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
/*!
Crate `walkdir` provides an efficient and cross platform implementation
of recursive directory traversal. Several options are exposed to control
iteration, such as whether to follow symbolic links (default off), limit the
maximum number of simultaneous open file descriptors and the ability to
efficiently skip descending into directories.

To use this crate, add `walkdir` as a dependency to your project's
`Cargo.toml`:

```toml
[dependencies]
walkdir = "2"
```

# From the top

The [`WalkDir`] type builds iterators. The [`DirEntry`] type describes values
yielded by the iterator. Finally, the [`Error`] type is a small wrapper around
[`std::io::Error`] with additional information, such as if a loop was detected
while following symbolic links (not enabled by default).

[`WalkDir`]: struct.WalkDir.html
[`DirEntry`]: struct.DirEntry.html
[`Error`]: struct.Error.html
[`std::io::Error`]: https://doc.rust-lang.org/stable/std/io/struct.Error.html

# Example

The following code recursively iterates over the directory given and prints
the path for each entry:

```no_run
use walkdir::WalkDir;
# use walkdir::Error;

# fn try_main() -> Result<(), Error> {
for entry in WalkDir::new("foo") {
    println!("{}", entry?.path().display());
}
# Ok(())
# }
```

Or, if you'd like to iterate over all entries and ignore any errors that
may arise, use [`filter_map`]. (e.g., This code below will silently skip
directories that the owner of the running process does not have permission to
access.)

```no_run
use walkdir::WalkDir;

for entry in WalkDir::new("foo").into_iter().filter_map(|e| e.ok()) {
    println!("{}", entry.path().display());
}
```

[`filter_map`]: https://doc.rust-lang.org/stable/std/iter/trait.Iterator.html#method.filter_map

# Example: follow symbolic links

The same code as above, except [`follow_links`] is enabled:

```no_run
use walkdir::WalkDir;
# use walkdir::Error;

# fn try_main() -> Result<(), Error> {
for entry in WalkDir::new("foo").follow_links(true) {
    println!("{}", entry?.path().display());
}
# Ok(())
# }
```

[`follow_links`]: struct.WalkDir.html#method.follow_links

# Example: skip hidden files and directories on unix

This uses the [`filter_entry`] iterator adapter to avoid yielding hidden files
and directories efficiently (i.e. without recursing into hidden directories):

```no_run
use walkdir::{DirEntry, WalkDir};
# use walkdir::Error;

fn is_hidden(entry: &DirEntry) -> bool {
    entry.file_name()
         .to_str()
         .map(|s| s.starts_with("."))
         .unwrap_or(false)
}

# fn try_main() -> Result<(), Error> {
let walker = WalkDir::new("foo").into_iter();
for entry in walker.filter_entry(|e| !is_hidden(e)) {
    println!("{}", entry?.path().display());
}
# Ok(())
# }
```

[`filter_entry`]: struct.IntoIter.html#method.filter_entry
*/

#![deny(missing_docs)]
#![allow(bare_trait_objects)]

#[cfg(test)]
extern crate quickcheck;
#[cfg(test)]
extern crate rand;
extern crate same_file;
#[cfg(windows)]
extern crate winapi;
#[cfg(windows)]
extern crate winapi_util;
#[cfg(test)]
#[macro_use]
extern crate doc_comment;

#[cfg(test)]
doctest!("../README.md");

use std::cmp::{Ordering, min};
use std::error;
use std::fmt;
use std::fs::{self, FileType, ReadDir};
use std::io;
use std::ffi::OsStr;
use std::path::{Path, PathBuf};
use std::result;
use std::vec;

use same_file::Handle;

#[cfg(unix)]
pub use unix::DirEntryExt;

#[cfg(test)]
mod tests;
#[cfg(unix)]
mod unix;

/// Like try, but for iterators that return [`Option<Result<_, _>>`].
///
/// [`Option<Result<_, _>>`]: https://doc.rust-lang.org/stable/std/option/enum.Option.html
macro_rules! itry {
    ($e:expr) => {
        match $e {
            Ok(v) => v,
            Err(err) => return Some(Err(From::from(err))),
        }
    }
}

/// A result type for walkdir operations.
///
/// Note that this result type embeds the error type in this crate. This
/// is only useful if you care about the additional information provided by
/// the error (such as the path associated with the error or whether a loop
/// was dectected). If you want things to Just Work, then you can use
/// [`io::Result`] instead since the error type in this package will
/// automatically convert to an [`io::Result`] when using the [`try!`] macro.
///
/// [`io::Result`]: https://doc.rust-lang.org/stable/std/io/type.Result.html
/// [`try!`]: https://doc.rust-lang.org/stable/std/macro.try.html
pub type Result<T> = ::std::result::Result<T, Error>;

/// A builder to create an iterator for recursively walking a directory.
///
/// Results are returned in depth first fashion, with directories yielded
/// before their contents. If [`contents_first`] is true, contents are yielded
/// before their directories. The order is unspecified but if [`sort_by`] is
/// given, directory entries are sorted according to this function. Directory
/// entries `.` and `..` are always omitted.
///
/// If an error occurs at any point during iteration, then it is returned in
/// place of its corresponding directory entry and iteration continues as
/// normal. If an error occurs while opening a directory for reading, then it
/// is not descended into (but the error is still yielded by the iterator).
/// Iteration may be stopped at any time. When the iterator is destroyed, all
/// resources associated with it are freed.
///
/// [`contents_first`]: struct.WalkDir.html#method.contents_first
/// [`sort_by`]: struct.WalkDir.html#method.sort_by
///
/// # Usage
///
/// This type implements [`IntoIterator`] so that it may be used as the subject
/// of a `for` loop. You may need to call [`into_iter`] explicitly if you want
/// to use iterator adapters such as [`filter_entry`].
///
/// Idiomatic use of this type should use method chaining to set desired
/// options. For example, this only shows entries with a depth of `1`, `2` or
/// `3` (relative to `foo`):
///
/// ```no_run
/// use walkdir::WalkDir;
/// # use walkdir::Error;
///
/// # fn try_main() -> Result<(), Error> {
/// for entry in WalkDir::new("foo").min_depth(1).max_depth(3) {
///     println!("{}", entry?.path().display());
/// }
/// # Ok(())
/// # }
/// ```
///
/// [`IntoIterator`]: https://doc.rust-lang.org/stable/std/iter/trait.IntoIterator.html
/// [`into_iter`]: https://doc.rust-lang.org/nightly/core/iter/trait.IntoIterator.html#tymethod.into_iter
/// [`filter_entry`]: struct.IntoIter.html#method.filter_entry
///
/// Note that the iterator by default includes the top-most directory. Since
/// this is the only directory yielded with depth `0`, it is easy to ignore it
/// with the [`min_depth`] setting:
///
/// ```no_run
/// use walkdir::WalkDir;
/// # use walkdir::Error;
///
/// # fn try_main() -> Result<(), Error> {
/// for entry in WalkDir::new("foo").min_depth(1) {
///     println!("{}", entry?.path().display());
/// }
/// # Ok(())
/// # }
/// ```
///
/// [`min_depth`]: struct.WalkDir.html#method.min_depth
///
/// This will only return descendents of the `foo` directory and not `foo`
/// itself.
///
/// # Loops
///
/// This iterator (like most/all recursive directory iterators) assumes that
/// no loops can be made with *hard* links on your file system. In particular,
/// this would require creating a hard link to a directory such that it creates
/// a loop. On most platforms, this operation is illegal.
///
/// Note that when following symbolic/soft links, loops are detected and an
/// error is reported.
#[derive(Debug)]
pub struct WalkDir {
    opts: WalkDirOptions,
    root: PathBuf,
}

