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
use std::collections::{HashMap, HashSet};
use std::task::{ready, Poll};

use crate::core::PackageSet;
use crate::core::{Dependency, PackageId, SourceId, Summary};
use crate::sources::config::SourceConfigMap;
use crate::sources::source::QueryKind;
use crate::sources::source::Source;
use crate::sources::source::SourceMap;
use crate::util::errors::CargoResult;
use crate::util::interning::InternedString;
use crate::util::{CanonicalUrl, Config};
use anyhow::{bail, Context as _};
use tracing::{debug, trace};
use url::Url;

/// Source of information about a group of packages.
///
/// See also `core::Source`.
pub trait Registry {
    /// Attempt to find the packages that match a dependency request.
    fn query(
        &mut self,
        dep: &Dependency,
        kind: QueryKind,
        f: &mut dyn FnMut(Summary),
    ) -> Poll<CargoResult<()>>;

    fn query_vec(&mut self, dep: &Dependency, kind: QueryKind) -> Poll<CargoResult<Vec<Summary>>> {
        let mut ret = Vec::new();
        self.query(dep, kind, &mut |s| ret.push(s)).map_ok(|()| ret)
    }

    fn describe_source(&self, source: SourceId) -> String;
    fn is_replaced(&self, source: SourceId) -> bool;

    /// Block until all outstanding Poll::Pending requests are Poll::Ready.
    fn block_until_ready(&mut self) -> CargoResult<()>;
}

/// This structure represents a registry of known packages. It internally
/// contains a number of `Box<Source>` instances which are used to load a
/// `Package` from.
///
/// The resolution phase of Cargo uses this to drive knowledge about new
/// packages as well as querying for lists of new packages. It is here that
/// sources are updated (e.g., network operations) and overrides are
/// handled.
///
/// The general idea behind this registry is that it is centered around the
/// `SourceMap` structure, contained within which is a mapping of a `SourceId` to
/// a `Source`. Each `Source` in the map has been updated (using network
/// operations if necessary) and is ready to be queried for packages.
pub struct PackageRegistry<'cfg> {
    config: &'cfg Config,
    sources: SourceMap<'cfg>,

    // A list of sources which are considered "overrides" which take precedent
    // when querying for packages.
    overrides: Vec<SourceId>,

    // Note that each SourceId does not take into account its `precise` field
    // when hashing or testing for equality. When adding a new `SourceId`, we
    // want to avoid duplicates in the `SourceMap` (to prevent re-updating the
    // same git repo twice for example), but we also want to ensure that the
    // loaded source is always updated.
    //
    // Sources with a `precise` field normally don't need to be updated because
    // their contents are already on disk, but sources without a `precise` field
    // almost always need to be updated. If we have a cached `Source` for a
    // precise `SourceId`, then when we add a new `SourceId` that is not precise
    // we want to ensure that the underlying source is updated.
    //
    // This is basically a long-winded way of saying that we want to know
    // precisely what the keys of `sources` are, so this is a mapping of key to
    // what exactly the key is.
    source_ids: HashMap<SourceId, (SourceId, Kind)>,

    locked: LockedMap,
    yanked_whitelist: HashSet<PackageId>,
    source_config: SourceConfigMap<'cfg>,

    patches: HashMap<CanonicalUrl, Vec<Summary>>,
    patches_locked: bool,
    patches_available: HashMap<CanonicalUrl, Vec<PackageId>>,
}

/// A map of all "locked packages" which is filled in when parsing a lock file
/// and is used to guide dependency resolution by altering summaries as they're
/// queried from this source.
///
/// This map can be thought of as a glorified `Vec<MySummary>` where `MySummary`
/// has a `PackageId` for which package it represents as well as a list of
/// `PackageId` for the resolved dependencies. The hash map is otherwise
/// structured though for easy access throughout this registry.
type LockedMap = HashMap<
    // The first level of key-ing done in this hash map is the source that
    // dependencies come from, identified by a `SourceId`.
    // The next level is keyed by the name of the package...
    (SourceId, InternedString),
    // ... and the value here is a list of tuples. The first element of each
    // tuple is a package which has the source/name used to get to this
    // point. The second element of each tuple is the list of locked
    // dependencies that the first element has.
    Vec<(PackageId, Vec<PackageId>)>,
>;

