1 #![feature(fmt_helpers_for_derive)]
2 #![feature(min_specialization)]
3 #![feature(rustc_attrs)]
8 extern crate rustc_macros;
10 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
11 use rustc_data_structures::unify::{EqUnifyValue, UnifyKey};
12 use smallvec::SmallVec;
16 use std::mem::discriminant;
25 type AdtDef: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
26 type SubstsRef: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
27 type DefId: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
28 type Ty: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
29 type Const: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
30 type Region: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
31 type TypeAndMut: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
32 type Mutability: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
33 type Movability: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
34 type PolyFnSig: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
35 type ListBinderExistentialPredicate: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
36 type BinderListTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
37 type ListTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
38 type ProjectionTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
39 type ParamTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
40 type BoundTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
41 type PlaceholderType: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
42 type InferTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
43 type DelaySpanBugEmitted: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
44 type PredicateKind: Clone + Debug + Hash + PartialEq + Eq;
45 type AllocId: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
47 type EarlyBoundRegion: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
48 type BoundRegion: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
49 type FreeRegion: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
50 type RegionVid: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
51 type PlaceholderRegion: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
54 pub trait InternAs<T: ?Sized, R> {
56 fn intern_with<F>(self, f: F) -> Self::Output
61 impl<I, T, R, E> InternAs<[T], R> for I
63 E: InternIteratorElement<T, R>,
64 I: Iterator<Item = E>,
66 type Output = E::Output;
67 fn intern_with<F>(self, f: F) -> Self::Output
71 E::intern_with(self, f)
75 pub trait InternIteratorElement<T, R>: Sized {
77 fn intern_with<I: Iterator<Item = Self>, F: FnOnce(&[T]) -> R>(iter: I, f: F) -> Self::Output;
80 impl<T, R> InternIteratorElement<T, R> for T {
82 fn intern_with<I: Iterator<Item = Self>, F: FnOnce(&[T]) -> R>(
86 // This code is hot enough that it's worth specializing for the most
87 // common length lists, to avoid the overhead of `SmallVec` creation.
88 // Lengths 0, 1, and 2 typically account for ~95% of cases. If
89 // `size_hint` is incorrect a panic will occur via an `unwrap` or an
91 match iter.size_hint() {
93 assert!(iter.next().is_none());
97 let t0 = iter.next().unwrap();
98 assert!(iter.next().is_none());
102 let t0 = iter.next().unwrap();
103 let t1 = iter.next().unwrap();
104 assert!(iter.next().is_none());
107 _ => f(&iter.collect::<SmallVec<[_; 8]>>()),
112 impl<'a, T, R> InternIteratorElement<T, R> for &'a T
117 fn intern_with<I: Iterator<Item = Self>, F: FnOnce(&[T]) -> R>(iter: I, f: F) -> Self::Output {
118 // This code isn't hot.
119 f(&iter.cloned().collect::<SmallVec<[_; 8]>>())
123 impl<T, R, E> InternIteratorElement<T, R> for Result<T, E> {
124 type Output = Result<R, E>;
125 fn intern_with<I: Iterator<Item = Self>, F: FnOnce(&[T]) -> R>(
129 // This code is hot enough that it's worth specializing for the most
130 // common length lists, to avoid the overhead of `SmallVec` creation.
131 // Lengths 0, 1, and 2 typically account for ~95% of cases. If
132 // `size_hint` is incorrect a panic will occur via an `unwrap` or an
133 // `assert`, unless a failure happens first, in which case the result
134 // will be an error anyway.
135 Ok(match iter.size_hint() {
137 assert!(iter.next().is_none());
141 let t0 = iter.next().unwrap()?;
142 assert!(iter.next().is_none());
146 let t0 = iter.next().unwrap()?;
147 let t1 = iter.next().unwrap()?;
148 assert!(iter.next().is_none());
151 _ => f(&iter.collect::<Result<SmallVec<[_; 8]>, _>>()?),
157 /// Flags that we track on types. These flags are propagated upwards
158 /// through the type during type construction, so that we can quickly check
159 /// whether the type has various kinds of types in it without recursing
160 /// over the type itself.
161 pub struct TypeFlags: u32 {
162 // Does this have parameters? Used to determine whether substitution is
164 /// Does this have `Param`?
165 const HAS_TY_PARAM = 1 << 0;
166 /// Does this have `ReEarlyBound`?
