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_errors::{DiagnosticArgValue, IntoDiagnosticArg};
11 use rustc_hir::def_id::DefId;
12 use rustc_macros::HashStable;
13 use rustc_serialize::{self, Decodable, Encodable};
14 use rustc_type_ir::WithCachedTypeInfo;
15 use smallvec::SmallVec;
18 use std::cmp::Ordering;
20 use std::marker::PhantomData;
22 use std::num::NonZeroUsize;
23 use std::ops::{ControlFlow, Deref};
26 /// An entity in the Rust type system, which can be one of
27 /// several kinds (types, lifetimes, and consts).
28 /// To reduce memory usage, a `GenericArg` is an interned pointer,
29 /// with the lowest 2 bits being reserved for a tag to
30 /// indicate the type (`Ty`, `Region`, or `Const`) it points to.
32 /// Note: the `PartialEq`, `Eq` and `Hash` derives are only valid because `Ty`,
33 /// `Region` and `Const` are all interned.
34 #[derive(Copy, Clone, PartialEq, Eq, Hash)]
35 pub struct GenericArg<'tcx> {
37 marker: PhantomData<(Ty<'tcx>, ty::Region<'tcx>, ty::Const<'tcx>)>,
40 impl<'tcx> IntoDiagnosticArg for GenericArg<'tcx> {
41 fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
42 self.to_string().into_diagnostic_arg()
46 const TAG_MASK: usize = 0b11;
47 const TYPE_TAG: usize = 0b00;
48 const REGION_TAG: usize = 0b01;
49 const CONST_TAG: usize = 0b10;
51 #[derive(Debug, TyEncodable, TyDecodable, PartialEq, Eq, PartialOrd, Ord)]
52 pub enum GenericArgKind<'tcx> {
53 Lifetime(ty::Region<'tcx>),
55 Const(ty::Const<'tcx>),
58 /// This function goes from `&'a [Ty<'tcx>]` to `&'a [GenericArg<'tcx>]`
60 /// This is sound as, for types, `GenericArg` is just
61 /// `NonZeroUsize::new_unchecked(ty as *const _ as usize)` as
62 /// long as we use `0` for the `TYPE_TAG`.
63 pub fn ty_slice_as_generic_args<'a, 'tcx>(ts: &'a [Ty<'tcx>]) -> &'a [GenericArg<'tcx>] {
64 assert_eq!(TYPE_TAG, 0);
65 // SAFETY: the whole slice is valid and immutable.
66 // `Ty` and `GenericArg` is explained above.
67 unsafe { slice::from_raw_parts(ts.as_ptr().cast(), ts.len()) }
70 impl<'tcx> List<Ty<'tcx>> {
71 /// Allows to freely switch between `List<Ty<'tcx>>` and `List<GenericArg<'tcx>>`.
73 /// As lists are interned, `List<Ty<'tcx>>` and `List<GenericArg<'tcx>>` have
74 /// be interned together, see `intern_type_list` for more details.
76 pub fn as_substs(&'tcx self) -> SubstsRef<'tcx> {
77 assert_eq!(TYPE_TAG, 0);
78 // SAFETY: `List<T>` is `#[repr(C)]`. `Ty` and `GenericArg` is explained above.
79 unsafe { &*(self as *const List<Ty<'tcx>> as *const List<GenericArg<'tcx>>) }
83 impl<'tcx> GenericArgKind<'tcx> {
85 fn pack(self) -> GenericArg<'tcx> {
86 let (tag, ptr) = match self {
87 GenericArgKind::Lifetime(lt) => {
88 // Ensure we can use the tag bits.
89 assert_eq!(mem::align_of_val(&*lt.0.0) & TAG_MASK, 0);
90 (REGION_TAG, lt.0.0 as *const ty::RegionKind<'tcx> as usize)
92 GenericArgKind::Type(ty) => {
93 // Ensure we can use the tag bits.
94 assert_eq!(mem::align_of_val(&*ty.0.0) & TAG_MASK, 0);
95 (TYPE_TAG, ty.0.0 as *const WithCachedTypeInfo<ty::TyKind<'tcx>> as usize)
97 GenericArgKind::Const(ct) => {
98 // Ensure we can use the tag bits.
