1 #![feature(fmt_helpers_for_derive)]
2 #![feature(min_specialization)]
3 #![feature(rustc_attrs)]
4 #![deny(rustc::untranslatable_diagnostic)]
5 #![deny(rustc::diagnostic_outside_of_impl)]
10 extern crate rustc_macros;
12 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
13 use rustc_data_structures::unify::{EqUnifyValue, UnifyKey};
14 use smallvec::SmallVec;
18 use std::mem::discriminant;
28 /// Needed so we can use #[derive(HashStable_Generic)]
29 pub trait HashStableContext {}
32 type AdtDef: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
33 type SubstsRef: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
34 type DefId: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
35 type Ty: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
36 type Const: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
37 type Region: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
38 type TypeAndMut: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
39 type Mutability: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
40 type Movability: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
41 type PolyFnSig: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
42 type ListBinderExistentialPredicate: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
43 type BinderListTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
44 type ListTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
45 type ProjectionTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
46 type ParamTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
47 type BoundTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
48 type PlaceholderType: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
49 type InferTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
50 type ErrorGuaranteed: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
51 type PredicateKind: Clone + Debug + Hash + PartialEq + Eq;
52 type AllocId: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
54 type EarlyBoundRegion: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
55 type BoundRegion: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
56 type FreeRegion: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
57 type RegionVid: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
58 type PlaceholderRegion: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
61 pub trait InternAs<T: ?Sized, R> {
63 fn intern_with<F>(self, f: F) -> Self::Output
68 impl<I, T, R, E> InternAs<T, R> for I
70 E: InternIteratorElement<T, R>,
71 I: Iterator<Item = E>,
73 type Output = E::Output;
74 fn intern_with<F>(self, f: F) -> Self::Output
78 E::intern_with(self, f)
82 pub trait InternIteratorElement<T, R>: Sized {
84 fn intern_with<I: Iterator<Item = Self>, F: FnOnce(&[T]) -> R>(iter: I, f: F) -> Self::Output;
87 impl<T, R> InternIteratorElement<T, R> for T {
89 fn intern_with<I: Iterator<Item = Self>, F: FnOnce(&[T]) -> R>(
93 // This code is hot enough that it's worth specializing for the most
94 // common length lists, to avoid the overhead of `SmallVec` creation.
95 // Lengths 0, 1, and 2 typically account for ~95% of cases. If
96 // `size_hint` is incorrect a panic will occur via an `unwrap` or an
98 match iter.size_hint() {
100 assert!(iter.next().is_none());
104 let t0 = iter.next().unwrap();
105 assert!(iter.next().is_none());
109 let t0 = iter.next().unwrap();
110 let t1 = iter.next().unwrap();
111 assert!(iter.next().is_none());
114 _ => f(&iter.collect::<SmallVec<[_; 8]>>()),
119 impl<'a, T, R> InternIteratorElement<T, R> for &'a T
124 fn intern_with<I: Iterator<Item = Self>, F: FnOnce(&[T]) -> R>(iter: I, f: F) -> Self::Output {
125 // This code isn't hot.
126 f(&iter.cloned().collect::<SmallVec<[_; 8]>>())
130 impl<T, R, E> InternIteratorElement<T, R> for Result<T, E> {
131 type Output = Result<R, E>;
132 fn intern_with<I: Iterator<Item = Self>, F: FnOnce(&[T]) -> R>(
136 // This code is hot enough that it's worth specializing for the most
137 // common length lists, to avoid the overhead of `SmallVec` creation.
138 // Lengths 0, 1, and 2 typically account for ~95% of cases. If
139 // `size_hint` is incorrect a panic will occur via an `unwrap` or an
140 // `assert`, unless a failure happens first, in which case the result
141 // will be an error anyway.
142 Ok(match iter.size_hint() {
144 assert!(iter.next().is_none());
148 let t0 = iter.next().unwrap()?;
149 assert!(iter.next().is_none());
153 let t0 = iter.next().unwrap()?;
154 let t1 = iter.next().unwrap()?;
155 assert!(iter.next().is_none());
158 _ => f(&iter.collect::<Result<SmallVec<[_; 8]>, _>>()?),
164 /// Flags that we track on types. These flags are propagated upwards
165 /// through the type during type construction, so that we can quickly check
166 /// whether the type has various kinds of types in it without recursing
167 /// over the type itself.
