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
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
// Copyright (c) The cargo-guppy Contributors
// SPDX-License-Identifier: MIT OR Apache-2.0

use crate::{
    graph::{
        cargo_version_matches,
        feature::{FeatureGraphImpl, FeatureId, FeatureLabel, FeatureNode},
        BuildTarget, BuildTargetId, BuildTargetImpl, BuildTargetKind, Cycles, DependencyDirection,
        OwnedBuildTargetId, PackageIx, PackageQuery, PackageSet,
    },
    petgraph_support::{scc::Sccs, topo::TopoWithCycles, IxBitSet},
    platform::{EnabledTernary, PlatformSpec, PlatformStatus, PlatformStatusImpl},
    CargoMetadata, DependencyKind, Error, JsonValue, MetadataCommand, PackageId,
};
use ahash::AHashMap;
use camino::{Utf8Path, Utf8PathBuf};
use fixedbitset::FixedBitSet;
use indexmap::{IndexMap, IndexSet};
use once_cell::sync::OnceCell;
use petgraph::{
    algo::{has_path_connecting, DfsSpace},
    graph::EdgeReference,
    prelude::*,
    visit::EdgeFiltered,
};
use semver::{Version, VersionReq};
use smallvec::SmallVec;
use std::{
    collections::{BTreeMap, HashSet},
    fmt, iter,
    iter::FromIterator,
};

use super::feature::{FeatureFilter, FeatureSet};

/// A graph of packages and dependencies between them, parsed from metadata returned by `cargo
/// metadata`.
///
/// For examples on how to use `PackageGraph`, see
/// [the `examples` directory](https://github.com/guppy-rs/guppy/tree/main/guppy/examples)
/// in this crate.
#[derive(Clone, Debug)]
pub struct PackageGraph {
    // Source of truth data.
    pub(super) dep_graph: Graph<PackageId, PackageLinkImpl, Directed, PackageIx>,
    // The strongly connected components of the graph, computed on demand.
    pub(super) sccs: OnceCell<Sccs<PackageIx>>,
    // Feature graph, computed on demand.
    pub(super) feature_graph: OnceCell<FeatureGraphImpl>,
    // XXX Should this be in an Arc for quick cloning? Not clear how this would work with node
    // filters though.
    pub(super) data: PackageGraphData,
}

/// Per-package data for a PackageGraph instance.
#[derive(Clone, Debug)]
pub(super) struct PackageGraphData {
    pub(super) packages: AHashMap<PackageId, PackageMetadataImpl>,
    pub(super) workspace: WorkspaceImpl,
}

impl PackageGraph {
    /// Executes the given `MetadataCommand` and constructs a `PackageGraph` from it.
    pub fn from_command(command: &mut MetadataCommand) -> Result<Self, Error> {
        command.build_graph()
    }

    /// Parses the given `Metadata` and constructs a `PackageGraph` from it.
    pub fn from_metadata(metadata: CargoMetadata) -> Result<Self, Error> {
        Self::build(metadata.0).map_err(|error| *error)
    }

    /// Constructs a package graph from the given JSON output of `cargo metadata`.
    ///
    /// Generally, `guppy` expects the `cargo metadata` command to be run with `--all-features`, so
    /// that `guppy` has a full view of the dependency graph.
    ///
    /// For full functionality, `cargo metadata` should be run without `--no-deps`, so that `guppy`
    /// knows about third-party crates and dependency edges. However, `guppy` supports a "light"
    /// mode if `--no-deps` is run, in which case the following limitations will apply:
    /// * dependency queries will not work
    /// * there will be no information about non-workspace crates
    pub fn from_json(json: impl AsRef<str>) -> Result<Self, Error> {
        let metadata = CargoMetadata::parse_json(json)?;
        Self::from_metadata(metadata)
    }

    /// Verifies internal invariants on this graph. Not part of the documented API.
    #[doc(hidden)]
    pub fn verify(&self) -> Result<(), Error> {
        // Graph structure checks.
        let node_count = self.dep_graph.node_count();
        let package_count = self.data.packages.len();
        if node_count != package_count {
            return Err(Error::PackageGraphInternalError(format!(
                "number of nodes = {} different from packages = {}",
                node_count, package_count,
            )));
        }

        // TODO: The dependency graph can have cyclic dev-dependencies. Add a check to ensure that
        // the graph without any dev-only dependencies is acyclic.

        let workspace = self.workspace();
        let workspace_ids: HashSet<_> = workspace.member_ids().collect();

        for metadata in self.packages() {
            let package_id = metadata.id();

            match metadata.source().workspace_path() {
                Some(workspace_path) => {
                    // This package is in the workspace, so the workspace should have information
                    // about it.
                    let metadata2 = workspace.member_by_path(workspace_path);
                    let metadata2_id = metadata2.map(|metadata| metadata.id());
                    if !matches!(metadata2_id, Ok(id) if id == package_id) {
                        return Err(Error::PackageGraphInternalError(format!(
                            "package {} has workspace path {:?} but query by path returned {:?}",
                            package_id, workspace_path, metadata2_id,
                        )));
                    }

                    let metadata3 = workspace.member_by_name(metadata.name());
                    let metadata3_id = metadata3.map(|metadata| metadata.id());
                    if !matches!(metadata3_id, Ok(id) if id == package_id) {
                        return Err(Error::PackageGraphInternalError(format!(
                            "package {} has name {}, but workspace query by name returned {:?}",
                            package_id,
                            metadata.name(),
                            metadata3_id,
                        )));
                    }
                }
                None => {
                    // This package is not in the workspace.
                    if workspace_ids.contains(package_id) {
                        return Err(Error::PackageGraphInternalError(format!(
                            "package {} has no workspace path but is in workspace",
                            package_id,
                        )));
                    }
                }
            }

            for build_target in metadata.build_targets() {
                match build_target.id() {
                    BuildTargetId::Library | BuildTargetId::BuildScript => {
                        // Ensure that the name is populated (this may panic if it isn't).
                        build_target.name();
                    }
                    BuildTargetId::Binary(name)
                    | BuildTargetId::Example(name)
                    | BuildTargetId::Test(name)
                    | BuildTargetId::Benchmark(name) => {
                        if name != build_target.name() {
                            return Err(Error::PackageGraphInternalError(format!(
                                "package {} has build target name mismatch ({} != {})",
                                package_id,
                                name,
                                build_target.name(),
                            )));
                        }
                    }
                }

                let id_kind_mismatch = match build_target.id() {
                    BuildTargetId::Library => match build_target.kind() {
                        BuildTargetKind::LibraryOrExample(_) | BuildTargetKind::ProcMacro => false,
                        BuildTargetKind::Binary => true,
                    },
                    BuildTargetId::Example(_) => match build_target.kind() {
                        BuildTargetKind::LibraryOrExample(_) => false,
                        BuildTargetKind::ProcMacro | BuildTargetKind::Binary => true,
                    },
                    BuildTargetId::BuildScript
                    | BuildTargetId::Binary(_)
                    | BuildTargetId::Test(_)
                    | BuildTargetId::Benchmark(_) => match build_target.kind() {
                        BuildTargetKind::LibraryOrExample(_) | BuildTargetKind::ProcMacro => true,
                        BuildTargetKind::Binary => false,
                    },
                };

                if id_kind_mismatch {
                    return Err(Error::PackageGraphInternalError(format!(
                        "package {} has build target id {:?}, which doesn't match kind {:?}",
                        package_id,
                        build_target.id(),
                        build_target.kind(),
                    )));
                }
            }

            for link in self.dep_links_ixs_directed(metadata.package_ix(), Outgoing) {
                let to = link.to();
                let to_id = to.id();
                let to_version = to.version();

                // Two invariants:
                // 1. At least one of the edges should be specified.
                // 2. The specified package should match the version dependency.

                let req = link.version_req();
                // A requirement of "*" filters out pre-release versions with the semver crate,
                // but cargo accepts them.
                // See https://github.com/steveklabnik/semver/issues/98.
                if !cargo_version_matches(req, to_version) {
                    return Err(Error::PackageGraphInternalError(format!(
                        "{} -> {}: version ({}) doesn't match requirement ({:?})",
                        package_id, to_id, to_version, req,
                    )));
                }

                let is_any = link.normal().is_present()
                    || link.build().is_present()
                    || link.dev().is_present();

                if !is_any {
                    return Err(Error::PackageGraphInternalError(format!(
                        "{} -> {}: no edge info found",
                        package_id, to_id,
                    )));
                }
            }
        }

        // Construct and check the feature graph for internal consistency.
        self.feature_graph().verify()?;

        Ok(())
    }

    /// Returns information about the workspace.
    pub fn workspace(&self) -> Workspace {
        Workspace {
            graph: self,
            inner: &self.data.workspace,
        }
    }

    /// Returns an iterator over all the package IDs in this graph.
    pub fn package_ids(&self) -> impl ExactSizeIterator<Item = &PackageId> {
        self.data.package_ids()
    }

    /// Returns an iterator over all the packages in this graph.
    pub fn packages(&self) -> impl ExactSizeIterator<Item = PackageMetadata> {
        self.data
            .packages
            .values()
            .map(move |inner| PackageMetadata::new(self, inner))
    }

    /// Returns the metadata for the given package ID.
    pub fn metadata(&self, package_id: &PackageId) -> Result<PackageMetadata, Error> {
        let inner = self
            .data
            .metadata_impl(package_id)
            .ok_or_else(|| Error::UnknownPackageId(package_id.clone()))?;
        Ok(PackageMetadata::new(self, inner))
    }