99 assert_eq!(mem::align_of_val(&*ct.0.0) & TAG_MASK, 0);
100 (CONST_TAG, ct.0.0 as *const ty::ConstData<'tcx> as usize)
104 GenericArg { ptr: unsafe { NonZeroUsize::new_unchecked(ptr | tag) }, marker: PhantomData }
108 impl<'tcx> fmt::Debug for GenericArg<'tcx> {
109 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
110 match self.unpack() {
111 GenericArgKind::Lifetime(lt) => lt.fmt(f),
112 GenericArgKind::Type(ty) => ty.fmt(f),
113 GenericArgKind::Const(ct) => ct.fmt(f),
118 impl<'tcx> Ord for GenericArg<'tcx> {
119 fn cmp(&self, other: &GenericArg<'tcx>) -> Ordering {
120 self.unpack().cmp(&other.unpack())
124 impl<'tcx> PartialOrd for GenericArg<'tcx> {
125 fn partial_cmp(&self, other: &GenericArg<'tcx>) -> Option<Ordering> {
126 Some(self.cmp(&other))
130 impl<'tcx> From<ty::Region<'tcx>> for GenericArg<'tcx> {
132 fn from(r: ty::Region<'tcx>) -> GenericArg<'tcx> {
133 GenericArgKind::Lifetime(r).pack()
137 impl<'tcx> From<Ty<'tcx>> for GenericArg<'tcx> {
139 fn from(ty: Ty<'tcx>) -> GenericArg<'tcx> {
140 GenericArgKind::Type(ty).pack()
144 impl<'tcx> From<ty::Const<'tcx>> for GenericArg<'tcx> {
146 fn from(c: ty::Const<'tcx>) -> GenericArg<'tcx> {
147 GenericArgKind::Const(c).pack()
151 impl<'tcx> From<ty::Term<'tcx>> for GenericArg<'tcx> {
152 fn from(value: ty::Term<'tcx>) -> Self {
153 match value.unpack() {
154 ty::TermKind::Ty(t) => t.into(),
155 ty::TermKind::Const(c) => c.into(),
160 impl<'tcx> GenericArg<'tcx> {
162 pub fn unpack(self) -> GenericArgKind<'tcx> {
163 let ptr = self.ptr.get();
164 // SAFETY: use of `Interned::new_unchecked` here is ok because these
165 // pointers were originally created from `Interned` types in `pack()`,
166 // and this is just going in the other direction.
168 match ptr & TAG_MASK {
169 REGION_TAG => GenericArgKind::Lifetime(ty::Region(Interned::new_unchecked(
170 &*((ptr & !TAG_MASK) as *const ty::RegionKind<'tcx>),
172 TYPE_TAG => GenericArgKind::Type(Ty(Interned::new_unchecked(
173 &*((ptr & !TAG_MASK) as *const WithCachedTypeInfo<ty::TyKind<'tcx>>),
175 CONST_TAG => GenericArgKind::Const(ty::Const(Interned::new_unchecked(
176 &*((ptr & !TAG_MASK) as *const ty::ConstData<'tcx>),
178 _ => intrinsics::unreachable(),
183 /// Unpack the `GenericArg` as a region when it is known certainly to be a region.
184 pub fn expect_region(self) -> ty::Region<'tcx> {
185 match self.unpack() {
186 GenericArgKind::Lifetime(lt) => lt,
187 _ => bug!("expected a region, but found another kind"),
191 /// Unpack the `GenericArg` as a type when it is known certainly to be a type.
192 /// This is true in cases where `Substs` is used in places where the kinds are known
193 /// to be limited (e.g. in tuples, where the only parameters are type parameters).
194 pub fn expect_ty(self) -> Ty<'tcx> {
195 match self.unpack() {
196 GenericArgKind::Type(ty) => ty,
197 _ => bug!("expected a type, but found another kind"),
201 /// Unpack the `GenericArg` as a const when it is known certainly to be a const.
