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
//! Validates all used crates and extern libraries and loads their metadata

use crate::locator::{CrateError, CrateLocator, CratePaths};
use crate::rmeta::{CrateDep, CrateMetadata, CrateNumMap, CrateRoot, MetadataBlob};

use rustc_ast::expand::allocator::AllocatorKind;
use rustc_ast::{self as ast, *};
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_data_structures::svh::Svh;
use rustc_data_structures::sync::Lrc;
use rustc_expand::base::SyntaxExtension;
use rustc_hir::def_id::{CrateNum, LocalDefId, StableCrateId, LOCAL_CRATE};
use rustc_hir::definitions::Definitions;
use rustc_index::vec::IndexVec;
use rustc_middle::ty::TyCtxt;
use rustc_session::config::{self, CrateType, ExternLocation};
use rustc_session::cstore::{CrateDepKind, CrateSource, ExternCrate};
use rustc_session::cstore::{ExternCrateSource, MetadataLoaderDyn};
use rustc_session::lint;
use rustc_session::output::validate_crate_name;
use rustc_session::search_paths::PathKind;
use rustc_session::Session;
use rustc_span::edition::Edition;
use rustc_span::symbol::{sym, Symbol};
use rustc_span::{Span, DUMMY_SP};
use rustc_target::spec::{PanicStrategy, TargetTriple};

use proc_macro::bridge::client::ProcMacro;
use std::ops::Fn;
use std::path::Path;
use std::{cmp, env};
use tracing::{debug, info};

#[derive(Clone)]
pub struct CStore {
    metas: IndexVec<CrateNum, Option<Lrc<CrateMetadata>>>,
    injected_panic_runtime: Option<CrateNum>,
    /// This crate needs an allocator and either provides it itself, or finds it in a dependency.
    /// If the above is true, then this field denotes the kind of the found allocator.
    allocator_kind: Option<AllocatorKind>,
    /// This crate has a `#[global_allocator]` item.
    has_global_allocator: bool,

    /// This map is used to verify we get no hash conflicts between
    /// `StableCrateId` values.
    pub(crate) stable_crate_ids: FxHashMap<StableCrateId, CrateNum>,

    /// Unused externs of the crate
    unused_externs: Vec<Symbol>,
}

impl std::fmt::Debug for CStore {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("CStore").finish_non_exhaustive()
    }
}

pub struct CrateLoader<'a> {
    // Immutable configuration.
    sess: &'a Session,
    metadata_loader: Box<MetadataLoaderDyn>,
    local_crate_name: Symbol,
    // Mutable output.
    cstore: CStore,
    used_extern_options: FxHashSet<Symbol>,
}

pub enum LoadedMacro {
    MacroDef(ast::Item, Edition),
    ProcMacro(SyntaxExtension),
}

pub(crate) struct Library {
    pub source: CrateSource,
    pub metadata: MetadataBlob,
}

enum LoadResult {
    Previous(CrateNum),
    Loaded(Library),
}

/// A reference to `CrateMetadata` that can also give access to whole crate store when necessary.
#[derive(Clone, Copy)]
pub(crate) struct CrateMetadataRef<'a> {
    pub cdata: &'a CrateMetadata,
    pub cstore: &'a CStore,
}

impl std::ops::Deref for CrateMetadataRef<'_> {
    type Target = CrateMetadata;

    fn deref(&self) -> &Self::Target {
        self.cdata
    }
}

struct CrateDump<'a>(&'a CStore);

impl<'a> std::fmt::Debug for CrateDump<'a> {
    fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        writeln!(fmt, "resolved crates:")?;
        for (cnum, data) in self.0.iter_crate_data() {
            writeln!(fmt, "  name: {}", data.name())?;
            writeln!(fmt, "  cnum: {}", cnum)?;
            writeln!(fmt, "  hash: {}", data.hash())?;
            writeln!(fmt, "  reqd: {:?}", data.dep_kind())?;
            let CrateSource { dylib, rlib, rmeta } = data.source();
            if let Some(dylib) = dylib {
                writeln!(fmt, "  dylib: {}", dylib.0.display())?;
            }
            if let Some(rlib) = rlib {
                writeln!(fmt, "   rlib: {}", rlib.0.display())?;
            }
            if let Some(rmeta) = rmeta {
                writeln!(fmt, "   rmeta: {}", rmeta.0.display())?;
            }
        }
        Ok(())
    }
}

impl CStore {
    pub fn from_tcx(tcx: TyCtxt<'_>) -> &CStore {
        tcx.cstore_untracked()
            .as_any()
            .downcast_ref::<CStore>()
            .expect("`tcx.cstore` is not a `CStore`")
    }

