 15083590 | 48.1
478 // 3 | 7540067 | 24.0
479 // 1 | 5300377 | 16.9
483 // I've tried it with some private repositories and got
484 // close to the same result, with 4 and 0 swapping places
488 let param0 = self[0].try_fold_with(folder)?;
489 let param1 = self[1].try_fold_with(folder)?;
490 if param0 == self[0] && param1 == self[1] {
493 Ok(folder.tcx().intern_type_list(&[param0, param1]))
496 _ => ty::util::fold_list(self, folder, |tcx, v| tcx.intern_type_list(v)),
501 impl<'tcx, T: TypeVisitable<'tcx>> TypeVisitable<'tcx> for &'tcx ty::List<T> {
503 fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
504 self.iter().try_for_each(|t| t.visit_with(visitor))
508 /// Similar to [`super::Binder`] except that it tracks early bound generics, i.e. `struct Foo<T>(T)`
509 /// needs `T` substituted immediately. This type primarily exists to avoid forgetting to call
511 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
512 #[derive(Encodable, Decodable, HashStable)]
513 pub struct EarlyBinder<T>(pub T);
515 /// For early binders, you should first call `subst` before using any visitors.
516 impl<'tcx, T> !TypeFoldable<'tcx> for ty::EarlyBinder<T> {}
517 impl<'tcx, T> !TypeVisitable<'tcx> for ty::EarlyBinder<T> {}
519 impl<T> EarlyBinder<T> {
520 pub fn as_ref(&self) -> EarlyBinder<&T> {
524 pub fn map_bound_ref<F, U>(&self, f: F) -> EarlyBinder<U>
528 self.as_ref().map_bound(f)
531 pub fn map_bound<F, U>(self, f: F) -> EarlyBinder<U>
535 let value = f(self.0);
539 pub fn try_map_bound<F, U, E>(self, f: F) -> Result<EarlyBinder<U>, E>
541 F: FnOnce(T) -> Result<U, E>,
543 let value = f(self.0)?;
544 Ok(EarlyBinder(value))
547 pub fn rebind<U>(&self, value: U) -> EarlyBinder<U> {
552 impl<T> EarlyBinder<Option<T>> {
553 pub fn transpose(self) -> Option<EarlyBinder<T>> {
554 self.0.map(|v| EarlyBinder(v))
558 impl<T, U> EarlyBinder<(T, U)> {
559 pub fn transpose_tuple2(self) -> (EarlyBinder<T>, EarlyBinder<U>) {
560 (EarlyBinder(self.0.0), EarlyBinder(self.0.1))
564 impl<'tcx, 's, I: IntoIterator> EarlyBinder<I>
566 I::Item: TypeFoldable<'tcx>,
571 substs: &'s [GenericArg<'tcx>],
572 ) -> SubstIter<'s, 'tcx, I> {
573 SubstIter { it: self.0.into_iter(), tcx, substs }
577 pub struct SubstIter<'s, 'tcx, I: IntoIterator> {
580 substs: &'s [GenericArg<'tcx>],
583 impl<'tcx, I: IntoIterator> Iterator for SubstIter<'_, 'tcx, I>
585 I::Item: TypeFoldable<'tcx>,
589 fn next(&mut self) -> Option<Self::Item> {
590 Some(EarlyBinder(self.it.next()?).subst(self.tcx, self.substs))
594 impl<'tcx, I: IntoIterator> DoubleEndedIterator for SubstIter<'_, 'tcx, I>
596 I::IntoIter: DoubleEndedIterator,
597 I::Item: TypeFoldable<'tcx>,
599 fn next_back(&mut self) -> Option<Self::Item> {
600 Some(EarlyBinder(self.it.next_back()?).subst(self.tcx, self.substs))
604 impl<'tcx, 's, I: IntoIterator> EarlyBinder<I>
607 <I::Item as Deref>::Target: Copy + TypeFoldable<'tcx>,
609 pub fn subst_iter_copied(
612 substs: &'s [GenericArg<'tcx>],
613 ) -> SubstIterCopied<'s, 'tcx, I> {
614 SubstIterCopied { it: self.0.into_iter(), tcx, substs }
618 pub struct SubstIterCopied<'a, 'tcx, I: IntoIterator> {
621 substs: &'a [GenericArg<'tcx>],
624 impl<'tcx, I: IntoIterator> Iterator for SubstIterCopied<'_, 'tcx, I>
627 <I::Item as Deref>::Target: Copy + TypeFoldable<'tcx>,
629 type Item = <I::Item as Deref>::Target;
631 fn next(&mut self) -> Option<Self::Item> {
632 Some(EarlyBinder(*self.it.next()?).subst(self.tcx, self.substs))
636 impl<'tcx, I: IntoIterator> DoubleEndedIterator for SubstIterCopied<'_, 'tcx, I>
638 I::IntoIter: DoubleEndedIterator,
640 <I::Item as Deref>::Target: Copy + TypeFoldable<'tcx>,
642 fn next_back(&mut self) -> Option<Self::Item> {
643 Some(EarlyBinder(*self.it.next_back()?).subst(self.tcx, self.substs))
647 pub struct EarlyBinderIter<T> {
651 impl<T: IntoIterator> EarlyBinder<T> {
652 pub fn transpose_iter(self) -> EarlyBinderIter<T::IntoIter> {
653 EarlyBinderIter { t: self.0.into_iter() }
657 impl<T: Iterator> Iterator for EarlyBinderIter<T> {
658 type Item = EarlyBinder<T::Item>;
660 fn next(&mut self) -> Option<Self::Item> {
661 self.t.next().map(|i| EarlyBinder(i))
665 impl<'tcx, T: TypeFoldable<'tcx>> ty::EarlyBinder<T> {
666 pub fn subst(self, tcx: TyCtxt<'tcx>, substs: &[GenericArg<'tcx>]) -> T {
667 let mut folder = SubstFolder { tcx, substs, binders_passed: 0 };
668 self.0.fold_with(&mut folder)
672 ///////////////////////////////////////////////////////////////////////////
673 // The actual substitution engine itself is a type folder.
