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
//! A wrapper around the procedural macro API of the compiler's [`proc_macro`]
//! crate. This library serves two purposes:
//!
//! [`proc_macro`]: https://doc.rust-lang.org/proc_macro/
//!
//! - **Bring proc-macro-like functionality to other contexts like build.rs and
//!   main.rs.** Types from `proc_macro` are entirely specific to procedural
//!   macros and cannot ever exist in code outside of a procedural macro.
//!   Meanwhile `proc_macro2` types may exist anywhere including non-macro code.
//!   By developing foundational libraries like [syn] and [quote] against
//!   `proc_macro2` rather than `proc_macro`, the procedural macro ecosystem
//!   becomes easily applicable to many other use cases and we avoid
//!   reimplementing non-macro equivalents of those libraries.
//!
//! - **Make procedural macros unit testable.** As a consequence of being
//!   specific to procedural macros, nothing that uses `proc_macro` can be
//!   executed from a unit test. In order for helper libraries or components of
//!   a macro to be testable in isolation, they must be implemented using
//!   `proc_macro2`.
//!
//! [syn]: https://github.com/dtolnay/syn
//! [quote]: https://github.com/dtolnay/quote
//!
//! # Usage
//!
//! The skeleton of a typical procedural macro typically looks like this:
//!
//! ```
//! extern crate proc_macro;
//!
//! # const IGNORE: &str = stringify! {
//! #[proc_macro_derive(MyDerive)]
//! # };
//! # #[cfg(wrap_proc_macro)]
//! pub fn my_derive(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
//!     let input = proc_macro2::TokenStream::from(input);
//!
//!     let output: proc_macro2::TokenStream = {
//!         /* transform input */
//!         # input
//!     };
//!
//!     proc_macro::TokenStream::from(output)
//! }
//! ```
//!
//! If parsing with [Syn], you'll use [`parse_macro_input!`] instead to
//! propagate parse errors correctly back to the compiler when parsing fails.
//!
//! [`parse_macro_input!`]: https://docs.rs/syn/1.0/syn/macro.parse_macro_input.html
//!
//! # Unstable features
//!
//! The default feature set of proc-macro2 tracks the most recent stable
//! compiler API. Functionality in `proc_macro` that is not yet stable is not
//! exposed by proc-macro2 by default.
//!
//! To opt into the additional APIs available in the most recent nightly
//! compiler, the `procmacro2_semver_exempt` config flag must be passed to
//! rustc. We will polyfill those nightly-only APIs back to Rust 1.31.0. As
//! these are unstable APIs that track the nightly compiler, minor versions of
//! proc-macro2 may make breaking changes to them at any time.
//!
//! ```sh
//! RUSTFLAGS='--cfg procmacro2_semver_exempt' cargo build
//! ```
//!
//! Note that this must not only be done for your crate, but for any crate that
//! depends on your crate. This infectious nature is intentional, as it serves
//! as a reminder that you are outside of the normal semver guarantees.
//!
//! Semver exempt methods are marked as such in the proc-macro2 documentation.
//!
//! # Thread-Safety
//!
//! Most types in this crate are `!Sync` because the underlying compiler
//! types make use of thread-local memory, meaning they cannot be accessed from
//! a different thread.

// Proc-macro2 types in rustdoc of other crates get linked to here.
#![doc(html_root_url = "https://docs.rs/proc-macro2/1.0.29")]
#![cfg_attr(any(proc_macro_span, super_unstable), feature(proc_macro_span))]
#![cfg_attr(super_unstable, feature(proc_macro_raw_ident, proc_macro_def_site))]
#![cfg_attr(doc_cfg, feature(doc_cfg))]
#![allow(clippy::needless_doctest_main, clippy::vec_init_then_push)]

#[cfg(use_proc_macro)]
extern crate proc_macro;

mod marker;
mod parse;

#[cfg(wrap_proc_macro)]
mod detection;

// Public for proc_macro2::fallback::force() and unforce(), but those are quite
// a niche use case so we omit it from rustdoc.
#[doc(hidden)]
pub mod fallback;

#[cfg(not(wrap_proc_macro))]
use crate::fallback as imp;
#[path = "wrapper.rs"]
#[cfg(wrap_proc_macro)]
mod imp;

use crate::marker::Marker;
use std::cmp::Ordering;
use std::error::Error;
use std::fmt::{self, Debug, Display};
use std::hash::{Hash, Hasher};
use std::iter::FromIterator;
use std::ops::RangeBounds;
#[cfg(procmacro2_semver_exempt)]
use std::path::PathBuf;
use std::str::FromStr;

/// An abstract stream of tokens, or more concretely a sequence of token trees.
///
/// This type provides interfaces for iterating over token trees and for
/// collecting token trees into one stream.
///
/// Token stream is both the input and output of `#[proc_macro]`,
/// `#[proc_macro_attribute]` and `#[proc_macro_derive]` definitions.
#[derive(Clone)]
pub struct TokenStream {
    inner: imp::TokenStream,
    _marker: Marker,
}

