summaryrefslogtreecommitdiffstats
path: root/compiler/rustc_span/src/hygiene.rs
blob: 9f2ff4378425edad21cd47d7446efe7bbf021880 (plain)
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
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
//! Machinery for hygienic macros.
//!
//! Inspired by Matthew Flatt et al., “Macros That Work Together: Compile-Time Bindings, Partial
//! Expansion, and Definition Contexts,” *Journal of Functional Programming* 22, no. 2
//! (March 1, 2012): 181–216, <https://doi.org/10.1017/S0956796812000093>.

// Hygiene data is stored in a global variable and accessed via TLS, which
// means that accesses are somewhat expensive. (`HygieneData::with`
// encapsulates a single access.) Therefore, on hot code paths it is worth
// ensuring that multiple HygieneData accesses are combined into a single
// `HygieneData::with`.
//
// This explains why `HygieneData`, `SyntaxContext` and `ExpnId` have interfaces
// with a certain amount of redundancy in them. For example,
// `SyntaxContext::outer_expn_data` combines `SyntaxContext::outer` and
// `ExpnId::expn_data` so that two `HygieneData` accesses can be performed within
// a single `HygieneData::with` call.
//
// It also explains why many functions appear in `HygieneData` and again in
// `SyntaxContext` or `ExpnId`. For example, `HygieneData::outer` and
// `SyntaxContext::outer` do the same thing, but the former is for use within a
// `HygieneData::with` call while the latter is for use outside such a call.
// When modifying this file it is important to understand this distinction,
// because getting it wrong can lead to nested `HygieneData::with` calls that
// trigger runtime aborts. (Fortunately these are obvious and easy to fix.)

use crate::edition::Edition;
use crate::symbol::{kw, sym, Symbol};
use crate::with_session_globals;
use crate::{HashStableContext, Span, DUMMY_SP};

use crate::def_id::{CrateNum, DefId, StableCrateId, CRATE_DEF_ID, LOCAL_CRATE};
use rustc_data_structures::fingerprint::Fingerprint;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_data_structures::stable_hasher::HashingControls;
use rustc_data_structures::stable_hasher::{Hash64, HashStable, StableHasher};
use rustc_data_structures::sync::{Lock, Lrc};
use rustc_data_structures::unhash::UnhashMap;
use rustc_index::IndexVec;
use rustc_macros::HashStable_Generic;
use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
use std::fmt;
use std::hash::Hash;

/// A `SyntaxContext` represents a chain of pairs `(ExpnId, Transparency)` named "marks".
#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct SyntaxContext(u32);

#[derive(Debug, Encodable, Decodable, Clone)]
pub struct SyntaxContextData {
    outer_expn: ExpnId,
    outer_transparency: Transparency,
    parent: SyntaxContext,
    /// This context, but with all transparent and semi-transparent expansions filtered away.
    opaque: SyntaxContext,
    /// This context, but with all transparent expansions filtered away.
    opaque_and_semitransparent: SyntaxContext,
    /// Name of the crate to which `$crate` with this context would resolve.
    dollar_crate_name: Symbol,
}

rustc_index::newtype_index! {
    /// A unique ID associated with a macro invocation and expansion.
    #[custom_encodable]
    pub struct ExpnIndex {}
}

/// A unique ID associated with a macro invocation and expansion.
#[derive(Clone, Copy, PartialEq, Eq, Hash)]
pub struct ExpnId {
    pub krate: CrateNum,
    pub local_id: ExpnIndex,
}

impl fmt::Debug for ExpnId {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // Generate crate_::{{expn_}}.
        write!(f, "{:?}::{{{{expn{}}}}}", self.krate, self.local_id.as_u32())
    }
}

rustc_index::newtype_index! {
    /// A unique ID associated with a macro invocation and expansion.
    #[custom_encodable]
    #[no_ord_impl]
    #[debug_format = "expn{}"]
    pub struct LocalExpnId {}
}

// To ensure correctness of incremental compilation,
// `LocalExpnId` must not implement `Ord` or `PartialOrd`.
// See https://github.com/rust-lang/rust/issues/90317.
impl !Ord for LocalExpnId {}
impl !PartialOrd for LocalExpnId {}

/// Assert that the provided `HashStableContext` is configured with the 'default'
/// `HashingControls`. We should always have bailed out before getting to here
/// with a non-default mode. With this check in place, we can avoid the need
/// to maintain separate versions of `ExpnData` hashes for each permutation
/// of `HashingControls` settings.
fn assert_default_hashing_controls<CTX: HashStableContext>(ctx: &CTX, msg: &str) {
    match ctx.hashing_controls() {
        // Note that we require that `hash_spans` be set according to the global
        // `-Z incremental-ignore-spans` option. Normally, this option is disabled,
        // which will cause us to require that this method always be called with `Span` hashing
        // enabled.
        //
        // Span hashing can also be disabled without `-Z incremental-ignore-spans`.
        // This is the case for instance when building a hash for name mangling.
        // Such configuration must not be used for metadata.
        HashingControls { hash_spans }
            if hash_spans != ctx.unstable_opts_incremental_ignore_spans() => {}
        other => panic!("Attempted hashing of {msg} with non-default HashingControls: {other:?}"),
    }
}

/// A unique hash value associated to an expansion.
#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, Encodable, Decodable, HashStable_Generic)]
pub struct ExpnHash(Fingerprint);

impl ExpnHash {
    /// Returns the [StableCrateId] identifying the crate this [ExpnHash]
    /// originates from.
    #[inline]
    pub fn stable_crate_id(self) -> StableCrateId {
        StableCrateId(self.0.split().0)
    }

    /// Returns the crate-local part of the [ExpnHash].
    ///
    /// Used for tests.
    #[inline]
    pub fn local_hash(self) -> Hash64 {
        self.0.split().1
    }

    #[inline]
    pub fn is_root(self) -> bool {
        self.0 == Fingerprint::ZERO
    }

    /// Builds a new [ExpnHash] with the given [StableCrateId] and
    /// `local_hash`, where `local_hash` must be unique within its crate.
    fn new(stable_crate_id: StableCrateId, local_hash: Hash64) -> ExpnHash {
        ExpnHash(Fingerprint::new(stable_crate_id.0, local_hash))
    }
}

/// A property of a macro expansion that determines how identifiers
/// produced by that expansion are resolved.
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Hash, Debug, Encodable, Decodable)]
#[derive(HashStable_Generic)]
pub enum Transparency {
    /// Identifier produced by a transparent expansion is always resolved at call-site.
    /// Call-site spans in procedural macros, hygiene opt-out in `macro` should use this.
    Transparent,
    /// Identifier produced by a semi-transparent expansion may be resolved
    /// either at call-site or at definition-site.
    /// If it's a local variable, label or `$crate` then it's resolved at def-site.
    /// Otherwise it's resolved at call-site.
    /// `macro_rules` macros behave like this, built-in macros currently behave like this too,
    /// but that's an implementation detail.
    SemiTransparent,
    /// Identifier produced by an opaque expansion is always resolved at definition-site.
    /// Def-site spans in procedural macros, identifiers from `macro` by default use this.
    Opaque,
}

impl LocalExpnId {
    /// The ID of the theoretical expansion that generates freshly parsed, unexpanded AST.
    pub const ROOT: LocalExpnId = LocalExpnId::from_u32(0);

    #[inline]
    pub fn from_raw(idx: ExpnIndex) -> LocalExpnId {
        LocalExpnId::from_u32(idx.as_u32())
    }

