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    //! High-level APIs for executing the resolver.
    //!
    //! This module provides functions for running the resolver given a workspace, including loading
    //! the `Cargo.lock` file and checkinf if it needs updating.
    //!
    //! There are roughly 3 main functions:
    //!
    //! - [`resolve_ws`]: A simple, high-level function with no options.
    //! - [`resolve_ws_with_opts`]: A medium-level function with options like
    //!   user-provided features. This is the most appropriate function to use in
    //!   most cases.
    //! - [`resolve_with_previous`]: A low-level function for running the resolver,
    //!   providing the most power and flexibility.
    //!
    //! ### Data Structures
    //!
    //! - [`Workspace`]:
    //!   Usually created by [`crate::util::command_prelude::ArgMatchesExt::workspace`] which discovers the root of the
    //!   workspace, and loads all the workspace members as a [`Package`] object
    //!   - [`Package`]
    //!     Corresponds with `Cargo.toml` manifest (deserialized as [`Manifest`]) and its associated files.
    //!     - [`Target`]s are crates such as the library, binaries, integration test, or examples.
    //!       They are what is actually compiled by `rustc`.
    //!       Each `Target` defines a crate root, like `src/lib.rs` or `examples/foo.rs`.
    //!     - [`PackageId`] --- A unique identifier for a package.
    //! - [`PackageRegistry`]:
    //!   The primary interface for how the dependency
    //!   resolver finds packages. It contains the `SourceMap`, and handles things
    //!   like the `[patch]` table. The dependency resolver
    //!   sends a query to the `PackageRegistry` to "get me all packages that match
    //!   this dependency declaration". The `Registry` trait provides a generic interface
    //!   to the `PackageRegistry`, but this is only used for providing an alternate
    //!   implementation of the `PackageRegistry` for testing.
    //! - [`SourceMap`]: Map of all available sources.
    //!   - [`Source`]: An abstraction for something that can fetch packages (a remote
    //!     registry, a git repo, the local filesystem, etc.). Check out the [source
    //!     implementations] for all the details about registries, indexes, git
    //!     dependencies, etc.
    //!       * [`SourceId`]: A unique identifier for a source.
    //!   - [`Summary`]: A of a [`Manifest`], and is essentially
    //!     the information that can be found in a registry index. Queries against the
    //!     `PackageRegistry` yields a `Summary`. The resolver uses the summary
    //!     information to build the dependency graph.
    //! - [`PackageSet`] --- Contains all of the `Package` objects. This works with the
    //!   [`Downloads`] struct to coordinate downloading packages. It has a reference
    //!   to the `SourceMap` to get the `Source` objects which tell the `Downloads`
    //!   struct which URLs to fetch.
    //!
    //! [`Package`]: crate::core::package
    //! [`Target`]: crate::core::Target
    //! [`Manifest`]: crate::core::Manifest
    //! [`Source`]: crate::sources::source::Source
    //! [`SourceMap`]: crate::sources::source::SourceMap
    //! [`PackageRegistry`]: crate::core::registry::PackageRegistry
    //! [source implementations]: crate::sources
    //! [`Downloads`]: crate::core::package::Downloads

    use crate::core::compiler::{CompileKind, RustcTargetData};
    use crate::core::registry::{LockedPatchDependency, PackageRegistry};
    use crate::core::resolver::features::{
        CliFeatures, FeatureOpts, FeatureResolver, ForceAllTargets, RequestedFeatures, ResolvedFeatures,
    };
    use crate::core::resolver::{
        self, HasDevUnits, Resolve, ResolveOpts, ResolveVersion, VersionOrdering, VersionPreferences,
    };
    use crate::core::summary::Summary;
    use crate::core::{
        GitReference, PackageId, PackageIdSpec, PackageIdSpecQuery, PackageSet, SourceId, Workspace,
    };
    use crate::ops;
    use crate::sources::PathSource;
    use crate::util::cache_lock::CacheLockMode;
    use crate::util::errors::CargoResult;
    use crate::util::{profile, CanonicalUrl};
    use anyhow::Context as _;
    use cargo_util_schemas::manifest::RustVersion;
    use std::collections::{HashMap, HashSet};
    use tracing::{debug, trace};