    /// Returns the number of packages in this graph.
    pub fn package_count(&self) -> usize {
        // This can be obtained in two different ways: self.dep_graph.node_count() or
        // self.data.packages.len(). verify() checks that they return the same results.
        //
        // Use this way for symmetry with link_count below (which can only be obtained through the
        // graph).
        self.dep_graph.node_count()
    }

    /// Returns the number of links in this graph.
    pub fn link_count(&self) -> usize {
        self.dep_graph.edge_count()
    }

    /// Creates a new cache for `depends_on` queries.
    ///
    /// The cache is optional but can speed up some queries.
    pub fn new_depends_cache(&self) -> DependsCache {
        DependsCache::new(self)
    }

    /// Returns true if `package_a` depends (directly or indirectly) on `package_b`.
    ///
    /// In other words, this returns true if `package_b` is a (possibly transitive) dependency of
    /// `package_a`.
    ///
    /// This also returns true if `package_a` is the same as `package_b`.
    ///
    /// For repeated queries, consider using `new_depends_cache` to speed up queries.
    pub fn depends_on(&self, package_a: &PackageId, package_b: &PackageId) -> Result<bool, Error> {
        let mut depends_cache = self.new_depends_cache();
        depends_cache.depends_on(package_a, package_b)
    }

    /// Returns true if `package_a` directly depends on `package_b`.
    ///
    /// In other words, this returns true if `package_b` is a direct dependency of `package_a`.
    ///
    /// This returns false if `package_a` is the same as `package_b`.
    pub fn directly_depends_on(
        &self,
        package_a: &PackageId,
        package_b: &PackageId,
    ) -> Result<bool, Error> {
        let a_ix = self.package_ix(package_a)?;
        let b_ix = self.package_ix(package_b)?;
        Ok(self.dep_graph.contains_edge(a_ix, b_ix))
    }

    /// Returns information about dependency cycles in this graph.
    ///
    /// For more information, see the documentation for `Cycles`.
    pub fn cycles(&self) -> Cycles {
        Cycles::new(self)
    }

    // For more traversals, see query.rs.

    // ---
    // Helper methods
    // ---

    fn dep_links_ixs_directed(
        &self,
        package_ix: NodeIndex<PackageIx>,
        dir: Direction,
    ) -> impl Iterator<Item = PackageLink<'_>> {
        self.dep_graph
            .edges_directed(package_ix, dir)
            .map(move |edge| self.edge_ref_to_link(edge))
    }

    fn link_between_ixs(
        &self,
        from_ix: NodeIndex<PackageIx>,
        to_ix: NodeIndex<PackageIx>,
    ) -> Option<PackageLink<'_>> {
        self.dep_graph
            .find_edge(from_ix, to_ix)
            .map(|edge_ix| self.edge_ix_to_link(edge_ix))
    }

    /// Constructs a map of strongly connected components for this graph.
    pub(super) fn sccs(&self) -> &Sccs<PackageIx> {
        self.sccs.get_or_init(|| {
            let edge_filtered =
                EdgeFiltered::from_fn(&self.dep_graph, |edge| !edge.weight().dev_only());
            // Sort the entire graph without dev-only edges -- a correct graph would be cycle-free
            // but we don't currently do a consistency check for this so handle cycles.
            // TODO: should we check at construction time? or bubble up a warning somehow?
            let topo = TopoWithCycles::new(&edge_filtered);

            Sccs::new(&self.dep_graph, |scc| {
                topo.sort_nodes(scc);
            })
        })
    }

    /// Invalidates internal caches. Primarily for testing.
    #[doc(hidden)]
    pub fn invalidate_caches(&mut self) {
        self.sccs.take();
        self.feature_graph.take();
    }

    /// Returns the inner dependency graph.
    ///
    /// Should this be exposed publicly? Not sure.
    pub(super) fn dep_graph(&self) -> &Graph<PackageId, PackageLinkImpl, Directed, PackageIx> {
        &self.dep_graph
    }

    /// Maps an edge reference to a dependency link.
    pub(super) fn edge_ref_to_link<'g>(
        &'g self,
        edge: EdgeReference<'g, PackageLinkImpl, PackageIx>,
    ) -> PackageLink<'g> {
        PackageLink::new(
            self,
            edge.source(),
            edge.target(),
            edge.id(),
            Some(edge.weight()),
        )
    }

    /// Maps an edge index to a dependency link.
    pub(super) fn edge_ix_to_link(&self, edge_ix: EdgeIndex<PackageIx>) -> PackageLink {
        let (source_ix, target_ix) = self
            .dep_graph
            .edge_endpoints(edge_ix)
            .expect("valid edge ix");
        PackageLink::new(
            self,
            source_ix,
            target_ix,
            edge_ix,
            self.dep_graph.edge_weight(edge_ix),
        )
    }

    /// Maps an iterator of package IDs to their internal graph node indexes.
    pub(super) fn package_ixs<'g, 'a, B>(
        &'g self,
        package_ids: impl IntoIterator<Item = &'a PackageId>,
    ) -> Result<B, Error>
    where
        B: iter::FromIterator<NodeIndex<PackageIx>>,
    {
        package_ids
            .into_iter()
            .map(|package_id| self.package_ix(package_id))
            .collect()
    }

    /// Maps a package ID to its internal graph node index, and returns an `UnknownPackageId` error
    /// if the package isn't found.
    pub(super) fn package_ix(&self, package_id: &PackageId) -> Result<NodeIndex<PackageIx>, Error> {
        Ok(self.metadata(package_id)?.package_ix())
    }
}

impl PackageGraphData {
    /// Returns an iterator over all the package IDs in this graph.
    pub fn package_ids(&self) -> impl ExactSizeIterator<Item = &PackageId> {
        self.packages.keys()
    }

    // ---
    // Helper methods
    // ---

    #[inline]
    pub(super) fn metadata_impl(&self, package_id: &PackageId) -> Option<&PackageMetadataImpl> {
        self.packages.get(package_id)
    }
}

/// An optional cache used to speed up `depends_on` queries.
///
/// Created with `PackageGraph::new_depends_cache()`.
#[derive(Clone, Debug)]
pub struct DependsCache<'g> {
    package_graph: &'g PackageGraph,
    dfs_space: DfsSpace<NodeIndex<PackageIx>, FixedBitSet>,
}

impl<'g> DependsCache<'g> {
    /// Creates a new cache for `depends_on` queries for this package graph.
    ///
    /// This holds a shared reference to the package graph. This is to ensure that the cache is
    /// invalidated if the package graph is mutated.
    pub fn new(package_graph: &'g PackageGraph) -> Self {
        Self {
            package_graph,
            dfs_space: DfsSpace::new(&package_graph.dep_graph),
        }
    }

    /// Returns true if `package_a` depends (directly or indirectly) on `package_b`.
    ///
    /// In other words, this returns true if `package_b` is a (possibly transitive) dependency of
    /// `package_a`.
    pub fn depends_on(
        &mut self,
        package_a: &PackageId,
        package_b: &PackageId,
    ) -> Result<bool, Error> {
        let a_ix = self.package_graph.package_ix(package_a)?;
        let b_ix = self.package_graph.package_ix(package_b)?;
        Ok(has_path_connecting(
            self.package_graph.dep_graph(),
            a_ix,
            b_ix,
            Some(&mut self.dfs_space),
        ))
    }
}

/// Information about a workspace, parsed from metadata returned by `cargo metadata`.
///
/// For more about workspaces, see
/// [Cargo Workspaces](https://doc.rust-lang.org/book/ch14-03-cargo-workspaces.html) in *The Rust
/// Programming Language*.
#[derive(Clone, Debug)]
pub struct Workspace<'g> {
    graph: &'g PackageGraph,
    pub(super) inner: &'g WorkspaceImpl,
}

impl<'g> Workspace<'g> {
    /// Returns the workspace root.
    pub fn root(&self) -> &'g Utf8Path {
        &self.inner.root
    }

    /// Returns the target directory in which output artifacts are stored.
    pub fn target_directory(&self) -> &'g Utf8Path {
        &self.inner.target_directory
    }

    /// Returns the number of packages in this workspace.
    pub fn member_count(&self) -> usize {
        self.inner.members_by_path.len()
    }

    /// Returns true if the workspace contains a package by the given name.
    pub fn contains_name(&self, name: impl AsRef<str>) -> bool {
        self.inner.members_by_name.contains_key(name.as_ref())
    }

    /// Returns true if the workspace contains a package by the given workspace path.
    pub fn contains_path(&self, path: impl AsRef<Utf8Path>) -> bool {
        self.inner.members_by_path.contains_key(path.as_ref())
    }

    /// Returns an iterator over package metadatas, sorted by the path they're in.
    pub fn iter(&self) -> impl ExactSizeIterator<Item = PackageMetadata<'g>> {
        self.iter_by_path().map(|(_, package)| package)
    }

    /// Returns an iterator over workspace paths and package metadatas, sorted by the path
    /// they're in.
    pub fn iter_by_path(
        &self,
    ) -> impl ExactSizeIterator<Item = (&'g Utf8Path, PackageMetadata<'g>)> {
        let graph = self.graph;
        self.inner.members_by_path.iter().map(move |(path, id)| {
            (
                path.as_path(),
                graph.metadata(id).expect("valid package ID"),
            )
        })
    }

    /// Returns an iterator over workspace names and package metadatas, sorted by names.
    pub fn iter_by_name(&self) -> impl ExactSizeIterator<Item = (&'g str, PackageMetadata<'g>)> {
        let graph = self.graph;
        self.inner
            .members_by_name
            .iter()
            .map(move |(name, id)| (name.as_ref(), graph.metadata(id).expect("valid package ID")))
    }