    fn alloc_new_crate_num(&mut self) -> CrateNum {
        self.metas.push(None);
        CrateNum::new(self.metas.len() - 1)
    }

    pub(crate) fn get_crate_data(&self, cnum: CrateNum) -> CrateMetadataRef<'_> {
        let cdata = self.metas[cnum]
            .as_ref()
            .unwrap_or_else(|| panic!("Failed to get crate data for {:?}", cnum));
        CrateMetadataRef { cdata, cstore: self }
    }

    fn set_crate_data(&mut self, cnum: CrateNum, data: CrateMetadata) {
        assert!(self.metas[cnum].is_none(), "Overwriting crate metadata entry");
        self.metas[cnum] = Some(Lrc::new(data));
    }

    pub(crate) fn iter_crate_data(&self) -> impl Iterator<Item = (CrateNum, &CrateMetadata)> {
        self.metas
            .iter_enumerated()
            .filter_map(|(cnum, data)| data.as_ref().map(|data| (cnum, &**data)))
    }

    fn push_dependencies_in_postorder(&self, deps: &mut Vec<CrateNum>, cnum: CrateNum) {
        if !deps.contains(&cnum) {
            let data = self.get_crate_data(cnum);
            for &dep in data.dependencies().iter() {
                if dep != cnum {
                    self.push_dependencies_in_postorder(deps, dep);
                }
            }

            deps.push(cnum);
        }
    }

    pub(crate) fn crate_dependencies_in_postorder(&self, cnum: CrateNum) -> Vec<CrateNum> {
        let mut deps = Vec::new();
        if cnum == LOCAL_CRATE {
            for (cnum, _) in self.iter_crate_data() {
                self.push_dependencies_in_postorder(&mut deps, cnum);
            }
        } else {
            self.push_dependencies_in_postorder(&mut deps, cnum);
        }
        deps
    }

    fn crate_dependencies_in_reverse_postorder(&self, cnum: CrateNum) -> Vec<CrateNum> {
        let mut deps = self.crate_dependencies_in_postorder(cnum);
        deps.reverse();
        deps
    }

    pub(crate) fn injected_panic_runtime(&self) -> Option<CrateNum> {
        self.injected_panic_runtime
    }

    pub(crate) fn allocator_kind(&self) -> Option<AllocatorKind> {
        self.allocator_kind
    }

    pub(crate) fn has_global_allocator(&self) -> bool {
        self.has_global_allocator
    }

    pub fn report_unused_deps(&self, tcx: TyCtxt<'_>) {
        let json_unused_externs = tcx.sess.opts.json_unused_externs;

        // We put the check for the option before the lint_level_at_node call
        // because the call mutates internal state and introducing it
        // leads to some ui tests failing.
        if !json_unused_externs.is_enabled() {
            return;
        }
        let level = tcx
            .lint_level_at_node(lint::builtin::UNUSED_CRATE_DEPENDENCIES, rustc_hir::CRATE_HIR_ID)
            .0;
        if level != lint::Level::Allow {
            let unused_externs =
                self.unused_externs.iter().map(|ident| ident.to_ident_string()).collect::<Vec<_>>();
            let unused_externs = unused_externs.iter().map(String::as_str).collect::<Vec<&str>>();
            tcx.sess.parse_sess.span_diagnostic.emit_unused_externs(
                level,
                json_unused_externs.is_loud(),
                &unused_externs,
            );
        }
    }
}

impl<'a> CrateLoader<'a> {
    pub fn new(
        sess: &'a Session,
        metadata_loader: Box<MetadataLoaderDyn>,
        local_crate_name: &str,
    ) -> Self {
        let mut stable_crate_ids = FxHashMap::default();
        stable_crate_ids.insert(sess.local_stable_crate_id(), LOCAL_CRATE);

        CrateLoader {
            sess,
            metadata_loader,
            local_crate_name: Symbol::intern(local_crate_name),
            cstore: CStore {
                // We add an empty entry for LOCAL_CRATE (which maps to zero) in
                // order to make array indices in `metas` match with the
                // corresponding `CrateNum`. This first entry will always remain
                // `None`.
                metas: IndexVec::from_elem_n(None, 1),
                injected_panic_runtime: None,
                allocator_kind: None,
                has_global_allocator: false,
                stable_crate_ids,
                unused_externs: Vec::new(),
            },
            used_extern_options: Default::default(),
        }
    }

    pub fn cstore(&self) -> &CStore {
        &self.cstore
    }

    pub fn into_cstore(self) -> CStore {
        self.cstore
    }

    fn existing_match(&self, name: Symbol, hash: Option<Svh>, kind: PathKind) -> Option<CrateNum> {
        for (cnum, data) in self.cstore.iter_crate_data() {
            if data.name() != name {
                tracing::trace!("{} did not match {}", data.name(), name);
                continue;
            }

            match hash {
                Some(hash) if hash == data.hash() => return Some(cnum),
                Some(hash) => {
                    debug!("actual hash {} did not match expected {}", hash, data.hash());
                    continue;
                }
                None => {}
            }

