summaryrefslogtreecommitdiffstats
path: root/compiler/rustc_parse/src/parser/pat.rs
blob: 120a3c267f106684507b44c141a32e167ac8b543 (plain)
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
use super::{ForceCollect, Parser, PathStyle, TrailingToken};
use crate::parser::diagnostics::RemoveLet;
use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
use rustc_ast::mut_visit::{noop_visit_pat, MutVisitor};
use rustc_ast::ptr::P;
use rustc_ast::token::{self, Delimiter};
use rustc_ast::{
    self as ast, AttrVec, BindingAnnotation, ByRef, Expr, ExprKind, MacCall, Mutability, Pat,
    PatField, PatKind, Path, QSelf, RangeEnd, RangeSyntax,
};
use rustc_ast_pretty::pprust;
use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed, PResult};
use rustc_span::source_map::{respan, Span, Spanned};
use rustc_span::symbol::{kw, sym, Ident};

pub(super) type Expected = Option<&'static str>;

/// `Expected` for function and lambda parameter patterns.
pub(super) const PARAM_EXPECTED: Expected = Some("parameter name");

const WHILE_PARSING_OR_MSG: &str = "while parsing this or-pattern starting here";

/// Whether or not to recover a `,` when parsing or-patterns.
#[derive(PartialEq, Copy, Clone)]
pub enum RecoverComma {
    Yes,
    No,
}

/// Whether or not to recover a `:` when parsing patterns that were meant to be paths.
#[derive(PartialEq, Copy, Clone)]
pub enum RecoverColon {
    Yes,
    No,
}

/// Whether or not to recover a `a, b` when parsing patterns as `(a, b)` or that *and* `a | b`.
#[derive(PartialEq, Copy, Clone)]
pub enum CommaRecoveryMode {
    LikelyTuple,
    EitherTupleOrPipe,
}

/// The result of `eat_or_separator`. We want to distinguish which case we are in to avoid
/// emitting duplicate diagnostics.
#[derive(Debug, Clone, Copy)]
enum EatOrResult {
    /// We recovered from a trailing vert.
    TrailingVert,
    /// We ate an `|` (or `||` and recovered).
    AteOr,
    /// We did not eat anything (i.e. the current token is not `|` or `||`).
    None,
}

impl<'a> Parser<'a> {
    /// Parses a pattern.
    ///
    /// Corresponds to `pat<no_top_alt>` in RFC 2535 and does not admit or-patterns
    /// at the top level. Used when parsing the parameters of lambda expressions,
    /// functions, function pointers, and `pat` macro fragments.
    pub fn parse_pat_no_top_alt(&mut self, expected: Expected) -> PResult<'a, P<Pat>> {
        self.parse_pat_with_range_pat(true, expected)
    }

    /// Parses a pattern.
    ///
    /// Corresponds to `top_pat` in RFC 2535 and allows or-pattern at the top level.
    /// Used for parsing patterns in all cases when `pat<no_top_alt>` is not used.
    ///
    /// Note that after the FCP in <https://github.com/rust-lang/rust/issues/81415>,
    /// a leading vert is allowed in nested or-patterns, too. This allows us to
    /// simplify the grammar somewhat.
    pub fn parse_pat_allow_top_alt(
        &mut self,
        expected: Expected,
        rc: RecoverComma,
        ra: RecoverColon,
        rt: CommaRecoveryMode,
    ) -> PResult<'a, P<Pat>> {
        self.parse_pat_allow_top_alt_inner(expected, rc, ra, rt).map(|(pat, _)| pat)
    }

    /// Returns the pattern and a bool indicating whether we recovered from a trailing vert (true =
    /// recovered).
    fn parse_pat_allow_top_alt_inner(
        &mut self,
        expected: Expected,
        rc: RecoverComma,
        ra: RecoverColon,
        rt: CommaRecoveryMode,
    ) -> PResult<'a, (P<Pat>, bool)> {
        // Keep track of whether we recovered from a trailing vert so that we can avoid duplicated
        // suggestions (which bothers rustfix).
        //
        // Allow a '|' before the pats (RFCs 1925, 2530, and 2535).
        let (leading_vert_span, mut trailing_vert) = match self.eat_or_separator(None) {
            EatOrResult::AteOr => (Some(self.prev_token.span), false),
            EatOrResult::TrailingVert => (None, true),
            EatOrResult::None => (None, false),
        };

        // Parse the first pattern (`p_0`).
        let mut first_pat = self.parse_pat_no_top_alt(expected)?;
        if rc == RecoverComma::Yes {
            self.maybe_recover_unexpected_comma(first_pat.span, rt)?;
        }

        // If the next token is not a `|`,
        // this is not an or-pattern and we should exit here.
        if !self.check(&token::BinOp(token::Or)) && self.token != token::OrOr {
            // If we parsed a leading `|` which should be gated,
            // then we should really gate the leading `|`.
            // This complicated procedure is done purely for diagnostics UX.

