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> From<ty::Term<'tcx>> for GenericArg<'tcx> {
144 fn from(value: ty::Term<'tcx>) -> Self {
145 match value.unpack() {
146 ty::TermKind::Ty(t) => t.into(),
147 ty::TermKind::Const(c) => c.into(),
152 impl<'tcx> GenericArg<'tcx> {
154 pub fn unpack(self) -> GenericArgKind<'tcx> {
155 let ptr = self.ptr.get();
156 // SAFETY: use of `Interned::new_unchecked` here is ok because these
157 // pointers were originally created from `Interned` types in `pack()`,
158 // and this is just going in the other direction.
160 match ptr & TAG_MASK {
161 REGION_TAG => GenericArgKind::Lifetime(ty::Region(Interned::new_unchecked(
162 &*((ptr & !TAG_MASK) as *const ty::RegionKind<'tcx>),
164 TYPE_TAG => GenericArgKind::Type(Ty(Interned::new_unchecked(
165 &*((ptr & !TAG_MASK) as *const WithStableHash<ty::TyS<'tcx>>),
167 CONST_TAG => GenericArgKind::Const(ty::Const(Interned::new_unchecked(
168 &*((ptr & !TAG_MASK) as *const ty::ConstS<'tcx>),
170 _ => intrinsics::unreachable(),
175 /// Unpack the `GenericArg` as a region when it is known certainly to be a region.
176 pub fn expect_region(self) -> ty::Region<'tcx> {
177 match self.unpack() {
178 GenericArgKind::Lifetime(lt) => lt,
179 _ => bug!("expected a region, but found another kind"),
183 /// Unpack the `GenericArg` as a type when it is known certainly to be a type.
184 /// This is true in cases where `Substs` is used in places where the kinds are known
185 /// to be limited (e.g. in tuples, where the only parameters are type parameters).
186 pub fn expect_ty(self) -> Ty<'tcx> {
187 match self.unpack() {
188 GenericArgKind::Type(ty) => ty,
189 _ => bug!("expected a type, but found another kind"),
193 /// Unpack the `GenericArg` as a const when it is known certainly to be a const.
194 pub fn expect_const(self) -> ty::Const<'tcx> {
195 match self.unpack() {
196 GenericArgKind::Const(c) => c,
197 _ => bug!("expected a const, but found another kind"),
201 pub fn is_non_region_infer(self) -> bool {
202 match self.unpack() {
203 GenericArgKind::Lifetime(_) => false,
204 GenericArgKind::Type(ty) => ty.is_ty_infer(),
205 GenericArgKind::Const(ct) => ct.is_ct_infer(),
210 impl<'a, 'tcx> Lift<'tcx> for GenericArg<'a> {
211 type Lifted = GenericArg<'tcx>;
213 fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
214 match self.unpack() {
215 GenericArgKind::Lifetime(lt) => tcx.lift(lt).map(|lt| lt.into()),
216 GenericArgKind::Type(ty) => tcx.lift(ty).map(|ty| ty.into()),
217 GenericArgKind::Const(ct) => tcx.lift(ct).map(|ct| ct.into()),
222 impl<'tcx> TypeFoldable<'tcx> for GenericArg<'tcx> {
223 fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
224 match self.unpack() {
225 GenericArgKind::Lifetime(lt) => lt.try_fold_with(folder).map(Into::into),
226 GenericArgKind::Type(ty) => ty.try_fold_with(folder).map(Into::into),
227 GenericArgKind::Const(ct) => ct.try_fold_with(folder).map(Into::into),
232 impl<'tcx> TypeVisitable<'tcx> for GenericArg<'tcx> {
233 fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
234 match self.unpack() {
235 GenericArgKind::Lifetime(lt) => lt.visit_with(visitor),
236 GenericArgKind::Type(ty) => ty.visit_with(visitor),
237 GenericArgKind::Const(ct) => ct.visit_with(visitor),
242 impl<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<E> for GenericArg<'tcx> {
243 fn encode(&self, e: &mut E) {
244 self.unpack().encode(e)
248 impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for GenericArg<'tcx> {
249 fn decode(d: &mut D) -> GenericArg<'tcx> {
250 GenericArgKind::decode(d).pack()
254 /// A substitution mapping generic parameters to new values.
255 pub type InternalSubsts<'tcx> = List<GenericArg<'tcx>>;
257 pub type SubstsRef<'tcx> = &'tcx InternalSubsts<'tcx>;
259 impl<'tcx> InternalSubsts<'tcx> {
260 /// Checks whether all elements of this list are types, if so, transmute.