#[derive(PartialEq, Eq, Clone, Copy)]
enum Kind {
    Override,
    Locked,
    Normal,
}

/// Argument to `PackageRegistry::patch` which is information about a `[patch]`
/// directive that we found in a lockfile, if present.
pub struct LockedPatchDependency {
    /// The original `Dependency` directive, except "locked" so it's version
    /// requirement is `=foo` and its `SourceId` has a "precise" listed.
    pub dependency: Dependency,
    /// The `PackageId` that was previously found in a lock file which
    /// `dependency` matches.
    pub package_id: PackageId,
    /// Something only used for backwards compatibility with the v2 lock file
    /// format where `branch=master` is considered the same as `DefaultBranch`.
    /// For more comments on this see the code in `ops/resolve.rs`.
    pub alt_package_id: Option<PackageId>,
}

impl<'cfg> PackageRegistry<'cfg> {
    pub fn new(config: &'cfg Config) -> CargoResult<PackageRegistry<'cfg>> {
        let source_config = SourceConfigMap::new(config)?;
        Ok(PackageRegistry {
            config,
            sources: SourceMap::new(),
            source_ids: HashMap::new(),
            overrides: Vec::new(),
            source_config,
            locked: HashMap::new(),
            yanked_whitelist: HashSet::new(),
            patches: HashMap::new(),
            patches_locked: false,
            patches_available: HashMap::new(),
        })
    }

    pub fn get(self, package_ids: &[PackageId]) -> CargoResult<PackageSet<'cfg>> {
        trace!("getting packages; sources={}", self.sources.len());
        PackageSet::new(package_ids, self.sources, self.config)
    }

    fn ensure_loaded(&mut self, namespace: SourceId, kind: Kind) -> CargoResult<()> {
        match self.source_ids.get(&namespace) {
            // We've previously loaded this source, and we've already locked it,
            // so we're not allowed to change it even if `namespace` has a
            // slightly different precise version listed.
            Some((_, Kind::Locked)) => {
                debug!("load/locked   {}", namespace);
                return Ok(());
            }

            // If the previous source was not a precise source, then we can be
            // sure that it's already been updated if we've already loaded it.
            Some((previous, _)) if previous.precise().is_none() => {
                debug!("load/precise  {}", namespace);
                return Ok(());
            }

            // If the previous source has the same precise version as we do,
            // then we're done, otherwise we need to need to move forward
            // updating this source.
            Some((previous, _)) => {
                if previous.precise() == namespace.precise() {
                    debug!("load/match    {}", namespace);
                    return Ok(());
                }
                debug!("load/mismatch {}", namespace);
            }
            None => {
                debug!("load/missing  {}", namespace);
            }
        }

        self.load(namespace, kind)?;

        // This isn't strictly necessary since it will be called later.
        // However it improves error messages for sources that issue errors
        // in `block_until_ready` because the callers here have context about
        // which deps are being resolved.
        self.block_until_ready()?;
        Ok(())
    }

    pub fn add_sources(&mut self, ids: impl IntoIterator<Item = SourceId>) -> CargoResult<()> {
        for id in ids {
            self.ensure_loaded(id, Kind::Locked)?;
        }
        Ok(())
    }

    pub fn add_preloaded(&mut self, source: Box<dyn Source + 'cfg>) {
        self.add_source(source, Kind::Locked);
    }

    fn add_source(&mut self, source: Box<dyn Source + 'cfg>, kind: Kind) {
        let id = source.source_id();
        self.sources.insert(source);
        self.source_ids.insert(id, (id, kind));
    }

    pub fn add_override(&mut self, source: Box<dyn Source + 'cfg>) {
        self.overrides.push(source.source_id());
        self.add_source(source, Kind::Override);
    }

    pub fn add_to_yanked_whitelist(&mut self, iter: impl Iterator<Item = PackageId>) {
        let pkgs = iter.collect::<Vec<_>>();
        for (_, source) in self.sources.sources_mut() {
            source.add_to_yanked_whitelist(&pkgs);
        }
        self.yanked_whitelist.extend(pkgs);
    }