168 pub struct TypeFlags: u32 {
169 // Does this have parameters? Used to determine whether substitution is
171 /// Does this have `Param`?
172 const HAS_TY_PARAM = 1 << 0;
173 /// Does this have `ReEarlyBound`?
174 const HAS_RE_PARAM = 1 << 1;
175 /// Does this have `ConstKind::Param`?
176 const HAS_CT_PARAM = 1 << 2;
178 const NEEDS_SUBST = TypeFlags::HAS_TY_PARAM.bits
179 | TypeFlags::HAS_RE_PARAM.bits
180 | TypeFlags::HAS_CT_PARAM.bits;
182 /// Does this have `Infer`?
183 const HAS_TY_INFER = 1 << 3;
184 /// Does this have `ReVar`?
185 const HAS_RE_INFER = 1 << 4;
186 /// Does this have `ConstKind::Infer`?
187 const HAS_CT_INFER = 1 << 5;
189 /// Does this have inference variables? Used to determine whether
190 /// inference is required.
191 const NEEDS_INFER = TypeFlags::HAS_TY_INFER.bits
192 | TypeFlags::HAS_RE_INFER.bits
193 | TypeFlags::HAS_CT_INFER.bits;
195 /// Does this have `Placeholder`?
196 const HAS_TY_PLACEHOLDER = 1 << 6;
197 /// Does this have `RePlaceholder`?
198 const HAS_RE_PLACEHOLDER = 1 << 7;
199 /// Does this have `ConstKind::Placeholder`?
200 const HAS_CT_PLACEHOLDER = 1 << 8;
202 /// `true` if there are "names" of regions and so forth
203 /// that are local to a particular fn/inferctxt
204 const HAS_FREE_LOCAL_REGIONS = 1 << 9;
206 /// `true` if there are "names" of types and regions and so forth
207 /// that are local to a particular fn
208 const HAS_FREE_LOCAL_NAMES = TypeFlags::HAS_TY_PARAM.bits
209 | TypeFlags::HAS_CT_PARAM.bits
210 | TypeFlags::HAS_TY_INFER.bits
211 | TypeFlags::HAS_CT_INFER.bits
212 | TypeFlags::HAS_TY_PLACEHOLDER.bits
213 | TypeFlags::HAS_CT_PLACEHOLDER.bits
214 // We consider 'freshened' types and constants
215 // to depend on a particular fn.
216 // The freshening process throws away information,
217 // which can make things unsuitable for use in a global
218 // cache. Note that there is no 'fresh lifetime' flag -
219 // freshening replaces all lifetimes with `ReErased`,
220 // which is different from how types/const are freshened.
221 | TypeFlags::HAS_TY_FRESH.bits
222 | TypeFlags::HAS_CT_FRESH.bits
223 | TypeFlags::HAS_FREE_LOCAL_REGIONS.bits;
225 /// Does this have `Projection`?
226 const HAS_TY_PROJECTION = 1 << 10;
227 /// Does this have `Opaque`?
228 const HAS_TY_OPAQUE = 1 << 11;
229 /// Does this have `ConstKind::Unevaluated`?
230 const HAS_CT_PROJECTION = 1 << 12;
232 /// Could this type be normalized further?
233 const HAS_PROJECTION = TypeFlags::HAS_TY_PROJECTION.bits
234 | TypeFlags::HAS_TY_OPAQUE.bits
235 | TypeFlags::HAS_CT_PROJECTION.bits;
237 /// Is an error type/const reachable?
238 const HAS_ERROR = 1 << 13;
240 /// Does this have any region that "appears free" in the type?
241 /// Basically anything but `ReLateBound` and `ReErased`.
242 const HAS_FREE_REGIONS = 1 << 14;
244 /// Does this have any `ReLateBound` regions? Used to check
245 /// if a global bound is safe to evaluate.
246 const HAS_RE_LATE_BOUND = 1 << 15;
248 /// Does this have any `ReErased` regions?
249 const HAS_RE_ERASED = 1 << 16;
251 /// Does this value have parameters/placeholders/inference variables which could be
252 /// replaced later, in a way that would change the results of `impl` specialization?