            // Check if the user wrote `foo:bar` instead of `foo::bar`.
            if ra == RecoverColon::Yes {
                first_pat = self.maybe_recover_colon_colon_in_pat_typo(first_pat, expected);
            }

            if let Some(leading_vert_span) = leading_vert_span {
                // If there was a leading vert, treat this as an or-pattern. This improves
                // diagnostics.
                let span = leading_vert_span.to(self.prev_token.span);
                return Ok((self.mk_pat(span, PatKind::Or(vec![first_pat])), trailing_vert));
            }

            return Ok((first_pat, trailing_vert));
        }

        // Parse the patterns `p_1 | ... | p_n` where `n > 0`.
        let lo = leading_vert_span.unwrap_or(first_pat.span);
        let mut pats = vec![first_pat];
        loop {
            match self.eat_or_separator(Some(lo)) {
                EatOrResult::AteOr => {}
                EatOrResult::None => break,
                EatOrResult::TrailingVert => {
                    trailing_vert = true;
                    break;
                }
            }
            let pat = self.parse_pat_no_top_alt(expected).map_err(|mut err| {
                err.span_label(lo, WHILE_PARSING_OR_MSG);
                err
            })?;
            if rc == RecoverComma::Yes {
                self.maybe_recover_unexpected_comma(pat.span, rt)?;
            }
            pats.push(pat);
        }
        let or_pattern_span = lo.to(self.prev_token.span);

        Ok((self.mk_pat(or_pattern_span, PatKind::Or(pats)), trailing_vert))
    }

    /// Parse a pattern and (maybe) a `Colon` in positions where a pattern may be followed by a
    /// type annotation (e.g. for `let` bindings or `fn` params).
    ///
    /// Generally, this corresponds to `pat_no_top_alt` followed by an optional `Colon`. It will
    /// eat the `Colon` token if one is present.
    ///
    /// The return value represents the parsed pattern and `true` if a `Colon` was parsed (`false`
    /// otherwise).
    pub(super) fn parse_pat_before_ty(
        &mut self,
        expected: Expected,
        rc: RecoverComma,
        syntax_loc: &str,
    ) -> PResult<'a, (P<Pat>, bool)> {
        // We use `parse_pat_allow_top_alt` regardless of whether we actually want top-level
        // or-patterns so that we can detect when a user tries to use it. This allows us to print a
        // better error message.
        let (pat, trailing_vert) = self.parse_pat_allow_top_alt_inner(
            expected,
            rc,
            RecoverColon::No,
            CommaRecoveryMode::LikelyTuple,
        )?;
        let colon = self.eat(&token::Colon);

        if let PatKind::Or(pats) = &pat.kind {
            let msg = format!("top-level or-patterns are not allowed in {}", syntax_loc);
            let (help, fix) = if pats.len() == 1 {
                // If all we have is a leading vert, then print a special message. This is the case
                // if `parse_pat_allow_top_alt` returns an or-pattern with one variant.
                let msg = "remove the `|`";
                let fix = pprust::pat_to_string(&pat);
                (msg, fix)
            } else {
                let msg = "wrap the pattern in parentheses";
                let fix = format!("({})", pprust::pat_to_string(&pat));
                (msg, fix)
            };

            if trailing_vert {
                // We already emitted an error and suggestion to remove the trailing vert. Don't
                // emit again.
                self.sess.span_diagnostic.delay_span_bug(pat.span, &msg);
            } else {
                self.struct_span_err(pat.span, &msg)
                    .span_suggestion(pat.span, help, fix, Applicability::MachineApplicable)
                    .emit();
            }
        }

        Ok((pat, colon))
    }

    /// Parse the pattern for a function or function pointer parameter, followed by a colon.
    ///
    /// The return value represents the parsed pattern and `true` if a `Colon` was parsed (`false`
    /// otherwise).
    pub(super) fn parse_fn_param_pat_colon(&mut self) -> PResult<'a, (P<Pat>, bool)> {
        // In order to get good UX, we first recover in the case of a leading vert for an illegal
        // top-level or-pat. Normally, this means recovering both `|` and `||`, but in this case,
        // a leading `||` probably doesn't indicate an or-pattern attempt, so we handle that
        // separately.
        if let token::OrOr = self.token.kind {
            let span = self.token.span;
            let mut err = self.struct_span_err(span, "unexpected `||` before function parameter");
            err.span_suggestion(span, "remove the `||`", "", Applicability::MachineApplicable);
            err.note("alternatives in or-patterns are separated with `|`, not `||`");
            err.emit();
            self.bump();
        }

        self.parse_pat_before_ty(PARAM_EXPECTED, RecoverComma::No, "function parameters")
    }

    /// Eat the or-pattern `|` separator.
    /// If instead a `||` token is encountered, recover and pretend we parsed `|`.
    fn eat_or_separator(&mut self, lo: Option<Span>) -> EatOrResult {
        if self.recover_trailing_vert(lo) {
            EatOrResult::TrailingVert
        } else if matches!(self.token.kind, token::OrOr) {
            // Found `||`; Recover and pretend we parsed `|`.
            self.ban_unexpected_or_or(lo);
            self.bump();
            EatOrResult::AteOr
        } else if self.eat(&token::BinOp(token::Or)) {
            EatOrResult::AteOr
        } else {
            EatOrResult::None
        }
    }

    /// Recover if `|` or `||` is the current token and we have one of the
    /// tokens `=>`, `if`, `=`, `:`, `;`, `,`, `]`, `)`, or `}` ahead of us.
    ///
    /// These tokens all indicate that we reached the end of the or-pattern
    /// list and can now reliably say that the `|` was an illegal trailing vert.
    /// Note that there are more tokens such as `@` for which we know that the `|`
    /// is an illegal parse. However, the user's intent is less clear in that case.
    fn recover_trailing_vert(&mut self, lo: Option<Span>) -> bool {
        let is_end_ahead = self.look_ahead(1, |token| {
            matches!(
                &token.uninterpolate().kind,
                token::FatArrow // e.g. `a | => 0,`.
                | token::Ident(kw::If, false) // e.g. `a | if expr`.
                | token::Eq // e.g. `let a | = 0`.
                | token::Semi // e.g. `let a |;`.
                | token::Colon // e.g. `let a | :`.
                | token::Comma // e.g. `let (a |,)`.
                | token::CloseDelim(Delimiter::Bracket) // e.g. `let [a | ]`.
                | token::CloseDelim(Delimiter::Parenthesis) // e.g. `let (a | )`.
                | token::CloseDelim(Delimiter::Brace) // e.g. `let A { f: a | }`.
            )
        });
        match (is_end_ahead, &self.token.kind) {
            (true, token::BinOp(token::Or) | token::OrOr) => {
                self.ban_illegal_vert(lo, "trailing", "not allowed in an or-pattern");
                self.bump();
                true
            }
            _ => false,
        }
    }