    /// remove all residual state from previous lock files.
    pub fn clear_lock(&mut self) {
        trace!("clear_lock");
        self.locked = HashMap::new();
    }

    pub fn register_lock(&mut self, id: PackageId, deps: Vec<PackageId>) {
        trace!("register_lock: {}", id);
        for dep in deps.iter() {
            trace!("\t-> {}", dep);
        }
        let sub_vec = self
            .locked
            .entry((id.source_id(), id.name()))
            .or_insert_with(Vec::new);
        sub_vec.push((id, deps));
    }

    /// Insert a `[patch]` section into this registry.
    ///
    /// This method will insert a `[patch]` section for the `url` specified,
    /// with the given list of dependencies. The `url` specified is the URL of
    /// the source to patch (for example this is `crates-io` in the manifest).
    /// The `deps` is an array of all the entries in the `[patch]` section of
    /// the manifest.
    ///
    /// Here the `deps` will be resolved to a precise version and stored
    /// internally for future calls to `query` below. `deps` should be a tuple
    /// where the first element is the patch definition straight from the
    /// manifest, and the second element is an optional variant where the
    /// patch has been locked. This locked patch is the patch locked to
    /// a specific version found in Cargo.lock. This will be `None` if
    /// `Cargo.lock` doesn't exist, or the patch did not match any existing
    /// entries in `Cargo.lock`.
    ///
    /// Note that the patch list specified here *will not* be available to
    /// `query` until `lock_patches` is called below, which should be called
    /// once all patches have been added.
    ///
    /// The return value is a `Vec` of patches that should *not* be locked.
    /// This happens when the patch is locked, but the patch has been updated
    /// so the locked value is no longer correct.
    pub fn patch(
        &mut self,
        url: &Url,
        deps: &[(&Dependency, Option<LockedPatchDependency>)],
    ) -> CargoResult<Vec<(Dependency, PackageId)>> {
        // NOTE: None of this code is aware of required features. If a patch
        // is missing a required feature, you end up with an "unused patch"
        // warning, which is very hard to understand. Ideally the warning
        // would be tailored to indicate *why* it is unused.
        let canonical = CanonicalUrl::new(url)?;

        // Return value of patches that shouldn't be locked.
        let mut unlock_patches = Vec::new();

        // First up we need to actually resolve each `deps` specification to
        // precisely one summary. We're not using the `query` method below as it
        // internally uses maps we're building up as part of this method
        // (`patches_available` and `patches`). Instead we're going straight to
        // the source to load information from it.
        //
        // Remember that each dependency listed in `[patch]` has to resolve to
        // precisely one package, so that's why we're just creating a flat list
        // of summaries which should be the same length as `deps` above.

        let mut deps_remaining: Vec<_> = deps.iter().collect();
        let mut unlocked_summaries = Vec::new();
        while !deps_remaining.is_empty() {
            let mut deps_pending = Vec::new();
            for dep_remaining in deps_remaining {
                let (orig_patch, locked) = dep_remaining;

                // Use the locked patch if it exists, otherwise use the original.
                let dep = match locked {
                    Some(lock) => &lock.dependency,
                    None => *orig_patch,
                };
                debug!(
                    "registering a patch for `{}` with `{}`",
                    url,
                    dep.package_name()
                );

                if dep.features().len() != 0 || !dep.uses_default_features() {
                    self.source_config.config().shell().warn(format!(
                        "patch for `{}` uses the features mechanism. \
                        default-features and features will not take effect because the patch dependency does not support this mechanism",
                        dep.package_name()
                    ))?;
                }