    #[inline]
    pub fn as_raw(self) -> ExpnIndex {
        ExpnIndex::from_u32(self.as_u32())
    }

    pub fn fresh_empty() -> LocalExpnId {
        HygieneData::with(|data| {
            let expn_id = data.local_expn_data.push(None);
            let _eid = data.local_expn_hashes.push(ExpnHash(Fingerprint::ZERO));
            debug_assert_eq!(expn_id, _eid);
            expn_id
        })
    }

    pub fn fresh(mut expn_data: ExpnData, ctx: impl HashStableContext) -> LocalExpnId {
        debug_assert_eq!(expn_data.parent.krate, LOCAL_CRATE);
        let expn_hash = update_disambiguator(&mut expn_data, ctx);
        HygieneData::with(|data| {
            let expn_id = data.local_expn_data.push(Some(expn_data));
            let _eid = data.local_expn_hashes.push(expn_hash);
            debug_assert_eq!(expn_id, _eid);
            let _old_id = data.expn_hash_to_expn_id.insert(expn_hash, expn_id.to_expn_id());
            debug_assert!(_old_id.is_none());
            expn_id
        })
    }

    #[inline]
    pub fn expn_hash(self) -> ExpnHash {
        HygieneData::with(|data| data.local_expn_hash(self))
    }

    #[inline]
    pub fn expn_data(self) -> ExpnData {
        HygieneData::with(|data| data.local_expn_data(self).clone())
    }

    #[inline]
    pub fn to_expn_id(self) -> ExpnId {
        ExpnId { krate: LOCAL_CRATE, local_id: self.as_raw() }
    }

    #[inline]
    pub fn set_expn_data(self, mut expn_data: ExpnData, ctx: impl HashStableContext) {
        debug_assert_eq!(expn_data.parent.krate, LOCAL_CRATE);
        let expn_hash = update_disambiguator(&mut expn_data, ctx);
        HygieneData::with(|data| {
            let old_expn_data = &mut data.local_expn_data[self];
            assert!(old_expn_data.is_none(), "expansion data is reset for an expansion ID");
            *old_expn_data = Some(expn_data);
            debug_assert_eq!(data.local_expn_hashes[self].0, Fingerprint::ZERO);
            data.local_expn_hashes[self] = expn_hash;
            let _old_id = data.expn_hash_to_expn_id.insert(expn_hash, self.to_expn_id());
            debug_assert!(_old_id.is_none());
        });
    }

    #[inline]
    pub fn is_descendant_of(self, ancestor: LocalExpnId) -> bool {
        self.to_expn_id().is_descendant_of(ancestor.to_expn_id())
    }

    /// `expn_id.outer_expn_is_descendant_of(ctxt)` is equivalent to but faster than
    /// `expn_id.is_descendant_of(ctxt.outer_expn())`.
    #[inline]
    pub fn outer_expn_is_descendant_of(self, ctxt: SyntaxContext) -> bool {
        self.to_expn_id().outer_expn_is_descendant_of(ctxt)
    }

    /// Returns span for the macro which originally caused this expansion to happen.
    ///
    /// Stops backtracing at include! boundary.
    #[inline]
    pub fn expansion_cause(self) -> Option<Span> {
        self.to_expn_id().expansion_cause()
    }

    #[inline]
    #[track_caller]
    pub fn parent(self) -> LocalExpnId {
        self.expn_data().parent.as_local().unwrap()
    }
}

impl ExpnId {
    /// The ID of the theoretical expansion that generates freshly parsed, unexpanded AST.
    /// Invariant: we do not create any ExpnId with local_id == 0 and krate != 0.
    pub const fn root() -> ExpnId {
        ExpnId { krate: LOCAL_CRATE, local_id: ExpnIndex::from_u32(0) }
    }

    #[inline]
    pub fn expn_hash(self) -> ExpnHash {
        HygieneData::with(|data| data.expn_hash(self))
    }

    #[inline]
    pub fn from_hash(hash: ExpnHash) -> Option<ExpnId> {
        HygieneData::with(|data| data.expn_hash_to_expn_id.get(&hash).copied())
    }

    #[inline]
    pub fn as_local(self) -> Option<LocalExpnId> {
        if self.krate == LOCAL_CRATE { Some(LocalExpnId::from_raw(self.local_id)) } else { None }
    }

    #[inline]
    #[track_caller]
    pub fn expect_local(self) -> LocalExpnId {
        self.as_local().unwrap()
    }

    #[inline]
    pub fn expn_data(self) -> ExpnData {
        HygieneData::with(|data| data.expn_data(self).clone())
    }

    #[inline]
    pub fn is_descendant_of(self, ancestor: ExpnId) -> bool {
        // a few "fast path" cases to avoid locking HygieneData
        if ancestor == ExpnId::root() || ancestor == self {
            return true;
        }
        if ancestor.krate != self.krate {
            return false;
        }
        HygieneData::with(|data| data.is_descendant_of(self, ancestor))
    }

    /// `expn_id.outer_expn_is_descendant_of(ctxt)` is equivalent to but faster than
    /// `expn_id.is_descendant_of(ctxt.outer_expn())`.
    pub fn outer_expn_is_descendant_of(self, ctxt: SyntaxContext) -> bool {
        HygieneData::with(|data| data.is_descendant_of(self, data.outer_expn(ctxt)))
    }

    /// Returns span for the macro which originally caused this expansion to happen.
    ///
    /// Stops backtracing at include! boundary.
    pub fn expansion_cause(mut self) -> Option<Span> {
        let mut last_macro = None;
        loop {
            let expn_data = self.expn_data();
            // Stop going up the backtrace once include! is encountered
            if expn_data.is_root()
                || expn_data.kind == ExpnKind::Macro(MacroKind::Bang, sym::include)
            {
                break;
            }
            self = expn_data.call_site.ctxt().outer_expn();
            last_macro = Some(expn_data.call_site);
        }
        last_macro
    }
}

#[derive(Debug)]
pub struct HygieneData {
    /// Each expansion should have an associated expansion data, but sometimes there's a delay
    /// between creation of an expansion ID and obtaining its data (e.g. macros are collected
    /// first and then resolved later), so we use an `Option` here.
    local_expn_data: IndexVec<LocalExpnId, Option<ExpnData>>,
    local_expn_hashes: IndexVec<LocalExpnId, ExpnHash>,
    /// Data and hash information from external crates. We may eventually want to remove these
    /// maps, and fetch the information directly from the other crate's metadata like DefIds do.
    foreign_expn_data: FxHashMap<ExpnId, ExpnData>,
    foreign_expn_hashes: FxHashMap<ExpnId, ExpnHash>,
    expn_hash_to_expn_id: UnhashMap<ExpnHash, ExpnId>,
    syntax_context_data: Vec<SyntaxContextData>,
    syntax_context_map: FxHashMap<(SyntaxContext, ExpnId, Transparency), SyntaxContext>,
    /// Maps the `local_hash` of an `ExpnData` to the next disambiguator value.
    /// This is used by `update_disambiguator` to keep track of which `ExpnData`s
    /// would have collisions without a disambiguator.
    /// The keys of this map are always computed with `ExpnData.disambiguator`
    /// set to 0.
    expn_data_disambiguators: FxHashMap<Hash64, u32>,
}

impl HygieneData {
    pub(crate) fn new(edition: Edition) -> Self {
        let root_data = ExpnData::default(
            ExpnKind::Root,
            DUMMY_SP,
            edition,
            Some(CRATE_DEF_ID.to_def_id()),
            None,
        );