/// Error returned from `TokenStream::from_str`.
pub struct LexError {
    inner: imp::LexError,
    _marker: Marker,
}

impl TokenStream {
    fn _new(inner: imp::TokenStream) -> TokenStream {
        TokenStream {
            inner,
            _marker: Marker,
        }
    }

    fn _new_stable(inner: fallback::TokenStream) -> TokenStream {
        TokenStream {
            inner: inner.into(),
            _marker: Marker,
        }
    }

    /// Returns an empty `TokenStream` containing no token trees.
    pub fn new() -> TokenStream {
        TokenStream::_new(imp::TokenStream::new())
    }

    /// Checks if this `TokenStream` is empty.
    pub fn is_empty(&self) -> bool {
        self.inner.is_empty()
    }
}

/// `TokenStream::default()` returns an empty stream,
/// i.e. this is equivalent with `TokenStream::new()`.
impl Default for TokenStream {
    fn default() -> Self {
        TokenStream::new()
    }
}

/// Attempts to break the string into tokens and parse those tokens into a token
/// stream.
///
/// May fail for a number of reasons, for example, if the string contains
/// unbalanced delimiters or characters not existing in the language.
///
/// NOTE: Some errors may cause panics instead of returning `LexError`. We
/// reserve the right to change these errors into `LexError`s later.
impl FromStr for TokenStream {
    type Err = LexError;

    fn from_str(src: &str) -> Result<TokenStream, LexError> {
        let e = src.parse().map_err(|e| LexError {
            inner: e,
            _marker: Marker,
        })?;
        Ok(TokenStream::_new(e))
    }
}

#[cfg(use_proc_macro)]
impl From<proc_macro::TokenStream> for TokenStream {
    fn from(inner: proc_macro::TokenStream) -> TokenStream {
        TokenStream::_new(inner.into())
    }
}

#[cfg(use_proc_macro)]
impl From<TokenStream> for proc_macro::TokenStream {
    fn from(inner: TokenStream) -> proc_macro::TokenStream {
        inner.inner.into()
    }
}

impl From<TokenTree> for TokenStream {
    fn from(token: TokenTree) -> Self {
        TokenStream::_new(imp::TokenStream::from(token))
    }
}

impl Extend<TokenTree> for TokenStream {
    fn extend<I: IntoIterator<Item = TokenTree>>(&mut self, streams: I) {
        self.inner.extend(streams)
    }
}

impl Extend<TokenStream> for TokenStream {
    fn extend<I: IntoIterator<Item = TokenStream>>(&mut self, streams: I) {
        self.inner
            .extend(streams.into_iter().map(|stream| stream.inner))
    }
}

/// Collects a number of token trees into a single stream.
impl FromIterator<TokenTree> for TokenStream {
    fn from_iter<I: IntoIterator<Item = TokenTree>>(streams: I) -> Self {
        TokenStream::_new(streams.into_iter().collect())
    }
}
impl FromIterator<TokenStream> for TokenStream {
    fn from_iter<I: IntoIterator<Item = TokenStream>>(streams: I) -> Self {
        TokenStream::_new(streams.into_iter().map(|i| i.inner).collect())
    }
}

/// Prints the token stream as a string that is supposed to be losslessly
/// convertible back into the same token stream (modulo spans), except for
/// possibly `TokenTree::Group`s with `Delimiter::None` delimiters and negative
/// numeric literals.
impl Display for TokenStream {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        Display::fmt(&self.inner, f)
    }
}

/// Prints token in a form convenient for debugging.
impl Debug for TokenStream {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        Debug::fmt(&self.inner, f)
    }
}

impl LexError {
    pub fn span(&self) -> Span {
        Span::_new(self.inner.span())
    }
}

impl Debug for LexError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        Debug::fmt(&self.inner, f)
    }
}

impl Display for LexError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        Display::fmt(&self.inner, f)
    }
}

impl Error for LexError {}

/// The source file of a given `Span`.
///
/// This type is semver exempt and not exposed by default.
#[cfg(procmacro2_semver_exempt)]
#[cfg_attr(doc_cfg, doc(cfg(procmacro2_semver_exempt)))]
#[derive(Clone, PartialEq, Eq)]
pub struct SourceFile {
    inner: imp::SourceFile,
    _marker: Marker,
}

#[cfg(procmacro2_semver_exempt)]
impl SourceFile {
    fn _new(inner: imp::SourceFile) -> Self {
        SourceFile {
            inner,
            _marker: Marker,
        }
    }

    /// Get the path to this source file.
    ///
    /// ### Note
    ///
    /// If the code span associated with this `SourceFile` was generated by an
    /// external macro, this may not be an actual path on the filesystem. Use
    /// [`is_real`] to check.
    ///
    /// Also note that even if `is_real` returns `true`, if
    /// `--remap-path-prefix` was passed on the command line, the path as given
    /// may not actually be valid.
    ///
    /// [`is_real`]: #method.is_real
    pub fn path(&self) -> PathBuf {
        self.inner.path()
    }