202 pub fn expect_const(self) -> ty::Const<'tcx> {
203 match self.unpack() {
204 GenericArgKind::Const(c) => c,
205 _ => bug!("expected a const, but found another kind"),
209 pub fn is_non_region_infer(self) -> bool {
210 match self.unpack() {
211 GenericArgKind::Lifetime(_) => false,
212 GenericArgKind::Type(ty) => ty.is_ty_or_numeric_infer(),
213 GenericArgKind::Const(ct) => ct.is_ct_infer(),
218 impl<'a, 'tcx> Lift<'tcx> for GenericArg<'a> {
219 type Lifted = GenericArg<'tcx>;
221 fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
222 match self.unpack() {
223 GenericArgKind::Lifetime(lt) => tcx.lift(lt).map(|lt| lt.into()),
224 GenericArgKind::Type(ty) => tcx.lift(ty).map(|ty| ty.into()),
225 GenericArgKind::Const(ct) => tcx.lift(ct).map(|ct| ct.into()),
230 impl<'tcx> TypeFoldable<'tcx> for GenericArg<'tcx> {
231 fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
232 match self.unpack() {
233 GenericArgKind::Lifetime(lt) => lt.try_fold_with(folder).map(Into::into),
234 GenericArgKind::Type(ty) => ty.try_fold_with(folder).map(Into::into),
235 GenericArgKind::Const(ct) => ct.try_fold_with(folder).map(Into::into),
240 impl<'tcx> TypeVisitable<'tcx> for GenericArg<'tcx> {
241 fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
242 match self.unpack() {
243 GenericArgKind::Lifetime(lt) => lt.visit_with(visitor),
244 GenericArgKind::Type(ty) => ty.visit_with(visitor),
245 GenericArgKind::Const(ct) => ct.visit_with(visitor),
250 impl<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<E> for GenericArg<'tcx> {
251 fn encode(&self, e: &mut E) {
252 self.unpack().encode(e)
256 impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for GenericArg<'tcx> {
257 fn decode(d: &mut D) -> GenericArg<'tcx> {
258 GenericArgKind::decode(d).pack()
262 /// List of generic arguments that are gonna be used to substitute generic parameters.
263 pub type InternalSubsts<'tcx> = List<GenericArg<'tcx>>;
265 pub type SubstsRef<'tcx> = &'tcx InternalSubsts<'tcx>;
267 impl<'tcx> InternalSubsts<'tcx> {
268 /// Checks whether all elements of this list are types, if so, transmute.
269 pub fn try_as_type_list(&'tcx self) -> Option<&'tcx List<Ty<'tcx>>> {
270 if self.iter().all(|arg| matches!(arg.unpack(), GenericArgKind::Type(_))) {
271 assert_eq!(TYPE_TAG, 0);
272 // SAFETY: All elements are types, see `List<Ty<'tcx>>::as_substs`.
273 Some(unsafe { &*(self as *const List<GenericArg<'tcx>> as *const List<Ty<'tcx>>) })
279 /// Interpret these substitutions as the substitutions of a closure type.
280 /// Closure substitutions have a particular structure controlled by the
281 /// compiler that encodes information like the signature and closure kind;
282 /// see `ty::ClosureSubsts` struct for more comments.
283 pub fn as_closure(&'tcx self) -> ClosureSubsts<'tcx> {
284 ClosureSubsts { substs: self }
287 /// Interpret these substitutions as the substitutions of a generator type.
288 /// Generator substitutions have a particular structure controlled by the
289 /// compiler that encodes information like the signature and generator kind;
290 /// see `ty::GeneratorSubsts` struct for more comments.
291 pub fn as_generator(&'tcx self) -> GeneratorSubsts<'tcx> {
292 GeneratorSubsts { substs: self }
295 /// Interpret these substitutions as the substitutions of an inline const.
296 /// Inline const substitutions have a particular structure controlled by the
297 /// compiler that encodes information like the inferred type;
298 /// see `ty::InlineConstSubsts` struct for more comments.
299 pub fn as_inline_const(&'tcx self) -> InlineConstSubsts<'tcx> {
300 InlineConstSubsts { substs: self }
303 /// Creates an `InternalSubsts` that maps each generic parameter to itself.
304 pub fn identity_for_item(tcx: TyCtxt<'tcx>, def_id: DefId) -> SubstsRef<'tcx> {
305 Self::for_item(tcx, def_id, |param, _| tcx.mk_param_from_def(param))
308 /// Creates an `InternalSubsts` for generic parameter definitions,
309 /// by calling closures to obtain each kind.
310 /// The closures get to observe the `InternalSubsts` as they're
311 /// being built, which can be used to correctly
312 /// substitute defaults of generic parameters.