    /// We have parsed `||` instead of `|`. Error and suggest `|` instead.
    fn ban_unexpected_or_or(&mut self, lo: Option<Span>) {
        let mut err = self.struct_span_err(self.token.span, "unexpected token `||` in pattern");
        err.span_suggestion(
            self.token.span,
            "use a single `|` to separate multiple alternative patterns",
            "|",
            Applicability::MachineApplicable,
        );
        if let Some(lo) = lo {
            err.span_label(lo, WHILE_PARSING_OR_MSG);
        }
        err.emit();
    }

    /// A `|` or possibly `||` token shouldn't be here. Ban it.
    fn ban_illegal_vert(&mut self, lo: Option<Span>, pos: &str, ctx: &str) {
        let span = self.token.span;
        let mut err = self.struct_span_err(span, &format!("a {} `|` is {}", pos, ctx));
        err.span_suggestion(
            span,
            &format!("remove the `{}`", pprust::token_to_string(&self.token)),
            "",
            Applicability::MachineApplicable,
        );
        if let Some(lo) = lo {
            err.span_label(lo, WHILE_PARSING_OR_MSG);
        }
        if let token::OrOr = self.token.kind {
            err.note("alternatives in or-patterns are separated with `|`, not `||`");
        }
        err.emit();
    }

    /// Parses a pattern, with a setting whether modern range patterns (e.g., `a..=b`, `a..b` are
    /// allowed).
    fn parse_pat_with_range_pat(
        &mut self,
        allow_range_pat: bool,
        expected: Expected,
    ) -> PResult<'a, P<Pat>> {
        maybe_recover_from_interpolated_ty_qpath!(self, true);
        maybe_whole!(self, NtPat, |x| x);

        let mut lo = self.token.span;

        if self.token.is_keyword(kw::Let) && self.look_ahead(1, |tok| tok.can_begin_pattern()) {
            self.bump();
            self.sess.emit_err(RemoveLet { span: lo });
            lo = self.token.span;
        }

        let pat = if self.check(&token::BinOp(token::And)) || self.token.kind == token::AndAnd {
            self.parse_pat_deref(expected)?
        } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
            self.parse_pat_tuple_or_parens()?
        } else if self.check(&token::OpenDelim(Delimiter::Bracket)) {
            // Parse `[pat, pat,...]` as a slice pattern.
            let (pats, _) = self.parse_delim_comma_seq(Delimiter::Bracket, |p| {
                p.parse_pat_allow_top_alt(
                    None,
                    RecoverComma::No,
                    RecoverColon::No,
                    CommaRecoveryMode::EitherTupleOrPipe,
                )
            })?;
            PatKind::Slice(pats)
        } else if self.check(&token::DotDot) && !self.is_pat_range_end_start(1) {
            // A rest pattern `..`.
            self.bump(); // `..`
            PatKind::Rest
        } else if self.check(&token::DotDotDot) && !self.is_pat_range_end_start(1) {
            self.recover_dotdotdot_rest_pat(lo)
        } else if let Some(form) = self.parse_range_end() {
            self.parse_pat_range_to(form)? // `..=X`, `...X`, or `..X`.
        } else if self.eat_keyword(kw::Underscore) {
            // Parse _
            PatKind::Wild
        } else if self.eat_keyword(kw::Mut) {
            self.parse_pat_ident_mut()?
        } else if self.eat_keyword(kw::Ref) {
            // Parse ref ident @ pat / ref mut ident @ pat
            let mutbl = self.parse_mutability();
            self.parse_pat_ident(BindingAnnotation(ByRef::Yes, mutbl))?
        } else if self.eat_keyword(kw::Box) {
            self.parse_pat_box()?
        } else if self.check_inline_const(0) {
            // Parse `const pat`
            let const_expr = self.parse_const_block(lo.to(self.token.span), true)?;

            if let Some(re) = self.parse_range_end() {
                self.parse_pat_range_begin_with(const_expr, re)?
            } else {
                PatKind::Lit(const_expr)
            }
        } else if self.can_be_ident_pat() {
            // Parse `ident @ pat`
            // This can give false positives and parse nullary enums,
            // they are dealt with later in resolve.
            self.parse_pat_ident(BindingAnnotation::NONE)?
        } else if self.is_start_of_pat_with_path() {
            // Parse pattern starting with a path
            let (qself, path) = if self.eat_lt() {
                // Parse a qualified path
                let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
                (Some(qself), path)
            } else {
                // Parse an unqualified path
                (None, self.parse_path(PathStyle::Expr)?)
            };
            let span = lo.to(self.prev_token.span);

            if qself.is_none() && self.check(&token::Not) {
                self.parse_pat_mac_invoc(path)?
            } else if let Some(form) = self.parse_range_end() {
                let begin = self.mk_expr(span, ExprKind::Path(qself, path));
                self.parse_pat_range_begin_with(begin, form)?
            } else if self.check(&token::OpenDelim(Delimiter::Brace)) {
                self.parse_pat_struct(qself, path)?
            } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
                self.parse_pat_tuple_struct(qself, path)?
            } else {
                PatKind::Path(qself, path)
            }
        } else {
            // Try to parse everything else as literal with optional minus
            match self.parse_literal_maybe_minus() {
                Ok(begin) => match self.parse_range_end() {
                    Some(form) => self.parse_pat_range_begin_with(begin, form)?,
                    None => PatKind::Lit(begin),
                },
                Err(err) => return self.fatal_unexpected_non_pat(err, expected),
            }
        };

        let pat = self.mk_pat(lo.to(self.prev_token.span), pat);
        let pat = self.maybe_recover_from_bad_qpath(pat)?;
        let pat = self.recover_intersection_pat(pat)?;

        if !allow_range_pat {
            self.ban_pat_range_if_ambiguous(&pat)
        }

