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
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
use crate::{
    archetype::{Archetype, ArchetypeEntity, Archetypes},
    component::Tick,
    entity::{Entities, Entity},
    query::{ArchetypeFilter, DebugCheckedUnwrap, QueryState, StorageId},
    storage::{Table, TableRow, Tables},
    world::unsafe_world_cell::UnsafeWorldCell,
};
use std::{
    borrow::Borrow,
    cmp::Ordering,
    fmt::{self, Debug, Formatter},
    iter::FusedIterator,
    mem::MaybeUninit,
    ops::Range,
};

use super::{QueryData, QueryFilter, ReadOnlyQueryData};

/// An [`Iterator`] over query results of a [`Query`](crate::system::Query).
///
/// This struct is created by the [`Query::iter`](crate::system::Query::iter) and
/// [`Query::iter_mut`](crate::system::Query::iter_mut) methods.
pub struct QueryIter<'w, 's, D: QueryData, F: QueryFilter> {
    world: UnsafeWorldCell<'w>,
    tables: &'w Tables,
    archetypes: &'w Archetypes,
    query_state: &'s QueryState<D, F>,
    cursor: QueryIterationCursor<'w, 's, D, F>,
}

impl<'w, 's, D: QueryData, F: QueryFilter> QueryIter<'w, 's, D, F> {
    /// # Safety
    /// - `world` must have permission to access any of the components registered in `query_state`.
    /// - `world` must be the same one used to initialize `query_state`.
    pub(crate) unsafe fn new(
        world: UnsafeWorldCell<'w>,
        query_state: &'s QueryState<D, F>,
        last_run: Tick,
        this_run: Tick,
    ) -> Self {
        QueryIter {
            world,
            query_state,
            // SAFETY: We only access table data that has been registered in `query_state`.
            tables: unsafe { &world.storages().tables },
            archetypes: world.archetypes(),
            // SAFETY: The invariants are uphold by the caller.
            cursor: unsafe { QueryIterationCursor::init(world, query_state, last_run, this_run) },
        }
    }

    /// Executes the equivalent of [`Iterator::fold`] over a contiguous segment
    /// from an table.
    ///
    /// # Safety
    ///  - all `rows` must be in `[0, table.entity_count)`.
    ///  - `table` must match D and F
    ///  - Both `D::IS_DENSE` and `F::IS_DENSE` must be true.
    #[inline]
    pub(super) unsafe fn fold_over_table_range<B, Func>(
        &mut self,
        mut accum: B,
        func: &mut Func,
        table: &'w Table,
        rows: Range<usize>,
    ) -> B
    where
        Func: FnMut(B, D::Item<'w>) -> B,
    {
        assert!(
            rows.end <= u32::MAX as usize,
            "TableRow is only valid up to u32::MAX"
        );

        D::set_table(&mut self.cursor.fetch, &self.query_state.fetch_state, table);
        F::set_table(
            &mut self.cursor.filter,
            &self.query_state.filter_state,
            table,
        );

        let entities = table.entities();
        for row in rows {
            // SAFETY: Caller assures `row` in range of the current archetype.
            let entity = unsafe { entities.get_unchecked(row) };
            let row = TableRow::from_usize(row);

            // SAFETY: set_table was called prior.
            // Caller assures `row` in range of the current archetype.
            let fetched = unsafe { !F::filter_fetch(&mut self.cursor.filter, *entity, row) };
            if fetched {
                continue;
            }

            // SAFETY: set_table was called prior.
            // Caller assures `row` in range of the current archetype.
            let item = D::fetch(&mut self.cursor.fetch, *entity, row);

            accum = func(accum, item);
        }
        accum
    }

    /// Executes the equivalent of [`Iterator::fold`] over a contiguous segment
    /// from an archetype.
    ///
    /// # Safety
    ///  - all `indices` must be in `[0, archetype.len())`.
    ///  - `archetype` must match D and F
    ///  - Either `D::IS_DENSE` or `F::IS_DENSE` must be false.
    #[inline]
    pub(super) unsafe fn fold_over_archetype_range<B, Func>(
        &mut self,
        mut accum: B,
        func: &mut Func,
        archetype: &'w Archetype,
        indices: Range<usize>,
    ) -> B
    where
        Func: FnMut(B, D::Item<'w>) -> B,
    {
        let table = self.tables.get(archetype.table_id()).debug_checked_unwrap();
        D::set_archetype(
            &mut self.cursor.fetch,
            &self.query_state.fetch_state,
            archetype,
            table,
        );
        F::set_archetype(
            &mut self.cursor.filter,
            &self.query_state.filter_state,
            archetype,
            table,
        );

        let entities = archetype.entities();
        for index in indices {
            // SAFETY: Caller assures `index` in range of the current archetype.
            let archetype_entity = unsafe { entities.get_unchecked(index) };

            // SAFETY: set_archetype was called prior.
            // Caller assures `index` in range of the current archetype.
            let fetched = unsafe {
                !F::filter_fetch(
                    &mut self.cursor.filter,
                    archetype_entity.id(),
                    archetype_entity.table_row(),
                )
            };
            if fetched {
                continue;
            }

            // SAFETY: set_archetype was called prior, `index` is an archetype index in range of the current archetype
            // Caller assures `index` in range of the current archetype.
            let item = unsafe {
                D::fetch(
                    &mut self.cursor.fetch,
                    archetype_entity.id(),
                    archetype_entity.table_row(),
                )
            };

            accum = func(accum, item);
        }
        accum
    }

    /// Sorts all query items into a new iterator, using the query lens as a key.
    ///
    /// This sort is stable (i.e., does not reorder equal elements).
    ///
    /// This uses [`slice::sort`] internally.
    ///
    /// Defining the lens works like [`transmute_lens`](crate::system::Query::transmute_lens).
    /// This includes the allowed parameter type changes listed under [allowed transmutes].
    /// However, the lens uses the filter of the original query when present.
    ///
    /// The sort is not cached across system runs.
    ///
    /// [allowed transmutes]: crate::system::Query#allowed-transmutes
    ///
    /// # Panics
    ///
    /// This will panic if `next` has been called on `QueryIter` before, unless the underlying `Query` is empty.
    ///
    /// # Examples
    /// ```rust
    /// # use bevy_ecs::prelude::*;
    /// # use std::{ops::{Deref, DerefMut}, iter::Sum};
    /// #
    /// # #[derive(Component)]
    /// # struct PartMarker;
    /// #
    /// # #[derive(Component, PartialEq, Eq, PartialOrd, Ord)]
    /// # struct PartIndex(usize);
    /// #
    /// # #[derive(Component, Clone, Copy)]
    /// # struct PartValue(f32);
    /// #
    /// # impl Deref for PartValue {
    /// #     type Target = f32;
    /// #
    /// #     fn deref(&self) -> &Self::Target {
    /// #         &self.0
    /// #     }
    /// # }
    /// #
    /// # #[derive(Component)]
    /// # struct ParentValue(f32);
    /// #
    /// # impl Deref for ParentValue {
    /// #     type Target = f32;
    /// #
    /// #     fn deref(&self) -> &Self::Target {
    /// #         &self.0
    /// #     }
    /// # }
    /// #
    /// # impl DerefMut for ParentValue {
    /// #     fn deref_mut(&mut self) -> &mut Self::Target {
    /// #         &mut self.0
    /// #     }
    /// # }
    /// #
    /// # #[derive(Component, Debug, PartialEq, Eq, PartialOrd, Ord)]
    /// # struct Length(usize);
    /// #
    /// # #[derive(Component, Debug, PartialEq, Eq, PartialOrd, Ord)]
    /// # struct Width(usize);
    /// #
    /// # #[derive(Component, Debug, PartialEq, Eq, PartialOrd, Ord)]
    /// # struct Height(usize);
    /// #
    /// # #[derive(Component, PartialEq, Eq, PartialOrd, Ord)]
    /// # struct ParentEntity(Entity);
    /// #
    /// # #[derive(Component, Clone, Copy)]
    /// # struct ChildPartCount(usize);
    /// #
    /// # impl Deref for ChildPartCount {
    /// #     type Target = usize;
    /// #
    /// #     fn deref(&self) -> &Self::Target {
    /// #         &self.0
    /// #     }
    /// # }
    /// # let mut world = World::new();
    /// // We can ensure that a query always returns in the same order.
    /// fn system_1(query: Query<(Entity, &PartIndex)>) {
    ///     let parts: Vec<(Entity, &PartIndex)> = query.iter().sort::<&PartIndex>().collect();
    /// }
    ///
    /// // We can freely rearrange query components in the key.
    /// fn system_2(query: Query<(&Length, &Width, &Height), With<PartMarker>>) {
    ///     for (length, width, height) in query.iter().sort::<(&Height, &Length, &Width)>() {
    ///         println!("height: {height:?}, width: {width:?}, length: {length:?}")
    ///     }
    /// }
    ///
    /// // We can sort by Entity without including it in the original Query.
    /// // Here, we match iteration orders between query iterators.
    /// fn system_3(
    ///     part_query: Query<(&PartValue, &ParentEntity)>,
    ///     mut parent_query: Query<(&ChildPartCount, &mut ParentValue)>,
    /// ) {
    ///     let part_values = &mut part_query
    ///         .into_iter()
    ///         .sort::<&ParentEntity>()
    ///         .map(|(&value, parent_entity)| *value);
    ///
    ///     for (&child_count, mut parent_value) in parent_query.iter_mut().sort::<Entity>() {
    ///         **parent_value = part_values.take(*child_count).sum();
    ///     }
    /// }
    /// #
    /// # let mut schedule = Schedule::default();
    /// # schedule.add_systems((system_1, system_2, system_3));
    /// # schedule.run(&mut world);
    /// ```
    pub fn sort<L: ReadOnlyQueryData + 'w>(
        self,
    ) -> QuerySortedIter<
        'w,
        's,
        D,
        F,
        impl ExactSizeIterator<Item = Entity> + DoubleEndedIterator + FusedIterator + 'w,
    >
    where
        L::Item<'w>: Ord,
    {
        // On the first successful iteration of `QueryIterationCursor`, `archetype_entities` or `table_entities`
        // will be set to a non-zero value. The correctness of this method relies on this.
        // I.e. this sort method will execute if and only if `next` on `QueryIterationCursor` of a
        // non-empty `QueryIter` has not yet been called. When empty, this sort method will not panic.
        if !self.cursor.archetype_entities.is_empty() || !self.cursor.table_entities.is_empty() {
            panic!("it is not valid to call sort() after next()")
        }

