rustc_lint/
levels.rs

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
use rustc_ast_pretty::pprust;
use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
use rustc_errors::{Diag, LintDiagnostic, MultiSpan};
use rustc_feature::{Features, GateIssue};
use rustc_hir::intravisit::{self, Visitor};
use rustc_hir::{CRATE_HIR_ID, HirId};
use rustc_index::IndexVec;
use rustc_middle::bug;
use rustc_middle::hir::nested_filter;
use rustc_middle::lint::{
    LevelAndSource, LintExpectation, LintLevelSource, ShallowLintLevelMap, lint_level,
    reveal_actual_level,
};
use rustc_middle::query::Providers;
use rustc_middle::ty::{RegisteredTools, TyCtxt};
use rustc_session::Session;
use rustc_session::lint::builtin::{
    self, FORBIDDEN_LINT_GROUPS, RENAMED_AND_REMOVED_LINTS, SINGLE_USE_LIFETIMES,
    UNFULFILLED_LINT_EXPECTATIONS, UNKNOWN_LINTS, UNUSED_ATTRIBUTES,
};
use rustc_session::lint::{Level, Lint, LintExpectationId, LintId};
use rustc_span::symbol::{Symbol, sym};
use rustc_span::{DUMMY_SP, Span};
use tracing::{debug, instrument};
use {rustc_ast as ast, rustc_hir as hir};

use crate::builtin::MISSING_DOCS;
use crate::context::{CheckLintNameResult, LintStore};
use crate::errors::{
    CheckNameUnknownTool, MalformedAttribute, MalformedAttributeSub, OverruledAttribute,
    OverruledAttributeSub, RequestedLevel, UnknownToolInScopedLint, UnsupportedGroup,
};
use crate::fluent_generated as fluent;
use crate::late::unerased_lint_store;
use crate::lints::{
    DeprecatedLintName, DeprecatedLintNameFromCommandLine, IgnoredUnlessCrateSpecified,
    OverruledAttributeLint, RemovedLint, RemovedLintFromCommandLine, RenamedLint,
    RenamedLintFromCommandLine, RenamedLintSuggestion, UnknownLint, UnknownLintFromCommandLine,
    UnknownLintSuggestion,
};

/// Collection of lint levels for the whole crate.
/// This is used by AST-based lints, which do not
/// wait until we have built HIR to be emitted.
#[derive(Debug)]
struct LintLevelSets {
    /// Linked list of specifications.
    list: IndexVec<LintStackIndex, LintSet>,
}

rustc_index::newtype_index! {
    struct LintStackIndex {
        const COMMAND_LINE = 0;
    }
}

/// Specifications found at this position in the stack. This map only represents the lints
/// found for one set of attributes (like `shallow_lint_levels_on` does).
///
/// We store the level specifications as a linked list.
/// Each `LintSet` represents a set of attributes on the same AST node.
/// The `parent` forms a linked list that matches the AST tree.
/// This way, walking the linked list is equivalent to walking the AST bottom-up
/// to find the specifications for a given lint.
#[derive(Debug)]
struct LintSet {
    // -A,-W,-D flags, a `Symbol` for the flag itself and `Level` for which
    // flag.
    specs: FxIndexMap<LintId, LevelAndSource>,
    parent: LintStackIndex,
}

impl LintLevelSets {
    fn new() -> Self {
        LintLevelSets { list: IndexVec::new() }
    }

    fn get_lint_level(
        &self,
        lint: &'static Lint,
        idx: LintStackIndex,
        aux: Option<&FxIndexMap<LintId, LevelAndSource>>,
        sess: &Session,
    ) -> LevelAndSource {
        let lint = LintId::of(lint);
        let (level, mut src) = self.raw_lint_id_level(lint, idx, aux);
        let level = reveal_actual_level(level, &mut src, sess, lint, |id| {
            self.raw_lint_id_level(id, idx, aux)
        });
        (level, src)
    }

    fn raw_lint_id_level(
        &self,
        id: LintId,
        mut idx: LintStackIndex,
        aux: Option<&FxIndexMap<LintId, LevelAndSource>>,
    ) -> (Option<Level>, LintLevelSource) {
        if let Some(specs) = aux
            && let Some(&(level, src)) = specs.get(&id)
        {
            return (Some(level), src);
        }

        loop {
            let LintSet { ref specs, parent } = self.list[idx];
            if let Some(&(level, src)) = specs.get(&id) {
                return (Some(level), src);
            }
            if idx == COMMAND_LINE {
                return (None, LintLevelSource::Default);
            }
            idx = parent;
        }
    }
}

fn lints_that_dont_need_to_run(tcx: TyCtxt<'_>, (): ()) -> FxIndexSet<LintId> {
    let store = unerased_lint_store(&tcx.sess);

