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
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
//! Utilities for formatting and printing strings.

#![stable(feature = "rust1", since = "1.0.0")]

use crate::cell::{UnsafeCell, Cell, RefCell, Ref, RefMut};
use crate::marker::PhantomData;
use crate::mem;
use crate::num::flt2dec;
use crate::ops::Deref;
use crate::result;
use crate::slice;
use crate::str;

mod float;
mod num;
mod builders;

#[stable(feature = "fmt_flags_align", since = "1.28.0")]
/// Possible alignments returned by `Formatter::align`
#[derive(Debug)]
pub enum Alignment {
    #[stable(feature = "fmt_flags_align", since = "1.28.0")]
    /// Indication that contents should be left-aligned.
    Left,
    #[stable(feature = "fmt_flags_align", since = "1.28.0")]
    /// Indication that contents should be right-aligned.
    Right,
    #[stable(feature = "fmt_flags_align", since = "1.28.0")]
    /// Indication that contents should be center-aligned.
    Center,
}

#[stable(feature = "debug_builders", since = "1.2.0")]
pub use self::builders::{DebugStruct, DebugTuple, DebugSet, DebugList, DebugMap};

#[unstable(feature = "fmt_internals", reason = "internal to format_args!",
           issue = "0")]
#[doc(hidden)]
pub mod rt {
    pub mod v1;
}

/// The type returned by formatter methods.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// #[derive(Debug)]
/// struct Triangle {
///     a: f32,
///     b: f32,
///     c: f32
/// }
///
/// impl fmt::Display for Triangle {
///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
///         write!(f, "({}, {}, {})", self.a, self.b, self.c)
///     }
/// }
///
/// let pythagorean_triple = Triangle { a: 3.0, b: 4.0, c: 5.0 };
///
/// println!("{}", pythagorean_triple);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub type Result = result::Result<(), Error>;

/// The error type which is returned from formatting a message into a stream.
///
/// This type does not support transmission of an error other than that an error
/// occurred. Any extra information must be arranged to be transmitted through
/// some other means.
///
/// An important thing to remember is that the type `fmt::Error` should not be
/// confused with [`std::io::Error`] or [`std::error::Error`], which you may also
/// have in scope.
///
/// [`std::io::Error`]: ../../std/io/struct.Error.html
/// [`std::error::Error`]: ../../std/error/trait.Error.html
///
/// # Examples
///
/// ```rust
/// use std::fmt::{self, write};
///
/// let mut output = String::new();
/// if let Err(fmt::Error) = write(&mut output, format_args!("Hello {}!", "world")) {
///     panic!("An error occurred");
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Copy, Clone, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct Error;

/// A collection of methods that are required to format a message into a stream.
///
/// This trait is the type which this modules requires when formatting
/// information. This is similar to the standard library's [`io::Write`] trait,
/// but it is only intended for use in libcore.
///
/// This trait should generally not be implemented by consumers of the standard
/// library. The [`write!`] macro accepts an instance of [`io::Write`], and the
/// [`io::Write`] trait is favored over implementing this trait.
///
/// [`write!`]: ../../std/macro.write.html
/// [`io::Write`]: ../../std/io/trait.Write.html
#[stable(feature = "rust1", since = "1.0.0")]
pub trait Write {
    /// Writes a slice of bytes into this writer, returning whether the write
    /// succeeded.
    ///
    /// This method can only succeed if the entire byte slice was successfully
    /// written, and this method will not return until all data has been
    /// written or an error occurs.
    ///
    /// # Errors
    ///
    /// This function will return an instance of [`Error`] on error.
    ///
    /// [`Error`]: struct.Error.html
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fmt::{Error, Write};
    ///
    /// fn writer<W: Write>(f: &mut W, s: &str) -> Result<(), Error> {
    ///     f.write_str(s)
    /// }
    ///
    /// let mut buf = String::new();
    /// writer(&mut buf, "hola").unwrap();
    /// assert_eq!(&buf, "hola");
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    fn write_str(&mut self, s: &str) -> Result;

    /// Writes a [`char`] into this writer, returning whether the write succeeded.
    ///
    /// A single [`char`] may be encoded as more than one byte.
    /// This method can only succeed if the entire byte sequence was successfully
    /// written, and this method will not return until all data has been
    /// written or an error occurs.
    ///
    /// # Errors
    ///
    /// This function will return an instance of [`Error`] on error.
    ///
    /// [`char`]: ../../std/primitive.char.html
    /// [`Error`]: struct.Error.html
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fmt::{Error, Write};
    ///
    /// fn writer<W: Write>(f: &mut W, c: char) -> Result<(), Error> {
    ///     f.write_char(c)
    /// }
    ///
    /// let mut buf = String::new();
    /// writer(&mut buf, 'a').unwrap();
    /// writer(&mut buf, 'b').unwrap();
    /// assert_eq!(&buf, "ab");
    /// ```
    #[stable(feature = "fmt_write_char", since = "1.1.0")]
    fn write_char(&mut self, c: char) -> Result {
        self.write_str(c.encode_utf8(&mut [0; 4]))
    }

    /// Glue for usage of the [`write!`] macro with implementors of this trait.
    ///
    /// This method should generally not be invoked manually, but rather through
    /// the [`write!`] macro itself.
    ///
    /// [`write!`]: ../../std/macro.write.html
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fmt::{Error, Write};
    ///
    /// fn writer<W: Write>(f: &mut W, s: &str) -> Result<(), Error> {
    ///     f.write_fmt(format_args!("{}", s))
    /// }
    ///
    /// let mut buf = String::new();
    /// writer(&mut buf, "world").unwrap();
    /// assert_eq!(&buf, "world");
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    fn write_fmt(mut self: &mut Self, args: Arguments<'_>) -> Result {
        write(&mut self, args)
    }
}

#[stable(feature = "fmt_write_blanket_impl", since = "1.4.0")]
impl<W: Write + ?Sized> Write for &mut W {
    fn write_str(&mut self, s: &str) -> Result {
        (**self).write_str(s)
    }

    fn write_char(&mut self, c: char) -> Result {
        (**self).write_char(c)
    }

    fn write_fmt(&mut self, args: Arguments<'_>) -> Result {
        (**self).write_fmt(args)
    }
}

/// Configuration for formatting.
///
/// A `Formatter` represents various options related to formatting. Users do not
/// construct `Formatter`s directly; a mutable reference to one is passed to
/// the `fmt` method of all formatting traits, like [`Debug`] and [`Display`].
///
/// To interact with a `Formatter`, you'll call various methods to change the
/// various options related to formatting. For examples, please see the
/// documentation of the methods defined on `Formatter` below.
///
/// [`Debug`]: trait.Debug.html
/// [`Display`]: trait.Display.html
#[allow(missing_debug_implementations)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Formatter<'a> {
    flags: u32,
    fill: char,
    align: rt::v1::Alignment,
    width: Option<usize>,
    precision: Option<usize>,

    buf: &'a mut (dyn Write+'a),
    curarg: slice::Iter<'a, ArgumentV1<'a>>,
    args: &'a [ArgumentV1<'a>],
}

// NB. Argument is essentially an optimized partially applied formatting function,
// equivalent to `exists T.(&T, fn(&T, &mut Formatter<'_>) -> Result`.

struct Void {
    _priv: (),
    /// Erases all oibits, because `Void` erases the type of the object that
    /// will be used to produce formatted output. Since we do not know what
    /// oibits the real types have (and they can have any or none), we need to
    /// take the most conservative approach and forbid all oibits.
    ///
    /// It was added after #45197 showed that one could share a `!Sync`
    /// object across threads by passing it into `format_args!`.
    _oibit_remover: PhantomData<*mut dyn Fn()>,
}