struct WalkDirOptions {
    follow_links: bool,
    max_open: usize,
    min_depth: usize,
    max_depth: usize,
    sorter: Option<Box<
        FnMut(&DirEntry,&DirEntry) -> Ordering + Send + Sync + 'static
    >>,
    contents_first: bool,
    same_file_system: bool,
}

impl fmt::Debug for WalkDirOptions {
    fn fmt(&self, f: &mut fmt::Formatter) -> result::Result<(), fmt::Error> {
        let sorter_str = if self.sorter.is_some() {
            // FnMut isn't `Debug`
            "Some(...)"
        } else {
            "None"
        };
        f.debug_struct("WalkDirOptions")
            .field("follow_links", &self.follow_links)
            .field("max_open", &self.max_open)
            .field("min_depth", &self.min_depth)
            .field("max_depth", &self.max_depth)
            .field("sorter", &sorter_str)
            .field("contents_first", &self.contents_first)
            .field("same_file_system", &self.same_file_system)
            .finish()
    }
}

impl WalkDir {
    /// Create a builder for a recursive directory iterator starting at the
    /// file path `root`. If `root` is a directory, then it is the first item
    /// yielded by the iterator. If `root` is a file, then it is the first
    /// and only item yielded by the iterator. If `root` is a symlink, then it
    /// is always followed for the purposes of directory traversal. (A root
    /// `DirEntry` still obeys its documentation with respect to symlinks and
    /// the `follow_links` setting.)
    pub fn new<P: AsRef<Path>>(root: P) -> Self {
        WalkDir {
            opts: WalkDirOptions {
                follow_links: false,
                max_open: 10,
                min_depth: 0,
                max_depth: ::std::usize::MAX,
                sorter: None,
                contents_first: false,
                same_file_system: false,
            },
            root: root.as_ref().to_path_buf(),
        }
    }

    /// Set the minimum depth of entries yielded by the iterator.
    ///
    /// The smallest depth is `0` and always corresponds to the path given
    /// to the `new` function on this type. Its direct descendents have depth
    /// `1`, and their descendents have depth `2`, and so on.
    pub fn min_depth(mut self, depth: usize) -> Self {
        self.opts.min_depth = depth;
        if self.opts.min_depth > self.opts.max_depth {
            self.opts.min_depth = self.opts.max_depth;
        }
        self
    }

    /// Set the maximum depth of entries yield by the iterator.
    ///
    /// The smallest depth is `0` and always corresponds to the path given
    /// to the `new` function on this type. Its direct descendents have depth
    /// `1`, and their descendents have depth `2`, and so on.
    ///
    /// Note that this will not simply filter the entries of the iterator, but
    /// it will actually avoid descending into directories when the depth is
    /// exceeded.
    pub fn max_depth(mut self, depth: usize) -> Self {
        self.opts.max_depth = depth;
        if self.opts.max_depth < self.opts.min_depth {
            self.opts.max_depth = self.opts.min_depth;
        }
        self
    }

    /// Follow symbolic links. By default, this is disabled.
    ///
    /// When `yes` is `true`, symbolic links are followed as if they were
    /// normal directories and files. If a symbolic link is broken or is
    /// involved in a loop, an error is yielded.
    ///
    /// When enabled, the yielded [`DirEntry`] values represent the target of
    /// the link while the path corresponds to the link. See the [`DirEntry`]
    /// type for more details.
    ///
    /// [`DirEntry`]: struct.DirEntry.html
    pub fn follow_links(mut self, yes: bool) -> Self {
        self.opts.follow_links = yes;
        self
    }

    /// Set the maximum number of simultaneously open file descriptors used
    /// by the iterator.
    ///
    /// `n` must be greater than or equal to `1`. If `n` is `0`, then it is set
    /// to `1` automatically. If this is not set, then it defaults to some
    /// reasonably low number.
    ///
    /// This setting has no impact on the results yielded by the iterator
    /// (even when `n` is `1`). Instead, this setting represents a trade off
    /// between scarce resources (file descriptors) and memory. Namely, when
    /// the maximum number of file descriptors is reached and a new directory
    /// needs to be opened to continue iteration, then a previous directory
    /// handle is closed and has its unyielded entries stored in memory. In
    /// practice, this is a satisfying trade off because it scales with respect
    /// to the *depth* of your file tree. Therefore, low values (even `1`) are
    /// acceptable.
    ///
    /// Note that this value does not impact the number of system calls made by
    /// an exhausted iterator.
    ///
    /// # Platform behavior
    ///
    /// On Windows, if `follow_links` is enabled, then this limit is not
    /// respected. In particular, the maximum number of file descriptors opened
    /// is proportional to the depth of the directory tree traversed.
    pub fn max_open(mut self, mut n: usize) -> Self {
        if n == 0 {
            n = 1;
        }
        self.opts.max_open = n;
        self
    }

    /// Set a function for sorting directory entries.
    ///
    /// If a compare function is set, the resulting iterator will return all
    /// paths in sorted order. The compare function will be called to compare
    /// entries from the same directory.
    ///
    /// ```rust,no-run
    /// use std::cmp;
    /// use std::ffi::OsString;
    /// use walkdir::WalkDir;
    ///
    /// WalkDir::new("foo").sort_by(|a,b| a.file_name().cmp(b.file_name()));
    /// ```
    pub fn sort_by<F>(mut self, cmp: F) -> Self
    where F: FnMut(&DirEntry, &DirEntry) -> Ordering + Send + Sync + 'static
    {
        self.opts.sorter = Some(Box::new(cmp));
        self
    }

    /// Yield a directory's contents before the directory itself. By default,
    /// this is disabled.
    ///
    /// When `yes` is `false` (as is the default), the directory is yielded
    /// before its contents are read. This is useful when, e.g. you want to
    /// skip processing of some directories.
    ///
    /// When `yes` is `true`, the iterator yields the contents of a directory
    /// before yielding the directory itself. This is useful when, e.g. you
    /// want to recursively delete a directory.
    ///
    /// # Example
    ///
    /// Assume the following directory tree:
    ///
    /// ```text
    /// foo/
    ///   abc/
    ///     qrs
    ///     tuv
    ///   def/
    /// ```
    ///
    /// With contents_first disabled (the default), the following code visits
    /// the directory tree in depth-first order:
    ///
    /// ```no_run
    /// use walkdir::WalkDir;
    ///
    /// for entry in WalkDir::new("foo") {
    ///     let entry = entry.unwrap();
    ///     println!("{}", entry.path().display());
    /// }
    ///
    /// // foo
    /// // foo/abc
    /// // foo/abc/qrs
    /// // foo/abc/tuv
    /// // foo/def
    /// ```
    ///
    /// With contents_first enabled:
    ///
    /// ```no_run
    /// use walkdir::WalkDir;
    ///
    /// for entry in WalkDir::new("foo").contents_first(true) {
    ///     let entry = entry.unwrap();
    ///     println!("{}", entry.path().display());
    /// }
    ///
    /// // foo/abc/qrs
    /// // foo/abc/tuv
    /// // foo/abc
    /// // foo/def
    /// // foo
    /// ```
    pub fn contents_first(mut self, yes: bool) -> Self {
        self.opts.contents_first = yes;
        self
    }

