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    //! The entry point for starting the compilation process for commands like
    //! `build`, `test`, `doc`, `rustc`, etc.
    //!
    //! The [`compile`] function will do all the work to compile a workspace. A
    //! rough outline is:
    //!
    //! 1. Resolve the dependency graph (see [`ops::resolve`]).
    //! 2. Download any packages needed (see [`PackageSet`](crate::core::PackageSet)).
    //! 3. Generate a list of top-level "units" of work for the targets the user
    //!   requested on the command-line. Each [`Unit`] corresponds to a compiler
    //!   invocation. This is done in this module ([`UnitGenerator::generate_root_units`]).
    //! 4. Starting from the root [`Unit`]s, generate the [`UnitGraph`] by walking the dependency graph
    //!   from the resolver.  See also [`unit_dependencies`].
    //! 5. Construct the [`BuildContext`] with all of the information collected so
    //!   far. This is the end of the "front end" of compilation.
    //! 6. Create a [`Context`] which coordinates the compilation process
    //!   and will perform the following steps:
    //!     1. Prepare the `target` directory (see [`Layout`]).
    //!     2. Create a [`JobQueue`]. The queue checks the
    //!       fingerprint of each `Unit` to determine if it should run or be
    //!       skipped.
    //!     3. Execute the queue via [`drain_the_queue`]. Each leaf in the queue's dependency graph is
    //!        executed, and then removed from the graph when finished. This repeats until the queue is
    //!        empty.  Note that this is the only point in cargo that currently uses threads.
    //! 7. The result of the compilation is stored in the [`Compilation`] struct. This can be used for
    //!    various things, such as running tests after the compilation  has finished.
    //!
    //! **Note**: "target" inside this module generally refers to ["Cargo Target"],
    //! which corresponds to artifact that will be built in a package. Not to be
    //! confused with target-triple or target architecture.
    //!
    //! [`unit_dependencies`]: crate::core::compiler::unit_dependencies
    //! [`Layout`]: crate::core::compiler::Layout
    //! [`JobQueue`]: crate::core::compiler::job_queue
    //! [`drain_the_queue`]: crate::core::compiler::job_queue
    //! ["Cargo Target"]: https://doc.rust-lang.org/nightly/cargo/reference/cargo-targets.html

    use std::collections::{HashMap, HashSet};
    use std::hash::{Hash, Hasher};
    use std::sync::Arc;

    use crate::core::compiler::unit_dependencies::build_unit_dependencies;
    use crate::core::compiler::unit_graph::{self, UnitDep, UnitGraph};
    use crate::core::compiler::{standard_lib, CrateType, TargetInfo};
    use crate::core::compiler::{BuildConfig, BuildContext, Compilation, Context};
    use crate::core::compiler::{CompileKind, CompileMode, CompileTarget, RustcTargetData, Unit};
    use crate::core::compiler::{DefaultExecutor, Executor, UnitInterner};
    use crate::core::profiles::Profiles;
    use crate::core::resolver::features::{self, CliFeatures, FeaturesFor};
    use crate::core::resolver::{HasDevUnits, Resolve};
    use crate::core::{PackageId, PackageSet, SourceId, TargetKind, Workspace};
    use crate::drop_println;
    use crate::ops;
    use crate::ops::resolve::WorkspaceResolve;
    use crate::util::config::Config;
    use crate::util::interning::InternedString;
    use crate::util::{profile, CargoResult, StableHasher};

    mod compile_filter;
    pub use compile_filter::{CompileFilter, FilterRule, LibRule};

    mod unit_generator;
    use unit_generator::UnitGenerator;

    mod packages;

    pub use packages::Packages;