675 struct SubstFolder<'a, 'tcx> {
677 substs: &'a [GenericArg<'tcx>],
679 /// Number of region binders we have passed through while doing the substitution
683 impl<'a, 'tcx> TypeFolder<'tcx> for SubstFolder<'a, 'tcx> {
685 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
689 fn fold_binder<T: TypeFoldable<'tcx>>(
691 t: ty::Binder<'tcx, T>,
692 ) -> ty::Binder<'tcx, T> {
693 self.binders_passed += 1;
694 let t = t.super_fold_with(self);
695 self.binders_passed -= 1;
699 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
702 fn region_param_out_of_range(data: ty::EarlyBoundRegion, substs: &[GenericArg<'_>]) -> ! {
704 "Region parameter out of range when substituting in region {} (index={}, substs = {:?})",
713 fn region_param_invalid(data: ty::EarlyBoundRegion, other: GenericArgKind<'_>) -> ! {
715 "Unexpected parameter {:?} when substituting in region {} (index={})",
722 // Note: This routine only handles regions that are bound on
723 // type declarations and other outer declarations, not those
724 // bound in *fn types*. Region substitution of the bound
725 // regions that appear in a function signature is done using
726 // the specialized routine `ty::replace_late_regions()`.
728 ty::ReEarlyBound(data) => {
729 let rk = self.substs.get(data.index as usize).map(|k| k.unpack());
731 Some(GenericArgKind::Lifetime(lt)) => self.shift_region_through_binders(lt),
732 Some(other) => region_param_invalid(data, other),
733 None => region_param_out_of_range(data, self.substs),
740 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
741 if !t.needs_subst() {
746 ty::Param(p) => self.ty_for_param(p, t),
747 _ => t.super_fold_with(self),
751 fn fold_const(&mut self, c: ty::Const<'tcx>) -> ty::Const<'tcx> {
752 if let ty::ConstKind::Param(p) = c.kind() {
753 self.const_for_param(p, c)
755 c.super_fold_with(self)
760 impl<'a, 'tcx> SubstFolder<'a, 'tcx> {
761 fn ty_for_param(&self, p: ty::ParamTy, source_ty: Ty<'tcx>) -> Ty<'tcx> {
762 // Look up the type in the substitutions. It really should be in there.
763 let opt_ty = self.substs.get(p.index as usize).map(|k| k.unpack());
764 let ty = match opt_ty {
765 Some(GenericArgKind::Type(ty)) => ty,
766 Some(kind) => self.type_param_expected(p, source_ty, kind),
767 None => self.type_param_out_of_range(p, source_ty),
770 self.shift_vars_through_binders(ty)
775 fn type_param_expected(&self, p: ty::ParamTy, ty: Ty<'tcx>, kind: GenericArgKind<'tcx>) -> ! {
777 "expected type for `{:?}` ({:?}/{}) but found {:?} when substituting, substs={:?}",
788 fn type_param_out_of_range(&self, p: ty::ParamTy, ty: Ty<'tcx>) -> ! {
790 "type parameter `{:?}` ({:?}/{}) out of range when substituting, substs={:?}",
798 fn const_for_param(&self, p: ParamConst, source_ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
799 // Look up the const in the substitutions. It really should be in there.