    /// Result for `resolve_ws_with_opts`.
    pub struct WorkspaceResolve<'cfg> {
        /// Packages to be downloaded.
        pub pkg_set: PackageSet<'cfg>,
        /// The resolve for the entire workspace.
        ///
        /// This may be `None` for things like `cargo install` and `-Zavoid-dev-deps`.
        /// This does not include `paths` overrides.
        pub workspace_resolve: Option<Resolve>,
        /// The narrowed resolve, with the specific features enabled, and only the
        /// given package specs requested.
        pub targeted_resolve: Resolve,
        /// The features activated per package.
        pub resolved_features: ResolvedFeatures,
    }

    const UNUSED_PATCH_WARNING: &str = "\
    Check that the patched package version and available features are compatible
    with the dependency requirements. If the patch has a different version from
    what is locked in the Cargo.lock file, run `cargo update` to use the new
    version. This may also occur with an optional dependency that is not enabled.";

    /// Resolves all dependencies for the workspace using the previous
    /// lock file as a guide if present.
    ///
    /// This function will also write the result of resolution as a new lock file
    /// (unless it is an ephemeral workspace such as `cargo install` or `cargo
    /// package`).
    ///
    /// This is a simple interface used by commands like `clean`, `fetch`, and
    /// `package`, which don't specify any options or features.
    pub fn resolve_ws<'a>(ws: &Workspace<'a>) -> CargoResult<(PackageSet<'a>, Resolve)> {
        let max_rust_version = ws.rust_version();

        let mut registry = PackageRegistry::new(ws.config())?;
        let resolve = resolve_with_registry(ws, &mut registry, max_rust_version)?;
        let packages = get_resolved_packages(&resolve, registry)?;
        Ok((packages, resolve))
    }

    /// Resolves dependencies for some packages of the workspace,
    /// taking into account `paths` overrides and activated features.
    ///
    /// This function will also write the result of resolution as a new lock file
    /// (unless `Workspace::require_optional_deps` is false, such as `cargo
    /// install` or `-Z avoid-dev-deps`), or it is an ephemeral workspace (`cargo
    /// install` or `cargo package`).
    ///
    /// `specs` may be empty, which indicates it should resolve all workspace
    /// members. In this case, `opts.all_features` must be `true`.
    pub fn resolve_ws_with_opts<'cfg>(
        ws: &Workspace<'cfg>,
        target_data: &mut RustcTargetData<'cfg>,
        requested_targets: &[CompileKind],
        cli_features: &CliFeatures,
        specs: &[PackageIdSpec],
        has_dev_units: HasDevUnits,
        force_all_targets: ForceAllTargets,
        max_rust_version: Option<&RustVersion>,
    ) -> CargoResult<WorkspaceResolve<'cfg>> {
        let mut registry = PackageRegistry::new(ws.config())?;
        let mut add_patches = true;
        let resolve = if ws.ignore_lock() {
            None
        } else if ws.require_optional_deps() {
            // First, resolve the root_package's *listed* dependencies, as well as
            // downloading and updating all remotes and such.
            let resolve = resolve_with_registry(ws, &mut registry, max_rust_version)?;
            // No need to add patches again, `resolve_with_registry` has done it.
            add_patches = false;

            // Second, resolve with precisely what we're doing. Filter out
            // transitive dependencies if necessary, specify features, handle
            // overrides, etc.
            let _p = profile::start("resolving with overrides...");

            add_overrides(&mut registry, ws)?;

            for (replace_spec, dep) in ws.root_replace() {
                if !resolve
                    .iter()
                    .any(|r| replace_spec.matches(r) && !dep.matches_id(r))
                {
                    ws.config()
                        .shell()
                        .warn(format!("package replacement is not used: {}", replace_spec))?
                }

