1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
//! A bunch of methods and structures more or less related to resolving imports.

use crate::diagnostics::Suggestion;
use crate::Determinacy::{self, *};
use crate::Namespace::{MacroNS, TypeNS};
use crate::{module_to_string, names_to_string};
use crate::{AmbiguityKind, BindingKey, ModuleKind, ResolutionError, Resolver, Segment};
use crate::{Finalize, Module, ModuleOrUniformRoot, ParentScope, PerNS, ScopeSet};
use crate::{NameBinding, NameBindingKind, PathResult};

use rustc_ast::NodeId;
use rustc_data_structures::fx::FxHashSet;
use rustc_data_structures::intern::Interned;
use rustc_errors::{pluralize, struct_span_err, Applicability, MultiSpan};
use rustc_hir::def::{self, DefKind, PartialRes};
use rustc_middle::metadata::ModChild;
use rustc_middle::span_bug;
use rustc_middle::ty;
use rustc_session::lint::builtin::{PUB_USE_OF_PRIVATE_EXTERN_CRATE, UNUSED_IMPORTS};
use rustc_session::lint::BuiltinLintDiagnostics;
use rustc_span::hygiene::LocalExpnId;
use rustc_span::lev_distance::find_best_match_for_name;
use rustc_span::symbol::{kw, Ident, Symbol};
use rustc_span::Span;

use std::cell::Cell;
use std::{mem, ptr};

type Res = def::Res<NodeId>;

/// Contains data for specific kinds of imports.
#[derive(Clone)]
pub enum ImportKind<'a> {
    Single {
        /// `source` in `use prefix::source as target`.
        source: Ident,
        /// `target` in `use prefix::source as target`.
        target: Ident,
        /// Bindings to which `source` refers to.
        source_bindings: PerNS<Cell<Result<&'a NameBinding<'a>, Determinacy>>>,
        /// Bindings introduced by `target`.
        target_bindings: PerNS<Cell<Option<&'a NameBinding<'a>>>>,
        /// `true` for `...::{self [as target]}` imports, `false` otherwise.
        type_ns_only: bool,
        /// Did this import result from a nested import? ie. `use foo::{bar, baz};`
        nested: bool,
        /// Additional `NodeId`s allocated to a `ast::UseTree` for automatically generated `use` statement
        /// (eg. implicit struct constructors)
        additional_ids: (NodeId, NodeId),
    },
    Glob {
        is_prelude: bool,
        max_vis: Cell<Option<ty::Visibility>>, // The visibility of the greatest re-export.
                                               // n.b. `max_vis` is only used in `finalize_import` to check for re-export errors.
    },
    ExternCrate {
        source: Option<Symbol>,
        target: Ident,
    },
    MacroUse,
}

/// Manually implement `Debug` for `ImportKind` because the `source/target_bindings`
/// contain `Cell`s which can introduce infinite loops while printing.
impl<'a> std::fmt::Debug for ImportKind<'a> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        use ImportKind::*;
        match self {
            Single {
                ref source,
                ref target,
                ref type_ns_only,
                ref nested,
                ref additional_ids,
                // Ignore the following to avoid an infinite loop while printing.
                source_bindings: _,
                target_bindings: _,
            } => f
                .debug_struct("Single")
                .field("source", source)
                .field("target", target)
                .field("type_ns_only", type_ns_only)
                .field("nested", nested)
                .field("additional_ids", additional_ids)
                .finish_non_exhaustive(),
            Glob { ref is_prelude, ref max_vis } => f
                .debug_struct("Glob")
                .field("is_prelude", is_prelude)
                .field("max_vis", max_vis)
                .finish(),
            ExternCrate { ref source, ref target } => f
                .debug_struct("ExternCrate")
                .field("source", source)
                .field("target", target)
                .finish(),
            MacroUse => f.debug_struct("MacroUse").finish(),
        }
    }
}

/// One import.
#[derive(Debug, Clone)]
pub(crate) struct Import<'a> {
    pub kind: ImportKind<'a>,

    /// The ID of the `extern crate`, `UseTree` etc that imported this `Import`.
    ///
    /// In the case where the `Import` was expanded from a "nested" use tree,
    /// this id is the ID of the leaf tree. For example:
    ///
    /// ```ignore (pacify the merciless tidy)
    /// use foo::bar::{a, b}
    /// ```
    ///
    /// If this is the import for `foo::bar::a`, we would have the ID of the `UseTree`
    /// for `a` in this field.
    pub id: NodeId,

    /// The `id` of the "root" use-kind -- this is always the same as
    /// `id` except in the case of "nested" use trees, in which case
    /// it will be the `id` of the root use tree. e.g., in the example
    /// from `id`, this would be the ID of the `use foo::bar`
    /// `UseTree` node.
    pub root_id: NodeId,

    /// Span of the entire use statement.
    pub use_span: Span,

    /// Span of the entire use statement with attributes.
    pub use_span_with_attributes: Span,

