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;
27 type AdtDef: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
28 type SubstsRef: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
29 type DefId: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
30 type Ty: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
31 type Const: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
32 type Region: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
33 type TypeAndMut: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
34 type Mutability: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
35 type Movability: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
36 type PolyFnSig: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
37 type ListBinderExistentialPredicate: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
38 type BinderListTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
39 type ListTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
40 type ProjectionTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
41 type ParamTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
42 type BoundTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
43 type PlaceholderType: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
44 type InferTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
45 type DelaySpanBugEmitted: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
46 type PredicateKind: Clone + Debug + Hash + PartialEq + Eq;
47 type AllocId: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
49 type EarlyBoundRegion: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
50 type BoundRegion: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
51 type FreeRegion: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
52 type RegionVid: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
53 type PlaceholderRegion: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
56 pub trait InternAs<T: ?Sized, R> {
58 fn intern_with<F>(self, f: F) -> Self::Output
63 impl<I, T, R, E> InternAs<[T], R> for I
65 E: InternIteratorElement<T, R>,
66 I: Iterator<Item = E>,
68 type Output = E::Output;
69 fn intern_with<F>(self, f: F) -> Self::Output
73 E::intern_with(self, f)
77 pub trait InternIteratorElement<T, R>: Sized {
79 fn intern_with<I: Iterator<Item = Self>, F: FnOnce(&[T]) -> R>(iter: I, f: F) -> Self::Output;
82 impl<T, R> InternIteratorElement<T, R> for T {
84 fn intern_with<I: Iterator<Item = Self>, F: FnOnce(&[T]) -> R>(
88 // This code is hot enough that it's worth specializing for the most
89 // common length lists, to avoid the overhead of `SmallVec` creation.
90 // Lengths 0, 1, and 2 typically account for ~95% of cases. If
91 // `size_hint` is incorrect a panic will occur via an `unwrap` or an
93 match iter.size_hint() {
95 assert!(iter.next().is_none());
99 let t0 = iter.next().unwrap();
100 assert!(iter.next().is_none());
104 let t0 = iter.next().unwrap();
105 let t1 = iter.next().unwrap();
106 assert!(iter.next().is_none());
109 _ => f(&iter.collect::<SmallVec<[_; 8]>>()),
114 impl<'a, T, R> InternIteratorElement<T, R> for &'a T
119 fn intern_with<I: Iterator<Item = Self>, F: FnOnce(&[T]) -> R>(iter: I, f: F) -> Self::Output {
120 // This code isn't hot.
121 f(&iter.cloned().collect::<SmallVec<[_; 8]>>())
125 impl<T, R, E> InternIteratorElement<T, R> for Result<T, E> {
126 type Output = Result<R, E>;
127 fn intern_with<I: Iterator<Item = Self>, F: FnOnce(&[T]) -> R>(
131 // This code is hot enough that it's worth specializing for the most
132 // common length lists, to avoid the overhead of `SmallVec` creation.
133 // Lengths 0, 1, and 2 typically account for ~95% of cases. If
134 // `size_hint` is incorrect a panic will occur via an `unwrap` or an
135 // `assert`, unless a failure happens first, in which case the result
136 // will be an error anyway.
137 Ok(match iter.size_hint() {
139 assert!(iter.next().is_none());
143 let t0 = iter.next().unwrap()?;
144 assert!(iter.next().is_none());
148 let t0 = iter.next().unwrap()?;
149 let t1 = iter.next().unwrap()?;
150 assert!(iter.next().is_none());
153 _ => f(&iter.collect::<Result<SmallVec<[_; 8]>, _>>()?),
159 /// Flags that we track on types. These flags are propagated upwards
160 /// through the type during type construction, so that we can quickly check
161 /// whether the type has various kinds of types in it without recursing
162 /// over the type itself.
163 pub struct TypeFlags: u32 {
164 // Does this have parameters? Used to determine whether substitution is
166 /// Does this have `Param`?
167 const HAS_TY_PARAM = 1 << 0;
168 /// Does this have `ReEarlyBound`?
169 const HAS_RE_PARAM = 1 << 1;
170 /// Does this have `ConstKind::Param`?
171 const HAS_CT_PARAM = 1 << 2;
173 const NEEDS_SUBST = TypeFlags::HAS_TY_PARAM.bits
174 | TypeFlags::HAS_RE_PARAM.bits
175 | TypeFlags::HAS_CT_PARAM.bits;
177 /// Does this have `Infer`?