800 let opt_ct = self.substs.get(p.index as usize).map(|k| k.unpack());
801 let ct = match opt_ct {
802 Some(GenericArgKind::Const(ct)) => ct,
803 Some(kind) => self.const_param_expected(p, source_ct, kind),
804 None => self.const_param_out_of_range(p, source_ct),
807 self.shift_vars_through_binders(ct)
812 fn const_param_expected(
816 kind: GenericArgKind<'tcx>,
819 "expected const for `{:?}` ({:?}/{}) but found {:?} when substituting substs={:?}",
830 fn const_param_out_of_range(&self, p: ty::ParamConst, ct: ty::Const<'tcx>) -> ! {
832 "const parameter `{:?}` ({:?}/{}) out of range when substituting substs={:?}",
840 /// It is sometimes necessary to adjust the De Bruijn indices during substitution. This occurs
841 /// when we are substituting a type with escaping bound vars into a context where we have
842 /// passed through binders. That's quite a mouthful. Let's see an example:
845 /// type Func<A> = fn(A);
846 /// type MetaFunc = for<'a> fn(Func<&'a i32>);
849 /// The type `MetaFunc`, when fully expanded, will be
850 /// ```ignore (illustrative)
851 /// for<'a> fn(fn(&'a i32))
854 /// // | | DebruijnIndex of 2
857 /// Here the `'a` lifetime is bound in the outer function, but appears as an argument of the
858 /// inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip
859 /// over the inner binder (remember that we count De Bruijn indices from 1). However, in the
860 /// definition of `MetaFunc`, the binder is not visible, so the type `&'a i32` will have a
861 /// De Bruijn index of 1. It's only during the substitution that we can see we must increase the
862 /// depth by 1 to account for the binder that we passed through.
864 /// As a second example, consider this twist:
867 /// type FuncTuple<A> = (A,fn(A));
868 /// type MetaFuncTuple = for<'a> fn(FuncTuple<&'a i32>);
871 /// Here the final type will be:
872 /// ```ignore (illustrative)
873 /// for<'a> fn((&'a i32, fn(&'a i32)))
876 /// // DebruijnIndex of 1 |
877 /// // DebruijnIndex of 2
879 /// As indicated in the diagram, here the same type `&'a i32` is substituted once, but in the
880 /// first case we do not increase the De Bruijn index and in the second case we do. The reason
881 /// is that only in the second case have we passed through a fn binder.
882 fn shift_vars_through_binders<T: TypeFoldable<'tcx>>(&self, val: T) -> T {
884 "shift_vars(val={:?}, binders_passed={:?}, has_escaping_bound_vars={:?})",
887 val.has_escaping_bound_vars()
890 if self.binders_passed == 0 || !val.has_escaping_bound_vars() {
894 let result = ty::fold::shift_vars(TypeFolder::tcx(self), val, self.binders_passed);
895 debug!("shift_vars: shifted result = {:?}", result);
900 fn shift_region_through_binders(&self, region: ty::Region<'tcx>) -> ty::Region<'tcx> {
901 if self.binders_passed == 0 || !region.has_escaping_bound_vars() {
904 ty::fold::shift_region(self.tcx, region, self.binders_passed)
908 /// Stores the user-given substs to reach some fully qualified path
909 /// (e.g., `<T>::Item` or `<T as Trait>::Item`).
910 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable)]
911 #[derive(HashStable, TypeFoldable, TypeVisitable, Lift)]
912 pub struct UserSubsts<'tcx> {
913 /// The substitutions for the item as given by the user.
914 pub substs: SubstsRef<'tcx>,
916 /// The self type, in the case of a `<T>::Item` path (when applied
917 /// to an inherent impl). See `UserSelfTy` below.
918 pub user_self_ty: Option<UserSelfTy<'tcx>>,
921 /// Specifies the user-given self type. In the case of a path that
922 /// refers to a member in an inherent impl, this self type is
923 /// sometimes needed to constrain the type parameters on the impl. For
924 /// example, in this code:
926 /// ```ignore (illustrative)
927 /// struct Foo<T> { }
928 /// impl<A> Foo<A> { fn method() { } }
931 /// when you then have a path like `<Foo<&'static u32>>::method`,
932 /// this struct would carry the `DefId` of the impl along with the
933 /// self type `Foo<u32>`. Then we can instantiate the parameters of
934 /// the impl (with the substs from `UserSubsts`) and apply those to
935 /// the self type, giving `Foo<?A>`. Finally, we unify that with
936 /// the self type here, which contains `?A` to be `&'static u32`
937 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable)]
938 #[derive(HashStable, TypeFoldable, TypeVisitable, Lift)]
939 pub struct UserSelfTy<'tcx> {
940 pub impl_def_id: DefId,
941 pub self_ty: Ty<'tcx>,