/// This struct represents the generic "argument" which is taken by the Xprintf
/// family of functions. It contains a function to format the given value. At
/// compile time it is ensured that the function and the value have the correct
/// types, and then this struct is used to canonicalize arguments to one type.
#[derive(Copy, Clone)]
#[allow(missing_debug_implementations)]
#[unstable(feature = "fmt_internals", reason = "internal to format_args!",
           issue = "0")]
#[doc(hidden)]
pub struct ArgumentV1<'a> {
    value: &'a Void,
    formatter: fn(&Void, &mut Formatter<'_>) -> Result,
}

impl<'a> ArgumentV1<'a> {
    #[inline(never)]
    fn show_usize(x: &usize, f: &mut Formatter<'_>) -> Result {
        Display::fmt(x, f)
    }

    #[doc(hidden)]
    #[unstable(feature = "fmt_internals", reason = "internal to format_args!",
               issue = "0")]
    pub fn new<'b, T>(x: &'b T,
                      f: fn(&T, &mut Formatter<'_>) -> Result) -> ArgumentV1<'b> {
        unsafe {
            ArgumentV1 {
                formatter: mem::transmute(f),
                value: mem::transmute(x)
            }
        }
    }

    #[doc(hidden)]
    #[unstable(feature = "fmt_internals", reason = "internal to format_args!",
               issue = "0")]
    pub fn from_usize(x: &usize) -> ArgumentV1<'_> {
        ArgumentV1::new(x, ArgumentV1::show_usize)
    }

    fn as_usize(&self) -> Option<usize> {
        if self.formatter as usize == ArgumentV1::show_usize as usize {
            Some(unsafe { *(self.value as *const _ as *const usize) })
        } else {
            None
        }
    }
}

// flags available in the v1 format of format_args
#[derive(Copy, Clone)]
enum FlagV1 { SignPlus, SignMinus, Alternate, SignAwareZeroPad, DebugLowerHex, DebugUpperHex }

impl<'a> Arguments<'a> {
    /// When using the format_args!() macro, this function is used to generate the
    /// Arguments structure.
    #[doc(hidden)] #[inline]
    #[unstable(feature = "fmt_internals", reason = "internal to format_args!",
               issue = "0")]
    pub fn new_v1(pieces: &'a [&'a str],
                  args: &'a [ArgumentV1<'a>]) -> Arguments<'a> {
        Arguments {
            pieces,
            fmt: None,
            args,
        }
    }

    /// This function is used to specify nonstandard formatting parameters.
    /// The `pieces` array must be at least as long as `fmt` to construct
    /// a valid Arguments structure. Also, any `Count` within `fmt` that is
    /// `CountIsParam` or `CountIsNextParam` has to point to an argument
    /// created with `argumentusize`. However, failing to do so doesn't cause
    /// unsafety, but will ignore invalid .
    #[doc(hidden)] #[inline]
    #[unstable(feature = "fmt_internals", reason = "internal to format_args!",
               issue = "0")]
    pub fn new_v1_formatted(pieces: &'a [&'a str],
                            args: &'a [ArgumentV1<'a>],
                            fmt: &'a [rt::v1::Argument]) -> Arguments<'a> {
        Arguments {
            pieces,
            fmt: Some(fmt),
            args,
        }
    }

    /// Estimates the length of the formatted text.
    ///
    /// This is intended to be used for setting initial `String` capacity
    /// when using `format!`. Note: this is neither the lower nor upper bound.
    #[doc(hidden)] #[inline]
    #[unstable(feature = "fmt_internals", reason = "internal to format_args!",
               issue = "0")]
    pub fn estimated_capacity(&self) -> usize {
        let pieces_length: usize = self.pieces.iter()
            .map(|x| x.len()).sum();

        if self.args.is_empty() {
            pieces_length
        } else if self.pieces[0] == "" && pieces_length < 16 {
            // If the format string starts with an argument,
            // don't preallocate anything, unless length
            // of pieces is significant.
            0
        } else {
            // There are some arguments, so any additional push
            // will reallocate the string. To avoid that,
            // we're "pre-doubling" the capacity here.
            pieces_length.checked_mul(2).unwrap_or(0)
        }
    }
}

/// This structure represents a safely precompiled version of a format string
/// and its arguments. This cannot be generated at runtime because it cannot
/// safely be done, so no constructors are given and the fields are private
/// to prevent modification.
///
/// The [`format_args!`] macro will safely create an instance of this structure.
/// The macro validates the format string at compile-time so usage of the
/// [`write`] and [`format`] functions can be safely performed.
///
/// You can use the `Arguments<'a>` that [`format_args!`] returns in `Debug`
/// and `Display` contexts as seen below. The example also shows that `Debug`
/// and `Display` format to the same thing: the interpolated format string
/// in `format_args!`.
///
/// ```rust
/// let debug = format!("{:?}", format_args!("{} foo {:?}", 1, 2));
/// let display = format!("{}", format_args!("{} foo {:?}", 1, 2));
/// assert_eq!("1 foo 2", display);
/// assert_eq!(display, debug);
/// ```
///
/// [`format_args!`]: ../../std/macro.format_args.html
/// [`format`]: ../../std/fmt/fn.format.html
/// [`write`]: ../../std/fmt/fn.write.html
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Copy, Clone)]
pub struct Arguments<'a> {
    // Format string pieces to print.
    pieces: &'a [&'a str],

    // Placeholder specs, or `None` if all specs are default (as in "{}{}").
    fmt: Option<&'a [rt::v1::Argument]>,

    // Dynamic arguments for interpolation, to be interleaved with string
    // pieces. (Every argument is preceded by a string piece.)
    args: &'a [ArgumentV1<'a>],
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for Arguments<'_> {
    fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
        Display::fmt(self, fmt)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Display for Arguments<'_> {
    fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
        write(fmt.buf, *self)
    }
}