178 const HAS_TY_INFER = 1 << 3;
179 /// Does this have `ReVar`?
180 const HAS_RE_INFER = 1 << 4;
181 /// Does this have `ConstKind::Infer`?
182 const HAS_CT_INFER = 1 << 5;
184 /// Does this have inference variables? Used to determine whether
185 /// inference is required.
186 const NEEDS_INFER = TypeFlags::HAS_TY_INFER.bits
187 | TypeFlags::HAS_RE_INFER.bits
188 | TypeFlags::HAS_CT_INFER.bits;
190 /// Does this have `Placeholder`?
191 const HAS_TY_PLACEHOLDER = 1 << 6;
192 /// Does this have `RePlaceholder`?
193 const HAS_RE_PLACEHOLDER = 1 << 7;
194 /// Does this have `ConstKind::Placeholder`?
195 const HAS_CT_PLACEHOLDER = 1 << 8;
197 /// `true` if there are "names" of regions and so forth
198 /// that are local to a particular fn/inferctxt
199 const HAS_FREE_LOCAL_REGIONS = 1 << 9;
201 /// `true` if there are "names" of types and regions and so forth
202 /// that are local to a particular fn
203 const HAS_FREE_LOCAL_NAMES = TypeFlags::HAS_TY_PARAM.bits
204 | TypeFlags::HAS_CT_PARAM.bits
205 | TypeFlags::HAS_TY_INFER.bits
206 | TypeFlags::HAS_CT_INFER.bits
207 | TypeFlags::HAS_TY_PLACEHOLDER.bits
208 | TypeFlags::HAS_CT_PLACEHOLDER.bits
209 // We consider 'freshened' types and constants
210 // to depend on a particular fn.
211 // The freshening process throws away information,
212 // which can make things unsuitable for use in a global
213 // cache. Note that there is no 'fresh lifetime' flag -
214 // freshening replaces all lifetimes with `ReErased`,
215 // which is different from how types/const are freshened.
216 | TypeFlags::HAS_TY_FRESH.bits
217 | TypeFlags::HAS_CT_FRESH.bits
218 | TypeFlags::HAS_FREE_LOCAL_REGIONS.bits;
220 /// Does this have `Projection`?
221 const HAS_TY_PROJECTION = 1 << 10;
222 /// Does this have `Opaque`?
223 const HAS_TY_OPAQUE = 1 << 11;
224 /// Does this have `ConstKind::Unevaluated`?
225 const HAS_CT_PROJECTION = 1 << 12;
227 /// Could this type be normalized further?
228 const HAS_PROJECTION = TypeFlags::HAS_TY_PROJECTION.bits
229 | TypeFlags::HAS_TY_OPAQUE.bits
230 | TypeFlags::HAS_CT_PROJECTION.bits;
232 /// Is an error type/const reachable?
233 const HAS_ERROR = 1 << 13;
235 /// Does this have any region that "appears free" in the type?
236 /// Basically anything but `ReLateBound` and `ReErased`.
237 const HAS_FREE_REGIONS = 1 << 14;
239 /// Does this have any `ReLateBound` regions? Used to check
240 /// if a global bound is safe to evaluate.
241 const HAS_RE_LATE_BOUND = 1 << 15;
243 /// Does this have any `ReErased` regions?
244 const HAS_RE_ERASED = 1 << 16;
246 /// Does this value have parameters/placeholders/inference variables which could be
247 /// replaced later, in a way that would change the results of `impl` specialization?
248 const STILL_FURTHER_SPECIALIZABLE = 1 << 17;
250 /// Does this value have `InferTy::FreshTy/FreshIntTy/FreshFloatTy`?
251 const HAS_TY_FRESH = 1 << 18;
253 /// Does this value have `InferConst::Fresh`?