    /// Did the use statement have any attributes?
    pub has_attributes: bool,

    /// Span of this use tree.
    pub span: Span,

    /// Span of the *root* use tree (see `root_id`).
    pub root_span: Span,

    pub parent_scope: ParentScope<'a>,
    pub module_path: Vec<Segment>,
    /// The resolution of `module_path`.
    pub imported_module: Cell<Option<ModuleOrUniformRoot<'a>>>,
    pub vis: Cell<Option<ty::Visibility>>,
    pub used: Cell<bool>,
}

impl<'a> Import<'a> {
    pub fn is_glob(&self) -> bool {
        matches!(self.kind, ImportKind::Glob { .. })
    }

    pub fn is_nested(&self) -> bool {
        match self.kind {
            ImportKind::Single { nested, .. } => nested,
            _ => false,
        }
    }

    pub(crate) fn expect_vis(&self) -> ty::Visibility {
        self.vis.get().expect("encountered cleared import visibility")
    }
}

/// Records information about the resolution of a name in a namespace of a module.
#[derive(Clone, Default, Debug)]
pub(crate) struct NameResolution<'a> {
    /// Single imports that may define the name in the namespace.
    /// Imports are arena-allocated, so it's ok to use pointers as keys.
    pub single_imports: FxHashSet<Interned<'a, Import<'a>>>,
    /// The least shadowable known binding for this name, or None if there are no known bindings.
    pub binding: Option<&'a NameBinding<'a>>,
    pub shadowed_glob: Option<&'a NameBinding<'a>>,
}

impl<'a> NameResolution<'a> {
    // Returns the binding for the name if it is known or None if it not known.
    pub(crate) fn binding(&self) -> Option<&'a NameBinding<'a>> {
        self.binding.and_then(|binding| {
            if !binding.is_glob_import() || self.single_imports.is_empty() {
                Some(binding)
            } else {
                None
            }
        })
    }

    pub(crate) fn add_single_import(&mut self, import: &'a Import<'a>) {
        self.single_imports.insert(Interned::new_unchecked(import));
    }
}

// Reexports of the form `pub use foo as bar;` where `foo` is `extern crate foo;`
// are permitted for backward-compatibility under a deprecation lint.
fn pub_use_of_private_extern_crate_hack(import: &Import<'_>, binding: &NameBinding<'_>) -> bool {
    match (&import.kind, &binding.kind) {
        (
            ImportKind::Single { .. },
            NameBindingKind::Import {
                import: Import { kind: ImportKind::ExternCrate { .. }, .. },
                ..
            },
        ) => import.expect_vis().is_public(),
        _ => false,
    }
}

impl<'a> Resolver<'a> {
    // Given a binding and an import that resolves to it,
    // return the corresponding binding defined by the import.
    pub(crate) fn import(
        &self,
        binding: &'a NameBinding<'a>,
        import: &'a Import<'a>,
    ) -> &'a NameBinding<'a> {
        let import_vis = import.expect_vis().to_def_id();
        let vis = if binding.vis.is_at_least(import_vis, self)
            || pub_use_of_private_extern_crate_hack(import, binding)
        {
            import_vis
        } else {
            binding.vis
        };

        if let ImportKind::Glob { ref max_vis, .. } = import.kind {
            if vis == import_vis
                || max_vis.get().map_or(true, |max_vis| vis.is_at_least(max_vis, self))
            {
                max_vis.set(Some(vis.expect_local()))
            }
        }

        self.arenas.alloc_name_binding(NameBinding {
            kind: NameBindingKind::Import { binding, import, used: Cell::new(false) },
            ambiguity: None,
            span: import.span,
            vis,
            expansion: import.parent_scope.expansion,
        })
    }

    // Define the name or return the existing binding if there is a collision.
    pub(crate) fn try_define(
        &mut self,
        module: Module<'a>,
        key: BindingKey,
        binding: &'a NameBinding<'a>,
    ) -> Result<(), &'a NameBinding<'a>> {
        let res = binding.res();
        self.check_reserved_macro_name(key.ident, res);
        self.set_binding_parent_module(binding, module);
        self.update_resolution(module, key, |this, resolution| {
            if let Some(old_binding) = resolution.binding {
                if res == Res::Err {
                    // Do not override real bindings with `Res::Err`s from error recovery.
                    return Ok(());
                }
                match (old_binding.is_glob_import(), binding.is_glob_import()) {
                    (true, true) => {
                        if res != old_binding.res() {
                            resolution.binding = Some(this.ambiguity(
                                AmbiguityKind::GlobVsGlob,
                                old_binding,
                                binding,
                            ));
                        } else if !old_binding.vis.is_at_least(binding.vis, &*this) {
                            // We are glob-importing the same item but with greater visibility.
                            resolution.binding = Some(binding);
                        }
                    }
                    (old_glob @ true, false) | (old_glob @ false, true) => {
                        let (glob_binding, nonglob_binding) =
                            if old_glob { (old_binding, binding) } else { (binding, old_binding) };
                        if glob_binding.res() != nonglob_binding.res()
                            && key.ns == MacroNS
                            && nonglob_binding.expansion != LocalExpnId::ROOT
                        {
                            resolution.binding = Some(this.ambiguity(
                                AmbiguityKind::GlobVsExpanded,
                                nonglob_binding,
                                glob_binding,
                            ));
                        } else {
                            resolution.binding = Some(nonglob_binding);
                        }
                        resolution.shadowed_glob = Some(glob_binding);
                    }
                    (false, false) => {
                        return Err(old_binding);
                    }
                }
            } else {
                resolution.binding = Some(binding);
            }