/// `?` formatting.
///
/// `Debug` should format the output in a programmer-facing, debugging context.
///
/// Generally speaking, you should just `derive` a `Debug` implementation.
///
/// When used with the alternate format specifier `#?`, the output is pretty-printed.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// This trait can be used with `#[derive]` if all fields implement `Debug`. When
/// `derive`d for structs, it will use the name of the `struct`, then `{`, then a
/// comma-separated list of each field's name and `Debug` value, then `}`. For
/// `enum`s, it will use the name of the variant and, if applicable, `(`, then the
/// `Debug` values of the fields, then `)`.
///
/// # Examples
///
/// Deriving an implementation:
///
/// ```
/// #[derive(Debug)]
/// struct Point {
///     x: i32,
///     y: i32,
/// }
///
/// let origin = Point { x: 0, y: 0 };
///
/// println!("The origin is: {:?}", origin);
/// ```
///
/// Manually implementing:
///
/// ```
/// use std::fmt;
///
/// struct Point {
///     x: i32,
///     y: i32,
/// }
///
/// impl fmt::Debug for Point {
///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
///         write!(f, "Point {{ x: {}, y: {} }}", self.x, self.y)
///     }
/// }
///
/// let origin = Point { x: 0, y: 0 };
///
/// println!("The origin is: {:?}", origin);
/// ```
///
/// This outputs:
///
/// ```text
/// The origin is: Point { x: 0, y: 0 }
/// ```
///
/// There are a number of `debug_*` methods on [`Formatter`] to help you with manual
/// implementations, such as [`debug_struct`][debug_struct].
///
/// `Debug` implementations using either `derive` or the debug builder API
/// on [`Formatter`] support pretty-printing using the alternate flag: `{:#?}`.
///
/// [debug_struct]: ../../std/fmt/struct.Formatter.html#method.debug_struct
/// [`Formatter`]: ../../std/fmt/struct.Formatter.html
///
/// Pretty-printing with `#?`:
///
/// ```
/// #[derive(Debug)]
/// struct Point {
///     x: i32,
///     y: i32,
/// }
///
/// let origin = Point { x: 0, y: 0 };
///
/// println!("The origin is: {:#?}", origin);
/// ```
///
/// This outputs:
///
/// ```text
/// The origin is: Point {
///     x: 0,
///     y: 0
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_on_unimplemented(
    on(crate_local, label="`{Self}` cannot be formatted using `{{:?}}`",
                    note="add `#[derive(Debug)]` or manually implement `{Debug}`"),
    message="`{Self}` doesn't implement `{Debug}`",
    label="`{Self}` cannot be formatted using `{{:?}}` because it doesn't implement `{Debug}`",
)]
#[doc(alias = "{:?}")]
#[cfg_attr(boostrap_stdarch_ignore_this, lang = "debug_trait")]
#[cfg_attr(not(boostrap_stdarch_ignore_this), rustc_diagnostic_item = "debug_trait")]
pub trait Debug {
    /// Formats the value using the given formatter.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fmt;
    ///
    /// struct Position {
    ///     longitude: f32,
    ///     latitude: f32,
    /// }
    ///
    /// impl fmt::Debug for Position {
    ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
    ///         write!(f, "({:?}, {:?})", self.longitude, self.latitude)
    ///     }
    /// }
    ///
    /// assert_eq!("(1.987, 2.983)".to_owned(),
    ///            format!("{:?}", Position { longitude: 1.987, latitude: 2.983, }));
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}

// Separate module to reexport the macro `Debug` from prelude without the trait `Debug`.
pub(crate) mod macros {
    /// Derive macro generating an impl of the trait `Debug`.
    #[rustc_builtin_macro]
    #[cfg_attr(boostrap_stdarch_ignore_this, rustc_macro_transparency = "semitransparent")]
    #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
    #[allow_internal_unstable(core_intrinsics)]
    pub macro Debug($item:item) { /* compiler built-in */ }
}
#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
#[doc(inline)]
pub use macros::Debug;

/// Format trait for an empty format, `{}`.
///
/// `Display` is similar to [`Debug`][debug], but `Display` is for user-facing
/// output, and so cannot be derived.
///
/// [debug]: trait.Debug.html
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Implementing `Display` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Point {
///     x: i32,
///     y: i32,
/// }
///
/// impl fmt::Display for Point {
///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
///         write!(f, "({}, {})", self.x, self.y)
///     }
/// }
///
/// let origin = Point { x: 0, y: 0 };
///
/// println!("The origin is: {}", origin);
/// ```
#[rustc_on_unimplemented(
    on(
        _Self="std::path::Path",
        label="`{Self}` cannot be formatted with the default formatter; call `.display()` on it",
        note="call `.display()` or `.to_string_lossy()` to safely print paths, \
              as they may contain non-Unicode data"
    ),
    message="`{Self}` doesn't implement `{Display}`",
    label="`{Self}` cannot be formatted with the default formatter",
    note="in format strings you may be able to use `{{:?}}` (or {{:#?}} for pretty-print) instead",
)]
#[doc(alias = "{}")]
#[stable(feature = "rust1", since = "1.0.0")]
pub trait Display {
    /// Formats the value using the given formatter.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fmt;
    ///
    /// struct Position {
    ///     longitude: f32,
    ///     latitude: f32,
    /// }
    ///
    /// impl fmt::Display for Position {
    ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
    ///         write!(f, "({}, {})", self.longitude, self.latitude)
    ///     }
    /// }
    ///
    /// assert_eq!("(1.987, 2.983)".to_owned(),
    ///            format!("{}", Position { longitude: 1.987, latitude: 2.983, }));
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}

/// `o` formatting.
///
/// The `Octal` trait should format its output as a number in base-8.
///
/// For primitive signed integers (`i8` to `i128`, and `isize`),
/// negative values are formatted as the two’s complement representation.
///
/// The alternate flag, `#`, adds a `0o` in front of the output.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with `i32`:
///
/// ```
/// let x = 42; // 42 is '52' in octal
///
/// assert_eq!(format!("{:o}", x), "52");
/// assert_eq!(format!("{:#o}", x), "0o52");
///
/// assert_eq!(format!("{:o}", -16), "37777777760");
/// ```
///
/// Implementing `Octal` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::Octal for Length {
///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
///         let val = self.0;
///
///         write!(f, "{:o}", val) // delegate to i32's implementation
///     }
/// }
///
/// let l = Length(9);
///
/// println!("l as octal is: {:o}", l);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait Octal {
    /// Formats the value using the given formatter.
    #[stable(feature = "rust1", since = "1.0.0")]
    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}

/// `b` formatting.
///
/// The `Binary` trait should format its output as a number in binary.
///
/// For primitive signed integers ([`i8`] to [`i128`], and [`isize`]),
/// negative values are formatted as the two’s complement representation.
///
/// The alternate flag, `#`, adds a `0b` in front of the output.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// # Examples
///
/// Basic usage with [`i32`]:
///
/// ```
/// let x = 42; // 42 is '101010' in binary
///
/// assert_eq!(format!("{:b}", x), "101010");
/// assert_eq!(format!("{:#b}", x), "0b101010");
///
/// assert_eq!(format!("{:b}", -16), "11111111111111111111111111110000");
/// ```
///
/// Implementing `Binary` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::Binary for Length {
///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
///         let val = self.0;
///
///         write!(f, "{:b}", val) // delegate to i32's implementation
///     }
/// }
///
/// let l = Length(107);
///
/// println!("l as binary is: {:b}", l);
/// ```
///
/// [module]: ../../std/fmt/index.html
/// [`i8`]: ../../std/primitive.i8.html
/// [`i128`]: ../../std/primitive.i128.html
/// [`isize`]: ../../std/primitive.isize.html
/// [`i32`]: ../../std/primitive.i32.html
#[stable(feature = "rust1", since = "1.0.0")]
pub trait Binary {
    /// Formats the value using the given formatter.
    #[stable(feature = "rust1", since = "1.0.0")]
    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}

/// `x` formatting.
///
/// The `LowerHex` trait should format its output as a number in hexadecimal, with `a` through `f`
/// in lower case.
///
/// For primitive signed integers (`i8` to `i128`, and `isize`),
/// negative values are formatted as the two’s complement representation.
///
/// The alternate flag, `#`, adds a `0x` in front of the output.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with `i32`:
///
/// ```
/// let x = 42; // 42 is '2a' in hex
///
/// assert_eq!(format!("{:x}", x), "2a");
/// assert_eq!(format!("{:#x}", x), "0x2a");
///
/// assert_eq!(format!("{:x}", -16), "fffffff0");
/// ```
///
/// Implementing `LowerHex` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::LowerHex for Length {
///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
///         let val = self.0;
///
///         write!(f, "{:x}", val) // delegate to i32's implementation
///     }
/// }
///
/// let l = Length(9);
///
/// println!("l as hex is: {:x}", l);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait LowerHex {
    /// Formats the value using the given formatter.
    #[stable(feature = "rust1", since = "1.0.0")]
    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}