    /// Returns an iterator over package IDs for workspace members. The package IDs will be returned
    /// in the same order as `members`, sorted by the path they're in.
    pub fn member_ids(&self) -> impl ExactSizeIterator<Item = &'g PackageId> {
        self.inner.members_by_path.values()
    }

    /// Maps the given path to the corresponding workspace member.
    ///
    /// Returns an error if the path didn't match any workspace members.
    pub fn member_by_path(&self, path: impl AsRef<Utf8Path>) -> Result<PackageMetadata<'g>, Error> {
        let path = path.as_ref();
        let id = self
            .inner
            .members_by_path
            .get(path)
            .ok_or_else(|| Error::UnknownWorkspacePath(path.to_path_buf()))?;
        Ok(self.graph.metadata(id).expect("valid package ID"))
    }

    /// Maps the given paths to their corresponding workspace members, returning a new value of
    /// the specified collection type (e.g. `Vec`).
    ///
    /// Returns an error if any of the paths were unknown.
    pub fn members_by_paths<B>(
        &self,
        paths: impl IntoIterator<Item = impl AsRef<Utf8Path>>,
    ) -> Result<B, Error>
    where
        B: FromIterator<PackageMetadata<'g>>,
    {
        paths
            .into_iter()
            .map(|path| self.member_by_path(path.as_ref()))
            .collect()
    }

    /// Maps the given name to the corresponding workspace member.
    ///
    /// Returns an error if the name didn't match any workspace members.
    pub fn member_by_name(&self, name: impl AsRef<str>) -> Result<PackageMetadata<'g>, Error> {
        let name = name.as_ref();
        let id = self
            .inner
            .members_by_name
            .get(name)
            .ok_or_else(|| Error::UnknownWorkspaceName(name.to_string()))?;
        Ok(self.graph.metadata(id).expect("valid package ID"))
    }

    /// Maps the given names to their corresponding workspace members, returning a new value of
    /// the specified collection type (e.g. `Vec`).
    ///
    /// Returns an error if any of the paths were unknown.
    pub fn members_by_names<B>(
        &self,
        names: impl IntoIterator<Item = impl AsRef<str>>,
    ) -> Result<B, Error>
    where
        B: FromIterator<PackageMetadata<'g>>,
    {
        names
            .into_iter()
            .map(|name| self.member_by_name(name.as_ref()))
            .collect()
    }

    /// Returns the freeform metadata table for this workspace.
    ///
    /// This is the same as the `workspace.metadata` section of `Cargo.toml`. This section is
    /// typically used by tools which would like to store workspace configuration in `Cargo.toml`.
    pub fn metadata_table(&self) -> &'g JsonValue {
        &self.inner.metadata_table
    }
}

#[cfg(feature = "rayon1")]
mod workspace_rayon {
    use super::*;
    use rayon::prelude::*;

    /// These parallel iterators require the `rayon1` feature is enabled.
    impl<'g> Workspace<'g> {
        /// Returns a parallel iterator over package metadatas, sorted by workspace path.
        ///
        /// Requires the `rayon1` feature to be enabled.
        pub fn par_iter(&self) -> impl ParallelIterator<Item = PackageMetadata<'g>> {
            self.par_iter_by_path().map(|(_, package)| package)
        }

        /// Returns a parallel iterator over workspace paths and package metadatas, sorted by
        /// workspace paths.
        ///
        /// Requires the `rayon1` feature to be enabled.
        pub fn par_iter_by_path(
            &self,
        ) -> impl ParallelIterator<Item = (&'g Utf8Path, PackageMetadata<'g>)> {
            let graph = self.graph;
            self.inner
                .members_by_path
                .par_iter()
                .map(move |(path, id)| {
                    (
                        path.as_path(),
                        graph.metadata(id).expect("valid package ID"),
                    )
                })
        }

        /// Returns a parallel iterator over workspace names and package metadatas, sorted by
        /// package names.
        ///
        /// Requires the `rayon1` feature to be enabled.
        pub fn par_iter_by_name(
            &self,
        ) -> impl ParallelIterator<Item = (&'g str, PackageMetadata<'g>)> {
            let graph = self.graph;
            self.inner
                .members_by_name
                .par_iter()
                .map(move |(name, id)| {
                    (name.as_ref(), graph.metadata(id).expect("valid package ID"))
                })
        }
    }
}

#[derive(Clone, Debug)]
pub(super) struct WorkspaceImpl {
    pub(super) root: Utf8PathBuf,
    pub(super) target_directory: Utf8PathBuf,
    pub(super) metadata_table: JsonValue,
    // This is a BTreeMap to allow presenting data in sorted order.
    pub(super) members_by_path: BTreeMap<Utf8PathBuf, PackageId>,
    pub(super) members_by_name: BTreeMap<Box<str>, PackageId>,
    // Cache for members by name (only used for proptests)
    #[cfg(feature = "proptest1")]
    pub(super) name_list: OnceCell<Vec<Box<str>>>,
}

/// Information about a specific package in a `PackageGraph`.
///
/// Most of the metadata is extracted from `Cargo.toml` files. See
/// [the `Cargo.toml` reference](https://doc.rust-lang.org/cargo/reference/manifest.html) for more
/// details.
#[derive(Copy, Clone)]
pub struct PackageMetadata<'g> {
    graph: &'g PackageGraph,
    inner: &'g PackageMetadataImpl,
}

impl<'g> fmt::Debug for PackageMetadata<'g> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("PackageMetadata")
            .field("package_id", &self.id().repr())
            .field("..", &"..")
            .finish()
    }
}

assert_covariant!(PackageMetadata);

impl<'g> PackageMetadata<'g> {
    pub(super) fn new(graph: &'g PackageGraph, inner: &'g PackageMetadataImpl) -> Self {
        Self { graph, inner }
    }

    /// Returns the unique identifier for this package.
    pub fn id(&self) -> &'g PackageId {
        &self.graph.dep_graph[self.inner.package_ix]
    }

    /// Returns the package graph this `PackageMetadata` is derived from.
    pub fn graph(&self) -> &'g PackageGraph {
        self.graph
    }

    /// Creates a `PackageQuery` consisting of this package, in the given direction.
    ///
    /// The `PackageQuery` can be used to inspect dependencies in this graph.
    pub fn to_package_query(&self, direction: DependencyDirection) -> PackageQuery<'g> {
        self.graph
            .query_from_parts(iter::once(self.inner.package_ix).collect(), direction)
    }

    /// Creates a `PackageSet` consisting of just this package.
    pub fn to_package_set(&self) -> PackageSet<'g> {
        let included: IxBitSet = iter::once(self.package_ix()).collect();
        PackageSet::from_included(self.graph, included)
    }

    /// Creates a `FeatureSet` that consists of all features in the package that match the given
    /// named filter.
    pub fn to_feature_set(&self, features: impl FeatureFilter<'g>) -> FeatureSet<'g> {
        self.to_package_set().to_feature_set(features)
    }

    // ---
    // Dependency traversals
    // ---

    /// Returns `PackageLink` instances corresponding to the direct dependencies for this package in
    /// the specified direction.
    pub fn direct_links_directed(
        &self,
        direction: DependencyDirection,
    ) -> impl Iterator<Item = PackageLink<'g>> + 'g {
        self.direct_links_impl(direction.into())
    }

    /// Returns `PackageLink` instances corresponding to the direct dependencies for this package.
    pub fn direct_links(&self) -> impl Iterator<Item = PackageLink<'g>> + 'g {
        self.direct_links_impl(Outgoing)
    }

    /// Returns `PackageLink` instances corresponding to the packages that directly depend on this
    /// one.
    pub fn reverse_direct_links(&self) -> impl Iterator<Item = PackageLink<'g>> + 'g {
        self.direct_links_impl(Incoming)
    }

    /// Returns the direct `PackageLink` between `self` and `other` in the specified direction:
    /// * `Forward`: from `self` to `other`
    /// * `Reverse`: from `other` to `self`
    ///
    /// Returns `None` if the direct link does not exist, or an error if `to` isn't found in
    /// `self.graph()`.
    pub fn link_between(
        &self,
        other: &PackageId,
        direction: DependencyDirection,
    ) -> Result<Option<PackageLink<'g>>, Error> {
        self.link_between_impl(other, direction.into())
    }

    /// Returns the direct `PackageLink` from `self` to the specified package, or `None` if `self`
    /// does not directly depend on the specified package.
    ///
    /// Returns an error if `to` isn't found in `self.graph()`.
    pub fn link_to(&self, to: &PackageId) -> Result<Option<PackageLink<'g>>, Error> {
        self.link_between_impl(to, Outgoing)
    }

    /// Returns the direct `PackageLink` from the specified package to `self`, or `None` if the
    /// specified package does not directly depend on `self`.
    ///
    /// Returns an error if `from` isn't found in `self.graph()`.
    pub fn link_from(&self, from: &PackageId) -> Result<Option<PackageLink<'g>>, Error> {
        self.link_between_impl(from, Incoming)
    }

    // ---
    // Package fields
    // ---

    /// Returns the name of this package.
    ///
    /// This is the same as the `name` field of `Cargo.toml`.
    pub fn name(&self) -> &'g str {
        &self.inner.name
    }

    /// Returns the version of this package as resolved by Cargo.
    ///
    /// This is the same as the `version` field of `Cargo.toml`.
    pub fn version(&self) -> &'g Version {
        &self.inner.version
    }