254 const HAS_CT_FRESH = 1 << 19;
258 rustc_index::newtype_index! {
259 /// A [De Bruijn index][dbi] is a standard means of representing
260 /// regions (and perhaps later types) in a higher-ranked setting. In
261 /// particular, imagine a type like this:
262 /// ```ignore (illustrative)
263 /// for<'a> fn(for<'b> fn(&'b isize, &'a isize), &'a char)
266 /// // | +------------+ 0 | |
268 /// // +----------------------------------+ 1 |
270 /// // +----------------------------------------------+ 0
272 /// In this type, there are two binders (the outer fn and the inner
273 /// fn). We need to be able to determine, for any given region, which
274 /// fn type it is bound by, the inner or the outer one. There are
275 /// various ways you can do this, but a De Bruijn index is one of the
276 /// more convenient and has some nice properties. The basic idea is to
277 /// count the number of binders, inside out. Some examples should help
278 /// clarify what I mean.
280 /// Let's start with the reference type `&'b isize` that is the first
281 /// argument to the inner function. This region `'b` is assigned a De
282 /// Bruijn index of 0, meaning "the innermost binder" (in this case, a
283 /// fn). The region `'a` that appears in the second argument type (`&'a
284 /// isize`) would then be assigned a De Bruijn index of 1, meaning "the
285 /// second-innermost binder". (These indices are written on the arrows
288 /// What is interesting is that De Bruijn index attached to a particular
289 /// variable will vary depending on where it appears. For example,
290 /// the final type `&'a char` also refers to the region `'a` declared on
291 /// the outermost fn. But this time, this reference is not nested within
292 /// any other binders (i.e., it is not an argument to the inner fn, but
293 /// rather the outer one). Therefore, in this case, it is assigned a
294 /// De Bruijn index of 0, because the innermost binder in that location
297 /// [dbi]: https://en.wikipedia.org/wiki/De_Bruijn_index
298 pub struct DebruijnIndex {
299 DEBUG_FORMAT = "DebruijnIndex({})",
305 /// Returns the resulting index when this value is moved into
306 /// `amount` number of new binders. So, e.g., if you had
308 /// for<'a> fn(&'a x)
310 /// and you wanted to change it to
312 /// for<'a> fn(for<'b> fn(&'a x))
314 /// you would need to shift the index for `'a` into a new binder.
317 pub fn shifted_in(self, amount: u32) -> DebruijnIndex {
318 DebruijnIndex::from_u32(self.as_u32() + amount)
321 /// Update this index in place by shifting it "in" through
322 /// `amount` number of binders.
324 pub fn shift_in(&mut self, amount: u32) {
325 *self = self.shifted_in(amount);
328 /// Returns the resulting index when this value is moved out from
329 /// `amount` number of new binders.
332 pub fn shifted_out(self, amount: u32) -> DebruijnIndex {
333 DebruijnIndex::from_u32(self.as_u32() - amount)
336 /// Update in place by shifting out from `amount` binders.
338 pub fn shift_out(&mut self, amount: u32) {
339 *self = self.shifted_out(amount);
342 /// Adjusts any De Bruijn indices so as to make `to_binder` the
343 /// innermost binder. That is, if we have something bound at `to_binder`,
344 /// it will now be bound at INNERMOST. This is an appropriate thing to do
345 /// when moving a region out from inside binders:
347 /// ```ignore (illustrative)
348 /// for<'a> fn(for<'b> for<'c> fn(&'a u32), _)
349 /// // Binder: D3 D2 D1 ^^
352 /// Here, the region `'a` would have the De Bruijn index D3,
353 /// because it is the bound 3 binders out. However, if we wanted
354 /// to refer to that region `'a` in the second argument (the `_`),
355 /// those two binders would not be in scope. In that case, we
356 /// might invoke `shift_out_to_binder(D3)`. This would adjust the
357 /// De Bruijn index of `'a` to D1 (the innermost binder).
359 /// If we invoke `shift_out_to_binder` and the region is in fact
360 /// bound by one of the binders we are shifting out of, that is an
361 /// error (and should fail an assertion failure).
