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    use std::cell::RefCell;
    use std::collections::{HashMap, HashSet};
    use std::fmt::Write;

    use crate::core::compiler::rustdoc::RustdocScrapeExamples;
    use crate::core::compiler::unit_dependencies::IsArtifact;
    use crate::core::compiler::{CompileKind, CompileMode, Unit};
    use crate::core::compiler::{RustcTargetData, UnitInterner};
    use crate::core::dependency::DepKind;
    use crate::core::profiles::{Profiles, UnitFor};
    use crate::core::resolver::features::{self, FeaturesFor};
    use crate::core::resolver::{HasDevUnits, Resolve};
    use crate::core::{FeatureValue, Package, PackageSet, Summary, Target};
    use crate::core::{TargetKind, Workspace};
    use crate::util::restricted_names::is_glob_pattern;
    use crate::util::{closest_msg, CargoResult};

    use super::compile_filter::{CompileFilter, FilterRule, LibRule};
    use super::packages::build_glob;

    /// A proposed target.
    ///
    /// Proposed targets are later filtered into actual `Unit`s based on whether or
    /// not the target requires its features to be present.
    #[derive(Debug)]
    struct Proposal<'a> {
        pkg: &'a Package,
        target: &'a Target,
        /// Indicates whether or not all required features *must* be present. If
        /// false, and the features are not available, then it will be silently
        /// skipped. Generally, targets specified by name (`--bin foo`) are
        /// required, all others can be silently skipped if features are missing.
        requires_features: bool,
        mode: CompileMode,
    }

    /// The context needed for generating root units,
    /// which are packages the user has requested to compile.
    ///
    /// To generate a full [`UnitGraph`],
    /// generally you need to call [`generate_root_units`] first,
    /// and then provide the output to [`build_unit_dependencies`].
    ///
    /// [`generate_root_units`]: UnitGenerator::generate_root_units
    /// [`build_unit_dependencies`]: crate::core::compiler::unit_dependencies::build_unit_dependencies
    /// [`UnitGraph`]: crate::core::compiler::unit_graph::UnitGraph
    pub(super) struct UnitGenerator<'a, 'gctx> {
        pub ws: &'a Workspace<'gctx>,
        pub packages: &'a [&'a Package],
        pub target_data: &'a RustcTargetData<'gctx>,
        pub filter: &'a CompileFilter,
        pub requested_kinds: &'a [CompileKind],
        pub explicit_host_kind: CompileKind,
        pub mode: CompileMode,
        pub resolve: &'a Resolve,
        pub workspace_resolve: &'a Option<Resolve>,
        pub resolved_features: &'a features::ResolvedFeatures,
        pub package_set: &'a PackageSet<'gctx>,
        pub profiles: &'a Profiles,
        pub interner: &'a UnitInterner,
        pub has_dev_units: HasDevUnits,
    }

    impl<'a> UnitGenerator<'a, '_> {
        /// Helper for creating a list of `Unit` structures
        fn new_units(
            &self,
            pkg: &Package,
            target: &Target,
            initial_target_mode: CompileMode,
        ) -> Vec<Unit> {
            // Custom build units are added in `build_unit_dependencies`.
            assert!(!target.is_custom_build());
            let target_mode = match initial_target_mode {
                CompileMode::Test => {
                    if target.is_example() && !self.filter.is_specific() && !target.tested() {
                        // Examples are included as regular binaries to verify
                        // that they compile.
                        CompileMode::Build
                    } else {
                        CompileMode::Test
                    }
                }
                CompileMode::Build => match *target.kind() {
                    TargetKind::Test => CompileMode::Test,
                    TargetKind::Bench => CompileMode::Bench,
                    _ => CompileMode::Build,
                },
                // `CompileMode::Bench` is only used to inform `filter_default_targets`
                // which command is being used (`cargo bench`). Afterwards, tests
                // and benches are treated identically. Switching the mode allows
                // de-duplication of units that are essentially identical. For
                // example, `cargo build --all-targets --release` creates the units
                // (lib profile:bench, mode:test) and (lib profile:bench, mode:bench)
                // and since these are the same, we want them to be de-duplicated in
                // `unit_dependencies`.
                CompileMode::Bench => CompileMode::Test,
                _ => initial_target_mode,
            };

            let is_local = pkg.package_id().source_id().is_path();

            // No need to worry about build-dependencies, roots are never build dependencies.
            let features_for = FeaturesFor::from_for_host(target.proc_macro());
            let features = self
                .resolved_features
                .activated_features(pkg.package_id(), features_for);