    /// Returns `true` if this source file is a real source file, and not
    /// generated by an external macro's expansion.
    pub fn is_real(&self) -> bool {
        self.inner.is_real()
    }
}

#[cfg(procmacro2_semver_exempt)]
impl Debug for SourceFile {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        Debug::fmt(&self.inner, f)
    }
}

/// A line-column pair representing the start or end of a `Span`.
///
/// This type is semver exempt and not exposed by default.
#[cfg(span_locations)]
#[cfg_attr(doc_cfg, doc(cfg(feature = "span-locations")))]
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub struct LineColumn {
    /// The 1-indexed line in the source file on which the span starts or ends
    /// (inclusive).
    pub line: usize,
    /// The 0-indexed column (in UTF-8 characters) in the source file on which
    /// the span starts or ends (inclusive).
    pub column: usize,
}

#[cfg(span_locations)]
impl Ord for LineColumn {
    fn cmp(&self, other: &Self) -> Ordering {
        self.line
            .cmp(&other.line)
            .then(self.column.cmp(&other.column))
    }
}

#[cfg(span_locations)]
impl PartialOrd for LineColumn {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

/// A region of source code, along with macro expansion information.
#[derive(Copy, Clone)]
pub struct Span {
    inner: imp::Span,
    _marker: Marker,
}

impl Span {
    fn _new(inner: imp::Span) -> Span {
        Span {
            inner,
            _marker: Marker,
        }
    }

    fn _new_stable(inner: fallback::Span) -> Span {
        Span {
            inner: inner.into(),
            _marker: Marker,
        }
    }

    /// The span of the invocation of the current procedural macro.
    ///
    /// Identifiers created with this span will be resolved as if they were
    /// written directly at the macro call location (call-site hygiene) and
    /// other code at the macro call site will be able to refer to them as well.
    pub fn call_site() -> Span {
        Span::_new(imp::Span::call_site())
    }

    /// The span located at the invocation of the procedural macro, but with
    /// local variables, labels, and `$crate` resolved at the definition site
    /// of the macro. This is the same hygiene behavior as `macro_rules`.
    ///
    /// This function requires Rust 1.45 or later.
    #[cfg(hygiene)]
    pub fn mixed_site() -> Span {
        Span::_new(imp::Span::mixed_site())
    }

    /// A span that resolves at the macro definition site.
    ///
    /// This method is semver exempt and not exposed by default.
    #[cfg(procmacro2_semver_exempt)]
    #[cfg_attr(doc_cfg, doc(cfg(procmacro2_semver_exempt)))]
    pub fn def_site() -> Span {
        Span::_new(imp::Span::def_site())
    }

    /// Creates a new span with the same line/column information as `self` but
    /// that resolves symbols as though it were at `other`.
    pub fn resolved_at(&self, other: Span) -> Span {
        Span::_new(self.inner.resolved_at(other.inner))
    }

    /// Creates a new span with the same name resolution behavior as `self` but
    /// with the line/column information of `other`.
    pub fn located_at(&self, other: Span) -> Span {
        Span::_new(self.inner.located_at(other.inner))
    }

    /// Convert `proc_macro2::Span` to `proc_macro::Span`.
    ///
    /// This method is available when building with a nightly compiler, or when
    /// building with rustc 1.29+ *without* semver exempt features.
    ///
    /// # Panics
    ///
    /// Panics if called from outside of a procedural macro. Unlike
    /// `proc_macro2::Span`, the `proc_macro::Span` type can only exist within
    /// the context of a procedural macro invocation.
    #[cfg(wrap_proc_macro)]
    pub fn unwrap(self) -> proc_macro::Span {
        self.inner.unwrap()
    }

    // Soft deprecated. Please use Span::unwrap.
    #[cfg(wrap_proc_macro)]
    #[doc(hidden)]
    pub fn unstable(self) -> proc_macro::Span {
        self.unwrap()
    }

    /// The original source file into which this span points.
    ///
    /// This method is semver exempt and not exposed by default.
    #[cfg(procmacro2_semver_exempt)]
    #[cfg_attr(doc_cfg, doc(cfg(procmacro2_semver_exempt)))]
    pub fn source_file(&self) -> SourceFile {
        SourceFile::_new(self.inner.source_file())
    }

    /// Get the starting line/column in the source file for this span.
    ///
    /// This method requires the `"span-locations"` feature to be enabled.
    ///
    /// When executing in a procedural macro context, the returned line/column
    /// are only meaningful if compiled with a nightly toolchain. The stable
    /// toolchain does not have this information available. When executing
    /// outside of a procedural macro, such as main.rs or build.rs, the
    /// line/column are always meaningful regardless of toolchain.
    #[cfg(span_locations)]
    #[cfg_attr(doc_cfg, doc(cfg(feature = "span-locations")))]
    pub fn start(&self) -> LineColumn {
        let imp::LineColumn { line, column } = self.inner.start();
        LineColumn { line, column }
    }