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

            Some(resolve)
        } else {
            ops::load_pkg_lockfile(ws)?
        };

        let resolved_with_overrides = resolve_with_previous(
            &mut registry,
            ws,
            cli_features,
            has_dev_units,
            resolve.as_ref(),
            None,
            specs,
            add_patches,
            max_rust_version,
        )?;

        let pkg_set = get_resolved_packages(&resolved_with_overrides, registry)?;

        let member_ids = ws
            .members_with_features(specs, cli_features)?
            .into_iter()
            .map(|(p, _fts)| p.package_id())
            .collect::<Vec<_>>();
        pkg_set.download_accessible(
            &resolved_with_overrides,
            &member_ids,
            has_dev_units,
            requested_targets,
            target_data,
            force_all_targets,
        )?;

        let feature_opts = FeatureOpts::new(ws, has_dev_units, force_all_targets)?;
        let resolved_features = FeatureResolver::resolve(
            ws,
            target_data,
            &resolved_with_overrides,
            &pkg_set,
            cli_features,
            specs,
            requested_targets,
            feature_opts,
        )?;

        pkg_set.warn_no_lib_packages_and_artifact_libs_overlapping_deps(
            ws,
            &resolved_with_overrides,
            &member_ids,
            has_dev_units,
            requested_targets,
            target_data,
            force_all_targets,
        )?;

        Ok(WorkspaceResolve {
            pkg_set,
            workspace_resolve: resolve,
            targeted_resolve: resolved_with_overrides,
            resolved_features,
        })
    }

    fn resolve_with_registry<'cfg>(
        ws: &Workspace<'cfg>,
        registry: &mut PackageRegistry<'cfg>,
        max_rust_version: Option<&RustVersion>,
    ) -> CargoResult<Resolve> {
        let prev = ops::load_pkg_lockfile(ws)?;
        let mut resolve = resolve_with_previous(
            registry,
            ws,
            &CliFeatures::new_all(true),
            HasDevUnits::Yes,
            prev.as_ref(),
            None,
            &[],
            true,
            max_rust_version,
        )?;

        if !ws.is_ephemeral() && ws.require_optional_deps() {
            ops::write_pkg_lockfile(ws, &mut resolve)?;
        }
        Ok(resolve)
    }

    /// Resolves all dependencies for a package using an optional previous instance
    /// of resolve to guide the resolution process.
    ///
    /// This also takes an optional hash set, `to_avoid`, which is a list of package
    /// IDs that should be avoided when consulting the previous instance of resolve
    /// (often used in pairings with updates).
    ///
    /// The previous resolve normally comes from a lock file. This function does not
    /// read or write lock files from the filesystem.
    ///
    /// `specs` may be empty, which indicates it should resolve all workspace
    /// members. In this case, `opts.all_features` must be `true`.
    ///
    /// If `register_patches` is true, then entries from the `[patch]` table in
    /// the manifest will be added to the given `PackageRegistry`.
    pub fn resolve_with_previous<'cfg>(
        registry: &mut PackageRegistry<'cfg>,
        ws: &Workspace<'cfg>,
        cli_features: &CliFeatures,
        has_dev_units: HasDevUnits,
        previous: Option<&Resolve>,
        to_avoid: Option<&HashSet<PackageId>>,
        specs: &[PackageIdSpec],
        register_patches: bool,
        max_rust_version: Option<&RustVersion>,
    ) -> CargoResult<Resolve> {
        // We only want one Cargo at a time resolving a crate graph since this can
        // involve a lot of frobbing of the global caches.
        let _lock = ws
            .config()
            .acquire_package_cache_lock(CacheLockMode::DownloadExclusive)?;

        // Here we place an artificial limitation that all non-registry sources
        // cannot be locked at more than one revision. This means that if a Git
        // repository provides more than one package, they must all be updated in
        // step when any of them are updated.
        //
        // TODO: this seems like a hokey reason to single out the registry as being
        // different.
        let to_avoid_sources: HashSet<SourceId> = to_avoid
            .map(|set| {
                set.iter()
                    .map(|p| p.source_id())
                    .filter(|s| !s.is_registry())
                    .collect()
            })
            .unwrap_or_default();

        let pre_patch_keep = |p: &PackageId| {
            !to_avoid_sources.contains(&p.source_id())
                && match to_avoid {
                    Some(set) => !set.contains(p),
                    None => true,
                }
        };