            Ok(())
        })
    }

    fn ambiguity(
        &self,
        kind: AmbiguityKind,
        primary_binding: &'a NameBinding<'a>,
        secondary_binding: &'a NameBinding<'a>,
    ) -> &'a NameBinding<'a> {
        self.arenas.alloc_name_binding(NameBinding {
            ambiguity: Some((secondary_binding, kind)),
            ..primary_binding.clone()
        })
    }

    // Use `f` to mutate the resolution of the name in the module.
    // If the resolution becomes a success, define it in the module's glob importers.
    fn update_resolution<T, F>(&mut self, module: Module<'a>, key: BindingKey, f: F) -> T
    where
        F: FnOnce(&mut Resolver<'a>, &mut NameResolution<'a>) -> T,
    {
        // Ensure that `resolution` isn't borrowed when defining in the module's glob importers,
        // during which the resolution might end up getting re-defined via a glob cycle.
        let (binding, t) = {
            let resolution = &mut *self.resolution(module, key).borrow_mut();
            let old_binding = resolution.binding();

            let t = f(self, resolution);

            match resolution.binding() {
                _ if old_binding.is_some() => return t,
                None => return t,
                Some(binding) => match old_binding {
                    Some(old_binding) if ptr::eq(old_binding, binding) => return t,
                    _ => (binding, t),
                },
            }
        };

        // Define `binding` in `module`s glob importers.
        for import in module.glob_importers.borrow_mut().iter() {
            let mut ident = key.ident;
            let scope = match ident.span.reverse_glob_adjust(module.expansion, import.span) {
                Some(Some(def)) => self.expn_def_scope(def),
                Some(None) => import.parent_scope.module,
                None => continue,
            };
            if self.is_accessible_from(binding.vis, scope) {
                let imported_binding = self.import(binding, import);
                let key = BindingKey { ident, ..key };
                let _ = self.try_define(import.parent_scope.module, key, imported_binding);
            }
        }

        t
    }

    // Define a dummy resolution containing a `Res::Err` as a placeholder for a failed resolution,
    // also mark such failed imports as used to avoid duplicate diagnostics.
    fn import_dummy_binding(&mut self, import: &'a Import<'a>) {
        if let ImportKind::Single { target, ref target_bindings, .. } = import.kind {
            if target_bindings.iter().any(|binding| binding.get().is_some()) {
                return; // Has resolution, do not create the dummy binding
            }
            let dummy_binding = self.dummy_binding;
            let dummy_binding = self.import(dummy_binding, import);
            self.per_ns(|this, ns| {
                let key = this.new_key(target, ns);
                let _ = this.try_define(import.parent_scope.module, key, dummy_binding);
            });
            self.record_use(target, dummy_binding, false);
        } else if import.imported_module.get().is_none() {
            import.used.set(true);
            self.used_imports.insert(import.id);
        }
    }
}

/// An error that may be transformed into a diagnostic later. Used to combine multiple unresolved
/// import errors within the same use tree into a single diagnostic.
#[derive(Debug, Clone)]
struct UnresolvedImportError {
    span: Span,
    label: Option<String>,
    note: Option<String>,
    suggestion: Option<Suggestion>,
}

pub struct ImportResolver<'a, 'b> {
    pub r: &'a mut Resolver<'b>,
}

impl<'a, 'b> ImportResolver<'a, 'b> {
    // Import resolution
    //
    // This is a fixed-point algorithm. We resolve imports until our efforts
    // are stymied by an unresolved import; then we bail out of the current
    // module and continue. We terminate successfully once no more imports
    // remain or unsuccessfully when no forward progress in resolving imports
    // is made.

    /// Resolves all imports for the crate. This method performs the fixed-
    /// point iteration.
    pub fn resolve_imports(&mut self) {
        let mut prev_num_indeterminates = self.r.indeterminate_imports.len() + 1;
        while self.r.indeterminate_imports.len() < prev_num_indeterminates {
            prev_num_indeterminates = self.r.indeterminate_imports.len();
            for import in mem::take(&mut self.r.indeterminate_imports) {
                match self.resolve_import(&import) {
                    true => self.r.determined_imports.push(import),
                    false => self.r.indeterminate_imports.push(import),
                }
            }
        }
    }

    pub fn finalize_imports(&mut self) {
        for module in self.r.arenas.local_modules().iter() {
            self.finalize_resolutions_in(module);
        }

        let mut seen_spans = FxHashSet::default();
        let mut errors = vec![];
        let mut prev_root_id: NodeId = NodeId::from_u32(0);
        let determined_imports = mem::take(&mut self.r.determined_imports);
        let indeterminate_imports = mem::take(&mut self.r.indeterminate_imports);

        for (is_indeterminate, import) in determined_imports
            .into_iter()
            .map(|i| (false, i))
            .chain(indeterminate_imports.into_iter().map(|i| (true, i)))
        {
            let unresolved_import_error = self.finalize_import(import);