261 pub fn try_as_type_list(&'tcx self) -> Option<&'tcx List<Ty<'tcx>>> {
262 if self.iter().all(|arg| matches!(arg.unpack(), GenericArgKind::Type(_))) {
263 assert_eq!(TYPE_TAG, 0);
264 // SAFETY: All elements are types, see `List<Ty<'tcx>>::as_substs`.
265 Some(unsafe { &*(self as *const List<GenericArg<'tcx>> as *const List<Ty<'tcx>>) })
271 /// Interpret these substitutions as the substitutions of a closure type.
272 /// Closure substitutions have a particular structure controlled by the
273 /// compiler that encodes information like the signature and closure kind;
274 /// see `ty::ClosureSubsts` struct for more comments.
275 pub fn as_closure(&'tcx self) -> ClosureSubsts<'tcx> {
276 ClosureSubsts { substs: self }
279 /// Interpret these substitutions as the substitutions of a generator type.
280 /// Generator substitutions have a particular structure controlled by the
281 /// compiler that encodes information like the signature and generator kind;
282 /// see `ty::GeneratorSubsts` struct for more comments.
283 pub fn as_generator(&'tcx self) -> GeneratorSubsts<'tcx> {
284 GeneratorSubsts { substs: self }
287 /// Interpret these substitutions as the substitutions of an inline const.
288 /// Inline const substitutions have a particular structure controlled by the
289 /// compiler that encodes information like the inferred type;
290 /// see `ty::InlineConstSubsts` struct for more comments.
291 pub fn as_inline_const(&'tcx self) -> InlineConstSubsts<'tcx> {
292 InlineConstSubsts { substs: self }
295 /// Creates an `InternalSubsts` that maps each generic parameter to itself.
296 pub fn identity_for_item(tcx: TyCtxt<'tcx>, def_id: DefId) -> SubstsRef<'tcx> {
297 Self::for_item(tcx, def_id, |param, _| tcx.mk_param_from_def(param))
300 /// Creates an `InternalSubsts` for generic parameter definitions,
301 /// by calling closures to obtain each kind.
302 /// The closures get to observe the `InternalSubsts` as they're
303 /// being built, which can be used to correctly
304 /// substitute defaults of generic parameters.
305 pub fn for_item<F>(tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx>
307 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
309 let defs = tcx.generics_of(def_id);
310 let count = defs.count();
311 let mut substs = SmallVec::with_capacity(count);
312 Self::fill_item(&mut substs, tcx, defs, &mut mk_kind);
313 tcx.intern_substs(&substs)
316 pub fn extend_to<F>(&self, tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx>
318 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
320 Self::for_item(tcx, def_id, |param, substs| {
321 self.get(param.index as usize).cloned().unwrap_or_else(|| mk_kind(param, substs))
326 substs: &mut SmallVec<[GenericArg<'tcx>; 8]>,
331 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
333 if let Some(def_id) = defs.parent {
334 let parent_defs = tcx.generics_of(def_id);
335 Self::fill_item(substs, tcx, parent_defs, mk_kind);
337 Self::fill_single(substs, defs, mk_kind)
340 pub fn fill_single<F>(
341 substs: &mut SmallVec<[GenericArg<'tcx>; 8]>,
345 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
347 substs.reserve(defs.params.len());
348 for param in &defs.params {
349 let kind = mk_kind(param, substs);
350 assert_eq!(param.index as usize, substs.len());
356 pub fn types(&'tcx self) -> impl DoubleEndedIterator<Item = Ty<'tcx>> + 'tcx {
358 .filter_map(|k| if let GenericArgKind::Type(ty) = k.unpack() { Some(ty) } else { None })
362 pub fn regions(&'tcx self) -> impl DoubleEndedIterator<Item = ty::Region<'tcx>> + 'tcx {
363 self.iter().filter_map(|k| {
364 if let GenericArgKind::Lifetime(lt) = k.unpack() { Some(lt) } else { None }
369 pub fn consts(&'tcx self) -> impl DoubleEndedIterator<Item = ty::Const<'tcx>> + 'tcx {
370 self.iter().filter_map(|k| {
371 if let GenericArgKind::Const(ct) = k.unpack() { Some(ct) } else { None }
376 pub fn non_erasable_generics(
378 ) -> impl DoubleEndedIterator<Item = GenericArgKind<'tcx>> + 'tcx {
379 self.iter().filter_map(|k| match k.unpack() {
380 GenericArgKind::Lifetime(_) => None,
381 generic => Some(generic),
386 pub fn type_at(&self, i: usize) -> Ty<'tcx> {
387 if let GenericArgKind::Type(ty) = self[i].unpack() {
390 bug!("expected type for param #{} in {:?}", i, self);
395 pub fn region_at(&self, i: usize) -> ty::Region<'tcx> {
396 if let GenericArgKind::Lifetime(lt) = self[i].unpack() {
399 bug!("expected region for param #{} in {:?}", i, self);
404 pub fn const_at(&self, i: usize) -> ty::Const<'tcx> {
405 if let GenericArgKind::Const(ct) = self[i].unpack() {
408 bug!("expected const for param #{} in {:?}", i, self);
413 pub fn type_for_def(&self, def: &ty::GenericParamDef) -> GenericArg<'tcx> {
414 self.type_at(def.index as usize).into()
417 /// Transform from substitutions for a child of `source_ancestor`
418 /// (e.g., a trait or impl) to substitutions for the same child
419 /// in a different item, with `target_substs` as the base for
420 /// the target impl/trait, with the source child-specific
421 /// parameters (e.g., method parameters) on top of that base.
