1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
use std::hash::{BuildHasher, Hash, Hasher};
use std::marker::PhantomData;
use std::mem;
use std::num::NonZero;

use rustc_index::bit_set::{self, BitSet};
use rustc_index::{Idx, IndexSlice, IndexVec};
use smallvec::SmallVec;

#[cfg(test)]
mod tests;

pub use rustc_stable_hash::{
    FromStableHash, SipHasher128Hash as StableHasherHash, StableSipHasher128 as StableHasher,
};

pub use crate::hashes::{Hash128, Hash64};

/// Something that implements `HashStable<CTX>` can be hashed in a way that is
/// stable across multiple compilation sessions.
///
/// Note that `HashStable` imposes rather more strict requirements than usual
/// hash functions:
///
/// - Stable hashes are sometimes used as identifiers. Therefore they must
///   conform to the corresponding `PartialEq` implementations:
///
///     - `x == y` implies `hash_stable(x) == hash_stable(y)`, and
///     - `x != y` implies `hash_stable(x) != hash_stable(y)`.
///
///   That second condition is usually not required for hash functions
///   (e.g. `Hash`). In practice this means that `hash_stable` must feed any
///   information into the hasher that a `PartialEq` comparison takes into
///   account. See [#49300](https://github.com/rust-lang/rust/issues/49300)
///   for an example where violating this invariant has caused trouble in the
///   past.
///
/// - `hash_stable()` must be independent of the current
///    compilation session. E.g. they must not hash memory addresses or other
///    things that are "randomly" assigned per compilation session.
///
/// - `hash_stable()` must be independent of the host architecture. The
///   `StableHasher` takes care of endianness and `isize`/`usize` platform
///   differences.
pub trait HashStable<CTX> {
    fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher);
}

/// Implement this for types that can be turned into stable keys like, for
/// example, for DefId that can be converted to a DefPathHash. This is used for
/// bringing maps into a predictable order before hashing them.
pub trait ToStableHashKey<HCX> {
    type KeyType: Ord + Sized + HashStable<HCX>;
    fn to_stable_hash_key(&self, hcx: &HCX) -> Self::KeyType;
}

/// Trait for marking a type as having a sort order that is
/// stable across compilation session boundaries. More formally:
///
/// ```txt
/// Ord::cmp(a1, b1) == Ord::cmp(a2, b2)
///    where a2 = decode(encode(a1, context1), context2)
///          b2 = decode(encode(b1, context1), context2)
/// ```
///
/// i.e. the result of `Ord::cmp` is not influenced by encoding
/// the values in one session and then decoding them in another
/// session.
///
/// This is trivially true for types where encoding and decoding
/// don't change the bytes of the values that are used during
/// comparison and comparison only depends on these bytes (as
/// opposed to some non-local state). Examples are u32, String,
/// Path, etc.
///
/// But it is not true for:
///  - `*const T` and `*mut T` because the values of these pointers
///    will change between sessions.
///  - `DefIndex`, `CrateNum`, `LocalDefId`, because their concrete
///    values depend on state that might be different between
///    compilation sessions.
///
/// The associated constant `CAN_USE_UNSTABLE_SORT` denotes whether
/// unstable sorting can be used for this type. Set to true if and
/// only if `a == b` implies `a` and `b` are fully indistinguishable.
pub trait StableOrd: Ord {
    const CAN_USE_UNSTABLE_SORT: bool;

    /// Marker to ensure that implementors have carefully considered
    /// whether their `Ord` implementation obeys this trait's contract.
    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: ();
}

impl<T: StableOrd> StableOrd for &T {
    const CAN_USE_UNSTABLE_SORT: bool = T::CAN_USE_UNSTABLE_SORT;

    // Ordering of a reference is exactly that of the referent, and since
    // the ordering of the referet is stable so must be the ordering of the
    // reference.
    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
}