            // If `--target` has not been specified, then the unit
            // graph is built almost like if `--target $HOST` was
            // specified. See `rebuild_unit_graph_shared` for more on
            // why this is done. However, if the package has its own
            // `package.target` key, then this gets used instead of
            // `$HOST`
            let explicit_kinds = if let Some(k) = pkg.manifest().forced_kind() {
                vec![k]
            } else {
                self.requested_kinds
                    .iter()
                    .map(|kind| match kind {
                        CompileKind::Host => pkg
                            .manifest()
                            .default_kind()
                            .unwrap_or(self.explicit_host_kind),
                        CompileKind::Target(t) => CompileKind::Target(*t),
                    })
                    .collect()
            };

            explicit_kinds
                .into_iter()
                .map(move |kind| {
                    let unit_for = if initial_target_mode.is_any_test() {
                        // NOTE: the `UnitFor` here is subtle. If you have a profile
                        // with `panic` set, the `panic` flag is cleared for
                        // tests/benchmarks and their dependencies. If this
                        // was `normal`, then the lib would get compiled three
                        // times (once with panic, once without, and once with
                        // `--test`).
                        //
                        // This would cause a problem for doc tests, which would fail
                        // because `rustdoc` would attempt to link with both libraries
                        // at the same time. Also, it's probably not important (or
                        // even desirable?) for rustdoc to link with a lib with
                        // `panic` set.
                        //
                        // As a consequence, Examples and Binaries get compiled
                        // without `panic` set. This probably isn't a bad deal.
                        //
                        // Forcing the lib to be compiled three times during `cargo
                        // test` is probably also not desirable.
                        UnitFor::new_test(self.ws.gctx(), kind)
                    } else if target.for_host() {
                        // Proc macro / plugin should not have `panic` set.
                        UnitFor::new_compiler(kind)
                    } else {
                        UnitFor::new_normal(kind)
                    };
                    let profile = self.profiles.get_profile(
                        pkg.package_id(),
                        self.ws.is_member(pkg),
                        is_local,
                        unit_for,
                        kind,
                    );
                    let kind = kind.for_target(target);
                    self.interner.intern(
                        pkg,
                        target,
                        profile,
                        kind,
                        target_mode,
                        features.clone(),
                        self.target_data.info(kind).rustflags.clone(),
                        self.target_data.info(kind).rustdocflags.clone(),
                        /*is_std*/ false,
                        /*dep_hash*/ 0,
                        IsArtifact::No,
                        None,
                    )
                })
                .collect()
        }

        /// Given a list of all targets for a package, filters out only the targets
        /// that are automatically included when the user doesn't specify any targets.
        fn filter_default_targets<'b>(&self, targets: &'b [Target]) -> Vec<&'b Target> {
            match self.mode {
                CompileMode::Bench => targets.iter().filter(|t| t.benched()).collect(),
                CompileMode::Test => targets
                    .iter()
                    .filter(|t| t.tested() || t.is_example())
                    .collect(),
                CompileMode::Build | CompileMode::Check { .. } => targets
                    .iter()
                    .filter(|t| t.is_bin() || t.is_lib())
                    .collect(),
                CompileMode::Doc { .. } => {
                    // `doc` does lib and bins (bin with same name as lib is skipped).
                    targets
                        .iter()
                        .filter(|t| {
                            t.documented()
                                && (!t.is_bin()
                                    || !targets
                                        .iter()
                                        .any(|l| l.is_lib() && l.crate_name() == t.crate_name()))
                        })
                        .collect()
                }
                CompileMode::Doctest | CompileMode::RunCustomBuild | CompileMode::Docscrape => {
                    panic!("Invalid mode {:?}", self.mode)
                }
            }
        }

        /// Filters the set of all possible targets based on the provided predicate.
        fn filter_targets(
            &self,
            predicate: impl Fn(&Target) -> bool,
            requires_features: bool,
            mode: CompileMode,
        ) -> Vec<Proposal<'a>> {
            self.packages
                .iter()
                .flat_map(|pkg| {
                    pkg.targets()
                        .iter()
                        .filter(|t| predicate(t))
                        .map(|target| Proposal {
                            pkg,
                            target,
                            requires_features,
                            mode,
                        })
                })
                .collect()
        }

        /// Finds the targets for a specifically named target.
        fn find_named_targets(
            &self,
            target_name: &str,
            target_desc: &'static str,
            is_expected_kind: fn(&Target) -> bool,
            mode: CompileMode,
        ) -> CargoResult<Vec<Proposal<'a>>> {
            let is_glob = is_glob_pattern(target_name);
            let proposals = if is_glob {
                let pattern = build_glob(target_name)?;
                let filter = |t: &Target| is_expected_kind(t) && pattern.matches(t.name());
                self.filter_targets(filter, true, mode)
            } else {
                let filter = |t: &Target| t.name() == target_name && is_expected_kind(t);
                self.filter_targets(filter, true, mode)
            };

