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    //! Code for building the graph used by `cargo tree`.

    use super::TreeOptions;
    use crate::core::compiler::{CompileKind, RustcTargetData};
    use crate::core::dependency::DepKind;
    use crate::core::resolver::features::{CliFeatures, FeaturesFor, ResolvedFeatures};
    use crate::core::resolver::Resolve;
    use crate::core::{FeatureMap, FeatureValue, Package, PackageId, PackageIdSpec, Workspace};
    use crate::util::interning::{InternedString, INTERNED_DEFAULT};
    use crate::util::CargoResult;
    use std::collections::{HashMap, HashSet};

    #[derive(Debug, Clone, Eq, PartialEq, Hash, Ord, PartialOrd)]
    pub enum Node {
        Package {
            package_id: PackageId,
            /// Features that are enabled on this package.
            features: Vec<InternedString>,
            kind: CompileKind,
        },
        Feature {
            /// Index of the package node this feature is for.
            node_index: usize,
            /// Name of the feature.
            name: InternedString,
        },
    }

    /// The kind of edge, for separating dependencies into different sections.
    #[derive(Debug, Copy, Hash, Eq, Clone, PartialEq)]
    pub enum EdgeKind {
        Dep(DepKind),
        Feature,
    }

    /// Set of outgoing edges for a single node.
    ///
    /// Edges are separated by the edge kind (`DepKind` or `Feature`). This is
    /// primarily done so that the output can easily display separate sections
    /// like `[build-dependencies]`.
    ///
    /// The value is a `Vec` because each edge kind can have multiple outgoing
    /// edges. For example, package "foo" can have multiple normal dependencies.
    #[derive(Clone)]
    struct Edges(HashMap<EdgeKind, Vec<usize>>);

    impl Edges {
        fn new() -> Edges {
            Edges(HashMap::new())
        }

        /// Adds an edge pointing to the given node.
        fn add_edge(&mut self, kind: EdgeKind, index: usize) {
            let indexes = self.0.entry(kind).or_default();
            if !indexes.contains(&index) {
                indexes.push(index)
            }
        }
    }

    /// A graph of dependencies.
    pub struct Graph<'a> {
        nodes: Vec<Node>,
        /// The indexes of `edges` correspond to the `nodes`. That is, `edges[0]`
        /// is the set of outgoing edges for `nodes[0]`. They should always be in
        /// sync.
        edges: Vec<Edges>,
        /// Index maps a node to an index, for fast lookup.
        index: HashMap<Node, usize>,
        /// Map for looking up packages.
        package_map: HashMap<PackageId, &'a Package>,
        /// Set of indexes of feature nodes that were added via the command-line.
        ///
        /// For example `--features foo` will mark the "foo" node here.
        cli_features: HashSet<usize>,
        /// Map of dependency names, used for building internal feature map for
        /// dep_name/feat_name syntax.
        ///
        /// Key is the index of a package node, value is a map of dep_name to a
        /// set of `(pkg_node_index, is_optional)`.
        dep_name_map: HashMap<usize, HashMap<InternedString, HashSet<(usize, bool)>>>,
    }

    impl<'a> Graph<'a> {
        fn new(package_map: HashMap<PackageId, &'a Package>) -> Graph<'a> {
            Graph {
                nodes: Vec::new(),
                edges: Vec::new(),
                index: HashMap::new(),
                package_map,
                cli_features: HashSet::new(),
                dep_name_map: HashMap::new(),
            }
        }

        /// Adds a new node to the graph, returning its new index.
        fn add_node(&mut self, node: Node) -> usize {
            let from_index = self.nodes.len();
            self.nodes.push(node);
            self.edges.push(Edges::new());
            self.index
                .insert(self.nodes[from_index].clone(), from_index);
            from_index
        }

        /// Returns a list of nodes the given node index points to for the given kind.
        pub fn connected_nodes(&self, from: usize, kind: &EdgeKind) -> Vec<usize> {
            match self.edges[from].0.get(kind) {
                Some(indexes) => {
                    // Created a sorted list for consistent output.
                    let mut indexes = indexes.clone();
                    indexes.sort_unstable_by(|a, b| self.nodes[*a].cmp(&self.nodes[*b]));
                    indexes
                }
                None => Vec::new(),
            }
        }

        /// Returns `true` if the given node has any outgoing edges.
        pub fn has_outgoing_edges(&self, index: usize) -> bool {
            !self.edges[index].0.is_empty()
        }