/// This is a companion trait to `StableOrd`. Some types like `Symbol` can be
/// compared in a cross-session stable way, but their `Ord` implementation is
/// not stable. In such cases, a `StableOrd` implementation can be provided
/// to offer a lightweight way for stable sorting. (The more heavyweight option
/// is to sort via `ToStableHashKey`, but then sorting needs to have access to
/// a stable hashing context and `ToStableHashKey` can also be expensive as in
/// the case of `Symbol` where it has to allocate a `String`.)
///
/// See the documentation of [StableOrd] for how stable sort order is defined.
/// The same definition applies here. Be careful when implementing this trait.
pub trait StableCompare {
    const CAN_USE_UNSTABLE_SORT: bool;

    fn stable_cmp(&self, other: &Self) -> std::cmp::Ordering;
}

/// `StableOrd` denotes that the type's `Ord` implementation is stable, so
/// we can implement `StableCompare` by just delegating to `Ord`.
impl<T: StableOrd> StableCompare for T {
    const CAN_USE_UNSTABLE_SORT: bool = T::CAN_USE_UNSTABLE_SORT;

    fn stable_cmp(&self, other: &Self) -> std::cmp::Ordering {
        self.cmp(other)
    }
}

/// Implement HashStable by just calling `Hash::hash()`. Also implement `StableOrd` for the type since
/// that has the same requirements.
///
/// **WARNING** This is only valid for types that *really* don't need any context for fingerprinting.
/// But it is easy to misuse this macro (see [#96013](https://github.com/rust-lang/rust/issues/96013)
/// for examples). Therefore this macro is not exported and should only be used in the limited cases
/// here in this module.
///
/// Use `#[derive(HashStable_Generic)]` instead.
macro_rules! impl_stable_traits_for_trivial_type {
    ($t:ty) => {
        impl<CTX> $crate::stable_hasher::HashStable<CTX> for $t {
            #[inline]
            fn hash_stable(&self, _: &mut CTX, hasher: &mut $crate::stable_hasher::StableHasher) {
                ::std::hash::Hash::hash(self, hasher);
            }
        }

        impl $crate::stable_hasher::StableOrd for $t {
            const CAN_USE_UNSTABLE_SORT: bool = true;

            // Encoding and decoding doesn't change the bytes of trivial types
            // and `Ord::cmp` depends only on those bytes.
            const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
        }
    };
}

pub(crate) use impl_stable_traits_for_trivial_type;

impl_stable_traits_for_trivial_type!(i8);
impl_stable_traits_for_trivial_type!(i16);
impl_stable_traits_for_trivial_type!(i32);
impl_stable_traits_for_trivial_type!(i64);
impl_stable_traits_for_trivial_type!(isize);

impl_stable_traits_for_trivial_type!(u8);
impl_stable_traits_for_trivial_type!(u16);
impl_stable_traits_for_trivial_type!(u32);
impl_stable_traits_for_trivial_type!(u64);
impl_stable_traits_for_trivial_type!(usize);

impl_stable_traits_for_trivial_type!(u128);
impl_stable_traits_for_trivial_type!(i128);

impl_stable_traits_for_trivial_type!(char);
impl_stable_traits_for_trivial_type!(());

impl_stable_traits_for_trivial_type!(Hash64);

// We need a custom impl as the default hash function will only hash half the bits. For stable
// hashing we want to hash the full 128-bit hash.
impl<CTX> HashStable<CTX> for Hash128 {
    #[inline]
    fn hash_stable(&self, _: &mut CTX, hasher: &mut StableHasher) {
        self.as_u128().hash(hasher);
    }
}

impl StableOrd for Hash128 {
    const CAN_USE_UNSTABLE_SORT: bool = true;

    // Encoding and decoding doesn't change the bytes of `Hash128`
    // and `Ord::cmp` depends only on those bytes.
    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
}

impl<CTX> HashStable<CTX> for ! {
    fn hash_stable(&self, _ctx: &mut CTX, _hasher: &mut StableHasher) {
        unreachable!()
    }
}

impl<CTX, T> HashStable<CTX> for PhantomData<T> {
    fn hash_stable(&self, _ctx: &mut CTX, _hasher: &mut StableHasher) {}
}

impl<CTX> HashStable<CTX> for NonZero<u32> {
    #[inline]
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        self.get().hash_stable(ctx, hasher)
    }
}