313 pub fn for_item<F>(tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx>
315 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
317 let defs = tcx.generics_of(def_id);
318 let count = defs.count();
319 let mut substs = SmallVec::with_capacity(count);
320 Self::fill_item(&mut substs, tcx, defs, &mut mk_kind);
321 tcx.intern_substs(&substs)
324 pub fn extend_to<F>(&self, tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx>
326 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
328 Self::for_item(tcx, def_id, |param, substs| {
329 self.get(param.index as usize).cloned().unwrap_or_else(|| mk_kind(param, substs))
334 substs: &mut SmallVec<[GenericArg<'tcx>; 8]>,
339 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
341 if let Some(def_id) = defs.parent {
342 let parent_defs = tcx.generics_of(def_id);
343 Self::fill_item(substs, tcx, parent_defs, mk_kind);
345 Self::fill_single(substs, defs, mk_kind)
348 pub fn fill_single<F>(
349 substs: &mut SmallVec<[GenericArg<'tcx>; 8]>,
353 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
355 substs.reserve(defs.params.len());
356 for param in &defs.params {
357 let kind = mk_kind(param, substs);
358 assert_eq!(param.index as usize, substs.len(), "{substs:#?}, {defs:#?}");
363 // Extend an `original_substs` list to the full number of substs expected by `def_id`,
364 // filling in the missing parameters with error ty/ct or 'static regions.
365 pub fn extend_with_error(
368 original_substs: &[GenericArg<'tcx>],
369 ) -> SubstsRef<'tcx> {
370 ty::InternalSubsts::for_item(tcx, def_id, |def, substs| {
371 if let Some(subst) = original_substs.get(def.index as usize) {
374 def.to_error(tcx, substs)
380 pub fn types(&'tcx self) -> impl DoubleEndedIterator<Item = Ty<'tcx>> + 'tcx {
382 .filter_map(|k| if let GenericArgKind::Type(ty) = k.unpack() { Some(ty) } else { None })
386 pub fn regions(&'tcx self) -> impl DoubleEndedIterator<Item = ty::Region<'tcx>> + 'tcx {
387 self.iter().filter_map(|k| {
388 if let GenericArgKind::Lifetime(lt) = k.unpack() { Some(lt) } else { None }
393 pub fn consts(&'tcx self) -> impl DoubleEndedIterator<Item = ty::Const<'tcx>> + 'tcx {
394 self.iter().filter_map(|k| {
395 if let GenericArgKind::Const(ct) = k.unpack() { Some(ct) } else { None }
400 pub fn non_erasable_generics(
402 ) -> impl DoubleEndedIterator<Item = GenericArgKind<'tcx>> + 'tcx {
403 self.iter().filter_map(|k| match k.unpack() {
404 GenericArgKind::Lifetime(_) => None,
405 generic => Some(generic),
411 pub fn type_at(&self, i: usize) -> Ty<'tcx> {
412 if let GenericArgKind::Type(ty) = self[i].unpack() {
415 bug!("expected type for param #{} in {:?}", i, self);
421 pub fn region_at(&self, i: usize) -> ty::Region<'tcx> {
422 if let GenericArgKind::Lifetime(lt) = self[i].unpack() {
425 bug!("expected region for param #{} in {:?}", i, self);
431 pub fn const_at(&self, i: usize) -> ty::Const<'tcx> {
432 if let GenericArgKind::Const(ct) = self[i].unpack() {
435 bug!("expected const for param #{} in {:?}", i, self);
441 pub fn type_for_def(&self, def: &ty::GenericParamDef) -> GenericArg<'tcx> {
442 self.type_at(def.index as usize).into()
445 /// Transform from substitutions for a child of `source_ancestor`
446 /// (e.g., a trait or impl) to substitutions for the same child
447 /// in a different item, with `target_substs` as the base for
448 /// the target impl/trait, with the source child-specific
449 /// parameters (e.g., method parameters) on top of that base.
451 /// For example given:
454 /// trait X<S> { fn f<T>(); }
455 /// impl<U> X<U> for U { fn f<V>() {} }
458 /// * If `self` is `[Self, S, T]`: the identity substs of `f` in the trait.
459 /// * If `source_ancestor` is the def_id of the trait.
460 /// * If `target_substs` is `[U]`, the substs for the impl.
461 /// * Then we will return `[U, T]`, the subst for `f` in the impl that
462 /// are needed for it to match the trait.
466 source_ancestor: DefId,
467 target_substs: SubstsRef<'tcx>,
468 ) -> SubstsRef<'tcx> {
469 let defs = tcx.generics_of(source_ancestor);
470 tcx.mk_substs(target_substs.iter().chain(self.iter().skip(defs.params.len())))
473 pub fn truncate_to(&self, tcx: TyCtxt<'tcx>, generics: &ty::Generics) -> SubstsRef<'tcx> {
474 tcx.mk_substs(self.iter().take(generics.count()))
478 impl<'tcx> TypeFoldable<'tcx> for SubstsRef<'tcx> {
479 fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
480 // This code is hot enough that it's worth specializing for the most
481 // common length lists, to avoid the overhead of `SmallVec` creation.