    /// Do not cross file system boundaries.
    ///
    /// When this option is enabled, directory traversal will not descend into
    /// directories that are on a different file system from the root path.
    ///
    /// Currently, this option is only supported on Unix and Windows. If this
    /// option is used on an unsupported platform, then directory traversal
    /// will immediately return an error and will not yield any entries.
    pub fn same_file_system(mut self, yes: bool) -> Self {
        self.opts.same_file_system = yes;
        self
    }
}

impl IntoIterator for WalkDir {
    type Item = Result<DirEntry>;
    type IntoIter = IntoIter;

    fn into_iter(self) -> IntoIter {
        IntoIter {
            opts: self.opts,
            start: Some(self.root),
            stack_list: vec![],
            stack_path: vec![],
            oldest_opened: 0,
            depth: 0,
            deferred_dirs: vec![],
            root_device: None,
        }
    }
}

/// An iterator for recursively descending into a directory.
///
/// A value with this type must be constructed with the [`WalkDir`] type, which
/// uses a builder pattern to set options such as min/max depth, max open file
/// descriptors and whether the iterator should follow symbolic links. After
/// constructing a `WalkDir`, call [`.into_iter()`] at the end of the chain.
///
/// The order of elements yielded by this iterator is unspecified.
///
/// [`WalkDir`]: struct.WalkDir.html
/// [`.into_iter()`]: struct.WalkDir.html#into_iter.v
#[derive(Debug)]
pub struct IntoIter {
    /// Options specified in the builder. Depths, max fds, etc.
    opts: WalkDirOptions,
    /// The start path.
    ///
    /// This is only `Some(...)` at the beginning. After the first iteration,
    /// this is always `None`.
    start: Option<PathBuf>,
    /// A stack of open (up to max fd) or closed handles to directories.
    /// An open handle is a plain [`fs::ReadDir`] while a closed handle is
    /// a `Vec<fs::DirEntry>` corresponding to the as-of-yet consumed entries.
    ///
    /// [`fs::ReadDir`]: https://doc.rust-lang.org/stable/std/fs/struct.ReadDir.html
    stack_list: Vec<DirList>,
    /// A stack of file paths.
    ///
    /// This is *only* used when [`follow_links`] is enabled. In all other
    /// cases this stack is empty.
    ///
    /// [`follow_links`]: struct.WalkDir.html#method.follow_links
    stack_path: Vec<Ancestor>,
    /// An index into `stack_list` that points to the oldest open directory
    /// handle. If the maximum fd limit is reached and a new directory needs to
    /// be read, the handle at this index is closed before the new directory is
    /// opened.
    oldest_opened: usize,
    /// The current depth of iteration (the length of the stack at the
    /// beginning of each iteration).
    depth: usize,
    /// A list of DirEntries corresponding to directories, that are
    /// yielded after their contents has been fully yielded. This is only
    /// used when `contents_first` is enabled.
    deferred_dirs: Vec<DirEntry>,
    /// The device of the root file path when the first call to `next` was
    /// made.
    ///
    /// If the `same_file_system` option isn't enabled, then this is always
    /// `None`. Conversely, if it is enabled, this is always `Some(...)` after
    /// handling the root path.
    root_device: Option<u64>,
}

/// An ancestor is an item in the directory tree traversed by walkdir, and is
/// used to check for loops in the tree when traversing symlinks.
#[derive(Debug)]
struct Ancestor {
    /// The path of this ancestor.
    path: PathBuf,
    /// An open file to this ancesor. This is only used on Windows where
    /// opening a file handle appears to be quite expensive, so we choose to
    /// cache it. This comes at the cost of not respecting the file descriptor
    /// limit set by the user.
    #[cfg(windows)]
    handle: Handle,
}

impl Ancestor {
    /// Create a new ancestor from the given directory path.
    #[cfg(windows)]
    fn new(dent: &DirEntry) -> io::Result<Ancestor> {
        let handle = Handle::from_path(dent.path())?;
        Ok(Ancestor {
            path: dent.path().to_path_buf(),
            handle: handle,
        })
    }

    /// Create a new ancestor from the given directory path.
    #[cfg(not(windows))]
    fn new(dent: &DirEntry) -> io::Result<Ancestor> {
        Ok(Ancestor { path: dent.path().to_path_buf() })
    }

    /// Returns true if and only if the given open file handle corresponds to
    /// the same directory as this ancestor.
    #[cfg(windows)]
    fn is_same(&self, child: &Handle) -> io::Result<bool> {
        Ok(child == &self.handle)
    }

    /// Returns true if and only if the given open file handle corresponds to
    /// the same directory as this ancestor.
    #[cfg(not(windows))]
    fn is_same(&self, child: &Handle) -> io::Result<bool> {
        Ok(child == &Handle::from_path(&self.path)?)
    }
}

/// A sequence of unconsumed directory entries.
///
/// This represents the opened or closed state of a directory handle. When
/// open, future entries are read by iterating over the raw `fs::ReadDir`.
/// When closed, all future entries are read into memory. Iteration then
/// proceeds over a [`Vec<fs::DirEntry>`].
///
/// [`fs::ReadDir`]: https://doc.rust-lang.org/stable/std/fs/struct.ReadDir.html
/// [`Vec<fs::DirEntry>`]: https://doc.rust-lang.org/stable/std/vec/struct.Vec.html
#[derive(Debug)]
enum DirList {
    /// An opened handle.
    ///
    /// This includes the depth of the handle itself.
    ///
    /// If there was an error with the initial [`fs::read_dir`] call, then it
    /// is stored here. (We use an [`Option<...>`] to make yielding the error
    /// exactly once simpler.)
    ///
    /// [`fs::read_dir`]: https://doc.rust-lang.org/stable/std/fs/fn.read_dir.html
    /// [`Option<...>`]: https://doc.rust-lang.org/stable/std/option/enum.Option.html
    Opened { depth: usize, it: result::Result<ReadDir, Option<Error>> },
    /// A closed handle.
    ///
    /// All remaining directory entries are read into memory.
    Closed(vec::IntoIter<Result<DirEntry>>),
}