                // Go straight to the source for resolving `dep`. Load it as we
                // normally would and then ask it directly for the list of summaries
                // corresponding to this `dep`.
                self.ensure_loaded(dep.source_id(), Kind::Normal)
                    .with_context(|| {
                        format!(
                            "failed to load source for dependency `{}`",
                            dep.package_name()
                        )
                    })?;

                let source = self
                    .sources
                    .get_mut(dep.source_id())
                    .expect("loaded source not present");

                let summaries = match source.query_vec(dep, QueryKind::Exact)? {
                    Poll::Ready(deps) => deps,
                    Poll::Pending => {
                        deps_pending.push(dep_remaining);
                        continue;
                    }
                };

                let (summary, should_unlock) =
                    match summary_for_patch(orig_patch, &locked, summaries, source) {
                        Poll::Ready(x) => x,
                        Poll::Pending => {
                            deps_pending.push(dep_remaining);
                            continue;
                        }
                    }
                    .with_context(|| {
                        format!(
                            "patch for `{}` in `{}` failed to resolve",
                            orig_patch.package_name(),
                            url,
                        )
                    })
                    .with_context(|| format!("failed to resolve patches for `{}`", url))?;

                debug!(
                    "patch summary is {:?} should_unlock={:?}",
                    summary, should_unlock
                );
                if let Some(unlock_id) = should_unlock {
                    unlock_patches.push(((*orig_patch).clone(), unlock_id));
                }

                if *summary.package_id().source_id().canonical_url() == canonical {
                    return Err(anyhow::anyhow!(
                        "patch for `{}` in `{}` points to the same source, but \
                        patches must point to different sources",
                        dep.package_name(),
                        url
                    ))
                    .context(format!("failed to resolve patches for `{}`", url));
                }
                unlocked_summaries.push(summary);
            }

            deps_remaining = deps_pending;
            self.block_until_ready()?;
        }

        let mut name_and_version = HashSet::new();
        for summary in unlocked_summaries.iter() {
            let name = summary.package_id().name();
            let version = summary.package_id().version();
            if !name_and_version.insert((name, version)) {
                bail!(
                    "cannot have two `[patch]` entries which both resolve \
                     to `{} v{}`",
                    name,
                    version
                );
            }
        }

        // Calculate a list of all patches available for this source which is
        // then used later during calls to `lock` to rewrite summaries to point
        // directly at these patched entries.
        //
        // Note that this is somewhat subtle where the list of `ids` for a
        // canonical URL is extend with possibly two ids per summary. This is done
        // to handle the transition from the v2->v3 lock file format where in
        // v2 DefaultBranch was either DefaultBranch or Branch("master") for
        // git dependencies. In this case if `summary.package_id()` is
        // Branch("master") then alt_package_id will be DefaultBranch. This
        // signifies that there's a patch available for either of those
        // dependency directives if we see them in the dependency graph.
        //
        // This is a bit complicated and hopefully an edge case we can remove
        // in the future, but for now it hopefully doesn't cause too much
        // harm...
        let mut ids = Vec::new();
        for (summary, (_, lock)) in unlocked_summaries.iter().zip(deps) {
            ids.push(summary.package_id());
            if let Some(lock) = lock {
                ids.extend(lock.alt_package_id);
            }
        }
        self.patches_available.insert(canonical.clone(), ids);

        // Note that we do not use `lock` here to lock summaries! That step
        // happens later once `lock_patches` is invoked. In the meantime though
        // we want to fill in the `patches_available` map (later used in the
        // `lock` method) and otherwise store the unlocked summaries in
        // `patches` to get locked in a future call to `lock_patches`.
        self.patches.insert(canonical, unlocked_summaries);

        Ok(unlock_patches)
    }

    /// Lock all patch summaries added via `patch`, making them available to
    /// resolution via `query`.
    ///
    /// This function will internally `lock` each summary added via `patch`
    /// above now that the full set of `patch` packages are known. This'll allow
    /// us to correctly resolve overridden dependencies between patches
    /// hopefully!
    pub fn lock_patches(&mut self) {
        assert!(!self.patches_locked);
        for summaries in self.patches.values_mut() {
            for summary in summaries {
                debug!("locking patch {:?}", summary);
                *summary = lock(&self.locked, &self.patches_available, summary.clone());
            }
        }
        self.patches_locked = true;
    }