/// `X` formatting.
///
/// The `UpperHex` trait should format its output as a number in hexadecimal, with `A` through `F`
/// in upper case.
///
/// For primitive signed integers (`i8` to `i128`, and `isize`),
/// negative values are formatted as the two’s complement representation.
///
/// The alternate flag, `#`, adds a `0x` in front of the output.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with `i32`:
///
/// ```
/// let x = 42; // 42 is '2A' in hex
///
/// assert_eq!(format!("{:X}", x), "2A");
/// assert_eq!(format!("{:#X}", x), "0x2A");
///
/// assert_eq!(format!("{:X}", -16), "FFFFFFF0");
/// ```
///
/// Implementing `UpperHex` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::UpperHex for Length {
///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
///         let val = self.0;
///
///         write!(f, "{:X}", val) // delegate to i32's implementation
///     }
/// }
///
/// let l = Length(9);
///
/// println!("l as hex is: {:X}", l);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait UpperHex {
    /// Formats the value using the given formatter.
    #[stable(feature = "rust1", since = "1.0.0")]
    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}

/// `p` formatting.
///
/// The `Pointer` trait should format its output as a memory location. This is commonly presented
/// as hexadecimal.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with `&i32`:
///
/// ```
/// let x = &42;
///
/// let address = format!("{:p}", x); // this produces something like '0x7f06092ac6d0'
/// ```
///
/// Implementing `Pointer` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::Pointer for Length {
///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
///         // use `as` to convert to a `*const T`, which implements Pointer, which we can use
///
///         write!(f, "{:p}", self as *const Length)
///     }
/// }
///
/// let l = Length(42);
///
/// println!("l is in memory here: {:p}", l);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait Pointer {
    /// Formats the value using the given formatter.
    #[stable(feature = "rust1", since = "1.0.0")]
    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}

/// `e` formatting.
///
/// The `LowerExp` trait should format its output in scientific notation with a lower-case `e`.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with `f64`:
///
/// ```
/// let x = 42.0; // 42.0 is '4.2e1' in scientific notation
///
/// assert_eq!(format!("{:e}", x), "4.2e1");
/// ```
///
/// Implementing `LowerExp` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::LowerExp for Length {
///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
///         let val = self.0;
///         write!(f, "{}e1", val / 10)
///     }
/// }
///
/// let l = Length(100);
///
/// println!("l in scientific notation is: {:e}", l);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait LowerExp {
    /// Formats the value using the given formatter.
    #[stable(feature = "rust1", since = "1.0.0")]
    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}

/// `E` formatting.
///
/// The `UpperExp` trait should format its output in scientific notation with an upper-case `E`.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with `f64`:
///
/// ```
/// let x = 42.0; // 42.0 is '4.2E1' in scientific notation
///
/// assert_eq!(format!("{:E}", x), "4.2E1");
/// ```
///
/// Implementing `UpperExp` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::UpperExp for Length {
///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
///         let val = self.0;
///         write!(f, "{}E1", val / 10)
///     }
/// }
///
/// let l = Length(100);
///
/// println!("l in scientific notation is: {:E}", l);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait UpperExp {
    /// Formats the value using the given formatter.
    #[stable(feature = "rust1", since = "1.0.0")]
    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}

/// The `write` function takes an output stream, and an `Arguments` struct
/// that can be precompiled with the `format_args!` macro.
///
/// The arguments will be formatted according to the specified format string
/// into the output stream provided.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::fmt;
///
/// let mut output = String::new();
/// fmt::write(&mut output, format_args!("Hello {}!", "world"))
///     .expect("Error occurred while trying to write in String");
/// assert_eq!(output, "Hello world!");
/// ```
///
/// Please note that using [`write!`] might be preferable. Example:
///
/// ```
/// use std::fmt::Write;
///
/// let mut output = String::new();
/// write!(&mut output, "Hello {}!", "world")
///     .expect("Error occurred while trying to write in String");
/// assert_eq!(output, "Hello world!");
/// ```
///
/// [`write!`]: ../../std/macro.write.html
#[stable(feature = "rust1", since = "1.0.0")]
pub fn write(output: &mut dyn Write, args: Arguments<'_>) -> Result {
    let mut formatter = Formatter {
        flags: 0,
        width: None,
        precision: None,
        buf: output,
        align: rt::v1::Alignment::Unknown,
        fill: ' ',
        args: args.args,
        curarg: args.args.iter(),
    };

    let mut idx = 0;

    match args.fmt {
        None => {
            // We can use default formatting parameters for all arguments.
            for (arg, piece) in args.args.iter().zip(args.pieces.iter()) {
                formatter.buf.write_str(*piece)?;
                (arg.formatter)(arg.value, &mut formatter)?;
                idx += 1;
            }
        }
        Some(fmt) => {
            // Every spec has a corresponding argument that is preceded by
            // a string piece.
            for (arg, piece) in fmt.iter().zip(args.pieces.iter()) {
                formatter.buf.write_str(*piece)?;
                formatter.run(arg)?;
                idx += 1;
            }
        }
    }

    // There can be only one trailing string piece left.
    if let Some(piece) = args.pieces.get(idx) {
        formatter.buf.write_str(*piece)?;
    }

    Ok(())
}

/// Padding after the end of something. Returned by `Formatter::padding`.
#[must_use = "don't forget to write the post padding"]
struct PostPadding {
    fill: char,
    padding: usize,
}

impl PostPadding {
    fn new(fill: char, padding: usize) -> PostPadding {
        PostPadding { fill, padding }
    }

    /// Write this post padding.
    fn write(self, buf: &mut dyn Write) -> Result {
        for _ in 0..self.padding {
            buf.write_char(self.fill)?;
        }
        Ok(())
    }
}

impl<'a> Formatter<'a> {
    fn wrap_buf<'b, 'c, F>(&'b mut self, wrap: F) -> Formatter<'c>
        where 'b: 'c, F: FnOnce(&'b mut (dyn Write+'b)) -> &'c mut (dyn Write+'c)
    {
        Formatter {
            // We want to change this
            buf: wrap(self.buf),

            // And preserve these
            flags: self.flags,
            fill: self.fill,
            align: self.align,
            width: self.width,
            precision: self.precision,

            // These only exist in the struct for the `run` method,
            // which won’t be used together with this method.
            curarg: self.curarg.clone(),
            args: self.args,
        }
    }

    // First up is the collection of functions used to execute a format string
    // at runtime. This consumes all of the compile-time statics generated by
    // the format! syntax extension.
    fn run(&mut self, arg: &rt::v1::Argument) -> Result {
        // Fill in the format parameters into the formatter
        self.fill = arg.format.fill;
        self.align = arg.format.align;
        self.flags = arg.format.flags;
        self.width = self.getcount(&arg.format.width);
        self.precision = self.getcount(&arg.format.precision);

        // Extract the correct argument
        let value = match arg.position {
            rt::v1::Position::Next => { *self.curarg.next().unwrap() }
            rt::v1::Position::At(i) => self.args[i],
        };

        // Then actually do some printing
        (value.formatter)(value.value, self)
    }

    fn getcount(&mut self, cnt: &rt::v1::Count) -> Option<usize> {
        match *cnt {
            rt::v1::Count::Is(n) => Some(n),
            rt::v1::Count::Implied => None,
            rt::v1::Count::Param(i) => {
                self.args[i].as_usize()
            }
            rt::v1::Count::NextParam => {
                self.curarg.next()?.as_usize()
            }
        }
    }

    // Helper methods used for padding and processing formatting arguments that
    // all formatting traits can use.