    /// Returns the authors of this package.
    ///
    /// This is the same as the `authors` field of `Cargo.toml`.
    pub fn authors(&self) -> &'g [String] {
        &self.inner.authors
    }

    /// Returns a short description for this package.
    ///
    /// This is the same as the `description` field of `Cargo.toml`.
    pub fn description(&self) -> Option<&'g str> {
        self.inner.description.as_ref().map(|x| x.as_ref())
    }

    /// Returns an SPDX 2.1 license expression for this package, if specified.
    ///
    /// This is the same as the `license` field of `Cargo.toml`. Note that `guppy` does not perform
    /// any validation on this, though `crates.io` does if a crate is uploaded there.
    pub fn license(&self) -> Option<&'g str> {
        self.inner.license.as_ref().map(|x| x.as_ref())
    }

    /// Returns the path to a license file for this package, if specified.
    ///
    /// This is the same as the `license_file` field of `Cargo.toml`. It is typically only specified
    /// for nonstandard licenses.
    pub fn license_file(&self) -> Option<&'g Utf8Path> {
        self.inner.license_file.as_ref().map(|path| path.as_ref())
    }

    /// Returns the source from which this package was retrieved.
    ///
    /// This may be the workspace path, an external path, or a registry like `crates.io`.
    pub fn source(&self) -> PackageSource<'g> {
        PackageSource::new(&self.inner.source)
    }

    /// Returns true if this package is in the workspace.
    ///
    /// For more detailed information, use `source()`.
    pub fn in_workspace(&self) -> bool {
        self.source().is_workspace()
    }

    /// Returns the full path to the `Cargo.toml` for this package.
    ///
    /// This is specific to the system that `cargo metadata` was run on.
    pub fn manifest_path(&self) -> &'g Utf8Path {
        &self.inner.manifest_path
    }

    /// Returns categories for this package.
    ///
    /// This is the same as the `categories` field of `Cargo.toml`. For packages on `crates.io`,
    /// returned values are guaranteed to be
    /// [valid category slugs](https://crates.io/category_slugs).
    pub fn categories(&self) -> &'g [String] {
        &self.inner.categories
    }

    /// Returns keywords for this package.
    ///
    /// This is the same as the `keywords` field of `Cargo.toml`.
    pub fn keywords(&self) -> &'g [String] {
        &self.inner.keywords
    }

    /// Returns a path to the README for this package, if specified.
    ///
    /// This is the same as the `readme` field of `Cargo.toml`. The path returned is relative to the
    /// directory the `Cargo.toml` is in (i.e. relative to the parent of `self.manifest_path()`).
    pub fn readme(&self) -> Option<&'g Utf8Path> {
        self.inner.readme.as_ref().map(|path| path.as_ref())
    }

    /// Returns the source code repository for this package, if specified.
    ///
    /// This is the same as the `repository` field of `Cargo.toml`.
    pub fn repository(&self) -> Option<&'g str> {
        self.inner.repository.as_ref().map(|x| x.as_ref())
    }

    /// Returns the homepage for this package, if specified.
    ///
    /// This is the same as the `homepage` field of `Cargo.toml`.
    pub fn homepage(&self) -> Option<&'g str> {
        self.inner.homepage.as_ref().map(|x| x.as_ref())
    }

    /// Returns the documentation URL for this package, if specified.
    ///
    /// This is the same as the `homepage` field of `Cargo.toml`.
    pub fn documentation(&self) -> Option<&'g str> {
        self.inner.documentation.as_ref().map(|x| x.as_ref())
    }

    /// Returns the Rust edition this package is written against.
    ///
    /// This is the same as the `edition` field of `Cargo.toml`. It is `"2015"` by default.
    pub fn edition(&self) -> &'g str {
        &self.inner.edition
    }

    /// Returns the freeform metadata table for this package.
    ///
    /// This is the same as the `package.metadata` section of `Cargo.toml`. This section is
    /// typically used by tools which would like to store package configuration in `Cargo.toml`.
    pub fn metadata_table(&self) -> &'g JsonValue {
        &self.inner.metadata_table
    }

    /// Returns the name of a native library this package links to, if specified.
    ///
    /// This is the same as the `links` field of `Cargo.toml`. See [The `links` Manifest
    /// Key](https://doc.rust-lang.org/cargo/reference/build-scripts.html#the-links-manifest-key) in
    /// the Cargo book for more details.
    pub fn links(&self) -> Option<&'g str> {
        self.inner.links.as_ref().map(|x| x.as_ref())
    }

    /// Returns the registries to which this package may be published.
    ///
    /// This is derived from the `publish` field of `Cargo.toml`.
    pub fn publish(&self) -> PackagePublish<'g> {
        PackagePublish::new(&self.inner.publish)
    }

    /// Returns the binary that is run by default, if specified.
    ///
    /// Information about this binary can be queried using [the `build_target`
    /// method](Self::build_target).
    ///
    /// This is derived from the `default-run` field of `Cargo.toml`.
    pub fn default_run(&self) -> Option<&'g str> {
        self.inner.default_run.as_ref().map(|x| x.as_ref())
    }

    /// Returns the minimum Rust compiler version, which should be able to compile the package, if
    /// specified.
    ///
    /// This is the same as the `rust-version` field of `Cargo.toml`. For more, see [the
    /// `rust-version` field](https://doc.rust-lang.org/cargo/reference/manifest.html#the-rust-version-field)
    /// in the Cargo reference.
    pub fn minimum_rust_version(&self) -> Option<&'g Version> {
        self.inner.rust_version.as_ref()
    }

    /// Returns the minimum Rust compiler version, which should be able to compile the package, if
    /// specified.
    ///
    /// Returned as a [`semver::VersionReq`]. This is actually not correct -- it is deprecated and
    /// will go away in the next major version of guppy: use [`Self::minimum_rust_version`] instead.
    ///
    /// This is the same as the `rust-version` field of `Cargo.toml`. For more, see [the
    /// `rust-version`
    /// field](https://doc.rust-lang.org/cargo/reference/manifest.html#the-rust-version-field) in
    /// the Cargo reference.
    #[deprecated(
        since = "0.17.1",
        note = "use Self::rust_version instead, it returns a Version"
    )]
    pub fn rust_version(&self) -> Option<&'g VersionReq> {
        self.inner.rust_version_req.as_ref()
    }

    /// Returns all the build targets for this package.
    ///
    /// For more, see [Cargo
    /// Targets](https://doc.rust-lang.org/nightly/cargo/reference/cargo-targets.html#cargo-targets)
    /// in the Cargo reference.
    pub fn build_targets(&self) -> impl Iterator<Item = BuildTarget<'g>> {
        self.inner.build_targets.iter().map(BuildTarget::new)
    }

    /// Looks up a build target by identifier.
    pub fn build_target(&self, id: &BuildTargetId<'_>) -> Option<BuildTarget<'g>> {
        self.inner
            .build_targets
            .get_key_value(id.as_key())
            .map(BuildTarget::new)
    }

    /// Returns true if this package is a procedural macro.
    ///
    /// For more about procedural macros, see [Procedural
    /// Macros](https://doc.rust-lang.org/reference/procedural-macros.html) in the Rust reference.
    pub fn is_proc_macro(&self) -> bool {
        match self.build_target(&BuildTargetId::Library) {
            Some(build_target) => matches!(build_target.kind(), BuildTargetKind::ProcMacro),
            None => false,
        }
    }

    /// Returns true if this package has a build script.
    ///
    /// Cargo only follows build dependencies if a build script is set.
    ///
    /// For more about build scripts, see [Build
    /// Scripts](https://doc.rust-lang.org/cargo/reference/build-scripts.html) in the Cargo
    /// reference.
    pub fn has_build_script(&self) -> bool {
        self.build_target(&BuildTargetId::BuildScript).is_some()
    }

    /// Returns true if this package has a named feature named `default`.
    ///
    /// For more about default features, see [The `[features]`
    /// section](https://doc.rust-lang.org/cargo/reference/manifest.html#the-features-section) in
    /// the Cargo reference.
    pub fn has_default_feature(&self) -> bool {
        self.inner.has_default_feature
    }

    /// Returns the `FeatureId` corresponding to the default feature.
    pub fn default_feature_id(&self) -> FeatureId<'g> {
        if self.inner.has_default_feature {
            FeatureId::new(self.id(), FeatureLabel::Named("default"))
        } else {
            FeatureId::base(self.id())
        }
    }

    /// Returns the list of named features available for this package. This will include a feature
    /// named "default" if it is defined.
    ///
    /// A named feature is listed in the `[features]` section of `Cargo.toml`. For more, see
    /// [the reference](https://doc.rust-lang.org/cargo/reference/manifest.html#the-features-section).
    pub fn named_features(&self) -> impl Iterator<Item = &'g str> + 'g {
        self.named_features_full()
            .map(|(_, named_feature, _)| named_feature)
    }