impl<CTX> HashStable<CTX> for NonZero<usize> {
    #[inline]
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        self.get().hash_stable(ctx, hasher)
    }
}

impl<CTX> HashStable<CTX> for f32 {
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        let val: u32 = self.to_bits();
        val.hash_stable(ctx, hasher);
    }
}

impl<CTX> HashStable<CTX> for f64 {
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        let val: u64 = self.to_bits();
        val.hash_stable(ctx, hasher);
    }
}

impl<CTX> HashStable<CTX> for ::std::cmp::Ordering {
    #[inline]
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        (*self as i8).hash_stable(ctx, hasher);
    }
}

impl<T1: HashStable<CTX>, CTX> HashStable<CTX> for (T1,) {
    #[inline]
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        let (ref _0,) = *self;
        _0.hash_stable(ctx, hasher);
    }
}

impl<T1: HashStable<CTX>, T2: HashStable<CTX>, CTX> HashStable<CTX> for (T1, T2) {
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        let (ref _0, ref _1) = *self;
        _0.hash_stable(ctx, hasher);
        _1.hash_stable(ctx, hasher);
    }
}

impl<T1: StableOrd, T2: StableOrd> StableOrd for (T1, T2) {
    const CAN_USE_UNSTABLE_SORT: bool = T1::CAN_USE_UNSTABLE_SORT && T2::CAN_USE_UNSTABLE_SORT;

    // Ordering of tuples is a pure function of their elements' ordering, and since
    // the ordering of each element is stable so must be the ordering of the tuple.
    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
}

impl<T1, T2, T3, CTX> HashStable<CTX> for (T1, T2, T3)
where
    T1: HashStable<CTX>,
    T2: HashStable<CTX>,
    T3: HashStable<CTX>,
{
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        let (ref _0, ref _1, ref _2) = *self;
        _0.hash_stable(ctx, hasher);
        _1.hash_stable(ctx, hasher);
        _2.hash_stable(ctx, hasher);
    }
}

impl<T1: StableOrd, T2: StableOrd, T3: StableOrd> StableOrd for (T1, T2, T3) {
    const CAN_USE_UNSTABLE_SORT: bool =
        T1::CAN_USE_UNSTABLE_SORT && T2::CAN_USE_UNSTABLE_SORT && T3::CAN_USE_UNSTABLE_SORT;

    // Ordering of tuples is a pure function of their elements' ordering, and since
    // the ordering of each element is stable so must be the ordering of the tuple.
    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
}

impl<T1, T2, T3, T4, CTX> HashStable<CTX> for (T1, T2, T3, T4)
where
    T1: HashStable<CTX>,
    T2: HashStable<CTX>,
    T3: HashStable<CTX>,
    T4: HashStable<CTX>,
{
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        let (ref _0, ref _1, ref _2, ref _3) = *self;
        _0.hash_stable(ctx, hasher);
        _1.hash_stable(ctx, hasher);
        _2.hash_stable(ctx, hasher);
        _3.hash_stable(ctx, hasher);
    }
}

impl<T1: StableOrd, T2: StableOrd, T3: StableOrd, T4: StableOrd> StableOrd for (T1, T2, T3, T4) {
    const CAN_USE_UNSTABLE_SORT: bool = T1::CAN_USE_UNSTABLE_SORT
        && T2::CAN_USE_UNSTABLE_SORT
        && T3::CAN_USE_UNSTABLE_SORT
        && T4::CAN_USE_UNSTABLE_SORT;

    // Ordering of tuples is a pure function of their elements' ordering, and since
    // the ordering of each element is stable so must be the ordering of the tuple.
    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
}

impl<T: HashStable<CTX>, CTX> HashStable<CTX> for [T] {
    default fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        self.len().hash_stable(ctx, hasher);
        for item in self {
            item.hash_stable(ctx, hasher);
        }
    }
}

impl<CTX> HashStable<CTX> for [u8] {
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        self.len().hash_stable(ctx, hasher);
        hasher.write(self);
    }
}

impl<T: HashStable<CTX>, CTX> HashStable<CTX> for Vec<T> {
    #[inline]
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        self[..].hash_stable(ctx, hasher);
    }
}