        /// Gets a node by index.
        pub fn node(&self, index: usize) -> &Node {
            &self.nodes[index]
        }

        /// Given a slice of PackageIds, returns the indexes of all nodes that match.
        pub fn indexes_from_ids(&self, package_ids: &[PackageId]) -> Vec<usize> {
            let mut result: Vec<(&Node, usize)> = self
                .nodes
                .iter()
                .enumerate()
                .filter(|(_i, node)| match node {
                    Node::Package { package_id, .. } => package_ids.contains(package_id),
                    _ => false,
                })
                .map(|(i, node)| (node, i))
                .collect();
            // Sort for consistent output (the same command should always return
            // the same output). "unstable" since nodes should always be unique.
            result.sort_unstable();
            result.into_iter().map(|(_node, i)| i).collect()
        }

        pub fn package_for_id(&self, id: PackageId) -> &Package {
            self.package_map[&id]
        }

        fn package_id_for_index(&self, index: usize) -> PackageId {
            match self.nodes[index] {
                Node::Package { package_id, .. } => package_id,
                Node::Feature { .. } => panic!("unexpected feature node"),
            }
        }

        /// Returns `true` if the given feature node index is a feature enabled
        /// via the command-line.
        pub fn is_cli_feature(&self, index: usize) -> bool {
            self.cli_features.contains(&index)
        }

        /// Returns a new graph by removing all nodes not reachable from the
        /// given nodes.
        pub fn from_reachable(&self, roots: &[usize]) -> Graph<'a> {
            // Graph built with features does not (yet) support --duplicates.
            assert!(self.dep_name_map.is_empty());
            let mut new_graph = Graph::new(self.package_map.clone());
            // Maps old index to new index. None if not yet visited.
            let mut remap: Vec<Option<usize>> = vec![None; self.nodes.len()];

            fn visit(
                graph: &Graph<'_>,
                new_graph: &mut Graph<'_>,
                remap: &mut Vec<Option<usize>>,
                index: usize,
            ) -> usize {
                if let Some(new_index) = remap[index] {
                    // Already visited.
                    return new_index;
                }
                let node = graph.node(index).clone();
                let new_from = new_graph.add_node(node);
                remap[index] = Some(new_from);
                // Visit dependencies.
                for (edge_kind, edge_indexes) in &graph.edges[index].0 {
                    for edge_index in edge_indexes {
                        let new_to_index = visit(graph, new_graph, remap, *edge_index);
                        new_graph.edges[new_from].add_edge(*edge_kind, new_to_index);
                    }
                }
                new_from
            }

            // Walk the roots, generating a new graph as it goes along.
            for root in roots {
                visit(self, &mut new_graph, &mut remap, *root);
            }

            new_graph
        }

        /// Inverts the direction of all edges.
        pub fn invert(&mut self) {
            let mut new_edges = vec![Edges::new(); self.edges.len()];
            for (from_idx, node_edges) in self.edges.iter().enumerate() {
                for (kind, edges) in &node_edges.0 {
                    for edge_idx in edges {
                        new_edges[*edge_idx].add_edge(*kind, from_idx);
                    }
                }
            }
            self.edges = new_edges;
        }

        /// Returns a list of nodes that are considered "duplicates" (same package
        /// name, with different versions/features/source/etc.).
        pub fn find_duplicates(&self) -> Vec<usize> {
            // Graph built with features does not (yet) support --duplicates.
            assert!(self.dep_name_map.is_empty());

            // Collect a map of package name to Vec<(&Node, usize)>.
            let mut packages = HashMap::new();
            for (i, node) in self.nodes.iter().enumerate() {
                if let Node::Package { package_id, .. } = node {
                    packages
                        .entry(package_id.name())
                        .or_insert_with(Vec::new)
                        .push((node, i));
                }
            }

            let mut dupes: Vec<(&Node, usize)> = packages
                .into_iter()
                .filter(|(_name, indexes)| {
                    indexes
                        .into_iter()
                        .map(|(node, _)| {
                            match node {
                                Node::Package {
                                    package_id,
                                    features,
                                    ..
                                } => {
                                    // Do not treat duplicates on the host or target as duplicates.
                                    Node::Package {
                                        package_id: package_id.clone(),
                                        features: features.clone(),
                                        kind: CompileKind::Host,
                                    }
                                }
                                _ => unreachable!(),
                            }
                        })
                        .collect::<HashSet<_>>()
                        .len()
                        > 1
                })
                .flat_map(|(_name, indexes)| indexes)
                .collect();