        // While registering patches, we will record preferences for particular versions
        // of various packages.
        let mut version_prefs = VersionPreferences::default();
        if ws.config().cli_unstable().minimal_versions {
            version_prefs.version_ordering(VersionOrdering::MinimumVersionsFirst)
        }
        if ws.config().cli_unstable().msrv_policy {
            version_prefs.max_rust_version(max_rust_version.cloned());
        }

        // This is a set of PackageIds of `[patch]` entries, and some related locked PackageIds, for
        // which locking should be avoided (but which will be preferred when searching dependencies,
        // via prefer_patch_deps below)
        let mut avoid_patch_ids = HashSet::new();

        if register_patches {
            for (url, patches) in ws.root_patch()?.iter() {
                for patch in patches {
                    version_prefs.prefer_dependency(patch.clone());
                }
                let Some(previous) = previous else {
                    let patches: Vec<_> = patches.iter().map(|p| (p, None)).collect();
                    let unlock_ids = registry.patch(url, &patches)?;
                    // Since nothing is locked, this shouldn't possibly return anything.
                    assert!(unlock_ids.is_empty());
                    continue;
                };

                // This is a list of pairs where the first element of the pair is
                // the raw `Dependency` which matches what's listed in `Cargo.toml`.
                // The second element is, if present, the "locked" version of
                // the `Dependency` as well as the `PackageId` that it previously
                // resolved to. This second element is calculated by looking at the
                // previous resolve graph, which is primarily what's done here to
                // build the `registrations` list.
                let mut registrations = Vec::new();
                for dep in patches {
                    let candidates = || {
                        previous
                            .iter()
                            .chain(previous.unused_patches().iter().cloned())
                            .filter(&pre_patch_keep)
                    };

                    let lock = match candidates().find(|id| dep.matches_id(*id)) {
                        // If we found an exactly matching candidate in our list of
                        // candidates, then that's the one to use.
                        Some(package_id) => {
                            let mut locked_dep = dep.clone();
                            locked_dep.lock_to(package_id);
                            Some(LockedPatchDependency {
                                dependency: locked_dep,
                                package_id,
                                alt_package_id: None,
                            })
                        }
                        None => {
                            // If the candidate does not have a matching source id
                            // then we may still have a lock candidate. If we're
                            // loading a v2-encoded resolve graph and `dep` is a
                            // git dep with `branch = 'master'`, then this should
                            // also match candidates without `branch = 'master'`
                            // (which is now treated separately in Cargo).
                            //
                            // In this scenario we try to convert candidates located
                            // in the resolve graph to explicitly having the
                            // `master` branch (if they otherwise point to
                            // `DefaultBranch`). If this works and our `dep`
                            // matches that then this is something we'll lock to.
                            match candidates().find(|&id| {
                                match master_branch_git_source(id, previous) {
                                    Some(id) => dep.matches_id(id),
                                    None => false,
                                }
                            }) {
                                Some(id_using_default) => {
                                    let id_using_master = id_using_default.with_source_id(
                                        dep.source_id()
                                            .with_precise_from(id_using_default.source_id()),
                                    );

                                    let mut locked_dep = dep.clone();
                                    locked_dep.lock_to(id_using_master);
                                    Some(LockedPatchDependency {
                                        dependency: locked_dep,
                                        package_id: id_using_master,
                                        // Note that this is where the magic
                                        // happens, where the resolve graph
                                        // probably has locks pointing to
                                        // DefaultBranch sources, and by including
                                        // this here those will get transparently
                                        // rewritten to Branch("master") which we
                                        // have a lock entry for.
                                        alt_package_id: Some(id_using_default),
                                    })
                                }

