4 use crate::ty::codec::{TyDecoder, TyEncoder};
5 use crate::ty::fold::{FallibleTypeFolder, TypeFoldable, TypeFolder, TypeVisitor};
6 use crate::ty::sty::{ClosureSubsts, GeneratorSubsts, InlineConstSubsts};
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 rustc_span::{Span, DUMMY_SP};
14 use smallvec::SmallVec;
17 use std::cmp::Ordering;
19 use std::marker::PhantomData;
21 use std::num::NonZeroUsize;
22 use std::ops::ControlFlow;
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 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 WithStableHash<ty::TyS<'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::ConstS<'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<'_>) -> Ordering {
113 self.unpack().cmp(&other.unpack())
117 impl<'tcx> PartialOrd for GenericArg<'tcx> {
118 fn partial_cmp(&self, other: &GenericArg<'_>) -> 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> GenericArg<'tcx> {
146 pub fn unpack(self) -> GenericArgKind<'tcx> {
147 let ptr = self.ptr.get();
148 // SAFETY: use of `Interned::new_unchecked` here is ok because these
149 // pointers were originally created from `Interned` types in `pack()`,
150 // and this is just going in the other direction.
152 match ptr & TAG_MASK {
153 REGION_TAG => GenericArgKind::Lifetime(ty::Region(Interned::new_unchecked(
154 &*((ptr & !TAG_MASK) as *const ty::RegionKind),
156 TYPE_TAG => GenericArgKind::Type(Ty(Interned::new_unchecked(
157 &*((ptr & !TAG_MASK) as *const WithStableHash<ty::TyS<'tcx>>),
159 CONST_TAG => GenericArgKind::Const(ty::Const(Interned::new_unchecked(
160 &*((ptr & !TAG_MASK) as *const ty::ConstS<'tcx>),
162 _ => intrinsics::unreachable(),
167 /// Unpack the `GenericArg` as a type when it is known certainly to be a type.
168 /// This is true in cases where `Substs` is used in places where the kinds are known
169 /// to be limited (e.g. in tuples, where the only parameters are type parameters).
170 pub fn expect_ty(self) -> Ty<'tcx> {
171 match self.unpack() {
172 GenericArgKind::Type(ty) => ty,
173 _ => bug!("expected a type, but found another kind"),
177 /// Unpack the `GenericArg` as a const when it is known certainly to be a const.
178 pub fn expect_const(self) -> ty::Const<'tcx> {
179 match self.unpack() {
180 GenericArgKind::Const(c) => c,
181 _ => bug!("expected a const, but found another kind"),
186 impl<'a, 'tcx> Lift<'tcx> for GenericArg<'a> {
187 type Lifted = GenericArg<'tcx>;
189 fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
190 match self.unpack() {
191 GenericArgKind::Lifetime(lt) => tcx.lift(lt).map(|lt| lt.into()),
192 GenericArgKind::Type(ty) => tcx.lift(ty).map(|ty| ty.into()),
193 GenericArgKind::Const(ct) => tcx.lift(ct).map(|ct| ct.into()),
198 impl<'tcx> TypeFoldable<'tcx> for GenericArg<'tcx> {
199 fn try_super_fold_with<F: FallibleTypeFolder<'tcx>>(
202 ) -> Result<Self, F::Error> {
203 match self.unpack() {
204 GenericArgKind::Lifetime(lt) => lt.try_fold_with(folder).map(Into::into),
205 GenericArgKind::Type(ty) => ty.try_fold_with(folder).map(Into::into),
206 GenericArgKind::Const(ct) => ct.try_fold_with(folder).map(Into::into),
210 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
211 match self.unpack() {
212 GenericArgKind::Lifetime(lt) => lt.visit_with(visitor),
213 GenericArgKind::Type(ty) => ty.visit_with(visitor),
214 GenericArgKind::Const(ct) => ct.visit_with(visitor),
219 impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for GenericArg<'tcx> {
220 fn encode(&self, e: &mut E) -> Result<(), E::Error> {
221 self.unpack().encode(e)
225 impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for GenericArg<'tcx> {
226 fn decode(d: &mut D) -> GenericArg<'tcx> {
227 GenericArgKind::decode(d).pack()
231 /// A substitution mapping generic parameters to new values.