    /// Performs the correct padding for an integer which has already been
    /// emitted into a str. The str should *not* contain the sign for the
    /// integer, that will be added by this method.
    ///
    /// # Arguments
    ///
    /// * is_nonnegative - whether the original integer was either positive or zero.
    /// * prefix - if the '#' character (Alternate) is provided, this
    ///   is the prefix to put in front of the number.
    /// * buf - the byte array that the number has been formatted into
    ///
    /// This function will correctly account for the flags provided as well as
    /// the minimum width. It will not take precision into account.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fmt;
    ///
    /// struct Foo { nb: i32 };
    ///
    /// impl Foo {
    ///     fn new(nb: i32) -> Foo {
    ///         Foo {
    ///             nb,
    ///         }
    ///     }
    /// }
    ///
    /// impl fmt::Display for Foo {
    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
    ///         // We need to remove "-" from the number output.
    ///         let tmp = self.nb.abs().to_string();
    ///
    ///         formatter.pad_integral(self.nb > 0, "Foo ", &tmp)
    ///     }
    /// }
    ///
    /// assert_eq!(&format!("{}", Foo::new(2)), "2");
    /// assert_eq!(&format!("{}", Foo::new(-1)), "-1");
    /// assert_eq!(&format!("{:#}", Foo::new(-1)), "-Foo 1");
    /// assert_eq!(&format!("{:0>#8}", Foo::new(-1)), "00-Foo 1");
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn pad_integral(&mut self,
                        is_nonnegative: bool,
                        prefix: &str,
                        buf: &str)
                        -> Result {
        let mut width = buf.len();

        let mut sign = None;
        if !is_nonnegative {
            sign = Some('-'); width += 1;
        } else if self.sign_plus() {
            sign = Some('+'); width += 1;
        }

        let prefix = if self.alternate() {
            width += prefix.chars().count();
            Some(prefix)
        } else {
            None
        };

        // Writes the sign if it exists, and then the prefix if it was requested
        #[inline(never)]
        fn write_prefix(f: &mut Formatter<'_>, sign: Option<char>, prefix: Option<&str>) -> Result {
            if let Some(c) = sign {
                f.buf.write_char(c)?;
            }
            if let Some(prefix) = prefix {
                f.buf.write_str(prefix)
            } else {
                Ok(())
            }
        }

        // The `width` field is more of a `min-width` parameter at this point.
        match self.width {
            // If there's no minimum length requirements then we can just
            // write the bytes.
            None => {
                write_prefix(self, sign, prefix)?;
                self.buf.write_str(buf)
            }
            // Check if we're over the minimum width, if so then we can also
            // just write the bytes.
            Some(min) if width >= min => {
                write_prefix(self, sign, prefix)?;
                self.buf.write_str(buf)
            }
            // The sign and prefix goes before the padding if the fill character
            // is zero
            Some(min) if self.sign_aware_zero_pad() => {
                self.fill = '0';
                self.align = rt::v1::Alignment::Right;
                write_prefix(self, sign, prefix)?;
                let post_padding = self.padding(min - width, rt::v1::Alignment::Right)?;
                self.buf.write_str(buf)?;
                post_padding.write(self.buf)
            }
            // Otherwise, the sign and prefix goes after the padding
            Some(min) => {
                let post_padding = self.padding(min - width, rt::v1::Alignment::Right)?;
                write_prefix(self, sign, prefix)?;
                self.buf.write_str(buf)?;
                post_padding.write(self.buf)
            }
        }
    }

    /// This function takes a string slice and emits it to the internal buffer
    /// after applying the relevant formatting flags specified. The flags
    /// recognized for generic strings are:
    ///
    /// * width - the minimum width of what to emit
    /// * fill/align - what to emit and where to emit it if the string
    ///                provided needs to be padded
    /// * precision - the maximum length to emit, the string is truncated if it
    ///               is longer than this length
    ///
    /// Notably this function ignores the `flag` parameters.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fmt;
    ///
    /// struct Foo;
    ///
    /// impl fmt::Display for Foo {
    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
    ///         formatter.pad("Foo")
    ///     }
    /// }
    ///
    /// assert_eq!(&format!("{:<4}", Foo), "Foo ");
    /// assert_eq!(&format!("{:0>4}", Foo), "0Foo");
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn pad(&mut self, s: &str) -> Result {
        // Make sure there's a fast path up front
        if self.width.is_none() && self.precision.is_none() {
            return self.buf.write_str(s);
        }
        // The `precision` field can be interpreted as a `max-width` for the
        // string being formatted.
        let s = if let Some(max) = self.precision {
            // If our string is longer that the precision, then we must have
            // truncation. However other flags like `fill`, `width` and `align`
            // must act as always.
            if let Some((i, _)) = s.char_indices().nth(max) {
                // LLVM here can't prove that `..i` won't panic `&s[..i]`, but
                // we know that it can't panic. Use `get` + `unwrap_or` to avoid
                // `unsafe` and otherwise don't emit any panic-related code
                // here.
                s.get(..i).unwrap_or(&s)
            } else {
                &s
            }
        } else {
            &s
        };
        // The `width` field is more of a `min-width` parameter at this point.
        match self.width {
            // If we're under the maximum length, and there's no minimum length
            // requirements, then we can just emit the string
            None => self.buf.write_str(s),
            // If we're under the maximum width, check if we're over the minimum
            // width, if so it's as easy as just emitting the string.
            Some(width) if s.chars().count() >= width => {
                self.buf.write_str(s)
            }
            // If we're under both the maximum and the minimum width, then fill
            // up the minimum width with the specified string + some alignment.
            Some(width) => {
                let align = rt::v1::Alignment::Left;
                let post_padding = self.padding(width - s.chars().count(), align)?;
                self.buf.write_str(s)?;
                post_padding.write(self.buf)
            }
        }
    }

    /// Write the pre-padding and return the unwritten post-padding. Callers are
    /// responsible for ensuring post-padding is written after the thing that is
    /// being padded.
    fn padding(
        &mut self,
        padding: usize,
        default: rt::v1::Alignment
    ) -> result::Result<PostPadding, Error> {
        let align = match self.align {
            rt::v1::Alignment::Unknown => default,
            _ => self.align
        };

        let (pre_pad, post_pad) = match align {
            rt::v1::Alignment::Left => (0, padding),
            rt::v1::Alignment::Right |
            rt::v1::Alignment::Unknown => (padding, 0),
            rt::v1::Alignment::Center => (padding / 2, (padding + 1) / 2),
        };

        for _ in 0..pre_pad {
            self.buf.write_char(self.fill)?;
        }

        Ok(PostPadding::new(self.fill, post_pad))
    }

    /// Takes the formatted parts and applies the padding.
    /// Assumes that the caller already has rendered the parts with required precision,
    /// so that `self.precision` can be ignored.
    fn pad_formatted_parts(&mut self, formatted: &flt2dec::Formatted<'_>) -> Result {
        if let Some(mut width) = self.width {
            // for the sign-aware zero padding, we render the sign first and
            // behave as if we had no sign from the beginning.
            let mut formatted = formatted.clone();
            let old_fill = self.fill;
            let old_align = self.align;
            let mut align = old_align;
            if self.sign_aware_zero_pad() {
                // a sign always goes first
                let sign = unsafe { str::from_utf8_unchecked(formatted.sign) };
                self.buf.write_str(sign)?;