423 /// For example given:
426 /// trait X<S> { fn f<T>(); }
427 /// impl<U> X<U> for U { fn f<V>() {} }
430 /// * If `self` is `[Self, S, T]`: the identity substs of `f` in the trait.
431 /// * If `source_ancestor` is the def_id of the trait.
432 /// * If `target_substs` is `[U]`, the substs for the impl.
433 /// * Then we will return `[U, T]`, the subst for `f` in the impl that
434 /// are needed for it to match the trait.
438 source_ancestor: DefId,
439 target_substs: SubstsRef<'tcx>,
440 ) -> SubstsRef<'tcx> {
441 let defs = tcx.generics_of(source_ancestor);
442 tcx.mk_substs(target_substs.iter().chain(self.iter().skip(defs.params.len())))
445 pub fn truncate_to(&self, tcx: TyCtxt<'tcx>, generics: &ty::Generics) -> SubstsRef<'tcx> {
446 tcx.mk_substs(self.iter().take(generics.count()))
450 impl<'tcx> TypeFoldable<'tcx> for SubstsRef<'tcx> {
451 fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
452 // This code is hot enough that it's worth specializing for the most
453 // common length lists, to avoid the overhead of `SmallVec` creation.
454 // The match arms are in order of frequency. The 1, 2, and 0 cases are
455 // typically hit in 90--99.99% of cases. When folding doesn't change
456 // the substs, it's faster to reuse the existing substs rather than
457 // calling `intern_substs`.
460 let param0 = self[0].try_fold_with(folder)?;
461 if param0 == self[0] { Ok(self) } else { Ok(folder.tcx().intern_substs(&[param0])) }
464 let param0 = self[0].try_fold_with(folder)?;
465 let param1 = self[1].try_fold_with(folder)?;
466 if param0 == self[0] && param1 == self[1] {
469 Ok(folder.tcx().intern_substs(&[param0, param1]))
473 _ => ty::util::fold_list(self, folder, |tcx, v| tcx.intern_substs(v)),
478 impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<Ty<'tcx>> {
479 fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
480 // This code is fairly hot, though not as hot as `SubstsRef`.
482 // When compiling stage 2, I get the following results:
485 // --- | --------- | -----
486 // 2 | 15083590 | 48.1
487 // 3 | 7540067 | 24.0
488 // 1 | 5300377 | 16.9
492 // I've tried it with some private repositories and got
493 // close to the same result, with 4 and 0 swapping places
497 let param0 = self[0].try_fold_with(folder)?;
498 let param1 = self[1].try_fold_with(folder)?;
499 if param0 == self[0] && param1 == self[1] {
502 Ok(folder.tcx().intern_type_list(&[param0, param1]))
505 _ => ty::util::fold_list(self, folder, |tcx, v| tcx.intern_type_list(v)),
510 impl<'tcx, T: TypeVisitable<'tcx>> TypeVisitable<'tcx> for &'tcx ty::List<T> {
512 fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
513 self.iter().try_for_each(|t| t.visit_with(visitor))
517 /// Similar to [`super::Binder`] except that it tracks early bound generics, i.e. `struct Foo<T>(T)`
518 /// needs `T` substituted immediately. This type primarily exists to avoid forgetting to call
520 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
521 #[derive(Encodable, Decodable, HashStable)]
522 pub struct EarlyBinder<T>(pub T);
524 /// For early binders, you should first call `subst` before using any visitors.