        HygieneData {
            local_expn_data: IndexVec::from_elem_n(Some(root_data), 1),
            local_expn_hashes: IndexVec::from_elem_n(ExpnHash(Fingerprint::ZERO), 1),
            foreign_expn_data: FxHashMap::default(),
            foreign_expn_hashes: FxHashMap::default(),
            expn_hash_to_expn_id: std::iter::once((ExpnHash(Fingerprint::ZERO), ExpnId::root()))
                .collect(),
            syntax_context_data: vec![SyntaxContextData {
                outer_expn: ExpnId::root(),
                outer_transparency: Transparency::Opaque,
                parent: SyntaxContext(0),
                opaque: SyntaxContext(0),
                opaque_and_semitransparent: SyntaxContext(0),
                dollar_crate_name: kw::DollarCrate,
            }],
            syntax_context_map: FxHashMap::default(),
            expn_data_disambiguators: FxHashMap::default(),
        }
    }

    pub fn with<T, F: FnOnce(&mut HygieneData) -> T>(f: F) -> T {
        with_session_globals(|session_globals| f(&mut session_globals.hygiene_data.borrow_mut()))
    }

    #[inline]
    fn local_expn_hash(&self, expn_id: LocalExpnId) -> ExpnHash {
        self.local_expn_hashes[expn_id]
    }

    #[inline]
    fn expn_hash(&self, expn_id: ExpnId) -> ExpnHash {
        match expn_id.as_local() {
            Some(expn_id) => self.local_expn_hashes[expn_id],
            None => self.foreign_expn_hashes[&expn_id],
        }
    }

    fn local_expn_data(&self, expn_id: LocalExpnId) -> &ExpnData {
        self.local_expn_data[expn_id].as_ref().expect("no expansion data for an expansion ID")
    }

    fn expn_data(&self, expn_id: ExpnId) -> &ExpnData {
        if let Some(expn_id) = expn_id.as_local() {
            self.local_expn_data[expn_id].as_ref().expect("no expansion data for an expansion ID")
        } else {
            &self.foreign_expn_data[&expn_id]
        }
    }

    fn is_descendant_of(&self, mut expn_id: ExpnId, ancestor: ExpnId) -> bool {
        // a couple "fast path" cases to avoid traversing parents in the loop below
        if ancestor == ExpnId::root() {
            return true;
        }
        if expn_id.krate != ancestor.krate {
            return false;
        }
        loop {
            if expn_id == ancestor {
                return true;
            }
            if expn_id == ExpnId::root() {
                return false;
            }
            expn_id = self.expn_data(expn_id).parent;
        }
    }

    fn normalize_to_macros_2_0(&self, ctxt: SyntaxContext) -> SyntaxContext {
        self.syntax_context_data[ctxt.0 as usize].opaque
    }

    fn normalize_to_macro_rules(&self, ctxt: SyntaxContext) -> SyntaxContext {
        self.syntax_context_data[ctxt.0 as usize].opaque_and_semitransparent
    }

    fn outer_expn(&self, ctxt: SyntaxContext) -> ExpnId {
        self.syntax_context_data[ctxt.0 as usize].outer_expn
    }

    fn outer_mark(&self, ctxt: SyntaxContext) -> (ExpnId, Transparency) {
        let data = &self.syntax_context_data[ctxt.0 as usize];
        (data.outer_expn, data.outer_transparency)
    }

    fn parent_ctxt(&self, ctxt: SyntaxContext) -> SyntaxContext {
        self.syntax_context_data[ctxt.0 as usize].parent
    }

    fn remove_mark(&self, ctxt: &mut SyntaxContext) -> (ExpnId, Transparency) {
        let outer_mark = self.outer_mark(*ctxt);
        *ctxt = self.parent_ctxt(*ctxt);
        outer_mark
    }

    fn marks(&self, mut ctxt: SyntaxContext) -> Vec<(ExpnId, Transparency)> {
        let mut marks = Vec::new();
        while ctxt != SyntaxContext::root() {
            debug!("marks: getting parent of {:?}", ctxt);
            marks.push(self.outer_mark(ctxt));
            ctxt = self.parent_ctxt(ctxt);
        }
        marks.reverse();
        marks
    }

    fn walk_chain(&self, mut span: Span, to: SyntaxContext) -> Span {
        debug!("walk_chain({:?}, {:?})", span, to);
        debug!("walk_chain: span ctxt = {:?}", span.ctxt());
        while span.from_expansion() && span.ctxt() != to {
            let outer_expn = self.outer_expn(span.ctxt());
            debug!("walk_chain({:?}): outer_expn={:?}", span, outer_expn);
            let expn_data = self.expn_data(outer_expn);
            debug!("walk_chain({:?}): expn_data={:?}", span, expn_data);
            span = expn_data.call_site;
        }
        span
    }

    fn adjust(&self, ctxt: &mut SyntaxContext, expn_id: ExpnId) -> Option<ExpnId> {
        let mut scope = None;
        while !self.is_descendant_of(expn_id, self.outer_expn(*ctxt)) {
            scope = Some(self.remove_mark(ctxt).0);
        }
        scope
    }

    fn apply_mark(
        &mut self,
        ctxt: SyntaxContext,
        expn_id: ExpnId,
        transparency: Transparency,
    ) -> SyntaxContext {
        assert_ne!(expn_id, ExpnId::root());
        if transparency == Transparency::Opaque {
            return self.apply_mark_internal(ctxt, expn_id, transparency);
        }

        let call_site_ctxt = self.expn_data(expn_id).call_site.ctxt();
        let mut call_site_ctxt = if transparency == Transparency::SemiTransparent {
            self.normalize_to_macros_2_0(call_site_ctxt)
        } else {
            self.normalize_to_macro_rules(call_site_ctxt)
        };

        if call_site_ctxt.is_root() {
            return self.apply_mark_internal(ctxt, expn_id, transparency);
        }

        // Otherwise, `expn_id` is a macros 1.0 definition and the call site is in a
        // macros 2.0 expansion, i.e., a macros 1.0 invocation is in a macros 2.0 definition.
        //
        // In this case, the tokens from the macros 1.0 definition inherit the hygiene
        // at their invocation. That is, we pretend that the macros 1.0 definition
        // was defined at its invocation (i.e., inside the macros 2.0 definition)
        // so that the macros 2.0 definition remains hygienic.
        //
        // See the example at `test/ui/hygiene/legacy_interaction.rs`.
        for (expn_id, transparency) in self.marks(ctxt) {
            call_site_ctxt = self.apply_mark_internal(call_site_ctxt, expn_id, transparency);
        }
        self.apply_mark_internal(call_site_ctxt, expn_id, transparency)
    }

    fn apply_mark_internal(
        &mut self,
        ctxt: SyntaxContext,
        expn_id: ExpnId,
        transparency: Transparency,
    ) -> SyntaxContext {
        let syntax_context_data = &mut self.syntax_context_data;
        let mut opaque = syntax_context_data[ctxt.0 as usize].opaque;
        let mut opaque_and_semitransparent =
            syntax_context_data[ctxt.0 as usize].opaque_and_semitransparent;