    /// Contains information about how a package should be compiled.
    ///
    /// Note on distinction between `CompileOptions` and [`BuildConfig`]:
    /// `BuildConfig` contains values that need to be retained after
    /// [`BuildContext`] is created. The other fields are no longer necessary. Think
    /// of it as `CompileOptions` are high-level settings requested on the
    /// command-line, and `BuildConfig` are low-level settings for actually
    /// driving `rustc`.
    #[derive(Debug, Clone)]
    pub struct CompileOptions {
        /// Configuration information for a rustc build
        pub build_config: BuildConfig,
        /// Feature flags requested by the user.
        pub cli_features: CliFeatures,
        /// A set of packages to build.
        pub spec: Packages,
        /// Filter to apply to the root package to select which targets will be
        /// built.
        pub filter: CompileFilter,
        /// Extra arguments to be passed to rustdoc (single target only)
        pub target_rustdoc_args: Option<Vec<String>>,
        /// The specified target will be compiled with all the available arguments,
        /// note that this only accounts for the *final* invocation of rustc
        pub target_rustc_args: Option<Vec<String>>,
        /// Crate types to be passed to rustc (single target only)
        pub target_rustc_crate_types: Option<Vec<String>>,
        /// Whether the `--document-private-items` flags was specified and should
        /// be forwarded to `rustdoc`.
        pub rustdoc_document_private_items: bool,
        /// Whether the build process should check the minimum Rust version
        /// defined in the cargo metadata for a crate.
        pub honor_rust_version: bool,
    }

    impl CompileOptions {
        pub fn new(config: &Config, mode: CompileMode) -> CargoResult<CompileOptions> {
            let jobs = None;
            let keep_going = false;
            Ok(CompileOptions {
                build_config: BuildConfig::new(config, jobs, keep_going, &[], mode)?,
                cli_features: CliFeatures::new_all(false),
                spec: ops::Packages::Packages(Vec::new()),
                filter: CompileFilter::Default {
                    required_features_filterable: false,
                },
                target_rustdoc_args: None,
                target_rustc_args: None,
                target_rustc_crate_types: None,
                rustdoc_document_private_items: false,
                honor_rust_version: true,
            })
        }
    }

    /// Compiles!
    ///
    /// This uses the [`DefaultExecutor`]. To use a custom [`Executor`], see [`compile_with_exec`].
    pub fn compile<'a>(ws: &Workspace<'a>, options: &CompileOptions) -> CargoResult<Compilation<'a>> {
        let exec: Arc<dyn Executor> = Arc::new(DefaultExecutor);
        compile_with_exec(ws, options, &exec)
    }

    /// Like [`compile`] but allows specifying a custom [`Executor`]
    /// that will be able to intercept build calls and add custom logic.
    ///
    /// [`compile`] uses [`DefaultExecutor`] which just passes calls through.
    pub fn compile_with_exec<'a>(
        ws: &Workspace<'a>,
        options: &CompileOptions,
        exec: &Arc<dyn Executor>,
    ) -> CargoResult<Compilation<'a>> {
        ws.emit_warnings()?;
        compile_ws(ws, options, exec)
    }

    /// Like [`compile_with_exec`] but without warnings from manifest parsing.
    pub fn compile_ws<'a>(
        ws: &Workspace<'a>,
        options: &CompileOptions,
        exec: &Arc<dyn Executor>,
    ) -> CargoResult<Compilation<'a>> {
        let interner = UnitInterner::new();
        let bcx = create_bcx(ws, options, &interner)?;
        if options.build_config.unit_graph {
            unit_graph::emit_serialized_unit_graph(&bcx.roots, &bcx.unit_graph, ws.config())?;
            return Compilation::new(&bcx);
        }
        let _p = profile::start("compiling");
        let cx = Context::new(&bcx)?;
        cx.compile(exec)
    }

    /// Executes `rustc --print <VALUE>`.
    ///
    /// * `print_opt_value` is the VALUE passed through.
    pub fn print<'a>(
        ws: &Workspace<'a>,
        options: &CompileOptions,
        print_opt_value: &str,
    ) -> CargoResult<()> {
        let CompileOptions {
            ref build_config,
            ref target_rustc_args,
            ..
        } = *options;
        let config = ws.config();
        let rustc = config.load_global_rustc(Some(ws))?;
        for (index, kind) in build_config.requested_kinds.iter().enumerate() {
            if index != 0 {
                drop_println!(config);
            }
            let target_info = TargetInfo::new(config, &build_config.requested_kinds, &rustc, *kind)?;
            let mut process = rustc.process();
            process.args(&target_info.rustflags);
            if let Some(args) = target_rustc_args {
                process.args(args);
            }
            if let CompileKind::Target(t) = kind {
                process.arg("--target").arg(t.short_name());
            }
            process.arg("--print").arg(print_opt_value);
            process.exec()?;
        }
        Ok(())
    }

