    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 Locked to `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.has_precise() => {
                    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.has_same_precise_as(namespace) {
                        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
            // `"locked"` as other values indicate a `cargo update
            // --precise` request
            if !source_id.has_locked_precise() {
                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()
            )
        }))
    }