    /// Get the ending line/column in the source file for this span.
    ///
    /// This method requires the `"span-locations"` feature to be enabled.
    ///
    /// When executing in a procedural macro context, the returned line/column
    /// are only meaningful if compiled with a nightly toolchain. The stable
    /// toolchain does not have this information available. When executing
    /// outside of a procedural macro, such as main.rs or build.rs, the
    /// line/column are always meaningful regardless of toolchain.
    #[cfg(span_locations)]
    #[cfg_attr(doc_cfg, doc(cfg(feature = "span-locations")))]
    pub fn end(&self) -> LineColumn {
        let imp::LineColumn { line, column } = self.inner.end();
        LineColumn { line, column }
    }

    /// Create a new span encompassing `self` and `other`.
    ///
    /// Returns `None` if `self` and `other` are from different files.
    ///
    /// Warning: the underlying [`proc_macro::Span::join`] method is
    /// nightly-only. When called from within a procedural macro not using a
    /// nightly compiler, this method will always return `None`.
    ///
    /// [`proc_macro::Span::join`]: https://doc.rust-lang.org/proc_macro/struct.Span.html#method.join
    pub fn join(&self, other: Span) -> Option<Span> {
        self.inner.join(other.inner).map(Span::_new)
    }

    /// Compares two spans to see if they're equal.
    ///
    /// This method is semver exempt and not exposed by default.
    #[cfg(procmacro2_semver_exempt)]
    #[cfg_attr(doc_cfg, doc(cfg(procmacro2_semver_exempt)))]
    pub fn eq(&self, other: &Span) -> bool {
        self.inner.eq(&other.inner)
    }
}

/// Prints a span in a form convenient for debugging.
impl Debug for Span {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        Debug::fmt(&self.inner, f)
    }
}

/// A single token or a delimited sequence of token trees (e.g. `[1, (), ..]`).
#[derive(Clone)]
pub enum TokenTree {
    /// A token stream surrounded by bracket delimiters.
    Group(Group),
    /// An identifier.
    Ident(Ident),
    /// A single punctuation character (`+`, `,`, `$`, etc.).
    Punct(Punct),
    /// A literal character (`'a'`), string (`"hello"`), number (`2.3`), etc.
    Literal(Literal),
}

impl TokenTree {
    /// Returns the span of this tree, delegating to the `span` method of
    /// the contained token or a delimited stream.
    pub fn span(&self) -> Span {
        match self {
            TokenTree::Group(t) => t.span(),
            TokenTree::Ident(t) => t.span(),
            TokenTree::Punct(t) => t.span(),
            TokenTree::Literal(t) => t.span(),
        }
    }

    /// Configures the span for *only this token*.
    ///
    /// Note that if this token is a `Group` then this method will not configure
    /// the span of each of the internal tokens, this will simply delegate to
    /// the `set_span` method of each variant.
    pub fn set_span(&mut self, span: Span) {
        match self {
            TokenTree::Group(t) => t.set_span(span),
            TokenTree::Ident(t) => t.set_span(span),
            TokenTree::Punct(t) => t.set_span(span),
            TokenTree::Literal(t) => t.set_span(span),
        }
    }
}

impl From<Group> for TokenTree {
    fn from(g: Group) -> TokenTree {
        TokenTree::Group(g)
    }
}

impl From<Ident> for TokenTree {
    fn from(g: Ident) -> TokenTree {
        TokenTree::Ident(g)
    }
}

impl From<Punct> for TokenTree {
    fn from(g: Punct) -> TokenTree {
        TokenTree::Punct(g)
    }
}

impl From<Literal> for TokenTree {
    fn from(g: Literal) -> TokenTree {
        TokenTree::Literal(g)
    }
}

/// Prints the token tree as a string that is supposed to be losslessly
/// convertible back into the same token tree (modulo spans), except for
/// possibly `TokenTree::Group`s with `Delimiter::None` delimiters and negative
/// numeric literals.
impl Display for TokenTree {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            TokenTree::Group(t) => Display::fmt(t, f),
            TokenTree::Ident(t) => Display::fmt(t, f),
            TokenTree::Punct(t) => Display::fmt(t, f),
            TokenTree::Literal(t) => Display::fmt(t, f),
        }
    }
}

/// Prints token tree in a form convenient for debugging.
impl Debug for TokenTree {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        // Each of these has the name in the struct type in the derived debug,
        // so don't bother with an extra layer of indirection
        match self {
            TokenTree::Group(t) => Debug::fmt(t, f),
            TokenTree::Ident(t) => {
                let mut debug = f.debug_struct("Ident");
                debug.field("sym", &format_args!("{}", t));
                imp::debug_span_field_if_nontrivial(&mut debug, t.span().inner);
                debug.finish()
            }
            TokenTree::Punct(t) => Debug::fmt(t, f),
            TokenTree::Literal(t) => Debug::fmt(t, f),
        }
    }
}

/// A delimited token stream.
///
/// A `Group` internally contains a `TokenStream` which is surrounded by
/// `Delimiter`s.
#[derive(Clone)]
pub struct Group {
    inner: imp::Group,
}