    let map = tcx.shallow_lint_levels_on(rustc_hir::CRATE_OWNER_ID);

    let dont_need_to_run: FxIndexSet<LintId> = store
        .get_lints()
        .into_iter()
        .filter(|lint| {
            // Lints that show up in future-compat reports must always be run.
            let has_future_breakage =
                lint.future_incompatible.is_some_and(|fut| fut.reason.has_future_breakage());
            !has_future_breakage && !lint.eval_always
        })
        .filter_map(|lint| {
            let lint_level = map.lint_level_id_at_node(tcx, LintId::of(lint), CRATE_HIR_ID);
            if matches!(lint_level, (Level::Allow, ..))
                || (matches!(lint_level, (.., LintLevelSource::Default)))
                    && lint.default_level(tcx.sess.edition()) == Level::Allow
            {
                Some(LintId::of(lint))
            } else {
                None
            }
        })
        .collect();

    let mut visitor = LintLevelMaximum { tcx, dont_need_to_run };
    visitor.process_opts();
    tcx.hir().walk_attributes(&mut visitor);

    visitor.dont_need_to_run
}

#[instrument(level = "trace", skip(tcx), ret)]
fn shallow_lint_levels_on(tcx: TyCtxt<'_>, owner: hir::OwnerId) -> ShallowLintLevelMap {
    let store = unerased_lint_store(tcx.sess);
    let attrs = tcx.hir_attrs(owner);

    let mut levels = LintLevelsBuilder {
        sess: tcx.sess,
        features: tcx.features(),
        provider: LintLevelQueryMap {
            tcx,
            cur: owner.into(),
            specs: ShallowLintLevelMap::default(),
            empty: FxIndexMap::default(),
            attrs,
        },
        lint_added_lints: false,
        store,
        registered_tools: tcx.registered_tools(()),
    };

    if owner == hir::CRATE_OWNER_ID {
        levels.add_command_line();
    }

    match attrs.map.range(..) {
        // There is only something to do if there are attributes at all.
        [] => {}
        // Most of the time, there is only one attribute. Avoid fetching HIR in that case.
        &[(local_id, _)] => levels.add_id(HirId { owner, local_id }),
        // Otherwise, we need to visit the attributes in source code order, so we fetch HIR and do
        // a standard visit.
        // FIXME(#102522) Just iterate on attrs once that iteration order matches HIR's.
        _ => match tcx.hir_owner_node(owner) {
            hir::OwnerNode::Item(item) => levels.visit_item(item),
            hir::OwnerNode::ForeignItem(item) => levels.visit_foreign_item(item),
            hir::OwnerNode::TraitItem(item) => levels.visit_trait_item(item),
            hir::OwnerNode::ImplItem(item) => levels.visit_impl_item(item),
            hir::OwnerNode::Crate(mod_) => {
                levels.add_id(hir::CRATE_HIR_ID);
                levels.visit_mod(mod_, mod_.spans.inner_span, hir::CRATE_HIR_ID)
            }
            hir::OwnerNode::Synthetic => unreachable!(),
        },
    }

    let specs = levels.provider.specs;

    #[cfg(debug_assertions)]
    for (_, v) in specs.specs.iter() {
        debug_assert!(!v.is_empty());
    }

    specs
}

pub struct TopDown {
    sets: LintLevelSets,
    cur: LintStackIndex,
}

pub trait LintLevelsProvider {
    fn current_specs(&self) -> &FxIndexMap<LintId, LevelAndSource>;
    fn insert(&mut self, id: LintId, lvl: LevelAndSource);
    fn get_lint_level(&self, lint: &'static Lint, sess: &Session) -> LevelAndSource;
    fn push_expectation(&mut self, id: LintExpectationId, expectation: LintExpectation);
}

impl LintLevelsProvider for TopDown {
    fn current_specs(&self) -> &FxIndexMap<LintId, LevelAndSource> {
        &self.sets.list[self.cur].specs
    }

    fn insert(&mut self, id: LintId, lvl: LevelAndSource) {
        self.sets.list[self.cur].specs.insert(id, lvl);
    }

    fn get_lint_level(&self, lint: &'static Lint, sess: &Session) -> LevelAndSource {
        self.sets.get_lint_level(lint, self.cur, Some(self.current_specs()), sess)
    }

    fn push_expectation(&mut self, _: LintExpectationId, _: LintExpectation) {}
}

struct LintLevelQueryMap<'tcx> {
    tcx: TyCtxt<'tcx>,
    cur: HirId,
    specs: ShallowLintLevelMap,
    /// Empty hash map to simplify code.
    empty: FxIndexMap<LintId, LevelAndSource>,
    attrs: &'tcx hir::AttributeMap<'tcx>,
}