                                // No locked candidate was found
                                None => None,
                            }
                        }
                    };

                    registrations.push((dep, lock));
                }

                let canonical = CanonicalUrl::new(url)?;
                for (orig_patch, unlock_id) in registry.patch(url, &registrations)? {
                    // Avoid the locked patch ID.
                    avoid_patch_ids.insert(unlock_id);
                    // Also avoid the thing it is patching.
                    avoid_patch_ids.extend(previous.iter().filter(|id| {
                        orig_patch.matches_ignoring_source(*id)
                            && *id.source_id().canonical_url() == canonical
                    }));
                }
            }
        }
        debug!("avoid_patch_ids={:?}", avoid_patch_ids);

        let keep = |p: &PackageId| pre_patch_keep(p) && !avoid_patch_ids.contains(p);

        let dev_deps = ws.require_optional_deps() || has_dev_units == HasDevUnits::Yes;

        if let Some(r) = previous {
            trace!("previous: {:?}", r);

            // In the case where a previous instance of resolve is available, we
            // want to lock as many packages as possible to the previous version
            // without disturbing the graph structure.
            register_previous_locks(ws, registry, r, &keep, dev_deps);

            // Prefer to use anything in the previous lock file, aka we want to have conservative updates.
            for id in r.iter().filter(keep) {
                debug!("attempting to prefer {}", id);
                version_prefs.prefer_package_id(id);
            }
        }

        if register_patches {
            registry.lock_patches();
        }

        // Some packages are already loaded when setting up a workspace. This
        // makes it so anything that was already loaded will not be loaded again.
        // Without this there were cases where members would be parsed multiple times
        ws.preload(registry);

        // In case any members were not already loaded or the Workspace is_ephemeral.
        for member in ws.members() {
            registry.add_sources(Some(member.package_id().source_id()))?;
        }

        let summaries: Vec<(Summary, ResolveOpts)> = ws
            .members_with_features(specs, cli_features)?
            .into_iter()
            .map(|(member, features)| {
                let summary = registry.lock(member.summary().clone());
                (
                    summary,
                    ResolveOpts {
                        dev_deps,
                        features: RequestedFeatures::CliFeatures(features),
                    },
                )
            })
            .collect();

        let root_replace = ws.root_replace();

        let replace = match previous {
            Some(r) => root_replace
                .iter()
                .map(|(spec, dep)| {
                    for (&key, &val) in r.replacements().iter() {
                        if spec.matches(key) && dep.matches_id(val) && keep(&val) {
                            let mut dep = dep.clone();
                            dep.lock_to(val);
                            return (spec.clone(), dep);
                        }
                    }
                    (spec.clone(), dep.clone())
                })
                .collect::<Vec<_>>(),
            None => root_replace.to_vec(),
        };

        ws.preload(registry);
        let mut resolved = resolver::resolve(
            &summaries,
            &replace,
            registry,
            &version_prefs,
            Some(ws.config()),
        )?;
        let patches: Vec<_> = registry
            .patches()
            .values()
            .flat_map(|v| v.iter().cloned())
            .collect();
        resolved.register_used_patches(&patches[..]);

        if register_patches && !resolved.unused_patches().is_empty() {
            emit_warnings_of_unused_patches(ws, &resolved, registry)?;
        }

        if let Some(previous) = previous {
            resolved.merge_from(previous)?;
        }
        let config = ws.config();
        let mut deferred = config.deferred_global_last_use()?;
        deferred.save_no_error(config);
        Ok(resolved)
    }

    /// Read the `paths` configuration variable to discover all path overrides that
    /// have been configured.
    pub fn add_overrides<'a>(
        registry: &mut PackageRegistry<'a>,
        ws: &Workspace<'a>,
    ) -> CargoResult<()> {
        let config = ws.config();
        let Some(paths) = config.get_list("paths")? else {
            return Ok(());
        };

        let paths = paths.val.iter().map(|(s, def)| {
            // The path listed next to the string is the config file in which the
            // key was located, so we want to pop off the `.cargo/config` component
            // to get the directory containing the `.cargo` folder.
            (def.root(config).join(s), def)
        });

        for (path, definition) in paths {
            let id = SourceId::for_path(&path)?;
            let mut source = PathSource::new_recursive(&path, id, ws.config());
            source.update().with_context(|| {
                format!(
                    "failed to update path override `{}` \
                     (defined in `{}`)",
                    path.display(),
                    definition
                )
            })?;
            registry.add_override(Box::new(source));
        }
        Ok(())
    }

    pub fn get_resolved_packages<'cfg>(
        resolve: &Resolve,
        registry: PackageRegistry<'cfg>,
    ) -> CargoResult<PackageSet<'cfg>> {
        let ids: Vec<PackageId> = resolve.iter().collect();
        registry.get(&ids)
    }