            // When the hash is None we're dealing with a top-level dependency
            // in which case we may have a specification on the command line for
            // this library. Even though an upstream library may have loaded
            // something of the same name, we have to make sure it was loaded
            // from the exact same location as well.
            //
            // We're also sure to compare *paths*, not actual byte slices. The
            // `source` stores paths which are normalized which may be different
            // from the strings on the command line.
            let source = self.cstore.get_crate_data(cnum).cdata.source();
            if let Some(entry) = self.sess.opts.externs.get(name.as_str()) {
                // Only use `--extern crate_name=path` here, not `--extern crate_name`.
                if let Some(mut files) = entry.files() {
                    if files.any(|l| {
                        let l = l.canonicalized();
                        source.dylib.as_ref().map(|(p, _)| p) == Some(l)
                            || source.rlib.as_ref().map(|(p, _)| p) == Some(l)
                            || source.rmeta.as_ref().map(|(p, _)| p) == Some(l)
                    }) {
                        return Some(cnum);
                    }
                }
                continue;
            }

            // Alright, so we've gotten this far which means that `data` has the
            // right name, we don't have a hash, and we don't have a --extern
            // pointing for ourselves. We're still not quite yet done because we
            // have to make sure that this crate was found in the crate lookup
            // path (this is a top-level dependency) as we don't want to
            // implicitly load anything inside the dependency lookup path.
            let prev_kind = source
                .dylib
                .as_ref()
                .or(source.rlib.as_ref())
                .or(source.rmeta.as_ref())
                .expect("No sources for crate")
                .1;
            if kind.matches(prev_kind) {
                return Some(cnum);
            } else {
                debug!(
                    "failed to load existing crate {}; kind {:?} did not match prev_kind {:?}",
                    name, kind, prev_kind
                );
            }
        }

        None
    }

    fn verify_no_symbol_conflicts(&self, root: &CrateRoot<'_>) -> Result<(), CrateError> {
        // Check for (potential) conflicts with the local crate
        if self.sess.local_stable_crate_id() == root.stable_crate_id() {
            return Err(CrateError::SymbolConflictsCurrent(root.name()));
        }

        // Check for conflicts with any crate loaded so far
        for (_, other) in self.cstore.iter_crate_data() {
            // Same stable crate id but different SVH
            if other.stable_crate_id() == root.stable_crate_id() && other.hash() != root.hash() {
                return Err(CrateError::SymbolConflictsOthers(root.name()));
            }
        }

        Ok(())
    }

    fn verify_no_stable_crate_id_hash_conflicts(
        &mut self,
        root: &CrateRoot<'_>,
        cnum: CrateNum,
    ) -> Result<(), CrateError> {
        if let Some(existing) = self.cstore.stable_crate_ids.insert(root.stable_crate_id(), cnum) {
            let crate_name0 = root.name();
            let crate_name1 = self.cstore.get_crate_data(existing).name();
            return Err(CrateError::StableCrateIdCollision(crate_name0, crate_name1));
        }

        Ok(())
    }

    fn register_crate(
        &mut self,
        host_lib: Option<Library>,
        root: Option<&CratePaths>,
        lib: Library,
        dep_kind: CrateDepKind,
        name: Symbol,
    ) -> Result<CrateNum, CrateError> {
        let _prof_timer = self.sess.prof.generic_activity("metadata_register_crate");

        let Library { source, metadata } = lib;
        let crate_root = metadata.get_root();
        let host_hash = host_lib.as_ref().map(|lib| lib.metadata.get_root().hash());

        let private_dep =
            self.sess.opts.externs.get(name.as_str()).map_or(false, |e| e.is_private_dep);

        // Claim this crate number and cache it
        let cnum = self.cstore.alloc_new_crate_num();

        info!(
            "register crate `{}` (cnum = {}. private_dep = {})",
            crate_root.name(),
            cnum,
            private_dep
        );