            // For consistent output.
            dupes.sort_unstable();
            dupes.into_iter().map(|(_node, i)| i).collect()
        }
    }

    /// Builds the graph.
    pub fn build<'a>(
        ws: &Workspace<'_>,
        resolve: &Resolve,
        resolved_features: &ResolvedFeatures,
        specs: &[PackageIdSpec],
        cli_features: &CliFeatures,
        target_data: &RustcTargetData<'_>,
        requested_kinds: &[CompileKind],
        package_map: HashMap<PackageId, &'a Package>,
        opts: &TreeOptions,
    ) -> CargoResult<Graph<'a>> {
        let mut graph = Graph::new(package_map);
        let mut members_with_features = ws.members_with_features(specs, cli_features)?;
        members_with_features.sort_unstable_by_key(|e| e.0.package_id());
        for (member, cli_features) in members_with_features {
            let member_id = member.package_id();
            let features_for = FeaturesFor::from_for_host(member.proc_macro());
            for kind in requested_kinds {
                let member_index = add_pkg(
                    &mut graph,
                    resolve,
                    resolved_features,
                    member_id,
                    features_for,
                    target_data,
                    *kind,
                    opts,
                );
                if opts.graph_features {
                    let fmap = resolve.summary(member_id).features();
                    add_cli_features(&mut graph, member_index, &cli_features, fmap);
                }
            }
        }
        if opts.graph_features {
            add_internal_features(&mut graph, resolve);
        }
        Ok(graph)
    }

    /// Adds a single package node (if it does not already exist).
    ///
    /// This will also recursively add all of its dependencies.
    ///
    /// Returns the index to the package node.
    fn add_pkg(
        graph: &mut Graph<'_>,
        resolve: &Resolve,
        resolved_features: &ResolvedFeatures,
        package_id: PackageId,
        features_for: FeaturesFor,
        target_data: &RustcTargetData<'_>,
        requested_kind: CompileKind,
        opts: &TreeOptions,
    ) -> usize {
        let node_features = resolved_features.activated_features(package_id, features_for);
        let node_kind = match features_for {
            FeaturesFor::HostDep => CompileKind::Host,
            FeaturesFor::ArtifactDep(target) => CompileKind::Target(target),
            FeaturesFor::NormalOrDev => requested_kind,
        };
        let node = Node::Package {
            package_id,
            features: node_features,
            kind: node_kind,
        };
        if let Some(idx) = graph.index.get(&node) {
            return *idx;
        }
        let from_index = graph.add_node(node);
        // Compute the dep name map which is later used for foo/bar feature lookups.
        let mut dep_name_map: HashMap<InternedString, HashSet<(usize, bool)>> = HashMap::new();
        let mut deps: Vec<_> = resolve.deps(package_id).collect();
        deps.sort_unstable_by_key(|(dep_id, _)| *dep_id);
        let show_all_targets = opts.target == super::Target::All;
        for (dep_id, deps) in deps {
            let mut deps: Vec<_> = deps
                .iter()
                // This filter is *similar* to the one found in `unit_dependencies::compute_deps`.
                // Try to keep them in sync!
                .filter(|dep| {
                    let kind = match (node_kind, dep.kind()) {
                        (CompileKind::Host, _) => CompileKind::Host,
                        (_, DepKind::Build) => CompileKind::Host,
                        (_, DepKind::Normal) => node_kind,
                        (_, DepKind::Development) => node_kind,
                    };
                    // Filter out inactivated targets.
                    if !show_all_targets && !target_data.dep_platform_activated(dep, kind) {
                        return false;
                    }
                    // Filter out dev-dependencies if requested.
                    if !opts.edge_kinds.contains(&EdgeKind::Dep(dep.kind())) {
                        return false;
                    }
                    // Filter out proc-macrcos if requested.
                    if opts.no_proc_macro && graph.package_for_id(dep_id).proc_macro() {
                        return false;
                    }
                    if dep.is_optional() {
                        // If the new feature resolver does not enable this
                        // optional dep, then don't use it.
                        if !resolved_features.is_dep_activated(
                            package_id,
                            features_for,
                            dep.name_in_toml(),
                        ) {
                            return false;
                        }
                    }
                    true
                })
                .collect();