/// Describes how a sequence of token trees is delimited.
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub enum Delimiter {
    /// `( ... )`
    Parenthesis,
    /// `{ ... }`
    Brace,
    /// `[ ... ]`
    Bracket,
    /// `Ø ... Ø`
    ///
    /// An implicit delimiter, that may, for example, appear around tokens
    /// coming from a "macro variable" `$var`. It is important to preserve
    /// operator priorities in cases like `$var * 3` where `$var` is `1 + 2`.
    /// Implicit delimiters may not survive roundtrip of a token stream through
    /// a string.
    None,
}

impl Group {
    fn _new(inner: imp::Group) -> Self {
        Group { inner }
    }

    fn _new_stable(inner: fallback::Group) -> Self {
        Group {
            inner: inner.into(),
        }
    }

    /// Creates a new `Group` with the given delimiter and token stream.
    ///
    /// This constructor will set the span for this group to
    /// `Span::call_site()`. To change the span you can use the `set_span`
    /// method below.
    pub fn new(delimiter: Delimiter, stream: TokenStream) -> Group {
        Group {
            inner: imp::Group::new(delimiter, stream.inner),
        }
    }

    /// Returns the delimiter of this `Group`
    pub fn delimiter(&self) -> Delimiter {
        self.inner.delimiter()
    }

    /// Returns the `TokenStream` of tokens that are delimited in this `Group`.
    ///
    /// Note that the returned token stream does not include the delimiter
    /// returned above.
    pub fn stream(&self) -> TokenStream {
        TokenStream::_new(self.inner.stream())
    }

    /// Returns the span for the delimiters of this token stream, spanning the
    /// entire `Group`.
    ///
    /// ```text
    /// pub fn span(&self) -> Span {
    ///            ^^^^^^^
    /// ```
    pub fn span(&self) -> Span {
        Span::_new(self.inner.span())
    }

    /// Returns the span pointing to the opening delimiter of this group.
    ///
    /// ```text
    /// pub fn span_open(&self) -> Span {
    ///                 ^
    /// ```
    pub fn span_open(&self) -> Span {
        Span::_new(self.inner.span_open())
    }

    /// Returns the span pointing to the closing delimiter of this group.
    ///
    /// ```text
    /// pub fn span_close(&self) -> Span {
    ///                        ^
    /// ```
    pub fn span_close(&self) -> Span {
        Span::_new(self.inner.span_close())
    }

    /// Configures the span for this `Group`'s delimiters, but not its internal
    /// tokens.
    ///
    /// This method will **not** set the span of all the internal tokens spanned
    /// by this group, but rather it will only set the span of the delimiter
    /// tokens at the level of the `Group`.
    pub fn set_span(&mut self, span: Span) {
        self.inner.set_span(span.inner)
    }
}

/// Prints the group as a string that should be losslessly convertible back
/// into the same group (modulo spans), except for possibly `TokenTree::Group`s
/// with `Delimiter::None` delimiters.
impl Display for Group {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        Display::fmt(&self.inner, formatter)
    }
}

impl Debug for Group {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        Debug::fmt(&self.inner, formatter)
    }
}

/// A `Punct` is a single punctuation character like `+`, `-` or `#`.
///
/// Multicharacter operators like `+=` are represented as two instances of
/// `Punct` with different forms of `Spacing` returned.
#[derive(Clone)]
pub struct Punct {
    ch: char,
    spacing: Spacing,
    span: Span,
}

/// Whether a `Punct` is followed immediately by another `Punct` or followed by
/// another token or whitespace.
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub enum Spacing {
    /// E.g. `+` is `Alone` in `+ =`, `+ident` or `+()`.
    Alone,
    /// E.g. `+` is `Joint` in `+=` or `'` is `Joint` in `'#`.
    ///
    /// Additionally, single quote `'` can join with identifiers to form
    /// lifetimes `'ident`.
    Joint,
}

impl Punct {
    /// Creates a new `Punct` from the given character and spacing.
    ///
    /// The `ch` argument must be a valid punctuation character permitted by the
    /// language, otherwise the function will panic.
    ///
    /// The returned `Punct` will have the default span of `Span::call_site()`
    /// which can be further configured with the `set_span` method below.
    pub fn new(ch: char, spacing: Spacing) -> Punct {
        Punct {
            ch,
            spacing,
            span: Span::call_site(),
        }
    }

    /// Returns the value of this punctuation character as `char`.
    pub fn as_char(&self) -> char {
        self.ch
    }

    /// Returns the spacing of this punctuation character, indicating whether
    /// it's immediately followed by another `Punct` in the token stream, so
    /// they can potentially be combined into a multicharacter operator
    /// (`Joint`), or it's followed by some other token or whitespace (`Alone`)
    /// so the operator has certainly ended.
    pub fn spacing(&self) -> Spacing {
        self.spacing
    }

    /// Returns the span for this punctuation character.
    pub fn span(&self) -> Span {
        self.span
    }

    /// Configure the span for this punctuation character.
    pub fn set_span(&mut self, span: Span) {
        self.span = span;
    }
}