        // Maintain a reference to the top most crate.
        // Stash paths for top-most crate locally if necessary.
        let crate_paths;
        let root = if let Some(root) = root {
            root
        } else {
            crate_paths = CratePaths::new(crate_root.name(), source.clone());
            &crate_paths
        };

        let cnum_map = self.resolve_crate_deps(root, &crate_root, &metadata, cnum, dep_kind)?;

        let raw_proc_macros = if crate_root.is_proc_macro_crate() {
            let temp_root;
            let (dlsym_source, dlsym_root) = match &host_lib {
                Some(host_lib) => (&host_lib.source, {
                    temp_root = host_lib.metadata.get_root();
                    &temp_root
                }),
                None => (&source, &crate_root),
            };
            let dlsym_dylib = dlsym_source.dylib.as_ref().expect("no dylib for a proc-macro crate");
            Some(self.dlsym_proc_macros(&dlsym_dylib.0, dlsym_root.stable_crate_id())?)
        } else {
            None
        };

        // Perform some verification *after* resolve_crate_deps() above is
        // known to have been successful. It seems that - in error cases - the
        // cstore can be in a temporarily invalid state between cnum allocation
        // and dependency resolution and the verification code would produce
        // ICEs in that case (see #83045).
        self.verify_no_symbol_conflicts(&crate_root)?;
        self.verify_no_stable_crate_id_hash_conflicts(&crate_root, cnum)?;

        let crate_metadata = CrateMetadata::new(
            self.sess,
            &self.cstore,
            metadata,
            crate_root,
            raw_proc_macros,
            cnum,
            cnum_map,
            dep_kind,
            source,
            private_dep,
            host_hash,
        );

        self.cstore.set_crate_data(cnum, crate_metadata);

        Ok(cnum)
    }

    fn load_proc_macro<'b>(
        &self,
        locator: &mut CrateLocator<'b>,
        path_kind: PathKind,
        host_hash: Option<Svh>,
    ) -> Result<Option<(LoadResult, Option<Library>)>, CrateError>
    where
        'a: 'b,
    {
        // Use a new crate locator so trying to load a proc macro doesn't affect the error
        // message we emit
        let mut proc_macro_locator = locator.clone();

        // Try to load a proc macro
        proc_macro_locator.is_proc_macro = true;

        // Load the proc macro crate for the target
        let (locator, target_result) = if self.sess.opts.debugging_opts.dual_proc_macros {
            proc_macro_locator.reset();
            let result = match self.load(&mut proc_macro_locator)? {
                Some(LoadResult::Previous(cnum)) => {
                    return Ok(Some((LoadResult::Previous(cnum), None)));
                }
                Some(LoadResult::Loaded(library)) => Some(LoadResult::Loaded(library)),
                None => return Ok(None),
            };
            locator.hash = host_hash;
            // Use the locator when looking for the host proc macro crate, as that is required
            // so we want it to affect the error message
            (locator, result)
        } else {
            (&mut proc_macro_locator, None)
        };

        // Load the proc macro crate for the host

        locator.reset();
        locator.is_proc_macro = true;
        locator.target = &self.sess.host;
        locator.triple = TargetTriple::from_triple(config::host_triple());
        locator.filesearch = self.sess.host_filesearch(path_kind);

        let Some(host_result) = self.load(locator)? else {
            return Ok(None);
        };

        Ok(Some(if self.sess.opts.debugging_opts.dual_proc_macros {
            let host_result = match host_result {
                LoadResult::Previous(..) => {
                    panic!("host and target proc macros must be loaded in lock-step")
                }
                LoadResult::Loaded(library) => library,
            };
            (target_result.unwrap(), Some(host_result))
        } else {
            (host_result, None)
        }))
    }

    fn resolve_crate<'b>(
        &'b mut self,
        name: Symbol,
        span: Span,
        dep_kind: CrateDepKind,
    ) -> Option<CrateNum> {
        self.used_extern_options.insert(name);
        match self.maybe_resolve_crate(name, dep_kind, None) {
            Ok(cnum) => Some(cnum),
            Err(err) => {
                let missing_core =
                    self.maybe_resolve_crate(sym::core, CrateDepKind::Explicit, None).is_err();
                err.report(&self.sess, span, missing_core);
                None
            }
        }
    }