    // ---
    // Helper methods
    // --

    #[inline]
    pub(super) fn package_ix(&self) -> NodeIndex<PackageIx> {
        self.inner.package_ix
    }

    fn link_between_impl(
        &self,
        other: &PackageId,
        dir: Direction,
    ) -> Result<Option<PackageLink<'g>>, Error> {
        let other_ix = self.graph.package_ix(other)?;
        match dir {
            Direction::Outgoing => Ok(self.graph.link_between_ixs(self.package_ix(), other_ix)),
            Direction::Incoming => Ok(self.graph.link_between_ixs(other_ix, self.package_ix())),
        }
    }

    fn direct_links_impl(&self, dir: Direction) -> impl Iterator<Item = PackageLink<'g>> + 'g {
        self.graph.dep_links_ixs_directed(self.package_ix(), dir)
    }

    pub(super) fn get_feature_idx(&self, label: FeatureLabel<'_>) -> Option<FeatureIndexInPackage> {
        match label {
            FeatureLabel::Base => Some(FeatureIndexInPackage::Base),
            FeatureLabel::OptionalDependency(dep_name) => self
                .inner
                .optional_deps
                .get_index_of(dep_name)
                .map(FeatureIndexInPackage::OptionalDependency),
            FeatureLabel::Named(feature_name) => self
                .inner
                .named_features
                .get_index_of(feature_name)
                .map(FeatureIndexInPackage::Named),
        }
    }

    pub(super) fn feature_idx_to_label(&self, idx: FeatureIndexInPackage) -> FeatureLabel<'g> {
        match idx {
            FeatureIndexInPackage::Base => FeatureLabel::Base,
            FeatureIndexInPackage::OptionalDependency(idx) => FeatureLabel::OptionalDependency(
                self.inner
                    .optional_deps
                    .get_index(idx)
                    .expect("feature idx in optional_deps should be valid")
                    .as_ref(),
            ),
            FeatureIndexInPackage::Named(idx) => FeatureLabel::Named(
                self.inner
                    .named_features
                    .get_index(idx)
                    .expect("feature idx in optional_deps should be valid")
                    .0
                    .as_ref(),
            ),
        }
    }

    #[allow(dead_code)]
    pub(super) fn all_feature_nodes(&self) -> impl Iterator<Item = FeatureNode> + 'g {
        let package_ix = self.package_ix();
        iter::once(FeatureNode::new(
            self.package_ix(),
            FeatureIndexInPackage::Base,
        ))
        .chain(
            (0..self.inner.named_features.len())
                .map(move |named_idx| FeatureNode::named_feature(package_ix, named_idx)),
        )
        .chain(
            (0..self.inner.optional_deps.len())
                .map(move |dep_idx| FeatureNode::optional_dep(package_ix, dep_idx)),
        )
    }

    pub(super) fn named_features_full(
        &self,
    ) -> impl Iterator<Item = (FeatureIndexInPackage, &'g str, &'g [NamedFeatureDep])> + 'g {
        self.inner
            .named_features
            .iter()
            // IndexMap is documented to use indexes 0..n without holes, so this enumerate()
            // is correct.
            .enumerate()
            .map(|(idx, (feature, deps))| {
                (
                    FeatureIndexInPackage::Named(idx),
                    feature.as_ref(),
                    deps.as_slice(),
                )
            })
    }

    pub(super) fn optional_deps_full(
        &self,
    ) -> impl Iterator<Item = (FeatureIndexInPackage, &'g str)> + 'g {
        self.inner
            .optional_deps
            .iter()
            // IndexMap is documented to use indexes 0..n without holes, so this enumerate()
            // is correct.
            .enumerate()
            .map(|(idx, dep_name)| {
                (
                    FeatureIndexInPackage::OptionalDependency(idx),
                    dep_name.as_ref(),
                )
            })
    }
}

#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
pub(crate) enum FeatureIndexInPackage {
    Base,
    OptionalDependency(usize),
    Named(usize),
}

/// `PackageMetadata`'s `PartialEq` implementation uses pointer equality for the `PackageGraph`.
impl<'g> PartialEq for PackageMetadata<'g> {
    fn eq(&self, other: &Self) -> bool {
        // Checking for the same package ix is enough as each package is guaranteed to be a 1:1 map
        // with ixs.
        std::ptr::eq(self.graph, other.graph) && self.package_ix() == other.package_ix()
    }
}

impl<'g> Eq for PackageMetadata<'g> {}

#[derive(Clone, Debug)]
pub(crate) struct PackageMetadataImpl {
    // Implementation note: we use Box<str> and Box<Path> to save on memory use when possible.

    // Fields extracted from the package.
    pub(super) name: String,
    pub(super) version: Version,
    pub(super) authors: Vec<String>,
    pub(super) description: Option<Box<str>>,
    pub(super) license: Option<Box<str>>,
    pub(super) license_file: Option<Box<Utf8Path>>,
    pub(super) manifest_path: Box<Utf8Path>,
    pub(super) categories: Vec<String>,
    pub(super) keywords: Vec<String>,
    pub(super) readme: Option<Box<Utf8Path>>,
    pub(super) repository: Option<Box<str>>,
    pub(super) homepage: Option<Box<str>>,
    pub(super) documentation: Option<Box<str>>,
    pub(super) edition: Box<str>,
    pub(super) metadata_table: JsonValue,
    pub(super) links: Option<Box<str>>,
    pub(super) publish: PackagePublishImpl,
    pub(super) default_run: Option<Box<str>>,
    pub(super) rust_version: Option<Version>,
    pub(super) rust_version_req: Option<VersionReq>,
    pub(super) named_features: IndexMap<Box<str>, SmallVec<[NamedFeatureDep; 4]>>,
    pub(super) optional_deps: IndexSet<Box<str>>,

    // Other information.
    pub(super) package_ix: NodeIndex<PackageIx>,
    pub(super) source: PackageSourceImpl,
    pub(super) build_targets: BTreeMap<OwnedBuildTargetId, BuildTargetImpl>,
    pub(super) has_default_feature: bool,
}

/// The source of a package.
///
/// This enum contains information about where a package is found, and whether it is inside or
/// outside the workspace.
#[derive(Copy, Clone, Debug, Eq, Hash, PartialEq)]
pub enum PackageSource<'g> {
    /// This package is in the workspace.
    ///
    /// The path is relative to the workspace root.
    Workspace(&'g Utf8Path),

    /// This package is a path dependency that isn't in the workspace.
    ///
    /// The path is relative to the workspace root.
    Path(&'g Utf8Path),

    /// This package is an external dependency.
    ///
    /// * For packages retrieved from `crates.io`, the source is the string
    ///   `"registry+https://github.com/rust-lang/crates.io-index"`.
    /// * For packages retrieved from other registries, the source begins with `"registry+"`.
    /// * For packages retrieved from Git repositories, the source begins with `"git+"`.
    External(&'g str),
}

assert_covariant!(PackageSource);

impl<'g> PackageSource<'g> {
    /// The path to the crates.io registry.
    pub const CRATES_IO_REGISTRY: &'static str =
        "registry+https://github.com/rust-lang/crates.io-index";

    pub(super) fn new(inner: &'g PackageSourceImpl) -> Self {
        match inner {
            PackageSourceImpl::Workspace(path) => PackageSource::Workspace(path),
            PackageSourceImpl::Path(path) => PackageSource::Path(path),
            PackageSourceImpl::CratesIo => PackageSource::External(Self::CRATES_IO_REGISTRY),
            PackageSourceImpl::External(source) => PackageSource::External(source),
        }
    }

    /// Returns true if this package source represents a workspace.
    pub fn is_workspace(&self) -> bool {
        matches!(self, PackageSource::Workspace(_))
    }

    /// Returns true if this package source represents a path dependency that isn't in the
    /// workspace.
    pub fn is_path(&self) -> bool {
        matches!(self, PackageSource::Path(_))
    }

    /// Returns true if this package source represents an external dependency.
    pub fn is_external(&self) -> bool {
        matches!(self, PackageSource::External(_))
    }

    /// Returns true if the source is `crates.io`.
    pub fn is_crates_io(&self) -> bool {
        matches!(self, PackageSource::External(Self::CRATES_IO_REGISTRY))
    }

    /// Returns true if this package is a local dependency, i.e. either in the workspace or a local
    /// path.
    pub fn is_local(&self) -> bool {
        !self.is_external()
    }

    /// Returns the path if this is a workspace dependency, or `None` if this is a non-workspace
    /// dependency.
    ///
    /// The path is relative to the workspace root.
    pub fn workspace_path(&self) -> Option<&'g Utf8Path> {
        match self {
            PackageSource::Workspace(path) => Some(path),
            _ => None,
        }
    }

    /// Returns the local path if this is a local dependency, or `None` if it is an external
    /// dependency.
    ///
    /// The path is relative to the workspace root.
    pub fn local_path(&self) -> Option<&'g Utf8Path> {
        match self {
            PackageSource::Path(path) | PackageSource::Workspace(path) => Some(path),
            _ => None,
        }
    }

    /// Returns the external source if this is an external dependency, or `None` if it is a local
    /// dependency.
    pub fn external_source(&self) -> Option<&'g str> {
        match self {
            PackageSource::External(source) => Some(source),
            _ => None,
        }
    }

    /// Attempts to parse an external source.
    ///
    /// Returns `None` if the external dependency could not be recognized, or if it is a local
    /// dependency.
    ///
    /// For more about external sources, see the documentation for [`ExternalSource`](ExternalSource).
    pub fn parse_external(&self) -> Option<ExternalSource<'g>> {
        match self {
            PackageSource::External(source) => ExternalSource::new(source),
            _ => None,
        }
    }
}

impl<'g> fmt::Display for PackageSource<'g> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            PackageSource::Workspace(path) => write!(f, "{}", path),
            PackageSource::Path(path) => write!(f, "{}", path),
            PackageSource::External(source) => write!(f, "{}", source),
        }
    }
}