            if proposals.is_empty() {
                let targets = self
                    .packages
                    .iter()
                    .flat_map(|pkg| {
                        pkg.targets()
                            .iter()
                            .filter(|target| is_expected_kind(target))
                    })
                    .collect::<Vec<_>>();
                let suggestion = closest_msg(target_name, targets.iter(), |t| t.name());
                if !suggestion.is_empty() {
                    anyhow::bail!(
                        "no {} target {} `{}`{}",
                        target_desc,
                        if is_glob { "matches pattern" } else { "named" },
                        target_name,
                        suggestion
                    );
                } else {
                    let mut msg = String::new();
                    writeln!(
                        msg,
                        "no {} target {} `{}`.",
                        target_desc,
                        if is_glob { "matches pattern" } else { "named" },
                        target_name,
                    )?;
                    if !targets.is_empty() {
                        writeln!(msg, "Available {} targets:", target_desc)?;
                        for target in targets {
                            writeln!(msg, "    {}", target.name())?;
                        }
                    }
                    anyhow::bail!(msg);
                }
            }
            Ok(proposals)
        }

        /// Returns a list of proposed targets based on command-line target selection flags.
        fn list_rule_targets(
            &self,
            rule: &FilterRule,
            target_desc: &'static str,
            is_expected_kind: fn(&Target) -> bool,
            mode: CompileMode,
        ) -> CargoResult<Vec<Proposal<'a>>> {
            let mut proposals = Vec::new();
            match rule {
                FilterRule::All => proposals.extend(self.filter_targets(is_expected_kind, false, mode)),
                FilterRule::Just(names) => {
                    for name in names {
                        proposals.extend(self.find_named_targets(
                            name,
                            target_desc,
                            is_expected_kind,
                            mode,
                        )?);
                    }
                }
            }
            Ok(proposals)
        }

        /// Create a list of proposed targets given the context in `UnitGenerator`
        fn create_proposals(&self) -> CargoResult<Vec<Proposal<'_>>> {
            let mut proposals: Vec<Proposal<'_>> = Vec::new();

            match *self.filter {
                CompileFilter::Default {
                    required_features_filterable,
                } => {
                    for pkg in self.packages {
                        let default = self.filter_default_targets(pkg.targets());
                        proposals.extend(default.into_iter().map(|target| Proposal {
                            pkg,
                            target,
                            requires_features: !required_features_filterable,
                            mode: self.mode,
                        }));
                        if self.mode == CompileMode::Test {
                            if let Some(t) = pkg
                                .targets()
                                .iter()
                                .find(|t| t.is_lib() && t.doctested() && t.doctestable())
                            {
                                proposals.push(Proposal {
                                    pkg,
                                    target: t,
                                    requires_features: false,
                                    mode: CompileMode::Doctest,
                                });
                            }
                        }
                    }
                }
                CompileFilter::Only {
                    all_targets,
                    ref lib,
                    ref bins,
                    ref examples,
                    ref tests,
                    ref benches,
                } => {
                    if *lib != LibRule::False {
                        let mut libs = Vec::new();
                        for proposal in self.filter_targets(Target::is_lib, false, self.mode) {
                            let Proposal { target, pkg, .. } = proposal;
                            if self.mode.is_doc_test() && !target.doctestable() {
                                let types = target.rustc_crate_types();
                                let types_str: Vec<&str> = types.iter().map(|t| t.as_str()).collect();
                                self.ws.gctx().shell().warn(format!(
                          "doc tests are not supported for crate type(s) `{}` in package `{}`",
                          types_str.join(", "),
                          pkg.name()
                      ))?;
                            } else {
                                libs.push(proposal)
                            }
                        }
                        if !all_targets && libs.is_empty() && *lib == LibRule::True {
                            let names = self
                                .packages
                                .iter()
                                .map(|pkg| pkg.name())
                                .collect::<Vec<_>>();
                            if names.len() == 1 {
                                anyhow::bail!("no library targets found in package `{}`", names[0]);
                            } else {
                                anyhow::bail!(
                                    "no library targets found in packages: {}",
                                    names.join(", ")
                                );
                            }
                        }
                        proposals.extend(libs);
                    }

                    // If `--tests` was specified, add all targets that would be
                    // generated by `cargo test`.
                    let test_filter = match tests {
                        FilterRule::All => Target::tested,
                        FilterRule::Just(_) => Target::is_test,
                    };
                    let test_mode = match self.mode {
                        CompileMode::Build => CompileMode::Test,
                        CompileMode::Check { .. } => CompileMode::Check { test: true },
                        _ => self.mode,
                    };
                    // If `--benches` was specified, add all targets that would be
                    // generated by `cargo bench`.
                    let bench_filter = match benches {
                        FilterRule::All => Target::benched,
                        FilterRule::Just(_) => Target::is_bench,
                    };
                    let bench_mode = match self.mode {
                        CompileMode::Build => CompileMode::Bench,
                        CompileMode::Check { .. } => CompileMode::Check { test: true },
                        _ => self.mode,
                    };

                    proposals.extend(self.list_rule_targets(bins, "bin", Target::is_bin, self.mode)?);
                    proposals.extend(self.list_rule_targets(
                        examples,
                        "example",
                        Target::is_example,
                        self.mode,
                    )?);
                    proposals.extend(self.list_rule_targets(tests, "test", test_filter, test_mode)?);
                    proposals.extend(self.list_rule_targets(
                        benches,
                        "bench",
                        bench_filter,
                        bench_mode,
                    )?);
                }
            }