    /// In this function we're responsible for informing the `registry` of all
    /// locked dependencies from the previous lock file we had, `resolve`.
    ///
    /// This gets particularly tricky for a couple of reasons. The first is that we
    /// want all updates to be conservative, so we actually want to take the
    /// `resolve` into account (and avoid unnecessary registry updates and such).
    /// the second, however, is that we want to be resilient to updates of
    /// manifests. For example if a dependency is added or a version is changed we
    /// want to make sure that we properly re-resolve (conservatively) instead of
    /// providing an opaque error.
    ///
    /// The logic here is somewhat subtle, but there should be more comments below to
    /// clarify things.
    ///
    /// Note that this function, at the time of this writing, is basically the
    /// entire fix for issue #4127.
    fn register_previous_locks(
        ws: &Workspace<'_>,
        registry: &mut PackageRegistry<'_>,
        resolve: &Resolve,
        keep: &dyn Fn(&PackageId) -> bool,
        dev_deps: bool,
    ) {
        let path_pkg = |id: SourceId| {
            if !id.is_path() {
                return None;
            }
            if let Ok(path) = id.url().to_file_path() {
                if let Ok(pkg) = ws.load(&path.join("Cargo.toml")) {
                    return Some(pkg);
                }
            }
            None
        };

        // Ok so we've been passed in a `keep` function which basically says "if I
        // return `true` then this package wasn't listed for an update on the command
        // line". That is, if we run `cargo update foo` then `keep(bar)` will return
        // `true`, whereas `keep(foo)` will return `false` (roughly speaking).
        //
        // This isn't actually quite what we want, however. Instead we want to
        // further refine this `keep` function with *all transitive dependencies* of
        // the packages we're not keeping. For example, consider a case like this:
        //
        // * There's a crate `log`.
        // * There's a crate `serde` which depends on `log`.
        //
        // Let's say we then run `cargo update serde`. This may *also* want to
        // update the `log` dependency as our newer version of `serde` may have a
        // new minimum version required for `log`. Now this isn't always guaranteed
        // to work. What'll happen here is we *won't* lock the `log` dependency nor
        // the `log` crate itself, but we will inform the registry "please prefer
        // this version of `log`". That way if our newer version of serde works with
        // the older version of `log`, we conservatively won't update `log`. If,
        // however, nothing else in the dependency graph depends on `log` and the
        // newer version of `serde` requires a new version of `log` it'll get pulled
        // in (as we didn't accidentally lock it to an old version).
        let mut avoid_locking = HashSet::new();
        registry.add_to_yanked_whitelist(resolve.iter().filter(keep));
        for node in resolve.iter() {
            if !keep(&node) {
                add_deps(resolve, node, &mut avoid_locking);
            }
        }