/// More information about an external source.
///
/// This provides information about whether an external dependency is a Git dependency or fetched
/// from a registry.
///
/// Returned by [`PackageSource::parse_external`](PackageSource::parse_external).
#[derive(Copy, Clone, Debug, Eq, Hash, PartialEq)]
#[non_exhaustive]
pub enum ExternalSource<'g> {
    /// This is a registry source, e.g. `"registry+https://github.com/rust-lang/crates.io-index"`.
    ///
    /// The associated data is the part of the string after the initial `"registry+"`.
    ///
    /// # Examples
    ///
    /// ```
    /// use guppy::graph::ExternalSource;
    ///
    /// let source = "registry+https://github.com/rust-lang/crates.io-index";
    /// let parsed = ExternalSource::new(source).expect("this source is understood by guppy");
    ///
    /// assert_eq!(
    ///     parsed,
    ///     ExternalSource::Registry("https://github.com/rust-lang/crates.io-index"),
    /// );
    /// ```
    Registry(&'g str),

    /// This is a Git source.
    ///
    /// An example of a Git source string is `"git+https://github.com/rust-lang/cargo.git?branch=main#0227f048fcb7c798026ede6cc20c92befc84c3a4"`.
    /// In this case, the `Cargo.toml` would have contained:
    ///
    /// ```toml
    /// cargo = { git = "https://github.com/rust-lang/cargo.git", branch = "main" }
    /// ```
    ///
    /// and the `Cargo.lock` would have contained:
    ///
    /// ```toml
    /// [[package]]
    /// name = "cargo"
    /// version = "0.46.0"
    /// source = "git+https://github.com/rust-lang/cargo.git?branch=main#0227f048fcb7c798026ede6cc20c92befc84c3a4
    /// dependencies = [ ... ]
    /// ```
    ///
    /// For more, see [Specifying dependencies from `git` repositories](https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#specifying-dependencies-from-git-repositories)
    /// in the Cargo book.
    ///
    /// # Examples
    ///
    /// ```
    /// use guppy::graph::{ExternalSource, GitReq};
    ///
    /// // A branch source.
    /// let source = "git+https://github.com/rust-lang/cargo.git?branch=main#0227f048fcb7c798026ede6cc20c92befc84c3a4";
    /// let parsed = ExternalSource::new(source).expect("this source is understood by guppy");
    ///
    /// assert_eq!(
    ///     parsed,
    ///     ExternalSource::Git {
    ///         repository: "https://github.com/rust-lang/cargo.git",
    ///         req: GitReq::Branch("main"),
    ///         resolved: "0227f048fcb7c798026ede6cc20c92befc84c3a4",
    ///     }
    /// );
    ///
    /// // A tag source.
    /// let source = "git+https://github.com/rust-lang/cargo.git?tag=v0.46.0#0227f048fcb7c798026ede6cc20c92befc84c3a4";
    /// let parsed = ExternalSource::new(source).expect("this source is understood by guppy");
    ///
    /// assert_eq!(
    ///     parsed,
    ///     ExternalSource::Git {
    ///         repository: "https://github.com/rust-lang/cargo.git",
    ///         req: GitReq::Tag("v0.46.0"),
    ///         resolved: "0227f048fcb7c798026ede6cc20c92befc84c3a4",
    ///     }
    /// );
    ///
    /// // A revision source.
    /// let source = "git+https://github.com/rust-lang/cargo.git?rev=0227f048fcb7c798026ede6cc20c92befc84c3a4#0227f048fcb7c798026ede6cc20c92befc84c3a4";
    /// let parsed = ExternalSource::new(source).expect("this source is understood by guppy");
    ///
    /// assert_eq!(
    ///     parsed,
    ///     ExternalSource::Git {
    ///         repository: "https://github.com/rust-lang/cargo.git",
    ///         req: GitReq::Rev("0227f048fcb7c798026ede6cc20c92befc84c3a4"),
    ///         resolved: "0227f048fcb7c798026ede6cc20c92befc84c3a4",
    ///     }
    /// );
    ///
    /// // A default source.
    /// let source = "git+https://github.com/gyscos/zstd-rs.git#bc874a57298bdb500cdb5aeac5f23878b6480d0b";
    /// let parsed = ExternalSource::new(source).expect("this source is understood by guppy");
    ///
    /// assert_eq!(
    ///     parsed,
    ///     ExternalSource::Git {
    ///         repository: "https://github.com/gyscos/zstd-rs.git",
    ///         req: GitReq::Default,
    ///         resolved: "bc874a57298bdb500cdb5aeac5f23878b6480d0b",
    ///     }
    /// );
    /// ```
    Git {
        /// The repository for this Git source. For the above example, this would be
        /// `"https://github.com/rust-lang/cargo.git"`.
        repository: &'g str,

        /// The revision requested in `Cargo.toml`. This may be a tag, a branch or a specific
        /// revision (commit hash).
        ///
        /// For the above example, `req` would be `GitSource::Branch("main")`.
        req: GitReq<'g>,

        /// The resolved revision, as specified in `Cargo.lock`.
        ///
        /// For the above example, `resolved_hash` would be `"0227f048fcb7c798026ede6cc20c92befc84c3a4"`.
        ///
        /// This is always a commit hash, and if `req` is `GitReq::Rev` then it is expected
        /// to be the same hash. (However, this is not verified by guppy.)
        resolved: &'g str,
    },
}

impl<'g> ExternalSource<'g> {
    /// The string `"registry+"`.
    ///
    /// Used for matching with the `Registry` variant.
    pub const REGISTRY_PLUS: &'static str = "registry+";

    /// The string `"git+"`.
    ///
    /// Used for matching with the `Git` variant.
    pub const GIT_PLUS: &'static str = "git+";

    /// The string `"?branch="`.
    ///
    /// Used for matching with the `Git` variant.
    pub const BRANCH_EQ: &'static str = "?branch=";

    /// The string `"?tag="`.
    ///
    /// Used for matching with the `Git` variant.
    pub const TAG_EQ: &'static str = "?tag=";

    /// The string `"?rev="`.
    ///
    /// Used for matching with the `Git` variant.
    pub const REV_EQ: &'static str = "?rev=";

    /// The URL for the `crates.io` registry.
    ///
    /// This lacks the leading `"registry+`" that's part of the [`PackageSource`].
    pub const CRATES_IO_URL: &'static str = "https://github.com/rust-lang/crates.io-index";

    /// Attempts to parse the given string as an external source.
    ///
    /// Returns `None` if the string could not be recognized as an external source.
    pub fn new(source: &'g str) -> Option<Self> {
        // We *could* pull in a URL parsing library, but Cargo's sources are so limited that it
        // seems like a waste to.
        if let Some(registry) = source.strip_prefix(Self::REGISTRY_PLUS) {
            // A registry source.
            Some(ExternalSource::Registry(registry))
        } else if let Some(rest) = source.strip_prefix(Self::GIT_PLUS) {
            // A Git source.
            // Look for a trailing #, which indicates the resolved revision.
            let (rest, resolved) = rest.rsplit_once('#')?;

            let (repository, req) = if let Some(idx) = rest.find(Self::BRANCH_EQ) {
                (
                    &rest[..idx],
                    GitReq::Branch(&rest[idx + Self::BRANCH_EQ.len()..]),
                )
            } else if let Some(idx) = rest.find(Self::TAG_EQ) {
                (&rest[..idx], GitReq::Tag(&rest[idx + Self::TAG_EQ.len()..]))
            } else if let Some(idx) = rest.find(Self::REV_EQ) {
                (&rest[..idx], GitReq::Rev(&rest[idx + Self::TAG_EQ.len()..]))
            } else {
                (rest, GitReq::Default)
            };

            Some(ExternalSource::Git {
                repository,
                req,
                resolved,
            })
        } else {
            None
        }
    }
}

/// The `Display` implementation for `ExternalSource` returns the string it was constructed from.
///
/// # Examples
///
/// ```
/// use guppy::graph::{ExternalSource, GitReq};
///
/// let source = ExternalSource::Git {
///     repository: "https://github.com/rust-lang/cargo.git",
///     req: GitReq::Branch("main"),
///     resolved: "0227f048fcb7c798026ede6cc20c92befc84c3a4",
/// };
///
/// assert_eq!(
///     format!("{}", source),
///     "git+https://github.com/rust-lang/cargo.git?branch=main#0227f048fcb7c798026ede6cc20c92befc84c3a4",
/// );
/// ```
impl<'g> fmt::Display for ExternalSource<'g> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            ExternalSource::Registry(url) => write!(f, "{}{}", Self::REGISTRY_PLUS, url),
            ExternalSource::Git {
                repository,
                req,
                resolved,
            } => {
                write!(f, "{}{}", Self::GIT_PLUS, repository)?;
                match req {
                    GitReq::Branch(branch) => write!(f, "{}{}", Self::BRANCH_EQ, branch)?,
                    GitReq::Tag(tag) => write!(f, "{}{}", Self::TAG_EQ, tag)?,
                    GitReq::Rev(rev) => write!(f, "{}{}", Self::REV_EQ, rev)?,
                    GitReq::Default => {}
                };
                write!(f, "#{}", resolved)
            }
        }
    }
}

/// A `Cargo.toml` specification for a Git branch, tag, or revision.
///
/// For more, including examples, see the documentation for [`ExternalSource::Git`](ExternalSource::Git).
#[derive(Copy, Clone, Debug, Eq, Hash, PartialEq)]
#[non_exhaustive]
pub enum GitReq<'g> {
    /// A branch, e.g. `"main"`.
    ///
    /// This is specified in `Cargo.toml` as:
    ///
    /// ```toml
    /// [dependencies]
    /// cargo = { git = "...", branch = "main" }
    /// ```
    Branch(&'g str),