525 impl<'tcx, T> !TypeFoldable<'tcx> for ty::EarlyBinder<T> {}
526 impl<'tcx, T> !TypeVisitable<'tcx> for ty::EarlyBinder<T> {}
528 impl<T> EarlyBinder<T> {
529 pub fn as_ref(&self) -> EarlyBinder<&T> {
533 pub fn map_bound_ref<F, U>(&self, f: F) -> EarlyBinder<U>
537 self.as_ref().map_bound(f)
540 pub fn map_bound<F, U>(self, f: F) -> EarlyBinder<U>
544 let value = f(self.0);
548 pub fn try_map_bound<F, U, E>(self, f: F) -> Result<EarlyBinder<U>, E>
550 F: FnOnce(T) -> Result<U, E>,
552 let value = f(self.0)?;
553 Ok(EarlyBinder(value))
556 pub fn rebind<U>(&self, value: U) -> EarlyBinder<U> {
561 impl<T> EarlyBinder<Option<T>> {
562 pub fn transpose(self) -> Option<EarlyBinder<T>> {
563 self.0.map(|v| EarlyBinder(v))
567 impl<T, U> EarlyBinder<(T, U)> {
568 pub fn transpose_tuple2(self) -> (EarlyBinder<T>, EarlyBinder<U>) {
569 (EarlyBinder(self.0.0), EarlyBinder(self.0.1))
573 impl<'tcx, 's, I: IntoIterator> EarlyBinder<I>
575 I::Item: TypeFoldable<'tcx>,
580 substs: &'s [GenericArg<'tcx>],
581 ) -> SubstIter<'s, 'tcx, I> {
582 SubstIter { it: self.0.into_iter(), tcx, substs }
586 pub struct SubstIter<'s, 'tcx, I: IntoIterator> {
589 substs: &'s [GenericArg<'tcx>],
592 impl<'tcx, I: IntoIterator> Iterator for SubstIter<'_, 'tcx, I>
594 I::Item: TypeFoldable<'tcx>,
598 fn next(&mut self) -> Option<Self::Item> {
599 Some(EarlyBinder(self.it.next()?).subst(self.tcx, self.substs))
602 fn size_hint(&self) -> (usize, Option<usize>) {
607 impl<'tcx, I: IntoIterator> DoubleEndedIterator for SubstIter<'_, 'tcx, I>
609 I::IntoIter: DoubleEndedIterator,
610 I::Item: TypeFoldable<'tcx>,
612 fn next_back(&mut self) -> Option<Self::Item> {
613 Some(EarlyBinder(self.it.next_back()?).subst(self.tcx, self.substs))
617 impl<'tcx, 's, I: IntoIterator> EarlyBinder<I>
620 <I::Item as Deref>::Target: Copy + TypeFoldable<'tcx>,
622 pub fn subst_iter_copied(
625 substs: &'s [GenericArg<'tcx>],
626 ) -> SubstIterCopied<'s, 'tcx, I> {
627 SubstIterCopied { it: self.0.into_iter(), tcx, substs }
631 pub struct SubstIterCopied<'a, 'tcx, I: IntoIterator> {
634 substs: &'a [GenericArg<'tcx>],
637 impl<'tcx, I: IntoIterator> Iterator for SubstIterCopied<'_, 'tcx, I>
640 <I::Item as Deref>::Target: Copy + TypeFoldable<'tcx>,
642 type Item = <I::Item as Deref>::Target;
644 fn next(&mut self) -> Option<Self::Item> {
645 Some(EarlyBinder(*self.it.next()?).subst(self.tcx, self.substs))
648 fn size_hint(&self) -> (usize, Option<usize>) {
653 impl<'tcx, I: IntoIterator> DoubleEndedIterator for SubstIterCopied<'_, 'tcx, I>
655 I::IntoIter: DoubleEndedIterator,
657 <I::Item as Deref>::Target: Copy + TypeFoldable<'tcx>,
659 fn next_back(&mut self) -> Option<Self::Item> {
660 Some(EarlyBinder(*self.it.next_back()?).subst(self.tcx, self.substs))
664 pub struct EarlyBinderIter<T> {
668 impl<T: IntoIterator> EarlyBinder<T> {
669 pub fn transpose_iter(self) -> EarlyBinderIter<T::IntoIter> {
670 EarlyBinderIter { t: self.0.into_iter() }
674 impl<T: Iterator> Iterator for EarlyBinderIter<T> {
675 type Item = EarlyBinder<T::Item>;
677 fn next(&mut self) -> Option<Self::Item> {
678 self.t.next().map(|i| EarlyBinder(i))
681 fn size_hint(&self) -> (usize, Option<usize>) {
686 impl<'tcx, T: TypeFoldable<'tcx>> ty::EarlyBinder<T> {
687 pub fn subst(self, tcx: TyCtxt<'tcx>, substs: &[GenericArg<'tcx>]) -> T {
688 let mut folder = SubstFolder { tcx, substs, binders_passed: 0 };
689 self.0.fold_with(&mut folder)
693 ///////////////////////////////////////////////////////////////////////////
694 // The actual substitution engine itself is a type folder.