            // If this import is unresolved then create a dummy import
            // resolution for it so that later resolve stages won't complain.
            self.r.import_dummy_binding(import);

            if let Some(err) = unresolved_import_error {
                if let ImportKind::Single { source, ref source_bindings, .. } = import.kind {
                    if source.name == kw::SelfLower {
                        // Silence `unresolved import` error if E0429 is already emitted
                        if let Err(Determined) = source_bindings.value_ns.get() {
                            continue;
                        }
                    }
                }

                if prev_root_id.as_u32() != 0
                    && prev_root_id.as_u32() != import.root_id.as_u32()
                    && !errors.is_empty()
                {
                    // In the case of a new import line, throw a diagnostic message
                    // for the previous line.
                    self.throw_unresolved_import_error(errors, None);
                    errors = vec![];
                }
                if seen_spans.insert(err.span) {
                    let path = import_path_to_string(
                        &import.module_path.iter().map(|seg| seg.ident).collect::<Vec<_>>(),
                        &import.kind,
                        err.span,
                    );
                    errors.push((path, err));
                    prev_root_id = import.root_id;
                }
            } else if is_indeterminate {
                let path = import_path_to_string(
                    &import.module_path.iter().map(|seg| seg.ident).collect::<Vec<_>>(),
                    &import.kind,
                    import.span,
                );
                let err = UnresolvedImportError {
                    span: import.span,
                    label: None,
                    note: None,
                    suggestion: None,
                };
                if path.contains("::") {
                    errors.push((path, err))
                }
            }
        }

        if !errors.is_empty() {
            self.throw_unresolved_import_error(errors, None);
        }
    }

    fn throw_unresolved_import_error(
        &self,
        errors: Vec<(String, UnresolvedImportError)>,
        span: Option<MultiSpan>,
    ) {
        /// Upper limit on the number of `span_label` messages.
        const MAX_LABEL_COUNT: usize = 10;

        let (span, msg) = if errors.is_empty() {
            (span.unwrap(), "unresolved import".to_string())
        } else {
            let span = MultiSpan::from_spans(errors.iter().map(|(_, err)| err.span).collect());

            let paths = errors.iter().map(|(path, _)| format!("`{}`", path)).collect::<Vec<_>>();

            let msg = format!("unresolved import{} {}", pluralize!(paths.len()), paths.join(", "),);

            (span, msg)
        };

        let mut diag = struct_span_err!(self.r.session, span, E0432, "{}", &msg);

        if let Some((_, UnresolvedImportError { note: Some(note), .. })) = errors.iter().last() {
            diag.note(note);
        }

        for (_, err) in errors.into_iter().take(MAX_LABEL_COUNT) {
            if let Some(label) = err.label {
                diag.span_label(err.span, label);
            }

            if let Some((suggestions, msg, applicability)) = err.suggestion {
                if suggestions.is_empty() {
                    diag.help(&msg);
                    continue;
                }
                diag.multipart_suggestion(&msg, suggestions, applicability);
            }
        }

        diag.emit();
    }

    /// Attempts to resolve the given import, returning true if its resolution is determined.
    /// If successful, the resolved bindings are written into the module.
    fn resolve_import(&mut self, import: &'b Import<'b>) -> bool {
        debug!(
            "(resolving import for module) resolving import `{}::...` in `{}`",
            Segment::names_to_string(&import.module_path),
            module_to_string(import.parent_scope.module).unwrap_or_else(|| "???".to_string()),
        );

        let module = if let Some(module) = import.imported_module.get() {
            module
        } else {
            // For better failure detection, pretend that the import will
            // not define any names while resolving its module path.
            let orig_vis = import.vis.take();
            let path_res =
                self.r.maybe_resolve_path(&import.module_path, None, &import.parent_scope);
            import.vis.set(orig_vis);

            match path_res {
                PathResult::Module(module) => module,
                PathResult::Indeterminate => return false,
                PathResult::NonModule(..) | PathResult::Failed { .. } => return true,
            }
        };

        import.imported_module.set(Some(module));
        let (source, target, source_bindings, target_bindings, type_ns_only) = match import.kind {
            ImportKind::Single {
                source,
                target,
                ref source_bindings,
                ref target_bindings,
                type_ns_only,
                ..
            } => (source, target, source_bindings, target_bindings, type_ns_only),
            ImportKind::Glob { .. } => {
                self.resolve_glob_import(import);
                return true;
            }
            _ => unreachable!(),
        };