482 // The match arms are in order of frequency. The 1, 2, and 0 cases are
483 // typically hit in 90--99.99% of cases. When folding doesn't change
484 // the substs, it's faster to reuse the existing substs rather than
485 // calling `intern_substs`.
488 let param0 = self[0].try_fold_with(folder)?;
489 if param0 == self[0] { Ok(self) } else { Ok(folder.tcx().intern_substs(&[param0])) }
492 let param0 = self[0].try_fold_with(folder)?;
493 let param1 = self[1].try_fold_with(folder)?;
494 if param0 == self[0] && param1 == self[1] {
497 Ok(folder.tcx().intern_substs(&[param0, param1]))
501 _ => ty::util::fold_list(self, folder, |tcx, v| tcx.intern_substs(v)),
506 impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<Ty<'tcx>> {
507 fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
508 // This code is fairly hot, though not as hot as `SubstsRef`.
510 // When compiling stage 2, I get the following results:
513 // --- | --------- | -----
514 // 2 | 15083590 | 48.1
515 // 3 | 7540067 | 24.0
516 // 1 | 5300377 | 16.9
520 // I've tried it with some private repositories and got
521 // close to the same result, with 4 and 0 swapping places
525 let param0 = self[0].try_fold_with(folder)?;
526 let param1 = self[1].try_fold_with(folder)?;
527 if param0 == self[0] && param1 == self[1] {
530 Ok(folder.tcx().intern_type_list(&[param0, param1]))
533 _ => ty::util::fold_list(self, folder, |tcx, v| tcx.intern_type_list(v)),
538 impl<'tcx, T: TypeVisitable<'tcx>> TypeVisitable<'tcx> for &'tcx ty::List<T> {
540 fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
541 self.iter().try_for_each(|t| t.visit_with(visitor))
545 /// Similar to [`super::Binder`] except that it tracks early bound generics, i.e. `struct Foo<T>(T)`
546 /// needs `T` substituted immediately. This type primarily exists to avoid forgetting to call
549 /// If you don't have anything to `subst`, you may be looking for
550 /// [`subst_identity`](EarlyBinder::subst_identity) or [`skip_binder`](EarlyBinder::skip_binder).
551 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
552 #[derive(Encodable, Decodable, HashStable)]
553 pub struct EarlyBinder<T>(pub T);
555 /// For early binders, you should first call `subst` before using any visitors.
556 impl<'tcx, T> !TypeFoldable<'tcx> for ty::EarlyBinder<T> {}
557 impl<'tcx, T> !TypeVisitable<'tcx> for ty::EarlyBinder<T> {}
559 impl<T> EarlyBinder<T> {
560 pub fn as_ref(&self) -> EarlyBinder<&T> {
564 pub fn map_bound_ref<F, U>(&self, f: F) -> EarlyBinder<U>
568 self.as_ref().map_bound(f)
571 pub fn map_bound<F, U>(self, f: F) -> EarlyBinder<U>
575 let value = f(self.0);
579 pub fn try_map_bound<F, U, E>(self, f: F) -> Result<EarlyBinder<U>, E>
581 F: FnOnce(T) -> Result<U, E>,
583 let value = f(self.0)?;
584 Ok(EarlyBinder(value))
587 pub fn rebind<U>(&self, value: U) -> EarlyBinder<U> {
591 /// Skips the binder and returns the "bound" value.
592 /// This can be used to extract data that does not depend on generic parameters
593 /// (e.g., getting the `DefId` of the inner value or getting the number of
594 /// arguments of an `FnSig`). Otherwise, consider using
595 /// [`subst_identity`](EarlyBinder::subst_identity).
597 /// See also [`Binder::skip_binder`](super::Binder::skip_binder), which is
598 /// the analogous operation on [`super::Binder`].