    /// Gets all patches grouped by the source URLS they are going to patch.
    ///
    /// These patches are mainly collected from [`patch`](Self::patch).
    /// They might not be the same as patches actually used during dependency resolving.
    pub fn patches(&self) -> &HashMap<CanonicalUrl, Vec<Summary>> {
        &self.patches
    }

    fn load(&mut self, source_id: SourceId, kind: Kind) -> CargoResult<()> {
        debug!("loading source {}", source_id);
        let source = self
            .source_config
            .load(source_id, &self.yanked_whitelist)
            .with_context(|| format!("Unable to update {}", source_id))?;
        assert_eq!(source.source_id(), source_id);

        if kind == Kind::Override {
            self.overrides.push(source_id);
        }
        self.add_source(source, kind);

        // If we have an imprecise version then we don't know what we're going
        // to look for, so we always attempt to perform an update here.
        //
        // If we have a precise version, then we'll update lazily during the
        // querying phase. Note that precise in this case is only
        // `Some("locked")` as other `Some` values indicate a `cargo update
        // --precise` request
        if source_id.precise() != Some("locked") {
            self.sources.get_mut(source_id).unwrap().invalidate_cache();
        } else {
            debug!("skipping update due to locked registry");
        }
        Ok(())
    }

    fn query_overrides(&mut self, dep: &Dependency) -> Poll<CargoResult<Option<Summary>>> {
        for &s in self.overrides.iter() {
            let src = self.sources.get_mut(s).unwrap();
            let dep = Dependency::new_override(dep.package_name(), s);
            let mut results = ready!(src.query_vec(&dep, QueryKind::Exact))?;
            if !results.is_empty() {
                return Poll::Ready(Ok(Some(results.remove(0))));
            }
        }
        Poll::Ready(Ok(None))
    }

    /// This function is used to transform a summary to another locked summary
    /// if possible. This is where the concept of a lock file comes into play.
    ///
    /// If a summary points at a package ID which was previously locked, then we
    /// override the summary's ID itself, as well as all dependencies, to be
    /// rewritten to the locked versions. This will transform the summary's
    /// source to a precise source (listed in the locked version) as well as
    /// transforming all of the dependencies from range requirements on
    /// imprecise sources to exact requirements on precise sources.
    ///
    /// If a summary does not point at a package ID which was previously locked,
    /// or if any dependencies were added and don't have a previously listed
    /// version, we still want to avoid updating as many dependencies as
    /// possible to keep the graph stable. In this case we map all of the
    /// summary's dependencies to be rewritten to a locked version wherever
    /// possible. If we're unable to map a dependency though, we just pass it on
    /// through.
    pub fn lock(&self, summary: Summary) -> Summary {
        assert!(self.patches_locked);
        lock(&self.locked, &self.patches_available, summary)
    }

    fn warn_bad_override(
        &self,
        override_summary: &Summary,
        real_summary: &Summary,
    ) -> CargoResult<()> {
        let mut real_deps = real_summary.dependencies().iter().collect::<Vec<_>>();

        let boilerplate = "\
This is currently allowed but is known to produce buggy behavior with spurious
recompiles and changes to the crate graph. Path overrides unfortunately were
never intended to support this feature, so for now this message is just a
warning. In the future, however, this message will become a hard error.

To change the dependency graph via an override it's recommended to use the
`[patch]` feature of Cargo instead of the path override feature. This is
documented online at the url below for more information.

https://doc.rust-lang.org/cargo/reference/overriding-dependencies.html
";

        for dep in override_summary.dependencies() {
            if let Some(i) = real_deps.iter().position(|d| dep == *d) {
                real_deps.remove(i);
                continue;
            }
            let msg = format!(
                "path override for crate `{}` has altered the original list of\n\
                 dependencies; the dependency on `{}` was either added or\n\
                 modified to not match the previously resolved version\n\n\
                 {}",
                override_summary.package_id().name(),
                dep.package_name(),
                boilerplate
            );
            self.source_config.config().shell().warn(&msg)?;
            return Ok(());
        }

        if let Some(dep) = real_deps.get(0) {
            let msg = format!(
                "path override for crate `{}` has altered the original list of\n\
                 dependencies; the dependency on `{}` was removed\n\n\
                 {}",
                override_summary.package_id().name(),
                dep.package_name(),
                boilerplate
            );
            self.source_config.config().shell().warn(&msg)?;
            return Ok(());
        }