/// A directory entry.
///
/// This is the type of value that is yielded from the iterators defined in
/// this crate.
///
/// On Unix systems, this type implements the [`DirEntryExt`] trait, which
/// provides efficient access to the inode number of the directory entry.
///
/// # Differences with `std::fs::DirEntry`
///
/// This type mostly mirrors the type by the same name in [`std::fs`]. There
/// are some differences however:
///
/// * All recursive directory iterators must inspect the entry's type.
/// Therefore, the value is stored and its access is guaranteed to be cheap and
/// successful.
/// * [`path`] and [`file_name`] return borrowed variants.
/// * If [`follow_links`] was enabled on the originating iterator, then all
/// operations except for [`path`] operate on the link target. Otherwise, all
/// operations operate on the symbolic link.
///
/// [`std::fs`]: https://doc.rust-lang.org/stable/std/fs/index.html
/// [`path`]: #method.path
/// [`file_name`]: #method.file_name
/// [`follow_links`]: struct.WalkDir.html#method.follow_links
/// [`DirEntryExt`]: trait.DirEntryExt.html
pub struct DirEntry {
    /// The path as reported by the [`fs::ReadDir`] iterator (even if it's a
    /// symbolic link).
    ///
    /// [`fs::ReadDir`]: https://doc.rust-lang.org/stable/std/fs/struct.ReadDir.html
    path: PathBuf,
    /// The file type. Necessary for recursive iteration, so store it.
    ty: FileType,
    /// Is set when this entry was created from a symbolic link and the user
    /// expects the iterator to follow symbolic links.
    follow_link: bool,
    /// The depth at which this entry was generated relative to the root.
    depth: usize,
    /// The underlying inode number (Unix only).
    #[cfg(unix)]
    ino: u64,
    /// The underlying metadata (Windows only). We store this on Windows
    /// because this comes for free while reading a directory.
    ///
    /// We use this to determine whether an entry is a directory or not, which
    /// works around a bug in Rust's standard library:
    /// https://github.com/rust-lang/rust/issues/46484
    #[cfg(windows)]
    metadata: fs::Metadata,
}

impl Iterator for IntoIter {
    type Item = Result<DirEntry>;
    /// Advances the iterator and returns the next value.
    ///
    /// # Errors
    ///
    /// If the iterator fails to retrieve the next value, this method returns
    /// an error value. The error will be wrapped in an Option::Some.
    fn next(&mut self) -> Option<Result<DirEntry>> {
        if let Some(start) = self.start.take() {
            if self.opts.same_file_system {
                let result = device_num(&start)
                    .map_err(|e| Error::from_path(0, start.clone(), e));
                self.root_device = Some(itry!(result));
            }
            let dent = itry!(DirEntry::from_path(0, start, false));
            if let Some(result) = self.handle_entry(dent) {
                return Some(result);
            }
        }
        while !self.stack_list.is_empty() {
            self.depth = self.stack_list.len();
            if let Some(dentry) = self.get_deferred_dir() {
                return Some(Ok(dentry));
            }
            if self.depth > self.opts.max_depth {
                // If we've exceeded the max depth, pop the current dir
                // so that we don't descend.
                self.pop();
                continue;
            }
            // Unwrap is safe here because we've verified above that
            // `self.stack_list` is not empty
            let next = self.stack_list
                .last_mut()
                .expect("BUG: stack should be non-empty")
                .next();
            match next {
                None => self.pop(),
                Some(Err(err)) => return Some(Err(err)),
                Some(Ok(dent)) => {
                    if let Some(result) = self.handle_entry(dent) {
                        return Some(result);
                    }
                }
            }
        }
        if self.opts.contents_first {
            self.depth = self.stack_list.len();
            if let Some(dentry) = self.get_deferred_dir() {
                return Some(Ok(dentry));
            }
        }
        None
    }
}

impl IntoIter {
    /// Skips the current directory.
    ///
    /// This causes the iterator to stop traversing the contents of the least
    /// recently yielded directory. This means any remaining entries in that
    /// directory will be skipped (including sub-directories).
    ///
    /// Note that the ergonomics of this method are questionable since it
    /// borrows the iterator mutably. Namely, you must write out the looping
    /// condition manually. For example, to skip hidden entries efficiently on
    /// unix systems:
    ///
    /// ```no_run
    /// use walkdir::{DirEntry, WalkDir};
    ///
    /// fn is_hidden(entry: &DirEntry) -> bool {
    ///     entry.file_name()
    ///          .to_str()
    ///          .map(|s| s.starts_with("."))
    ///          .unwrap_or(false)
    /// }
    ///
    /// let mut it = WalkDir::new("foo").into_iter();
    /// loop {
    ///     let entry = match it.next() {
    ///         None => break,
    ///         Some(Err(err)) => panic!("ERROR: {}", err),
    ///         Some(Ok(entry)) => entry,
    ///     };
    ///     if is_hidden(&entry) {
    ///         if entry.file_type().is_dir() {
    ///             it.skip_current_dir();
    ///         }
    ///         continue;
    ///     }
    ///     println!("{}", entry.path().display());
    /// }
    /// ```
    ///
    /// You may find it more convenient to use the [`filter_entry`] iterator
    /// adapter. (See its documentation for the same example functionality as
    /// above.)
    ///
    /// [`filter_entry`]: #method.filter_entry
    pub fn skip_current_dir(&mut self) {
        if !self.stack_list.is_empty() {
            self.stack_list.pop();
        }
        if !self.stack_path.is_empty() {
            self.stack_path.pop();
        }
    }

    /// Yields only entries which satisfy the given predicate and skips
    /// descending into directories that do not satisfy the given predicate.
    ///
    /// The predicate is applied to all entries. If the predicate is
    /// true, iteration carries on as normal. If the predicate is false, the
    /// entry is ignored and if it is a directory, it is not descended into.
    ///
    /// This is often more convenient to use than [`skip_current_dir`]. For
    /// example, to skip hidden files and directories efficiently on unix
    /// systems:
    ///
    /// ```no_run
    /// use walkdir::{DirEntry, WalkDir};
    /// # use walkdir::Error;
    ///
    /// fn is_hidden(entry: &DirEntry) -> bool {
    ///     entry.file_name()
    ///          .to_str()
    ///          .map(|s| s.starts_with("."))
    ///          .unwrap_or(false)
    /// }
    ///
    /// # fn try_main() -> Result<(), Error> {
    /// for entry in WalkDir::new("foo")
    ///                      .into_iter()
    ///                      .filter_entry(|e| !is_hidden(e)) {
    ///     println!("{}", entry?.path().display());
    /// }
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// Note that the iterator will still yield errors for reading entries that
    /// may not satisfy the predicate.
    ///
    /// Note that entries skipped with [`min_depth`] and [`max_depth`] are not
    /// passed to this predicate.
    ///
    /// Note that if the iterator has `contents_first` enabled, then this
    /// method is no different than calling the standard `Iterator::filter`
    /// method (because directory entries are yielded after they've been
    /// descended into).
    ///
    /// [`skip_current_dir`]: #method.skip_current_dir
    /// [`min_depth`]: struct.WalkDir.html#method.min_depth
    /// [`max_depth`]: struct.WalkDir.html#method.max_depth
    pub fn filter_entry<P>(self, predicate: P) -> FilterEntry<Self, P>
    where P: FnMut(&DirEntry) -> bool
    {
        FilterEntry { it: self, predicate: predicate }
    }

    fn handle_entry(
        &mut self,
        mut dent: DirEntry,
    ) -> Option<Result<DirEntry>> {
        if self.opts.follow_links && dent.file_type().is_symlink() {
            dent = itry!(self.follow(dent));
        }
        let is_normal_dir = !dent.file_type().is_symlink() && dent.is_dir();
        if is_normal_dir {
            if self.opts.same_file_system && dent.depth > 0 {
                if itry!(self.is_same_file_system(&dent)) {
                    itry!(self.push(&dent));
                }
            } else {
                itry!(self.push(&dent));
            }
        } else if dent.depth() == 0 && dent.file_type().is_symlink() {
            // As a special case, if we are processing a root entry, then we
            // always follow it even if it's a symlink and follow_links is
            // false. We are careful to not let this change the semantics of
            // the DirEntry however. Namely, the DirEntry should still respect
            // the follow_links setting. When it's disabled, it should report
            // itself as a symlink. When it's enabled, it should always report
            // itself as the target.
            let md = itry!(fs::metadata(dent.path()).map_err(|err| {
                Error::from_path(dent.depth(), dent.path().to_path_buf(), err)
            }));
            if md.file_type().is_dir() {
                itry!(self.push(&dent));
            }
        }
        if is_normal_dir && self.opts.contents_first {
            self.deferred_dirs.push(dent);
            None
        } else if self.skippable() {
            None
        } else {
            Some(Ok(dent))
        }
    }