599 pub fn skip_binder(self) -> T {
604 impl<T> EarlyBinder<Option<T>> {
605 pub fn transpose(self) -> Option<EarlyBinder<T>> {
606 self.0.map(|v| EarlyBinder(v))
610 impl<T, U> EarlyBinder<(T, U)> {
611 pub fn transpose_tuple2(self) -> (EarlyBinder<T>, EarlyBinder<U>) {
612 (EarlyBinder(self.0.0), EarlyBinder(self.0.1))
616 impl<'tcx, 's, I: IntoIterator> EarlyBinder<I>
618 I::Item: TypeFoldable<'tcx>,
623 substs: &'s [GenericArg<'tcx>],
624 ) -> SubstIter<'s, 'tcx, I> {
625 SubstIter { it: self.0.into_iter(), tcx, substs }
629 pub struct SubstIter<'s, 'tcx, I: IntoIterator> {
632 substs: &'s [GenericArg<'tcx>],
635 impl<'tcx, I: IntoIterator> Iterator for SubstIter<'_, 'tcx, I>
637 I::Item: TypeFoldable<'tcx>,
641 fn next(&mut self) -> Option<Self::Item> {
642 Some(EarlyBinder(self.it.next()?).subst(self.tcx, self.substs))
645 fn size_hint(&self) -> (usize, Option<usize>) {
650 impl<'tcx, I: IntoIterator> DoubleEndedIterator for SubstIter<'_, 'tcx, I>
652 I::IntoIter: DoubleEndedIterator,
653 I::Item: TypeFoldable<'tcx>,
655 fn next_back(&mut self) -> Option<Self::Item> {
656 Some(EarlyBinder(self.it.next_back()?).subst(self.tcx, self.substs))
660 impl<'tcx, I: IntoIterator> ExactSizeIterator for SubstIter<'_, 'tcx, I>
662 I::IntoIter: ExactSizeIterator,
663 I::Item: TypeFoldable<'tcx>,
667 impl<'tcx, 's, I: IntoIterator> EarlyBinder<I>
670 <I::Item as Deref>::Target: Copy + TypeFoldable<'tcx>,
672 pub fn subst_iter_copied(
675 substs: &'s [GenericArg<'tcx>],
676 ) -> SubstIterCopied<'s, 'tcx, I> {
677 SubstIterCopied { it: self.0.into_iter(), tcx, substs }
681 pub struct SubstIterCopied<'a, 'tcx, I: IntoIterator> {
684 substs: &'a [GenericArg<'tcx>],
687 impl<'tcx, I: IntoIterator> Iterator for SubstIterCopied<'_, 'tcx, I>
690 <I::Item as Deref>::Target: Copy + TypeFoldable<'tcx>,
692 type Item = <I::Item as Deref>::Target;
694 fn next(&mut self) -> Option<Self::Item> {
695 Some(EarlyBinder(*self.it.next()?).subst(self.tcx, self.substs))
698 fn size_hint(&self) -> (usize, Option<usize>) {
703 impl<'tcx, I: IntoIterator> DoubleEndedIterator for SubstIterCopied<'_, 'tcx, I>
705 I::IntoIter: DoubleEndedIterator,
707 <I::Item as Deref>::Target: Copy + TypeFoldable<'tcx>,
709 fn next_back(&mut self) -> Option<Self::Item> {
710 Some(EarlyBinder(*self.it.next_back()?).subst(self.tcx, self.substs))
714 impl<'tcx, I: IntoIterator> ExactSizeIterator for SubstIterCopied<'_, 'tcx, I>
716 I::IntoIter: ExactSizeIterator,
718 <I::Item as Deref>::Target: Copy + TypeFoldable<'tcx>,
722 pub struct EarlyBinderIter<T> {
726 impl<T: IntoIterator> EarlyBinder<T> {
727 pub fn transpose_iter(self) -> EarlyBinderIter<T::IntoIter> {
728 EarlyBinderIter { t: self.0.into_iter() }
732 impl<T: Iterator> Iterator for EarlyBinderIter<T> {
733 type Item = EarlyBinder<T::Item>;
735 fn next(&mut self) -> Option<Self::Item> {
736 self.t.next().map(|i| EarlyBinder(i))
739 fn size_hint(&self) -> (usize, Option<usize>) {
744 impl<'tcx, T: TypeFoldable<'tcx>> ty::EarlyBinder<T> {
745 pub fn subst(self, tcx: TyCtxt<'tcx>, substs: &[GenericArg<'tcx>]) -> T {
746 let mut folder = SubstFolder { tcx, substs, binders_passed: 0 };
747 self.0.fold_with(&mut folder)
750 /// Makes the identity substitution `T0 => T0, ..., TN => TN`.