        let world = self.world;

        let query_lens_state = self
            .query_state
            .transmute_filtered::<(L, Entity), F>(world.components());

        // SAFETY:
        // `self.world` has permission to access the required components.
        // The original query iter has not been iterated on, so no items are aliased from it.
        let query_lens = unsafe {
            query_lens_state.iter_unchecked_manual(
                world,
                world.last_change_tick(),
                world.change_tick(),
            )
        };
        let mut keyed_query: Vec<_> = query_lens
            .map(|(key, entity)| (key, NeutralOrd(entity)))
            .collect();
        keyed_query.sort();
        let entity_iter = keyed_query.into_iter().map(|(.., entity)| entity.0);
        // SAFETY:
        // `self.world` has permission to access the required components.
        // Each lens query item is dropped before the respective actual query item is accessed.
        unsafe {
            QuerySortedIter::new(
                world,
                self.query_state,
                entity_iter,
                world.last_change_tick(),
                world.change_tick(),
            )
        }
    }

    /// Sorts all query items into a new iterator, using the query lens as a key.
    ///
    /// This sort is unstable (i.e., may reorder equal elements).
    ///
    /// This uses [`slice::sort_unstable`] internally.
    ///
    /// Defining the lens works like [`transmute_lens`](crate::system::Query::transmute_lens).
    /// This includes the allowed parameter type changes listed under [allowed transmutes]..
    /// However, the lens uses the filter of the original query when present.
    ///
    /// The sort is not cached across system runs.
    ///
    /// [allowed transmutes]: crate::system::Query#allowed-transmutes
    ///
    /// # Panics
    ///
    /// This will panic if `next` has been called on `QueryIter` before, unless the underlying `Query` is empty.
    ///
    /// # Example
    /// ```
    /// # use bevy_ecs::prelude::*;
    /// #
    /// # let mut world = World::new();
    /// #
    /// # #[derive(Component)]
    /// # struct PartMarker;
    /// #
    /// #[derive(Component, PartialEq, Eq, PartialOrd, Ord)]
    /// enum Flying {
    ///     Enabled,
    ///     Disabled
    /// };
    ///
    /// // We perform an unstable sort by a Component with few values.
    /// fn system_1(query: Query<&Flying, With<PartMarker>>) {
    ///     let part_values: Vec<&Flying> = query.iter().sort_unstable::<&Flying>().collect();
    /// }
    /// #
    /// # let mut schedule = Schedule::default();
    /// # schedule.add_systems((system_1));
    /// # schedule.run(&mut world);
    /// ```
    pub fn sort_unstable<L: ReadOnlyQueryData + 'w>(
        self,
    ) -> QuerySortedIter<
        'w,
        's,
        D,
        F,
        impl ExactSizeIterator<Item = Entity> + DoubleEndedIterator + FusedIterator + 'w,
    >
    where
        L::Item<'w>: Ord,
    {
        // On the first successful iteration of `QueryIterationCursor`, `archetype_entities` or `table_entities`
        // will be set to a non-zero value. The correctness of this method relies on this.
        // I.e. this sort method will execute if and only if `next` on `QueryIterationCursor` of a
        // non-empty `QueryIter` has not yet been called. When empty, this sort method will not panic.
        if !self.cursor.archetype_entities.is_empty() || !self.cursor.table_entities.is_empty() {
            panic!("it is not valid to call sort() after next()")
        }

        let world = self.world;

        let query_lens_state = self
            .query_state
            .transmute_filtered::<(L, Entity), F>(world.components());

        // SAFETY:
        // `self.world` has permission to access the required components.
        // The original query iter has not been iterated on, so no items are aliased from it.
        let query_lens = unsafe {
            query_lens_state.iter_unchecked_manual(
                world,
                world.last_change_tick(),
                world.change_tick(),
            )
        };
        let mut keyed_query: Vec<_> = query_lens
            .map(|(key, entity)| (key, NeutralOrd(entity)))
            .collect();
        keyed_query.sort_unstable();
        let entity_iter = keyed_query.into_iter().map(|(.., entity)| entity.0);
        // SAFETY:
        // `self.world` has permission to access the required components.
        // Each lens query item is dropped before the respective actual query item is accessed.
        unsafe {
            QuerySortedIter::new(
                world,
                self.query_state,
                entity_iter,
                world.last_change_tick(),
                world.change_tick(),
            )
        }
    }

    /// Sorts all query items into a new iterator with a comparator function over the query lens.
    ///
    /// This sort is stable (i.e., does not reorder equal elements).
    ///
    /// This uses [`slice::sort_by`] internally.
    ///
    /// Defining the lens works like [`transmute_lens`](crate::system::Query::transmute_lens).
    /// This includes the allowed parameter type changes listed under [allowed transmutes].
    /// However, the lens uses the filter of the original query when present.
    ///
    /// The sort is not cached across system runs.
    ///
    /// [allowed transmutes]: crate::system::Query#allowed-transmutes
    ///
    /// # Panics
    ///
    /// This will panic if `next` has been called on `QueryIter` before, unless the underlying `Query` is empty.
    ///
    /// # Example
    /// ```
    /// # use bevy_ecs::prelude::*;
    /// # use std::ops::Deref;
    /// #
    /// # impl Deref for PartValue {
    /// #     type Target = f32;
    /// #
    /// #     fn deref(&self) -> &Self::Target {
    /// #         &self.0
    /// #     }
    /// # }
    /// #
    /// # let mut world = World::new();
    /// #
    /// #[derive(Component)]
    /// struct PartValue(f32);
    ///
    /// // We can use a cmp function on components do not implement Ord.
    /// fn system_1(query: Query<&PartValue>) {
    ///     // Sort part values according to `f32::total_comp`.
    ///     let part_values: Vec<&PartValue> = query
    ///         .iter()
    ///         .sort_by::<&PartValue>(|value_1, value_2| value_1.total_cmp(*value_2))
    ///         .collect();
    /// }
    /// #
    /// # let mut schedule = Schedule::default();
    /// # schedule.add_systems((system_1));
    /// # schedule.run(&mut world);
    /// ```
    pub fn sort_by<L: ReadOnlyQueryData + 'w>(
        self,
        mut compare: impl FnMut(&L::Item<'w>, &L::Item<'w>) -> Ordering,
    ) -> QuerySortedIter<
        'w,
        's,
        D,
        F,
        impl ExactSizeIterator<Item = Entity> + DoubleEndedIterator + FusedIterator + 'w,
    > {
        // On the first successful iteration of `QueryIterationCursor`, `archetype_entities` or `table_entities`
        // will be set to a non-zero value. The correctness of this method relies on this.
        // I.e. this sort method will execute if and only if `next` on `QueryIterationCursor` of a
        // non-empty `QueryIter` has not yet been called. When empty, this sort method will not panic.
        if !self.cursor.archetype_entities.is_empty() || !self.cursor.table_entities.is_empty() {
            panic!("it is not valid to call sort() after next()")
        }

        let world = self.world;

        let query_lens_state = self
            .query_state
            .transmute_filtered::<(L, Entity), F>(world.components());