    /// Prepares all required information for the actual compilation.
    ///
    /// For how it works and what data it collects,
    /// please see the [module-level documentation](self).
    pub fn create_bcx<'a, 'cfg>(
        ws: &'a Workspace<'cfg>,
        options: &'a CompileOptions,
        interner: &'a UnitInterner,
    ) -> CargoResult<BuildContext<'a, 'cfg>> {
        let CompileOptions {
            ref build_config,
            ref spec,
            ref cli_features,
            ref filter,
            ref target_rustdoc_args,
            ref target_rustc_args,
            ref target_rustc_crate_types,
            rustdoc_document_private_items,
            honor_rust_version,
        } = *options;
        let config = ws.config();

        // Perform some pre-flight validation.
        match build_config.mode {
            CompileMode::Test
            | CompileMode::Build
            | CompileMode::Check { .. }
            | CompileMode::Bench
            | CompileMode::RunCustomBuild => {
                if ws.config().get_env("RUST_FLAGS").is_ok() {
                    config.shell().warn(
                        "Cargo does not read `RUST_FLAGS` environment variable. Did you mean `RUSTFLAGS`?",
                    )?;
                }
            }
            CompileMode::Doc { .. } | CompileMode::Doctest | CompileMode::Docscrape => {
                if ws.config().get_env("RUSTDOC_FLAGS").is_ok() {
                    config.shell().warn(
                        "Cargo does not read `RUSTDOC_FLAGS` environment variable. Did you mean `RUSTDOCFLAGS`?"
                    )?;
                }
            }
        }
        config.validate_term_config()?;

        let target_data = RustcTargetData::new(ws, &build_config.requested_kinds)?;

        let specs = spec.to_package_id_specs(ws)?;
        let has_dev_units = {
            // Rustdoc itself doesn't need dev-dependencies. But to scrape examples from packages in the
            // workspace, if any of those packages need dev-dependencies, then we need include dev-dependencies
            // to scrape those packages.
            let any_pkg_has_scrape_enabled = ws
                .members_with_features(&specs, cli_features)?
                .iter()
                .any(|(pkg, _)| {
                    pkg.targets()
                        .iter()
                        .any(|target| target.is_example() && target.doc_scrape_examples().is_enabled())
                });

            if filter.need_dev_deps(build_config.mode)
                || (build_config.mode.is_doc() && any_pkg_has_scrape_enabled)
            {
                HasDevUnits::Yes
            } else {
                HasDevUnits::No
            }
        };
        let resolve = ops::resolve_ws_with_opts(
            ws,
            &target_data,
            &build_config.requested_kinds,
            cli_features,
            &specs,
            has_dev_units,
            crate::core::resolver::features::ForceAllTargets::No,
        )?;
        let WorkspaceResolve {
            mut pkg_set,
            workspace_resolve,
            targeted_resolve: resolve,
            resolved_features,
        } = resolve;

        let std_resolve_features = if let Some(crates) = &config.cli_unstable().build_std {
            let (std_package_set, std_resolve, std_features) =
                standard_lib::resolve_std(ws, &target_data, &build_config, crates)?;
            pkg_set.add_set(std_package_set);
            Some((std_resolve, std_features))
        } else {
            None
        };

        // Find the packages in the resolver that the user wants to build (those
        // passed in with `-p` or the defaults from the workspace), and convert
        // Vec<PackageIdSpec> to a Vec<PackageId>.
        let to_build_ids = resolve.specs_to_ids(&specs)?;
        // Now get the `Package` for each `PackageId`. This may trigger a download
        // if the user specified `-p` for a dependency that is not downloaded.
        // Dependencies will be downloaded during build_unit_dependencies.
        let mut to_builds = pkg_set.get_many(to_build_ids)?;