696 struct SubstFolder<'a, 'tcx> {
698 substs: &'a [GenericArg<'tcx>],
700 /// Number of region binders we have passed through while doing the substitution
704 impl<'a, 'tcx> TypeFolder<'tcx> for SubstFolder<'a, 'tcx> {
706 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
710 fn fold_binder<T: TypeFoldable<'tcx>>(
712 t: ty::Binder<'tcx, T>,
713 ) -> ty::Binder<'tcx, T> {
714 self.binders_passed += 1;
715 let t = t.super_fold_with(self);
716 self.binders_passed -= 1;
720 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
723 fn region_param_out_of_range(data: ty::EarlyBoundRegion, substs: &[GenericArg<'_>]) -> ! {
725 "Region parameter out of range when substituting in region {} (index={}, substs = {:?})",
734 fn region_param_invalid(data: ty::EarlyBoundRegion, other: GenericArgKind<'_>) -> ! {
736 "Unexpected parameter {:?} when substituting in region {} (index={})",
743 // Note: This routine only handles regions that are bound on
744 // type declarations and other outer declarations, not those
745 // bound in *fn types*. Region substitution of the bound
746 // regions that appear in a function signature is done using
747 // the specialized routine `ty::replace_late_regions()`.
749 ty::ReEarlyBound(data) => {
750 let rk = self.substs.get(data.index as usize).map(|k| k.unpack());
752 Some(GenericArgKind::Lifetime(lt)) => self.shift_region_through_binders(lt),
753 Some(other) => region_param_invalid(data, other),
754 None => region_param_out_of_range(data, self.substs),
761 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
762 if !t.needs_subst() {
767 ty::Param(p) => self.ty_for_param(p, t),
768 _ => t.super_fold_with(self),
772 fn fold_const(&mut self, c: ty::Const<'tcx>) -> ty::Const<'tcx> {
773 if let ty::ConstKind::Param(p) = c.kind() {
774 self.const_for_param(p, c)
776 c.super_fold_with(self)
781 impl<'a, 'tcx> SubstFolder<'a, 'tcx> {
782 fn ty_for_param(&self, p: ty::ParamTy, source_ty: Ty<'tcx>) -> Ty<'tcx> {
783 // Look up the type in the substitutions. It really should be in there.
784 let opt_ty = self.substs.get(p.index as usize).map(|k| k.unpack());
785 let ty = match opt_ty {
786 Some(GenericArgKind::Type(ty)) => ty,
787 Some(kind) => self.type_param_expected(p, source_ty, kind),
788 None => self.type_param_out_of_range(p, source_ty),
791 self.shift_vars_through_binders(ty)
796 fn type_param_expected(&self, p: ty::ParamTy, ty: Ty<'tcx>, kind: GenericArgKind<'tcx>) -> ! {
798 "expected type for `{:?}` ({:?}/{}) but found {:?} when substituting, substs={:?}",
809 fn type_param_out_of_range(&self, p: ty::ParamTy, ty: Ty<'tcx>) -> ! {
811 "type parameter `{:?}` ({:?}/{}) out of range when substituting, substs={:?}",
819 fn const_for_param(&self, p: ParamConst, source_ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
820 // Look up the const in the substitutions. It really should be in there.