                // remove the sign from the formatted parts
                formatted.sign = b"";
                width = width.saturating_sub(sign.len());
                align = rt::v1::Alignment::Right;
                self.fill = '0';
                self.align = rt::v1::Alignment::Right;
            }

            // remaining parts go through the ordinary padding process.
            let len = formatted.len();
            let ret = if width <= len { // no padding
                self.write_formatted_parts(&formatted)
            } else {
                let post_padding = self.padding(width - len, align)?;
                self.write_formatted_parts(&formatted)?;
                post_padding.write(self.buf)
            };
            self.fill = old_fill;
            self.align = old_align;
            ret
        } else {
            // this is the common case and we take a shortcut
            self.write_formatted_parts(formatted)
        }
    }

    fn write_formatted_parts(&mut self, formatted: &flt2dec::Formatted<'_>) -> Result {
        fn write_bytes(buf: &mut dyn Write, s: &[u8]) -> Result {
            buf.write_str(unsafe { str::from_utf8_unchecked(s) })
        }

        if !formatted.sign.is_empty() {
            write_bytes(self.buf, formatted.sign)?;
        }
        for part in formatted.parts {
            match *part {
                flt2dec::Part::Zero(mut nzeroes) => {
                    const ZEROES: &str = // 64 zeroes
                        "0000000000000000000000000000000000000000000000000000000000000000";
                    while nzeroes > ZEROES.len() {
                        self.buf.write_str(ZEROES)?;
                        nzeroes -= ZEROES.len();
                    }
                    if nzeroes > 0 {
                        self.buf.write_str(&ZEROES[..nzeroes])?;
                    }
                }
                flt2dec::Part::Num(mut v) => {
                    let mut s = [0; 5];
                    let len = part.len();
                    for c in s[..len].iter_mut().rev() {
                        *c = b'0' + (v % 10) as u8;
                        v /= 10;
                    }
                    write_bytes(self.buf, &s[..len])?;
                }
                flt2dec::Part::Copy(buf) => {
                    write_bytes(self.buf, buf)?;
                }
            }
        }
        Ok(())
    }

    /// Writes some data to the underlying buffer contained within this
    /// formatter.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fmt;
    ///
    /// struct Foo;
    ///
    /// impl fmt::Display for Foo {
    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
    ///         formatter.write_str("Foo")
    ///         // This is equivalent to:
    ///         // write!(formatter, "Foo")
    ///     }
    /// }
    ///
    /// assert_eq!(&format!("{}", Foo), "Foo");
    /// assert_eq!(&format!("{:0>8}", Foo), "Foo");
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn write_str(&mut self, data: &str) -> Result {
        self.buf.write_str(data)
    }

    /// Writes some formatted information into this instance.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fmt;
    ///
    /// struct Foo(i32);
    ///
    /// impl fmt::Display for Foo {
    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
    ///         formatter.write_fmt(format_args!("Foo {}", self.0))
    ///     }
    /// }
    ///
    /// assert_eq!(&format!("{}", Foo(-1)), "Foo -1");
    /// assert_eq!(&format!("{:0>8}", Foo(2)), "Foo 2");
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result {
        write(self.buf, fmt)
    }

    /// Flags for formatting
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_deprecated(since = "1.24.0",
                       reason = "use the `sign_plus`, `sign_minus`, `alternate`, \
                                 or `sign_aware_zero_pad` methods instead")]
    pub fn flags(&self) -> u32 { self.flags }

    /// Character used as 'fill' whenever there is alignment.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fmt;
    ///
    /// struct Foo;
    ///
    /// impl fmt::Display for Foo {
    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
    ///         let c = formatter.fill();
    ///         if let Some(width) = formatter.width() {
    ///             for _ in 0..width {
    ///                 write!(formatter, "{}", c)?;
    ///             }
    ///             Ok(())
    ///         } else {
    ///             write!(formatter, "{}", c)
    ///         }
    ///     }
    /// }
    ///
    /// // We set alignment to the left with ">".
    /// assert_eq!(&format!("{:G>3}", Foo), "GGG");
    /// assert_eq!(&format!("{:t>6}", Foo), "tttttt");
    /// ```
    #[stable(feature = "fmt_flags", since = "1.5.0")]
    pub fn fill(&self) -> char { self.fill }

    /// Flag indicating what form of alignment was requested.
    ///
    /// # Examples
    ///
    /// ```
    /// extern crate core;
    ///
    /// use std::fmt::{self, Alignment};
    ///
    /// struct Foo;
    ///
    /// impl fmt::Display for Foo {
    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
    ///         let s = if let Some(s) = formatter.align() {
    ///             match s {
    ///                 Alignment::Left    => "left",
    ///                 Alignment::Right   => "right",
    ///                 Alignment::Center  => "center",
    ///             }
    ///         } else {
    ///             "into the void"
    ///         };
    ///         write!(formatter, "{}", s)
    ///     }
    /// }
    ///
    /// fn main() {
    ///     assert_eq!(&format!("{:<}", Foo), "left");
    ///     assert_eq!(&format!("{:>}", Foo), "right");
    ///     assert_eq!(&format!("{:^}", Foo), "center");
    ///     assert_eq!(&format!("{}", Foo), "into the void");
    /// }
    /// ```
    #[stable(feature = "fmt_flags_align", since = "1.28.0")]
    pub fn align(&self) -> Option<Alignment> {
        match self.align {
            rt::v1::Alignment::Left => Some(Alignment::Left),
            rt::v1::Alignment::Right => Some(Alignment::Right),
            rt::v1::Alignment::Center => Some(Alignment::Center),
            rt::v1::Alignment::Unknown => None,
        }
    }

    /// Optionally specified integer width that the output should be.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fmt;
    ///
    /// struct Foo(i32);
    ///
    /// impl fmt::Display for Foo {
    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
    ///         if let Some(width) = formatter.width() {
    ///             // If we received a width, we use it
    ///             write!(formatter, "{:width$}", &format!("Foo({})", self.0), width = width)
    ///         } else {
    ///             // Otherwise we do nothing special
    ///             write!(formatter, "Foo({})", self.0)
    ///         }
    ///     }
    /// }
    ///
    /// assert_eq!(&format!("{:10}", Foo(23)), "Foo(23)   ");
    /// assert_eq!(&format!("{}", Foo(23)), "Foo(23)");
    /// ```
    #[stable(feature = "fmt_flags", since = "1.5.0")]
    pub fn width(&self) -> Option<usize> { self.width }

    /// Optionally specified precision for numeric types.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fmt;
    ///
    /// struct Foo(f32);
    ///
    /// impl fmt::Display for Foo {
    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
    ///         if let Some(precision) = formatter.precision() {
    ///             // If we received a precision, we use it.
    ///             write!(formatter, "Foo({1:.*})", precision, self.0)
    ///         } else {
    ///             // Otherwise we default to 2.
    ///             write!(formatter, "Foo({:.2})", self.0)
    ///         }
    ///     }
    /// }
    ///
    /// assert_eq!(&format!("{:.4}", Foo(23.2)), "Foo(23.2000)");
    /// assert_eq!(&format!("{}", Foo(23.2)), "Foo(23.20)");
    /// ```
    #[stable(feature = "fmt_flags", since = "1.5.0")]
    pub fn precision(&self) -> Option<usize> { self.precision }