        // Ok, but the above loop isn't the entire story! Updates to the dependency
        // graph can come from two locations, the `cargo update` command or
        // manifests themselves. For example a manifest on the filesystem may
        // have been updated to have an updated version requirement on `serde`. In
        // this case both `keep(serde)` and `keep(log)` return `true` (the `keep`
        // that's an argument to this function). We, however, don't want to keep
        // either of those! Otherwise we'll get obscure resolve errors about locked
        // versions.
        //
        // To solve this problem we iterate over all packages with path sources
        // (aka ones with manifests that are changing) and take a look at all of
        // their dependencies. If any dependency does not match something in the
        // previous lock file, then we're guaranteed that the main resolver will
        // update the source of this dependency no matter what. Knowing this we
        // poison all packages from the same source, forcing them all to get
        // updated.
        //
        // This may seem like a heavy hammer, and it is! It means that if you change
        // anything from crates.io then all of crates.io becomes unlocked. Note,
        // however, that we still want conservative updates. This currently happens
        // because the first candidate the resolver picks is the previously locked
        // version, and only if that fails to activate to we move on and try
        // a different version. (giving the guise of conservative updates)
        //
        // For example let's say we had `serde = "0.1"` written in our lock file.
        // When we later edit this to `serde = "0.1.3"` we don't want to lock serde
        // at its old version, 0.1.1. Instead we want to allow it to update to
        // `0.1.3` and update its own dependencies (like above). To do this *all
        // crates from crates.io* are not locked (aka added to `avoid_locking`).
        // For dependencies like `log` their previous version in the lock file will
        // come up first before newer version, if newer version are available.
        let mut path_deps = ws.members().cloned().collect::<Vec<_>>();
        let mut visited = HashSet::new();
        while let Some(member) = path_deps.pop() {
            if !visited.insert(member.package_id()) {
                continue;
            }
            let is_ws_member = ws.is_member(&member);
            for dep in member.dependencies() {
                // If this dependency didn't match anything special then we may want
                // to poison the source as it may have been added. If this path
                // dependencies is **not** a workspace member, however, and it's an
                // optional/non-transitive dependency then it won't be necessarily
                // be in our lock file. If this shows up then we avoid poisoning
                // this source as otherwise we'd repeatedly update the registry.
                //
                // TODO: this breaks adding an optional dependency in a
                // non-workspace member and then simultaneously editing the
                // dependency on that crate to enable the feature. For now,
                // this bug is better than the always-updating registry though.
                if !is_ws_member && (dep.is_optional() || !dep.is_transitive()) {
                    continue;
                }

                // If dev-dependencies aren't being resolved, skip them.
                if !dep.is_transitive() && !dev_deps {
                    continue;
                }

                // If this is a path dependency, then try to push it onto our
                // worklist.
                if let Some(pkg) = path_pkg(dep.source_id()) {
                    path_deps.push(pkg);
                    continue;
                }

                // If we match *anything* in the dependency graph then we consider
                // ourselves all ok, and assume that we'll resolve to that.
                if resolve.iter().any(|id| dep.matches_ignoring_source(id)) {
                    continue;
                }

                // Ok if nothing matches, then we poison the source of these
                // dependencies and the previous lock file.
                debug!(
                    "poisoning {} because {} looks like it changed {}",
                    dep.source_id(),
                    member.package_id(),
                    dep.package_name()
                );
                for id in resolve
                    .iter()
                    .filter(|id| id.source_id() == dep.source_id())
                {
                    add_deps(resolve, id, &mut avoid_locking);
                }
            }
        }

        // Additionally, here we process all path dependencies listed in the previous
        // resolve. They can not only have their dependencies change but also
        // the versions of the package change as well. If this ends up happening
        // then we want to make sure we don't lock a package ID node that doesn't
        // actually exist. Note that we don't do transitive visits of all the
        // package's dependencies here as that'll be covered below to poison those
        // if they changed.
        //
        // This must come after all other `add_deps` calls to ensure it recursively walks the tree when
        // called.
        for node in resolve.iter() {
            if let Some(pkg) = path_pkg(node.source_id()) {
                if pkg.package_id() != node {
                    avoid_locking.insert(node);
                }
            }
        }

        // Alright now that we've got our new, fresh, shiny, and refined `keep`
        // function let's put it to action. Take a look at the previous lock file,
        // filter everything by this callback, and then shove everything else into
        // the registry as a locked dependency.
        let keep = |id: &PackageId| keep(id) && !avoid_locking.contains(id);

        registry.clear_lock();
        for node in resolve.iter().filter(keep) {
            let deps = resolve
                .deps_not_replaced(node)
                .map(|p| p.0)
                .filter(keep)
                .collect::<Vec<_>>();