        if transparency >= Transparency::Opaque {
            let parent = opaque;
            opaque = *self
                .syntax_context_map
                .entry((parent, expn_id, transparency))
                .or_insert_with(|| {
                    let new_opaque = SyntaxContext(syntax_context_data.len() as u32);
                    syntax_context_data.push(SyntaxContextData {
                        outer_expn: expn_id,
                        outer_transparency: transparency,
                        parent,
                        opaque: new_opaque,
                        opaque_and_semitransparent: new_opaque,
                        dollar_crate_name: kw::DollarCrate,
                    });
                    new_opaque
                });
        }

        if transparency >= Transparency::SemiTransparent {
            let parent = opaque_and_semitransparent;
            opaque_and_semitransparent = *self
                .syntax_context_map
                .entry((parent, expn_id, transparency))
                .or_insert_with(|| {
                    let new_opaque_and_semitransparent =
                        SyntaxContext(syntax_context_data.len() as u32);
                    syntax_context_data.push(SyntaxContextData {
                        outer_expn: expn_id,
                        outer_transparency: transparency,
                        parent,
                        opaque,
                        opaque_and_semitransparent: new_opaque_and_semitransparent,
                        dollar_crate_name: kw::DollarCrate,
                    });
                    new_opaque_and_semitransparent
                });
        }

        let parent = ctxt;
        *self.syntax_context_map.entry((parent, expn_id, transparency)).or_insert_with(|| {
            let new_opaque_and_semitransparent_and_transparent =
                SyntaxContext(syntax_context_data.len() as u32);
            syntax_context_data.push(SyntaxContextData {
                outer_expn: expn_id,
                outer_transparency: transparency,
                parent,
                opaque,
                opaque_and_semitransparent,
                dollar_crate_name: kw::DollarCrate,
            });
            new_opaque_and_semitransparent_and_transparent
        })
    }
}

pub fn clear_syntax_context_map() {
    HygieneData::with(|data| data.syntax_context_map = FxHashMap::default());
}

pub fn walk_chain(span: Span, to: SyntaxContext) -> Span {
    HygieneData::with(|data| data.walk_chain(span, to))
}

pub fn update_dollar_crate_names(mut get_name: impl FnMut(SyntaxContext) -> Symbol) {
    // The new contexts that need updating are at the end of the list and have `$crate` as a name.
    let (len, to_update) = HygieneData::with(|data| {
        (
            data.syntax_context_data.len(),
            data.syntax_context_data
                .iter()
                .rev()
                .take_while(|scdata| scdata.dollar_crate_name == kw::DollarCrate)
                .count(),
        )
    });
    // The callback must be called from outside of the `HygieneData` lock,
    // since it will try to acquire it too.
    let range_to_update = len - to_update..len;
    let names: Vec<_> =
        range_to_update.clone().map(|idx| get_name(SyntaxContext::from_u32(idx as u32))).collect();
    HygieneData::with(|data| {
        range_to_update.zip(names).for_each(|(idx, name)| {
            data.syntax_context_data[idx].dollar_crate_name = name;
        })
    })
}

pub fn debug_hygiene_data(verbose: bool) -> String {
    HygieneData::with(|data| {
        if verbose {
            format!("{data:#?}")
        } else {
            let mut s = String::from("Expansions:");
            let mut debug_expn_data = |(id, expn_data): (&ExpnId, &ExpnData)| {
                s.push_str(&format!(
                    "\n{:?}: parent: {:?}, call_site_ctxt: {:?}, def_site_ctxt: {:?}, kind: {:?}",
                    id,
                    expn_data.parent,
                    expn_data.call_site.ctxt(),
                    expn_data.def_site.ctxt(),
                    expn_data.kind,
                ))
            };
            data.local_expn_data.iter_enumerated().for_each(|(id, expn_data)| {
                let expn_data = expn_data.as_ref().expect("no expansion data for an expansion ID");
                debug_expn_data((&id.to_expn_id(), expn_data))
            });

            // Sort the hash map for more reproducible output.
            // Because of this, it is fine to rely on the unstable iteration order of the map.
            #[allow(rustc::potential_query_instability)]
            let mut foreign_expn_data: Vec<_> = data.foreign_expn_data.iter().collect();
            foreign_expn_data.sort_by_key(|(id, _)| (id.krate, id.local_id));
            foreign_expn_data.into_iter().for_each(debug_expn_data);
            s.push_str("\n\nSyntaxContexts:");
            data.syntax_context_data.iter().enumerate().for_each(|(id, ctxt)| {
                s.push_str(&format!(
                    "\n#{}: parent: {:?}, outer_mark: ({:?}, {:?})",
                    id, ctxt.parent, ctxt.outer_expn, ctxt.outer_transparency,
                ));
            });
            s
        }
    })
}

impl SyntaxContext {
    #[inline]
    pub const fn root() -> Self {
        SyntaxContext(0)
    }

    #[inline]
    pub const fn is_root(self) -> bool {
        self.0 == SyntaxContext::root().as_u32()
    }

    #[inline]
    pub(crate) const fn as_u32(self) -> u32 {
        self.0
    }

    #[inline]
    pub(crate) const fn from_u32(raw: u32) -> SyntaxContext {
        SyntaxContext(raw)
    }

    /// Extend a syntax context with a given expansion and transparency.
    pub(crate) fn apply_mark(self, expn_id: ExpnId, transparency: Transparency) -> SyntaxContext {
        HygieneData::with(|data| data.apply_mark(self, expn_id, transparency))
    }

    /// Pulls a single mark off of the syntax context. This effectively moves the
    /// context up one macro definition level. That is, if we have a nested macro
    /// definition as follows:
    ///
    /// ```ignore (illustrative)
    /// macro_rules! f {
    ///    macro_rules! g {
    ///        ...
    ///    }
    /// }
    /// ```
    ///
    /// and we have a SyntaxContext that is referring to something declared by an invocation
    /// of g (call it g1), calling remove_mark will result in the SyntaxContext for the
    /// invocation of f that created g1.
    /// Returns the mark that was removed.
    pub fn remove_mark(&mut self) -> ExpnId {
        HygieneData::with(|data| data.remove_mark(self).0)
    }

    pub fn marks(self) -> Vec<(ExpnId, Transparency)> {
        HygieneData::with(|data| data.marks(self))
    }

    /// Adjust this context for resolution in a scope created by the given expansion.
    /// For example, consider the following three resolutions of `f`:
    ///
    /// ```rust
    /// #![feature(decl_macro)]
    /// mod foo { pub fn f() {} } // `f`'s `SyntaxContext` is empty.
    /// m!(f);
    /// macro m($f:ident) {
    ///     mod bar {
    ///         pub fn f() {} // `f`'s `SyntaxContext` has a single `ExpnId` from `m`.
    ///         pub fn $f() {} // `$f`'s `SyntaxContext` is empty.
    ///     }
    ///     foo::f(); // `f`'s `SyntaxContext` has a single `ExpnId` from `m`
    ///     //^ Since `mod foo` is outside this expansion, `adjust` removes the mark from `f`,
    ///     //| and it resolves to `::foo::f`.
    ///     bar::f(); // `f`'s `SyntaxContext` has a single `ExpnId` from `m`
    ///     //^ Since `mod bar` not outside this expansion, `adjust` does not change `f`,
    ///     //| and it resolves to `::bar::f`.
    ///     bar::$f(); // `f`'s `SyntaxContext` is empty.
    ///     //^ Since `mod bar` is not outside this expansion, `adjust` does not change `$f`,
    ///     //| and it resolves to `::bar::$f`.
    /// }
    /// ```
    /// This returns the expansion whose definition scope we use to privacy check the resolution,
    /// or `None` if we privacy check as usual (i.e., not w.r.t. a macro definition scope).
    pub fn adjust(&mut self, expn_id: ExpnId) -> Option<ExpnId> {
        HygieneData::with(|data| data.adjust(self, expn_id))
    }