167 const HAS_RE_PARAM = 1 << 1;
168 /// Does this have `ConstKind::Param`?
169 const HAS_CT_PARAM = 1 << 2;
171 const NEEDS_SUBST = TypeFlags::HAS_TY_PARAM.bits
172 | TypeFlags::HAS_RE_PARAM.bits
173 | TypeFlags::HAS_CT_PARAM.bits;
175 /// Does this have `Infer`?
176 const HAS_TY_INFER = 1 << 3;
177 /// Does this have `ReVar`?
178 const HAS_RE_INFER = 1 << 4;
179 /// Does this have `ConstKind::Infer`?
180 const HAS_CT_INFER = 1 << 5;
182 /// Does this have inference variables? Used to determine whether
183 /// inference is required.
184 const NEEDS_INFER = TypeFlags::HAS_TY_INFER.bits
185 | TypeFlags::HAS_RE_INFER.bits
186 | TypeFlags::HAS_CT_INFER.bits;
188 /// Does this have `Placeholder`?
189 const HAS_TY_PLACEHOLDER = 1 << 6;
190 /// Does this have `RePlaceholder`?
191 const HAS_RE_PLACEHOLDER = 1 << 7;
192 /// Does this have `ConstKind::Placeholder`?
193 const HAS_CT_PLACEHOLDER = 1 << 8;
195 /// `true` if there are "names" of regions and so forth
196 /// that are local to a particular fn/inferctxt
197 const HAS_FREE_LOCAL_REGIONS = 1 << 9;
199 /// `true` if there are "names" of types and regions and so forth
200 /// that are local to a particular fn
201 const HAS_FREE_LOCAL_NAMES = TypeFlags::HAS_TY_PARAM.bits
202 | TypeFlags::HAS_CT_PARAM.bits
203 | TypeFlags::HAS_TY_INFER.bits
204 | TypeFlags::HAS_CT_INFER.bits
205 | TypeFlags::HAS_TY_PLACEHOLDER.bits
206 | TypeFlags::HAS_CT_PLACEHOLDER.bits
207 // We consider 'freshened' types and constants
208 // to depend on a particular fn.
209 // The freshening process throws away information,
210 // which can make things unsuitable for use in a global
211 // cache. Note that there is no 'fresh lifetime' flag -
212 // freshening replaces all lifetimes with `ReErased`,
213 // which is different from how types/const are freshened.
214 | TypeFlags::HAS_TY_FRESH.bits
215 | TypeFlags::HAS_CT_FRESH.bits
216 | TypeFlags::HAS_FREE_LOCAL_REGIONS.bits;
218 /// Does this have `Projection`?
219 const HAS_TY_PROJECTION = 1 << 10;
220 /// Does this have `Opaque`?
221 const HAS_TY_OPAQUE = 1 << 11;
222 /// Does this have `ConstKind::Unevaluated`?
223 const HAS_CT_PROJECTION = 1 << 12;
225 /// Could this type be normalized further?
226 const HAS_PROJECTION = TypeFlags::HAS_TY_PROJECTION.bits
227 | TypeFlags::HAS_TY_OPAQUE.bits
228 | TypeFlags::HAS_CT_PROJECTION.bits;
230 /// Is an error type/const reachable?
231 const HAS_ERROR = 1 << 13;
233 /// Does this have any region that "appears free" in the type?
234 /// Basically anything but `ReLateBound` and `ReErased`.
235 const HAS_FREE_REGIONS = 1 << 14;
237 /// Does this have any `ReLateBound` regions? Used to check
238 /// if a global bound is safe to evaluate.
239 const HAS_RE_LATE_BOUND = 1 << 15;
241 /// Does this have any `ReErased` regions?
242 const HAS_RE_ERASED = 1 << 16;
244 /// Does this value have parameters/placeholders/inference variables which could be
245 /// replaced later, in a way that would change the results of `impl` specialization?
246 const STILL_FURTHER_SPECIALIZABLE = 1 << 17;
248 /// Does this value have `InferTy::FreshTy/FreshIntTy/FreshFloatTy`?
249 const HAS_TY_FRESH = 1 << 18;
251 /// Does this value have `InferConst::Fresh`?