impl<K, V, R, CTX> HashStable<CTX> for indexmap::IndexMap<K, V, R>
where
    K: HashStable<CTX> + Eq + Hash,
    V: HashStable<CTX>,
    R: BuildHasher,
{
    #[inline]
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        self.len().hash_stable(ctx, hasher);
        for kv in self {
            kv.hash_stable(ctx, hasher);
        }
    }
}

impl<K, R, CTX> HashStable<CTX> for indexmap::IndexSet<K, R>
where
    K: HashStable<CTX> + Eq + Hash,
    R: BuildHasher,
{
    #[inline]
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        self.len().hash_stable(ctx, hasher);
        for key in self {
            key.hash_stable(ctx, hasher);
        }
    }
}

impl<A, const N: usize, CTX> HashStable<CTX> for SmallVec<[A; N]>
where
    A: HashStable<CTX>,
{
    #[inline]
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        self[..].hash_stable(ctx, hasher);
    }
}

impl<T: ?Sized + HashStable<CTX>, CTX> HashStable<CTX> for Box<T> {
    #[inline]
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        (**self).hash_stable(ctx, hasher);
    }
}

impl<T: ?Sized + HashStable<CTX>, CTX> HashStable<CTX> for ::std::rc::Rc<T> {
    #[inline]
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        (**self).hash_stable(ctx, hasher);
    }
}

impl<T: ?Sized + HashStable<CTX>, CTX> HashStable<CTX> for ::std::sync::Arc<T> {
    #[inline]
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        (**self).hash_stable(ctx, hasher);
    }
}

impl<CTX> HashStable<CTX> for str {
    #[inline]
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        self.as_bytes().hash_stable(ctx, hasher);
    }
}

impl StableOrd for &str {
    const CAN_USE_UNSTABLE_SORT: bool = true;

    // Encoding and decoding doesn't change the bytes of string slices
    // and `Ord::cmp` depends only on those bytes.
    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
}

impl<CTX> HashStable<CTX> for String {
    #[inline]
    fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
        self[..].hash_stable(hcx, hasher);
    }
}

impl StableOrd for String {
    const CAN_USE_UNSTABLE_SORT: bool = true;

    // String comparison only depends on their contents and the
    // contents are not changed by (de-)serialization.
    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
}

impl<HCX> ToStableHashKey<HCX> for String {
    type KeyType = String;
    #[inline]
    fn to_stable_hash_key(&self, _: &HCX) -> Self::KeyType {
        self.clone()
    }
}

impl<HCX, T1: ToStableHashKey<HCX>, T2: ToStableHashKey<HCX>> ToStableHashKey<HCX> for (T1, T2) {
    type KeyType = (T1::KeyType, T2::KeyType);
    #[inline]
    fn to_stable_hash_key(&self, hcx: &HCX) -> Self::KeyType {
        (self.0.to_stable_hash_key(hcx), self.1.to_stable_hash_key(hcx))
    }
}

impl<CTX> HashStable<CTX> for bool {
    #[inline]
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        (if *self { 1u8 } else { 0u8 }).hash_stable(ctx, hasher);
    }
}

impl StableOrd for bool {
    const CAN_USE_UNSTABLE_SORT: bool = true;

    // sort order of bools is not changed by (de-)serialization.
    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
}

impl<T, CTX> HashStable<CTX> for Option<T>
where
    T: HashStable<CTX>,
{
    #[inline]
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        if let Some(ref value) = *self {
            1u8.hash_stable(ctx, hasher);
            value.hash_stable(ctx, hasher);
        } else {
            0u8.hash_stable(ctx, hasher);
        }
    }
}

impl<T: StableOrd> StableOrd for Option<T> {
    const CAN_USE_UNSTABLE_SORT: bool = T::CAN_USE_UNSTABLE_SORT;