253 const STILL_FURTHER_SPECIALIZABLE = 1 << 17;
255 /// Does this value have `InferTy::FreshTy/FreshIntTy/FreshFloatTy`?
256 const HAS_TY_FRESH = 1 << 18;
258 /// Does this value have `InferConst::Fresh`?
259 const HAS_CT_FRESH = 1 << 19;
263 rustc_index::newtype_index! {
264 /// A [De Bruijn index][dbi] is a standard means of representing
265 /// regions (and perhaps later types) in a higher-ranked setting. In
266 /// particular, imagine a type like this:
267 /// ```ignore (illustrative)
268 /// for<'a> fn(for<'b> fn(&'b isize, &'a isize), &'a char)
271 /// // | +------------+ 0 | |
273 /// // +----------------------------------+ 1 |
275 /// // +----------------------------------------------+ 0
277 /// In this type, there are two binders (the outer fn and the inner
278 /// fn). We need to be able to determine, for any given region, which
279 /// fn type it is bound by, the inner or the outer one. There are
280 /// various ways you can do this, but a De Bruijn index is one of the
281 /// more convenient and has some nice properties. The basic idea is to
282 /// count the number of binders, inside out. Some examples should help
283 /// clarify what I mean.
285 /// Let's start with the reference type `&'b isize` that is the first
286 /// argument to the inner function. This region `'b` is assigned a De
287 /// Bruijn index of 0, meaning "the innermost binder" (in this case, a
288 /// fn). The region `'a` that appears in the second argument type (`&'a
289 /// isize`) would then be assigned a De Bruijn index of 1, meaning "the
290 /// second-innermost binder". (These indices are written on the arrows
293 /// What is interesting is that De Bruijn index attached to a particular
294 /// variable will vary depending on where it appears. For example,
295 /// the final type `&'a char` also refers to the region `'a` declared on
296 /// the outermost fn. But this time, this reference is not nested within
297 /// any other binders (i.e., it is not an argument to the inner fn, but
298 /// rather the outer one). Therefore, in this case, it is assigned a
299 /// De Bruijn index of 0, because the innermost binder in that location
302 /// [dbi]: https://en.wikipedia.org/wiki/De_Bruijn_index
303 #[derive(HashStable_Generic)]
304 pub struct DebruijnIndex {
305 DEBUG_FORMAT = "DebruijnIndex({})",
311 /// Returns the resulting index when this value is moved into
312 /// `amount` number of new binders. So, e.g., if you had
314 /// for<'a> fn(&'a x)
316 /// and you wanted to change it to
318 /// for<'a> fn(for<'b> fn(&'a x))
320 /// you would need to shift the index for `'a` into a new binder.
323 pub fn shifted_in(self, amount: u32) -> DebruijnIndex {
324 DebruijnIndex::from_u32(self.as_u32() + amount)
327 /// Update this index in place by shifting it "in" through
328 /// `amount` number of binders.
330 pub fn shift_in(&mut self, amount: u32) {
331 *self = self.shifted_in(amount);
334 /// Returns the resulting index when this value is moved out from
335 /// `amount` number of new binders.
338 pub fn shifted_out(self, amount: u32) -> DebruijnIndex {
339 DebruijnIndex::from_u32(self.as_u32() - amount)
342 /// Update in place by shifting out from `amount` binders.
344 pub fn shift_out(&mut self, amount: u32) {
345 *self = self.shifted_out(amount);
348 /// Adjusts any De Bruijn indices so as to make `to_binder` the
349 /// innermost binder. That is, if we have something bound at `to_binder`,
350 /// it will now be bound at INNERMOST. This is an appropriate thing to do
351 /// when moving a region out from inside binders:
353 /// ```ignore (illustrative)
354 /// for<'a> fn(for<'b> for<'c> fn(&'a u32), _)
355 /// // Binder: D3 D2 D1 ^^
358 /// Here, the region `'a` would have the De Bruijn index D3,
359 /// because it is the bound 3 binders out. However, if we wanted
360 /// to refer to that region `'a` in the second argument (the `_`),
361 /// those two binders would not be in scope. In that case, we
362 /// might invoke `shift_out_to_binder(D3)`. This would adjust the
363 /// De Bruijn index of `'a` to D1 (the innermost binder).
365 /// If we invoke `shift_out_to_binder` and the region is in fact
366 /// bound by one of the binders we are shifting out of, that is an
367 /// error (and should fail an assertion failure).