        // SAFETY:
        // `self.world` has permission to access the required components.
        // The original query iter has not been iterated on, so no items are aliased from it.
        let query_lens = unsafe {
            query_lens_state.iter_unchecked_manual(
                world,
                world.last_change_tick(),
                world.change_tick(),
            )
        };
        let mut keyed_query: Vec<_> = query_lens.collect();
        keyed_query.sort_by(|(key_1, _), (key_2, _)| compare(key_1, key_2));
        let entity_iter = keyed_query.into_iter().map(|(.., entity)| entity);
        // SAFETY:
        // `self.world` has permission to access the required components.
        // Each lens query item is dropped before the respective actual query item is accessed.
        unsafe {
            QuerySortedIter::new(
                world,
                self.query_state,
                entity_iter,
                world.last_change_tick(),
                world.change_tick(),
            )
        }
    }

    /// Sorts all query items into a new iterator with a comparator function over the query lens.
    ///
    /// This sort is unstable (i.e., may reorder equal elements).
    ///
    /// This uses [`slice::sort_unstable_by`] internally.
    ///
    /// Defining the lens works like [`transmute_lens`](crate::system::Query::transmute_lens).
    /// This includes the allowed parameter type changes listed under [allowed transmutes].
    /// However, the lens uses the filter of the original query when present.
    ///
    /// The sort is not cached across system runs.
    ///
    /// [allowed transmutes]: crate::system::Query#allowed-transmutes
    ///
    /// # Panics
    ///
    /// This will panic if `next` has been called on `QueryIter` before, unless the underlying `Query` is empty.
    pub fn sort_unstable_by<L: ReadOnlyQueryData + 'w>(
        self,
        mut compare: impl FnMut(&L::Item<'w>, &L::Item<'w>) -> Ordering,
    ) -> QuerySortedIter<
        'w,
        's,
        D,
        F,
        impl ExactSizeIterator<Item = Entity> + DoubleEndedIterator + FusedIterator + 'w,
    > {
        // On the first successful iteration of `QueryIterationCursor`, `archetype_entities` or `table_entities`
        // will be set to a non-zero value. The correctness of this method relies on this.
        // I.e. this sort method will execute if and only if `next` on `QueryIterationCursor` of a
        // non-empty `QueryIter` has not yet been called. When empty, this sort method will not panic.
        if !self.cursor.archetype_entities.is_empty() || !self.cursor.table_entities.is_empty() {
            panic!("it is not valid to call sort() after next()")
        }

        let world = self.world;

        let query_lens_state = self
            .query_state
            .transmute_filtered::<(L, Entity), F>(world.components());

        // SAFETY:
        // `self.world` has permission to access the required components.
        // The original query iter has not been iterated on, so no items are aliased from it.
        let query_lens = unsafe {
            query_lens_state.iter_unchecked_manual(
                world,
                world.last_change_tick(),
                world.change_tick(),
            )
        };
        let mut keyed_query: Vec<_> = query_lens.collect();
        keyed_query.sort_by(|(key_1, _), (key_2, _)| compare(key_1, key_2));
        let entity_iter = keyed_query.into_iter().map(|(.., entity)| entity);
        // SAFETY:
        // `self.world` has permission to access the required components.
        // Each lens query item is dropped before the respective actual query item is accessed.
        unsafe {
            QuerySortedIter::new(
                world,
                self.query_state,
                entity_iter,
                world.last_change_tick(),
                world.change_tick(),
            )
        }
    }

    /// Sorts all query items into a new iterator with a key extraction function over the query lens.
    ///
    /// This sort is stable (i.e., does not reorder equal elements).
    ///
    /// This uses [`slice::sort_by_key`] internally.
    ///
    /// Defining the lens works like [`transmute_lens`](crate::system::Query::transmute_lens).
    /// This includes the allowed parameter type changes listed under [allowed transmutes].
    /// However, the lens uses the filter of the original query when present.
    ///
    /// The sort is not cached across system runs.
    ///
    /// [allowed transmutes]: crate::system::Query#allowed-transmutes
    ///
    /// # Panics
    ///
    /// This will panic if `next` has been called on `QueryIter` before, unless the underlying `Query` is empty.
    ///
    /// # Example
    /// ```
    /// # use bevy_ecs::prelude::*;
    /// # use std::ops::Deref;
    /// #
    /// # #[derive(Component)]
    /// # struct PartMarker;
    /// #
    /// # impl Deref for PartValue {
    /// #     type Target = f32;
    /// #
    /// #     fn deref(&self) -> &Self::Target {
    /// #         &self.0
    /// #     }
    /// # }
    /// #
    /// # let mut world = World::new();
    /// #
    /// #[derive(Component)]
    /// struct AvailableMarker;
    ///
    /// #[derive(Component, PartialEq, Eq, PartialOrd, Ord)]
    /// enum Rarity {
    ///   Common,
    ///   Rare,
    ///   Epic,
    ///   Legendary
    /// };
    ///
    /// #[derive(Component)]
    /// struct PartValue(f32);
    ///
    /// // We can sort with the internals of components that do not implement Ord.
    /// fn system_1(query: Query<(Entity, &PartValue)>) {
    ///     // Sort by the sines of the part values.
    ///     let parts: Vec<(Entity, &PartValue)> = query
    ///         .iter()
    ///         .sort_by_key::<&PartValue, _>(|value| value.sin() as usize)
    ///         .collect();
    /// }
    ///
    /// // We can define our own custom comparison functions over an EntityRef.
    /// fn system_2(query: Query<EntityRef, With<PartMarker>>) {
    ///     // Sort by whether parts are available and their rarity.
    ///     // We want the available legendaries to come first, so we reverse the iterator.
    ///     let parts: Vec<EntityRef> = query.iter()
    ///         .sort_by_key::<EntityRef, _>(|entity_ref| {
    ///             (
    ///                 entity_ref.contains::<AvailableMarker>(),
    ///                 entity_ref.get::<Rarity>()
    ///             )
    ///         })
    ///         .rev()
    ///         .collect();
    /// }
    /// # let mut schedule = Schedule::default();
    /// # schedule.add_systems((system_1, system_2));
    /// # schedule.run(&mut world);
    /// ```
    pub fn sort_by_key<L: ReadOnlyQueryData + 'w, K>(
        self,
        mut f: impl FnMut(&L::Item<'w>) -> K,
    ) -> QuerySortedIter<
        'w,
        's,
        D,
        F,
        impl ExactSizeIterator<Item = Entity> + DoubleEndedIterator + FusedIterator + 'w,
    >
    where
        K: Ord,
    {
        // On the first successful iteration of `QueryIterationCursor`, `archetype_entities` or `table_entities`
        // will be set to a non-zero value. The correctness of this method relies on this.
        // I.e. this sort method will execute if and only if `next` on `QueryIterationCursor` of a
        // non-empty `QueryIter` has not yet been called. When empty, this sort method will not panic.
        if !self.cursor.archetype_entities.is_empty() || !self.cursor.table_entities.is_empty() {
            panic!("it is not valid to call sort() after next()")
        }

        let world = self.world;

        let query_lens_state = self
            .query_state
            .transmute_filtered::<(L, Entity), F>(world.components());

        // SAFETY:
        // `self.world` has permission to access the required components.
        // The original query iter has not been iterated on, so no items are aliased from it.
        let query_lens = unsafe {
            query_lens_state.iter_unchecked_manual(
                world,
                world.last_change_tick(),
                world.change_tick(),
            )
        };
        let mut keyed_query: Vec<_> = query_lens.collect();
        keyed_query.sort_by_key(|(lens, _)| f(lens));
        let entity_iter = keyed_query.into_iter().map(|(.., entity)| entity);
        // SAFETY:
        // `self.world` has permission to access the required components.
        // Each lens query item is dropped before the respective actual query item is accessed.
        unsafe {
            QuerySortedIter::new(
                world,
                self.query_state,
                entity_iter,
                world.last_change_tick(),
                world.change_tick(),
            )
        }
    }