            // In the v2 lockfile format and prior the `branch=master` dependency
            // directive was serialized the same way as the no-branch-listed
            // directive. Nowadays in Cargo, however, these two directives are
            // considered distinct and are no longer represented the same way. To
            // maintain compatibility with older lock files we register locked nodes
            // for *both* the master branch and the default branch.
            //
            // Note that this is only applicable for loading older resolves now at
            // this point. All new lock files are encoded as v3-or-later, so this is
            // just compat for loading an old lock file successfully.
            if let Some(node) = master_branch_git_source(node, resolve) {
                registry.register_lock(node, deps.clone());
            }

            registry.register_lock(node, deps);
        }

        /// Recursively add `node` and all its transitive dependencies to `set`.
        fn add_deps(resolve: &Resolve, node: PackageId, set: &mut HashSet<PackageId>) {
            if !set.insert(node) {
                return;
            }
            debug!("ignoring any lock pointing directly at {}", node);
            for (dep, _) in resolve.deps_not_replaced(node) {
                add_deps(resolve, dep, set);
            }
        }
    }

    fn master_branch_git_source(id: PackageId, resolve: &Resolve) -> Option<PackageId> {
        if resolve.version() <= ResolveVersion::V2 {
            let source = id.source_id();
            if let Some(GitReference::DefaultBranch) = source.git_reference() {
                let new_source =
                    SourceId::for_git(source.url(), GitReference::Branch("master".to_string()))
                        .unwrap()
                        .with_precise_from(source);
                return Some(id.with_source_id(new_source));
            }
        }
        None
    }

    /// Emits warnings of unused patches case by case.
    ///
    /// This function does its best to provide more targeted and helpful
    /// (such as showing close candidates that failed to match). However, that's
    /// not terribly easy to do, so just show a general help message if we cannot.
    fn emit_warnings_of_unused_patches(
        ws: &Workspace<'_>,
        resolve: &Resolve,
        registry: &PackageRegistry<'_>,
    ) -> CargoResult<()> {
        const MESSAGE: &str = "was not used in the crate graph.";

        // Patch package with the source URLs being patch
        let mut patch_pkgid_to_urls = HashMap::new();
        for (url, summaries) in registry.patches().iter() {
            for summary in summaries.iter() {
                patch_pkgid_to_urls
                    .entry(summary.package_id())
                    .or_insert_with(HashSet::new)
                    .insert(url);
            }
        }

        // pkg name -> all source IDs of under the same pkg name
        let mut source_ids_grouped_by_pkg_name = HashMap::new();
        for pkgid in resolve.iter() {
            source_ids_grouped_by_pkg_name
                .entry(pkgid.name())
                .or_insert_with(HashSet::new)
                .insert(pkgid.source_id());
        }

        let mut unemitted_unused_patches = Vec::new();
        for unused in resolve.unused_patches().iter() {
            // Show alternative source URLs if the source URLs being patch
            // cannot not be found in the crate graph.
            match (
                source_ids_grouped_by_pkg_name.get(&unused.name()),
                patch_pkgid_to_urls.get(unused),
            ) {
                (Some(ids), Some(patched_urls))
                    if ids
                        .iter()
                        .all(|id| !patched_urls.contains(id.canonical_url())) =>
                {
                    use std::fmt::Write;
                    let mut msg = String::new();
                    writeln!(msg, "Patch `{}` {}", unused, MESSAGE)?;
                    write!(
                        msg,
                        "Perhaps you misspelled the source URL being patched.\n\
                        Possible URLs for `[patch.<URL>]`:",
                    )?;
                    for id in ids.iter() {
                        write!(msg, "\n    {}", id.display_registry_name())?;
                    }
                    ws.config().shell().warn(msg)?;
                }
                _ => unemitted_unused_patches.push(unused),
            }
        }

        // Show general help message.
        if !unemitted_unused_patches.is_empty() {
            let warnings: Vec<_> = unemitted_unused_patches
                .iter()
                .map(|pkgid| format!("Patch `{}` {}", pkgid, MESSAGE))
                .collect();
            ws.config()
                .shell()
                .warn(format!("{}\n{}", warnings.join("\n"), UNUSED_PATCH_WARNING))?;
        }

        return Ok(());
    }