252 const HAS_CT_FRESH = 1 << 19;
256 rustc_index::newtype_index! {
257 /// A [De Bruijn index][dbi] is a standard means of representing
258 /// regions (and perhaps later types) in a higher-ranked setting. In
259 /// particular, imagine a type like this:
260 /// ```ignore (illustrative)
261 /// for<'a> fn(for<'b> fn(&'b isize, &'a isize), &'a char)
264 /// // | +------------+ 0 | |
266 /// // +----------------------------------+ 1 |
268 /// // +----------------------------------------------+ 0
270 /// In this type, there are two binders (the outer fn and the inner
271 /// fn). We need to be able to determine, for any given region, which
272 /// fn type it is bound by, the inner or the outer one. There are
273 /// various ways you can do this, but a De Bruijn index is one of the
274 /// more convenient and has some nice properties. The basic idea is to
275 /// count the number of binders, inside out. Some examples should help
276 /// clarify what I mean.
278 /// Let's start with the reference type `&'b isize` that is the first
279 /// argument to the inner function. This region `'b` is assigned a De
280 /// Bruijn index of 0, meaning "the innermost binder" (in this case, a
281 /// fn). The region `'a` that appears in the second argument type (`&'a
282 /// isize`) would then be assigned a De Bruijn index of 1, meaning "the
283 /// second-innermost binder". (These indices are written on the arrows
286 /// What is interesting is that De Bruijn index attached to a particular
287 /// variable will vary depending on where it appears. For example,
288 /// the final type `&'a char` also refers to the region `'a` declared on
289 /// the outermost fn. But this time, this reference is not nested within
290 /// any other binders (i.e., it is not an argument to the inner fn, but
291 /// rather the outer one). Therefore, in this case, it is assigned a
292 /// De Bruijn index of 0, because the innermost binder in that location
295 /// [dbi]: https://en.wikipedia.org/wiki/De_Bruijn_index
296 pub struct DebruijnIndex {
297 DEBUG_FORMAT = "DebruijnIndex({})",
303 /// Returns the resulting index when this value is moved into
304 /// `amount` number of new binders. So, e.g., if you had
306 /// for<'a> fn(&'a x)
308 /// and you wanted to change it to
310 /// for<'a> fn(for<'b> fn(&'a x))
312 /// you would need to shift the index for `'a` into a new binder.
315 pub fn shifted_in(self, amount: u32) -> DebruijnIndex {
316 DebruijnIndex::from_u32(self.as_u32() + amount)
319 /// Update this index in place by shifting it "in" through
320 /// `amount` number of binders.
322 pub fn shift_in(&mut self, amount: u32) {
323 *self = self.shifted_in(amount);
326 /// Returns the resulting index when this value is moved out from
327 /// `amount` number of new binders.
330 pub fn shifted_out(self, amount: u32) -> DebruijnIndex {
331 DebruijnIndex::from_u32(self.as_u32() - amount)
334 /// Update in place by shifting out from `amount` binders.
336 pub fn shift_out(&mut self, amount: u32) {
337 *self = self.shifted_out(amount);
340 /// Adjusts any De Bruijn indices so as to make `to_binder` the
341 /// innermost binder. That is, if we have something bound at `to_binder`,
342 /// it will now be bound at INNERMOST. This is an appropriate thing to do
343 /// when moving a region out from inside binders:
345 /// ```ignore (illustrative)
346 /// for<'a> fn(for<'b> for<'c> fn(&'a u32), _)
347 /// // Binder: D3 D2 D1 ^^
350 /// Here, the region `'a` would have the De Bruijn index D3,
351 /// because it is the bound 3 binders out. However, if we wanted
352 /// to refer to that region `'a` in the second argument (the `_`),
353 /// those two binders would not be in scope. In that case, we
354 /// might invoke `shift_out_to_binder(D3)`. This would adjust the
355 /// De Bruijn index of `'a` to D1 (the innermost binder).
357 /// If we invoke `shift_out_to_binder` and the region is in fact
358 /// bound by one of the binders we are shifting out of, that is an
359 /// error (and should fail an assertion failure).