        // The ordering here affects some error messages coming out of cargo, so
        // let's be test and CLI friendly by always printing in the same order if
        // there's an error.
        to_builds.sort_by_key(|p| p.package_id());

        for pkg in to_builds.iter() {
            pkg.manifest().print_teapot(config);

            if build_config.mode.is_any_test()
                && !ws.is_member(pkg)
                && pkg.dependencies().iter().any(|dep| !dep.is_transitive())
            {
                anyhow::bail!(
                    "package `{}` cannot be tested because it requires dev-dependencies \
                     and is not a member of the workspace",
                    pkg.name()
                );
            }
        }

        let (extra_args, extra_args_name) = match (target_rustc_args, target_rustdoc_args) {
            (&Some(ref args), _) => (Some(args.clone()), "rustc"),
            (_, &Some(ref args)) => (Some(args.clone()), "rustdoc"),
            _ => (None, ""),
        };

        if extra_args.is_some() && to_builds.len() != 1 {
            panic!(
                "`{}` should not accept multiple `-p` flags",
                extra_args_name
            );
        }

        let profiles = Profiles::new(ws, build_config.requested_profile)?;
        profiles.validate_packages(
            ws.profiles(),
            &mut config.shell(),
            workspace_resolve.as_ref().unwrap_or(&resolve),
        )?;

        // If `--target` has not been specified, then the unit graph is built
        // assuming `--target $HOST` was specified. See
        // `rebuild_unit_graph_shared` for more on why this is done.
        let explicit_host_kind = CompileKind::Target(CompileTarget::new(&target_data.rustc.host)?);
        let explicit_host_kinds: Vec<_> = build_config
            .requested_kinds
            .iter()
            .map(|kind| match kind {
                CompileKind::Host => explicit_host_kind,
                CompileKind::Target(t) => CompileKind::Target(*t),
            })
            .collect();

        // Passing `build_config.requested_kinds` instead of
        // `explicit_host_kinds` here so that `generate_root_units` can do
        // its own special handling of `CompileKind::Host`. It will
        // internally replace the host kind by the `explicit_host_kind`
        // before setting as a unit.
        let generator = UnitGenerator {
            ws,
            packages: &to_builds,
            filter,
            requested_kinds: &build_config.requested_kinds,
            explicit_host_kind,
            mode: build_config.mode,
            resolve: &resolve,
            workspace_resolve: &workspace_resolve,
            resolved_features: &resolved_features,
            package_set: &pkg_set,
            profiles: &profiles,
            interner,
            has_dev_units,
        };
        let mut units = generator.generate_root_units()?;

        if let Some(args) = target_rustc_crate_types {
            override_rustc_crate_types(&mut units, args, interner)?;
        }

        let should_scrape = build_config.mode.is_doc() && config.cli_unstable().rustdoc_scrape_examples;
        let mut scrape_units = if should_scrape {
            UnitGenerator {
                mode: CompileMode::Docscrape,
                ..generator
            }
            .generate_scrape_units(&units)?
        } else {
            Vec::new()
        };

        let std_roots = if let Some(crates) = standard_lib::std_crates(config, Some(&units)) {
            let (std_resolve, std_features) = std_resolve_features.as_ref().unwrap();
            standard_lib::generate_std_roots(
                &crates,
                std_resolve,
                std_features,
                &explicit_host_kinds,
                &pkg_set,
                interner,
                &profiles,
            )?
        } else {
            Default::default()
        };

        let mut unit_graph = build_unit_dependencies(
            ws,
            &pkg_set,
            &resolve,
            &resolved_features,
            std_resolve_features.as_ref(),
            &units,
            &scrape_units,
            &std_roots,
            build_config.mode,
            &target_data,
            &profiles,
            interner,
        )?;

        // TODO: In theory, Cargo should also dedupe the roots, but I'm uncertain
        // what heuristics to use in that case.
        if build_config.mode == (CompileMode::Doc { deps: true }) {
            remove_duplicate_doc(build_config, &units, &mut unit_graph);
        }

        let host_kind_requested = build_config
            .requested_kinds
            .iter()
            .any(CompileKind::is_host);
        let should_share_deps = host_kind_requested
            || config.cli_unstable().bindeps
                && unit_graph
                    .iter()
                    .any(|(unit, _)| unit.artifact_target_for_features.is_some());
        if should_share_deps {
            // Rebuild the unit graph, replacing the explicit host targets with
            // CompileKind::Host, removing `artifact_target_for_features` and merging any dependencies
            // shared with build and artifact dependencies.
            (units, scrape_units, unit_graph) = rebuild_unit_graph_shared(
                interner,
                unit_graph,
                &units,
                &scrape_units,
                host_kind_requested.then_some(explicit_host_kind),
            );
        }