    /// Sorts all query items into a new iterator with a key extraction function over the query lens.
    ///
    /// This sort is unstable (i.e., may reorder equal elements).
    ///
    /// This uses [`slice::sort_unstable_by_key`] internally.
    ///
    /// Defining the lens works like [`transmute_lens`](crate::system::Query::transmute_lens).
    /// This includes the allowed parameter type changes listed under [allowed transmutes].
    /// However, the lens uses the filter of the original query when present.
    ///
    /// The sort is not cached across system runs.
    ///
    /// [allowed transmutes]: crate::system::Query#allowed-transmutes
    ///
    /// # Panics
    ///
    /// This will panic if `next` has been called on `QueryIter` before, unless the underlying `Query` is empty.
    pub fn sort_unstable_by_key<L: ReadOnlyQueryData + 'w, K>(
        self,
        mut f: impl FnMut(&L::Item<'w>) -> K,
    ) -> QuerySortedIter<
        'w,
        's,
        D,
        F,
        impl ExactSizeIterator<Item = Entity> + DoubleEndedIterator + FusedIterator + 'w,
    >
    where
        K: Ord,
    {
        // On the first successful iteration of `QueryIterationCursor`, `archetype_entities` or `table_entities`
        // will be set to a non-zero value. The correctness of this method relies on this.
        // I.e. this sort method will execute if and only if `next` on `QueryIterationCursor` of a
        // non-empty `QueryIter` has not yet been called. When empty, this sort method will not panic.
        if !self.cursor.archetype_entities.is_empty() || !self.cursor.table_entities.is_empty() {
            panic!("it is not valid to call sort() after next()")
        }

        let world = self.world;

        let query_lens_state = self
            .query_state
            .transmute_filtered::<(L, Entity), F>(world.components());

        // SAFETY:
        // `self.world` has permission to access the required components.
        // The original query iter has not been iterated on, so no items are aliased from it.
        let query_lens = unsafe {
            query_lens_state.iter_unchecked_manual(
                world,
                world.last_change_tick(),
                world.change_tick(),
            )
        };
        let mut keyed_query: Vec<_> = query_lens.collect();
        keyed_query.sort_unstable_by_key(|(lens, _)| f(lens));
        let entity_iter = keyed_query.into_iter().map(|(.., entity)| entity);
        // SAFETY:
        // `self.world` has permission to access the required components.
        // Each lens query item is dropped before the respective actual query item is accessed.
        unsafe {
            QuerySortedIter::new(
                world,
                self.query_state,
                entity_iter,
                world.last_change_tick(),
                world.change_tick(),
            )
        }
    }

    /// Sort all query items into a new iterator with a key extraction function over the query lens.
    ///
    /// This sort is stable (i.e., does not reorder equal elements).
    ///
    /// This uses [`slice::sort_by_cached_key`] internally.
    ///
    /// Defining the lens works like [`transmute_lens`](crate::system::Query::transmute_lens).
    /// This includes the allowed parameter type changes listed under [allowed transmutes].
    /// However, the lens uses the filter of the original query when present.
    ///
    /// The sort is not cached across system runs.
    ///
    /// [allowed transmutes]: crate::system::Query#allowed-transmutes
    ///
    /// # Panics
    ///
    /// This will panic if `next` has been called on `QueryIter` before, unless the underlying `Query` is empty.
    ///
    pub fn sort_by_cached_key<L: ReadOnlyQueryData + 'w, K>(
        self,
        mut f: impl FnMut(&L::Item<'w>) -> K,
    ) -> QuerySortedIter<
        'w,
        's,
        D,
        F,
        impl ExactSizeIterator<Item = Entity> + DoubleEndedIterator + FusedIterator + 'w,
    >
    where
        K: Ord,
    {
        // On the first successful iteration of `QueryIterationCursor`, `archetype_entities` or `table_entities`
        // will be set to a non-zero value. The correctness of this method relies on this.
        // I.e. this sort method will execute if and only if `next` on `QueryIterationCursor` of a
        // non-empty `QueryIter` has not yet been called. When empty, this sort method will not panic.
        if !self.cursor.archetype_entities.is_empty() || !self.cursor.table_entities.is_empty() {
            panic!("it is not valid to call sort() after next()")
        }

        let world = self.world;

        let query_lens_state = self
            .query_state
            .transmute_filtered::<(L, Entity), F>(world.components());

        // SAFETY:
        // `self.world` has permission to access the required components.
        // The original query iter has not been iterated on, so no items are aliased from it.
        let query_lens = unsafe {
            query_lens_state.iter_unchecked_manual(
                world,
                world.last_change_tick(),
                world.change_tick(),
            )
        };
        let mut keyed_query: Vec<_> = query_lens.collect();
        keyed_query.sort_by_cached_key(|(lens, _)| f(lens));
        let entity_iter = keyed_query.into_iter().map(|(.., entity)| entity);
        // SAFETY:
        // `self.world` has permission to access the required components.
        // Each lens query item is dropped before the respective actual query item is accessed.
        unsafe {
            QuerySortedIter::new(
                world,
                self.query_state,
                entity_iter,
                world.last_change_tick(),
                world.change_tick(),
            )
        }
    }
}

impl<'w, 's, D: QueryData, F: QueryFilter> Iterator for QueryIter<'w, 's, D, F> {
    type Item = D::Item<'w>;

    #[inline(always)]
    fn next(&mut self) -> Option<Self::Item> {
        // SAFETY:
        // `tables` and `archetypes` belong to the same world that the cursor was initialized for.
        // `query_state` is the state that was passed to `QueryIterationCursor::init`.
        unsafe {
            self.cursor
                .next(self.tables, self.archetypes, self.query_state)
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        let max_size = self.cursor.max_remaining(self.tables, self.archetypes);
        let archetype_query = F::IS_ARCHETYPAL;
        let min_size = if archetype_query { max_size } else { 0 };
        (min_size, Some(max_size))
    }

    #[inline]
    fn fold<B, Func>(mut self, init: B, mut func: Func) -> B
    where
        Func: FnMut(B, Self::Item) -> B,
    {
        let mut accum = init;
        // Empty any remaining uniterated values from the current table/archetype
        while self.cursor.current_row != self.cursor.current_len {
            let Some(item) = self.next() else { break };
            accum = func(accum, item);
        }
        for id in self.cursor.storage_id_iter.clone() {
            if D::IS_DENSE && F::IS_DENSE {
                // SAFETY: Matched table IDs are guaranteed to still exist.
                let table = unsafe { self.tables.get(id.table_id).debug_checked_unwrap() };
                accum =
                    // SAFETY: 
                    // - The fetched table matches both D and F
                    // - The provided range is equivalent to [0, table.entity_count)
                    // - The if block ensures that D::IS_DENSE and F::IS_DENSE are both true
                    unsafe { self.fold_over_table_range(accum, &mut func, table, 0..table.entity_count()) };
            } else {
                let archetype =
                    // SAFETY: Matched archetype IDs are guaranteed to still exist.
                    unsafe { self.archetypes.get(id.archetype_id).debug_checked_unwrap() };
                accum =
                    // SAFETY:
                    // - The fetched archetype matches both D and F
                    // - The provided range is equivalent to [0, archetype.len)
                    // - The if block ensures that ether D::IS_DENSE or F::IS_DENSE are false
                    unsafe { self.fold_over_archetype_range(accum, &mut func, archetype, 0..archetype.len()) };
            }
        }
        accum
    }
}

// This is correct as [`QueryIter`] always returns `None` once exhausted.
impl<'w, 's, D: QueryData, F: QueryFilter> FusedIterator for QueryIter<'w, 's, D, F> {}

impl<'w, 's, D: QueryData, F: QueryFilter> Debug for QueryIter<'w, 's, D, F> {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        f.debug_struct("QueryIter").finish()
    }
}