361 pub fn shifted_out_to_binder(self, to_binder: DebruijnIndex) -> Self {
362 self.shifted_out(to_binder.as_u32() - INNERMOST.as_u32())
366 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
367 #[derive(Encodable, Decodable)]
378 pub fn name_str(&self) -> &'static str {
380 IntTy::Isize => "isize",
385 IntTy::I128 => "i128",
389 pub fn bit_width(&self) -> Option<u64> {
391 IntTy::Isize => return None,
400 pub fn normalize(&self, target_width: u32) -> Self {
402 IntTy::Isize => match target_width {
413 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Copy, Debug)]
414 #[derive(Encodable, Decodable)]
425 pub fn name_str(&self) -> &'static str {
427 UintTy::Usize => "usize",
429 UintTy::U16 => "u16",
430 UintTy::U32 => "u32",
431 UintTy::U64 => "u64",
432 UintTy::U128 => "u128",
436 pub fn bit_width(&self) -> Option<u64> {
438 UintTy::Usize => return None,
447 pub fn normalize(&self, target_width: u32) -> Self {
449 UintTy::Usize => match target_width {
460 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
461 #[derive(Encodable, Decodable)]
468 pub fn name_str(self) -> &'static str {
470 FloatTy::F32 => "f32",
471 FloatTy::F64 => "f64",
475 pub fn bit_width(self) -> u64 {
483 #[derive(Clone, Copy, PartialEq, Eq)]
484 pub enum IntVarValue {
489 #[derive(Clone, Copy, PartialEq, Eq)]
490 pub struct FloatVarValue(pub FloatTy);
492 rustc_index::newtype_index! {
493 /// A **ty**pe **v**ariable **ID**.
495 DEBUG_FORMAT = "_#{}t"
499 /// An **int**egral (`u32`, `i32`, `usize`, etc.) type **v**ariable **ID**.
500 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable, Decodable)]
505 /// An **float**ing-point (`f32` or `f64`) type **v**ariable **ID**.
506 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable, Decodable)]
507 pub struct FloatVid {
511 /// A placeholder for a type that hasn't been inferred yet.
513 /// E.g., if we have an empty array (`[]`), then we create a fresh
514 /// type variable for the element type since we won't know until it's
515 /// used what the element type is supposed to be.
516 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable, Decodable)]
520 /// An integral type variable (`{integer}`).
522 /// These are created when the compiler sees an integer literal like
523 /// `1` that could be several different types (`u8`, `i32`, `u32`, etc.).
524 /// We don't know until it's used what type it's supposed to be, so
525 /// we create a fresh type variable.
527 /// A floating-point type variable (`{float}`).
529 /// These are created when the compiler sees an float literal like
530 /// `1.0` that could be either an `f32` or an `f64`.
531 /// We don't know until it's used what type it's supposed to be, so
532 /// we create a fresh type variable.
535 /// A [`FreshTy`][Self::FreshTy] is one that is generated as a replacement
536 /// for an unbound type variable. This is convenient for caching etc. See
537 /// `rustc_infer::infer::freshen` for more details.
539 /// Compare with [`TyVar`][Self::TyVar].
541 /// Like [`FreshTy`][Self::FreshTy], but as a replacement for [`IntVar`][Self::IntVar].
543 /// Like [`FreshTy`][Self::FreshTy], but as a replacement for [`FloatVar`][Self::FloatVar].
547 /// Raw `TyVid` are used as the unification key for `sub_relations`;
548 /// they carry no values.
549 impl UnifyKey for TyVid {
552 fn index(&self) -> u32 {
556 fn from_index(i: u32) -> TyVid {
559 fn tag() -> &'static str {
564 impl EqUnifyValue for IntVarValue {}
566 impl UnifyKey for IntVid {
567 type Value = Option<IntVarValue>;
568 #[inline] // make this function eligible for inlining - it is quite hot.
569 fn index(&self) -> u32 {
573 fn from_index(i: u32) -> IntVid {
576 fn tag() -> &'static str {
581 impl EqUnifyValue for FloatVarValue {}
583 impl UnifyKey for FloatVid {
584 type Value = Option<FloatVarValue>;
586 fn index(&self) -> u32 {
590 fn from_index(i: u32) -> FloatVid {
591 FloatVid { index: i }
593 fn tag() -> &'static str {
598 #[derive(Copy, Clone, PartialEq, Decodable, Encodable, Hash)]
599 #[rustc_pass_by_value]
601 Covariant, // T<A> <: T<B> iff A <: B -- e.g., function return type
602 Invariant, // T<A> <: T<B> iff B == A -- e.g., type of mutable cell
603 Contravariant, // T<A> <: T<B> iff B <: A -- e.g., function param type
604 Bivariant, // T<A> <: T<B> -- e.g., unused type parameter
608 /// `a.xform(b)` combines the variance of a context with the
609 /// variance of a type with the following meaning. If we are in a
610 /// context with variance `a`, and we encounter a type argument in
611 /// a position with variance `b`, then `a.xform(b)` is the new
612 /// variance with which the argument appears.