    fn get_deferred_dir(&mut self) -> Option<DirEntry> {
        if self.opts.contents_first {
            if self.depth < self.deferred_dirs.len() {
                // Unwrap is safe here because we've guaranteed that
                // `self.deferred_dirs.len()` can never be less than 1
                let deferred: DirEntry = self.deferred_dirs.pop()
                    .expect("BUG: deferred_dirs should be non-empty");
                if !self.skippable() {
                    return Some(deferred);
                }
            }
        }
        None
    }

    fn push(&mut self, dent: &DirEntry) -> Result<()> {
        // Make room for another open file descriptor if we've hit the max.
        let free = self.stack_list
            .len()
            .checked_sub(self.oldest_opened).unwrap();
        if free == self.opts.max_open {
            self.stack_list[self.oldest_opened].close();
            // Unwrap is safe here because self.oldest_opened is guaranteed to
            // never be greater than `self.stack_list.len()`, which implies
            // that the subtraction won't underflow and that adding 1 will
            // never overflow.
            self.oldest_opened = self.oldest_opened.checked_add(1).unwrap();
        }
        // Open a handle to reading the directory's entries.
        let rd = fs::read_dir(dent.path()).map_err(|err| {
            Some(Error::from_path(self.depth, dent.path().to_path_buf(), err))
        });
        let mut list = DirList::Opened { depth: self.depth, it: rd };
        if let Some(ref mut cmp) = self.opts.sorter {
            let mut entries: Vec<_> = list.collect();
            entries.sort_by(|a, b| {
                match (a, b) {
                    (&Ok(ref a), &Ok(ref b)) => {
                        cmp(a, b)
                    }
                    (&Err(_), &Err(_)) => Ordering::Equal,
                    (&Ok(_), &Err(_)) => Ordering::Greater,
                    (&Err(_), &Ok(_)) => Ordering::Less,
                }
            });
            list = DirList::Closed(entries.into_iter());
        }
        if self.opts.follow_links {
            let ancestor = Ancestor::new(&dent).map_err(|err| {
                Error::from_io(self.depth, err)
            })?;
            self.stack_path.push(ancestor);
        }
        // We push this after stack_path since creating the Ancestor can fail.
        // If it fails, then we return the error and won't descend.
        self.stack_list.push(list);
        Ok(())
    }

    fn pop(&mut self) {
        self.stack_list.pop().expect("BUG: cannot pop from empty stack");
        if self.opts.follow_links {
            self.stack_path.pop().expect("BUG: list/path stacks out of sync");
        }
        // If everything in the stack is already closed, then there is
        // room for at least one more open descriptor and it will
        // always be at the top of the stack.
        self.oldest_opened = min(self.oldest_opened, self.stack_list.len());
    }

    fn follow(&self, mut dent: DirEntry) -> Result<DirEntry> {
        dent = DirEntry::from_path(
            self.depth,
            dent.path().to_path_buf(),
            true,
        )?;
        // The only way a symlink can cause a loop is if it points
        // to a directory. Otherwise, it always points to a leaf
        // and we can omit any loop checks.
        if dent.is_dir() {
            self.check_loop(dent.path())?;
        }
        Ok(dent)
    }

    fn check_loop<P: AsRef<Path>>(&self, child: P) -> Result<()> {
        let hchild = Handle::from_path(&child).map_err(|err| {
            Error::from_io(self.depth, err)
        })?;
        for ancestor in self.stack_path.iter().rev() {
            let is_same = ancestor.is_same(&hchild).map_err(|err| {
                Error::from_io(self.depth, err)
            })?;
            if is_same {
                return Err(Error {
                    depth: self.depth,
                    inner: ErrorInner::Loop {
                        ancestor: ancestor.path.to_path_buf(),
                        child: child.as_ref().to_path_buf(),
                    },
                });
            }
        }
        Ok(())
    }

    fn is_same_file_system(&mut self, dent: &DirEntry) -> Result<bool> {
        let dent_device = device_num(&dent.path)
            .map_err(|err| Error::from_entry(dent, err))?;
        Ok(self.root_device
            .map(|d| d == dent_device)
            .expect("BUG: called is_same_file_system without root device"))
    }

    fn skippable(&self) -> bool {
        self.depth < self.opts.min_depth || self.depth > self.opts.max_depth
    }
}

impl DirList {
    fn close(&mut self) {
        if let DirList::Opened { .. } = *self {
            *self = DirList::Closed(self.collect::<Vec<_>>().into_iter());
        }
    }
}

impl Iterator for DirList {
    type Item = Result<DirEntry>;

    #[inline(always)]
    fn next(&mut self) -> Option<Result<DirEntry>> {
        match *self {
            DirList::Closed(ref mut it) => it.next(),
            DirList::Opened { depth, ref mut it } => match *it {
                Err(ref mut err) => err.take().map(Err),
                Ok(ref mut rd) => rd.next().map(|r| match r {
                    Ok(r) => DirEntry::from_entry(depth + 1, &r),
                    Err(err) => Err(Error::from_io(depth + 1, err))
                }),
            }
        }
    }
}

impl DirEntry {
    /// The full path that this entry represents.
    ///
    /// The full path is created by joining the parents of this entry up to the
    /// root initially given to [`WalkDir::new`] with the file name of this
    /// entry.
    ///
    /// Note that this *always* returns the path reported by the underlying
    /// directory entry, even when symbolic links are followed. To get the
    /// target path, use [`path_is_symlink`] to (cheaply) check if this entry
    /// corresponds to a symbolic link, and [`std::fs::read_link`] to resolve
    /// the target.
    ///
    /// [`WalkDir::new`]: struct.WalkDir.html#method.new
    /// [`path_is_symlink`]: struct.DirEntry.html#method.path_is_symlink
    /// [`std::fs::read_link`]: https://doc.rust-lang.org/stable/std/fs/fn.read_link.html
    pub fn path(&self) -> &Path {
        &self.path
    }

    /// The full path that this entry represents.
    ///
    /// Analogous to [`path`], but moves ownership of the path.
    ///
    /// [`path`]: struct.DirEntry.html#method.path
    pub fn into_path(self) -> PathBuf {
        self.path
    }

    /// Returns `true` if and only if this entry was created from a symbolic
    /// link. This is unaffected by the [`follow_links`] setting.
    ///
    /// When `true`, the value returned by the [`path`] method is a
    /// symbolic link name. To get the full target path, you must call
    /// [`std::fs::read_link(entry.path())`].
    ///
    /// [`path`]: struct.DirEntry.html#method.path
    /// [`follow_links`]: struct.WalkDir.html#method.follow_links
    /// [`std::fs::read_link(entry.path())`]: https://doc.rust-lang.org/stable/std/fs/fn.read_link.html
    pub fn path_is_symlink(&self) -> bool {
        self.ty.is_symlink() || self.follow_link
    }