    /// Like `SyntaxContext::adjust`, but also normalizes `self` to macros 2.0.
    pub fn normalize_to_macros_2_0_and_adjust(&mut self, expn_id: ExpnId) -> Option<ExpnId> {
        HygieneData::with(|data| {
            *self = data.normalize_to_macros_2_0(*self);
            data.adjust(self, expn_id)
        })
    }

    /// Adjust this context for resolution in a scope created by the given expansion
    /// via a glob import with the given `SyntaxContext`.
    /// For example:
    ///
    /// ```compile_fail,E0425
    /// #![feature(decl_macro)]
    /// m!(f);
    /// macro m($i:ident) {
    ///     mod foo {
    ///         pub fn f() {} // `f`'s `SyntaxContext` has a single `ExpnId` from `m`.
    ///         pub fn $i() {} // `$i`'s `SyntaxContext` is empty.
    ///     }
    ///     n!(f);
    ///     macro n($j:ident) {
    ///         use foo::*;
    ///         f(); // `f`'s `SyntaxContext` has a mark from `m` and a mark from `n`
    ///         //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::f`.
    ///         $i(); // `$i`'s `SyntaxContext` has a mark from `n`
    ///         //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::$i`.
    ///         $j(); // `$j`'s `SyntaxContext` has a mark from `m`
    ///         //^ This cannot be glob-adjusted, so this is a resolution error.
    ///     }
    /// }
    /// ```
    /// This returns `None` if the context cannot be glob-adjusted.
    /// Otherwise, it returns the scope to use when privacy checking (see `adjust` for details).
    pub fn glob_adjust(&mut self, expn_id: ExpnId, glob_span: Span) -> Option<Option<ExpnId>> {
        HygieneData::with(|data| {
            let mut scope = None;
            let mut glob_ctxt = data.normalize_to_macros_2_0(glob_span.ctxt());
            while !data.is_descendant_of(expn_id, data.outer_expn(glob_ctxt)) {
                scope = Some(data.remove_mark(&mut glob_ctxt).0);
                if data.remove_mark(self).0 != scope.unwrap() {
                    return None;
                }
            }
            if data.adjust(self, expn_id).is_some() {
                return None;
            }
            Some(scope)
        })
    }

    /// Undo `glob_adjust` if possible:
    ///
    /// ```ignore (illustrative)
    /// if let Some(privacy_checking_scope) = self.reverse_glob_adjust(expansion, glob_ctxt) {
    ///     assert!(self.glob_adjust(expansion, glob_ctxt) == Some(privacy_checking_scope));
    /// }
    /// ```
    pub fn reverse_glob_adjust(
        &mut self,
        expn_id: ExpnId,
        glob_span: Span,
    ) -> Option<Option<ExpnId>> {
        HygieneData::with(|data| {
            if data.adjust(self, expn_id).is_some() {
                return None;
            }

            let mut glob_ctxt = data.normalize_to_macros_2_0(glob_span.ctxt());
            let mut marks = Vec::new();
            while !data.is_descendant_of(expn_id, data.outer_expn(glob_ctxt)) {
                marks.push(data.remove_mark(&mut glob_ctxt));
            }

            let scope = marks.last().map(|mark| mark.0);
            while let Some((expn_id, transparency)) = marks.pop() {
                *self = data.apply_mark(*self, expn_id, transparency);
            }
            Some(scope)
        })
    }

    pub fn hygienic_eq(self, other: SyntaxContext, expn_id: ExpnId) -> bool {
        HygieneData::with(|data| {
            let mut self_normalized = data.normalize_to_macros_2_0(self);
            data.adjust(&mut self_normalized, expn_id);
            self_normalized == data.normalize_to_macros_2_0(other)
        })
    }

    #[inline]
    pub fn normalize_to_macros_2_0(self) -> SyntaxContext {
        HygieneData::with(|data| data.normalize_to_macros_2_0(self))
    }

    #[inline]
    pub fn normalize_to_macro_rules(self) -> SyntaxContext {
        HygieneData::with(|data| data.normalize_to_macro_rules(self))
    }

    #[inline]
    pub fn outer_expn(self) -> ExpnId {
        HygieneData::with(|data| data.outer_expn(self))
    }

    /// `ctxt.outer_expn_data()` is equivalent to but faster than
    /// `ctxt.outer_expn().expn_data()`.
    #[inline]
    pub fn outer_expn_data(self) -> ExpnData {
        HygieneData::with(|data| data.expn_data(data.outer_expn(self)).clone())
    }

    #[inline]
    pub fn outer_mark(self) -> (ExpnId, Transparency) {
        HygieneData::with(|data| data.outer_mark(self))
    }

    pub fn dollar_crate_name(self) -> Symbol {
        HygieneData::with(|data| data.syntax_context_data[self.0 as usize].dollar_crate_name)
    }

    pub fn edition(self) -> Edition {
        HygieneData::with(|data| data.expn_data(data.outer_expn(self)).edition)
    }
}

impl fmt::Debug for SyntaxContext {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "#{}", self.0)
    }
}

impl Span {
    /// Creates a fresh expansion with given properties.
    /// Expansions are normally created by macros, but in some cases expansions are created for
    /// other compiler-generated code to set per-span properties like allowed unstable features.
    /// The returned span belongs to the created expansion and has the new properties,
    /// but its location is inherited from the current span.
    pub fn fresh_expansion(self, expn_id: LocalExpnId) -> Span {
        HygieneData::with(|data| {
            self.with_ctxt(data.apply_mark(
                self.ctxt(),
                expn_id.to_expn_id(),
                Transparency::Transparent,
            ))
        })
    }

    /// Reuses the span but adds information like the kind of the desugaring and features that are
    /// allowed inside this span.
    pub fn mark_with_reason(
        self,
        allow_internal_unstable: Option<Lrc<[Symbol]>>,
        reason: DesugaringKind,
        edition: Edition,
        ctx: impl HashStableContext,
    ) -> Span {
        let expn_data = ExpnData {
            allow_internal_unstable,
            ..ExpnData::default(ExpnKind::Desugaring(reason), self, edition, None, None)
        };
        let expn_id = LocalExpnId::fresh(expn_data, ctx);
        self.fresh_expansion(expn_id)
    }
}

/// A subset of properties from both macro definition and macro call available through global data.
/// Avoid using this if you have access to the original definition or call structures.
#[derive(Clone, Debug, Encodable, Decodable, HashStable_Generic)]
pub struct ExpnData {
    // --- The part unique to each expansion.
    /// The kind of this expansion - macro or compiler desugaring.
    pub kind: ExpnKind,
    /// The expansion that produced this expansion.
    pub parent: ExpnId,
    /// The location of the actual macro invocation or syntax sugar , e.g.
    /// `let x = foo!();` or `if let Some(y) = x {}`
    ///
    /// This may recursively refer to other macro invocations, e.g., if
    /// `foo!()` invoked `bar!()` internally, and there was an
    /// expression inside `bar!`; the call_site of the expression in
    /// the expansion would point to the `bar!` invocation; that
    /// call_site span would have its own ExpnData, with the call_site
    /// pointing to the `foo!` invocation.
    pub call_site: Span,
    /// Used to force two `ExpnData`s to have different `Fingerprint`s.
    /// Due to macro expansion, it's possible to end up with two `ExpnId`s
    /// that have identical `ExpnData`s. This violates the contract of `HashStable`
    /// - the two `ExpnId`s are not equal, but their `Fingerprint`s are equal
    /// (since the numerical `ExpnId` value is not considered by the `HashStable`
    /// implementation).
    ///
    /// The `disambiguator` field is set by `update_disambiguator` when two distinct
    /// `ExpnId`s would end up with the same `Fingerprint`. Since `ExpnData` includes
    /// a `krate` field, this value only needs to be unique within a single crate.
    disambiguator: u32,