    /// Determines if the `+` flag was specified.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fmt;
    ///
    /// struct Foo(i32);
    ///
    /// impl fmt::Display for Foo {
    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
    ///         if formatter.sign_plus() {
    ///             write!(formatter,
    ///                    "Foo({}{})",
    ///                    if self.0 < 0 { '-' } else { '+' },
    ///                    self.0)
    ///         } else {
    ///             write!(formatter, "Foo({})", self.0)
    ///         }
    ///     }
    /// }
    ///
    /// assert_eq!(&format!("{:+}", Foo(23)), "Foo(+23)");
    /// assert_eq!(&format!("{}", Foo(23)), "Foo(23)");
    /// ```
    #[stable(feature = "fmt_flags", since = "1.5.0")]
    pub fn sign_plus(&self) -> bool { self.flags & (1 << FlagV1::SignPlus as u32) != 0 }

    /// Determines if the `-` flag was specified.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fmt;
    ///
    /// struct Foo(i32);
    ///
    /// impl fmt::Display for Foo {
    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
    ///         if formatter.sign_minus() {
    ///             // You want a minus sign? Have one!
    ///             write!(formatter, "-Foo({})", self.0)
    ///         } else {
    ///             write!(formatter, "Foo({})", self.0)
    ///         }
    ///     }
    /// }
    ///
    /// assert_eq!(&format!("{:-}", Foo(23)), "-Foo(23)");
    /// assert_eq!(&format!("{}", Foo(23)), "Foo(23)");
    /// ```
    #[stable(feature = "fmt_flags", since = "1.5.0")]
    pub fn sign_minus(&self) -> bool { self.flags & (1 << FlagV1::SignMinus as u32) != 0 }

    /// Determines if the `#` flag was specified.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fmt;
    ///
    /// struct Foo(i32);
    ///
    /// impl fmt::Display for Foo {
    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
    ///         if formatter.alternate() {
    ///             write!(formatter, "Foo({})", self.0)
    ///         } else {
    ///             write!(formatter, "{}", self.0)
    ///         }
    ///     }
    /// }
    ///
    /// assert_eq!(&format!("{:#}", Foo(23)), "Foo(23)");
    /// assert_eq!(&format!("{}", Foo(23)), "23");
    /// ```
    #[stable(feature = "fmt_flags", since = "1.5.0")]
    pub fn alternate(&self) -> bool { self.flags & (1 << FlagV1::Alternate as u32) != 0 }

    /// Determines if the `0` flag was specified.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fmt;
    ///
    /// struct Foo(i32);
    ///
    /// impl fmt::Display for Foo {
    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
    ///         assert!(formatter.sign_aware_zero_pad());
    ///         assert_eq!(formatter.width(), Some(4));
    ///         // We ignore the formatter's options.
    ///         write!(formatter, "{}", self.0)
    ///     }
    /// }
    ///
    /// assert_eq!(&format!("{:04}", Foo(23)), "23");
    /// ```
    #[stable(feature = "fmt_flags", since = "1.5.0")]
    pub fn sign_aware_zero_pad(&self) -> bool {
        self.flags & (1 << FlagV1::SignAwareZeroPad as u32) != 0
    }

    // FIXME: Decide what public API we want for these two flags.
    // https://github.com/rust-lang/rust/issues/48584
    fn debug_lower_hex(&self) -> bool { self.flags & (1 << FlagV1::DebugLowerHex as u32) != 0 }

    fn debug_upper_hex(&self) -> bool { self.flags & (1 << FlagV1::DebugUpperHex as u32) != 0 }

    /// Creates a [`DebugStruct`] builder designed to assist with creation of
    /// [`fmt::Debug`] implementations for structs.
    ///
    /// [`DebugStruct`]: ../../std/fmt/struct.DebugStruct.html
    /// [`fmt::Debug`]: ../../std/fmt/trait.Debug.html
    ///
    /// # Examples
    ///
    /// ```rust
    /// use std::fmt;
    /// use std::net::Ipv4Addr;
    ///
    /// struct Foo {
    ///     bar: i32,
    ///     baz: String,
    ///     addr: Ipv4Addr,
    /// }
    ///
    /// impl fmt::Debug for Foo {
    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
    ///         fmt.debug_struct("Foo")
    ///             .field("bar", &self.bar)
    ///             .field("baz", &self.baz)
    ///             .field("addr", &format_args!("{}", self.addr))
    ///             .finish()
    ///     }
    /// }
    ///
    /// assert_eq!(
    ///     "Foo { bar: 10, baz: \"Hello World\", addr: 127.0.0.1 }",
    ///     format!("{:?}", Foo {
    ///         bar: 10,
    ///         baz: "Hello World".to_string(),
    ///         addr: Ipv4Addr::new(127, 0, 0, 1),
    ///     })
    /// );
    /// ```
    #[stable(feature = "debug_builders", since = "1.2.0")]
    pub fn debug_struct<'b>(&'b mut self, name: &str) -> DebugStruct<'b, 'a> {
        builders::debug_struct_new(self, name)
    }

    /// Creates a `DebugTuple` builder designed to assist with creation of
    /// `fmt::Debug` implementations for tuple structs.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use std::fmt;
    /// use std::marker::PhantomData;
    ///
    /// struct Foo<T>(i32, String, PhantomData<T>);
    ///
    /// impl<T> fmt::Debug for Foo<T> {
    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
    ///         fmt.debug_tuple("Foo")
    ///             .field(&self.0)
    ///             .field(&self.1)
    ///             .field(&format_args!("_"))
    ///             .finish()
    ///     }
    /// }
    ///
    /// assert_eq!(
    ///     "Foo(10, \"Hello\", _)",
    ///     format!("{:?}", Foo(10, "Hello".to_string(), PhantomData::<u8>))
    /// );
    /// ```
    #[stable(feature = "debug_builders", since = "1.2.0")]
    pub fn debug_tuple<'b>(&'b mut self, name: &str) -> DebugTuple<'b, 'a> {
        builders::debug_tuple_new(self, name)
    }

    /// Creates a `DebugList` builder designed to assist with creation of
    /// `fmt::Debug` implementations for list-like structures.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use std::fmt;
    ///
    /// struct Foo(Vec<i32>);
    ///
    /// impl fmt::Debug for Foo {
    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
    ///         fmt.debug_list().entries(self.0.iter()).finish()
    ///     }
    /// }
    ///
    /// // prints "[10, 11]"
    /// println!("{:?}", Foo(vec![10, 11]));
    /// ```
    #[stable(feature = "debug_builders", since = "1.2.0")]
    pub fn debug_list<'b>(&'b mut self) -> DebugList<'b, 'a> {
        builders::debug_list_new(self)
    }

    /// Creates a `DebugSet` builder designed to assist with creation of
    /// `fmt::Debug` implementations for set-like structures.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use std::fmt;
    ///
    /// struct Foo(Vec<i32>);
    ///
    /// impl fmt::Debug for Foo {
    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
    ///         fmt.debug_set().entries(self.0.iter()).finish()
    ///     }
    /// }
    ///
    /// // prints "{10, 11}"
    /// println!("{:?}", Foo(vec![10, 11]));
    /// ```
    ///
    /// [`format_args!`]: ../../std/macro.format_args.html
    ///
    /// In this more complex example, we use [`format_args!`] and `.debug_set()`
    /// to build a list of match arms:
    ///
    /// ```rust
    /// use std::fmt;
    ///
    /// struct Arm<'a, L: 'a, R: 'a>(&'a (L, R));
    /// struct Table<'a, K: 'a, V: 'a>(&'a [(K, V)], V);
    ///
    /// impl<'a, L, R> fmt::Debug for Arm<'a, L, R>
    /// where
    ///     L: 'a + fmt::Debug, R: 'a + fmt::Debug
    /// {
    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
    ///         L::fmt(&(self.0).0, fmt)?;
    ///         fmt.write_str(" => ")?;
    ///         R::fmt(&(self.0).1, fmt)
    ///     }
    /// }
    ///
    /// impl<'a, K, V> fmt::Debug for Table<'a, K, V>
    /// where
    ///     K: 'a + fmt::Debug, V: 'a + fmt::Debug
    /// {
    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
    ///         fmt.debug_set()
    ///         .entries(self.0.iter().map(Arm))
    ///         .entry(&Arm(&(format_args!("_"), &self.1)))
    ///         .finish()
    ///     }
    /// }
    /// ```
    #[stable(feature = "debug_builders", since = "1.2.0")]
    pub fn debug_set<'b>(&'b mut self) -> DebugSet<'b, 'a> {
        builders::debug_set_new(self)
    }