/// Prints the punctuation character as a string that should be losslessly
/// convertible back into the same character.
impl Display for Punct {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        Display::fmt(&self.ch, f)
    }
}

impl Debug for Punct {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        let mut debug = fmt.debug_struct("Punct");
        debug.field("char", &self.ch);
        debug.field("spacing", &self.spacing);
        imp::debug_span_field_if_nontrivial(&mut debug, self.span.inner);
        debug.finish()
    }
}

/// A word of Rust code, which may be a keyword or legal variable name.
///
/// An identifier consists of at least one Unicode code point, the first of
/// which has the XID_Start property and the rest of which have the XID_Continue
/// property.
///
/// - The empty string is not an identifier. Use `Option<Ident>`.
/// - A lifetime is not an identifier. Use `syn::Lifetime` instead.
///
/// An identifier constructed with `Ident::new` is permitted to be a Rust
/// keyword, though parsing one through its [`Parse`] implementation rejects
/// Rust keywords. Use `input.call(Ident::parse_any)` when parsing to match the
/// behaviour of `Ident::new`.
///
/// [`Parse`]: https://docs.rs/syn/1.0/syn/parse/trait.Parse.html
///
/// # Examples
///
/// A new ident can be created from a string using the `Ident::new` function.
/// A span must be provided explicitly which governs the name resolution
/// behavior of the resulting identifier.
///
/// ```
/// use proc_macro2::{Ident, Span};
///
/// fn main() {
///     let call_ident = Ident::new("calligraphy", Span::call_site());
///
///     println!("{}", call_ident);
/// }
/// ```
///
/// An ident can be interpolated into a token stream using the `quote!` macro.
///
/// ```
/// use proc_macro2::{Ident, Span};
/// use quote::quote;
///
/// fn main() {
///     let ident = Ident::new("demo", Span::call_site());
///
///     // Create a variable binding whose name is this ident.
///     let expanded = quote! { let #ident = 10; };
///
///     // Create a variable binding with a slightly different name.
///     let temp_ident = Ident::new(&format!("new_{}", ident), Span::call_site());
///     let expanded = quote! { let #temp_ident = 10; };
/// }
/// ```
///
/// A string representation of the ident is available through the `to_string()`
/// method.
///
/// ```
/// # use proc_macro2::{Ident, Span};
/// #
/// # let ident = Ident::new("another_identifier", Span::call_site());
/// #
/// // Examine the ident as a string.
/// let ident_string = ident.to_string();
/// if ident_string.len() > 60 {
///     println!("Very long identifier: {}", ident_string)
/// }
/// ```
#[derive(Clone)]
pub struct Ident {
    inner: imp::Ident,
    _marker: Marker,
}

impl Ident {
    fn _new(inner: imp::Ident) -> Ident {
        Ident {
            inner,
            _marker: Marker,
        }
    }

    /// Creates a new `Ident` with the given `string` as well as the specified
    /// `span`.
    ///
    /// The `string` argument must be a valid identifier permitted by the
    /// language, otherwise the function will panic.
    ///
    /// Note that `span`, currently in rustc, configures the hygiene information
    /// for this identifier.
    ///
    /// As of this time `Span::call_site()` explicitly opts-in to "call-site"
    /// hygiene meaning that identifiers created with this span will be resolved
    /// as if they were written directly at the location of the macro call, and
    /// other code at the macro call site will be able to refer to them as well.
    ///
    /// Later spans like `Span::def_site()` will allow to opt-in to
    /// "definition-site" hygiene meaning that identifiers created with this
    /// span will be resolved at the location of the macro definition and other
    /// code at the macro call site will not be able to refer to them.
    ///
    /// Due to the current importance of hygiene this constructor, unlike other
    /// tokens, requires a `Span` to be specified at construction.
    ///
    /// # Panics
    ///
    /// Panics if the input string is neither a keyword nor a legal variable
    /// name. If you are not sure whether the string contains an identifier and
    /// need to handle an error case, use
    /// <a href="https://docs.rs/syn/1.0/syn/fn.parse_str.html"><code
    ///   style="padding-right:0;">syn::parse_str</code></a><code
    ///   style="padding-left:0;">::&lt;Ident&gt;</code>
    /// rather than `Ident::new`.
    pub fn new(string: &str, span: Span) -> Ident {
        Ident::_new(imp::Ident::new(string, span.inner))
    }

    /// Same as `Ident::new`, but creates a raw identifier (`r#ident`).
    ///
    /// This method is semver exempt and not exposed by default.
    #[cfg(procmacro2_semver_exempt)]
    #[cfg_attr(doc_cfg, doc(cfg(procmacro2_semver_exempt)))]
    pub fn new_raw(string: &str, span: Span) -> Ident {
        Ident::_new_raw(string, span)
    }

    fn _new_raw(string: &str, span: Span) -> Ident {
        Ident::_new(imp::Ident::new_raw(string, span.inner))
    }

    /// Returns the span of this `Ident`.
    pub fn span(&self) -> Span {
        Span::_new(self.inner.span())
    }