        Ok(())
    }
}

impl<'cfg> Registry for PackageRegistry<'cfg> {
    fn query(
        &mut self,
        dep: &Dependency,
        kind: QueryKind,
        f: &mut dyn FnMut(Summary),
    ) -> Poll<CargoResult<()>> {
        assert!(self.patches_locked);
        let (override_summary, n, to_warn) = {
            // Look for an override and get ready to query the real source.
            let override_summary = ready!(self.query_overrides(dep))?;

            // Next up on our list of candidates is to check the `[patch]`
            // section of the manifest. Here we look through all patches
            // relevant to the source that `dep` points to, and then we match
            // name/version. Note that we don't use `dep.matches(..)` because
            // the patches, by definition, come from a different source.
            // This means that `dep.matches(..)` will always return false, when
            // what we really care about is the name/version match.
            let mut patches = Vec::<Summary>::new();
            if let Some(extra) = self.patches.get(dep.source_id().canonical_url()) {
                patches.extend(
                    extra
                        .iter()
                        .filter(|s| dep.matches_ignoring_source(s.package_id()))
                        .cloned(),
                );
            }

            // A crucial feature of the `[patch]` feature is that we *don't*
            // query the actual registry if we have a "locked" dependency. A
            // locked dep basically just means a version constraint of `=a.b.c`,
            // and because patches take priority over the actual source then if
            // we have a candidate we're done.
            if patches.len() == 1 && dep.is_locked() {
                let patch = patches.remove(0);
                match override_summary {
                    Some(summary) => (summary, 1, Some(patch)),
                    None => {
                        f(patch);
                        return Poll::Ready(Ok(()));
                    }
                }
            } else {
                if !patches.is_empty() {
                    debug!(
                        "found {} patches with an unlocked dep on `{}` at {} \
                         with `{}`, \
                         looking at sources",
                        patches.len(),
                        dep.package_name(),
                        dep.source_id(),
                        dep.version_req()
                    );
                }

                // Ensure the requested source_id is loaded
                self.ensure_loaded(dep.source_id(), Kind::Normal)
                    .with_context(|| {
                        format!(
                            "failed to load source for dependency `{}`",
                            dep.package_name()
                        )
                    })?;

                let source = self.sources.get_mut(dep.source_id());
                match (override_summary, source) {
                    (Some(_), None) => {
                        return Poll::Ready(Err(anyhow::anyhow!("override found but no real ones")))
                    }
                    (None, None) => return Poll::Ready(Ok(())),

                    // If we don't have an override then we just ship
                    // everything upstairs after locking the summary
                    (None, Some(source)) => {
                        for patch in patches.iter() {
                            f(patch.clone());
                        }

                        // Our sources shouldn't ever come back to us with two
                        // summaries that have the same version. We could,
                        // however, have an `[patch]` section which is in use
                        // to override a version in the registry. This means
                        // that if our `summary` in this loop has the same
                        // version as something in `patches` that we've
                        // already selected, then we skip this `summary`.
                        let locked = &self.locked;
                        let all_patches = &self.patches_available;
                        let callback = &mut |summary: Summary| {
                            for patch in patches.iter() {
                                let patch = patch.package_id().version();
                                if summary.package_id().version() == patch {
                                    return;
                                }
                            }
                            f(lock(locked, all_patches, summary))
                        };
                        return source.query(dep, kind, callback);
                    }