    fn maybe_resolve_crate<'b>(
        &'b mut self,
        name: Symbol,
        mut dep_kind: CrateDepKind,
        dep: Option<(&'b CratePaths, &'b CrateDep)>,
    ) -> Result<CrateNum, CrateError> {
        info!("resolving crate `{}`", name);
        if !name.as_str().is_ascii() {
            return Err(CrateError::NonAsciiName(name));
        }
        let (root, hash, host_hash, extra_filename, path_kind) = match dep {
            Some((root, dep)) => (
                Some(root),
                Some(dep.hash),
                dep.host_hash,
                Some(&dep.extra_filename[..]),
                PathKind::Dependency,
            ),
            None => (None, None, None, None, PathKind::Crate),
        };
        let result = if let Some(cnum) = self.existing_match(name, hash, path_kind) {
            (LoadResult::Previous(cnum), None)
        } else {
            info!("falling back to a load");
            let mut locator = CrateLocator::new(
                self.sess,
                &*self.metadata_loader,
                name,
                hash,
                extra_filename,
                false, // is_host
                path_kind,
            );

            match self.load(&mut locator)? {
                Some(res) => (res, None),
                None => {
                    dep_kind = CrateDepKind::MacrosOnly;
                    match self.load_proc_macro(&mut locator, path_kind, host_hash)? {
                        Some(res) => res,
                        None => return Err(locator.into_error(root.cloned())),
                    }
                }
            }
        };

        match result {
            (LoadResult::Previous(cnum), None) => {
                let data = self.cstore.get_crate_data(cnum);
                if data.is_proc_macro_crate() {
                    dep_kind = CrateDepKind::MacrosOnly;
                }
                data.update_dep_kind(|data_dep_kind| cmp::max(data_dep_kind, dep_kind));
                Ok(cnum)
            }
            (LoadResult::Loaded(library), host_library) => {
                self.register_crate(host_library, root, library, dep_kind, name)
            }
            _ => panic!(),
        }
    }

    fn load(&self, locator: &mut CrateLocator<'_>) -> Result<Option<LoadResult>, CrateError> {
        let Some(library) = locator.maybe_load_library_crate()? else {
            return Ok(None);
        };

        // In the case that we're loading a crate, but not matching
        // against a hash, we could load a crate which has the same hash
        // as an already loaded crate. If this is the case prevent
        // duplicates by just using the first crate.
        //
        // Note that we only do this for target triple crates, though, as we
        // don't want to match a host crate against an equivalent target one
        // already loaded.
        let root = library.metadata.get_root();
        // FIXME: why is this condition necessary? It was adding in #33625 but I
        // don't know why and the original author doesn't remember ...
        let can_reuse_cratenum =
            locator.triple == self.sess.opts.target_triple || locator.is_proc_macro;
        Ok(Some(if can_reuse_cratenum {
            let mut result = LoadResult::Loaded(library);
            for (cnum, data) in self.cstore.iter_crate_data() {
                if data.name() == root.name() && root.hash() == data.hash() {
                    assert!(locator.hash.is_none());
                    info!("load success, going to previous cnum: {}", cnum);
                    result = LoadResult::Previous(cnum);
                    break;
                }
            }
            result
        } else {
            LoadResult::Loaded(library)
        }))
    }

    fn update_extern_crate(&self, cnum: CrateNum, extern_crate: ExternCrate) {
        let cmeta = self.cstore.get_crate_data(cnum);
        if cmeta.update_extern_crate(extern_crate) {
            // Propagate the extern crate info to dependencies if it was updated.
            let extern_crate = ExternCrate { dependency_of: cnum, ..extern_crate };
            for &dep_cnum in cmeta.dependencies().iter() {
                self.update_extern_crate(dep_cnum, extern_crate);
            }
        }
    }

    // Go through the crate metadata and load any crates that it references
    fn resolve_crate_deps(
        &mut self,
        root: &CratePaths,
        crate_root: &CrateRoot<'_>,
        metadata: &MetadataBlob,
        krate: CrateNum,
        dep_kind: CrateDepKind,
    ) -> Result<CrateNumMap, CrateError> {
        debug!("resolving deps of external crate");
        if crate_root.is_proc_macro_crate() {
            return Ok(CrateNumMap::new());
        }

        // The map from crate numbers in the crate we're resolving to local crate numbers.
        // We map 0 and all other holes in the map to our parent crate. The "additional"
        // self-dependencies should be harmless.
        let deps = crate_root.decode_crate_deps(metadata);
        let mut crate_num_map = CrateNumMap::with_capacity(1 + deps.len());
        crate_num_map.push(krate);
        for dep in deps {
            info!(
                "resolving dep crate {} hash: `{}` extra filename: `{}`",
                dep.name, dep.hash, dep.extra_filename
            );
            let dep_kind = match dep_kind {
                CrateDepKind::MacrosOnly => CrateDepKind::MacrosOnly,
                _ => dep.kind,
            };
            let cnum = self.maybe_resolve_crate(dep.name, dep_kind, Some((root, &dep)))?;
            crate_num_map.push(cnum);
        }