        Ok(pat)
    }

    /// Recover from a typoed `...` pattern that was encountered
    /// Ref: Issue #70388
    fn recover_dotdotdot_rest_pat(&mut self, lo: Span) -> PatKind {
        // A typoed rest pattern `...`.
        self.bump(); // `...`

        // The user probably mistook `...` for a rest pattern `..`.
        self.struct_span_err(lo, "unexpected `...`")
            .span_label(lo, "not a valid pattern")
            .span_suggestion_short(
                lo,
                "for a rest pattern, use `..` instead of `...`",
                "..",
                Applicability::MachineApplicable,
            )
            .emit();
        PatKind::Rest
    }

    /// Try to recover the more general form `intersect ::= $pat_lhs @ $pat_rhs`.
    ///
    /// Allowed binding patterns generated by `binding ::= ref? mut? $ident @ $pat_rhs`
    /// should already have been parsed by now  at this point,
    /// if the next token is `@` then we can try to parse the more general form.
    ///
    /// Consult `parse_pat_ident` for the `binding` grammar.
    ///
    /// The notion of intersection patterns are found in
    /// e.g. [F#][and] where they are called AND-patterns.
    ///
    /// [and]: https://docs.microsoft.com/en-us/dotnet/fsharp/language-reference/pattern-matching
    fn recover_intersection_pat(&mut self, lhs: P<Pat>) -> PResult<'a, P<Pat>> {
        if self.token.kind != token::At {
            // Next token is not `@` so it's not going to be an intersection pattern.
            return Ok(lhs);
        }

        // At this point we attempt to parse `@ $pat_rhs` and emit an error.
        self.bump(); // `@`
        let mut rhs = self.parse_pat_no_top_alt(None)?;
        let sp = lhs.span.to(rhs.span);

        if let PatKind::Ident(_, _, ref mut sub @ None) = rhs.kind {
            // The user inverted the order, so help them fix that.
            let mut applicability = Applicability::MachineApplicable;
            // FIXME(bindings_after_at): Remove this code when stabilizing the feature.
            lhs.walk(&mut |p| match p.kind {
                // `check_match` is unhappy if the subpattern has a binding anywhere.
                PatKind::Ident(..) => {
                    applicability = Applicability::MaybeIncorrect;
                    false // Short-circuit.
                }
                _ => true,
            });

            let lhs_span = lhs.span;
            // Move the LHS into the RHS as a subpattern.
            // The RHS is now the full pattern.
            *sub = Some(lhs);

            self.struct_span_err(sp, "pattern on wrong side of `@`")
                .span_label(lhs_span, "pattern on the left, should be on the right")
                .span_label(rhs.span, "binding on the right, should be on the left")
                .span_suggestion(sp, "switch the order", pprust::pat_to_string(&rhs), applicability)
                .emit();
        } else {
            // The special case above doesn't apply so we may have e.g. `A(x) @ B(y)`.
            rhs.kind = PatKind::Wild;
            self.struct_span_err(sp, "left-hand side of `@` must be a binding")
                .span_label(lhs.span, "interpreted as a pattern, not a binding")
                .span_label(rhs.span, "also a pattern")
                .note("bindings are `x`, `mut x`, `ref x`, and `ref mut x`")
                .emit();
        }

        rhs.span = sp;
        Ok(rhs)
    }

    /// Ban a range pattern if it has an ambiguous interpretation.
    fn ban_pat_range_if_ambiguous(&self, pat: &Pat) {
        match pat.kind {
            PatKind::Range(
                ..,
                Spanned { node: RangeEnd::Included(RangeSyntax::DotDotDot), .. },
            ) => return,
            PatKind::Range(..) => {}
            _ => return,
        }

        self.struct_span_err(pat.span, "the range pattern here has ambiguous interpretation")
            .span_suggestion(
                pat.span,
                "add parentheses to clarify the precedence",
                format!("({})", pprust::pat_to_string(&pat)),
                // "ambiguous interpretation" implies that we have to be guessing
                Applicability::MaybeIncorrect,
            )
            .emit();
    }

    /// Parse `&pat` / `&mut pat`.
    fn parse_pat_deref(&mut self, expected: Expected) -> PResult<'a, PatKind> {
        self.expect_and()?;
        self.recover_lifetime_in_deref_pat();
        let mutbl = self.parse_mutability();
        let subpat = self.parse_pat_with_range_pat(false, expected)?;
        Ok(PatKind::Ref(subpat, mutbl))
    }

    fn recover_lifetime_in_deref_pat(&mut self) {
        if let token::Lifetime(name) = self.token.kind {
            self.bump(); // `'a`

            let span = self.prev_token.span;
            self.struct_span_err(span, &format!("unexpected lifetime `{}` in pattern", name))
                .span_suggestion(span, "remove the lifetime", "", Applicability::MachineApplicable)
                .emit();
        }
    }