impl LintLevelsProvider for LintLevelQueryMap<'_> {
    fn current_specs(&self) -> &FxIndexMap<LintId, LevelAndSource> {
        self.specs.specs.get(&self.cur.local_id).unwrap_or(&self.empty)
    }
    fn insert(&mut self, id: LintId, lvl: LevelAndSource) {
        self.specs.specs.get_mut_or_insert_default(self.cur.local_id).insert(id, lvl);
    }
    fn get_lint_level(&self, lint: &'static Lint, _: &Session) -> LevelAndSource {
        self.specs.lint_level_id_at_node(self.tcx, LintId::of(lint), self.cur)
    }
    fn push_expectation(&mut self, id: LintExpectationId, expectation: LintExpectation) {
        self.specs.expectations.push((id, expectation))
    }
}

impl<'tcx> LintLevelsBuilder<'_, LintLevelQueryMap<'tcx>> {
    fn add_id(&mut self, hir_id: HirId) {
        self.provider.cur = hir_id;
        self.add(
            self.provider.attrs.get(hir_id.local_id),
            hir_id == hir::CRATE_HIR_ID,
            Some(hir_id),
        );
    }
}

impl<'tcx> Visitor<'tcx> for LintLevelsBuilder<'_, LintLevelQueryMap<'tcx>> {
    type NestedFilter = nested_filter::OnlyBodies;

    fn nested_visit_map(&mut self) -> Self::Map {
        self.provider.tcx.hir()
    }

    fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
        self.add_id(param.hir_id);
        intravisit::walk_param(self, param);
    }

    fn visit_item(&mut self, it: &'tcx hir::Item<'tcx>) {
        self.add_id(it.hir_id());
        intravisit::walk_item(self, it);
    }

    fn visit_foreign_item(&mut self, it: &'tcx hir::ForeignItem<'tcx>) {
        self.add_id(it.hir_id());
        intravisit::walk_foreign_item(self, it);
    }

    fn visit_stmt(&mut self, s: &'tcx hir::Stmt<'tcx>) {
        self.add_id(s.hir_id);
        intravisit::walk_stmt(self, s);
    }

    fn visit_expr(&mut self, e: &'tcx hir::Expr<'tcx>) {
        self.add_id(e.hir_id);
        intravisit::walk_expr(self, e);
    }

    fn visit_expr_field(&mut self, f: &'tcx hir::ExprField<'tcx>) {
        self.add_id(f.hir_id);
        intravisit::walk_expr_field(self, f);
    }

    fn visit_field_def(&mut self, s: &'tcx hir::FieldDef<'tcx>) {
        self.add_id(s.hir_id);
        intravisit::walk_field_def(self, s);
    }

    fn visit_variant(&mut self, v: &'tcx hir::Variant<'tcx>) {
        self.add_id(v.hir_id);
        intravisit::walk_variant(self, v);
    }

    fn visit_local(&mut self, l: &'tcx hir::LetStmt<'tcx>) {
        self.add_id(l.hir_id);
        intravisit::walk_local(self, l);
    }

    fn visit_arm(&mut self, a: &'tcx hir::Arm<'tcx>) {
        self.add_id(a.hir_id);
        intravisit::walk_arm(self, a);
    }

    fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
        self.add_id(trait_item.hir_id());
        intravisit::walk_trait_item(self, trait_item);
    }

    fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
        self.add_id(impl_item.hir_id());
        intravisit::walk_impl_item(self, impl_item);
    }
}

/// Visitor with the only function of visiting every item-like in a crate and
/// computing the highest level that every lint gets put to.
///
/// E.g., if a crate has a global #![allow(lint)] attribute, but a single item
/// uses #[warn(lint)], this visitor will set that lint level as `Warn`
struct LintLevelMaximum<'tcx> {
    tcx: TyCtxt<'tcx>,
    /// The actual list of detected lints.
    dont_need_to_run: FxIndexSet<LintId>,
}

impl<'tcx> LintLevelMaximum<'tcx> {
    fn process_opts(&mut self) {
        let store = unerased_lint_store(self.tcx.sess);
        for (lint_group, level) in &self.tcx.sess.opts.lint_opts {
            if *level != Level::Allow {
                let Ok(lints) = store.find_lints(lint_group) else {
                    return;
                };
                for lint in lints {
                    self.dont_need_to_run.swap_remove(&lint);
                }
            }
        }
    }
}

impl<'tcx> Visitor<'tcx> for LintLevelMaximum<'tcx> {
    type NestedFilter = nested_filter::All;