            // This dependency is eliminated from the dependency tree under
            // the current target and feature set.
            if deps.is_empty() {
                continue;
            }

            deps.sort_unstable_by_key(|dep| dep.name_in_toml());
            let dep_pkg = graph.package_map[&dep_id];

            for dep in deps {
                let dep_features_for = if dep.is_build() || dep_pkg.proc_macro() {
                    FeaturesFor::HostDep
                } else {
                    features_for
                };
                let dep_index = add_pkg(
                    graph,
                    resolve,
                    resolved_features,
                    dep_id,
                    dep_features_for,
                    target_data,
                    requested_kind,
                    opts,
                );
                if opts.graph_features {
                    // Add the dependency node with feature nodes in-between.
                    dep_name_map
                        .entry(dep.name_in_toml())
                        .or_default()
                        .insert((dep_index, dep.is_optional()));
                    if dep.uses_default_features() {
                        add_feature(
                            graph,
                            INTERNED_DEFAULT,
                            Some(from_index),
                            dep_index,
                            EdgeKind::Dep(dep.kind()),
                        );
                    }
                    for feature in dep.features().iter() {
                        add_feature(
                            graph,
                            *feature,
                            Some(from_index),
                            dep_index,
                            EdgeKind::Dep(dep.kind()),
                        );
                    }
                    if !dep.uses_default_features() && dep.features().is_empty() {
                        // No features, use a direct connection.
                        graph.edges[from_index].add_edge(EdgeKind::Dep(dep.kind()), dep_index);
                    }
                } else {
                    graph.edges[from_index].add_edge(EdgeKind::Dep(dep.kind()), dep_index);
                }
            }
        }
        if opts.graph_features {
            assert!(graph
                .dep_name_map
                .insert(from_index, dep_name_map)
                .is_none());
        }

        from_index
    }

    /// Adds a feature node between two nodes.
    ///
    /// That is, it adds the following:
    ///
    /// ```text
    /// from -Edge-> featname -Edge::Feature-> to
    /// ```
    ///
    /// Returns a tuple `(missing, index)`.
    /// `missing` is true if this feature edge was already added.
    /// `index` is the index of the index in the graph of the `Feature` node.
    fn add_feature(
        graph: &mut Graph<'_>,
        name: InternedString,
        from: Option<usize>,
        to: usize,
        kind: EdgeKind,
    ) -> (bool, usize) {
        // `to` *must* point to a package node.
        assert!(matches! {graph.nodes[to], Node::Package{..}});
        let node = Node::Feature {
            node_index: to,
            name,
        };
        let (missing, node_index) = match graph.index.get(&node) {
            Some(idx) => (false, *idx),
            None => (true, graph.add_node(node)),
        };
        if let Some(from) = from {
            graph.edges[from].add_edge(kind, node_index);
        }
        graph.edges[node_index].add_edge(EdgeKind::Feature, to);
        (missing, node_index)
    }

    /// Adds nodes for features requested on the command-line for the given member.
    ///
    /// Feature nodes are added as "roots" (i.e., they have no "from" index),
    /// because they come from the outside world. They usually only appear with
    /// `--invert`.
    fn add_cli_features(
        graph: &mut Graph<'_>,
        package_index: usize,
        cli_features: &CliFeatures,
        feature_map: &FeatureMap,
    ) {
        // NOTE: Recursive enabling of features will be handled by
        // add_internal_features.

        // Create a set of feature names requested on the command-line.
        let mut to_add: HashSet<FeatureValue> = HashSet::new();
        if cli_features.all_features {
            to_add.extend(feature_map.keys().map(|feat| FeatureValue::Feature(*feat)));
        }

        if cli_features.uses_default_features {
            to_add.insert(FeatureValue::Feature(INTERNED_DEFAULT));
        }
        to_add.extend(cli_features.features.iter().cloned());

        // Add each feature as a node, and mark as "from command-line" in graph.cli_features.
        for fv in to_add {
            match fv {
                FeatureValue::Feature(feature) => {
                    let index = add_feature(graph, feature, None, package_index, EdgeKind::Feature).1;
                    graph.cli_features.insert(index);
                }
                // This is enforced by CliFeatures.
                FeatureValue::Dep { .. } => panic!("unexpected cli dep feature {}", fv),
                FeatureValue::DepFeature {
                    dep_name,
                    dep_feature,
                    weak,
                } => {
                    let dep_connections = match graph.dep_name_map[&package_index].get(&dep_name) {
                        // Clone to deal with immutable borrow of `graph`. :(
                        Some(dep_connections) => dep_connections.clone(),
                        None => {
                            // --features bar?/feat where `bar` is not activated should be ignored.
                            // If this wasn't weak, then this is a bug.
                            if weak {
                                continue;
                            }
                            panic!(
                                "missing dep graph connection for CLI feature `{}` for member {:?}\n\
                                 Please file a bug report at https://github.com/rust-lang/cargo/issues",
                                fv,
                                graph.nodes.get(package_index)
                            );
                        }
                    };
                    for (dep_index, is_optional) in dep_connections {
                        if is_optional {
                            // Activate the optional dep on self.
                            let index =
                                add_feature(graph, dep_name, None, package_index, EdgeKind::Feature).1;
                            graph.cli_features.insert(index);
                        }
                        let index =
                            add_feature(graph, dep_feature, None, dep_index, EdgeKind::Feature).1;
                        graph.cli_features.insert(index);
                    }
                }
            }
        }
    }