    /// Parse a tuple or parenthesis pattern.
    fn parse_pat_tuple_or_parens(&mut self) -> PResult<'a, PatKind> {
        let (fields, trailing_comma) = self.parse_paren_comma_seq(|p| {
            p.parse_pat_allow_top_alt(
                None,
                RecoverComma::No,
                RecoverColon::No,
                CommaRecoveryMode::LikelyTuple,
            )
        })?;

        // Here, `(pat,)` is a tuple pattern.
        // For backward compatibility, `(..)` is a tuple pattern as well.
        Ok(if fields.len() == 1 && !(trailing_comma || fields[0].is_rest()) {
            PatKind::Paren(fields.into_iter().next().unwrap())
        } else {
            PatKind::Tuple(fields)
        })
    }

    /// Parse a mutable binding with the `mut` token already eaten.
    fn parse_pat_ident_mut(&mut self) -> PResult<'a, PatKind> {
        let mut_span = self.prev_token.span;

        if self.eat_keyword(kw::Ref) {
            return self.recover_mut_ref_ident(mut_span);
        }

        self.recover_additional_muts();

        // Make sure we don't allow e.g. `let mut $p;` where `$p:pat`.
        if let token::Interpolated(ref nt) = self.token.kind {
            if let token::NtPat(_) = **nt {
                self.expected_ident_found().emit();
            }
        }

        // Parse the pattern we hope to be an identifier.
        let mut pat = self.parse_pat_no_top_alt(Some("identifier"))?;

        // If we don't have `mut $ident (@ pat)?`, error.
        if let PatKind::Ident(BindingAnnotation(ByRef::No, m @ Mutability::Not), ..) = &mut pat.kind
        {
            // Don't recurse into the subpattern.
            // `mut` on the outer binding doesn't affect the inner bindings.
            *m = Mutability::Mut;
        } else {
            // Add `mut` to any binding in the parsed pattern.
            let changed_any_binding = Self::make_all_value_bindings_mutable(&mut pat);
            self.ban_mut_general_pat(mut_span, &pat, changed_any_binding);
        }

        Ok(pat.into_inner().kind)
    }

    /// Recover on `mut ref? ident @ pat` and suggest
    /// that the order of `mut` and `ref` is incorrect.
    fn recover_mut_ref_ident(&mut self, lo: Span) -> PResult<'a, PatKind> {
        let mutref_span = lo.to(self.prev_token.span);
        self.struct_span_err(mutref_span, "the order of `mut` and `ref` is incorrect")
            .span_suggestion(
                mutref_span,
                "try switching the order",
                "ref mut",
                Applicability::MachineApplicable,
            )
            .emit();

        self.parse_pat_ident(BindingAnnotation::REF_MUT)
    }

    /// Turn all by-value immutable bindings in a pattern into mutable bindings.
    /// Returns `true` if any change was made.
    fn make_all_value_bindings_mutable(pat: &mut P<Pat>) -> bool {
        struct AddMut(bool);
        impl MutVisitor for AddMut {
            fn visit_pat(&mut self, pat: &mut P<Pat>) {
                if let PatKind::Ident(BindingAnnotation(ByRef::No, m @ Mutability::Not), ..) =
                    &mut pat.kind
                {
                    self.0 = true;
                    *m = Mutability::Mut;
                }
                noop_visit_pat(pat, self);
            }
        }

        let mut add_mut = AddMut(false);
        add_mut.visit_pat(pat);
        add_mut.0
    }

    /// Error on `mut $pat` where `$pat` is not an ident.
    fn ban_mut_general_pat(&self, lo: Span, pat: &Pat, changed_any_binding: bool) {
        let span = lo.to(pat.span);
        let fix = pprust::pat_to_string(&pat);
        let (problem, suggestion) = if changed_any_binding {
            ("`mut` must be attached to each individual binding", "add `mut` to each binding")
        } else {
            ("`mut` must be followed by a named binding", "remove the `mut` prefix")
        };
        self.struct_span_err(span, problem)
            .span_suggestion(span, suggestion, fix, Applicability::MachineApplicable)
            .note("`mut` may be followed by `variable` and `variable @ pattern`")
            .emit();
    }

    /// Eat any extraneous `mut`s and error + recover if we ate any.
    fn recover_additional_muts(&mut self) {
        let lo = self.token.span;
        while self.eat_keyword(kw::Mut) {}
        if lo == self.token.span {
            return;
        }

        let span = lo.to(self.prev_token.span);
        self.struct_span_err(span, "`mut` on a binding may not be repeated")
            .span_suggestion(
                span,
                "remove the additional `mut`s",
                "",
                Applicability::MachineApplicable,
            )
            .emit();
    }

    /// Parse macro invocation
    fn parse_pat_mac_invoc(&mut self, path: Path) -> PResult<'a, PatKind> {
        self.bump();
        let args = self.parse_mac_args()?;
        let mac = P(MacCall { path, args, prior_type_ascription: self.last_type_ascription });
        Ok(PatKind::MacCall(mac))
    }

    fn fatal_unexpected_non_pat(
        &mut self,
        err: DiagnosticBuilder<'a, ErrorGuaranteed>,
        expected: Expected,
    ) -> PResult<'a, P<Pat>> {
        err.cancel();

        let expected = expected.unwrap_or("pattern");
        let msg = format!("expected {}, found {}", expected, super::token_descr(&self.token));

        let mut err = self.struct_span_err(self.token.span, &msg);
        err.span_label(self.token.span, format!("expected {}", expected));

        let sp = self.sess.source_map().start_point(self.token.span);
        if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&sp) {
            self.sess.expr_parentheses_needed(&mut err, *sp);
        }