615 /// ```ignore (illustrative)
618 /// Here, the "ambient" variance starts as covariant. `*mut T` is
619 /// invariant with respect to `T`, so the variance in which the
620 /// `Vec<i32>` appears is `Covariant.xform(Invariant)`, which
621 /// yields `Invariant`. Now, the type `Vec<T>` is covariant with
622 /// respect to its type argument `T`, and hence the variance of
623 /// the `i32` here is `Invariant.xform(Covariant)`, which results
624 /// (again) in `Invariant`.
627 /// ```ignore (illustrative)
628 /// fn(*const Vec<i32>, *mut Vec<i32)
630 /// The ambient variance is covariant. A `fn` type is
631 /// contravariant with respect to its parameters, so the variance
632 /// within which both pointer types appear is
633 /// `Covariant.xform(Contravariant)`, or `Contravariant`. `*const
634 /// T` is covariant with respect to `T`, so the variance within
635 /// which the first `Vec<i32>` appears is
636 /// `Contravariant.xform(Covariant)` or `Contravariant`. The same
637 /// is true for its `i32` argument. In the `*mut T` case, the
638 /// variance of `Vec<i32>` is `Contravariant.xform(Invariant)`,
639 /// and hence the outermost type is `Invariant` with respect to
640 /// `Vec<i32>` (and its `i32` argument).
642 /// Source: Figure 1 of "Taming the Wildcards:
643 /// Combining Definition- and Use-Site Variance" published in PLDI'11.
644 pub fn xform(self, v: Variance) -> Variance {
646 // Figure 1, column 1.
647 (Variance::Covariant, Variance::Covariant) => Variance::Covariant,
648 (Variance::Covariant, Variance::Contravariant) => Variance::Contravariant,
649 (Variance::Covariant, Variance::Invariant) => Variance::Invariant,
650 (Variance::Covariant, Variance::Bivariant) => Variance::Bivariant,
652 // Figure 1, column 2.
653 (Variance::Contravariant, Variance::Covariant) => Variance::Contravariant,
654 (Variance::Contravariant, Variance::Contravariant) => Variance::Covariant,
655 (Variance::Contravariant, Variance::Invariant) => Variance::Invariant,
656 (Variance::Contravariant, Variance::Bivariant) => Variance::Bivariant,
658 // Figure 1, column 3.
659 (Variance::Invariant, _) => Variance::Invariant,
661 // Figure 1, column 4.
662 (Variance::Bivariant, _) => Variance::Bivariant,
667 impl<CTX> HashStable<CTX> for DebruijnIndex {
668 fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
669 self.as_u32().hash_stable(ctx, hasher);
673 impl<CTX> HashStable<CTX> for IntTy {
674 fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
675 discriminant(self).hash_stable(ctx, hasher);
679 impl<CTX> HashStable<CTX> for UintTy {
680 fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
681 discriminant(self).hash_stable(ctx, hasher);
685 impl<CTX> HashStable<CTX> for FloatTy {
686 fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
687 discriminant(self).hash_stable(ctx, hasher);
691 impl<CTX> HashStable<CTX> for InferTy {
692 fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
694 discriminant(self).hash_stable(ctx, hasher);
696 TyVar(v) => v.as_u32().hash_stable(ctx, hasher),
697 IntVar(v) => v.index.hash_stable(ctx, hasher),
698 FloatVar(v) => v.index.hash_stable(ctx, hasher),
699 FreshTy(v) | FreshIntTy(v) | FreshFloatTy(v) => v.hash_stable(ctx, hasher),
704 impl<CTX> HashStable<CTX> for Variance {
705 fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
706 discriminant(self).hash_stable(ctx, hasher);
710 impl fmt::Debug for IntVarValue {
711 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
713 IntVarValue::IntType(ref v) => v.fmt(f),
714 IntVarValue::UintType(ref v) => v.fmt(f),
719 impl fmt::Debug for FloatVarValue {
720 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
725 impl fmt::Debug for IntVid {
726 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
727 write!(f, "_#{}i", self.index)
731 impl fmt::Debug for FloatVid {
732 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
733 write!(f, "_#{}f", self.index)
737 impl fmt::Debug for InferTy {
738 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
741 TyVar(ref v) => v.fmt(f),
742 IntVar(ref v) => v.fmt(f),
743 FloatVar(ref v) => v.fmt(f),