821 let opt_ct = self.substs.get(p.index as usize).map(|k| k.unpack());
822 let ct = match opt_ct {
823 Some(GenericArgKind::Const(ct)) => ct,
824 Some(kind) => self.const_param_expected(p, source_ct, kind),
825 None => self.const_param_out_of_range(p, source_ct),
828 self.shift_vars_through_binders(ct)
833 fn const_param_expected(
837 kind: GenericArgKind<'tcx>,
840 "expected const for `{:?}` ({:?}/{}) but found {:?} when substituting substs={:?}",
851 fn const_param_out_of_range(&self, p: ty::ParamConst, ct: ty::Const<'tcx>) -> ! {
853 "const parameter `{:?}` ({:?}/{}) out of range when substituting substs={:?}",
861 /// It is sometimes necessary to adjust the De Bruijn indices during substitution. This occurs
862 /// when we are substituting a type with escaping bound vars into a context where we have
863 /// passed through binders. That's quite a mouthful. Let's see an example:
866 /// type Func<A> = fn(A);
867 /// type MetaFunc = for<'a> fn(Func<&'a i32>);
870 /// The type `MetaFunc`, when fully expanded, will be
871 /// ```ignore (illustrative)
872 /// for<'a> fn(fn(&'a i32))
875 /// // | | DebruijnIndex of 2
878 /// Here the `'a` lifetime is bound in the outer function, but appears as an argument of the
879 /// inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip
880 /// over the inner binder (remember that we count De Bruijn indices from 1). However, in the
881 /// definition of `MetaFunc`, the binder is not visible, so the type `&'a i32` will have a
882 /// De Bruijn index of 1. It's only during the substitution that we can see we must increase the
883 /// depth by 1 to account for the binder that we passed through.
885 /// As a second example, consider this twist:
888 /// type FuncTuple<A> = (A,fn(A));
889 /// type MetaFuncTuple = for<'a> fn(FuncTuple<&'a i32>);
892 /// Here the final type will be:
893 /// ```ignore (illustrative)
894 /// for<'a> fn((&'a i32, fn(&'a i32)))
897 /// // DebruijnIndex of 1 |
898 /// // DebruijnIndex of 2
900 /// As indicated in the diagram, here the same type `&'a i32` is substituted once, but in the
901 /// first case we do not increase the De Bruijn index and in the second case we do. The reason
902 /// is that only in the second case have we passed through a fn binder.
903 fn shift_vars_through_binders<T: TypeFoldable<'tcx>>(&self, val: T) -> T {
905 "shift_vars(val={:?}, binders_passed={:?}, has_escaping_bound_vars={:?})",
908 val.has_escaping_bound_vars()
911 if self.binders_passed == 0 || !val.has_escaping_bound_vars() {
915 let result = ty::fold::shift_vars(TypeFolder::tcx(self), val, self.binders_passed);
916 debug!("shift_vars: shifted result = {:?}", result);
921 fn shift_region_through_binders(&self, region: ty::Region<'tcx>) -> ty::Region<'tcx> {
922 if self.binders_passed == 0 || !region.has_escaping_bound_vars() {
925 ty::fold::shift_region(self.tcx, region, self.binders_passed)
929 /// Stores the user-given substs to reach some fully qualified path
930 /// (e.g., `<T>::Item` or `<T as Trait>::Item`).
931 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable)]
932 #[derive(HashStable, TypeFoldable, TypeVisitable, Lift)]
933 pub struct UserSubsts<'tcx> {
934 /// The substitutions for the item as given by the user.
935 pub substs: SubstsRef<'tcx>,
937 /// The self type, in the case of a `<T>::Item` path (when applied
938 /// to an inherent impl). See `UserSelfTy` below.
939 pub user_self_ty: Option<UserSelfTy<'tcx>>,
942 /// Specifies the user-given self type. In the case of a path that
943 /// refers to a member in an inherent impl, this self type is
944 /// sometimes needed to constrain the type parameters on the impl. For
945 /// example, in this code:
947 /// ```ignore (illustrative)
948 /// struct Foo<T> { }
949 /// impl<A> Foo<A> { fn method() { } }
952 /// when you then have a path like `<Foo<&'static u32>>::method`,
953 /// this struct would carry the `DefId` of the impl along with the
954 /// self type `Foo<u32>`. Then we can instantiate the parameters of
955 /// the impl (with the substs from `UserSubsts`) and apply those to
956 /// the self type, giving `Foo<?A>`. Finally, we unify that with
957 /// the self type here, which contains `?A` to be `&'static u32`
958 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable)]
959 #[derive(HashStable, TypeFoldable, TypeVisitable, Lift)]
960 pub struct UserSelfTy<'tcx> {
961 pub impl_def_id: DefId,
962 pub self_ty: Ty<'tcx>,