        Err(err)
    }

    /// Parses the range pattern end form `".." | "..." | "..=" ;`.
    fn parse_range_end(&mut self) -> Option<Spanned<RangeEnd>> {
        let re = if self.eat(&token::DotDotDot) {
            RangeEnd::Included(RangeSyntax::DotDotDot)
        } else if self.eat(&token::DotDotEq) {
            RangeEnd::Included(RangeSyntax::DotDotEq)
        } else if self.eat(&token::DotDot) {
            RangeEnd::Excluded
        } else {
            return None;
        };
        Some(respan(self.prev_token.span, re))
    }

    /// Parse a range pattern `$begin $form $end?` where `$form = ".." | "..." | "..=" ;`.
    /// `$begin $form` has already been parsed.
    fn parse_pat_range_begin_with(
        &mut self,
        begin: P<Expr>,
        re: Spanned<RangeEnd>,
    ) -> PResult<'a, PatKind> {
        let end = if self.is_pat_range_end_start(0) {
            // Parsing e.g. `X..=Y`.
            Some(self.parse_pat_range_end()?)
        } else {
            // Parsing e.g. `X..`.
            if let RangeEnd::Included(_) = re.node {
                // FIXME(Centril): Consider semantic errors instead in `ast_validation`.
                self.inclusive_range_with_incorrect_end(re.span);
            }
            None
        };
        Ok(PatKind::Range(Some(begin), end, re))
    }

    pub(super) fn inclusive_range_with_incorrect_end(&mut self, span: Span) {
        let tok = &self.token;

        // If the user typed "..==" instead of "..=", we want to give them
        // a specific error message telling them to use "..=".
        // Otherwise, we assume that they meant to type a half open exclusive
        // range and give them an error telling them to do that instead.
        if matches!(tok.kind, token::Eq) && tok.span.lo() == span.hi() {
            let span_with_eq = span.to(tok.span);

            // Ensure the user doesn't receive unhelpful unexpected token errors
            self.bump();
            if self.is_pat_range_end_start(0) {
                let _ = self.parse_pat_range_end().map_err(|e| e.cancel());
            }

            self.error_inclusive_range_with_extra_equals(span_with_eq);
        } else {
            self.error_inclusive_range_with_no_end(span);
        }
    }

    fn error_inclusive_range_with_extra_equals(&self, span: Span) {
        self.struct_span_err(span, "unexpected `=` after inclusive range")
            .span_suggestion_short(span, "use `..=` instead", "..=", Applicability::MaybeIncorrect)
            .note("inclusive ranges end with a single equals sign (`..=`)")
            .emit();
    }

    fn error_inclusive_range_with_no_end(&self, span: Span) {
        struct_span_err!(self.sess.span_diagnostic, span, E0586, "inclusive range with no end")
            .span_suggestion_short(span, "use `..` instead", "..", Applicability::MachineApplicable)
            .note("inclusive ranges must be bounded at the end (`..=b` or `a..=b`)")
            .emit();
    }

    /// Parse a range-to pattern, `..X` or `..=X` where `X` remains to be parsed.
    ///
    /// The form `...X` is prohibited to reduce confusion with the potential
    /// expression syntax `...expr` for splatting in expressions.
    fn parse_pat_range_to(&mut self, mut re: Spanned<RangeEnd>) -> PResult<'a, PatKind> {
        let end = self.parse_pat_range_end()?;
        self.sess.gated_spans.gate(sym::half_open_range_patterns, re.span.to(self.prev_token.span));
        if let RangeEnd::Included(ref mut syn @ RangeSyntax::DotDotDot) = &mut re.node {
            *syn = RangeSyntax::DotDotEq;
            self.struct_span_err(re.span, "range-to patterns with `...` are not allowed")
                .span_suggestion_short(
                    re.span,
                    "use `..=` instead",
                    "..=",
                    Applicability::MachineApplicable,
                )
                .emit();
        }
        Ok(PatKind::Range(None, Some(end), re))
    }

    /// Is the token `dist` away from the current suitable as the start of a range patterns end?
    fn is_pat_range_end_start(&self, dist: usize) -> bool {
        self.check_inline_const(dist)
            || self.look_ahead(dist, |t| {
                t.is_path_start() // e.g. `MY_CONST`;
                || t.kind == token::Dot // e.g. `.5` for recovery;
                || t.can_begin_literal_maybe_minus() // e.g. `42`.
                || t.is_whole_expr()
            })
    }

    fn parse_pat_range_end(&mut self) -> PResult<'a, P<Expr>> {
        if self.check_inline_const(0) {
            self.parse_const_block(self.token.span, true)
        } else if self.check_path() {
            let lo = self.token.span;
            let (qself, path) = if self.eat_lt() {
                // Parse a qualified path
                let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
                (Some(qself), path)
            } else {
                // Parse an unqualified path
                (None, self.parse_path(PathStyle::Expr)?)
            };
            let hi = self.prev_token.span;
            Ok(self.mk_expr(lo.to(hi), ExprKind::Path(qself, path)))
        } else {
            self.parse_literal_maybe_minus()
        }
    }

    /// Is this the start of a pattern beginning with a path?
    fn is_start_of_pat_with_path(&mut self) -> bool {
        self.check_path()
        // Just for recovery (see `can_be_ident`).
        || self.token.is_ident() && !self.token.is_bool_lit() && !self.token.is_keyword(kw::In)
    }