751 /// Conceptually, this converts universally bound variables into placeholders
752 /// when inside of a given item.
754 /// For example, consider `for<T> fn foo<T>(){ .. }`:
755 /// - Outside of `foo`, `T` is bound (represented by the presence of `EarlyBinder`).
756 /// - Inside of the body of `foo`, we treat `T` as a placeholder by calling
757 /// `subst_identity` to discharge the `EarlyBinder`.
758 pub fn subst_identity(self) -> T {
762 /// Returns the inner value, but only if it contains no bound vars.
763 pub fn no_bound_vars(self) -> Option<T> {
764 if !self.0.needs_subst() { Some(self.0) } else { None }
768 ///////////////////////////////////////////////////////////////////////////
769 // The actual substitution engine itself is a type folder.
771 struct SubstFolder<'a, 'tcx> {
773 substs: &'a [GenericArg<'tcx>],
775 /// Number of region binders we have passed through while doing the substitution
779 impl<'a, 'tcx> TypeFolder<'tcx> for SubstFolder<'a, 'tcx> {
781 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
785 fn fold_binder<T: TypeFoldable<'tcx>>(
787 t: ty::Binder<'tcx, T>,
788 ) -> ty::Binder<'tcx, T> {
789 self.binders_passed += 1;
790 let t = t.super_fold_with(self);
791 self.binders_passed -= 1;
795 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
798 fn region_param_out_of_range(data: ty::EarlyBoundRegion, substs: &[GenericArg<'_>]) -> ! {
800 "Region parameter out of range when substituting in region {} (index={}, substs = {:?})",
809 fn region_param_invalid(data: ty::EarlyBoundRegion, other: GenericArgKind<'_>) -> ! {
811 "Unexpected parameter {:?} when substituting in region {} (index={})",
818 // Note: This routine only handles regions that are bound on
819 // type declarations and other outer declarations, not those
820 // bound in *fn types*. Region substitution of the bound
821 // regions that appear in a function signature is done using
822 // the specialized routine `ty::replace_late_regions()`.
824 ty::ReEarlyBound(data) => {
825 let rk = self.substs.get(data.index as usize).map(|k| k.unpack());
827 Some(GenericArgKind::Lifetime(lt)) => self.shift_region_through_binders(lt),
828 Some(other) => region_param_invalid(data, other),
829 None => region_param_out_of_range(data, self.substs),
836 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
837 if !t.needs_subst() {
842 ty::Param(p) => self.ty_for_param(p, t),
843 _ => t.super_fold_with(self),
847 fn fold_const(&mut self, c: ty::Const<'tcx>) -> ty::Const<'tcx> {
848 if let ty::ConstKind::Param(p) = c.kind() {
849 self.const_for_param(p, c)
851 c.super_fold_with(self)
856 impl<'a, 'tcx> SubstFolder<'a, 'tcx> {
857 fn ty_for_param(&self, p: ty::ParamTy, source_ty: Ty<'tcx>) -> Ty<'tcx> {
858 // Look up the type in the substitutions. It really should be in there.
859 let opt_ty = self.substs.get(p.index as usize).map(|k| k.unpack());
860 let ty = match opt_ty {
861 Some(GenericArgKind::Type(ty)) => ty,
862 Some(kind) => self.type_param_expected(p, source_ty, kind),
863 None => self.type_param_out_of_range(p, source_ty),
866 self.shift_vars_through_binders(ty)
871 fn type_param_expected(&self, p: ty::ParamTy, ty: Ty<'tcx>, kind: GenericArgKind<'tcx>) -> ! {
873 "expected type for `{:?}` ({:?}/{}) but found {:?} when substituting, substs={:?}",
884 fn type_param_out_of_range(&self, p: ty::ParamTy, ty: Ty<'tcx>) -> ! {
886 "type parameter `{:?}` ({:?}/{}) out of range when substituting, substs={:?}",
894 fn const_for_param(&self, p: ParamConst, source_ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
895 // Look up the const in the substitutions. It really should be in there.