        let mut indeterminate = false;
        self.r.per_ns(|this, ns| {
            if !type_ns_only || ns == TypeNS {
                if let Err(Undetermined) = source_bindings[ns].get() {
                    // For better failure detection, pretend that the import will
                    // not define any names while resolving its module path.
                    let orig_vis = import.vis.take();
                    let binding = this.resolve_ident_in_module(
                        module,
                        source,
                        ns,
                        &import.parent_scope,
                        None,
                        None,
                    );
                    import.vis.set(orig_vis);
                    source_bindings[ns].set(binding);
                } else {
                    return;
                };

                let parent = import.parent_scope.module;
                match source_bindings[ns].get() {
                    Err(Undetermined) => indeterminate = true,
                    // Don't update the resolution, because it was never added.
                    Err(Determined) if target.name == kw::Underscore => {}
                    Ok(binding) if binding.is_importable() => {
                        let imported_binding = this.import(binding, import);
                        target_bindings[ns].set(Some(imported_binding));
                        this.define(parent, target, ns, imported_binding);
                    }
                    source_binding @ (Ok(..) | Err(Determined)) => {
                        if source_binding.is_ok() {
                            let msg = format!("`{}` is not directly importable", target);
                            struct_span_err!(this.session, import.span, E0253, "{}", &msg)
                                .span_label(import.span, "cannot be imported directly")
                                .emit();
                        }
                        let key = this.new_key(target, ns);
                        this.update_resolution(parent, key, |_, resolution| {
                            resolution.single_imports.remove(&Interned::new_unchecked(import));
                        });
                    }
                }
            }
        });

        !indeterminate
    }

    /// Performs final import resolution, consistency checks and error reporting.
    ///
    /// Optionally returns an unresolved import error. This error is buffered and used to
    /// consolidate multiple unresolved import errors into a single diagnostic.
    fn finalize_import(&mut self, import: &'b Import<'b>) -> Option<UnresolvedImportError> {
        let orig_vis = import.vis.take();
        let ignore_binding = match &import.kind {
            ImportKind::Single { target_bindings, .. } => target_bindings[TypeNS].get(),
            _ => None,
        };
        let prev_ambiguity_errors_len = self.r.ambiguity_errors.len();
        let finalize = Finalize::with_root_span(import.root_id, import.span, import.root_span);
        let path_res = self.r.resolve_path(
            &import.module_path,
            None,
            &import.parent_scope,
            Some(finalize),
            ignore_binding,
        );
        let no_ambiguity = self.r.ambiguity_errors.len() == prev_ambiguity_errors_len;
        import.vis.set(orig_vis);
        let module = match path_res {
            PathResult::Module(module) => {
                // Consistency checks, analogous to `finalize_macro_resolutions`.
                if let Some(initial_module) = import.imported_module.get() {
                    if !ModuleOrUniformRoot::same_def(module, initial_module) && no_ambiguity {
                        span_bug!(import.span, "inconsistent resolution for an import");
                    }
                } else if self.r.privacy_errors.is_empty() {
                    let msg = "cannot determine resolution for the import";
                    let msg_note = "import resolution is stuck, try simplifying other imports";
                    self.r.session.struct_span_err(import.span, msg).note(msg_note).emit();
                }

                module
            }
            PathResult::Failed { is_error_from_last_segment: false, span, label, suggestion } => {
                if no_ambiguity {
                    assert!(import.imported_module.get().is_none());
                    self.r
                        .report_error(span, ResolutionError::FailedToResolve { label, suggestion });
                }
                return None;
            }
            PathResult::Failed { is_error_from_last_segment: true, span, label, suggestion } => {
                if no_ambiguity {
                    assert!(import.imported_module.get().is_none());
                    let err = match self.make_path_suggestion(
                        span,
                        import.module_path.clone(),
                        &import.parent_scope,
                    ) {
                        Some((suggestion, note)) => UnresolvedImportError {
                            span,
                            label: None,
                            note,
                            suggestion: Some((
                                vec![(span, Segment::names_to_string(&suggestion))],
                                String::from("a similar path exists"),
                                Applicability::MaybeIncorrect,
                            )),
                        },
                        None => UnresolvedImportError {
                            span,
                            label: Some(label),
                            note: None,
                            suggestion,
                        },
                    };
                    return Some(err);
                }
                return None;
            }
            PathResult::NonModule(_) => {
                if no_ambiguity {
                    assert!(import.imported_module.get().is_none());
                }
                // The error was already reported earlier.
                return None;
            }
            PathResult::Indeterminate => unreachable!(),
        };

        let (ident, target, source_bindings, target_bindings, type_ns_only) = match import.kind {
            ImportKind::Single {
                source,
                target,
                ref source_bindings,
                ref target_bindings,
                type_ns_only,
                ..
            } => (source, target, source_bindings, target_bindings, type_ns_only),
            ImportKind::Glob { is_prelude, ref max_vis } => {
                if import.module_path.len() <= 1 {
                    // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
                    // 2 segments, so the `resolve_path` above won't trigger it.
                    let mut full_path = import.module_path.clone();
                    full_path.push(Segment::from_ident(Ident::empty()));
                    self.r.lint_if_path_starts_with_module(Some(finalize), &full_path, None);
                }