369 pub fn shifted_out_to_binder(self, to_binder: DebruijnIndex) -> Self {
370 self.shifted_out(to_binder.as_u32() - INNERMOST.as_u32())
374 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
375 #[derive(Encodable, Decodable, HashStable_Generic)]
386 pub fn name_str(&self) -> &'static str {
388 IntTy::Isize => "isize",
393 IntTy::I128 => "i128",
397 pub fn bit_width(&self) -> Option<u64> {
399 IntTy::Isize => return None,
408 pub fn normalize(&self, target_width: u32) -> Self {
410 IntTy::Isize => match target_width {
421 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Copy, Debug)]
422 #[derive(Encodable, Decodable, HashStable_Generic)]
433 pub fn name_str(&self) -> &'static str {
435 UintTy::Usize => "usize",
437 UintTy::U16 => "u16",
438 UintTy::U32 => "u32",
439 UintTy::U64 => "u64",
440 UintTy::U128 => "u128",
444 pub fn bit_width(&self) -> Option<u64> {
446 UintTy::Usize => return None,
455 pub fn normalize(&self, target_width: u32) -> Self {
457 UintTy::Usize => match target_width {
468 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
469 #[derive(Encodable, Decodable, HashStable_Generic)]
476 pub fn name_str(self) -> &'static str {
478 FloatTy::F32 => "f32",
479 FloatTy::F64 => "f64",
483 pub fn bit_width(self) -> u64 {
491 #[derive(Clone, Copy, PartialEq, Eq)]
492 pub enum IntVarValue {
497 #[derive(Clone, Copy, PartialEq, Eq)]
498 pub struct FloatVarValue(pub FloatTy);
500 rustc_index::newtype_index! {
501 /// A **ty**pe **v**ariable **ID**.
503 DEBUG_FORMAT = "_#{}t"
507 /// An **int**egral (`u32`, `i32`, `usize`, etc.) type **v**ariable **ID**.
508 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable, Decodable)]
513 /// An **float**ing-point (`f32` or `f64`) type **v**ariable **ID**.
514 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable, Decodable)]
515 pub struct FloatVid {
519 /// A placeholder for a type that hasn't been inferred yet.
521 /// E.g., if we have an empty array (`[]`), then we create a fresh
522 /// type variable for the element type since we won't know until it's
523 /// used what the element type is supposed to be.
524 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable, Decodable)]
528 /// An integral type variable (`{integer}`).
530 /// These are created when the compiler sees an integer literal like
531 /// `1` that could be several different types (`u8`, `i32`, `u32`, etc.).
532 /// We don't know until it's used what type it's supposed to be, so
533 /// we create a fresh type variable.
535 /// A floating-point type variable (`{float}`).
537 /// These are created when the compiler sees an float literal like
538 /// `1.0` that could be either an `f32` or an `f64`.
539 /// We don't know until it's used what type it's supposed to be, so
540 /// we create a fresh type variable.
543 /// A [`FreshTy`][Self::FreshTy] is one that is generated as a replacement
544 /// for an unbound type variable. This is convenient for caching etc. See
545 /// `rustc_infer::infer::freshen` for more details.
547 /// Compare with [`TyVar`][Self::TyVar].
549 /// Like [`FreshTy`][Self::FreshTy], but as a replacement for [`IntVar`][Self::IntVar].
551 /// Like [`FreshTy`][Self::FreshTy], but as a replacement for [`FloatVar`][Self::FloatVar].
555 /// Raw `TyVid` are used as the unification key for `sub_relations`;
556 /// they carry no values.
557 impl UnifyKey for TyVid {
560 fn index(&self) -> u32 {
564 fn from_index(i: u32) -> TyVid {
567 fn tag() -> &'static str {
572 impl EqUnifyValue for IntVarValue {}
574 impl UnifyKey for IntVid {
575 type Value = Option<IntVarValue>;
576 #[inline] // make this function eligible for inlining - it is quite hot.