    // the Option wrapper does not add instability to comparison.
    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
}

impl<T1, T2, CTX> HashStable<CTX> for Result<T1, T2>
where
    T1: HashStable<CTX>,
    T2: HashStable<CTX>,
{
    #[inline]
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        mem::discriminant(self).hash_stable(ctx, hasher);
        match *self {
            Ok(ref x) => x.hash_stable(ctx, hasher),
            Err(ref x) => x.hash_stable(ctx, hasher),
        }
    }
}

impl<'a, T, CTX> HashStable<CTX> for &'a T
where
    T: HashStable<CTX> + ?Sized,
{
    #[inline]
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        (**self).hash_stable(ctx, hasher);
    }
}

impl<T, CTX> HashStable<CTX> for ::std::mem::Discriminant<T> {
    #[inline]
    fn hash_stable(&self, _: &mut CTX, hasher: &mut StableHasher) {
        ::std::hash::Hash::hash(self, hasher);
    }
}

impl<T, CTX> HashStable<CTX> for ::std::ops::RangeInclusive<T>
where
    T: HashStable<CTX>,
{
    #[inline]
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        self.start().hash_stable(ctx, hasher);
        self.end().hash_stable(ctx, hasher);
    }
}

impl<I: Idx, T, CTX> HashStable<CTX> for IndexSlice<I, T>
where
    T: HashStable<CTX>,
{
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        self.len().hash_stable(ctx, hasher);
        for v in &self.raw {
            v.hash_stable(ctx, hasher);
        }
    }
}

impl<I: Idx, T, CTX> HashStable<CTX> for IndexVec<I, T>
where
    T: HashStable<CTX>,
{
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        self.len().hash_stable(ctx, hasher);
        for v in &self.raw {
            v.hash_stable(ctx, hasher);
        }
    }
}

impl<I: Idx, CTX> HashStable<CTX> for BitSet<I> {
    fn hash_stable(&self, _ctx: &mut CTX, hasher: &mut StableHasher) {
        ::std::hash::Hash::hash(self, hasher);
    }
}

impl<R: Idx, C: Idx, CTX> HashStable<CTX> for bit_set::BitMatrix<R, C> {
    fn hash_stable(&self, _ctx: &mut CTX, hasher: &mut StableHasher) {
        ::std::hash::Hash::hash(self, hasher);
    }
}

impl<T, CTX> HashStable<CTX> for bit_set::FiniteBitSet<T>
where
    T: HashStable<CTX> + bit_set::FiniteBitSetTy,
{
    fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
        self.0.hash_stable(hcx, hasher);
    }
}

impl_stable_traits_for_trivial_type!(::std::path::Path);
impl_stable_traits_for_trivial_type!(::std::path::PathBuf);

// It is not safe to implement HashStable for HashSet, HashMap or any other collection type
// with unstable but observable iteration order.
// See https://github.com/rust-lang/compiler-team/issues/533 for further information.
impl<V, HCX> !HashStable<HCX> for std::collections::HashSet<V> {}
impl<K, V, HCX> !HashStable<HCX> for std::collections::HashMap<K, V> {}

impl<K, V, HCX> HashStable<HCX> for ::std::collections::BTreeMap<K, V>
where
    K: HashStable<HCX> + StableOrd,
    V: HashStable<HCX>,
{
    fn hash_stable(&self, hcx: &mut HCX, hasher: &mut StableHasher) {
        self.len().hash_stable(hcx, hasher);
        for entry in self.iter() {
            entry.hash_stable(hcx, hasher);
        }
    }
}

impl<K, HCX> HashStable<HCX> for ::std::collections::BTreeSet<K>
where
    K: HashStable<HCX> + StableOrd,
{
    fn hash_stable(&self, hcx: &mut HCX, hasher: &mut StableHasher) {
        self.len().hash_stable(hcx, hasher);
        for entry in self.iter() {
            entry.hash_stable(hcx, hasher);
        }
    }
}

/// Controls what data we do or do not hash.
/// Whenever a `HashStable` implementation caches its
/// result, it needs to include `HashingControls` as part
/// of the key, to ensure that it does not produce an incorrect
/// result (for example, using a `Fingerprint` produced while
/// hashing `Span`s when a `Fingerprint` without `Span`s is
/// being requested)
#[derive(Clone, Hash, Eq, PartialEq, Debug)]
pub struct HashingControls {
    pub hash_spans: bool,
}