    // --- The part specific to the macro/desugaring definition.
    // --- It may be reasonable to share this part between expansions with the same definition,
    // --- but such sharing is known to bring some minor inconveniences without also bringing
    // --- noticeable perf improvements (PR #62898).
    /// The span of the macro definition (possibly dummy).
    /// This span serves only informational purpose and is not used for resolution.
    pub def_site: Span,
    /// List of `#[unstable]`/feature-gated features that the macro is allowed to use
    /// internally without forcing the whole crate to opt-in
    /// to them.
    pub allow_internal_unstable: Option<Lrc<[Symbol]>>,
    /// Edition of the crate in which the macro is defined.
    pub edition: Edition,
    /// The `DefId` of the macro being invoked,
    /// if this `ExpnData` corresponds to a macro invocation
    pub macro_def_id: Option<DefId>,
    /// The normal module (`mod`) in which the expanded macro was defined.
    pub parent_module: Option<DefId>,
    /// Suppresses the `unsafe_code` lint for code produced by this macro.
    pub allow_internal_unsafe: bool,
    /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`) for this macro.
    pub local_inner_macros: bool,
    /// Should debuginfo for the macro be collapsed to the outermost expansion site (in other
    /// words, was the macro definition annotated with `#[collapse_debuginfo]`)?
    pub collapse_debuginfo: bool,
}

impl !PartialEq for ExpnData {}
impl !Hash for ExpnData {}

impl ExpnData {
    pub fn new(
        kind: ExpnKind,
        parent: ExpnId,
        call_site: Span,
        def_site: Span,
        allow_internal_unstable: Option<Lrc<[Symbol]>>,
        edition: Edition,
        macro_def_id: Option<DefId>,
        parent_module: Option<DefId>,
        allow_internal_unsafe: bool,
        local_inner_macros: bool,
        collapse_debuginfo: bool,
    ) -> ExpnData {
        ExpnData {
            kind,
            parent,
            call_site,
            def_site,
            allow_internal_unstable,
            edition,
            macro_def_id,
            parent_module,
            disambiguator: 0,
            allow_internal_unsafe,
            local_inner_macros,
            collapse_debuginfo,
        }
    }

    /// Constructs expansion data with default properties.
    pub fn default(
        kind: ExpnKind,
        call_site: Span,
        edition: Edition,
        macro_def_id: Option<DefId>,
        parent_module: Option<DefId>,
    ) -> ExpnData {
        ExpnData {
            kind,
            parent: ExpnId::root(),
            call_site,
            def_site: DUMMY_SP,
            allow_internal_unstable: None,
            edition,
            macro_def_id,
            parent_module,
            disambiguator: 0,
            allow_internal_unsafe: false,
            local_inner_macros: false,
            collapse_debuginfo: false,
        }
    }

    pub fn allow_unstable(
        kind: ExpnKind,
        call_site: Span,
        edition: Edition,
        allow_internal_unstable: Lrc<[Symbol]>,
        macro_def_id: Option<DefId>,
        parent_module: Option<DefId>,
    ) -> ExpnData {
        ExpnData {
            allow_internal_unstable: Some(allow_internal_unstable),
            ..ExpnData::default(kind, call_site, edition, macro_def_id, parent_module)
        }
    }

    #[inline]
    pub fn is_root(&self) -> bool {
        matches!(self.kind, ExpnKind::Root)
    }

    #[inline]
    fn hash_expn(&self, ctx: &mut impl HashStableContext) -> Hash64 {
        let mut hasher = StableHasher::new();
        self.hash_stable(ctx, &mut hasher);
        hasher.finish()
    }
}

/// Expansion kind.
#[derive(Clone, Debug, PartialEq, Encodable, Decodable, HashStable_Generic)]
pub enum ExpnKind {
    /// No expansion, aka root expansion. Only `ExpnId::root()` has this kind.
    Root,
    /// Expansion produced by a macro.
    Macro(MacroKind, Symbol),
    /// Transform done by the compiler on the AST.
    AstPass(AstPass),
    /// Desugaring done by the compiler during HIR lowering.
    Desugaring(DesugaringKind),
}

impl ExpnKind {
    pub fn descr(&self) -> String {
        match *self {
            ExpnKind::Root => kw::PathRoot.to_string(),
            ExpnKind::Macro(macro_kind, name) => match macro_kind {
                MacroKind::Bang => format!("{name}!"),
                MacroKind::Attr => format!("#[{name}]"),
                MacroKind::Derive => format!("#[derive({name})]"),
            },
            ExpnKind::AstPass(kind) => kind.descr().to_string(),
            ExpnKind::Desugaring(kind) => format!("desugaring of {}", kind.descr()),
        }
    }
}

/// The kind of macro invocation or definition.
#[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Debug)]
#[derive(HashStable_Generic)]
pub enum MacroKind {
    /// A bang macro `foo!()`.
    Bang,
    /// An attribute macro `#[foo]`.
    Attr,
    /// A derive macro `#[derive(Foo)]`
    Derive,
}

impl MacroKind {
    pub fn descr(self) -> &'static str {
        match self {
            MacroKind::Bang => "macro",
            MacroKind::Attr => "attribute macro",
            MacroKind::Derive => "derive macro",
        }
    }

    pub fn descr_expected(self) -> &'static str {
        match self {
            MacroKind::Attr => "attribute",
            _ => self.descr(),
        }
    }

    pub fn article(self) -> &'static str {
        match self {
            MacroKind::Attr => "an",
            _ => "a",
        }
    }
}

/// The kind of AST transform.
#[derive(Clone, Copy, Debug, PartialEq, Encodable, Decodable, HashStable_Generic)]
pub enum AstPass {
    StdImports,
    TestHarness,
    ProcMacroHarness,
}

impl AstPass {
    pub fn descr(self) -> &'static str {
        match self {
            AstPass::StdImports => "standard library imports",
            AstPass::TestHarness => "test harness",
            AstPass::ProcMacroHarness => "proc macro harness",
        }
    }
}

/// The kind of compiler desugaring.
#[derive(Clone, Copy, PartialEq, Debug, Encodable, Decodable, HashStable_Generic)]
pub enum DesugaringKind {
    /// We desugar `if c { i } else { e }` to `match $ExprKind::Use(c) { true => i, _ => e }`.
    /// However, we do not want to blame `c` for unreachability but rather say that `i`
    /// is unreachable. This desugaring kind allows us to avoid blaming `c`.
    /// This also applies to `while` loops.
    CondTemporary,
    QuestionMark,
    TryBlock,
    YeetExpr,
    /// Desugaring of an `impl Trait` in return type position
    /// to an `type Foo = impl Trait;` and replacing the
    /// `impl Trait` with `Foo`.
    OpaqueTy,
    Async,
    Await,
    ForLoop,
    WhileLoop,
}

impl DesugaringKind {
    /// The description wording should combine well with "desugaring of {}".
    pub fn descr(self) -> &'static str {
        match self {
            DesugaringKind::CondTemporary => "`if` or `while` condition",
            DesugaringKind::Async => "`async` block or function",
            DesugaringKind::Await => "`await` expression",
            DesugaringKind::QuestionMark => "operator `?`",
            DesugaringKind::TryBlock => "`try` block",
            DesugaringKind::YeetExpr => "`do yeet` expression",
            DesugaringKind::OpaqueTy => "`impl Trait`",
            DesugaringKind::ForLoop => "`for` loop",
            DesugaringKind::WhileLoop => "`while` loop",
        }
    }
}