    /// Configures the span of this `Ident`, possibly changing its hygiene
    /// context.
    pub fn set_span(&mut self, span: Span) {
        self.inner.set_span(span.inner);
    }
}

impl PartialEq for Ident {
    fn eq(&self, other: &Ident) -> bool {
        self.inner == other.inner
    }
}

impl<T> PartialEq<T> for Ident
where
    T: ?Sized + AsRef<str>,
{
    fn eq(&self, other: &T) -> bool {
        self.inner == other
    }
}

impl Eq for Ident {}

impl PartialOrd for Ident {
    fn partial_cmp(&self, other: &Ident) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl Ord for Ident {
    fn cmp(&self, other: &Ident) -> Ordering {
        self.to_string().cmp(&other.to_string())
    }
}

impl Hash for Ident {
    fn hash<H: Hasher>(&self, hasher: &mut H) {
        self.to_string().hash(hasher)
    }
}

/// Prints the identifier as a string that should be losslessly convertible back
/// into the same identifier.
impl Display for Ident {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        Display::fmt(&self.inner, f)
    }
}

impl Debug for Ident {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        Debug::fmt(&self.inner, f)
    }
}

/// A literal string (`"hello"`), byte string (`b"hello"`), character (`'a'`),
/// byte character (`b'a'`), an integer or floating point number with or without
/// a suffix (`1`, `1u8`, `2.3`, `2.3f32`).
///
/// Boolean literals like `true` and `false` do not belong here, they are
/// `Ident`s.
#[derive(Clone)]
pub struct Literal {
    inner: imp::Literal,
    _marker: Marker,
}

macro_rules! suffixed_int_literals {
    ($($name:ident => $kind:ident,)*) => ($(
        /// Creates a new suffixed integer literal with the specified value.
        ///
        /// This function will create an integer like `1u32` where the integer
        /// value specified is the first part of the token and the integral is
        /// also suffixed at the end. Literals created from negative numbers may
        /// not survive roundtrips through `TokenStream` or strings and may be
        /// broken into two tokens (`-` and positive literal).
        ///
        /// Literals created through this method have the `Span::call_site()`
        /// span by default, which can be configured with the `set_span` method
        /// below.
        pub fn $name(n: $kind) -> Literal {
            Literal::_new(imp::Literal::$name(n))
        }
    )*)
}

macro_rules! unsuffixed_int_literals {
    ($($name:ident => $kind:ident,)*) => ($(
        /// Creates a new unsuffixed integer literal with the specified value.
        ///
        /// This function will create an integer like `1` where the integer
        /// value specified is the first part of the token. No suffix is
        /// specified on this token, meaning that invocations like
        /// `Literal::i8_unsuffixed(1)` are equivalent to
        /// `Literal::u32_unsuffixed(1)`. Literals created from negative numbers
        /// may not survive roundtrips through `TokenStream` or strings and may
        /// be broken into two tokens (`-` and positive literal).
        ///
        /// Literals created through this method have the `Span::call_site()`
        /// span by default, which can be configured with the `set_span` method
        /// below.
        pub fn $name(n: $kind) -> Literal {
            Literal::_new(imp::Literal::$name(n))
        }
    )*)
}

impl Literal {
    fn _new(inner: imp::Literal) -> Literal {
        Literal {
            inner,
            _marker: Marker,
        }
    }

    fn _new_stable(inner: fallback::Literal) -> Literal {
        Literal {
            inner: inner.into(),
            _marker: Marker,
        }
    }

    suffixed_int_literals! {
        u8_suffixed => u8,
        u16_suffixed => u16,
        u32_suffixed => u32,
        u64_suffixed => u64,
        u128_suffixed => u128,
        usize_suffixed => usize,
        i8_suffixed => i8,
        i16_suffixed => i16,
        i32_suffixed => i32,
        i64_suffixed => i64,
        i128_suffixed => i128,
        isize_suffixed => isize,
    }

    unsuffixed_int_literals! {
        u8_unsuffixed => u8,
        u16_unsuffixed => u16,
        u32_unsuffixed => u32,
        u64_unsuffixed => u64,
        u128_unsuffixed => u128,
        usize_unsuffixed => usize,
        i8_unsuffixed => i8,
        i16_unsuffixed => i16,
        i32_unsuffixed => i32,
        i64_unsuffixed => i64,
        i128_unsuffixed => i128,
        isize_unsuffixed => isize,
    }

    /// Creates a new unsuffixed floating-point literal.
    ///
    /// This constructor is similar to those like `Literal::i8_unsuffixed` where
    /// the float's value is emitted directly into the token but no suffix is
    /// used, so it may be inferred to be a `f64` later in the compiler.
    /// Literals created from negative numbers may not survive rountrips through
    /// `TokenStream` or strings and may be broken into two tokens (`-` and
    /// positive literal).
    ///
    /// # Panics
    ///
    /// This function requires that the specified float is finite, for example
    /// if it is infinity or NaN this function will panic.
    pub fn f64_unsuffixed(f: f64) -> Literal {
        assert!(f.is_finite());
        Literal::_new(imp::Literal::f64_unsuffixed(f))
    }