363 pub fn shifted_out_to_binder(self, to_binder: DebruijnIndex) -> Self {
364 self.shifted_out(to_binder.as_u32() - INNERMOST.as_u32())
368 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
369 #[derive(Encodable, Decodable)]
380 pub fn name_str(&self) -> &'static str {
382 IntTy::Isize => "isize",
387 IntTy::I128 => "i128",
391 pub fn bit_width(&self) -> Option<u64> {
393 IntTy::Isize => return None,
402 pub fn normalize(&self, target_width: u32) -> Self {
404 IntTy::Isize => match target_width {
415 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Copy, Debug)]
416 #[derive(Encodable, Decodable)]
427 pub fn name_str(&self) -> &'static str {
429 UintTy::Usize => "usize",
431 UintTy::U16 => "u16",
432 UintTy::U32 => "u32",
433 UintTy::U64 => "u64",
434 UintTy::U128 => "u128",
438 pub fn bit_width(&self) -> Option<u64> {
440 UintTy::Usize => return None,
449 pub fn normalize(&self, target_width: u32) -> Self {
451 UintTy::Usize => match target_width {
462 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
463 #[derive(Encodable, Decodable)]
470 pub fn name_str(self) -> &'static str {
472 FloatTy::F32 => "f32",
473 FloatTy::F64 => "f64",
477 pub fn bit_width(self) -> u64 {
485 #[derive(Clone, Copy, PartialEq, Eq)]
486 pub enum IntVarValue {
491 #[derive(Clone, Copy, PartialEq, Eq)]
492 pub struct FloatVarValue(pub FloatTy);
494 rustc_index::newtype_index! {
495 /// A **ty**pe **v**ariable **ID**.
497 DEBUG_FORMAT = "_#{}t"
501 /// An **int**egral (`u32`, `i32`, `usize`, etc.) type **v**ariable **ID**.
502 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable, Decodable)]
507 /// An **float**ing-point (`f32` or `f64`) type **v**ariable **ID**.
508 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable, Decodable)]
509 pub struct FloatVid {
513 /// A placeholder for a type that hasn't been inferred yet.
515 /// E.g., if we have an empty array (`[]`), then we create a fresh
516 /// type variable for the element type since we won't know until it's
517 /// used what the element type is supposed to be.
518 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable, Decodable)]
522 /// An integral type variable (`{integer}`).
524 /// These are created when the compiler sees an integer literal like
525 /// `1` that could be several different types (`u8`, `i32`, `u32`, etc.).
526 /// We don't know until it's used what type it's supposed to be, so
527 /// we create a fresh type variable.
529 /// A floating-point type variable (`{float}`).
531 /// These are created when the compiler sees an float literal like
532 /// `1.0` that could be either an `f32` or an `f64`.
533 /// We don't know until it's used what type it's supposed to be, so
534 /// we create a fresh type variable.
537 /// A [`FreshTy`][Self::FreshTy] is one that is generated as a replacement
538 /// for an unbound type variable. This is convenient for caching etc. See
539 /// `rustc_infer::infer::freshen` for more details.
541 /// Compare with [`TyVar`][Self::TyVar].
543 /// Like [`FreshTy`][Self::FreshTy], but as a replacement for [`IntVar`][Self::IntVar].
545 /// Like [`FreshTy`][Self::FreshTy], but as a replacement for [`FloatVar`][Self::FloatVar].
549 /// Raw `TyVid` are used as the unification key for `sub_relations`;
550 /// they carry no values.
551 impl UnifyKey for TyVid {
554 fn index(&self) -> u32 {
558 fn from_index(i: u32) -> TyVid {
561 fn tag() -> &'static str {
566 impl EqUnifyValue for IntVarValue {}
568 impl UnifyKey for IntVid {
569 type Value = Option<IntVarValue>;
570 #[inline] // make this function eligible for inlining - it is quite hot.
571 fn index(&self) -> u32 {
575 fn from_index(i: u32) -> IntVid {
578 fn tag() -> &'static str {
583 impl EqUnifyValue for FloatVarValue {}
585 impl UnifyKey for FloatVid {
586 type Value = Option<FloatVarValue>;
588 fn index(&self) -> u32 {
592 fn from_index(i: u32) -> FloatVid {
593 FloatVid { index: i }
595 fn tag() -> &'static str {
600 #[derive(Copy, Clone, PartialEq, Decodable, Encodable, Hash)]
601 #[rustc_pass_by_value]
603 Covariant, // T<A> <: T<B> iff A <: B -- e.g., function return type
604 Invariant, // T<A> <: T<B> iff B == A -- e.g., type of mutable cell
605 Contravariant, // T<A> <: T<B> iff B <: A -- e.g., function param type
606 Bivariant, // T<A> <: T<B> -- e.g., unused type parameter
610 /// `a.xform(b)` combines the variance of a context with the
611 /// variance of a type with the following meaning. If we are in a
612 /// context with variance `a`, and we encounter a type argument in
613 /// a position with variance `b`, then `a.xform(b)` is the new
614 /// variance with which the argument appears.