    /// Return the metadata for the file that this entry points to.
    ///
    /// This will follow symbolic links if and only if the [`WalkDir`] value
    /// has [`follow_links`] enabled.
    ///
    /// # Platform behavior
    ///
    /// This always calls [`std::fs::symlink_metadata`].
    ///
    /// If this entry is a symbolic link and [`follow_links`] is enabled, then
    /// [`std::fs::metadata`] is called instead.
    ///
    /// # Errors
    ///
    /// Similar to [`std::fs::metadata`], returns errors for path values that
    /// the program does not have permissions to access or if the path does not
    /// exist.
    ///
    /// [`WalkDir`]: struct.WalkDir.html
    /// [`follow_links`]: struct.WalkDir.html#method.follow_links
    /// [`std::fs::metadata`]: https://doc.rust-lang.org/std/fs/fn.metadata.html
    /// [`std::fs::symlink_metadata`]: https://doc.rust-lang.org/stable/std/fs/fn.symlink_metadata.html
    pub fn metadata(&self) -> Result<fs::Metadata> {
        self.metadata_internal()
    }

    #[cfg(windows)]
    fn metadata_internal(&self) -> Result<fs::Metadata> {
        if self.follow_link {
            fs::metadata(&self.path)
        } else {
            Ok(self.metadata.clone())
        }.map_err(|err| Error::from_entry(self, err))
    }

    #[cfg(not(windows))]
    fn metadata_internal(&self) -> Result<fs::Metadata> {
        if self.follow_link {
            fs::metadata(&self.path)
        } else {
            fs::symlink_metadata(&self.path)
        }.map_err(|err| Error::from_entry(self, err))
    }

    /// Return the file type for the file that this entry points to.
    ///
    /// If this is a symbolic link and [`follow_links`] is `true`, then this
    /// returns the type of the target.
    ///
    /// This never makes any system calls.
    ///
    /// [`follow_links`]: struct.WalkDir.html#method.follow_links
    pub fn file_type(&self) -> fs::FileType {
        self.ty
    }

    /// Return the file name of this entry.
    ///
    /// If this entry has no file name (e.g., `/`), then the full path is
    /// returned.
    pub fn file_name(&self) -> &OsStr {
        self.path.file_name().unwrap_or_else(|| self.path.as_os_str())
    }

    /// Returns the depth at which this entry was created relative to the root.
    ///
    /// The smallest depth is `0` and always corresponds to the path given
    /// to the `new` function on `WalkDir`. Its direct descendents have depth
    /// `1`, and their descendents have depth `2`, and so on.
    pub fn depth(&self) -> usize {
        self.depth
    }

    /// Returns true if and only if this entry points to a directory.
    ///
    /// This works around a bug in Rust's standard library:
    /// https://github.com/rust-lang/rust/issues/46484
    #[cfg(windows)]
    fn is_dir(&self) -> bool {
        use std::os::windows::fs::MetadataExt;
        use winapi::um::winnt::FILE_ATTRIBUTE_DIRECTORY;
        self.metadata.file_attributes() & FILE_ATTRIBUTE_DIRECTORY != 0
    }

    /// Returns true if and only if this entry points to a directory.
    #[cfg(not(windows))]
    fn is_dir(&self) -> bool {
        self.ty.is_dir()
    }

    #[cfg(windows)]
    fn from_entry(depth: usize, ent: &fs::DirEntry) -> Result<DirEntry> {
        let path = ent.path();
        let ty = ent.file_type().map_err(|err| {
            Error::from_path(depth, path.clone(), err)
        })?;
        let md = ent.metadata().map_err(|err| {
            Error::from_path(depth, path.clone(), err)
        })?;
        Ok(DirEntry {
            path: path,
            ty: ty,
            follow_link: false,
            depth: depth,
            metadata: md,
        })
    }

    #[cfg(unix)]
    fn from_entry(depth: usize, ent: &fs::DirEntry) -> Result<DirEntry> {
        use std::os::unix::fs::DirEntryExt;

        let ty = ent.file_type().map_err(|err| {
            Error::from_path(depth, ent.path(), err)
        })?;
        Ok(DirEntry {
            path: ent.path(),
            ty: ty,
            follow_link: false,
            depth: depth,
            ino: ent.ino(),
        })
    }

    #[cfg(not(any(unix, windows)))]
    fn from_entry(depth: usize, ent: &fs::DirEntry) -> Result<DirEntry> {
        let ty = ent.file_type().map_err(|err| {
            Error::from_path(depth, ent.path(), err)
        })?;
        Ok(DirEntry {
            path: ent.path(),
            ty: ty,
            follow_link: false,
            depth: depth,
        })
    }

    #[cfg(windows)]
    fn from_path(depth: usize, pb: PathBuf, follow: bool) -> Result<DirEntry> {
        let md =
            if follow {
                fs::metadata(&pb).map_err(|err| {
                    Error::from_path(depth, pb.clone(), err)
                })?
            } else {
                fs::symlink_metadata(&pb).map_err(|err| {
                    Error::from_path(depth, pb.clone(), err)
                })?
            };
        Ok(DirEntry {
            path: pb,
            ty: md.file_type(),
            follow_link: follow,
            depth: depth,
            metadata: md,
        })
    }

    #[cfg(unix)]
    fn from_path(depth: usize, pb: PathBuf, follow: bool) -> Result<DirEntry> {
        use std::os::unix::fs::MetadataExt;

        let md =
            if follow {
                fs::metadata(&pb).map_err(|err| {
                    Error::from_path(depth, pb.clone(), err)
                })?
            } else {
                fs::symlink_metadata(&pb).map_err(|err| {
                    Error::from_path(depth, pb.clone(), err)
                })?
            };
        Ok(DirEntry {
            path: pb,
            ty: md.file_type(),
            follow_link: follow,
            depth: depth,
            ino: md.ino(),
        })
    }

    #[cfg(not(any(unix, windows)))]
    fn from_path(depth: usize, pb: PathBuf, follow: bool) -> Result<DirEntry> {
        let md =
            if follow {
                fs::metadata(&pb).map_err(|err| {
                    Error::from_path(depth, pb.clone(), err)
                })?
            } else {
                fs::symlink_metadata(&pb).map_err(|err| {
                    Error::from_path(depth, pb.clone(), err)
                })?
            };
        Ok(DirEntry {
            path: pb,
            ty: md.file_type(),
            follow_link: follow,
            depth: depth,
        })
    }
}

impl Clone for DirEntry {
    #[cfg(windows)]
    fn clone(&self) -> DirEntry {
        DirEntry {
            path: self.path.clone(),
            ty: self.ty,
            follow_link: self.follow_link,
            depth: self.depth,
            metadata: self.metadata.clone(),
        }
    }

    #[cfg(unix)]
    fn clone(&self) -> DirEntry {
        DirEntry {
            path: self.path.clone(),
            ty: self.ty,
            follow_link: self.follow_link,
            depth: self.depth,
            ino: self.ino,
        }
    }

    #[cfg(not(any(unix, windows)))]
    fn clone(&self) -> DirEntry {
        DirEntry {
            path: self.path.clone(),
            ty: self.ty,
            follow_link: self.follow_link,
            depth: self.depth,
        }
    }
}

impl fmt::Debug for DirEntry {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "DirEntry({:?})", self.path)
    }
}