/// An [`Iterator`] over sorted query results of a [`Query`](crate::system::Query).
///
/// This struct is created by the [`QueryIter::sort`], [`QueryIter::sort_unstable`],
/// [`QueryIter::sort_by`], [`QueryIter::sort_unstable_by`], [`QueryIter::sort_by_key`],
/// [`QueryIter::sort_unstable_by_key`], and [`QueryIter::sort_by_cached_key`] methods.
pub struct QuerySortedIter<'w, 's, D: QueryData, F: QueryFilter, I>
where
    I: Iterator<Item = Entity>,
{
    entity_iter: I,
    entities: &'w Entities,
    tables: &'w Tables,
    archetypes: &'w Archetypes,
    fetch: D::Fetch<'w>,
    query_state: &'s QueryState<D, F>,
}

impl<'w, 's, D: QueryData, F: QueryFilter, I: Iterator> QuerySortedIter<'w, 's, D, F, I>
where
    I: Iterator<Item = Entity>,
{
    /// # Safety
    /// - `world` must have permission to access any of the components registered in `query_state`.
    /// - `world` must be the same one used to initialize `query_state`.
    /// - `entity_list` must only contain unique entities or be empty.
    pub(crate) unsafe fn new<EntityList: IntoIterator<IntoIter = I>>(
        world: UnsafeWorldCell<'w>,
        query_state: &'s QueryState<D, F>,
        entity_list: EntityList,
        last_run: Tick,
        this_run: Tick,
    ) -> QuerySortedIter<'w, 's, D, F, I> {
        let fetch = D::init_fetch(world, &query_state.fetch_state, last_run, this_run);
        QuerySortedIter {
            query_state,
            entities: world.entities(),
            archetypes: world.archetypes(),
            // SAFETY: We only access table data that has been registered in `query_state`.
            // This means `world` has permission to access the data we use.
            tables: &world.storages().tables,
            fetch,
            entity_iter: entity_list.into_iter(),
        }
    }

    /// # Safety
    /// `entity` must stem from `self.entity_iter`, and not have been passed before.
    #[inline(always)]
    unsafe fn fetch_next(&mut self, entity: Entity) -> D::Item<'w> {
        let (location, archetype, table);
        // SAFETY:
        // `tables` and `archetypes` belong to the same world that the [`QueryIter`]
        // was initialized for.
        unsafe {
            location = self.entities.get(entity).debug_checked_unwrap();
            archetype = self
                .archetypes
                .get(location.archetype_id)
                .debug_checked_unwrap();
            table = self.tables.get(location.table_id).debug_checked_unwrap();
        }

        // SAFETY: `archetype` is from the world that `fetch` was created for,
        // `fetch_state` is the state that `fetch` was initialized with
        unsafe {
            D::set_archetype(
                &mut self.fetch,
                &self.query_state.fetch_state,
                archetype,
                table,
            );
        }

        // The entity list has already been filtered by the query lens, so we forego filtering here.
        // SAFETY:
        // - set_archetype was called prior, `location.archetype_row` is an archetype index in range of the current archetype
        // - fetch is only called once for each entity.
        unsafe { D::fetch(&mut self.fetch, entity, location.table_row) }
    }
}

impl<'w, 's, D: QueryData, F: QueryFilter, I: Iterator> Iterator
    for QuerySortedIter<'w, 's, D, F, I>
where
    I: Iterator<Item = Entity>,
{
    type Item = D::Item<'w>;

    #[inline(always)]
    fn next(&mut self) -> Option<Self::Item> {
        let entity = self.entity_iter.next()?;
        // SAFETY: `entity` is passed from `entity_iter` the first time.
        unsafe { self.fetch_next(entity).into() }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        self.entity_iter.size_hint()
    }
}

impl<'w, 's, D: QueryData, F: QueryFilter, I: Iterator> DoubleEndedIterator
    for QuerySortedIter<'w, 's, D, F, I>
where
    I: DoubleEndedIterator<Item = Entity>,
{
    #[inline(always)]
    fn next_back(&mut self) -> Option<Self::Item> {
        let entity = self.entity_iter.next_back()?;
        // SAFETY: `entity` is passed from `entity_iter` the first time.
        unsafe { self.fetch_next(entity).into() }
    }
}

impl<'w, 's, D: QueryData, F: QueryFilter, I: Iterator> ExactSizeIterator
    for QuerySortedIter<'w, 's, D, F, I>
where
    I: ExactSizeIterator<Item = Entity>,
{
}

// This is correct as [`QuerySortedIter`] returns `None` once exhausted if `entity_iter` does.
impl<'w, 's, D: QueryData, F: QueryFilter, I: Iterator> FusedIterator
    for QuerySortedIter<'w, 's, D, F, I>
where
    I: FusedIterator<Item = Entity>,
{
}

impl<'w, 's, D: QueryData, F: QueryFilter, I: Iterator<Item = Entity>> Debug
    for QuerySortedIter<'w, 's, D, F, I>
{
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        f.debug_struct("QuerySortedIter").finish()
    }
}

/// An [`Iterator`] over the query items generated from an iterator of [`Entity`]s.
///
/// Items are returned in the order of the provided iterator.
/// Entities that don't match the query are skipped.
///
/// This struct is created by the [`Query::iter_many`](crate::system::Query::iter_many) and [`Query::iter_many_mut`](crate::system::Query::iter_many_mut) methods.
pub struct QueryManyIter<'w, 's, D: QueryData, F: QueryFilter, I: Iterator>
where
    I::Item: Borrow<Entity>,
{
    entity_iter: I,
    entities: &'w Entities,
    tables: &'w Tables,
    archetypes: &'w Archetypes,
    fetch: D::Fetch<'w>,
    filter: F::Fetch<'w>,
    query_state: &'s QueryState<D, F>,
}

impl<'w, 's, D: QueryData, F: QueryFilter, I: Iterator> QueryManyIter<'w, 's, D, F, I>
where
    I::Item: Borrow<Entity>,
{
    /// # Safety
    /// - `world` must have permission to access any of the components registered in `query_state`.
    /// - `world` must be the same one used to initialize `query_state`.
    pub(crate) unsafe fn new<EntityList: IntoIterator<IntoIter = I>>(
        world: UnsafeWorldCell<'w>,
        query_state: &'s QueryState<D, F>,
        entity_list: EntityList,
        last_run: Tick,
        this_run: Tick,
    ) -> QueryManyIter<'w, 's, D, F, I> {
        let fetch = D::init_fetch(world, &query_state.fetch_state, last_run, this_run);
        let filter = F::init_fetch(world, &query_state.filter_state, last_run, this_run);
        QueryManyIter {
            query_state,
            entities: world.entities(),
            archetypes: world.archetypes(),
            // SAFETY: We only access table data that has been registered in `query_state`.
            // This means `world` has permission to access the data we use.
            tables: &world.storages().tables,
            fetch,
            filter,
            entity_iter: entity_list.into_iter(),
        }
    }

    /// Safety:
    /// The lifetime here is not restrictive enough for Fetch with &mut access,
    /// as calling `fetch_next_aliased_unchecked` multiple times can produce multiple
    /// references to the same component, leading to unique reference aliasing.
    ///
    /// It is always safe for shared access.
    #[inline(always)]
    unsafe fn fetch_next_aliased_unchecked(&mut self) -> Option<D::Item<'w>> {
        for entity in self.entity_iter.by_ref() {
            let entity = *entity.borrow();
            let Some(location) = self.entities.get(entity) else {
                continue;
            };

            if !self
                .query_state
                .matched_archetypes
                .contains(location.archetype_id.index())
            {
                continue;
            }

            let archetype = self
                .archetypes
                .get(location.archetype_id)
                .debug_checked_unwrap();
            let table = self.tables.get(location.table_id).debug_checked_unwrap();

            // SAFETY: `archetype` is from the world that `fetch/filter` were created for,
            // `fetch_state`/`filter_state` are the states that `fetch/filter` were initialized with
            unsafe {
                D::set_archetype(
                    &mut self.fetch,
                    &self.query_state.fetch_state,
                    archetype,
                    table,
                );
            }
            // SAFETY: `table` is from the world that `fetch/filter` were created for,
            // `fetch_state`/`filter_state` are the states that `fetch/filter` were initialized with
            unsafe {
                F::set_archetype(
                    &mut self.filter,
                    &self.query_state.filter_state,
                    archetype,
                    table,
                );
            }

            // SAFETY: set_archetype was called prior.
            // `location.archetype_row` is an archetype index row in range of the current archetype, because if it was not, the match above would have `continue`d
            if unsafe { F::filter_fetch(&mut self.filter, entity, location.table_row) } {
                // SAFETY:
                // - set_archetype was called prior, `location.archetype_row` is an archetype index in range of the current archetype
                // - fetch is only called once for each entity.
                return Some(unsafe { D::fetch(&mut self.fetch, entity, location.table_row) });
            }
        }
        None
    }