232 pub type InternalSubsts<'tcx> = List<GenericArg<'tcx>>;
234 pub type SubstsRef<'tcx> = &'tcx InternalSubsts<'tcx>;
236 impl<'a, 'tcx> InternalSubsts<'tcx> {
237 /// Checks whether all elements of this list are types, if so, transmute.
238 pub fn try_as_type_list(&'tcx self) -> Option<&'tcx List<Ty<'tcx>>> {
239 if self.iter().all(|arg| matches!(arg.unpack(), GenericArgKind::Type(_))) {
240 assert_eq!(TYPE_TAG, 0);
241 // SAFETY: All elements are types, see `List<Ty<'tcx>>::as_substs`.
242 Some(unsafe { &*(self as *const List<GenericArg<'tcx>> as *const List<Ty<'tcx>>) })
248 /// Interpret these substitutions as the substitutions of a closure type.
249 /// Closure substitutions have a particular structure controlled by the
250 /// compiler that encodes information like the signature and closure kind;
251 /// see `ty::ClosureSubsts` struct for more comments.
252 pub fn as_closure(&'a self) -> ClosureSubsts<'a> {
253 ClosureSubsts { substs: self }
256 /// Interpret these substitutions as the substitutions of a generator type.
257 /// Generator substitutions have a particular structure controlled by the
258 /// compiler that encodes information like the signature and generator kind;
259 /// see `ty::GeneratorSubsts` struct for more comments.
260 pub fn as_generator(&'tcx self) -> GeneratorSubsts<'tcx> {
261 GeneratorSubsts { substs: self }
264 /// Interpret these substitutions as the substitutions of an inline const.
265 /// Inline const substitutions have a particular structure controlled by the
266 /// compiler that encodes information like the inferred type;
267 /// see `ty::InlineConstSubsts` struct for more comments.
268 pub fn as_inline_const(&'tcx self) -> InlineConstSubsts<'tcx> {
269 InlineConstSubsts { substs: self }
272 /// Creates an `InternalSubsts` that maps each generic parameter to itself.
273 pub fn identity_for_item(tcx: TyCtxt<'tcx>, def_id: DefId) -> SubstsRef<'tcx> {
274 Self::for_item(tcx, def_id, |param, _| tcx.mk_param_from_def(param))
277 /// Creates an `InternalSubsts` for generic parameter definitions,
278 /// by calling closures to obtain each kind.
279 /// The closures get to observe the `InternalSubsts` as they're
280 /// being built, which can be used to correctly
281 /// substitute defaults of generic parameters.
282 pub fn for_item<F>(tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx>
284 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
286 let defs = tcx.generics_of(def_id);
287 let count = defs.count();
288 let mut substs = SmallVec::with_capacity(count);
289 Self::fill_item(&mut substs, tcx, defs, &mut mk_kind);
290 tcx.intern_substs(&substs)
293 pub fn extend_to<F>(&self, tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx>
295 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
297 Self::for_item(tcx, def_id, |param, substs| {
298 self.get(param.index as usize).cloned().unwrap_or_else(|| mk_kind(param, substs))
303 substs: &mut SmallVec<[GenericArg<'tcx>; 8]>,
308 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
310 if let Some(def_id) = defs.parent {
311 let parent_defs = tcx.generics_of(def_id);
312 Self::fill_item(substs, tcx, parent_defs, mk_kind);
314 Self::fill_single(substs, defs, mk_kind)
317 pub fn fill_single<F>(
318 substs: &mut SmallVec<[GenericArg<'tcx>; 8]>,
322 F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>,
324 substs.reserve(defs.params.len());
325 for param in &defs.params {
326 let kind = mk_kind(param, substs);
327 assert_eq!(param.index as usize, substs.len());
333 pub fn types(&'a self) -> impl DoubleEndedIterator<Item = Ty<'tcx>> + 'a {
335 .filter_map(|k| if let GenericArgKind::Type(ty) = k.unpack() { Some(ty) } else { None })