    fn nested_visit_map(&mut self) -> Self::Map {
        self.tcx.hir()
    }

    /// FIXME(blyxyas): In a future revision, we should also graph #![allow]s,
    /// but that is handled with more care
    fn visit_attribute(&mut self, attribute: &'tcx ast::Attribute) {
        if matches!(
            Level::from_attr(attribute),
            Some(
                Level::Warn
                    | Level::Deny
                    | Level::Forbid
                    | Level::Expect(..)
                    | Level::ForceWarn(..),
            )
        ) {
            let store = unerased_lint_store(self.tcx.sess);
            let Some(meta) = attribute.meta() else { return };
            // Lint attributes are always a metalist inside a
            // metalist (even with just one lint).
            let Some(meta_item_list) = meta.meta_item_list() else { return };

            for meta_list in meta_item_list {
                // Convert Path to String
                let Some(meta_item) = meta_list.meta_item() else { return };
                let ident: &str = &meta_item
                    .path
                    .segments
                    .iter()
                    .map(|segment| segment.ident.as_str())
                    .collect::<Vec<&str>>()
                    .join("::");
                let Ok(lints) = store.find_lints(
                    // Lint attributes can only have literals
                    ident,
                ) else {
                    return;
                };
                for lint in lints {
                    self.dont_need_to_run.swap_remove(&lint);
                }
            }
        }
    }
}

pub struct LintLevelsBuilder<'s, P> {
    sess: &'s Session,
    features: &'s Features,
    provider: P,
    lint_added_lints: bool,
    store: &'s LintStore,
    registered_tools: &'s RegisteredTools,
}

pub(crate) struct BuilderPush {
    prev: LintStackIndex,
}

impl<'s> LintLevelsBuilder<'s, TopDown> {
    pub(crate) fn new(
        sess: &'s Session,
        features: &'s Features,
        lint_added_lints: bool,
        store: &'s LintStore,
        registered_tools: &'s RegisteredTools,
    ) -> Self {
        let mut builder = LintLevelsBuilder {
            sess,
            features,
            provider: TopDown { sets: LintLevelSets::new(), cur: COMMAND_LINE },
            lint_added_lints,
            store,
            registered_tools,
        };
        builder.process_command_line();
        assert_eq!(builder.provider.sets.list.len(), 1);
        builder
    }

    fn process_command_line(&mut self) {
        self.provider.cur = self
            .provider
            .sets
            .list
            .push(LintSet { specs: FxIndexMap::default(), parent: COMMAND_LINE });
        self.add_command_line();
    }

    /// Pushes a list of AST lint attributes onto this context.
    ///
    /// This function will return a `BuilderPush` object which should be passed
    /// to `pop` when this scope for the attributes provided is exited.
    ///
    /// This function will perform a number of tasks:
    ///
    /// * It'll validate all lint-related attributes in `attrs`
    /// * It'll mark all lint-related attributes as used
    /// * Lint levels will be updated based on the attributes provided
    /// * Lint attributes are validated, e.g., a `#[forbid]` can't be switched to
    ///   `#[allow]`
    ///
    /// Don't forget to call `pop`!
    pub(crate) fn push(
        &mut self,
        attrs: &[ast::Attribute],
        is_crate_node: bool,
        source_hir_id: Option<HirId>,
    ) -> BuilderPush {
        let prev = self.provider.cur;
        self.provider.cur =
            self.provider.sets.list.push(LintSet { specs: FxIndexMap::default(), parent: prev });

        self.add(attrs, is_crate_node, source_hir_id);

        if self.provider.current_specs().is_empty() {
            self.provider.sets.list.pop();
            self.provider.cur = prev;
        }

        BuilderPush { prev }
    }

    /// Called after `push` when the scope of a set of attributes are exited.
    pub(crate) fn pop(&mut self, push: BuilderPush) {
        self.provider.cur = push.prev;
        std::mem::forget(push);
    }
}

#[cfg(debug_assertions)]
impl Drop for BuilderPush {
    fn drop(&mut self) {
        panic!("Found a `push` without a `pop`.");
    }
}

impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
    pub(crate) fn sess(&self) -> &Session {
        self.sess
    }

    pub(crate) fn features(&self) -> &Features {
        self.features
    }

    fn current_specs(&self) -> &FxIndexMap<LintId, LevelAndSource> {
        self.provider.current_specs()
    }

    fn insert(&mut self, id: LintId, lvl: LevelAndSource) {
        self.provider.insert(id, lvl)
    }