        debug!("resolve_crate_deps: cnum_map for {:?} is {:?}", krate, crate_num_map);
        Ok(crate_num_map)
    }

    fn dlsym_proc_macros(
        &self,
        path: &Path,
        stable_crate_id: StableCrateId,
    ) -> Result<&'static [ProcMacro], CrateError> {
        // Make sure the path contains a / or the linker will search for it.
        let path = env::current_dir().unwrap().join(path);
        let lib = unsafe { libloading::Library::new(path) }
            .map_err(|err| CrateError::DlOpen(err.to_string()))?;

        let sym_name = self.sess.generate_proc_macro_decls_symbol(stable_crate_id);
        let sym = unsafe { lib.get::<*const &[ProcMacro]>(sym_name.as_bytes()) }
            .map_err(|err| CrateError::DlSym(err.to_string()))?;

        // Intentionally leak the dynamic library. We can't ever unload it
        // since the library can make things that will live arbitrarily long.
        let sym = unsafe { sym.into_raw() };
        std::mem::forget(lib);

        Ok(unsafe { **sym })
    }

    fn inject_panic_runtime(&mut self, krate: &ast::Crate) {
        // If we're only compiling an rlib, then there's no need to select a
        // panic runtime, so we just skip this section entirely.
        let any_non_rlib = self.sess.crate_types().iter().any(|ct| *ct != CrateType::Rlib);
        if !any_non_rlib {
            info!("panic runtime injection skipped, only generating rlib");
            return;
        }

        // If we need a panic runtime, we try to find an existing one here. At
        // the same time we perform some general validation of the DAG we've got
        // going such as ensuring everything has a compatible panic strategy.
        //
        // The logic for finding the panic runtime here is pretty much the same
        // as the allocator case with the only addition that the panic strategy
        // compilation mode also comes into play.
        let desired_strategy = self.sess.panic_strategy();
        let mut runtime_found = false;
        let mut needs_panic_runtime =
            self.sess.contains_name(&krate.attrs, sym::needs_panic_runtime);

        for (cnum, data) in self.cstore.iter_crate_data() {
            needs_panic_runtime = needs_panic_runtime || data.needs_panic_runtime();
            if data.is_panic_runtime() {
                // Inject a dependency from all #![needs_panic_runtime] to this
                // #![panic_runtime] crate.
                self.inject_dependency_if(cnum, "a panic runtime", &|data| {
                    data.needs_panic_runtime()
                });
                runtime_found = runtime_found || data.dep_kind() == CrateDepKind::Explicit;
            }
        }

        // If an explicitly linked and matching panic runtime was found, or if
        // we just don't need one at all, then we're done here and there's
        // nothing else to do.
        if !needs_panic_runtime || runtime_found {
            return;
        }

        // By this point we know that we (a) need a panic runtime and (b) no
        // panic runtime was explicitly linked. Here we just load an appropriate
        // default runtime for our panic strategy and then inject the
        // dependencies.
        //
        // We may resolve to an already loaded crate (as the crate may not have
        // been explicitly linked prior to this) and we may re-inject
        // dependencies again, but both of those situations are fine.
        //
        // Also note that we have yet to perform validation of the crate graph
        // in terms of everyone has a compatible panic runtime format, that's
        // performed later as part of the `dependency_format` module.
        let name = match desired_strategy {
            PanicStrategy::Unwind => sym::panic_unwind,
            PanicStrategy::Abort => sym::panic_abort,
        };
        info!("panic runtime not found -- loading {}", name);

        let Some(cnum) = self.resolve_crate(name, DUMMY_SP, CrateDepKind::Implicit) else { return; };
        let data = self.cstore.get_crate_data(cnum);

        // Sanity check the loaded crate to ensure it is indeed a panic runtime
        // and the panic strategy is indeed what we thought it was.
        if !data.is_panic_runtime() {
            self.sess.err(&format!("the crate `{}` is not a panic runtime", name));
        }
        if data.panic_strategy() != desired_strategy {
            self.sess.err(&format!(
                "the crate `{}` does not have the panic \
                                    strategy `{}`",
                name,
                desired_strategy.desc()
            ));
        }

        self.cstore.injected_panic_runtime = Some(cnum);
        self.inject_dependency_if(cnum, "a panic runtime", &|data| data.needs_panic_runtime());
    }

    fn inject_profiler_runtime(&mut self, krate: &ast::Crate) {
        if self.sess.opts.debugging_opts.no_profiler_runtime
            || !(self.sess.instrument_coverage()
                || self.sess.opts.debugging_opts.profile
                || self.sess.opts.cg.profile_generate.enabled())
        {
            return;
        }

        info!("loading profiler");

        let name = Symbol::intern(&self.sess.opts.debugging_opts.profiler_runtime);
        if name == sym::profiler_builtins && self.sess.contains_name(&krate.attrs, sym::no_core) {
            self.sess.err(
                "`profiler_builtins` crate (required by compiler options) \
                        is not compatible with crate attribute `#![no_core]`",
            );
        }

        let Some(cnum) = self.resolve_crate(name, DUMMY_SP, CrateDepKind::Implicit) else { return; };
        let data = self.cstore.get_crate_data(cnum);