    /// Creates a new suffixed floating-point literal.
    ///
    /// This constructor will create a literal like `1.0f64` where the value
    /// specified is the preceding part of the token and `f64` is the suffix of
    /// the token. This token will always be inferred to be an `f64` in the
    /// compiler. Literals created from negative numbers may not survive
    /// rountrips through `TokenStream` or strings and may be broken into two
    /// tokens (`-` and positive literal).
    ///
    /// # Panics
    ///
    /// This function requires that the specified float is finite, for example
    /// if it is infinity or NaN this function will panic.
    pub fn f64_suffixed(f: f64) -> Literal {
        assert!(f.is_finite());
        Literal::_new(imp::Literal::f64_suffixed(f))
    }

    /// Creates a new unsuffixed floating-point literal.
    ///
    /// This constructor is similar to those like `Literal::i8_unsuffixed` where
    /// the float's value is emitted directly into the token but no suffix is
    /// used, so it may be inferred to be a `f64` later in the compiler.
    /// Literals created from negative numbers may not survive rountrips through
    /// `TokenStream` or strings and may be broken into two tokens (`-` and
    /// positive literal).
    ///
    /// # Panics
    ///
    /// This function requires that the specified float is finite, for example
    /// if it is infinity or NaN this function will panic.
    pub fn f32_unsuffixed(f: f32) -> Literal {
        assert!(f.is_finite());
        Literal::_new(imp::Literal::f32_unsuffixed(f))
    }

    /// Creates a new suffixed floating-point literal.
    ///
    /// This constructor will create a literal like `1.0f32` where the value
    /// specified is the preceding part of the token and `f32` is the suffix of
    /// the token. This token will always be inferred to be an `f32` in the
    /// compiler. Literals created from negative numbers may not survive
    /// rountrips through `TokenStream` or strings and may be broken into two
    /// tokens (`-` and positive literal).
    ///
    /// # Panics
    ///
    /// This function requires that the specified float is finite, for example
    /// if it is infinity or NaN this function will panic.
    pub fn f32_suffixed(f: f32) -> Literal {
        assert!(f.is_finite());
        Literal::_new(imp::Literal::f32_suffixed(f))
    }

    /// String literal.
    pub fn string(string: &str) -> Literal {
        Literal::_new(imp::Literal::string(string))
    }

    /// Character literal.
    pub fn character(ch: char) -> Literal {
        Literal::_new(imp::Literal::character(ch))
    }

    /// Byte string literal.
    pub fn byte_string(s: &[u8]) -> Literal {
        Literal::_new(imp::Literal::byte_string(s))
    }

    /// Returns the span encompassing this literal.
    pub fn span(&self) -> Span {
        Span::_new(self.inner.span())
    }

    /// Configures the span associated for this literal.
    pub fn set_span(&mut self, span: Span) {
        self.inner.set_span(span.inner);
    }

    /// Returns a `Span` that is a subset of `self.span()` containing only
    /// the source bytes in range `range`. Returns `None` if the would-be
    /// trimmed span is outside the bounds of `self`.
    ///
    /// Warning: the underlying [`proc_macro::Literal::subspan`] method is
    /// nightly-only. When called from within a procedural macro not using a
    /// nightly compiler, this method will always return `None`.
    ///
    /// [`proc_macro::Literal::subspan`]: https://doc.rust-lang.org/proc_macro/struct.Literal.html#method.subspan
    pub fn subspan<R: RangeBounds<usize>>(&self, range: R) -> Option<Span> {
        self.inner.subspan(range).map(Span::_new)
    }
}

impl FromStr for Literal {
    type Err = LexError;

    fn from_str(repr: &str) -> Result<Self, LexError> {
        repr.parse().map(Literal::_new).map_err(|inner| LexError {
            inner,
            _marker: Marker,
        })
    }
}

impl Debug for Literal {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        Debug::fmt(&self.inner, f)
    }
}

impl Display for Literal {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        Display::fmt(&self.inner, f)
    }
}

/// Public implementation details for the `TokenStream` type, such as iterators.
pub mod token_stream {
    use crate::marker::Marker;
    use crate::{imp, TokenTree};
    use std::fmt::{self, Debug};

    pub use crate::TokenStream;

    /// An iterator over `TokenStream`'s `TokenTree`s.
    ///
    /// The iteration is "shallow", e.g. the iterator doesn't recurse into
    /// delimited groups, and returns whole groups as token trees.
    #[derive(Clone)]
    pub struct IntoIter {
        inner: imp::TokenTreeIter,
        _marker: Marker,
    }

    impl Iterator for IntoIter {
        type Item = TokenTree;

        fn next(&mut self) -> Option<TokenTree> {
            self.inner.next()
        }
    }

    impl Debug for IntoIter {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            Debug::fmt(&self.inner, f)
        }
    }

    impl IntoIterator for TokenStream {
        type Item = TokenTree;
        type IntoIter = IntoIter;

        fn into_iter(self) -> IntoIter {
            IntoIter {
                inner: self.inner.into_iter(),
                _marker: Marker,
            }
        }
    }
}