                    // If we have an override summary then we query the source
                    // to sanity check its results. We don't actually use any of
                    // the summaries it gives us though.
                    (Some(override_summary), Some(source)) => {
                        if !patches.is_empty() {
                            return Poll::Ready(Err(anyhow::anyhow!(
                                "found patches and a path override"
                            )));
                        }
                        let mut n = 0;
                        let mut to_warn = None;
                        {
                            let callback = &mut |summary| {
                                n += 1;
                                to_warn = Some(summary);
                            };
                            let pend = source.query(dep, kind, callback);
                            if pend.is_pending() {
                                return Poll::Pending;
                            }
                        }
                        (override_summary, n, to_warn)
                    }
                }
            }
        };

        if n > 1 {
            return Poll::Ready(Err(anyhow::anyhow!(
                "found an override with a non-locked list"
            )));
        } else if let Some(summary) = to_warn {
            self.warn_bad_override(&override_summary, &summary)?;
        }
        f(self.lock(override_summary));
        Poll::Ready(Ok(()))
    }

    fn describe_source(&self, id: SourceId) -> String {
        match self.sources.get(id) {
            Some(src) => src.describe(),
            None => id.to_string(),
        }
    }

    fn is_replaced(&self, id: SourceId) -> bool {
        match self.sources.get(id) {
            Some(src) => src.is_replaced(),
            None => false,
        }
    }

    fn block_until_ready(&mut self) -> CargoResult<()> {
        for (source_id, source) in self.sources.sources_mut() {
            source
                .block_until_ready()
                .with_context(|| format!("Unable to update {}", source_id))?;
        }
        Ok(())
    }
}

fn lock(
    locked: &LockedMap,
    patches: &HashMap<CanonicalUrl, Vec<PackageId>>,
    summary: Summary,
) -> Summary {
    let pair = locked
        .get(&(summary.source_id(), summary.name()))
        .and_then(|vec| vec.iter().find(|&&(id, _)| id == summary.package_id()));

    trace!("locking summary of {}", summary.package_id());

    // Lock the summary's ID if possible
    let summary = match pair {
        Some((precise, _)) => summary.override_id(*precise),
        None => summary,
    };
    summary.map_dependencies(|dep| {
        trace!(
            "\t{}/{}/{}",
            dep.package_name(),
            dep.version_req(),
            dep.source_id()
        );

        // If we've got a known set of overrides for this summary, then
        // one of a few cases can arise:
        //
        // 1. We have a lock entry for this dependency from the same
        //    source as it's listed as coming from. In this case we make
        //    sure to lock to precisely the given package ID.
        //
        // 2. We have a lock entry for this dependency, but it's from a
        //    different source than what's listed, or the version
        //    requirement has changed. In this case we must discard the
        //    locked version because the dependency needs to be
        //    re-resolved.
        //
        // 3. We have a lock entry for this dependency, but it's from a
        //    different source than what's listed. This lock though happens
        //    through `[patch]`, so we want to preserve it.
        //
        // 4. We don't have a lock entry for this dependency, in which
        //    case it was likely an optional dependency which wasn't
        //    included previously so we just pass it through anyway.
        //
        // Cases 1/2 are handled by `matches_id`, case 3 is handled specially,
        // and case 4 is handled by falling through to the logic below.
        if let Some((_, locked_deps)) = pair {
            let locked = locked_deps.iter().find(|&&id| {
                // If the dependency matches the package id exactly then we've
                // found a match, this is the id the dependency was previously
                // locked to.
                if dep.matches_id(id) {
                    return true;
                }

                // If the name/version doesn't match, then we definitely don't
                // have a match whatsoever. Otherwise we need to check
                // `[patch]`...
                if !dep.matches_ignoring_source(id) {
                    return false;
                }

                // ... so here we look up the dependency url in the patches
                // map, and we see if `id` is contained in the list of patches
                // for that url. If it is then this lock is still valid,
                // otherwise the lock is no longer valid.
                match patches.get(dep.source_id().canonical_url()) {
                    Some(list) => list.contains(&id),
                    None => false,
                }
            });

            if let Some(&locked) = locked {
                trace!("\tfirst hit on {}", locked);
                let mut dep = dep;

                // If we found a locked version where the sources match, then
                // we can `lock_to` to get an exact lock on this dependency.
                // Otherwise we got a lock via `[patch]` so we only lock the
                // version requirement, not the source.
                if locked.source_id() == dep.source_id() {
                    dep.lock_to(locked);
                } else {
                    dep.lock_version(locked.version());
                }
                return dep;
            }
        }