    fn add_command_line(&mut self) {
        for &(ref lint_name, level) in &self.sess.opts.lint_opts {
            // Checks the validity of lint names derived from the command line.
            let (tool_name, lint_name_only) = parse_lint_and_tool_name(lint_name);
            if lint_name_only == crate::WARNINGS.name_lower()
                && matches!(level, Level::ForceWarn(_))
            {
                self.sess
                    .dcx()
                    .emit_err(UnsupportedGroup { lint_group: crate::WARNINGS.name_lower() });
            }
            match self.store.check_lint_name(lint_name_only, tool_name, self.registered_tools) {
                CheckLintNameResult::Renamed(ref replace) => {
                    let name = lint_name.as_str();
                    let suggestion = RenamedLintSuggestion::WithoutSpan { replace };
                    let requested_level = RequestedLevel { level, lint_name };
                    let lint = RenamedLintFromCommandLine { name, suggestion, requested_level };
                    self.emit_lint(RENAMED_AND_REMOVED_LINTS, lint);
                }
                CheckLintNameResult::Removed(ref reason) => {
                    let name = lint_name.as_str();
                    let requested_level = RequestedLevel { level, lint_name };
                    let lint = RemovedLintFromCommandLine { name, reason, requested_level };
                    self.emit_lint(RENAMED_AND_REMOVED_LINTS, lint);
                }
                CheckLintNameResult::NoLint(suggestion) => {
                    let name = lint_name.clone();
                    let suggestion = suggestion.map(|(replace, from_rustc)| {
                        UnknownLintSuggestion::WithoutSpan { replace, from_rustc }
                    });
                    let requested_level = RequestedLevel { level, lint_name };
                    let lint = UnknownLintFromCommandLine { name, suggestion, requested_level };
                    self.emit_lint(UNKNOWN_LINTS, lint);
                }
                CheckLintNameResult::Tool(_, Some(ref replace)) => {
                    let name = lint_name.clone();
                    let requested_level = RequestedLevel { level, lint_name };
                    let lint = DeprecatedLintNameFromCommandLine { name, replace, requested_level };
                    self.emit_lint(RENAMED_AND_REMOVED_LINTS, lint);
                }
                CheckLintNameResult::NoTool => {
                    self.sess.dcx().emit_err(CheckNameUnknownTool {
                        tool_name: tool_name.unwrap(),
                        sub: RequestedLevel { level, lint_name },
                    });
                }
                _ => {}
            };

            let orig_level = level;
            let lint_flag_val = Symbol::intern(lint_name);

            let Ok(ids) = self.store.find_lints(lint_name) else {
                // errors already handled above
                continue;
            };
            for id in ids {
                // ForceWarn and Forbid cannot be overridden
                if let Some((Level::ForceWarn(_) | Level::Forbid, _)) =
                    self.current_specs().get(&id)
                {
                    continue;
                }

                if self.check_gated_lint(id, DUMMY_SP, true) {
                    let src = LintLevelSource::CommandLine(lint_flag_val, orig_level);
                    self.insert(id, (level, src));
                }
            }
        }
    }

    /// Attempts to insert the `id` to `level_src` map entry. If unsuccessful
    /// (e.g. if a forbid was already inserted on the same scope), then emits a
    /// diagnostic with no change to `specs`.
    fn insert_spec(&mut self, id: LintId, (level, src): LevelAndSource) {
        let (old_level, old_src) = self.provider.get_lint_level(id.lint, self.sess);

        // Setting to a non-forbid level is an error if the lint previously had
        // a forbid level. Note that this is not necessarily true even with a
        // `#[forbid(..)]` attribute present, as that is overridden by `--cap-lints`.
        //
        // This means that this only errors if we're truly lowering the lint
        // level from forbid.
        if self.lint_added_lints && level == Level::Deny && old_level == Level::Forbid {
            // Having a deny inside a forbid is fine and is ignored, so we skip this check.
            return;
        } else if self.lint_added_lints && level != Level::Forbid && old_level == Level::Forbid {
            // Backwards compatibility check:
            //
            // We used to not consider `forbid(lint_group)`
            // as preventing `allow(lint)` for some lint `lint` in
            // `lint_group`. For now, issue a future-compatibility
            // warning for this case.
            let id_name = id.lint.name_lower();
            let fcw_warning = match old_src {
                LintLevelSource::Default => false,
                LintLevelSource::Node { name, .. } => self.store.is_lint_group(name),
                LintLevelSource::CommandLine(symbol, _) => self.store.is_lint_group(symbol),
            };
            debug!(
                "fcw_warning={:?}, specs.get(&id) = {:?}, old_src={:?}, id_name={:?}",
                fcw_warning,
                self.current_specs(),
                old_src,
                id_name
            );
            let sub = match old_src {
                LintLevelSource::Default => {
                    OverruledAttributeSub::DefaultSource { id: id.to_string() }
                }
                LintLevelSource::Node { span, reason, .. } => {
                    OverruledAttributeSub::NodeSource { span, reason }
                }
                LintLevelSource::CommandLine(_, _) => OverruledAttributeSub::CommandLineSource,
            };
            if !fcw_warning {
                self.sess.dcx().emit_err(OverruledAttribute {
                    span: src.span(),
                    overruled: src.span(),
                    lint_level: level.as_str(),
                    lint_source: src.name(),
                    sub,
                });
            } else {
                self.emit_span_lint(
                    FORBIDDEN_LINT_GROUPS,
                    src.span().into(),
                    OverruledAttributeLint {
                        overruled: src.span(),
                        lint_level: level.as_str(),
                        lint_source: src.name(),
                        sub,
                    },
                );
            }