                if let ModuleOrUniformRoot::Module(module) = module {
                    if ptr::eq(module, import.parent_scope.module) {
                        // Importing a module into itself is not allowed.
                        return Some(UnresolvedImportError {
                            span: import.span,
                            label: Some(String::from("cannot glob-import a module into itself")),
                            note: None,
                            suggestion: None,
                        });
                    }
                }
                if !is_prelude
                    && let Some(max_vis) = max_vis.get()
                    && !max_vis.is_at_least(import.expect_vis(), &*self.r)
                {
                    let msg = "glob import doesn't reexport anything because no candidate is public enough";
                    self.r.lint_buffer.buffer_lint(UNUSED_IMPORTS, import.id, import.span, msg);
                }
                return None;
            }
            _ => unreachable!(),
        };

        let mut all_ns_err = true;
        self.r.per_ns(|this, ns| {
            if !type_ns_only || ns == TypeNS {
                let orig_vis = import.vis.take();
                let binding = this.resolve_ident_in_module(
                    module,
                    ident,
                    ns,
                    &import.parent_scope,
                    Some(Finalize { report_private: false, ..finalize }),
                    target_bindings[ns].get(),
                );
                import.vis.set(orig_vis);

                match binding {
                    Ok(binding) => {
                        // Consistency checks, analogous to `finalize_macro_resolutions`.
                        let initial_res = source_bindings[ns].get().map(|initial_binding| {
                            all_ns_err = false;
                            if let Some(target_binding) = target_bindings[ns].get() {
                                if target.name == kw::Underscore
                                    && initial_binding.is_extern_crate()
                                    && !initial_binding.is_import()
                                {
                                    this.record_use(
                                        ident,
                                        target_binding,
                                        import.module_path.is_empty(),
                                    );
                                }
                            }
                            initial_binding.res()
                        });
                        let res = binding.res();
                        if let Ok(initial_res) = initial_res {
                            if res != initial_res && this.ambiguity_errors.is_empty() {
                                span_bug!(import.span, "inconsistent resolution for an import");
                            }
                        } else if res != Res::Err
                            && this.ambiguity_errors.is_empty()
                            && this.privacy_errors.is_empty()
                        {
                            let msg = "cannot determine resolution for the import";
                            let msg_note =
                                "import resolution is stuck, try simplifying other imports";
                            this.session.struct_span_err(import.span, msg).note(msg_note).emit();
                        }
                    }
                    Err(..) => {
                        // FIXME: This assert may fire if public glob is later shadowed by a private
                        // single import (see test `issue-55884-2.rs`). In theory single imports should
                        // always block globs, even if they are not yet resolved, so that this kind of
                        // self-inconsistent resolution never happens.
                        // Re-enable the assert when the issue is fixed.
                        // assert!(result[ns].get().is_err());
                    }
                }
            }
        });

        if all_ns_err {
            let mut all_ns_failed = true;
            self.r.per_ns(|this, ns| {
                if !type_ns_only || ns == TypeNS {
                    let binding = this.resolve_ident_in_module(
                        module,
                        ident,
                        ns,
                        &import.parent_scope,
                        Some(finalize),
                        None,
                    );
                    if binding.is_ok() {
                        all_ns_failed = false;
                    }
                }
            });

            return if all_ns_failed {
                let resolutions = match module {
                    ModuleOrUniformRoot::Module(module) => {
                        Some(self.r.resolutions(module).borrow())
                    }
                    _ => None,
                };
                let resolutions = resolutions.as_ref().into_iter().flat_map(|r| r.iter());
                let names = resolutions
                    .filter_map(|(BindingKey { ident: i, .. }, resolution)| {
                        if *i == ident {
                            return None;
                        } // Never suggest the same name
                        match *resolution.borrow() {
                            NameResolution { binding: Some(name_binding), .. } => {
                                match name_binding.kind {
                                    NameBindingKind::Import { binding, .. } => {
                                        match binding.kind {
                                            // Never suggest the name that has binding error
                                            // i.e., the name that cannot be previously resolved
                                            NameBindingKind::Res(Res::Err, _) => None,
                                            _ => Some(i.name),
                                        }
                                    }
                                    _ => Some(i.name),
                                }
                            }
                            NameResolution { ref single_imports, .. }
                                if single_imports.is_empty() =>
                            {
                                None
                            }
                            _ => Some(i.name),
                        }
                    })
                    .collect::<Vec<Symbol>>();

                let lev_suggestion =
                    find_best_match_for_name(&names, ident.name, None).map(|suggestion| {
                        (
                            vec![(ident.span, suggestion.to_string())],
                            String::from("a similar name exists in the module"),
                            Applicability::MaybeIncorrect,
                        )
                    });

                let (suggestion, note) =
                    match self.check_for_module_export_macro(import, module, ident) {
                        Some((suggestion, note)) => (suggestion.or(lev_suggestion), note),
                        _ => (lev_suggestion, None),
                    };

                let label = match module {
                    ModuleOrUniformRoot::Module(module) => {
                        let module_str = module_to_string(module);
                        if let Some(module_str) = module_str {
                            format!("no `{}` in `{}`", ident, module_str)
                        } else {
                            format!("no `{}` in the root", ident)
                        }
                    }
                    _ => {
                        if !ident.is_path_segment_keyword() {
                            format!("no external crate `{}`", ident)
                        } else {
                            // HACK(eddyb) this shows up for `self` & `super`, which
                            // should work instead - for now keep the same error message.
                            format!("no `{}` in the root", ident)
                        }
                    }
                };