    /// Get next result from the query
    #[inline(always)]
    pub fn fetch_next(&mut self) -> Option<D::Item<'_>> {
        // SAFETY: we are limiting the returned reference to self,
        // making sure this method cannot be called multiple times without getting rid
        // of any previously returned unique references first, thus preventing aliasing.
        unsafe { self.fetch_next_aliased_unchecked().map(D::shrink) }
    }
}

impl<'w, 's, D: ReadOnlyQueryData, F: QueryFilter, I: Iterator> Iterator
    for QueryManyIter<'w, 's, D, F, I>
where
    I::Item: Borrow<Entity>,
{
    type Item = D::Item<'w>;

    #[inline(always)]
    fn next(&mut self) -> Option<Self::Item> {
        // SAFETY: It is safe to alias for ReadOnlyWorldQuery.
        unsafe { self.fetch_next_aliased_unchecked() }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        let (_, max_size) = self.entity_iter.size_hint();
        (0, max_size)
    }
}

// This is correct as [`QueryManyIter`] always returns `None` once exhausted.
impl<'w, 's, D: ReadOnlyQueryData, F: QueryFilter, I: Iterator> FusedIterator
    for QueryManyIter<'w, 's, D, F, I>
where
    I::Item: Borrow<Entity>,
{
}

impl<'w, 's, D: QueryData, F: QueryFilter, I: Iterator> Debug for QueryManyIter<'w, 's, D, F, I>
where
    I::Item: Borrow<Entity>,
{
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        f.debug_struct("QueryManyIter").finish()
    }
}

/// An iterator over `K`-sized combinations of query items without repetition.
///
/// A combination is an arrangement of a collection of items where order does not matter.
///
/// `K` is the number of items that make up each subset, and the number of items returned by the iterator.
/// `N` is the number of total entities output by the query.
///
/// For example, given the list [1, 2, 3, 4], where `K` is 2, the combinations without repeats are
/// [1, 2], [1, 3], [1, 4], [2, 3], [2, 4], [3, 4].
/// And in this case, `N` would be defined as 4 since the size of the input list is 4.
///
/// The number of combinations depend on how `K` relates to the number of entities matching the [`Query`]:
/// - if `K = N`, only one combination exists,
/// - if `K < N`, there are <sub>N</sub>C<sub>K</sub> combinations (see the [performance section] of `Query`),
/// - if `K > N`, there are no combinations.
///
/// The output combination is not guaranteed to have any order of iteration.
///
/// # Usage
///
/// This type is returned by calling [`Query::iter_combinations`] or [`Query::iter_combinations_mut`].
///
/// It implements [`Iterator`] only if it iterates over read-only query items ([learn more]).
///
/// In the case of mutable query items, it can be iterated by calling [`fetch_next`] in a `while let` loop.
///
/// # Examples
///
/// The following example shows how to traverse the iterator when the query items are read-only.
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Component)]
/// # struct ComponentA;
/// #
/// fn some_system(query: Query<&ComponentA>) {
///     for [a1, a2] in query.iter_combinations() {
///         // ...
///     }
/// }
/// ```
///
/// The following example shows how `fetch_next` should be called with a `while let` loop to traverse the iterator when the query items are mutable.
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Component)]
/// # struct ComponentA;
/// #
/// fn some_system(mut query: Query<&mut ComponentA>) {
///     let mut combinations = query.iter_combinations_mut();
///     while let Some([a1, a2]) = combinations.fetch_next() {
///         // ...
///     }
/// }
/// ```
///
/// [`fetch_next`]: Self::fetch_next
/// [learn more]: Self#impl-Iterator
/// [performance section]: crate::system::Query#performance
/// [`Query`]: crate::system::Query
/// [`Query::iter_combinations`]: crate::system::Query::iter_combinations
/// [`Query::iter_combinations_mut`]: crate::system::Query::iter_combinations_mut
pub struct QueryCombinationIter<'w, 's, D: QueryData, F: QueryFilter, const K: usize> {
    tables: &'w Tables,
    archetypes: &'w Archetypes,
    query_state: &'s QueryState<D, F>,
    cursors: [QueryIterationCursor<'w, 's, D, F>; K],
}

impl<'w, 's, D: QueryData, F: QueryFilter, const K: usize> QueryCombinationIter<'w, 's, D, F, K> {
    /// # Safety
    /// - `world` must have permission to access any of the components registered in `query_state`.
    /// - `world` must be the same one used to initialize `query_state`.
    pub(crate) unsafe fn new(
        world: UnsafeWorldCell<'w>,
        query_state: &'s QueryState<D, F>,
        last_run: Tick,
        this_run: Tick,
    ) -> Self {
        // Initialize array with cursors.
        // There is no FromIterator on arrays, so instead initialize it manually with MaybeUninit

        let mut array: MaybeUninit<[QueryIterationCursor<'w, 's, D, F>; K]> = MaybeUninit::uninit();
        let ptr = array
            .as_mut_ptr()
            .cast::<QueryIterationCursor<'w, 's, D, F>>();
        if K != 0 {
            ptr.write(QueryIterationCursor::init(
                world,
                query_state,
                last_run,
                this_run,
            ));
        }
        for slot in (1..K).map(|offset| ptr.add(offset)) {
            slot.write(QueryIterationCursor::init_empty(
                world,
                query_state,
                last_run,
                this_run,
            ));
        }

        QueryCombinationIter {
            query_state,
            // SAFETY: We only access table data that has been registered in `query_state`.
            tables: unsafe { &world.storages().tables },
            archetypes: world.archetypes(),
            cursors: array.assume_init(),
        }
    }

    /// Safety:
    /// The lifetime here is not restrictive enough for Fetch with &mut access,
    /// as calling `fetch_next_aliased_unchecked` multiple times can produce multiple
    /// references to the same component, leading to unique reference aliasing.
    ///.
    /// It is always safe for shared access.
    unsafe fn fetch_next_aliased_unchecked(&mut self) -> Option<[D::Item<'w>; K]> {
        if K == 0 {
            return None;
        }

        // PERF: can speed up the following code using `cursor.remaining()` instead of `next_item.is_none()`
        // when D::IS_ARCHETYPAL && F::IS_ARCHETYPAL
        //
        // let `i` be the index of `c`, the last cursor in `self.cursors` that
        // returns `K-i` or more elements.
        // Make cursor in index `j` for all `j` in `[i, K)` a copy of `c` advanced `j-i+1` times.
        // If no such `c` exists, return `None`
        'outer: for i in (0..K).rev() {
            match self.cursors[i].next(self.tables, self.archetypes, self.query_state) {
                Some(_) => {
                    for j in (i + 1)..K {
                        self.cursors[j] = self.cursors[j - 1].clone();
                        match self.cursors[j].next(self.tables, self.archetypes, self.query_state) {
                            Some(_) => {}
                            None if i > 0 => continue 'outer,
                            None => return None,
                        }
                    }
                    break;
                }
                None if i > 0 => continue,
                None => return None,
            }
        }

        let mut values = MaybeUninit::<[D::Item<'w>; K]>::uninit();

        let ptr = values.as_mut_ptr().cast::<D::Item<'w>>();
        for (offset, cursor) in self.cursors.iter_mut().enumerate() {
            ptr.add(offset).write(cursor.peek_last().unwrap());
        }

        Some(values.assume_init())
    }

    /// Get next combination of queried components
    #[inline]
    pub fn fetch_next(&mut self) -> Option<[D::Item<'_>; K]> {
        // SAFETY: we are limiting the returned reference to self,
        // making sure this method cannot be called multiple times without getting rid
        // of any previously returned unique references first, thus preventing aliasing.
        unsafe {
            self.fetch_next_aliased_unchecked()
                .map(|array| array.map(D::shrink))
        }
    }
}

// Iterator type is intentionally implemented only for read-only access.
// Doing so for mutable references would be unsound, because calling `next`
// multiple times would allow multiple owned references to the same data to exist.
impl<'w, 's, D: ReadOnlyQueryData, F: QueryFilter, const K: usize> Iterator
    for QueryCombinationIter<'w, 's, D, F, K>
{
    type Item = [D::Item<'w>; K];