        // Sanity check the loaded crate to ensure it is indeed a profiler runtime
        if !data.is_profiler_runtime() {
            self.sess.err(&format!("the crate `{}` is not a profiler runtime", name));
        }
    }

    fn inject_allocator_crate(&mut self, krate: &ast::Crate) {
        self.cstore.has_global_allocator = match &*global_allocator_spans(&self.sess, krate) {
            [span1, span2, ..] => {
                self.sess
                    .struct_span_err(*span2, "cannot define multiple global allocators")
                    .span_label(*span2, "cannot define a new global allocator")
                    .span_label(*span1, "previous global allocator defined here")
                    .emit();
                true
            }
            spans => !spans.is_empty(),
        };

        // Check to see if we actually need an allocator. This desire comes
        // about through the `#![needs_allocator]` attribute and is typically
        // written down in liballoc.
        if !self.sess.contains_name(&krate.attrs, sym::needs_allocator)
            && !self.cstore.iter_crate_data().any(|(_, data)| data.needs_allocator())
        {
            return;
        }

        // At this point we've determined that we need an allocator. Let's see
        // if our compilation session actually needs an allocator based on what
        // we're emitting.
        let all_rlib = self.sess.crate_types().iter().all(|ct| matches!(*ct, CrateType::Rlib));
        if all_rlib {
            return;
        }

        // Ok, we need an allocator. Not only that but we're actually going to
        // create an artifact that needs one linked in. Let's go find the one
        // that we're going to link in.
        //
        // First up we check for global allocators. Look at the crate graph here
        // and see what's a global allocator, including if we ourselves are a
        // global allocator.
        let mut global_allocator =
            self.cstore.has_global_allocator.then(|| Symbol::intern("this crate"));
        for (_, data) in self.cstore.iter_crate_data() {
            if data.has_global_allocator() {
                match global_allocator {
                    Some(other_crate) => {
                        self.sess.err(&format!(
                        "the `#[global_allocator]` in {} conflicts with global allocator in: {}",
                        other_crate,
                        data.name()
                    ));
                    }
                    None => global_allocator = Some(data.name()),
                }
            }
        }

        if global_allocator.is_some() {
            self.cstore.allocator_kind = Some(AllocatorKind::Global);
            return;
        }

        // Ok we haven't found a global allocator but we still need an
        // allocator. At this point our allocator request is typically fulfilled
        // by the standard library, denoted by the `#![default_lib_allocator]`
        // attribute.
        if !self.sess.contains_name(&krate.attrs, sym::default_lib_allocator)
            && !self.cstore.iter_crate_data().any(|(_, data)| data.has_default_lib_allocator())
        {
            self.sess.err(
                "no global memory allocator found but one is required; link to std or add \
                 `#[global_allocator]` to a static item that implements the GlobalAlloc trait",
            );
        }
        self.cstore.allocator_kind = Some(AllocatorKind::Default);
    }

    fn inject_dependency_if(
        &self,
        krate: CrateNum,
        what: &str,
        needs_dep: &dyn Fn(&CrateMetadata) -> bool,
    ) {
        // don't perform this validation if the session has errors, as one of
        // those errors may indicate a circular dependency which could cause
        // this to stack overflow.
        if self.sess.has_errors().is_some() {
            return;
        }

        // Before we inject any dependencies, make sure we don't inject a
        // circular dependency by validating that this crate doesn't
        // transitively depend on any crates satisfying `needs_dep`.
        for dep in self.cstore.crate_dependencies_in_reverse_postorder(krate) {
            let data = self.cstore.get_crate_data(dep);
            if needs_dep(&data) {
                self.sess.err(&format!(
                    "the crate `{}` cannot depend \
                                        on a crate that needs {}, but \
                                        it depends on `{}`",
                    self.cstore.get_crate_data(krate).name(),
                    what,
                    data.name()
                ));
            }
        }