#[derive(Default)]
pub struct HygieneEncodeContext {
    /// All `SyntaxContexts` for which we have written `SyntaxContextData` into crate metadata.
    /// This is `None` after we finish encoding `SyntaxContexts`, to ensure
    /// that we don't accidentally try to encode any more `SyntaxContexts`
    serialized_ctxts: Lock<FxHashSet<SyntaxContext>>,
    /// The `SyntaxContexts` that we have serialized (e.g. as a result of encoding `Spans`)
    /// in the most recent 'round' of serializing. Serializing `SyntaxContextData`
    /// may cause us to serialize more `SyntaxContext`s, so serialize in a loop
    /// until we reach a fixed point.
    latest_ctxts: Lock<FxHashSet<SyntaxContext>>,

    serialized_expns: Lock<FxHashSet<ExpnId>>,

    latest_expns: Lock<FxHashSet<ExpnId>>,
}

impl HygieneEncodeContext {
    /// Record the fact that we need to serialize the corresponding `ExpnData`.
    pub fn schedule_expn_data_for_encoding(&self, expn: ExpnId) {
        if !self.serialized_expns.lock().contains(&expn) {
            self.latest_expns.lock().insert(expn);
        }
    }

    pub fn encode<T>(
        &self,
        encoder: &mut T,
        mut encode_ctxt: impl FnMut(&mut T, u32, &SyntaxContextData),
        mut encode_expn: impl FnMut(&mut T, ExpnId, &ExpnData, ExpnHash),
    ) {
        // When we serialize a `SyntaxContextData`, we may end up serializing
        // a `SyntaxContext` that we haven't seen before
        while !self.latest_ctxts.lock().is_empty() || !self.latest_expns.lock().is_empty() {
            debug!(
                "encode_hygiene: Serializing a round of {:?} SyntaxContextData: {:?}",
                self.latest_ctxts.lock().len(),
                self.latest_ctxts
            );

            // Consume the current round of SyntaxContexts.
            // Drop the lock() temporary early
            let latest_ctxts = { std::mem::take(&mut *self.latest_ctxts.lock()) };

            // It's fine to iterate over a HashMap, because the serialization
            // of the table that we insert data into doesn't depend on insertion
            // order
            #[allow(rustc::potential_query_instability)]
            for_all_ctxts_in(latest_ctxts.into_iter(), |index, ctxt, data| {
                if self.serialized_ctxts.lock().insert(ctxt) {
                    encode_ctxt(encoder, index, data);
                }
            });

            let latest_expns = { std::mem::take(&mut *self.latest_expns.lock()) };

            // Same as above, this is fine as we are inserting into a order-independent hashset
            #[allow(rustc::potential_query_instability)]
            for_all_expns_in(latest_expns.into_iter(), |expn, data, hash| {
                if self.serialized_expns.lock().insert(expn) {
                    encode_expn(encoder, expn, data, hash);
                }
            });
        }
        debug!("encode_hygiene: Done serializing SyntaxContextData");
    }
}

#[derive(Default)]
/// Additional information used to assist in decoding hygiene data
pub struct HygieneDecodeContext {
    // Maps serialized `SyntaxContext` ids to a `SyntaxContext` in the current
    // global `HygieneData`. When we deserialize a `SyntaxContext`, we need to create
    // a new id in the global `HygieneData`. This map tracks the ID we end up picking,
    // so that multiple occurrences of the same serialized id are decoded to the same
    // `SyntaxContext`
    remapped_ctxts: Lock<Vec<Option<SyntaxContext>>>,
}

/// Register an expansion which has been decoded from the on-disk-cache for the local crate.
pub fn register_local_expn_id(data: ExpnData, hash: ExpnHash) -> ExpnId {
    HygieneData::with(|hygiene_data| {
        let expn_id = hygiene_data.local_expn_data.next_index();
        hygiene_data.local_expn_data.push(Some(data));
        let _eid = hygiene_data.local_expn_hashes.push(hash);
        debug_assert_eq!(expn_id, _eid);

        let expn_id = expn_id.to_expn_id();

        let _old_id = hygiene_data.expn_hash_to_expn_id.insert(hash, expn_id);
        debug_assert!(_old_id.is_none());
        expn_id
    })
}

/// Register an expansion which has been decoded from the metadata of a foreign crate.
pub fn register_expn_id(
    krate: CrateNum,
    local_id: ExpnIndex,
    data: ExpnData,
    hash: ExpnHash,
) -> ExpnId {
    debug_assert!(data.parent == ExpnId::root() || krate == data.parent.krate);
    let expn_id = ExpnId { krate, local_id };
    HygieneData::with(|hygiene_data| {
        let _old_data = hygiene_data.foreign_expn_data.insert(expn_id, data);
        debug_assert!(_old_data.is_none());
        let _old_hash = hygiene_data.foreign_expn_hashes.insert(expn_id, hash);
        debug_assert!(_old_hash.is_none());
        let _old_id = hygiene_data.expn_hash_to_expn_id.insert(hash, expn_id);
        debug_assert!(_old_id.is_none());
    });
    expn_id
}

/// Decode an expansion from the metadata of a foreign crate.
pub fn decode_expn_id(
    krate: CrateNum,
    index: u32,
    decode_data: impl FnOnce(ExpnId) -> (ExpnData, ExpnHash),
) -> ExpnId {
    if index == 0 {
        trace!("decode_expn_id: deserialized root");
        return ExpnId::root();
    }

    let index = ExpnIndex::from_u32(index);

    // This function is used to decode metadata, so it cannot decode information about LOCAL_CRATE.
    debug_assert_ne!(krate, LOCAL_CRATE);
    let expn_id = ExpnId { krate, local_id: index };

    // Fast path if the expansion has already been decoded.
    if HygieneData::with(|hygiene_data| hygiene_data.foreign_expn_data.contains_key(&expn_id)) {
        return expn_id;
    }

    // Don't decode the data inside `HygieneData::with`, since we need to recursively decode
    // other ExpnIds
    let (expn_data, hash) = decode_data(expn_id);

    register_expn_id(krate, index, expn_data, hash)
}

// Decodes `SyntaxContext`, using the provided `HygieneDecodeContext`
// to track which `SyntaxContext`s we have already decoded.
// The provided closure will be invoked to deserialize a `SyntaxContextData`
// if we haven't already seen the id of the `SyntaxContext` we are deserializing.
pub fn decode_syntax_context<D: Decoder, F: FnOnce(&mut D, u32) -> SyntaxContextData>(
    d: &mut D,
    context: &HygieneDecodeContext,
    decode_data: F,
) -> SyntaxContext {
    let raw_id: u32 = Decodable::decode(d);
    if raw_id == 0 {
        trace!("decode_syntax_context: deserialized root");
        // The root is special
        return SyntaxContext::root();
    }

    let outer_ctxts = &context.remapped_ctxts;

    // Ensure that the lock() temporary is dropped early
    {
        if let Some(ctxt) = outer_ctxts.lock().get(raw_id as usize).copied().flatten() {
            return ctxt;
        }
    }