    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        // Safety: it is safe to alias for ReadOnlyWorldQuery
        unsafe { QueryCombinationIter::fetch_next_aliased_unchecked(self) }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        // binomial coefficient: (n ; k) = n! / k!(n-k)! = (n*n-1*...*n-k+1) / k!
        // See https://en.wikipedia.org/wiki/Binomial_coefficient
        // See https://blog.plover.com/math/choose.html for implementation
        // It was chosen to reduce overflow potential.
        fn choose(n: usize, k: usize) -> Option<usize> {
            if k > n || n == 0 {
                return Some(0);
            }
            let k = k.min(n - k);
            let ks = 1..=k;
            let ns = (n - k + 1..=n).rev();
            ks.zip(ns)
                .try_fold(1_usize, |acc, (k, n)| Some(acc.checked_mul(n)? / k))
        }
        // sum_i=0..k choose(cursors[i].remaining, k-i)
        let max_combinations = self
            .cursors
            .iter()
            .enumerate()
            .try_fold(0, |acc, (i, cursor)| {
                let n = cursor.max_remaining(self.tables, self.archetypes);
                Some(acc + choose(n, K - i)?)
            });

        let archetype_query = F::IS_ARCHETYPAL;
        let known_max = max_combinations.unwrap_or(usize::MAX);
        let min_combinations = if archetype_query { known_max } else { 0 };
        (min_combinations, max_combinations)
    }
}

impl<'w, 's, D: QueryData, F: QueryFilter> ExactSizeIterator for QueryIter<'w, 's, D, F>
where
    F: ArchetypeFilter,
{
    fn len(&self) -> usize {
        self.size_hint().0
    }
}

// This is correct as [`QueryCombinationIter`] always returns `None` once exhausted.
impl<'w, 's, D: ReadOnlyQueryData, F: QueryFilter, const K: usize> FusedIterator
    for QueryCombinationIter<'w, 's, D, F, K>
{
}

impl<'w, 's, D: QueryData, F: QueryFilter, const K: usize> Debug
    for QueryCombinationIter<'w, 's, D, F, K>
{
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        f.debug_struct("QueryCombinationIter").finish()
    }
}

struct QueryIterationCursor<'w, 's, D: QueryData, F: QueryFilter> {
    storage_id_iter: std::slice::Iter<'s, StorageId>,
    table_entities: &'w [Entity],
    archetype_entities: &'w [ArchetypeEntity],
    fetch: D::Fetch<'w>,
    filter: F::Fetch<'w>,
    // length of the table or length of the archetype, depending on whether both `D`'s and `F`'s fetches are dense
    current_len: usize,
    // either table row or archetype index, depending on whether both `D`'s and `F`'s fetches are dense
    current_row: usize,
}

impl<D: QueryData, F: QueryFilter> Clone for QueryIterationCursor<'_, '_, D, F> {
    fn clone(&self) -> Self {
        Self {
            storage_id_iter: self.storage_id_iter.clone(),
            table_entities: self.table_entities,
            archetype_entities: self.archetype_entities,
            fetch: self.fetch.clone(),
            filter: self.filter.clone(),
            current_len: self.current_len,
            current_row: self.current_row,
        }
    }
}

impl<'w, 's, D: QueryData, F: QueryFilter> QueryIterationCursor<'w, 's, D, F> {
    const IS_DENSE: bool = D::IS_DENSE && F::IS_DENSE;

    unsafe fn init_empty(
        world: UnsafeWorldCell<'w>,
        query_state: &'s QueryState<D, F>,
        last_run: Tick,
        this_run: Tick,
    ) -> Self {
        QueryIterationCursor {
            storage_id_iter: [].iter(),
            ..Self::init(world, query_state, last_run, this_run)
        }
    }

    /// # Safety
    /// - `world` must have permission to access any of the components registered in `query_state`.
    /// - `world` must be the same one used to initialize `query_state`.
    unsafe fn init(
        world: UnsafeWorldCell<'w>,
        query_state: &'s QueryState<D, F>,
        last_run: Tick,
        this_run: Tick,
    ) -> Self {
        let fetch = D::init_fetch(world, &query_state.fetch_state, last_run, this_run);
        let filter = F::init_fetch(world, &query_state.filter_state, last_run, this_run);
        QueryIterationCursor {
            fetch,
            filter,
            table_entities: &[],
            archetype_entities: &[],
            storage_id_iter: query_state.matched_storage_ids.iter(),
            current_len: 0,
            current_row: 0,
        }
    }

    /// retrieve item returned from most recent `next` call again.
    #[inline]
    unsafe fn peek_last(&mut self) -> Option<D::Item<'w>> {
        if self.current_row > 0 {
            let index = self.current_row - 1;
            if Self::IS_DENSE {
                let entity = self.table_entities.get_unchecked(index);
                Some(D::fetch(
                    &mut self.fetch,
                    *entity,
                    TableRow::from_usize(index),
                ))
            } else {
                let archetype_entity = self.archetype_entities.get_unchecked(index);
                Some(D::fetch(
                    &mut self.fetch,
                    archetype_entity.id(),
                    archetype_entity.table_row(),
                ))
            }
        } else {
            None
        }
    }

    /// How many values will this cursor return at most?
    ///
    /// Note that if `F::IS_ARCHETYPAL`, the return value
    /// will be **the exact count of remaining values**.
    fn max_remaining(&self, tables: &'w Tables, archetypes: &'w Archetypes) -> usize {
        let ids = self.storage_id_iter.clone();
        let remaining_matched: usize = if Self::IS_DENSE {
            // SAFETY: The if check ensures that storage_id_iter stores TableIds
            unsafe { ids.map(|id| tables[id.table_id].entity_count()).sum() }
        } else {
            // SAFETY: The if check ensures that storage_id_iter stores ArchetypeIds
            unsafe { ids.map(|id| archetypes[id.archetype_id].len()).sum() }
        };
        remaining_matched + self.current_len - self.current_row
    }

    // NOTE: If you are changing query iteration code, remember to update the following places, where relevant:
    // QueryIter, QueryIterationCursor, QuerySortedIter, QueryManyIter, QueryCombinationIter, QueryState::par_fold_init_unchecked_manual
    /// # Safety
    /// `tables` and `archetypes` must belong to the same world that the [`QueryIterationCursor`]
    /// was initialized for.
    /// `query_state` must be the same [`QueryState`] that was passed to `init` or `init_empty`.
    #[inline(always)]
    unsafe fn next(
        &mut self,
        tables: &'w Tables,
        archetypes: &'w Archetypes,
        query_state: &'s QueryState<D, F>,
    ) -> Option<D::Item<'w>> {
        if Self::IS_DENSE {
            loop {
                // we are on the beginning of the query, or finished processing a table, so skip to the next
                if self.current_row == self.current_len {
                    let table_id = self.storage_id_iter.next()?.table_id;
                    let table = tables.get(table_id).debug_checked_unwrap();
                    // SAFETY: `table` is from the world that `fetch/filter` were created for,
                    // `fetch_state`/`filter_state` are the states that `fetch/filter` were initialized with
                    unsafe {
                        D::set_table(&mut self.fetch, &query_state.fetch_state, table);
                        F::set_table(&mut self.filter, &query_state.filter_state, table);
                    }
                    self.table_entities = table.entities();
                    self.current_len = table.entity_count();
                    self.current_row = 0;
                    continue;
                }

                // SAFETY: set_table was called prior.
                // `current_row` is a table row in range of the current table, because if it was not, then the above would have been executed.
                let entity = unsafe { self.table_entities.get_unchecked(self.current_row) };
                let row = TableRow::from_usize(self.current_row);
                if !F::filter_fetch(&mut self.filter, *entity, row) {
                    self.current_row += 1;
                    continue;
                }

                // SAFETY:
                // - set_table was called prior.
                // - `current_row` must be a table row in range of the current table,
                //   because if it was not, then the above would have been executed.
                // - fetch is only called once for each `entity`.
                let item = unsafe { D::fetch(&mut self.fetch, *entity, row) };

                self.current_row += 1;
                return Some(item);
            }
        } else {
            loop {
                if self.current_row == self.current_len {
                    let archetype_id = self.storage_id_iter.next()?.archetype_id;
                    let archetype = archetypes.get(archetype_id).debug_checked_unwrap();
                    let table = tables.get(archetype.table_id()).debug_checked_unwrap();
                    // SAFETY: `archetype` and `tables` are from the world that `fetch/filter` were created for,
                    // `fetch_state`/`filter_state` are the states that `fetch/filter` were initialized with
                    unsafe {
                        D::set_archetype(
                            &mut self.fetch,
                            &query_state.fetch_state,
                            archetype,
                            table,
                        );
                        F::set_archetype(
                            &mut self.filter,
                            &query_state.filter_state,
                            archetype,
                            table,
                        );
                    }
                    self.archetype_entities = archetype.entities();
                    self.current_len = archetype.len();
                    self.current_row = 0;
                    continue;
                }