        let mut extra_compiler_args = HashMap::new();
        if let Some(args) = extra_args {
            if units.len() != 1 {
                anyhow::bail!(
                    "extra arguments to `{}` can only be passed to one \
                     target, consider filtering\nthe package by passing, \
                     e.g., `--lib` or `--bin NAME` to specify a single target",
                    extra_args_name
                );
            }
            extra_compiler_args.insert(units[0].clone(), args);
        }

        for unit in units
            .iter()
            .filter(|unit| unit.mode.is_doc() || unit.mode.is_doc_test())
            .filter(|unit| rustdoc_document_private_items || unit.target.is_bin())
        {
            // Add `--document-private-items` rustdoc flag if requested or if
            // the target is a binary. Binary crates get their private items
            // documented by default.
            let mut args = vec!["--document-private-items".into()];
            if unit.target.is_bin() {
                // This warning only makes sense if it's possible to document private items
                // sometimes and ignore them at other times. But cargo consistently passes
                // `--document-private-items`, so the warning isn't useful.
                args.push("-Arustdoc::private-intra-doc-links".into());
            }
            extra_compiler_args
                .entry(unit.clone())
                .or_default()
                .extend(args);
        }

        if honor_rust_version {
            // Remove any pre-release identifiers for easier comparison
            let current_version = &target_data.rustc.version;
            let untagged_version = semver::Version::new(
                current_version.major,
                current_version.minor,
                current_version.patch,
            );

            for unit in unit_graph.keys() {
                let version = match unit.pkg.rust_version() {
                    Some(v) => v,
                    None => continue,
                };

                let req = semver::VersionReq::parse(version).unwrap();
                if req.matches(&untagged_version) {
                    continue;
                }

                let guidance = if ws.is_ephemeral() {
                    if ws.ignore_lock() {
                        "Try re-running cargo install with `--locked`".to_string()
                    } else {
                        String::new()
                    }
                } else if !unit.is_local() {
                    format!(
                        "Either upgrade to rustc {} or newer, or use\n\
                         cargo update -p {}@{} --precise ver\n\
                         where `ver` is the latest version of `{}` supporting rustc {}",
                        version,
                        unit.pkg.name(),
                        unit.pkg.version(),
                        unit.pkg.name(),
                        current_version,
                    )
                } else {
                    String::new()
                };

                anyhow::bail!(
                    "package `{}` cannot be built because it requires rustc {} or newer, \
                     while the currently active rustc version is {}\n{}",
                    unit.pkg,
                    version,
                    current_version,
                    guidance,
                );
            }
        }

        let bcx = BuildContext::new(
            ws,
            pkg_set,
            build_config,
            profiles,
            extra_compiler_args,
            target_data,
            units,
            unit_graph,
            scrape_units,
        )?;