/// A recursive directory iterator that skips entries.
///
/// Values of this type are created by calling [`.filter_entry()`] on an
/// `IntoIter`, which is formed by calling [`.into_iter()`] on a `WalkDir`.
///
/// Directories that fail the predicate `P` are skipped. Namely, they are
/// never yielded and never descended into.
///
/// Entries that are skipped with the [`min_depth`] and [`max_depth`] options
/// are not passed through this filter.
///
/// If opening a handle to a directory resulted in an error, then it is yielded
/// and no corresponding call to the predicate is made.
///
/// Type parameter `I` refers to the underlying iterator and `P` refers to the
/// predicate, which is usually `FnMut(&DirEntry) -> bool`.
///
/// [`.filter_entry()`]: struct.IntoIter.html#method.filter_entry
/// [`.into_iter()`]: struct.WalkDir.html#into_iter.v
/// [`min_depth`]: struct.WalkDir.html#method.min_depth
/// [`max_depth`]: struct.WalkDir.html#method.max_depth
#[derive(Debug)]
pub struct FilterEntry<I, P> {
    it: I,
    predicate: P,
}

impl<P> Iterator for FilterEntry<IntoIter, P>
where P: FnMut(&DirEntry) -> bool
{
    type Item = Result<DirEntry>;

    /// Advances the iterator and returns the next value.
    ///
    /// # Errors
    ///
    /// If the iterator fails to retrieve the next value, this method returns
    /// an error value. The error will be wrapped in an `Option::Some`.
    fn next(&mut self) -> Option<Result<DirEntry>> {
        loop {
            let dent = match self.it.next() {
                None => return None,
                Some(result) => itry!(result),
            };
            if !(self.predicate)(&dent) {
                if dent.is_dir() {
                    self.it.skip_current_dir();
                }
                continue;
            }
            return Some(Ok(dent));
        }
    }
}

impl<P> FilterEntry<IntoIter, P> where P: FnMut(&DirEntry) -> bool {
    /// Yields only entries which satisfy the given predicate and skips
    /// descending into directories that do not satisfy the given predicate.
    ///
    /// The predicate is applied to all entries. If the predicate is
    /// true, iteration carries on as normal. If the predicate is false, the
    /// entry is ignored and if it is a directory, it is not descended into.
    ///
    /// This is often more convenient to use than [`skip_current_dir`]. For
    /// example, to skip hidden files and directories efficiently on unix
    /// systems:
    ///
    /// ```no_run
    /// use walkdir::{DirEntry, WalkDir};
    /// # use walkdir::Error;
    ///
    /// fn is_hidden(entry: &DirEntry) -> bool {
    ///     entry.file_name()
    ///          .to_str()
    ///          .map(|s| s.starts_with("."))
    ///          .unwrap_or(false)
    /// }
    ///
    /// # fn try_main() -> Result<(), Error> {
    /// for entry in WalkDir::new("foo")
    ///                      .into_iter()
    ///                      .filter_entry(|e| !is_hidden(e)) {
    ///     println!("{}", entry?.path().display());
    /// }
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// Note that the iterator will still yield errors for reading entries that
    /// may not satisfy the predicate.
    ///
    /// Note that entries skipped with [`min_depth`] and [`max_depth`] are not
    /// passed to this predicate.
    ///
    /// Note that if the iterator has `contents_first` enabled, then this
    /// method is no different than calling the standard `Iterator::filter`
    /// method (because directory entries are yielded after they've been
    /// descended into).
    ///
    /// [`skip_current_dir`]: #method.skip_current_dir
    /// [`min_depth`]: struct.WalkDir.html#method.min_depth
    /// [`max_depth`]: struct.WalkDir.html#method.max_depth
    pub fn filter_entry(self, predicate: P) -> FilterEntry<Self, P> {
        FilterEntry { it: self, predicate: predicate }
    }

    /// Skips the current directory.
    ///
    /// This causes the iterator to stop traversing the contents of the least
    /// recently yielded directory. This means any remaining entries in that
    /// directory will be skipped (including sub-directories).
    ///
    /// Note that the ergonomics of this method are questionable since it
    /// borrows the iterator mutably. Namely, you must write out the looping
    /// condition manually. For example, to skip hidden entries efficiently on
    /// unix systems:
    ///
    /// ```no_run
    /// use walkdir::{DirEntry, WalkDir};
    ///
    /// fn is_hidden(entry: &DirEntry) -> bool {
    ///     entry.file_name()
    ///          .to_str()
    ///          .map(|s| s.starts_with("."))
    ///          .unwrap_or(false)
    /// }
    ///
    /// let mut it = WalkDir::new("foo").into_iter();
    /// loop {
    ///     let entry = match it.next() {
    ///         None => break,
    ///         Some(Err(err)) => panic!("ERROR: {}", err),
    ///         Some(Ok(entry)) => entry,
    ///     };
    ///     if is_hidden(&entry) {
    ///         if entry.file_type().is_dir() {
    ///             it.skip_current_dir();
    ///         }
    ///         continue;
    ///     }
    ///     println!("{}", entry.path().display());
    /// }
    /// ```
    ///
    /// You may find it more convenient to use the [`filter_entry`] iterator
    /// adapter. (See its documentation for the same example functionality as
    /// above.)
    ///
    /// [`filter_entry`]: #method.filter_entry
    pub fn skip_current_dir(&mut self) {
        self.it.skip_current_dir();
    }
}

/// An error produced by recursively walking a directory.
///
/// This error type is a light wrapper around [`std::io::Error`]. In
/// particular, it adds the following information:
///
/// * The depth at which the error occurred in the file tree, relative to the
/// root.
/// * The path, if any, associated with the IO error.
/// * An indication that a loop occurred when following symbolic links. In this
/// case, there is no underlying IO error.
///
/// To maintain good ergonomics, this type has a
/// [`impl From<Error> for std::io::Error`][impl] defined which preserves the original context.
/// This allows you to use an [`io::Result`] with methods in this crate if you don't care about
/// accessing the underlying error data in a structured form.
///
/// [`std::io::Error`]: https://doc.rust-lang.org/stable/std/io/struct.Error.html
/// [`io::Result`]: https://doc.rust-lang.org/stable/std/io/type.Result.html
/// [impl]: struct.Error.html#impl-From%3CError%3E
#[derive(Debug)]
pub struct Error {
    depth: usize,
    inner: ErrorInner,
}

#[derive(Debug)]
enum ErrorInner {
    Io { path: Option<PathBuf>, err: io::Error },
    Loop { ancestor: PathBuf, child: PathBuf },
}

impl Error {
    /// Returns the path associated with this error if one exists.
    ///
    /// For example, if an error occurred while opening a directory handle,
    /// the error will include the path passed to [`std::fs::read_dir`].
    ///
    /// [`std::fs::read_dir`]: https://doc.rust-lang.org/stable/std/fs/fn.read_dir.html
    pub fn path(&self) -> Option<&Path> {
        match self.inner {
            ErrorInner::Io { path: None, .. } => None,
            ErrorInner::Io { path: Some(ref path), .. } => Some(path),
            ErrorInner::Loop { ref child, .. } => Some(child),
        }
    }