    /// Would `parse_pat_ident` be appropriate here?
    fn can_be_ident_pat(&mut self) -> bool {
        self.check_ident()
        && !self.token.is_bool_lit() // Avoid `true` or `false` as a binding as it is a literal.
        && !self.token.is_path_segment_keyword() // Avoid e.g. `Self` as it is a path.
        // Avoid `in`. Due to recovery in the list parser this messes with `for ( $pat in $expr )`.
        && !self.token.is_keyword(kw::In)
        // Try to do something more complex?
        && self.look_ahead(1, |t| !matches!(t.kind, token::OpenDelim(Delimiter::Parenthesis) // A tuple struct pattern.
            | token::OpenDelim(Delimiter::Brace) // A struct pattern.
            | token::DotDotDot | token::DotDotEq | token::DotDot // A range pattern.
            | token::ModSep // A tuple / struct variant pattern.
            | token::Not)) // A macro expanding to a pattern.
    }

    /// Parses `ident` or `ident @ pat`.
    /// Used by the copy foo and ref foo patterns to give a good
    /// error message when parsing mistakes like `ref foo(a, b)`.
    fn parse_pat_ident(&mut self, binding_annotation: BindingAnnotation) -> PResult<'a, PatKind> {
        let ident = self.parse_ident()?;
        let sub = if self.eat(&token::At) {
            Some(self.parse_pat_no_top_alt(Some("binding pattern"))?)
        } else {
            None
        };

        // Just to be friendly, if they write something like `ref Some(i)`,
        // we end up here with `(` as the current token.
        // This shortly leads to a parse error. Note that if there is no explicit
        // binding mode then we do not end up here, because the lookahead
        // will direct us over to `parse_enum_variant()`.
        if self.token == token::OpenDelim(Delimiter::Parenthesis) {
            return Err(self
                .struct_span_err(self.prev_token.span, "expected identifier, found enum pattern"));
        }

        Ok(PatKind::Ident(binding_annotation, ident, sub))
    }

    /// Parse a struct ("record") pattern (e.g. `Foo { ... }` or `Foo::Bar { ... }`).
    fn parse_pat_struct(&mut self, qself: Option<QSelf>, path: Path) -> PResult<'a, PatKind> {
        if qself.is_some() {
            // Feature gate the use of qualified paths in patterns
            self.sess.gated_spans.gate(sym::more_qualified_paths, path.span);
        }
        self.bump();
        let (fields, etc) = self.parse_pat_fields().unwrap_or_else(|mut e| {
            e.span_label(path.span, "while parsing the fields for this pattern");
            e.emit();
            self.recover_stmt();
            (vec![], true)
        });
        self.bump();
        Ok(PatKind::Struct(qself, path, fields, etc))
    }

    /// Parse tuple struct or tuple variant pattern (e.g. `Foo(...)` or `Foo::Bar(...)`).
    fn parse_pat_tuple_struct(&mut self, qself: Option<QSelf>, path: Path) -> PResult<'a, PatKind> {
        let (fields, _) = self.parse_paren_comma_seq(|p| {
            p.parse_pat_allow_top_alt(
                None,
                RecoverComma::No,
                RecoverColon::No,
                CommaRecoveryMode::EitherTupleOrPipe,
            )
        })?;
        if qself.is_some() {
            self.sess.gated_spans.gate(sym::more_qualified_paths, path.span);
        }
        Ok(PatKind::TupleStruct(qself, path, fields))
    }

    /// Are we sure this could not possibly be the start of a pattern?
    ///
    /// Currently, this only accounts for tokens that can follow identifiers
    /// in patterns, but this can be extended as necessary.
    fn isnt_pattern_start(&self) -> bool {
        [
            token::Eq,
            token::Colon,
            token::Comma,
            token::Semi,
            token::At,
            token::OpenDelim(Delimiter::Brace),
            token::CloseDelim(Delimiter::Brace),
            token::CloseDelim(Delimiter::Parenthesis),
        ]
        .contains(&self.token.kind)
    }

    /// Parses `box pat`
    fn parse_pat_box(&mut self) -> PResult<'a, PatKind> {
        let box_span = self.prev_token.span;

        if self.isnt_pattern_start() {
            self.struct_span_err(
                self.token.span,
                format!("expected pattern, found {}", super::token_descr(&self.token)),
            )
            .span_note(box_span, "`box` is a reserved keyword")
            .span_suggestion_verbose(
                box_span.shrink_to_lo(),
                "escape `box` to use it as an identifier",
                "r#",
                Applicability::MaybeIncorrect,
            )
            .emit();

            // We cannot use `parse_pat_ident()` since it will complain `box`
            // is not an identifier.
            let sub = if self.eat(&token::At) {
                Some(self.parse_pat_no_top_alt(Some("binding pattern"))?)
            } else {
                None
            };

            Ok(PatKind::Ident(BindingAnnotation::NONE, Ident::new(kw::Box, box_span), sub))
        } else {
            let pat = self.parse_pat_with_range_pat(false, None)?;
            self.sess.gated_spans.gate(sym::box_patterns, box_span.to(self.prev_token.span));
            Ok(PatKind::Box(pat))
        }
    }

    /// Parses the fields of a struct-like pattern.
    fn parse_pat_fields(&mut self) -> PResult<'a, (Vec<PatField>, bool)> {
        let mut fields = Vec::new();
        let mut etc = false;
        let mut ate_comma = true;
        let mut delayed_err: Option<DiagnosticBuilder<'a, ErrorGuaranteed>> = None;
        let mut etc_span = None;

        while self.token != token::CloseDelim(Delimiter::Brace) {
            let attrs = match self.parse_outer_attributes() {
                Ok(attrs) => attrs,
                Err(err) => {
                    if let Some(mut delayed) = delayed_err {
                        delayed.emit();
                    }
                    return Err(err);
                }
            };
            let lo = self.token.span;