617 /// ```ignore (illustrative)
620 /// Here, the "ambient" variance starts as covariant. `*mut T` is
621 /// invariant with respect to `T`, so the variance in which the
622 /// `Vec<i32>` appears is `Covariant.xform(Invariant)`, which
623 /// yields `Invariant`. Now, the type `Vec<T>` is covariant with
624 /// respect to its type argument `T`, and hence the variance of
625 /// the `i32` here is `Invariant.xform(Covariant)`, which results
626 /// (again) in `Invariant`.
629 /// ```ignore (illustrative)
630 /// fn(*const Vec<i32>, *mut Vec<i32)
632 /// The ambient variance is covariant. A `fn` type is
633 /// contravariant with respect to its parameters, so the variance
634 /// within which both pointer types appear is
635 /// `Covariant.xform(Contravariant)`, or `Contravariant`. `*const
636 /// T` is covariant with respect to `T`, so the variance within
637 /// which the first `Vec<i32>` appears is
638 /// `Contravariant.xform(Covariant)` or `Contravariant`. The same
639 /// is true for its `i32` argument. In the `*mut T` case, the
640 /// variance of `Vec<i32>` is `Contravariant.xform(Invariant)`,
641 /// and hence the outermost type is `Invariant` with respect to
642 /// `Vec<i32>` (and its `i32` argument).
644 /// Source: Figure 1 of "Taming the Wildcards:
645 /// Combining Definition- and Use-Site Variance" published in PLDI'11.
646 pub fn xform(self, v: Variance) -> Variance {
648 // Figure 1, column 1.
649 (Variance::Covariant, Variance::Covariant) => Variance::Covariant,
650 (Variance::Covariant, Variance::Contravariant) => Variance::Contravariant,
651 (Variance::Covariant, Variance::Invariant) => Variance::Invariant,
652 (Variance::Covariant, Variance::Bivariant) => Variance::Bivariant,
654 // Figure 1, column 2.
655 (Variance::Contravariant, Variance::Covariant) => Variance::Contravariant,
656 (Variance::Contravariant, Variance::Contravariant) => Variance::Covariant,
657 (Variance::Contravariant, Variance::Invariant) => Variance::Invariant,
658 (Variance::Contravariant, Variance::Bivariant) => Variance::Bivariant,
660 // Figure 1, column 3.
661 (Variance::Invariant, _) => Variance::Invariant,
663 // Figure 1, column 4.
664 (Variance::Bivariant, _) => Variance::Bivariant,
669 impl<CTX> HashStable<CTX> for DebruijnIndex {
670 fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
671 self.as_u32().hash_stable(ctx, hasher);
675 impl<CTX> HashStable<CTX> for IntTy {
676 fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
677 discriminant(self).hash_stable(ctx, hasher);
681 impl<CTX> HashStable<CTX> for UintTy {
682 fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
683 discriminant(self).hash_stable(ctx, hasher);
687 impl<CTX> HashStable<CTX> for FloatTy {
688 fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
689 discriminant(self).hash_stable(ctx, hasher);
693 impl<CTX> HashStable<CTX> for InferTy {
694 fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
696 discriminant(self).hash_stable(ctx, hasher);
698 TyVar(v) => v.as_u32().hash_stable(ctx, hasher),
699 IntVar(v) => v.index.hash_stable(ctx, hasher),
700 FloatVar(v) => v.index.hash_stable(ctx, hasher),
701 FreshTy(v) | FreshIntTy(v) | FreshFloatTy(v) => v.hash_stable(ctx, hasher),
706 impl<CTX> HashStable<CTX> for Variance {
707 fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
708 discriminant(self).hash_stable(ctx, hasher);
712 impl fmt::Debug for IntVarValue {
713 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
715 IntVarValue::IntType(ref v) => v.fmt(f),
716 IntVarValue::UintType(ref v) => v.fmt(f),
721 impl fmt::Debug for FloatVarValue {
722 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
727 impl fmt::Debug for IntVid {
728 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
729 write!(f, "_#{}i", self.index)
733 impl fmt::Debug for FloatVid {
734 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
735 write!(f, "_#{}f", self.index)
739 impl fmt::Debug for InferTy {
740 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
743 TyVar(ref v) => v.fmt(f),
744 IntVar(ref v) => v.fmt(f),
745 FloatVar(ref v) => v.fmt(f),