339 pub fn regions(&'a self) -> impl DoubleEndedIterator<Item = ty::Region<'tcx>> + 'a {
340 self.iter().filter_map(|k| {
341 if let GenericArgKind::Lifetime(lt) = k.unpack() { Some(lt) } else { None }
346 pub fn consts(&'a self) -> impl DoubleEndedIterator<Item = ty::Const<'tcx>> + 'a {
347 self.iter().filter_map(|k| {
348 if let GenericArgKind::Const(ct) = k.unpack() { Some(ct) } else { None }
353 pub fn non_erasable_generics(
355 ) -> impl DoubleEndedIterator<Item = GenericArgKind<'tcx>> + 'a {
356 self.iter().filter_map(|k| match k.unpack() {
357 GenericArgKind::Lifetime(_) => None,
358 generic => Some(generic),
363 pub fn type_at(&self, i: usize) -> Ty<'tcx> {
364 if let GenericArgKind::Type(ty) = self[i].unpack() {
367 bug!("expected type for param #{} in {:?}", i, self);
372 pub fn region_at(&self, i: usize) -> ty::Region<'tcx> {
373 if let GenericArgKind::Lifetime(lt) = self[i].unpack() {
376 bug!("expected region for param #{} in {:?}", i, self);
381 pub fn const_at(&self, i: usize) -> ty::Const<'tcx> {
382 if let GenericArgKind::Const(ct) = self[i].unpack() {
385 bug!("expected const for param #{} in {:?}", i, self);
390 pub fn type_for_def(&self, def: &ty::GenericParamDef) -> GenericArg<'tcx> {
391 self.type_at(def.index as usize).into()
394 /// Transform from substitutions for a child of `source_ancestor`
395 /// (e.g., a trait or impl) to substitutions for the same child
396 /// in a different item, with `target_substs` as the base for
397 /// the target impl/trait, with the source child-specific
398 /// parameters (e.g., method parameters) on top of that base.
400 /// For example given:
403 /// trait X<S> { fn f<T>(); }
404 /// impl<U> X<U> for U { fn f<V>() {} }
407 /// * If `self` is `[Self, S, T]`: the identity substs of `f` in the trait.
408 /// * If `source_ancestor` is the def_id of the trait.
409 /// * If `target_substs` is `[U]`, the substs for the impl.
410 /// * Then we will return `[U, T]`, the subst for `f` in the impl that
411 /// are needed for it to match the trait.
415 source_ancestor: DefId,
416 target_substs: SubstsRef<'tcx>,
417 ) -> SubstsRef<'tcx> {
418 let defs = tcx.generics_of(source_ancestor);
419 tcx.mk_substs(target_substs.iter().chain(self.iter().skip(defs.params.len())))
422 pub fn truncate_to(&self, tcx: TyCtxt<'tcx>, generics: &ty::Generics) -> SubstsRef<'tcx> {
423 tcx.mk_substs(self.iter().take(generics.count()))
427 impl<'tcx> TypeFoldable<'tcx> for SubstsRef<'tcx> {
428 fn try_super_fold_with<F: FallibleTypeFolder<'tcx>>(
431 ) -> Result<Self, F::Error> {
432 // This code is hot enough that it's worth specializing for the most
433 // common length lists, to avoid the overhead of `SmallVec` creation.
434 // The match arms are in order of frequency. The 1, 2, and 0 cases are
435 // typically hit in 90--99.99% of cases. When folding doesn't change
436 // the substs, it's faster to reuse the existing substs rather than
437 // calling `intern_substs`.
440 let param0 = self[0].try_fold_with(folder)?;
441 if param0 == self[0] { Ok(self) } else { Ok(folder.tcx().intern_substs(&[param0])) }
444 let param0 = self[0].try_fold_with(folder)?;
445 let param1 = self[1].try_fold_with(folder)?;
446 if param0 == self[0] && param1 == self[1] {
449 Ok(folder.tcx().intern_substs(&[param0, param1]))
453 _ => ty::util::fold_list(self, folder, |tcx, v| tcx.intern_substs(v)),
457 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
458 self.iter().try_for_each(|t| t.visit_with(visitor))
462 impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<Ty<'tcx>> {
463 fn try_super_fold_with<F: FallibleTypeFolder<'tcx>>(
466 ) -> Result<Self, F::Error> {
467 // This code is fairly hot, though not as hot as `SubstsRef`.