    /// A tag, e.g. `"guppy-0.5.0"`.
    ///
    /// This is specified in `Cargo.toml` as:
    ///
    /// ```toml
    /// [dependencies]
    /// guppy = { git = "...", tag = "guppy-0.5.0" }
    /// ```
    Tag(&'g str),

    /// A revision (commit hash), e.g. `"0227f048fcb7c798026ede6cc20c92befc84c3a4"`.
    ///
    /// This is specified in `Cargo.toml` as:
    ///
    /// ```toml
    /// [dependencies]
    /// cargo = { git = "...", rev = "0227f048fcb7c798026ede6cc20c92befc84c3a4" }
    /// ```
    Rev(&'g str),

    /// Not specified in `Cargo.toml`. Cargo treats this as the main branch by default.
    ///
    /// ```toml
    /// [dependencies]
    /// cargo = { git = "..." }
    /// ```
    Default,
}

/// Internal representation of the source of a package.
#[derive(Clone, Debug, PartialEq, Eq)]
pub(super) enum PackageSourceImpl {
    Workspace(Box<Utf8Path>),
    Path(Box<Utf8Path>),
    // Special, common case.
    CratesIo,
    External(Box<str>),
}

/// Locations that a package can be published to.
///
/// Returned by [`PackageMetadata::publish`].
#[derive(Copy, Clone, Debug, Eq, Hash, PartialEq)]
#[non_exhaustive]
pub enum PackagePublish<'g> {
    /// Publication of this package is unrestricted.
    Unrestricted,

    /// This package can only be published to the listed [package registry].
    ///
    /// If the list is empty, this package cannot be published to any registries.
    ///
    /// [package registry]: https://doc.rust-lang.org/cargo/reference/registries.html
    Registries(&'g [String]),
}

// TODO: implement PartialOrd/Ord for these as well using lattice rules

assert_covariant!(PackagePublish);

impl<'g> PackagePublish<'g> {
    pub(super) fn new(inner: &'g PackagePublishImpl) -> Self {
        match inner {
            PackagePublishImpl::Unrestricted => PackagePublish::Unrestricted,
            PackagePublishImpl::Registries(registries) => PackagePublish::Registries(registries),
        }
    }

    /// The string `"crates-io"`, indicating that a package can be published to
    /// [crates.io](https://crates.io/).
    pub const CRATES_IO: &'static str = "crates-io";

    /// Returns true if this package can be published to any package registry.
    ///
    /// # Examples
    ///
    /// ```
    /// use guppy::graph::PackagePublish;
    ///
    /// assert!(PackagePublish::Unrestricted.is_unrestricted());
    /// assert!(!PackagePublish::Registries(&[PackagePublish::CRATES_IO.to_owned()]).is_unrestricted());
    /// assert!(!PackagePublish::Registries(&[]).is_unrestricted());
    /// ```
    pub fn is_unrestricted(&self) -> bool {
        matches!(self, PackagePublish::Unrestricted)
    }

    /// Returns true if a package can be published to the given package registry.
    ///
    /// # Examples
    ///
    /// ```
    /// use guppy::graph::PackagePublish;
    ///
    /// // Unrestricted means this package can be published to any registry.
    /// assert!(PackagePublish::Unrestricted.can_publish_to(PackagePublish::CRATES_IO));
    /// assert!(PackagePublish::Unrestricted.can_publish_to("my-registry"));
    ///
    /// // Publish to specific registries but not others.
    /// let crates_io = &[PackagePublish::CRATES_IO.to_owned()];
    /// let crates_io_publish = PackagePublish::Registries(crates_io);
    /// assert!(crates_io_publish.can_publish_to(PackagePublish::CRATES_IO));
    /// assert!(!crates_io_publish.can_publish_to("my-registry"));
    ///
    /// // Cannot publish to any registries.
    /// assert!(!PackagePublish::Registries(&[]).can_publish_to(PackagePublish::CRATES_IO));
    /// ```
    pub fn can_publish_to(&self, registry: impl AsRef<str>) -> bool {
        let registry = registry.as_ref();
        match self {
            PackagePublish::Unrestricted => true,
            PackagePublish::Registries(registries) => registries.iter().any(|r| r == registry),
        }
    }

    /// Returns true if a package can be published to crates.io.
    pub fn can_publish_to_crates_io(&self) -> bool {
        self.can_publish_to(Self::CRATES_IO)
    }

    /// Returns true if a package cannot be published to any registries.
    ///
    /// # Examples
    ///
    /// ```
    /// use guppy::graph::PackagePublish;
    ///
    /// assert!(!PackagePublish::Unrestricted.is_never());
    /// assert!(!PackagePublish::Registries(&[PackagePublish::CRATES_IO.to_owned()]).is_never());
    /// assert!(PackagePublish::Registries(&[]).is_never());
    /// ```
    pub fn is_never(&self) -> bool {
        match self {
            PackagePublish::Unrestricted => false,
            PackagePublish::Registries(registries) => registries.is_empty(),
        }
    }
}

/// Internal representation of PackagePublish.
#[derive(Clone, Debug)]
pub(super) enum PackagePublishImpl {
    Unrestricted,
    Registries(Box<[String]>),
}

/// Represents a dependency from one package to another.
///
/// This struct contains information about:
/// * whether this dependency was renamed in the context of this crate.
/// * if this is a normal, dev and/or build dependency.
/// * platform-specific information about required, optional and status
#[derive(Copy, Clone, Debug)]
pub struct PackageLink<'g> {
    graph: &'g PackageGraph,
    from: &'g PackageMetadataImpl,
    to: &'g PackageMetadataImpl,
    edge_ix: EdgeIndex<PackageIx>,
    inner: &'g PackageLinkImpl,
}

assert_covariant!(PackageLink);

impl<'g> PackageLink<'g> {
    pub(super) fn new(
        graph: &'g PackageGraph,
        source_ix: NodeIndex<PackageIx>,
        target_ix: NodeIndex<PackageIx>,
        edge_ix: EdgeIndex<PackageIx>,
        inner: Option<&'g PackageLinkImpl>,
    ) -> Self {
        let from = graph
            .data
            .metadata_impl(&graph.dep_graph[source_ix])
            .expect("'from' should have associated metadata");
        let to = graph
            .data
            .metadata_impl(&graph.dep_graph[target_ix])
            .expect("'to' should have associated metadata");
        Self {
            graph,
            from,
            to,
            edge_ix,
            inner: inner.unwrap_or_else(|| &graph.dep_graph[edge_ix]),
        }
    }

    /// Returns the package which depends on the `to` package.
    pub fn from(&self) -> PackageMetadata<'g> {
        PackageMetadata::new(self.graph, self.from)
    }

    /// Returns the package which is depended on by the `from` package.
    pub fn to(&self) -> PackageMetadata<'g> {
        PackageMetadata::new(self.graph, self.to)
    }

    /// Returns the endpoints as a pair of packages `(from, to)`.
    pub fn endpoints(&self) -> (PackageMetadata<'g>, PackageMetadata<'g>) {
        (self.from(), self.to())
    }

    /// Returns the name for this dependency edge. This can be affected by a crate rename.
    pub fn dep_name(&self) -> &'g str {
        &self.inner.dep_name
    }

    /// Returns the resolved name for this dependency edge. This may involve renaming the crate and
    /// replacing - with _.
    pub fn resolved_name(&self) -> &'g str {
        &self.inner.resolved_name
    }

    /// Returns the semver requirements specified for this dependency.
    ///
    /// To get the resolved version, see the `to` field of the `PackageLink` this was part of.
    ///
    /// ## Notes
    ///
    /// A dependency can be requested multiple times, possibly with different version requirements,
    /// even if they all end up resolving to the same version. `version_req` will return any of
    /// those requirements.
    ///
    /// See [Specifying Dependencies](https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#specifying-dependencies)
    /// in the Cargo reference for more details.
    pub fn version_req(&self) -> &'g VersionReq {
        &self.inner.version_req
    }

    /// Returns details about this dependency from the `[dependencies]` section.
    pub fn normal(&self) -> DependencyReq<'g> {
        DependencyReq {
            inner: &self.inner.normal,
        }
    }

    /// Returns details about this dependency from the `[build-dependencies]` section.
    pub fn build(&self) -> DependencyReq<'g> {
        DependencyReq {
            inner: &self.inner.build,
        }
    }

    /// Returns details about this dependency from the `[dev-dependencies]` section.
    pub fn dev(&self) -> DependencyReq<'g> {
        DependencyReq {
            inner: &self.inner.dev,
        }
    }

    /// Returns details about this dependency from the section specified by the given dependency
    /// kind.
    pub fn req_for_kind(&self, kind: DependencyKind) -> DependencyReq<'g> {
        match kind {
            DependencyKind::Normal => self.normal(),
            DependencyKind::Development => self.dev(),
            DependencyKind::Build => self.build(),
        }
    }

    /// Return true if this edge is dev-only, i.e. code from this edge will not be included in
    /// normal builds.
    pub fn dev_only(&self) -> bool {
        self.inner.dev_only()
    }

    // ---
    // Helper methods
    // ---

    /// Returns the edge index.
    #[allow(dead_code)]
    pub(super) fn edge_ix(&self) -> EdgeIndex<PackageIx> {
        self.edge_ix
    }

    /// Returns (source, target, edge) as a triple of pointers. Useful for testing.
    #[doc(hidden)]
    pub fn as_inner_ptrs(&self) -> PackageLinkPtrs {
        PackageLinkPtrs {
            from: self.from,
            to: self.to,
            inner: self.inner,
        }
    }
}