896 let opt_ct = self.substs.get(p.index as usize).map(|k| k.unpack());
897 let ct = match opt_ct {
898 Some(GenericArgKind::Const(ct)) => ct,
899 Some(kind) => self.const_param_expected(p, source_ct, kind),
900 None => self.const_param_out_of_range(p, source_ct),
903 self.shift_vars_through_binders(ct)
908 fn const_param_expected(
912 kind: GenericArgKind<'tcx>,
915 "expected const for `{:?}` ({:?}/{}) but found {:?} when substituting substs={:?}",
926 fn const_param_out_of_range(&self, p: ty::ParamConst, ct: ty::Const<'tcx>) -> ! {
928 "const parameter `{:?}` ({:?}/{}) out of range when substituting substs={:?}",
936 /// It is sometimes necessary to adjust the De Bruijn indices during substitution. This occurs
937 /// when we are substituting a type with escaping bound vars into a context where we have
938 /// passed through binders. That's quite a mouthful. Let's see an example:
941 /// type Func<A> = fn(A);
942 /// type MetaFunc = for<'a> fn(Func<&'a i32>);
945 /// The type `MetaFunc`, when fully expanded, will be
946 /// ```ignore (illustrative)
947 /// for<'a> fn(fn(&'a i32))
950 /// // | | DebruijnIndex of 2
953 /// Here the `'a` lifetime is bound in the outer function, but appears as an argument of the
954 /// inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip
955 /// over the inner binder (remember that we count De Bruijn indices from 1). However, in the
956 /// definition of `MetaFunc`, the binder is not visible, so the type `&'a i32` will have a
957 /// De Bruijn index of 1. It's only during the substitution that we can see we must increase the
958 /// depth by 1 to account for the binder that we passed through.
960 /// As a second example, consider this twist:
963 /// type FuncTuple<A> = (A,fn(A));
964 /// type MetaFuncTuple = for<'a> fn(FuncTuple<&'a i32>);
967 /// Here the final type will be:
968 /// ```ignore (illustrative)
969 /// for<'a> fn((&'a i32, fn(&'a i32)))
972 /// // DebruijnIndex of 1 |
973 /// // DebruijnIndex of 2
975 /// As indicated in the diagram, here the same type `&'a i32` is substituted once, but in the
976 /// first case we do not increase the De Bruijn index and in the second case we do. The reason
977 /// is that only in the second case have we passed through a fn binder.
978 fn shift_vars_through_binders<T: TypeFoldable<'tcx>>(&self, val: T) -> T {
980 "shift_vars(val={:?}, binders_passed={:?}, has_escaping_bound_vars={:?})",
983 val.has_escaping_bound_vars()
986 if self.binders_passed == 0 || !val.has_escaping_bound_vars() {
990 let result = ty::fold::shift_vars(TypeFolder::tcx(self), val, self.binders_passed);
991 debug!("shift_vars: shifted result = {:?}", result);
996 fn shift_region_through_binders(&self, region: ty::Region<'tcx>) -> ty::Region<'tcx> {
997 if self.binders_passed == 0 || !region.has_escaping_bound_vars() {
1000 ty::fold::shift_region(self.tcx, region, self.binders_passed)
1004 /// Stores the user-given substs to reach some fully qualified path
1005 /// (e.g., `<T>::Item` or `<T as Trait>::Item`).
1006 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable)]
1007 #[derive(HashStable, TypeFoldable, TypeVisitable, Lift)]
1008 pub struct UserSubsts<'tcx> {
1009 /// The substitutions for the item as given by the user.
1010 pub substs: SubstsRef<'tcx>,
1012 /// The self type, in the case of a `<T>::Item` path (when applied
1013 /// to an inherent impl). See `UserSelfTy` below.
1014 pub user_self_ty: Option<UserSelfTy<'tcx>>,
1017 /// Specifies the user-given self type. In the case of a path that
1018 /// refers to a member in an inherent impl, this self type is
1019 /// sometimes needed to constrain the type parameters on the impl. For
1020 /// example, in this code:
1022 /// ```ignore (illustrative)
1023 /// struct Foo<T> { }
1024 /// impl<A> Foo<A> { fn method() { } }
1027 /// when you then have a path like `<Foo<&'static u32>>::method`,
1028 /// this struct would carry the `DefId` of the impl along with the
1029 /// self type `Foo<u32>`. Then we can instantiate the parameters of
1030 /// the impl (with the substs from `UserSubsts`) and apply those to
1031 /// the self type, giving `Foo<?A>`. Finally, we unify that with
1032 /// the self type here, which contains `?A` to be `&'static u32`
1033 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable)]
1034 #[derive(HashStable, TypeFoldable, TypeVisitable, Lift)]
1035 pub struct UserSelfTy<'tcx> {
1036 pub impl_def_id: DefId,
1037 pub self_ty: Ty<'tcx>,