577 fn index(&self) -> u32 {
581 fn from_index(i: u32) -> IntVid {
584 fn tag() -> &'static str {
589 impl EqUnifyValue for FloatVarValue {}
591 impl UnifyKey for FloatVid {
592 type Value = Option<FloatVarValue>;
594 fn index(&self) -> u32 {
598 fn from_index(i: u32) -> FloatVid {
599 FloatVid { index: i }
601 fn tag() -> &'static str {
606 #[derive(Copy, Clone, PartialEq, Decodable, Encodable, Hash, HashStable_Generic)]
607 #[rustc_pass_by_value]
609 Covariant, // T<A> <: T<B> iff A <: B -- e.g., function return type
610 Invariant, // T<A> <: T<B> iff B == A -- e.g., type of mutable cell
611 Contravariant, // T<A> <: T<B> iff B <: A -- e.g., function param type
612 Bivariant, // T<A> <: T<B> -- e.g., unused type parameter
616 /// `a.xform(b)` combines the variance of a context with the
617 /// variance of a type with the following meaning. If we are in a
618 /// context with variance `a`, and we encounter a type argument in
619 /// a position with variance `b`, then `a.xform(b)` is the new
620 /// variance with which the argument appears.
623 /// ```ignore (illustrative)
626 /// Here, the "ambient" variance starts as covariant. `*mut T` is
627 /// invariant with respect to `T`, so the variance in which the
628 /// `Vec<i32>` appears is `Covariant.xform(Invariant)`, which
629 /// yields `Invariant`. Now, the type `Vec<T>` is covariant with
630 /// respect to its type argument `T`, and hence the variance of
631 /// the `i32` here is `Invariant.xform(Covariant)`, which results
632 /// (again) in `Invariant`.
635 /// ```ignore (illustrative)
636 /// fn(*const Vec<i32>, *mut Vec<i32)
638 /// The ambient variance is covariant. A `fn` type is
639 /// contravariant with respect to its parameters, so the variance
640 /// within which both pointer types appear is
641 /// `Covariant.xform(Contravariant)`, or `Contravariant`. `*const
642 /// T` is covariant with respect to `T`, so the variance within
643 /// which the first `Vec<i32>` appears is
644 /// `Contravariant.xform(Covariant)` or `Contravariant`. The same
645 /// is true for its `i32` argument. In the `*mut T` case, the
646 /// variance of `Vec<i32>` is `Contravariant.xform(Invariant)`,
647 /// and hence the outermost type is `Invariant` with respect to
648 /// `Vec<i32>` (and its `i32` argument).
650 /// Source: Figure 1 of "Taming the Wildcards:
651 /// Combining Definition- and Use-Site Variance" published in PLDI'11.
652 pub fn xform(self, v: Variance) -> Variance {
654 // Figure 1, column 1.
655 (Variance::Covariant, Variance::Covariant) => Variance::Covariant,
656 (Variance::Covariant, Variance::Contravariant) => Variance::Contravariant,
657 (Variance::Covariant, Variance::Invariant) => Variance::Invariant,
658 (Variance::Covariant, Variance::Bivariant) => Variance::Bivariant,
660 // Figure 1, column 2.
661 (Variance::Contravariant, Variance::Covariant) => Variance::Contravariant,
662 (Variance::Contravariant, Variance::Contravariant) => Variance::Covariant,
663 (Variance::Contravariant, Variance::Invariant) => Variance::Invariant,
664 (Variance::Contravariant, Variance::Bivariant) => Variance::Bivariant,
666 // Figure 1, column 3.
667 (Variance::Invariant, _) => Variance::Invariant,
669 // Figure 1, column 4.