/// An opaque identifier for a PackageLink's pointers. Used for tests.
#[derive(Copy, Clone, Debug, Eq, Ord, PartialEq, PartialOrd)]
#[doc(hidden)]
pub struct PackageLinkPtrs {
    from: *const PackageMetadataImpl,
    to: *const PackageMetadataImpl,
    inner: *const PackageLinkImpl,
}

#[derive(Clone, Debug)]
pub(crate) struct PackageLinkImpl {
    pub(super) dep_name: String,
    pub(super) resolved_name: String,
    pub(super) version_req: VersionReq,
    pub(super) normal: DependencyReqImpl,
    pub(super) build: DependencyReqImpl,
    pub(super) dev: DependencyReqImpl,
}

impl PackageLinkImpl {
    #[inline]
    fn dev_only(&self) -> bool {
        self.normal.enabled().is_never() && self.build.enabled().is_never()
    }
}

/// Information about a specific kind of dependency (normal, build or dev) from a package to another
/// package.
///
/// Usually found within the context of a [`PackageLink`](struct.PackageLink.html).
#[derive(Clone, Debug)]
pub struct DependencyReq<'g> {
    pub(super) inner: &'g DependencyReqImpl,
}

impl<'g> DependencyReq<'g> {
    /// Returns true if there is at least one `Cargo.toml` entry corresponding to this requirement.
    ///
    /// For example, if this dependency is specified in the `[dev-dependencies]` section,
    /// `edge.dev().is_present()` will return true.
    pub fn is_present(&self) -> bool {
        !self.inner.enabled().is_never()
    }

    /// Returns the enabled status of this dependency.
    ///
    /// `status` is the union of `default_features` and `no_default_features`.
    ///
    /// See the documentation for `EnabledStatus` for more.
    pub fn status(&self) -> EnabledStatus<'g> {
        self.inner.enabled()
    }

    /// Returns the enabled status of this dependency when `default-features = true`.
    ///
    /// See the documentation for `EnabledStatus` for more.
    pub fn default_features(&self) -> EnabledStatus<'g> {
        self.inner.default_features()
    }

    /// Returns the enabled status of this dependency when `default-features = false`.
    ///
    /// This is generally less useful than `status` or `default_features`, but is provided for
    /// completeness.
    ///
    /// See the documentation for `EnabledStatus` for more.
    pub fn no_default_features(&self) -> EnabledStatus<'g> {
        self.inner.no_default_features()
    }

    /// Returns a list of all features possibly enabled by this dependency. This includes features
    /// that are only turned on if the dependency is optional, or features enabled by inactive
    /// platforms.
    pub fn features(&self) -> impl Iterator<Item = &'g str> {
        self.inner.all_features()
    }

    /// Returns the enabled status of this feature.
    ///
    /// Note that as of Rust 1.42, the default feature resolver behaves in potentially surprising
    /// ways. See the [Cargo
    /// reference](https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#features) for
    /// more.
    ///
    /// See the documentation for `EnabledStatus` for more.
    pub fn feature_status(&self, feature: &str) -> EnabledStatus<'g> {
        self.inner.feature_status(feature)
    }
}

/// Whether a dependency or feature is required, optional, or disabled.
///
/// Returned by the methods on `DependencyMetadata`.
///
/// ## Examples
///
/// ```toml
/// [dependencies]
/// once_cell = "1"
/// ```
///
/// The dependency and default features are *required* on all platforms.
///
/// ```toml
/// [dependencies]
/// once_cell = { version = "1", optional = true }
/// ```
///
/// The dependency and default features are *optional* on all platforms.
///
/// ```toml
/// [target.'cfg(windows)'.dependencies]
/// once_cell = { version = "1", optional = true }
/// ```
///
/// The result is platform-dependent. On Windows, the dependency and default features are both
/// *optional*. On non-Windows platforms, the dependency and default features are *disabled*.
///
/// ```toml
/// [dependencies]
/// once_cell = { version = "1", optional = true }
///
/// [target.'cfg(windows)'.dependencies]
/// once_cell = { version = "1", optional = false, default-features = false }
/// ```
///
/// The result is platform-dependent. On Windows, the dependency is *mandatory* and default features
/// are *optional* (i.e. enabled if the `once_cell` feature is turned on).
///
/// On Unix platforms, the dependency and default features are both *optional*.
#[derive(Copy, Clone, Debug)]
pub struct EnabledStatus<'g> {
    required: PlatformStatus<'g>,
    optional: PlatformStatus<'g>,
}

assert_covariant!(EnabledStatus);

impl<'g> EnabledStatus<'g> {
    pub(super) fn new(required: &'g PlatformStatusImpl, optional: &'g PlatformStatusImpl) -> Self {
        Self {
            required: PlatformStatus::new(required),
            optional: PlatformStatus::new(optional),
        }
    }

    /// Returns true if this dependency is never enabled on any platform.
    pub fn is_never(&self) -> bool {
        self.required.is_never() && self.optional.is_never()
    }

    /// Evaluates whether this dependency is required on the given platform spec.
    ///
    /// Returns `Unknown` if the result was unknown, which may happen if evaluating against an
    /// individual platform and its target features are unknown.
    pub fn required_on(&self, platform_spec: &PlatformSpec) -> EnabledTernary {
        self.required.enabled_on(platform_spec)
    }

    /// Evaluates whether this dependency is enabled (required or optional) on the given platform
    /// spec.
    ///
    /// Returns `Unknown` if the result was unknown, which may happen if evaluating against an
    /// individual platform and its target features are unknown.
    pub fn enabled_on(&self, platform_spec: &PlatformSpec) -> EnabledTernary {
        let required = self.required.enabled_on(platform_spec);
        let optional = self.optional.enabled_on(platform_spec);

        required | optional
    }

    /// Returns the `PlatformStatus` corresponding to whether this dependency is required.
    pub fn required_status(&self) -> PlatformStatus<'g> {
        self.required
    }

    /// Returns the `PlatformStatus` corresponding to whether this dependency is optional.
    pub fn optional_status(&self) -> PlatformStatus<'g> {
        self.optional
    }
}

#[derive(Clone, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
pub(super) enum NamedFeatureDep {
    NamedFeature(Box<str>),
    OptionalDependency(Box<str>),
    DependencyNamedFeature {
        dep_name: Box<str>,
        feature: Box<str>,
        weak: bool,
    },
}

impl NamedFeatureDep {
    #[inline]
    pub(super) fn named_feature(feature_name: impl Into<String>) -> Self {
        Self::NamedFeature(feature_name.into().into_boxed_str())
    }

    #[inline]
    pub(super) fn optional_dependency(dep_name: impl Into<String>) -> Self {
        Self::OptionalDependency(dep_name.into().into_boxed_str())
    }

    #[inline]
    pub(super) fn dep_named_feature(
        dep_name: impl Into<String>,
        feature: impl Into<String>,
        weak: bool,
    ) -> Self {
        Self::DependencyNamedFeature {
            dep_name: dep_name.into().into_boxed_str(),
            feature: feature.into().into_boxed_str(),
            weak,
        }
    }
}

impl fmt::Display for NamedFeatureDep {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            Self::NamedFeature(feature) => write!(f, "{}", feature),
            Self::OptionalDependency(dep_name) => write!(f, "dep:{}", dep_name),
            Self::DependencyNamedFeature {
                dep_name,
                feature,
                weak,
            } => {
                write!(
                    f,
                    "{}{}/{}",
                    dep_name,
                    if *weak { "?" } else { "" },
                    feature
                )
            }
        }
    }
}

/// Information about dependency requirements.
#[derive(Clone, Debug, Default)]
pub(super) struct DependencyReqImpl {
    pub(super) required: DepRequiredOrOptional,
    pub(super) optional: DepRequiredOrOptional,
}

impl DependencyReqImpl {
    fn all_features(&self) -> impl Iterator<Item = &str> {
        self.required
            .all_features()
            .chain(self.optional.all_features())
    }

    pub(super) fn enabled(&self) -> EnabledStatus {
        self.make_status(|req_impl| &req_impl.build_if)
    }

    pub(super) fn default_features(&self) -> EnabledStatus {
        self.make_status(|req_impl| &req_impl.default_features_if)
    }

    pub(super) fn no_default_features(&self) -> EnabledStatus {
        self.make_status(|req_impl| &req_impl.no_default_features_if)
    }

    pub(super) fn feature_status(&self, feature: &str) -> EnabledStatus {
        // This PlatformStatusImpl in static memory is so that the lifetimes work out.
        static DEFAULT_STATUS: PlatformStatusImpl = PlatformStatusImpl::Specs(Vec::new());

        self.make_status(|req_impl| {
            req_impl
                .feature_targets
                .get(feature)
                .unwrap_or(&DEFAULT_STATUS)
        })
    }

    fn make_status(
        &self,
        pred_fn: impl Fn(&DepRequiredOrOptional) -> &PlatformStatusImpl,
    ) -> EnabledStatus {
        EnabledStatus::new(pred_fn(&self.required), pred_fn(&self.optional))
    }
}

/// Information about dependency requirements, scoped to either the dependency being required or
/// optional.
#[derive(Clone, Debug, Default)]
pub(super) struct DepRequiredOrOptional {
    pub(super) build_if: PlatformStatusImpl,
    pub(super) default_features_if: PlatformStatusImpl,
    pub(super) no_default_features_if: PlatformStatusImpl,
    pub(super) feature_targets: BTreeMap<String, PlatformStatusImpl>,
}

impl DepRequiredOrOptional {
    pub(super) fn all_features(&self) -> impl Iterator<Item = &str> {
        self.feature_targets.keys().map(|s| s.as_str())
    }
}