            // Retain the forbid lint level, unless we are
            // issuing a FCW. In the FCW case, we want to
            // respect the new setting.
            if !fcw_warning {
                return;
            }
        }

        // The lint `unfulfilled_lint_expectations` can't be expected, as it would suppress itself.
        // Handling expectations of this lint would add additional complexity with little to no
        // benefit. The expect level for this lint will therefore be ignored.
        if let Level::Expect(_) = level
            && id == LintId::of(UNFULFILLED_LINT_EXPECTATIONS)
        {
            return;
        }

        match (old_level, level) {
            // If the new level is an expectation store it in `ForceWarn`
            (Level::ForceWarn(_), Level::Expect(expectation_id)) => {
                self.insert(id, (Level::ForceWarn(Some(expectation_id)), old_src))
            }
            // Keep `ForceWarn` level but drop the expectation
            (Level::ForceWarn(_), _) => self.insert(id, (Level::ForceWarn(None), old_src)),
            // Set the lint level as normal
            _ => self.insert(id, (level, src)),
        };
    }

    fn add(&mut self, attrs: &[ast::Attribute], is_crate_node: bool, source_hir_id: Option<HirId>) {
        let sess = self.sess;
        for (attr_index, attr) in attrs.iter().enumerate() {
            if attr.has_name(sym::automatically_derived) {
                self.insert(
                    LintId::of(SINGLE_USE_LIFETIMES),
                    (Level::Allow, LintLevelSource::Default),
                );
                continue;
            }

            // `#[doc(hidden)]` disables missing_docs check.
            if attr.has_name(sym::doc)
                && attr
                    .meta_item_list()
                    .is_some_and(|l| ast::attr::list_contains_name(&l, sym::hidden))
            {
                self.insert(LintId::of(MISSING_DOCS), (Level::Allow, LintLevelSource::Default));
                continue;
            }

            let level = match Level::from_attr(attr) {
                None => continue,
                // This is the only lint level with a `LintExpectationId` that can be created from
                // an attribute.
                Some(Level::Expect(unstable_id)) if let Some(hir_id) = source_hir_id => {
                    let LintExpectationId::Unstable { lint_index: None, attr_id: _ } = unstable_id
                    else {
                        bug!("stable id Level::from_attr")
                    };

                    let stable_id = LintExpectationId::Stable {
                        hir_id,
                        attr_index: attr_index.try_into().unwrap(),
                        lint_index: None,
                    };

                    Level::Expect(stable_id)
                }
                Some(lvl) => lvl,
            };

            let Some(mut metas) = attr.meta_item_list() else { continue };

            // Check whether `metas` is empty, and get its last element.
            let Some(tail_li) = metas.last() else {
                // This emits the unused_attributes lint for `#[level()]`
                continue;
            };

            // Before processing the lint names, look for a reason (RFC 2383)
            // at the end.
            let mut reason = None;
            if let Some(item) = tail_li.meta_item() {
                match item.kind {
                    ast::MetaItemKind::Word => {} // actual lint names handled later
                    ast::MetaItemKind::NameValue(ref name_value) => {
                        if item.path == sym::reason {
                            if let ast::LitKind::Str(rationale, _) = name_value.kind {
                                reason = Some(rationale);
                            } else {
                                sess.dcx().emit_err(MalformedAttribute {
                                    span: name_value.span,
                                    sub: MalformedAttributeSub::ReasonMustBeStringLiteral(
                                        name_value.span,
                                    ),
                                });
                            }
                            // found reason, reslice meta list to exclude it
                            metas.pop().unwrap();
                        } else {
                            sess.dcx().emit_err(MalformedAttribute {
                                span: item.span,
                                sub: MalformedAttributeSub::BadAttributeArgument(item.span),
                            });
                        }
                    }
                    ast::MetaItemKind::List(_) => {
                        sess.dcx().emit_err(MalformedAttribute {
                            span: item.span,
                            sub: MalformedAttributeSub::BadAttributeArgument(item.span),
                        });
                    }
                }
            }

            for (lint_index, li) in metas.iter_mut().enumerate() {
                let level = match level {
                    Level::Expect(mut id) => {
                        id.set_lint_index(Some(lint_index as u16));
                        Level::Expect(id)
                    }
                    level => level,
                };

                let sp = li.span();
                let meta_item = match li {
                    ast::MetaItemInner::MetaItem(meta_item) if meta_item.is_word() => meta_item,
                    _ => {
                        let sub = if let Some(item) = li.meta_item()
                            && let ast::MetaItemKind::NameValue(_) = item.kind
                            && item.path == sym::reason
                        {
                            MalformedAttributeSub::ReasonMustComeLast(sp)
                        } else {
                            MalformedAttributeSub::BadAttributeArgument(sp)
                        };