        Ok(bcx)
    }

    /// This is used to rebuild the unit graph, sharing host dependencies if possible.
    ///
    /// This will translate any unit's `CompileKind::Target(host)` to
    /// `CompileKind::Host` if `to_host` is not `None` and the kind is equal to `to_host`.
    /// This also handles generating the unit `dep_hash`, and merging shared units if possible.
    ///
    /// This is necessary because if normal dependencies used `CompileKind::Host`,
    /// there would be no way to distinguish those units from build-dependency
    /// units or artifact dependency units.
    /// This can cause a problem if a shared normal/build/artifact dependency needs
    /// to link to another dependency whose features differ based on whether or
    /// not it is a normal, build or artifact dependency. If all units used
    /// `CompileKind::Host`, then they would end up being identical, causing a
    /// collision in the `UnitGraph`, and Cargo would end up randomly choosing one
    /// value or the other.
    ///
    /// The solution is to keep normal, build and artifact dependencies separate when
    /// building the unit graph, and then run this second pass which will try to
    /// combine shared dependencies safely. By adding a hash of the dependencies
    /// to the `Unit`, this allows the `CompileKind` to be changed back to `Host`
    /// and `artifact_target_for_features` to be removed without fear of an unwanted
    /// collision for build or artifact dependencies.
    fn rebuild_unit_graph_shared(
        interner: &UnitInterner,
        unit_graph: UnitGraph,
        roots: &[Unit],
        scrape_units: &[Unit],
        to_host: Option<CompileKind>,
    ) -> (Vec<Unit>, Vec<Unit>, UnitGraph) {
        let mut result = UnitGraph::new();
        // Map of the old unit to the new unit, used to avoid recursing into units
        // that have already been computed to improve performance.
        let mut memo = HashMap::new();
        let new_roots = roots
            .iter()
            .map(|root| {
                traverse_and_share(
                    interner,
                    &mut memo,
                    &mut result,
                    &unit_graph,
                    root,
                    false,
                    to_host,
                )
            })
            .collect();
        // If no unit in the unit graph ended up having scrape units attached as dependencies,
        // then they won't have been discovered in traverse_and_share and hence won't be in
        // memo. So we filter out missing scrape units.
        let new_scrape_units = scrape_units
            .iter()
            .map(|unit| memo.get(unit).unwrap().clone())
            .collect();
        (new_roots, new_scrape_units, result)
    }

    /// Recursive function for rebuilding the graph.
    ///
    /// This walks `unit_graph`, starting at the given `unit`. It inserts the new
    /// units into `new_graph`, and returns a new updated version of the given
    /// unit (`dep_hash` is filled in, and `kind` switched if necessary).
    fn traverse_and_share(
        interner: &UnitInterner,
        memo: &mut HashMap<Unit, Unit>,
        new_graph: &mut UnitGraph,
        unit_graph: &UnitGraph,
        unit: &Unit,
        unit_is_for_host: bool,
        to_host: Option<CompileKind>,
    ) -> Unit {
        if let Some(new_unit) = memo.get(unit) {
            // Already computed, no need to recompute.
            return new_unit.clone();
        }
        let mut dep_hash = StableHasher::new();
        let new_deps: Vec<_> = unit_graph[unit]
            .iter()
            .map(|dep| {
                let new_dep_unit = traverse_and_share(
                    interner,
                    memo,
                    new_graph,
                    unit_graph,
                    &dep.unit,
                    dep.unit_for.is_for_host(),
                    to_host,
                );
                new_dep_unit.hash(&mut dep_hash);
                UnitDep {
                    unit: new_dep_unit,
                    ..dep.clone()
                }
            })
            .collect();
        // Here, we have recursively traversed this unit's dependencies, and hashed them: we can
        // finalize the dep hash.
        let new_dep_hash = dep_hash.finish();

        // This is the key part of the sharing process: if the unit is a runtime dependency, whose
        // target is the same as the host, we canonicalize the compile kind to `CompileKind::Host`.
        // A possible host dependency counterpart to this unit would have that kind, and if such a unit
        // exists in the current `unit_graph`, they will unify in the new unit graph map `new_graph`.
        // The resulting unit graph will be optimized with less units, thanks to sharing these host
        // dependencies.
        let canonical_kind = match to_host {
            Some(to_host) if to_host == unit.kind => CompileKind::Host,
            _ => unit.kind,
        };

        let mut profile = unit.profile.clone();

        // If this is a build dependency, and it's not shared with runtime dependencies, we can weaken
        // its debuginfo level to optimize build times. We do nothing if it's an artifact dependency,
        // as it and its debuginfo may end up embedded in the main program.
        if unit_is_for_host
            && to_host.is_some()
            && profile.debuginfo.is_deferred()
            && !unit.artifact.is_true()
        {
            // We create a "probe" test to see if a unit with the same explicit debuginfo level exists
            // in the graph. This is the level we'd expect if it was set manually or the default value
            // set by a profile for a runtime dependency: its canonical value.
            let canonical_debuginfo = profile.debuginfo.finalize();
            let mut canonical_profile = profile.clone();
            canonical_profile.debuginfo = canonical_debuginfo;
            let unit_probe = interner.intern(
                &unit.pkg,
                &unit.target,
                canonical_profile,
                to_host.unwrap(),
                unit.mode,
                unit.features.clone(),
                unit.is_std,
                unit.dep_hash,
                unit.artifact,
                unit.artifact_target_for_features,
            );