469 // When compiling stage 2, I get the following results:
472 // --- | --------- | -----
473 // 2 | 15083590 | 48.1
474 // 3 | 7540067 | 24.0
475 // 1 | 5300377 | 16.9
479 // I've tried it with some private repositories and got
480 // close to the same result, with 4 and 0 swapping places
484 let param0 = self[0].try_fold_with(folder)?;
485 let param1 = self[1].try_fold_with(folder)?;
486 if param0 == self[0] && param1 == self[1] {
489 Ok(folder.tcx().intern_type_list(&[param0, param1]))
492 _ => ty::util::fold_list(self, folder, |tcx, v| tcx.intern_type_list(v)),
496 fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
497 self.iter().try_for_each(|t| t.visit_with(visitor))
501 ///////////////////////////////////////////////////////////////////////////
502 // Public trait `Subst`
504 // Just call `foo.subst(tcx, substs)` to perform a substitution across
505 // `foo`. Or use `foo.subst_spanned(tcx, substs, Some(span))` when
506 // there is more information available (for better errors).
508 pub trait Subst<'tcx>: Sized {
509 fn subst(self, tcx: TyCtxt<'tcx>, substs: &[GenericArg<'tcx>]) -> Self {
510 self.subst_spanned(tcx, substs, None)
516 substs: &[GenericArg<'tcx>],
521 impl<'tcx, T: TypeFoldable<'tcx>> Subst<'tcx> for T {
525 substs: &[GenericArg<'tcx>],
528 let mut folder = SubstFolder { tcx, substs, span, binders_passed: 0 };
529 self.fold_with(&mut folder)
533 ///////////////////////////////////////////////////////////////////////////
534 // The actual substitution engine itself is a type folder.
536 struct SubstFolder<'a, 'tcx> {
538 substs: &'a [GenericArg<'tcx>],
540 /// The location for which the substitution is performed, if available.
543 /// Number of region binders we have passed through while doing the substitution
547 impl<'a, 'tcx> TypeFolder<'tcx> for SubstFolder<'a, 'tcx> {
548 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
552 fn fold_binder<T: TypeFoldable<'tcx>>(
554 t: ty::Binder<'tcx, T>,
555 ) -> ty::Binder<'tcx, T> {
556 self.binders_passed += 1;
557 let t = t.super_fold_with(self);
558 self.binders_passed -= 1;
562 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
563 // Note: This routine only handles regions that are bound on
564 // type declarations and other outer declarations, not those
565 // bound in *fn types*. Region substitution of the bound
566 // regions that appear in a function signature is done using
567 // the specialized routine `ty::replace_late_regions()`.
569 ty::ReEarlyBound(data) => {
570 let rk = self.substs.get(data.index as usize).map(|k| k.unpack());
572 Some(GenericArgKind::Lifetime(lt)) => self.shift_region_through_binders(lt),
574 let span = self.span.unwrap_or(DUMMY_SP);
576 "Region parameter out of range \
577 when substituting in region {} (index={})",
578 data.name, data.index
580 span_bug!(span, "{}", msg);
588 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
589 if !t.needs_subst() {
594 ty::Param(p) => self.ty_for_param(p, t),
595 _ => t.super_fold_with(self),
599 fn fold_const(&mut self, c: ty::Const<'tcx>) -> ty::Const<'tcx> {
600 if let ty::ConstKind::Param(p) = c.val() {
601 self.const_for_param(p, c)
603 c.super_fold_with(self)
608 fn fold_mir_const(&mut self, c: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
609 c.super_fold_with(self)
613 impl<'a, 'tcx> SubstFolder<'a, 'tcx> {
614 fn ty_for_param(&self, p: ty::ParamTy, source_ty: Ty<'tcx>) -> Ty<'tcx> {
615 // Look up the type in the substitutions. It really should be in there.
616 let opt_ty = self.substs.get(p.index as usize).map(|k| k.unpack());
617 let ty = match opt_ty {
618 Some(GenericArgKind::Type(ty)) => ty,
620 let span = self.span.unwrap_or(DUMMY_SP);
623 "expected type for `{:?}` ({:?}/{}) but found {:?} \
624 when substituting, substs={:?}",
633 let span = self.span.unwrap_or(DUMMY_SP);
636 "type parameter `{:?}` ({:?}/{}) out of range \
637 when substituting, substs={:?}",
646 self.shift_vars_through_binders(ty)
649 fn const_for_param(&self, p: ParamConst, source_ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
650 // Look up the const in the substitutions. It really should be in there.