                Some(UnresolvedImportError {
                    span: import.span,
                    label: Some(label),
                    note,
                    suggestion,
                })
            } else {
                // `resolve_ident_in_module` reported a privacy error.
                None
            };
        }

        let mut reexport_error = None;
        let mut any_successful_reexport = false;
        let mut crate_private_reexport = false;
        self.r.per_ns(|this, ns| {
            if let Ok(binding) = source_bindings[ns].get() {
                if !binding.vis.is_at_least(import.expect_vis(), &*this) {
                    reexport_error = Some((ns, binding));
                    if let ty::Visibility::Restricted(binding_def_id) = binding.vis {
                        if binding_def_id.is_top_level_module() {
                            crate_private_reexport = true;
                        }
                    }
                } else {
                    any_successful_reexport = true;
                }
            }
        });

        // All namespaces must be re-exported with extra visibility for an error to occur.
        if !any_successful_reexport {
            let (ns, binding) = reexport_error.unwrap();
            if pub_use_of_private_extern_crate_hack(import, binding) {
                let msg = format!(
                    "extern crate `{}` is private, and cannot be \
                                   re-exported (error E0365), consider declaring with \
                                   `pub`",
                    ident
                );
                self.r.lint_buffer.buffer_lint(
                    PUB_USE_OF_PRIVATE_EXTERN_CRATE,
                    import.id,
                    import.span,
                    &msg,
                );
            } else {
                let error_msg = if crate_private_reexport {
                    format!(
                        "`{}` is only public within the crate, and cannot be re-exported outside",
                        ident
                    )
                } else {
                    format!("`{}` is private, and cannot be re-exported", ident)
                };

                if ns == TypeNS {
                    let label_msg = if crate_private_reexport {
                        format!("re-export of crate public `{}`", ident)
                    } else {
                        format!("re-export of private `{}`", ident)
                    };

                    struct_span_err!(self.r.session, import.span, E0365, "{}", error_msg)
                        .span_label(import.span, label_msg)
                        .note(&format!("consider declaring type or module `{}` with `pub`", ident))
                        .emit();
                } else {
                    let mut err =
                        struct_span_err!(self.r.session, import.span, E0364, "{error_msg}");
                    match binding.kind {
                        NameBindingKind::Res(Res::Def(DefKind::Macro(_), def_id), _)
                            // exclude decl_macro
                            if self.r.get_macro_by_def_id(def_id).macro_rules =>
                        {
                            err.span_help(
                                binding.span,
                                "consider adding a `#[macro_export]` to the macro in the imported module",
                            );
                        }
                        _ => {
                            err.span_note(
                                import.span,
                                &format!(
                                    "consider marking `{ident}` as `pub` in the imported module"
                                ),
                            );
                        }
                    }
                    err.emit();
                }
            }
        }

        if import.module_path.len() <= 1 {
            // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
            // 2 segments, so the `resolve_path` above won't trigger it.
            let mut full_path = import.module_path.clone();
            full_path.push(Segment::from_ident(ident));
            self.r.per_ns(|this, ns| {
                if let Ok(binding) = source_bindings[ns].get() {
                    this.lint_if_path_starts_with_module(Some(finalize), &full_path, Some(binding));
                }
            });
        }

        // Record what this import resolves to for later uses in documentation,
        // this may resolve to either a value or a type, but for documentation
        // purposes it's good enough to just favor one over the other.
        self.r.per_ns(|this, ns| {
            if let Ok(binding) = source_bindings[ns].get() {
                this.import_res_map.entry(import.id).or_default()[ns] = Some(binding.res());
            }
        });

        self.check_for_redundant_imports(ident, import, source_bindings, target_bindings, target);

        debug!("(resolving single import) successfully resolved import");
        None
    }

    fn check_for_redundant_imports(
        &mut self,
        ident: Ident,
        import: &'b Import<'b>,
        source_bindings: &PerNS<Cell<Result<&'b NameBinding<'b>, Determinacy>>>,
        target_bindings: &PerNS<Cell<Option<&'b NameBinding<'b>>>>,
        target: Ident,
    ) {
        // Skip if the import was produced by a macro.
        if import.parent_scope.expansion != LocalExpnId::ROOT {
            return;
        }