            // We can now turn the deferred value into its actual final value.
            profile.debuginfo = if unit_graph.contains_key(&unit_probe) {
                // The unit is present in both build time and runtime subgraphs: we canonicalize its
                // level to the other unit's, thus ensuring reuse between the two to optimize build times.
                canonical_debuginfo
            } else {
                // The unit is only present in the build time subgraph, we can weaken its debuginfo
                // level to optimize build times.
                canonical_debuginfo.weaken()
            }
        }

        let new_unit = interner.intern(
            &unit.pkg,
            &unit.target,
            profile,
            canonical_kind,
            unit.mode,
            unit.features.clone(),
            unit.is_std,
            new_dep_hash,
            unit.artifact,
            // Since `dep_hash` is now filled in, there's no need to specify the artifact target
            // for target-dependent feature resolution
            None,
        );
        assert!(memo.insert(unit.clone(), new_unit.clone()).is_none());
        new_graph.entry(new_unit.clone()).or_insert(new_deps);
        new_unit
    }

    /// Removes duplicate CompileMode::Doc units that would cause problems with
    /// filename collisions.
    ///
    /// Rustdoc only separates units by crate name in the file directory
    /// structure. If any two units with the same crate name exist, this would
    /// cause a filename collision, causing different rustdoc invocations to stomp
    /// on one another's files.
    ///
    /// Unfortunately this does not remove all duplicates, as some of them are
    /// either user error, or difficult to remove. Cases that I can think of:
    ///
    /// - Same target name in different packages. See the `collision_doc` test.
    /// - Different sources. See `collision_doc_sources` test.
    ///
    /// Ideally this would not be necessary.
    fn remove_duplicate_doc(
        build_config: &BuildConfig,
        root_units: &[Unit],
        unit_graph: &mut UnitGraph,
    ) {
        // First, create a mapping of crate_name -> Unit so we can see where the
        // duplicates are.
        let mut all_docs: HashMap<String, Vec<Unit>> = HashMap::new();
        for unit in unit_graph.keys() {
            if unit.mode.is_doc() {
                all_docs
                    .entry(unit.target.crate_name())
                    .or_default()
                    .push(unit.clone());
            }
        }
        // Keep track of units to remove so that they can be efficiently removed
        // from the unit_deps.
        let mut removed_units: HashSet<Unit> = HashSet::new();
        let mut remove = |units: Vec<Unit>, reason: &str, cb: &dyn Fn(&Unit) -> bool| -> Vec<Unit> {
            let (to_remove, remaining_units): (Vec<Unit>, Vec<Unit>) = units
                .into_iter()
                .partition(|unit| cb(unit) && !root_units.contains(unit));
            for unit in to_remove {
                log::debug!(
                    "removing duplicate doc due to {} for package {} target `{}`",
                    reason,
                    unit.pkg,
                    unit.target.name()
                );
                unit_graph.remove(&unit);
                removed_units.insert(unit);
            }
            remaining_units
        };
        // Iterate over the duplicates and try to remove them from unit_graph.
        for (_crate_name, mut units) in all_docs {
            if units.len() == 1 {
                continue;
            }
            // Prefer target over host if --target was not specified.
            if build_config
                .requested_kinds
                .iter()
                .all(CompileKind::is_host)
            {
                // Note these duplicates may not be real duplicates, since they
                // might get merged in rebuild_unit_graph_shared. Either way, it
                // shouldn't hurt to remove them early (although the report in the
                // log might be confusing).
                units = remove(units, "host/target merger", &|unit| unit.kind.is_host());
                if units.len() == 1 {
                    continue;
                }
            }
            // Prefer newer versions over older.
            let mut source_map: HashMap<(InternedString, SourceId, CompileKind), Vec<Unit>> =
                HashMap::new();
            for unit in units {
                let pkg_id = unit.pkg.package_id();
                // Note, this does not detect duplicates from different sources.
                source_map
                    .entry((pkg_id.name(), pkg_id.source_id(), unit.kind))
                    .or_default()
                    .push(unit);
            }
            let mut remaining_units = Vec::new();
            for (_key, mut units) in source_map {
                if units.len() > 1 {
                    units.sort_by(|a, b| a.pkg.version().partial_cmp(b.pkg.version()).unwrap());
                    // Remove any entries with version < newest.
                    let newest_version = units.last().unwrap().pkg.version().clone();
                    let keep_units = remove(units, "older version", &|unit| {
                        unit.pkg.version() < &newest_version
                    });
                    remaining_units.extend(keep_units);
                } else {
                    remaining_units.extend(units);
                }
            }
            if remaining_units.len() == 1 {
                continue;
            }
            // Are there other heuristics to remove duplicates that would make
            // sense? Maybe prefer path sources over all others?
        }
        // Also remove units from the unit_deps so there aren't any dangling edges.
        for unit_deps in unit_graph.values_mut() {
            unit_deps.retain(|unit_dep| !removed_units.contains(&unit_dep.unit));
        }
        // Remove any orphan units that were detached from the graph.
        let mut visited = HashSet::new();
        fn visit(unit: &Unit, graph: &UnitGraph, visited: &mut HashSet<Unit>) {
            if !visited.insert(unit.clone()) {
                return;
            }
            for dep in &graph[unit] {
                visit(&dep.unit, graph, visited);
            }
        }
        for unit in root_units {
            visit(unit, unit_graph, &mut visited);
        }
        unit_graph.retain(|unit, _| visited.contains(unit));
    }