    /// Recursively adds connections between features in the `[features]` table
    /// for every package.
    fn add_internal_features(graph: &mut Graph<'_>, resolve: &Resolve) {
        // Collect features already activated by dependencies or command-line.
        let feature_nodes: Vec<(PackageId, usize, usize, InternedString)> = graph
            .nodes
            .iter()
            .enumerate()
            .filter_map(|(i, node)| match node {
                Node::Package { .. } => None,
                Node::Feature { node_index, name } => {
                    let package_id = graph.package_id_for_index(*node_index);
                    Some((package_id, *node_index, i, *name))
                }
            })
            .collect();

        for (package_id, package_index, feature_index, feature_name) in feature_nodes {
            add_feature_rec(
                graph,
                resolve,
                feature_name,
                package_id,
                feature_index,
                package_index,
            );
        }
    }

    /// Recursively add feature nodes for all features enabled by the given feature.
    ///
    /// `from` is the index of the node that enables this feature.
    /// `package_index` is the index of the package node for the feature.
    fn add_feature_rec(
        graph: &mut Graph<'_>,
        resolve: &Resolve,
        feature_name: InternedString,
        package_id: PackageId,
        from: usize,
        package_index: usize,
    ) {
        let feature_map = resolve.summary(package_id).features();
        let Some(fvs) = feature_map.get(&feature_name) else {
            return;
        };
        for fv in fvs {
            match fv {
                FeatureValue::Feature(dep_name) => {
                    let (missing, feat_index) = add_feature(
                        graph,
                        *dep_name,
                        Some(from),
                        package_index,
                        EdgeKind::Feature,
                    );
                    // Don't recursive if the edge already exists to deal with cycles.
                    if missing {
                        add_feature_rec(
                            graph,
                            resolve,
                            *dep_name,
                            package_id,
                            feat_index,
                            package_index,
                        );
                    }
                }
                // Dependencies are already shown in the graph as dep edges. I'm
                // uncertain whether or not this might be confusing in some cases
                // (like feature `"somefeat" = ["dep:somedep"]`), so maybe in the
                // future consider explicitly showing this?
                FeatureValue::Dep { .. } => {}
                FeatureValue::DepFeature {
                    dep_name,
                    dep_feature,
                    // Note: `weak` is mostly handled when the graph is built in
                    // `is_dep_activated` which is responsible for skipping
                    // unactivated weak dependencies. Here it is only used to
                    // determine if the feature of the dependency name is
                    // activated on self.
                    weak,
                } => {
                    let dep_indexes = match graph.dep_name_map[&package_index].get(dep_name) {
                        Some(indexes) => indexes.clone(),
                        None => {
                            tracing::debug!(
                                "enabling feature {} on {}, found {}/{}, \
                                 dep appears to not be enabled",
                                feature_name,
                                package_id,
                                dep_name,
                                dep_feature
                            );
                            continue;
                        }
                    };
                    for (dep_index, is_optional) in dep_indexes {
                        let dep_pkg_id = graph.package_id_for_index(dep_index);
                        if is_optional && !weak {
                            // Activate the optional dep on self.
                            add_feature(
                                graph,
                                *dep_name,
                                Some(from),
                                package_index,
                                EdgeKind::Feature,
                            );
                        }
                        let (missing, feat_index) = add_feature(
                            graph,
                            *dep_feature,
                            Some(from),
                            dep_index,
                            EdgeKind::Feature,
                        );
                        if missing {
                            add_feature_rec(
                                graph,
                                resolve,
                                *dep_feature,
                                dep_pkg_id,
                                feat_index,
                                dep_index,
                            );
                        }
                    }
                }
            }
        }
    }