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
//! [![github]](https://github.com/dtolnay/proc-macro2) [![crates-io]](https://crates.io/crates/proc-macro2) [![docs-rs]](crate)
//!
//! [github]: https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github
//! [crates-io]: https://img.shields.io/badge/crates.io-fc8d62?style=for-the-badge&labelColor=555555&logo=rust
//! [docs-rs]: https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs
//!
//! <br>
//!
//! 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-macro2/1.0.54")]
#![cfg_attr(
    any(proc_macro_span, super_unstable),
    feature(proc_macro_span, proc_macro_span_shrink)
)]
#![cfg_attr(super_unstable, feature(proc_macro_def_site))]
#![cfg_attr(doc_cfg, feature(doc_cfg))]
#![allow(
    clippy::cast_lossless,
    clippy::cast_possible_truncation,
    clippy::doc_markdown,
    clippy::items_after_statements,
    clippy::let_underscore_untyped,
    clippy::manual_assert,
    clippy::must_use_candidate,
    clippy::needless_doctest_main,
    clippy::return_self_not_must_use,
    clippy::shadow_unrelated,
    clippy::trivially_copy_pass_by_ref,
    clippy::unnecessary_wraps,
    clippy::unused_self,
    clippy::used_underscore_binding,
    clippy::vec_init_then_push
)]

#[cfg(all(procmacro2_semver_exempt, wrap_proc_macro, not(super_unstable)))]
compile_error! {"\
    Something is not right. If you've tried to turn on \
    procmacro2_semver_exempt, you need to ensure that it \
    is turned on for the compilation of the proc-macro2 \
    build script as well.
"}

#[cfg(use_proc_macro)]
extern crate proc_macro;

mod marker;
mod parse;
mod rcvec;

#[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;

pub mod extra;

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

#[cfg(span_locations)]
mod location;

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

#[cfg(span_locations)]
pub use crate::location::LineColumn;

/// 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) -> Self {
        TokenStream {
            inner,
            _marker: Marker,
        }
    }

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

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

#[cfg(use_proc_macro)]
impl From<TokenStream> for proc_macro::TokenStream {
    fn from(inner: TokenStream) -> Self {
        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(all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)))]
#[cfg_attr(doc_cfg, doc(cfg(procmacro2_semver_exempt)))]
#[derive(Clone, PartialEq, Eq)]
pub struct SourceFile {
    inner: imp::SourceFile,
    _marker: Marker,
}

#[cfg(all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)))]
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(all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)))]
impl Debug for SourceFile {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        Debug::fmt(&self.inner, f)
    }
}

/// 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) -> Self {
        Span {
            inner,
            _marker: Marker,
        }
    }

    fn _new_fallback(inner: fallback::Span) -> Self {
        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() -> Self {
        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(not(no_hygiene))]
    pub fn mixed_site() -> Self {
        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() -> Self {
        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(all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)))]
    #[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 {
        self.inner.start()
    }

    /// 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 {
        self.inner.end()
    }

    /// Creates an empty span pointing to directly before this span.
    ///
    /// This method is semver exempt and not exposed by default.
    #[cfg(all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)))]
    #[cfg_attr(doc_cfg, doc(cfg(procmacro2_semver_exempt)))]
    pub fn before(&self) -> Span {
        Span::_new(self.inner.before())
    }

    /// Creates an empty span pointing to directly after this span.
    ///
    /// This method is semver exempt and not exposed by default.
    #[cfg(all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)))]
    #[cfg_attr(doc_cfg, doc(cfg(procmacro2_semver_exempt)))]
    pub fn after(&self) -> Span {
        Span::_new(self.inner.after())
    }

    /// 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)
    }

    /// Returns the source text behind a span. This preserves the original
    /// source code, including spaces and comments. It only returns a result if
    /// the span corresponds to real source code.
    ///
    /// Note: The observable result of a macro should only rely on the tokens
    /// and not on this source text. The result of this function is a best
    /// effort to be used for diagnostics only.
    pub fn source_text(&self) -> Option<String> {
        self.inner.source_text()
    }
}

/// 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) -> Self {
        TokenTree::Group(g)
    }
}

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

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

impl From<Literal> for TokenTree {
    fn from(g: Literal) -> Self {
        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_fallback(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) -> Self {
        Group {
            inner: imp::Group::new(delimiter, stream.inner),
        }
    }

    /// Returns the punctuation used as the delimiter for this group: a set of
    /// parentheses, square brackets, or curly braces.
    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())
    }

    /// Returns an object that holds this group's `span_open()` and
    /// `span_close()` together (in a more compact representation than holding
    /// those 2 spans individually).
    pub fn delim_span(&self) -> DelimSpan {
        DelimSpan::new(&self.inner)
    }

    /// 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) -> Self {
        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) -> Self {
        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) -> Self {
        Ident::_new(imp::Ident::new(string, span.inner))
    }

    /// Same as `Ident::new`, but creates a raw identifier (`r#ident`). The
    /// `string` argument must be a valid identifier permitted by the language
    /// (including keywords, e.g. `fn`). Keywords which are usable in path
    /// segments (e.g. `self`, `super`) are not supported, and will cause a
    /// panic.
    pub fn new_raw(string: &str, span: Span) -> Self {
        Ident::_new_raw(string, span)
    }

    fn _new_raw(string: &str, span: Span) -> Self {
        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) -> Self {
        Literal {
            inner,
            _marker: Marker,
        }
    }

    fn _new_fallback(inner: fallback::Literal) -> Self {
        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 round-trips
    /// 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
    /// round-trips 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 round-trips
    /// 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
    /// round-trips 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)
    }

    // Intended for the `quote!` macro to use when constructing a proc-macro2
    // token out of a macro_rules $:literal token, which is already known to be
    // a valid literal. This avoids reparsing/validating the literal's string
    // representation. This is not public API other than for quote.
    #[doc(hidden)]
    pub unsafe fn from_str_unchecked(repr: &str) -> Self {
        Literal::_new(imp::Literal::from_str_unchecked(repr))
    }
}

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 core::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()
        }

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

    impl Debug for IntoIter {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.write_str("TokenStream ")?;
            f.debug_list().entries(self.clone()).finish()
        }
    }

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

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