670 (Variance::Bivariant, _) => Variance::Bivariant,
675 impl<CTX> HashStable<CTX> for InferTy {
676 fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
678 discriminant(self).hash_stable(ctx, hasher);
680 TyVar(_) | IntVar(_) | FloatVar(_) => {
681 panic!("type variables should not be hashed: {self:?}")
683 FreshTy(v) | FreshIntTy(v) | FreshFloatTy(v) => v.hash_stable(ctx, hasher),
688 impl fmt::Debug for IntVarValue {
689 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
691 IntVarValue::IntType(ref v) => v.fmt(f),
692 IntVarValue::UintType(ref v) => v.fmt(f),
697 impl fmt::Debug for FloatVarValue {
698 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
703 impl fmt::Debug for IntVid {
704 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
705 write!(f, "_#{}i", self.index)
709 impl fmt::Debug for FloatVid {
710 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
711 write!(f, "_#{}f", self.index)
715 impl fmt::Debug for InferTy {
716 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
719 TyVar(ref v) => v.fmt(f),
720 IntVar(ref v) => v.fmt(f),
721 FloatVar(ref v) => v.fmt(f),
722 FreshTy(v) => write!(f, "FreshTy({:?})", v),
723 FreshIntTy(v) => write!(f, "FreshIntTy({:?})", v),
724 FreshFloatTy(v) => write!(f, "FreshFloatTy({:?})", v),
729 impl fmt::Debug for Variance {
730 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
731 f.write_str(match *self {
732 Variance::Covariant => "+",
733 Variance::Contravariant => "-",
734 Variance::Invariant => "o",
735 Variance::Bivariant => "*",
740 impl fmt::Display for InferTy {
741 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
744 TyVar(_) => write!(f, "_"),
745 IntVar(_) => write!(f, "{}", "{integer}"),
746 FloatVar(_) => write!(f, "{}", "{float}"),
747 FreshTy(v) => write!(f, "FreshTy({})", v),
748 FreshIntTy(v) => write!(f, "FreshIntTy({})", v),
749 FreshFloatTy(v) => write!(f, "FreshFloatTy({})", v),
754 rustc_index::newtype_index! {
755 /// "Universes" are used during type- and trait-checking in the
756 /// presence of `for<..>` binders to control what sets of names are
757 /// visible. Universes are arranged into a tree: the root universe
758 /// contains names that are always visible. Each child then adds a new
759 /// set of names that are visible, in addition to those of its parent.
760 /// We say that the child universe "extends" the parent universe with
763 /// To make this more concrete, consider this program:
765 /// ```ignore (illustrative)
767 /// fn bar<T>(x: T) {
768 /// let y: for<'a> fn(&'a u8, Foo) = ...;
772 /// The struct name `Foo` is in the root universe U0. But the type
773 /// parameter `T`, introduced on `bar`, is in an extended universe U1
774 /// -- i.e., within `bar`, we can name both `T` and `Foo`, but outside
775 /// of `bar`, we cannot name `T`. Then, within the type of `y`, the
776 /// region `'a` is in a universe U2 that extends U1, because we can
777 /// name it inside the fn type but not outside.
779 /// Universes are used to do type- and trait-checking around these
780 /// "forall" binders (also called **universal quantification**). The
781 /// idea is that when, in the body of `bar`, we refer to `T` as a
782 /// type, we aren't referring to any type in particular, but rather a
783 /// kind of "fresh" type that is distinct from all other types we have
784 /// actually declared. This is called a **placeholder** type, and we
785 /// use universes to talk about this. In other words, a type name in
786 /// universe 0 always corresponds to some "ground" type that the user
787 /// declared, but a type name in a non-zero universe is a placeholder
788 /// type -- an idealized representative of "types in general" that we
789 /// use for checking generic functions.
790 #[derive(HashStable_Generic)]
791 pub struct UniverseIndex {
792 DEBUG_FORMAT = "U{}",
797 pub const ROOT: UniverseIndex = UniverseIndex::from_u32(0);
799 /// Returns the "next" universe index in order -- this new index
800 /// is considered to extend all previous universes. This
801 /// corresponds to entering a `forall` quantifier. So, for
802 /// example, suppose we have this type in universe `U`:
804 /// ```ignore (illustrative)
805 /// for<'a> fn(&'a u32)
808 /// Once we "enter" into this `for<'a>` quantifier, we are in a
809 /// new universe that extends `U` -- in this new universe, we can
810 /// name the region `'a`, but that region was not nameable from
811 /// `U` because it was not in scope there.
812 pub fn next_universe(self) -> UniverseIndex {
813 UniverseIndex::from_u32(self.private.checked_add(1).unwrap())
816 /// Returns `true` if `self` can name a name from `other` -- in other words,
817 /// if the set of names in `self` is a superset of those in
818 /// `other` (`self >= other`).
819 pub fn can_name(self, other: UniverseIndex) -> bool {
820 self.private >= other.private
823 /// Returns `true` if `self` cannot name some names from `other` -- in other
824 /// words, if the set of names in `self` is a strict subset of
825 /// those in `other` (`self < other`).
826 pub fn cannot_name(self, other: UniverseIndex) -> bool {
827 self.private < other.private