                // SAFETY: set_archetype was called prior.
                // `current_row` is an archetype index row in range of the current archetype, because if it was not, then the if above would have been executed.
                let archetype_entity =
                    unsafe { self.archetype_entities.get_unchecked(self.current_row) };
                if !F::filter_fetch(
                    &mut self.filter,
                    archetype_entity.id(),
                    archetype_entity.table_row(),
                ) {
                    self.current_row += 1;
                    continue;
                }

                // SAFETY:
                // - set_archetype was called prior.
                // - `current_row` must be an archetype index row in range of the current archetype,
                //   because if it was not, then the if above would have been executed.
                // - fetch is only called once for each `archetype_entity`.
                let item = unsafe {
                    D::fetch(
                        &mut self.fetch,
                        archetype_entity.id(),
                        archetype_entity.table_row(),
                    )
                };
                self.current_row += 1;
                return Some(item);
            }
        }
    }
}

// A wrapper struct that gives its data a neutral ordering.
#[derive(Copy, Clone)]
struct NeutralOrd<T>(T);

impl<T> PartialEq for NeutralOrd<T> {
    fn eq(&self, _other: &Self) -> bool {
        true
    }
}

impl<T> Eq for NeutralOrd<T> {}

#[allow(clippy::non_canonical_partial_ord_impl)]
impl<T> PartialOrd for NeutralOrd<T> {
    fn partial_cmp(&self, _other: &Self) -> Option<Ordering> {
        Some(Ordering::Equal)
    }
}

impl<T> Ord for NeutralOrd<T> {
    fn cmp(&self, _other: &Self) -> Ordering {
        Ordering::Equal
    }
}

#[cfg(test)]
mod tests {
    #[allow(unused_imports)]
    use crate::{self as bevy_ecs, component::Component, entity::Entity, prelude::World};

    #[derive(Component, Debug, PartialEq, PartialOrd, Clone, Copy)]
    struct A(f32);
    #[derive(Component, Debug, Eq, PartialEq, Clone, Copy)]
    #[component(storage = "SparseSet")]
    struct Sparse(usize);

    #[allow(clippy::unnecessary_sort_by)]
    #[test]
    fn query_sorts() {
        let mut world = World::new();

        let mut query = world.query::<Entity>();

        let sort = query.iter(&world).sort::<Entity>().collect::<Vec<_>>();

        let sort_unstable = query
            .iter(&world)
            .sort_unstable::<Entity>()
            .collect::<Vec<_>>();

        let sort_by = query
            .iter(&world)
            .sort_by::<Entity>(|e1, e2| e1.cmp(e2))
            .collect::<Vec<_>>();

        let sort_unstable_by = query
            .iter(&world)
            .sort_unstable_by::<Entity>(|e1, e2| e1.cmp(e2))
            .collect::<Vec<_>>();

        let sort_by_key = query
            .iter(&world)
            .sort_by_key::<Entity, _>(|&e| e)
            .collect::<Vec<_>>();

        let sort_unstable_by_key = query
            .iter(&world)
            .sort_unstable_by_key::<Entity, _>(|&e| e)
            .collect::<Vec<_>>();

        let sort_by_cached_key = query
            .iter(&world)
            .sort_by_cached_key::<Entity, _>(|&e| e)
            .collect::<Vec<_>>();

        let mut sort_v2 = query.iter(&world).collect::<Vec<_>>();
        sort_v2.sort();

        let mut sort_unstable_v2 = query.iter(&world).collect::<Vec<_>>();
        sort_unstable_v2.sort_unstable();

        let mut sort_by_v2 = query.iter(&world).collect::<Vec<_>>();
        sort_by_v2.sort_by(|e1, e2| e1.cmp(e2));

        let mut sort_unstable_by_v2 = query.iter(&world).collect::<Vec<_>>();
        sort_unstable_by_v2.sort_unstable_by(|e1, e2| e1.cmp(e2));

        let mut sort_by_key_v2 = query.iter(&world).collect::<Vec<_>>();
        sort_by_key_v2.sort_by_key(|&e| e);

        let mut sort_unstable_by_key_v2 = query.iter(&world).collect::<Vec<_>>();
        sort_unstable_by_key_v2.sort_unstable_by_key(|&e| e);

        let mut sort_by_cached_key_v2 = query.iter(&world).collect::<Vec<_>>();
        sort_by_cached_key_v2.sort_by_cached_key(|&e| e);

        assert_eq!(sort, sort_v2);
        assert_eq!(sort_unstable, sort_unstable_v2);
        assert_eq!(sort_by, sort_by_v2);
        assert_eq!(sort_unstable_by, sort_unstable_by_v2);
        assert_eq!(sort_by_key, sort_by_key_v2);
        assert_eq!(sort_unstable_by_key, sort_unstable_by_key_v2);
        assert_eq!(sort_by_cached_key, sort_by_cached_key_v2);
    }

    #[test]
    #[should_panic]
    fn query_sort_after_next() {
        let mut world = World::new();
        world.spawn((A(0.),));
        world.spawn((A(1.1),));
        world.spawn((A(2.22),));

        {
            let mut query = world.query::<&A>();
            let mut iter = query.iter(&world);
            println!(
                "archetype_entities: {} table_entities: {} current_len: {} current_row: {}",
                iter.cursor.archetype_entities.len(),
                iter.cursor.table_entities.len(),
                iter.cursor.current_len,
                iter.cursor.current_row
            );
            _ = iter.next();
            println!(
                "archetype_entities: {} table_entities: {} current_len: {} current_row: {}",
                iter.cursor.archetype_entities.len(),
                iter.cursor.table_entities.len(),
                iter.cursor.current_len,
                iter.cursor.current_row
            );
            println!("{}", iter.sort::<Entity>().len());
        }
    }

    #[test]
    #[should_panic]
    fn query_sort_after_next_dense() {
        let mut world = World::new();
        world.spawn((Sparse(11),));
        world.spawn((Sparse(22),));
        world.spawn((Sparse(33),));

        {
            let mut query = world.query::<&Sparse>();
            let mut iter = query.iter(&world);
            println!(
                "before_next_call: archetype_entities: {} table_entities: {} current_len: {} current_row: {}", 
                iter.cursor.archetype_entities.len(),
                iter.cursor.table_entities.len(),
                iter.cursor.current_len,
                iter.cursor.current_row
            );
            _ = iter.next();
            println!(
                "after_next_call: archetype_entities: {} table_entities: {} current_len: {} current_row: {}", 
                iter.cursor.archetype_entities.len(),
                iter.cursor.table_entities.len(),
                iter.cursor.current_len,
                iter.cursor.current_row
            );
            println!("{}", iter.sort::<Entity>().len());
        }
    }

    #[test]
    fn empty_query_sort_after_next_does_not_panic() {
        let mut world = World::new();
        {
            let mut query = world.query::<(&A, &Sparse)>();
            let mut iter = query.iter(&world);
            println!(
                "before_next_call: archetype_entities: {} table_entities: {} current_len: {} current_row: {}", 
                iter.cursor.archetype_entities.len(),
                iter.cursor.table_entities.len(),
                iter.cursor.current_len,
                iter.cursor.current_row
            );
            _ = iter.next();
            println!(
                "after_next_call: archetype_entities: {} table_entities: {} current_len: {} current_row: {}", 
                iter.cursor.archetype_entities.len(),
                iter.cursor.table_entities.len(),
                iter.cursor.current_len,
                iter.cursor.current_row
            );
            println!("{}", iter.sort::<Entity>().len());
        }
    }

    #[test]
    fn query_iter_cursor_state_non_empty_after_next() {
        let mut world = World::new();
        world.spawn((A(0.), Sparse(11)));
        world.spawn((A(1.1), Sparse(22)));
        world.spawn((A(2.22), Sparse(33)));
        {
            let mut query = world.query::<(&A, &Sparse)>();
            let mut iter = query.iter(&world);
            println!(
                "before_next_call: archetype_entities: {} table_entities: {} current_len: {} current_row: {}", 
                iter.cursor.archetype_entities.len(),
                iter.cursor.table_entities.len(),
                iter.cursor.current_len,
                iter.cursor.current_row
            );
            assert!(iter.cursor.table_entities.len() | iter.cursor.archetype_entities.len() == 0);
            _ = iter.next();
            println!(
                "after_next_call: archetype_entities: {} table_entities: {} current_len: {} current_row: {}", 
                iter.cursor.archetype_entities.len(),
                iter.cursor.table_entities.len(),
                iter.cursor.current_len,
                iter.cursor.current_row
            );
            assert!(
                (
                    iter.cursor.table_entities.len(),
                    iter.cursor.archetype_entities.len()
                ) != (0, 0)
            );
        }
    }
}