        // Skip if we are inside a named module (in contrast to an anonymous
        // module defined by a block).
        if let ModuleKind::Def(..) = import.parent_scope.module.kind {
            return;
        }

        let mut is_redundant = PerNS { value_ns: None, type_ns: None, macro_ns: None };

        let mut redundant_span = PerNS { value_ns: None, type_ns: None, macro_ns: None };

        self.r.per_ns(|this, ns| {
            if let Ok(binding) = source_bindings[ns].get() {
                if binding.res() == Res::Err {
                    return;
                }

                match this.early_resolve_ident_in_lexical_scope(
                    target,
                    ScopeSet::All(ns, false),
                    &import.parent_scope,
                    None,
                    false,
                    target_bindings[ns].get(),
                ) {
                    Ok(other_binding) => {
                        is_redundant[ns] = Some(
                            binding.res() == other_binding.res() && !other_binding.is_ambiguity(),
                        );
                        redundant_span[ns] = Some((other_binding.span, other_binding.is_import()));
                    }
                    Err(_) => is_redundant[ns] = Some(false),
                }
            }
        });

        if !is_redundant.is_empty() && is_redundant.present_items().all(|is_redundant| is_redundant)
        {
            let mut redundant_spans: Vec<_> = redundant_span.present_items().collect();
            redundant_spans.sort();
            redundant_spans.dedup();
            self.r.lint_buffer.buffer_lint_with_diagnostic(
                UNUSED_IMPORTS,
                import.id,
                import.span,
                &format!("the item `{}` is imported redundantly", ident),
                BuiltinLintDiagnostics::RedundantImport(redundant_spans, ident),
            );
        }
    }

    fn resolve_glob_import(&mut self, import: &'b Import<'b>) {
        let ModuleOrUniformRoot::Module(module) = import.imported_module.get().unwrap() else {
            self.r.session.span_err(import.span, "cannot glob-import all possible crates");
            return;
        };

        if module.is_trait() {
            self.r.session.span_err(import.span, "items in traits are not importable");
            return;
        } else if ptr::eq(module, import.parent_scope.module) {
            return;
        } else if let ImportKind::Glob { is_prelude: true, .. } = import.kind {
            self.r.prelude = Some(module);
            return;
        }

        // Add to module's glob_importers
        module.glob_importers.borrow_mut().push(import);

        // Ensure that `resolutions` isn't borrowed during `try_define`,
        // since it might get updated via a glob cycle.
        let bindings = self
            .r
            .resolutions(module)
            .borrow()
            .iter()
            .filter_map(|(key, resolution)| {
                resolution.borrow().binding().map(|binding| (*key, binding))
            })
            .collect::<Vec<_>>();
        for (mut key, binding) in bindings {
            let scope = match key.ident.span.reverse_glob_adjust(module.expansion, import.span) {
                Some(Some(def)) => self.r.expn_def_scope(def),
                Some(None) => import.parent_scope.module,
                None => continue,
            };
            if self.r.is_accessible_from(binding.vis, scope) {
                let imported_binding = self.r.import(binding, import);
                let _ = self.r.try_define(import.parent_scope.module, key, imported_binding);
            }
        }

        // Record the destination of this import
        self.r.record_partial_res(import.id, PartialRes::new(module.res().unwrap()));
    }

    // Miscellaneous post-processing, including recording re-exports,
    // reporting conflicts, and reporting unresolved imports.
    fn finalize_resolutions_in(&mut self, module: Module<'b>) {
        // Since import resolution is finished, globs will not define any more names.
        *module.globs.borrow_mut() = Vec::new();

        if let Some(def_id) = module.opt_def_id() {
            let mut reexports = Vec::new();

            module.for_each_child(self.r, |this, ident, _, binding| {
                if let Some(res) = this.is_reexport(binding) {
                    reexports.push(ModChild {
                        ident,
                        res,
                        vis: binding.vis,
                        span: binding.span,
                        macro_rules: false,
                    });
                }
            });

            if !reexports.is_empty() {
                // Call to `expect_local` should be fine because current
                // code is only called for local modules.
                self.r.reexport_map.insert(def_id.expect_local(), reexports);
            }
        }
    }
}

fn import_path_to_string(names: &[Ident], import_kind: &ImportKind<'_>, span: Span) -> String {
    let pos = names.iter().position(|p| span == p.span && p.name != kw::PathRoot);
    let global = !names.is_empty() && names[0].name == kw::PathRoot;
    if let Some(pos) = pos {
        let names = if global { &names[1..pos + 1] } else { &names[..pos + 1] };
        names_to_string(&names.iter().map(|ident| ident.name).collect::<Vec<_>>())
    } else {
        let names = if global { &names[1..] } else { names };
        if names.is_empty() {
            import_kind_to_string(import_kind)
        } else {
            format!(
                "{}::{}",
                names_to_string(&names.iter().map(|ident| ident.name).collect::<Vec<_>>()),
                import_kind_to_string(import_kind),
            )
        }
    }
}

fn import_kind_to_string(import_kind: &ImportKind<'_>) -> String {
    match import_kind {
        ImportKind::Single { source, .. } => source.to_string(),
        ImportKind::Glob { .. } => "*".to_string(),
        ImportKind::ExternCrate { .. } => "<extern crate>".to_string(),
        ImportKind::MacroUse => "#[macro_use]".to_string(),
    }
}