746 FreshTy(v) => write!(f, "FreshTy({:?})", v),
747 FreshIntTy(v) => write!(f, "FreshIntTy({:?})", v),
748 FreshFloatTy(v) => write!(f, "FreshFloatTy({:?})", v),
753 impl fmt::Debug for Variance {
754 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
755 f.write_str(match *self {
756 Variance::Covariant => "+",
757 Variance::Contravariant => "-",
758 Variance::Invariant => "o",
759 Variance::Bivariant => "*",
764 impl fmt::Display for InferTy {
765 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
768 TyVar(_) => write!(f, "_"),
769 IntVar(_) => write!(f, "{}", "{integer}"),
770 FloatVar(_) => write!(f, "{}", "{float}"),
771 FreshTy(v) => write!(f, "FreshTy({})", v),
772 FreshIntTy(v) => write!(f, "FreshIntTy({})", v),
773 FreshFloatTy(v) => write!(f, "FreshFloatTy({})", v),
778 rustc_index::newtype_index! {
779 /// "Universes" are used during type- and trait-checking in the
780 /// presence of `for<..>` binders to control what sets of names are
781 /// visible. Universes are arranged into a tree: the root universe
782 /// contains names that are always visible. Each child then adds a new
783 /// set of names that are visible, in addition to those of its parent.
784 /// We say that the child universe "extends" the parent universe with
787 /// To make this more concrete, consider this program:
789 /// ```ignore (illustrative)
791 /// fn bar<T>(x: T) {
792 /// let y: for<'a> fn(&'a u8, Foo) = ...;
796 /// The struct name `Foo` is in the root universe U0. But the type
797 /// parameter `T`, introduced on `bar`, is in an extended universe U1
798 /// -- i.e., within `bar`, we can name both `T` and `Foo`, but outside
799 /// of `bar`, we cannot name `T`. Then, within the type of `y`, the
800 /// region `'a` is in a universe U2 that extends U1, because we can
801 /// name it inside the fn type but not outside.
803 /// Universes are used to do type- and trait-checking around these
804 /// "forall" binders (also called **universal quantification**). The
805 /// idea is that when, in the body of `bar`, we refer to `T` as a
806 /// type, we aren't referring to any type in particular, but rather a
807 /// kind of "fresh" type that is distinct from all other types we have
808 /// actually declared. This is called a **placeholder** type, and we
809 /// use universes to talk about this. In other words, a type name in
810 /// universe 0 always corresponds to some "ground" type that the user
811 /// declared, but a type name in a non-zero universe is a placeholder
812 /// type -- an idealized representative of "types in general" that we
813 /// use for checking generic functions.
814 pub struct UniverseIndex {
815 DEBUG_FORMAT = "U{}",
820 pub const ROOT: UniverseIndex = UniverseIndex::from_u32(0);
822 /// Returns the "next" universe index in order -- this new index
823 /// is considered to extend all previous universes. This
824 /// corresponds to entering a `forall` quantifier. So, for
825 /// example, suppose we have this type in universe `U`:
827 /// ```ignore (illustrative)
828 /// for<'a> fn(&'a u32)
831 /// Once we "enter" into this `for<'a>` quantifier, we are in a
832 /// new universe that extends `U` -- in this new universe, we can
833 /// name the region `'a`, but that region was not nameable from
834 /// `U` because it was not in scope there.
835 pub fn next_universe(self) -> UniverseIndex {
836 UniverseIndex::from_u32(self.private.checked_add(1).unwrap())
839 /// Returns `true` if `self` can name a name from `other` -- in other words,
840 /// if the set of names in `self` is a superset of those in
841 /// `other` (`self >= other`).
842 pub fn can_name(self, other: UniverseIndex) -> bool {
843 self.private >= other.private
846 /// Returns `true` if `self` cannot name some names from `other` -- in other
847 /// words, if the set of names in `self` is a strict subset of
848 /// those in `other` (`self < other`).
849 pub fn cannot_name(self, other: UniverseIndex) -> bool {
850 self.private < other.private
854 impl<CTX> HashStable<CTX> for UniverseIndex {
855 fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
856 self.private.hash_stable(ctx, hasher);