        // If this dependency did not have a locked version, then we query
        // all known locked packages to see if they match this dependency.
        // If anything does then we lock it to that and move on.
        let v = locked
            .get(&(dep.source_id(), dep.package_name()))
            .and_then(|vec| vec.iter().find(|&&(id, _)| dep.matches_id(id)));
        if let Some(&(id, _)) = v {
            trace!("\tsecond hit on {}", id);
            let mut dep = dep;
            dep.lock_to(id);
            return dep;
        }

        trace!("\tnope, unlocked");
        dep
    })
}

/// This is a helper for selecting the summary, or generating a helpful error message.
fn summary_for_patch(
    orig_patch: &Dependency,
    locked: &Option<LockedPatchDependency>,
    mut summaries: Vec<Summary>,
    source: &mut dyn Source,
) -> Poll<CargoResult<(Summary, Option<PackageId>)>> {
    if summaries.len() == 1 {
        return Poll::Ready(Ok((summaries.pop().unwrap(), None)));
    }
    if summaries.len() > 1 {
        // TODO: In the future, it might be nice to add all of these
        // candidates so that version selection would just pick the
        // appropriate one. However, as this is currently structured, if we
        // added these all as patches, the unselected versions would end up in
        // the "unused patch" listing, and trigger a warning. It might take a
        // fair bit of restructuring to make that work cleanly, and there
        // isn't any demand at this time to support that.
        let mut vers: Vec<_> = summaries.iter().map(|summary| summary.version()).collect();
        vers.sort();
        let versions: Vec<_> = vers.into_iter().map(|v| v.to_string()).collect();
        return Poll::Ready(Err(anyhow::anyhow!(
            "patch for `{}` in `{}` resolved to more than one candidate\n\
            Found versions: {}\n\
            Update the patch definition to select only one package.\n\
            For example, add an `=` version requirement to the patch definition, \
            such as `version = \"={}\"`.",
            orig_patch.package_name(),
            orig_patch.source_id(),
            versions.join(", "),
            versions.last().unwrap()
        )));
    }
    assert!(summaries.is_empty());
    // No summaries found, try to help the user figure out what is wrong.
    if let Some(locked) = locked {
        // Since the locked patch did not match anything, try the unlocked one.
        let orig_matches =
            ready!(source.query_vec(orig_patch, QueryKind::Exact)).unwrap_or_else(|e| {
                tracing::warn!(
                    "could not determine unlocked summaries for dep {:?}: {:?}",
                    orig_patch,
                    e
                );
                Vec::new()
            });

        let summary = ready!(summary_for_patch(orig_patch, &None, orig_matches, source))?;

        // The unlocked version found a match. This returns a value to
        // indicate that this entry should be unlocked.
        return Poll::Ready(Ok((summary.0, Some(locked.package_id))));
    }
    // Try checking if there are *any* packages that match this by name.
    let name_only_dep = Dependency::new_override(orig_patch.package_name(), orig_patch.source_id());

    let name_summaries =
        ready!(source.query_vec(&name_only_dep, QueryKind::Exact)).unwrap_or_else(|e| {
            tracing::warn!(
                "failed to do name-only summary query for {:?}: {:?}",
                name_only_dep,
                e
            );
            Vec::new()
        });
    let mut vers = name_summaries
        .iter()
        .map(|summary| summary.version())
        .collect::<Vec<_>>();
    let found = match vers.len() {
        0 => format!(""),
        1 => format!("version `{}`", vers[0]),
        _ => {
            vers.sort();
            let strs: Vec<_> = vers.into_iter().map(|v| v.to_string()).collect();
            format!("versions `{}`", strs.join(", "))
        }
    };
    Poll::Ready(Err(if found.is_empty() {
        anyhow::anyhow!(
            "The patch location `{}` does not appear to contain any packages \
            matching the name `{}`.",
            orig_patch.source_id(),
            orig_patch.package_name()
        )
    } else {
        anyhow::anyhow!(
            "The patch location `{}` contains a `{}` package with {}, but the patch \
            definition requires `{}`.\n\
            Check that the version in the patch location is what you expect, \
            and update the patch definition to match.",
            orig_patch.source_id(),
            orig_patch.package_name(),
            found,
            orig_patch.version_req()
        )
    }))
}