    /// Creates a `DebugMap` builder designed to assist with creation of
    /// `fmt::Debug` implementations for map-like structures.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use std::fmt;
    ///
    /// struct Foo(Vec<(String, i32)>);
    ///
    /// impl fmt::Debug for Foo {
    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
    ///         fmt.debug_map().entries(self.0.iter().map(|&(ref k, ref v)| (k, v))).finish()
    ///     }
    /// }
    ///
    /// // prints "{"A": 10, "B": 11}"
    /// println!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)]));
    /// ```
    #[stable(feature = "debug_builders", since = "1.2.0")]
    pub fn debug_map<'b>(&'b mut self) -> DebugMap<'b, 'a> {
        builders::debug_map_new(self)
    }
}

#[stable(since = "1.2.0", feature = "formatter_write")]
impl Write for Formatter<'_> {
    fn write_str(&mut self, s: &str) -> Result {
        self.buf.write_str(s)
    }

    fn write_char(&mut self, c: char) -> Result {
        self.buf.write_char(c)
    }

    fn write_fmt(&mut self, args: Arguments<'_>) -> Result {
        write(self.buf, args)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Display for Error {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        Display::fmt("an error occurred when formatting an argument", f)
    }
}

// Implementations of the core formatting traits

macro_rules! fmt_refs {
    ($($tr:ident),*) => {
        $(
        #[stable(feature = "rust1", since = "1.0.0")]
        impl<T: ?Sized + $tr> $tr for &T {
            fn fmt(&self, f: &mut Formatter<'_>) -> Result { $tr::fmt(&**self, f) }
        }
        #[stable(feature = "rust1", since = "1.0.0")]
        impl<T: ?Sized + $tr> $tr for &mut T {
            fn fmt(&self, f: &mut Formatter<'_>) -> Result { $tr::fmt(&**self, f) }
        }
        )*
    }
}

fmt_refs! { Debug, Display, Octal, Binary, LowerHex, UpperHex, LowerExp, UpperExp }

#[unstable(feature = "never_type", issue = "35121")]
impl Debug for ! {
    fn fmt(&self, _: &mut Formatter<'_>) -> Result {
        *self
    }
}

#[unstable(feature = "never_type", issue = "35121")]
impl Display for ! {
    fn fmt(&self, _: &mut Formatter<'_>) -> Result {
        *self
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for bool {
    #[inline]
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        Display::fmt(self, f)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Display for bool {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        Display::fmt(if *self { "true" } else { "false" }, f)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for str {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        f.write_char('"')?;
        let mut from = 0;
        for (i, c) in self.char_indices() {
            let esc = c.escape_debug();
            // If char needs escaping, flush backlog so far and write, else skip
            if esc.len() != 1 {
                f.write_str(&self[from..i])?;
                for c in esc {
                    f.write_char(c)?;
                }
                from = i + c.len_utf8();
            }
        }
        f.write_str(&self[from..])?;
        f.write_char('"')
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Display for str {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        f.pad(self)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for char {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        f.write_char('\'')?;
        for c in self.escape_debug() {
            f.write_char(c)?
        }
        f.write_char('\'')
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Display for char {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        if f.width.is_none() && f.precision.is_none() {
            f.write_char(*self)
        } else {
            f.pad(self.encode_utf8(&mut [0; 4]))
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Pointer for *const T {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        let old_width = f.width;
        let old_flags = f.flags;

        // The alternate flag is already treated by LowerHex as being special-
        // it denotes whether to prefix with 0x. We use it to work out whether
        // or not to zero extend, and then unconditionally set it to get the
        // prefix.
        if f.alternate() {
            f.flags |= 1 << (FlagV1::SignAwareZeroPad as u32);

            if let None = f.width {
                f.width = Some(((mem::size_of::<usize>() * 8) / 4) + 2);
            }
        }
        f.flags |= 1 << (FlagV1::Alternate as u32);

        let ret = LowerHex::fmt(&(*self as *const () as usize), f);

        f.width = old_width;
        f.flags = old_flags;

        ret
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Pointer for *mut T {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        Pointer::fmt(&(*self as *const T), f)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Pointer for &T {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        Pointer::fmt(&(*self as *const T), f)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Pointer for &mut T {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        Pointer::fmt(&(&**self as *const T), f)
    }
}

// Implementation of Display/Debug for various core types

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Debug for *const T {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result { Pointer::fmt(self, f) }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Debug for *mut T {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result { Pointer::fmt(self, f) }
}

macro_rules! peel {
    ($name:ident, $($other:ident,)*) => (tuple! { $($other,)* })
}

macro_rules! tuple {
    () => ();
    ( $($name:ident,)+ ) => (
        #[stable(feature = "rust1", since = "1.0.0")]
        impl<$($name:Debug),+> Debug for ($($name,)+) where last_type!($($name,)+): ?Sized {
            #[allow(non_snake_case, unused_assignments)]
            fn fmt(&self, f: &mut Formatter<'_>) -> Result {
                let mut builder = f.debug_tuple("");
                let ($(ref $name,)+) = *self;
                $(
                    builder.field(&$name);
                )+

                builder.finish()
            }
        }
        peel! { $($name,)+ }
    )
}

macro_rules! last_type {
    ($a:ident,) => { $a };
    ($a:ident, $($rest_a:ident,)+) => { last_type!($($rest_a,)+) };
}

tuple! { T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, }

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Debug> Debug for [T] {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        f.debug_list().entries(self.iter()).finish()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for () {
    #[inline]
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        f.pad("()")
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Debug for PhantomData<T> {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        f.pad("PhantomData")
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Copy + Debug> Debug for Cell<T> {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        f.debug_struct("Cell")
            .field("value", &self.get())
            .finish()
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + Debug> Debug for RefCell<T> {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        match self.try_borrow() {
            Ok(borrow) => {
                f.debug_struct("RefCell")
                    .field("value", &borrow)
                    .finish()
            }
            Err(_) => {
                // The RefCell is mutably borrowed so we can't look at its value
                // here. Show a placeholder instead.
                struct BorrowedPlaceholder;

                impl Debug for BorrowedPlaceholder {
                    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
                        f.write_str("<borrowed>")
                    }
                }

                f.debug_struct("RefCell")
                    .field("value", &BorrowedPlaceholder)
                    .finish()
            }
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + Debug> Debug for Ref<'_, T> {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        Debug::fmt(&**self, f)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + Debug> Debug for RefMut<'_, T> {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        Debug::fmt(&*(self.deref()), f)
    }
}

#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<T: ?Sized + Debug> Debug for UnsafeCell<T> {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        f.pad("UnsafeCell")
    }
}

// If you expected tests to be here, look instead at the ui/ifmt.rs test,
// it's a lot easier than creating all of the rt::Piece structures here.