    /// Override crate types for given units.
    ///
    /// This is primarily used by `cargo rustc --crate-type`.
    fn override_rustc_crate_types(
        units: &mut [Unit],
        args: &[String],
        interner: &UnitInterner,
    ) -> CargoResult<()> {
        if units.len() != 1 {
            anyhow::bail!(
                "crate types to rustc can only be passed to one \
                target, consider filtering\nthe package by passing, \
                e.g., `--lib` or `--example` to specify a single target"
            );
        }

        let unit = &units[0];
        let override_unit = |f: fn(Vec<CrateType>) -> TargetKind| {
            let crate_types = args.iter().map(|s| s.into()).collect();
            let mut target = unit.target.clone();
            target.set_kind(f(crate_types));
            interner.intern(
                &unit.pkg,
                &target,
                unit.profile.clone(),
                unit.kind,
                unit.mode,
                unit.features.clone(),
                unit.is_std,
                unit.dep_hash,
                unit.artifact,
                unit.artifact_target_for_features,
            )
        };
        units[0] = match unit.target.kind() {
            TargetKind::Lib(_) => override_unit(TargetKind::Lib),
            TargetKind::ExampleLib(_) => override_unit(TargetKind::ExampleLib),
            _ => {
                anyhow::bail!(
                    "crate types can only be specified for libraries and example libraries.\n\
                    Binaries, tests, and benchmarks are always the `bin` crate type"
                );
            }
        };

        Ok(())
    }

    /// Gets all of the features enabled for a package, plus its dependencies'
    /// features.
    ///
    /// Dependencies are added as `dep_name/feat_name` because `required-features`
    /// wants to support that syntax.
    pub fn resolve_all_features(
        resolve_with_overrides: &Resolve,
        resolved_features: &features::ResolvedFeatures,
        package_set: &PackageSet<'_>,
        package_id: PackageId,
    ) -> HashSet<String> {
        let mut features: HashSet<String> = resolved_features
            .activated_features(package_id, FeaturesFor::NormalOrDev)
            .iter()
            .map(|s| s.to_string())
            .collect();

        // Include features enabled for use by dependencies so targets can also use them with the
        // required-features field when deciding whether to be built or skipped.
        for (dep_id, deps) in resolve_with_overrides.deps(package_id) {
            let is_proc_macro = package_set
                .get_one(dep_id)
                .expect("packages downloaded")
                .proc_macro();
            for dep in deps {
                let features_for = FeaturesFor::from_for_host(is_proc_macro || dep.is_build());
                for feature in resolved_features
                    .activated_features_unverified(dep_id, features_for)
                    .unwrap_or_default()
                {
                    features.insert(format!("{}/{}", dep.name_in_toml(), feature));
                }
            }
        }

        features
    }