651 let opt_ct = self.substs.get(p.index as usize).map(|k| k.unpack());
652 let ct = match opt_ct {
653 Some(GenericArgKind::Const(ct)) => ct,
655 let span = self.span.unwrap_or(DUMMY_SP);
658 "expected const for `{:?}` ({:?}/{}) but found {:?} \
659 when substituting substs={:?}",
668 let span = self.span.unwrap_or(DUMMY_SP);
671 "const parameter `{:?}` ({:?}/{}) out of range \
672 when substituting substs={:?}",
681 self.shift_vars_through_binders(ct)
684 /// It is sometimes necessary to adjust the De Bruijn indices during substitution. This occurs
685 /// when we are substituting a type with escaping bound vars into a context where we have
686 /// passed through binders. That's quite a mouthful. Let's see an example:
689 /// type Func<A> = fn(A);
690 /// type MetaFunc = for<'a> fn(Func<&'a i32>)
693 /// The type `MetaFunc`, when fully expanded, will be
695 /// for<'a> fn(fn(&'a i32))
698 /// | | DebruijnIndex of 2
701 /// Here the `'a` lifetime is bound in the outer function, but appears as an argument of the
702 /// inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip
703 /// over the inner binder (remember that we count De Bruijn indices from 1). However, in the
704 /// definition of `MetaFunc`, the binder is not visible, so the type `&'a i32` will have a
705 /// De Bruijn index of 1. It's only during the substitution that we can see we must increase the
706 /// depth by 1 to account for the binder that we passed through.
708 /// As a second example, consider this twist:
711 /// type FuncTuple<A> = (A,fn(A));
712 /// type MetaFuncTuple = for<'a> fn(FuncTuple<&'a i32>)
715 /// Here the final type will be:
717 /// for<'a> fn((&'a i32, fn(&'a i32)))
720 /// DebruijnIndex of 1 |
721 /// DebruijnIndex of 2
723 /// As indicated in the diagram, here the same type `&'a i32` is substituted once, but in the
724 /// first case we do not increase the De Bruijn index and in the second case we do. The reason
725 /// is that only in the second case have we passed through a fn binder.
726 fn shift_vars_through_binders<T: TypeFoldable<'tcx>>(&self, val: T) -> T {
728 "shift_vars(val={:?}, binders_passed={:?}, has_escaping_bound_vars={:?})",
731 val.has_escaping_bound_vars()
734 if self.binders_passed == 0 || !val.has_escaping_bound_vars() {
738 let result = ty::fold::shift_vars(self.tcx(), val, self.binders_passed);
739 debug!("shift_vars: shifted result = {:?}", result);
744 fn shift_region_through_binders(&self, region: ty::Region<'tcx>) -> ty::Region<'tcx> {
745 if self.binders_passed == 0 || !region.has_escaping_bound_vars() {
748 ty::fold::shift_region(self.tcx, region, self.binders_passed)
752 /// Stores the user-given substs to reach some fully qualified path
753 /// (e.g., `<T>::Item` or `<T as Trait>::Item`).
754 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable)]
755 #[derive(HashStable, TypeFoldable, Lift)]
756 pub struct UserSubsts<'tcx> {
757 /// The substitutions for the item as given by the user.
758 pub substs: SubstsRef<'tcx>,
760 /// The self type, in the case of a `<T>::Item` path (when applied
761 /// to an inherent impl). See `UserSelfTy` below.
762 pub user_self_ty: Option<UserSelfTy<'tcx>>,
765 /// Specifies the user-given self type. In the case of a path that
766 /// refers to a member in an inherent impl, this self type is
767 /// sometimes needed to constrain the type parameters on the impl. For
768 /// example, in this code:
771 /// struct Foo<T> { }
772 /// impl<A> Foo<A> { fn method() { } }
775 /// when you then have a path like `<Foo<&'static u32>>::method`,
776 /// this struct would carry the `DefId` of the impl along with the
777 /// self type `Foo<u32>`. Then we can instantiate the parameters of
778 /// the impl (with the substs from `UserSubsts`) and apply those to
779 /// the self type, giving `Foo<?A>`. Finally, we unify that with
780 /// the self type here, which contains `?A` to be `&'static u32`
781 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable)]
782 #[derive(HashStable, TypeFoldable, Lift)]
783 pub struct UserSelfTy<'tcx> {
784 pub impl_def_id: DefId,
785 pub self_ty: Ty<'tcx>,