    // Allocate and store SyntaxContext id *before* calling the decoder function,
    // as the SyntaxContextData may reference itself.
    let new_ctxt = HygieneData::with(|hygiene_data| {
        let new_ctxt = SyntaxContext(hygiene_data.syntax_context_data.len() as u32);
        // Push a dummy SyntaxContextData to ensure that nobody else can get the
        // same ID as us. This will be overwritten after call `decode_Data`
        hygiene_data.syntax_context_data.push(SyntaxContextData {
            outer_expn: ExpnId::root(),
            outer_transparency: Transparency::Transparent,
            parent: SyntaxContext::root(),
            opaque: SyntaxContext::root(),
            opaque_and_semitransparent: SyntaxContext::root(),
            dollar_crate_name: kw::Empty,
        });
        let mut ctxts = outer_ctxts.lock();
        let new_len = raw_id as usize + 1;
        if ctxts.len() < new_len {
            ctxts.resize(new_len, None);
        }
        ctxts[raw_id as usize] = Some(new_ctxt);
        drop(ctxts);
        new_ctxt
    });

    // Don't try to decode data while holding the lock, since we need to
    // be able to recursively decode a SyntaxContext
    let mut ctxt_data = decode_data(d, raw_id);
    // Reset `dollar_crate_name` so that it will be updated by `update_dollar_crate_names`
    // We don't care what the encoding crate set this to - we want to resolve it
    // from the perspective of the current compilation session
    ctxt_data.dollar_crate_name = kw::DollarCrate;

    // Overwrite the dummy data with our decoded SyntaxContextData
    HygieneData::with(|hygiene_data| {
        let dummy = std::mem::replace(
            &mut hygiene_data.syntax_context_data[new_ctxt.as_u32() as usize],
            ctxt_data,
        );
        // Make sure nothing weird happening while `decode_data` was running
        assert_eq!(dummy.dollar_crate_name, kw::Empty);
    });

    new_ctxt
}

fn for_all_ctxts_in<F: FnMut(u32, SyntaxContext, &SyntaxContextData)>(
    ctxts: impl Iterator<Item = SyntaxContext>,
    mut f: F,
) {
    let all_data: Vec<_> = HygieneData::with(|data| {
        ctxts.map(|ctxt| (ctxt, data.syntax_context_data[ctxt.0 as usize].clone())).collect()
    });
    for (ctxt, data) in all_data.into_iter() {
        f(ctxt.0, ctxt, &data);
    }
}

fn for_all_expns_in(
    expns: impl Iterator<Item = ExpnId>,
    mut f: impl FnMut(ExpnId, &ExpnData, ExpnHash),
) {
    let all_data: Vec<_> = HygieneData::with(|data| {
        expns.map(|expn| (expn, data.expn_data(expn).clone(), data.expn_hash(expn))).collect()
    });
    for (expn, data, hash) in all_data.into_iter() {
        f(expn, &data, hash);
    }
}

impl<E: Encoder> Encodable<E> for LocalExpnId {
    fn encode(&self, e: &mut E) {
        self.to_expn_id().encode(e);
    }
}

impl<E: Encoder> Encodable<E> for ExpnId {
    default fn encode(&self, _: &mut E) {
        panic!("cannot encode `ExpnId` with `{}`", std::any::type_name::<E>());
    }
}

impl<D: Decoder> Decodable<D> for LocalExpnId {
    fn decode(d: &mut D) -> Self {
        ExpnId::expect_local(ExpnId::decode(d))
    }
}

impl<D: Decoder> Decodable<D> for ExpnId {
    default fn decode(_: &mut D) -> Self {
        panic!("cannot decode `ExpnId` with `{}`", std::any::type_name::<D>());
    }
}

pub fn raw_encode_syntax_context<E: Encoder>(
    ctxt: SyntaxContext,
    context: &HygieneEncodeContext,
    e: &mut E,
) {
    if !context.serialized_ctxts.lock().contains(&ctxt) {
        context.latest_ctxts.lock().insert(ctxt);
    }
    ctxt.0.encode(e);
}

impl<E: Encoder> Encodable<E> for SyntaxContext {
    default fn encode(&self, _: &mut E) {
        panic!("cannot encode `SyntaxContext` with `{}`", std::any::type_name::<E>());
    }
}

impl<D: Decoder> Decodable<D> for SyntaxContext {
    default fn decode(_: &mut D) -> Self {
        panic!("cannot decode `SyntaxContext` with `{}`", std::any::type_name::<D>());
    }
}

/// Updates the `disambiguator` field of the corresponding `ExpnData`
/// such that the `Fingerprint` of the `ExpnData` does not collide with
/// any other `ExpnIds`.
///
/// This method is called only when an `ExpnData` is first associated
/// with an `ExpnId` (when the `ExpnId` is initially constructed, or via
/// `set_expn_data`). It is *not* called for foreign `ExpnId`s deserialized
/// from another crate's metadata - since `ExpnHash` includes the stable crate id,
/// collisions are only possible between `ExpnId`s within the same crate.
fn update_disambiguator(expn_data: &mut ExpnData, mut ctx: impl HashStableContext) -> ExpnHash {
    // This disambiguator should not have been set yet.
    assert_eq!(expn_data.disambiguator, 0, "Already set disambiguator for ExpnData: {expn_data:?}");
    assert_default_hashing_controls(&ctx, "ExpnData (disambiguator)");
    let mut expn_hash = expn_data.hash_expn(&mut ctx);

    let disambiguator = HygieneData::with(|data| {
        // If this is the first ExpnData with a given hash, then keep our
        // disambiguator at 0 (the default u32 value)
        let disambig = data.expn_data_disambiguators.entry(expn_hash).or_default();
        let disambiguator = *disambig;
        *disambig += 1;
        disambiguator
    });

    if disambiguator != 0 {
        debug!("Set disambiguator for expn_data={:?} expn_hash={:?}", expn_data, expn_hash);

        expn_data.disambiguator = disambiguator;
        expn_hash = expn_data.hash_expn(&mut ctx);

        // Verify that the new disambiguator makes the hash unique
        #[cfg(debug_assertions)]
        HygieneData::with(|data| {
            assert_eq!(
                data.expn_data_disambiguators.get(&expn_hash),
                None,
                "Hash collision after disambiguator update!",
            );
        });
    }

    ExpnHash::new(ctx.def_path_hash(LOCAL_CRATE.as_def_id()).stable_crate_id(), expn_hash)
}

impl<CTX: HashStableContext> HashStable<CTX> for SyntaxContext {
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        const TAG_EXPANSION: u8 = 0;
        const TAG_NO_EXPANSION: u8 = 1;

        if self.is_root() {
            TAG_NO_EXPANSION.hash_stable(ctx, hasher);
        } else {
            TAG_EXPANSION.hash_stable(ctx, hasher);
            let (expn_id, transparency) = self.outer_mark();
            expn_id.hash_stable(ctx, hasher);
            transparency.hash_stable(ctx, hasher);
        }
    }
}

impl<CTX: HashStableContext> HashStable<CTX> for ExpnId {
    fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
        assert_default_hashing_controls(ctx, "ExpnId");
        let hash = if *self == ExpnId::root() {
            // Avoid fetching TLS storage for a trivial often-used value.
            Fingerprint::ZERO
        } else {
            self.expn_hash().0
        };

        hash.hash_stable(ctx, hasher);
    }
}