    /// Returns the path at which a cycle was detected.
    ///
    /// If no cycle was detected, [`None`] is returned.
    ///
    /// A cycle is detected when a directory entry is equivalent to one of
    /// its ancestors.
    ///
    /// To get the path to the child directory entry in the cycle, use the
    /// [`path`] method.
    ///
    /// [`None`]: https://doc.rust-lang.org/stable/std/option/enum.Option.html#variant.None
    /// [`path`]: struct.Error.html#path
    pub fn loop_ancestor(&self) -> Option<&Path> {
        match self.inner {
            ErrorInner::Loop { ref ancestor, .. } => Some(ancestor),
            _ => None,
        }
    }

    /// Returns the depth at which this error occurred relative to the root.
    ///
    /// The smallest depth is `0` and always corresponds to the path given to
    /// the [`new`] function on [`WalkDir`]. Its direct descendents have depth
    /// `1`, and their descendents have depth `2`, and so on.
    ///
    /// [`new`]: struct.WalkDir.html#method.new
    /// [`WalkDir`]: struct.WalkDir.html
    pub fn depth(&self) -> usize {
        self.depth
    }

    /// Inspect the original [`io::Error`] if there is one.
    ///
    /// [`None`] is returned if the [`Error`] doesn't correspond to an
    /// [`io::Error`]. This might happen, for example, when the error was
    /// produced because a cycle was found in the directory tree while
    /// following symbolic links.
    ///
    /// This method returns a borrowed value that is bound to the lifetime of the [`Error`]. To
    /// obtain an owned value, the [`into_io_error`] can be used instead.
    ///
    /// > This is the original [`io::Error`] and is _not_ the same as
    /// > [`impl From<Error> for std::io::Error`][impl] which contains additional context about the
    /// error.
    ///
    /// # Example
    ///
    /// ```rust,no-run
    /// use std::io;
    /// use std::path::Path;
    ///
    /// use walkdir::WalkDir;
    ///
    /// for entry in WalkDir::new("foo") {
    ///     match entry {
    ///         Ok(entry) => println!("{}", entry.path().display()),
    ///         Err(err) => {
    ///             let path = err.path().unwrap_or(Path::new("")).display();
    ///             println!("failed to access entry {}", path);
    ///             if let Some(inner) = err.io_error() {
    ///                 match inner.kind() {
    ///                     io::ErrorKind::InvalidData => {
    ///                         println!(
    ///                             "entry contains invalid data: {}",
    ///                             inner)
    ///                     }
    ///                     io::ErrorKind::PermissionDenied => {
    ///                         println!(
    ///                             "Missing permission to read entry: {}",
    ///                             inner)
    ///                     }
    ///                     _ => {
    ///                         println!(
    ///                             "Unexpected error occurred: {}",
    ///                             inner)
    ///                     }
    ///                 }
    ///             }
    ///         }
    ///     }
    /// }
    /// ```
    ///
    /// [`None`]: https://doc.rust-lang.org/stable/std/option/enum.Option.html#variant.None
    /// [`io::Error`]: https://doc.rust-lang.org/stable/std/io/struct.Error.html
    /// [`From`]: https://doc.rust-lang.org/stable/std/convert/trait.From.html
    /// [`Error`]: struct.Error.html
    /// [`into_io_error`]: struct.Error.html#method.into_io_error
    /// [impl]: struct.Error.html#impl-From%3CError%3E
    pub fn io_error(&self) -> Option<&io::Error> {
       match self.inner {
            ErrorInner::Io { ref err, .. } => Some(err),
            ErrorInner::Loop { .. } => None,
       }
    }

    /// Similar to [`io_error`] except consumes self to convert to the original
    /// [`io::Error`] if one exists.
    ///
    /// [`io_error`]: struct.Error.html#method.io_error
    /// [`io::Error`]: https://doc.rust-lang.org/stable/std/io/struct.Error.html
    pub fn into_io_error(self) -> Option<io::Error> {
       match self.inner {
            ErrorInner::Io { err, .. } => Some(err),
            ErrorInner::Loop { .. } => None,
       }
    }

    fn from_path(depth: usize, pb: PathBuf, err: io::Error) -> Self {
        Error {
            depth: depth,
            inner: ErrorInner::Io { path: Some(pb), err: err },
        }
    }

    fn from_entry(dent: &DirEntry, err: io::Error) -> Self {
        Error {
            depth: dent.depth,
            inner: ErrorInner::Io {
                path: Some(dent.path().to_path_buf()),
                err: err,
            },
        }
    }

    fn from_io(depth: usize, err: io::Error) -> Self {
        Error {
            depth: depth,
            inner: ErrorInner::Io { path: None, err: err },
        }
    }
}

impl error::Error for Error {
    fn description(&self) -> &str {
        match self.inner {
            ErrorInner::Io { ref err, .. } => err.description(),
            ErrorInner::Loop { .. } => "file system loop found",
        }
    }

    fn cause(&self) -> Option<&error::Error> {
        match self.inner {
            ErrorInner::Io { ref err, .. } => Some(err),
            ErrorInner::Loop { .. } => None,
        }
    }
}

impl fmt::Display for Error {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self.inner {
            ErrorInner::Io { path: None, ref err } => {
                err.fmt(f)
            }
            ErrorInner::Io { path: Some(ref path), ref err } => {
                write!(f, "IO error for operation on {}: {}",
                       path.display(), err)
            }
            ErrorInner::Loop { ref ancestor, ref child } => {
                write!(f, "File system loop found: \
                           {} points to an ancestor {}",
                       child.display(), ancestor.display())
            }
        }
    }
}

impl From<Error> for io::Error {
    /// Convert the [`Error`] to an [`io::Error`], preserving the original
    /// [`Error`] as the ["inner error"]. Note that this also makes the display
    /// of the error include the context.
    ///
    /// This is different from [`into_io_error`] which returns the original
    /// [`io::Error`].
    ///
    /// [`Error`]: struct.Error.html
    /// [`io::Error`]: https://doc.rust-lang.org/stable/std/io/struct.Error.html
    /// ["inner error"]: https://doc.rust-lang.org/std/io/struct.Error.html#method.into_inner
    /// [`into_io_error`]: struct.WalkDir.html#method.into_io_error
    fn from(walk_err: Error) -> io::Error {
        let kind = match walk_err {
            Error { inner: ErrorInner::Io { ref err, .. }, .. } => {
                err.kind()
            }
            Error { inner: ErrorInner::Loop { .. }, .. } => {
                io::ErrorKind::Other
            }
        };
        io::Error::new(kind, walk_err)
    }
}

#[cfg(unix)]
fn device_num<P: AsRef<Path>>(path: P)-> std::io::Result<u64> {
    use std::os::unix::fs::MetadataExt;

    path.as_ref().metadata().map(|md| md.dev())
}

 #[cfg(windows)]
fn device_num<P: AsRef<Path>>(path: P) -> std::io::Result<u64> {
    use winapi_util::{Handle, file};

    let h = Handle::from_path_any(path)?;
    file::information(h).map(|info| info.volume_serial_number())
}

#[cfg(not(any(unix, windows)))]
fn device_num<P: AsRef<Path>>(_: P)-> std::io::Result<u64> {
    Err(io::Error::new(
        io::ErrorKind::Other,
        "walkdir: same_file_system option not supported on this platform",
    ))
}