                        sess.dcx().emit_err(MalformedAttribute { span: sp, sub });
                        continue;
                    }
                };
                let tool_ident = if meta_item.path.segments.len() > 1 {
                    Some(meta_item.path.segments.remove(0).ident)
                } else {
                    None
                };
                let tool_name = tool_ident.map(|ident| ident.name);
                let name = pprust::path_to_string(&meta_item.path);
                let lint_result =
                    self.store.check_lint_name(&name, tool_name, self.registered_tools);

                let (ids, name) = match lint_result {
                    CheckLintNameResult::Ok(ids) => {
                        let name =
                            meta_item.path.segments.last().expect("empty lint name").ident.name;
                        (ids, name)
                    }

                    CheckLintNameResult::Tool(ids, new_lint_name) => {
                        let name = match new_lint_name {
                            None => {
                                let complete_name =
                                    &format!("{}::{}", tool_ident.unwrap().name, name);
                                Symbol::intern(complete_name)
                            }
                            Some(new_lint_name) => {
                                self.emit_span_lint(
                                    builtin::RENAMED_AND_REMOVED_LINTS,
                                    sp.into(),
                                    DeprecatedLintName {
                                        name,
                                        suggestion: sp,
                                        replace: &new_lint_name,
                                    },
                                );
                                Symbol::intern(&new_lint_name)
                            }
                        };
                        (ids, name)
                    }

                    CheckLintNameResult::MissingTool => {
                        // If `MissingTool` is returned, then either the lint does not
                        // exist in the tool or the code was not compiled with the tool and
                        // therefore the lint was never added to the `LintStore`. To detect
                        // this is the responsibility of the lint tool.
                        continue;
                    }

                    CheckLintNameResult::NoTool => {
                        sess.dcx().emit_err(UnknownToolInScopedLint {
                            span: tool_ident.map(|ident| ident.span),
                            tool_name: tool_name.unwrap(),
                            lint_name: pprust::path_to_string(&meta_item.path),
                            is_nightly_build: sess.is_nightly_build(),
                        });
                        continue;
                    }

                    CheckLintNameResult::Renamed(ref replace) => {
                        if self.lint_added_lints {
                            let suggestion =
                                RenamedLintSuggestion::WithSpan { suggestion: sp, replace };
                            let name =
                                tool_ident.map(|tool| format!("{tool}::{name}")).unwrap_or(name);
                            let lint = RenamedLint { name: name.as_str(), suggestion };
                            self.emit_span_lint(RENAMED_AND_REMOVED_LINTS, sp.into(), lint);
                        }

                        // If this lint was renamed, apply the new lint instead of ignoring the
                        // attribute. Ignore any errors or warnings that happen because the new
                        // name is inaccurate.
                        // NOTE: `new_name` already includes the tool name, so we don't
                        // have to add it again.
                        let CheckLintNameResult::Ok(ids) =
                            self.store.check_lint_name(replace, None, self.registered_tools)
                        else {
                            panic!("renamed lint does not exist: {replace}");
                        };

                        (ids, Symbol::intern(&replace))
                    }

                    CheckLintNameResult::Removed(ref reason) => {
                        if self.lint_added_lints {
                            let name =
                                tool_ident.map(|tool| format!("{tool}::{name}")).unwrap_or(name);
                            let lint = RemovedLint { name: name.as_str(), reason };
                            self.emit_span_lint(RENAMED_AND_REMOVED_LINTS, sp.into(), lint);
                        }
                        continue;
                    }

                    CheckLintNameResult::NoLint(suggestion) => {
                        if self.lint_added_lints {
                            let name =
                                tool_ident.map(|tool| format!("{tool}::{name}")).unwrap_or(name);
                            let suggestion = suggestion.map(|(replace, from_rustc)| {
                                UnknownLintSuggestion::WithSpan {
                                    suggestion: sp,
                                    replace,
                                    from_rustc,
                                }
                            });
                            let lint = UnknownLint { name, suggestion };
                            self.emit_span_lint(UNKNOWN_LINTS, sp.into(), lint);
                        }
                        continue;
                    }
                };

                let src = LintLevelSource::Node { name, span: sp, reason };
                for &id in ids {
                    if self.check_gated_lint(id, attr.span, false) {
                        self.insert_spec(id, (level, src));
                    }
                }