            // check that a comma comes after every field
            if !ate_comma {
                let err = self.struct_span_err(self.token.span, "expected `,`");
                if let Some(mut delayed) = delayed_err {
                    delayed.emit();
                }
                return Err(err);
            }
            ate_comma = false;

            if self.check(&token::DotDot) || self.token == token::DotDotDot {
                etc = true;
                let mut etc_sp = self.token.span;

                self.recover_one_fewer_dotdot();
                self.bump(); // `..` || `...`

                if self.token == token::CloseDelim(Delimiter::Brace) {
                    etc_span = Some(etc_sp);
                    break;
                }
                let token_str = super::token_descr(&self.token);
                let msg = &format!("expected `}}`, found {}", token_str);
                let mut err = self.struct_span_err(self.token.span, msg);

                err.span_label(self.token.span, "expected `}`");
                let mut comma_sp = None;
                if self.token == token::Comma {
                    // Issue #49257
                    let nw_span = self.sess.source_map().span_until_non_whitespace(self.token.span);
                    etc_sp = etc_sp.to(nw_span);
                    err.span_label(
                        etc_sp,
                        "`..` must be at the end and cannot have a trailing comma",
                    );
                    comma_sp = Some(self.token.span);
                    self.bump();
                    ate_comma = true;
                }

                etc_span = Some(etc_sp.until(self.token.span));
                if self.token == token::CloseDelim(Delimiter::Brace) {
                    // If the struct looks otherwise well formed, recover and continue.
                    if let Some(sp) = comma_sp {
                        err.span_suggestion_short(
                            sp,
                            "remove this comma",
                            "",
                            Applicability::MachineApplicable,
                        );
                    }
                    err.emit();
                    break;
                } else if self.token.is_ident() && ate_comma {
                    // Accept fields coming after `..,`.
                    // This way we avoid "pattern missing fields" errors afterwards.
                    // We delay this error until the end in order to have a span for a
                    // suggested fix.
                    if let Some(mut delayed_err) = delayed_err {
                        delayed_err.emit();
                        return Err(err);
                    } else {
                        delayed_err = Some(err);
                    }
                } else {
                    if let Some(mut err) = delayed_err {
                        err.emit();
                    }
                    return Err(err);
                }
            }

            let field =
                self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
                    let field = match this.parse_pat_field(lo, attrs) {
                        Ok(field) => Ok(field),
                        Err(err) => {
                            if let Some(mut delayed_err) = delayed_err.take() {
                                delayed_err.emit();
                            }
                            return Err(err);
                        }
                    }?;
                    ate_comma = this.eat(&token::Comma);
                    // We just ate a comma, so there's no need to use
                    // `TrailingToken::Comma`
                    Ok((field, TrailingToken::None))
                })?;

            fields.push(field)
        }

        if let Some(mut err) = delayed_err {
            if let Some(etc_span) = etc_span {
                err.multipart_suggestion(
                    "move the `..` to the end of the field list",
                    vec![
                        (etc_span, String::new()),
                        (self.token.span, format!("{}.. }}", if ate_comma { "" } else { ", " })),
                    ],
                    Applicability::MachineApplicable,
                );
            }
            err.emit();
        }
        Ok((fields, etc))
    }

    /// Recover on `...` as if it were `..` to avoid further errors.
    /// See issue #46718.
    fn recover_one_fewer_dotdot(&self) {
        if self.token != token::DotDotDot {
            return;
        }

        self.struct_span_err(self.token.span, "expected field pattern, found `...`")
            .span_suggestion(
                self.token.span,
                "to omit remaining fields, use one fewer `.`",
                "..",
                Applicability::MachineApplicable,
            )
            .emit();
    }

    fn parse_pat_field(&mut self, lo: Span, attrs: AttrVec) -> PResult<'a, PatField> {
        // Check if a colon exists one ahead. This means we're parsing a fieldname.
        let hi;
        let (subpat, fieldname, is_shorthand) = if self.look_ahead(1, |t| t == &token::Colon) {
            // Parsing a pattern of the form `fieldname: pat`.
            let fieldname = self.parse_field_name()?;
            self.bump();
            let pat = self.parse_pat_allow_top_alt(
                None,
                RecoverComma::No,
                RecoverColon::No,
                CommaRecoveryMode::EitherTupleOrPipe,
            )?;
            hi = pat.span;
            (pat, fieldname, false)
        } else {
            // Parsing a pattern of the form `(box) (ref) (mut) fieldname`.
            let is_box = self.eat_keyword(kw::Box);
            let boxed_span = self.token.span;
            let is_ref = self.eat_keyword(kw::Ref);
            let is_mut = self.eat_keyword(kw::Mut);
            let fieldname = self.parse_field_name()?;
            hi = self.prev_token.span;

            let mutability = match is_mut {
                false => Mutability::Not,
                true => Mutability::Mut,
            };
            let ann = BindingAnnotation(ByRef::from(is_ref), mutability);
            let fieldpat = self.mk_pat_ident(boxed_span.to(hi), ann, fieldname);
            let subpat =
                if is_box { self.mk_pat(lo.to(hi), PatKind::Box(fieldpat)) } else { fieldpat };
            (subpat, fieldname, true)
        };

        Ok(PatField {
            ident: fieldname,
            pat: subpat,
            is_shorthand,
            attrs,
            id: ast::DUMMY_NODE_ID,
            span: lo.to(hi),
            is_placeholder: false,
        })
    }

    pub(super) fn mk_pat_ident(&self, span: Span, ann: BindingAnnotation, ident: Ident) -> P<Pat> {
        self.mk_pat(span, PatKind::Ident(ann, ident, None))
    }

    pub(super) fn mk_pat(&self, span: Span, kind: PatKind) -> P<Pat> {
        P(Pat { kind, span, id: ast::DUMMY_NODE_ID, tokens: None })
    }
}