744 FreshTy(v) => write!(f, "FreshTy({:?})", v),
745 FreshIntTy(v) => write!(f, "FreshIntTy({:?})", v),
746 FreshFloatTy(v) => write!(f, "FreshFloatTy({:?})", v),
751 impl fmt::Debug for Variance {
752 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
753 f.write_str(match *self {
754 Variance::Covariant => "+",
755 Variance::Contravariant => "-",
756 Variance::Invariant => "o",
757 Variance::Bivariant => "*",
762 impl fmt::Display for InferTy {
763 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
766 TyVar(_) => write!(f, "_"),
767 IntVar(_) => write!(f, "{}", "{integer}"),
768 FloatVar(_) => write!(f, "{}", "{float}"),
769 FreshTy(v) => write!(f, "FreshTy({})", v),
770 FreshIntTy(v) => write!(f, "FreshIntTy({})", v),
771 FreshFloatTy(v) => write!(f, "FreshFloatTy({})", v),
776 rustc_index::newtype_index! {
777 /// "Universes" are used during type- and trait-checking in the
778 /// presence of `for<..>` binders to control what sets of names are
779 /// visible. Universes are arranged into a tree: the root universe
780 /// contains names that are always visible. Each child then adds a new
781 /// set of names that are visible, in addition to those of its parent.
782 /// We say that the child universe "extends" the parent universe with
785 /// To make this more concrete, consider this program:
787 /// ```ignore (illustrative)
789 /// fn bar<T>(x: T) {
790 /// let y: for<'a> fn(&'a u8, Foo) = ...;
794 /// The struct name `Foo` is in the root universe U0. But the type
795 /// parameter `T`, introduced on `bar`, is in an extended universe U1
796 /// -- i.e., within `bar`, we can name both `T` and `Foo`, but outside
797 /// of `bar`, we cannot name `T`. Then, within the type of `y`, the
798 /// region `'a` is in a universe U2 that extends U1, because we can
799 /// name it inside the fn type but not outside.
801 /// Universes are used to do type- and trait-checking around these
802 /// "forall" binders (also called **universal quantification**). The
803 /// idea is that when, in the body of `bar`, we refer to `T` as a
804 /// type, we aren't referring to any type in particular, but rather a
805 /// kind of "fresh" type that is distinct from all other types we have
806 /// actually declared. This is called a **placeholder** type, and we
807 /// use universes to talk about this. In other words, a type name in
808 /// universe 0 always corresponds to some "ground" type that the user
809 /// declared, but a type name in a non-zero universe is a placeholder
810 /// type -- an idealized representative of "types in general" that we
811 /// use for checking generic functions.
812 pub struct UniverseIndex {
813 DEBUG_FORMAT = "U{}",
818 pub const ROOT: UniverseIndex = UniverseIndex::from_u32(0);
820 /// Returns the "next" universe index in order -- this new index
821 /// is considered to extend all previous universes. This
822 /// corresponds to entering a `forall` quantifier. So, for
823 /// example, suppose we have this type in universe `U`:
825 /// ```ignore (illustrative)
826 /// for<'a> fn(&'a u32)
829 /// Once we "enter" into this `for<'a>` quantifier, we are in a
830 /// new universe that extends `U` -- in this new universe, we can
831 /// name the region `'a`, but that region was not nameable from
832 /// `U` because it was not in scope there.
833 pub fn next_universe(self) -> UniverseIndex {
834 UniverseIndex::from_u32(self.private.checked_add(1).unwrap())
837 /// Returns `true` if `self` can name a name from `other` -- in other words,
838 /// if the set of names in `self` is a superset of those in
839 /// `other` (`self >= other`).
840 pub fn can_name(self, other: UniverseIndex) -> bool {
841 self.private >= other.private
844 /// Returns `true` if `self` cannot name some names from `other` -- in other
845 /// words, if the set of names in `self` is a strict subset of
846 /// those in `other` (`self < other`).
847 pub fn cannot_name(self, other: UniverseIndex) -> bool {
848 self.private < other.private
852 impl<CTX> HashStable<CTX> for UniverseIndex {
853 fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
854 self.private.hash_stable(ctx, hasher);