                // This checks for instances where the user writes
                // `#[expect(unfulfilled_lint_expectations)]` in that case we want to avoid
                // overriding the lint level but instead add an expectation that can't be
                // fulfilled. The lint message will include an explanation, that the
                // `unfulfilled_lint_expectations` lint can't be expected.
                if let Level::Expect(expect_id) = level {
                    // The `unfulfilled_lint_expectations` lint is not part of any lint
                    // groups. Therefore. we only need to check the slice if it contains a
                    // single lint.
                    let is_unfulfilled_lint_expectations = match ids {
                        [lint] => *lint == LintId::of(UNFULFILLED_LINT_EXPECTATIONS),
                        _ => false,
                    };
                    self.provider.push_expectation(
                        expect_id,
                        LintExpectation::new(
                            reason,
                            sp,
                            is_unfulfilled_lint_expectations,
                            tool_name,
                        ),
                    );
                }
            }
        }

        if self.lint_added_lints && !is_crate_node {
            for (id, &(level, ref src)) in self.current_specs().iter() {
                if !id.lint.crate_level_only {
                    continue;
                }

                let LintLevelSource::Node { name: lint_attr_name, span: lint_attr_span, .. } = *src
                else {
                    continue;
                };

                self.emit_span_lint(
                    UNUSED_ATTRIBUTES,
                    lint_attr_span.into(),
                    IgnoredUnlessCrateSpecified { level: level.as_str(), name: lint_attr_name },
                );
                // don't set a separate error for every lint in the group
                break;
            }
        }
    }

    /// Checks if the lint is gated on a feature that is not enabled.
    ///
    /// Returns `true` if the lint's feature is enabled.
    #[track_caller]
    fn check_gated_lint(&self, lint_id: LintId, span: Span, lint_from_cli: bool) -> bool {
        let feature = if let Some(feature) = lint_id.lint.feature_gate
            && !self.features.enabled(feature)
        {
            // Lint is behind a feature that is not enabled; eventually return false.
            feature
        } else {
            // Lint is ungated or its feature is enabled; exit early.
            return true;
        };

        if self.lint_added_lints {
            let lint = builtin::UNKNOWN_LINTS;
            let (level, src) = self.lint_level(builtin::UNKNOWN_LINTS);
            // FIXME: make this translatable
            #[allow(rustc::diagnostic_outside_of_impl)]
            lint_level(self.sess, lint, level, src, Some(span.into()), |lint| {
                lint.primary_message(fluent::lint_unknown_gated_lint);
                lint.arg("name", lint_id.lint.name_lower());
                lint.note(fluent::lint_note);
                rustc_session::parse::add_feature_diagnostics_for_issue(
                    lint,
                    &self.sess,
                    feature,
                    GateIssue::Language,
                    lint_from_cli,
                    None,
                );
            });
        }

        false
    }

    /// Find the lint level for a lint.
    pub fn lint_level(&self, lint: &'static Lint) -> LevelAndSource {
        self.provider.get_lint_level(lint, self.sess)
    }

    /// Used to emit a lint-related diagnostic based on the current state of
    /// this lint context.
    ///
    /// [`lint_level`]: rustc_middle::lint::lint_level#decorate-signature
    #[rustc_lint_diagnostics]
    #[track_caller]
    pub(crate) fn opt_span_lint(
        &self,
        lint: &'static Lint,
        span: Option<MultiSpan>,
        decorate: impl for<'a, 'b> FnOnce(&'b mut Diag<'a, ()>),
    ) {
        let (level, src) = self.lint_level(lint);
        lint_level(self.sess, lint, level, src, span, decorate)
    }

    #[track_caller]
    pub fn emit_span_lint(
        &self,
        lint: &'static Lint,
        span: MultiSpan,
        decorate: impl for<'a> LintDiagnostic<'a, ()>,
    ) {
        let (level, src) = self.lint_level(lint);
        lint_level(self.sess, lint, level, src, Some(span), |lint| {
            decorate.decorate_lint(lint);
        });
    }

    #[track_caller]
    pub fn emit_lint(&self, lint: &'static Lint, decorate: impl for<'a> LintDiagnostic<'a, ()>) {
        let (level, src) = self.lint_level(lint);
        lint_level(self.sess, lint, level, src, None, |lint| {
            decorate.decorate_lint(lint);
        });
    }
}

pub(crate) fn provide(providers: &mut Providers) {
    *providers = Providers { shallow_lint_levels_on, lints_that_dont_need_to_run, ..*providers };
}

pub(crate) fn parse_lint_and_tool_name(lint_name: &str) -> (Option<Symbol>, &str) {
    match lint_name.split_once("::") {
        Some((tool_name, lint_name)) => {
            let tool_name = Symbol::intern(tool_name);

            (Some(tool_name), lint_name)
        }
        None => (None, lint_name),
    }
}