        // All crates satisfying `needs_dep` do not explicitly depend on the
        // crate provided for this compile, but in order for this compilation to
        // be successfully linked we need to inject a dependency (to order the
        // crates on the command line correctly).
        for (cnum, data) in self.cstore.iter_crate_data() {
            if needs_dep(data) {
                info!("injecting a dep from {} to {}", cnum, krate);
                data.add_dependency(krate);
            }
        }
    }

    fn report_unused_deps(&mut self, krate: &ast::Crate) {
        // Make a point span rather than covering the whole file
        let span = krate.spans.inner_span.shrink_to_lo();
        // Complain about anything left over
        for (name, entry) in self.sess.opts.externs.iter() {
            if let ExternLocation::FoundInLibrarySearchDirectories = entry.location {
                // Don't worry about pathless `--extern foo` sysroot references
                continue;
            }
            if entry.nounused_dep {
                // We're not worried about this one
                continue;
            }
            let name_interned = Symbol::intern(name);
            if self.used_extern_options.contains(&name_interned) {
                continue;
            }

            // Got a real unused --extern
            if self.sess.opts.json_unused_externs.is_enabled() {
                self.cstore.unused_externs.push(name_interned);
                continue;
            }

            self.sess.parse_sess.buffer_lint(
                    lint::builtin::UNUSED_CRATE_DEPENDENCIES,
                    span,
                    ast::CRATE_NODE_ID,
                    &format!(
                        "external crate `{}` unused in `{}`: remove the dependency or add `use {} as _;`",
                        name,
                        self.local_crate_name,
                        name),
                );
        }
    }

    pub fn postprocess(&mut self, krate: &ast::Crate) {
        self.inject_profiler_runtime(krate);
        self.inject_allocator_crate(krate);
        self.inject_panic_runtime(krate);

        self.report_unused_deps(krate);

        info!("{:?}", CrateDump(&self.cstore));
    }

    pub fn process_extern_crate(
        &mut self,
        item: &ast::Item,
        definitions: &Definitions,
        def_id: LocalDefId,
    ) -> Option<CrateNum> {
        match item.kind {
            ast::ItemKind::ExternCrate(orig_name) => {
                debug!(
                    "resolving extern crate stmt. ident: {} orig_name: {:?}",
                    item.ident, orig_name
                );
                let name = match orig_name {
                    Some(orig_name) => {
                        validate_crate_name(self.sess, orig_name.as_str(), Some(item.span));
                        orig_name
                    }
                    None => item.ident.name,
                };
                let dep_kind = if self.sess.contains_name(&item.attrs, sym::no_link) {
                    CrateDepKind::MacrosOnly
                } else {
                    CrateDepKind::Explicit
                };

                let cnum = self.resolve_crate(name, item.span, dep_kind)?;

                let path_len = definitions.def_path(def_id).data.len();
                self.update_extern_crate(
                    cnum,
                    ExternCrate {
                        src: ExternCrateSource::Extern(def_id.to_def_id()),
                        span: item.span,
                        path_len,
                        dependency_of: LOCAL_CRATE,
                    },
                );
                Some(cnum)
            }
            _ => bug!(),
        }
    }

    pub fn process_path_extern(&mut self, name: Symbol, span: Span) -> Option<CrateNum> {
        let cnum = self.resolve_crate(name, span, CrateDepKind::Explicit)?;

        self.update_extern_crate(
            cnum,
            ExternCrate {
                src: ExternCrateSource::Path,
                span,
                // to have the least priority in `update_extern_crate`
                path_len: usize::MAX,
                dependency_of: LOCAL_CRATE,
            },
        );

        Some(cnum)
    }

    pub fn maybe_process_path_extern(&mut self, name: Symbol) -> Option<CrateNum> {
        self.maybe_resolve_crate(name, CrateDepKind::Explicit, None).ok()
    }
}

fn global_allocator_spans(sess: &Session, krate: &ast::Crate) -> Vec<Span> {
    struct Finder<'a> {
        sess: &'a Session,
        name: Symbol,
        spans: Vec<Span>,
    }
    impl<'ast, 'a> visit::Visitor<'ast> for Finder<'a> {
        fn visit_item(&mut self, item: &'ast ast::Item) {
            if item.ident.name == self.name
                && self.sess.contains_name(&item.attrs, sym::rustc_std_internal_symbol)
            {
                self.spans.push(item.span);
            }
            visit::walk_item(self, item)
        }
    }

    let name = Symbol::intern(&AllocatorKind::Global.fn_name(sym::alloc));
    let mut f = Finder { sess, name, spans: Vec::new() };
    visit::walk_crate(&mut f, krate);
    f.spans
}