            Ok(proposals)
        }

        /// Proposes targets from which to scrape examples for documentation
        fn create_docscrape_proposals(&self, doc_units: &[Unit]) -> CargoResult<Vec<Proposal<'a>>> {
            // In general, the goal is to scrape examples from (a) whatever targets
            // the user is documenting, and (b) Example targets. However, if the user
            // is documenting a library with dev-dependencies, those dev-deps are not
            // needed for the library, while dev-deps are needed for the examples.
            //
            // If scrape-examples caused `cargo doc` to start requiring dev-deps, this
            // would be a breaking change to crates whose dev-deps don't compile.
            // Therefore we ONLY want to scrape Example targets if either:
            //    (1) No package has dev-dependencies, so this is a moot issue, OR
            //    (2) The provided CompileFilter requires dev-dependencies anyway.
            //
            // The next two variables represent these two conditions.
            let no_pkg_has_dev_deps = self.packages.iter().all(|pkg| {
                pkg.summary()
                    .dependencies()
                    .iter()
                    .all(|dep| !matches!(dep.kind(), DepKind::Development))
            });
            let reqs_dev_deps = matches!(self.has_dev_units, HasDevUnits::Yes);
            let safe_to_scrape_example_targets = no_pkg_has_dev_deps || reqs_dev_deps;

            let pkgs_to_scrape = doc_units
                .iter()
                .filter(|unit| self.ws.unit_needs_doc_scrape(unit))
                .map(|u| &u.pkg)
                .collect::<HashSet<_>>();

            let skipped_examples = RefCell::new(Vec::new());
            let can_scrape = |target: &Target| {
                match (target.doc_scrape_examples(), target.is_example()) {
                    // Targets configured by the user to not be scraped should never be scraped
                    (RustdocScrapeExamples::Disabled, _) => false,
                    // Targets configured by the user to be scraped should always be scraped
                    (RustdocScrapeExamples::Enabled, _) => true,
                    // Example targets with no configuration should be conditionally scraped if
                    // it's guaranteed not to break the build
                    (RustdocScrapeExamples::Unset, true) => {
                        if !safe_to_scrape_example_targets {
                            skipped_examples
                                .borrow_mut()
                                .push(target.name().to_string());
                        }
                        safe_to_scrape_example_targets
                    }
                    // All other targets are ignored for now. This may change in the future!
                    (RustdocScrapeExamples::Unset, false) => false,
                }
            };

            let mut scrape_proposals = self.filter_targets(can_scrape, false, CompileMode::Docscrape);
            scrape_proposals.retain(|proposal| pkgs_to_scrape.contains(proposal.pkg));

            let skipped_examples = skipped_examples.into_inner();
            if !skipped_examples.is_empty() {
                let mut shell = self.ws.gctx().shell();
                let example_str = skipped_examples.join(", ");
                shell.warn(format!(
                    "\
    Rustdoc did not scrape the following examples because they require dev-dependencies: {example_str}
        If you want Rustdoc to scrape these examples, then add `doc-scrape-examples = true`
        to the [[example]] target configuration of at least one example."
                ))?;
            }

            Ok(scrape_proposals)
        }

        /// Checks if the unit list is empty and the user has passed any combination of
        /// --tests, --examples, --benches or --bins, and we didn't match on any targets.
        /// We want to emit a warning to make sure the user knows that this run is a no-op,
        /// and their code remains unchecked despite cargo not returning any errors
        fn unmatched_target_filters(&self, units: &[Unit]) -> CargoResult<()> {
            let mut shell = self.ws.gctx().shell();
            if let CompileFilter::Only {
                all_targets,
                lib: _,
                ref bins,
                ref examples,
                ref tests,
                ref benches,
            } = *self.filter
            {
                if units.is_empty() {
                    let mut filters = String::new();
                    let mut miss_count = 0;

                    let mut append = |t: &FilterRule, s| {
                        if let FilterRule::All = *t {
                            miss_count += 1;
                            filters.push_str(s);
                        }
                    };

                    if all_targets {
                        filters.push_str(" `all-targets`");
                    } else {
                        append(bins, " `bins`,");
                        append(tests, " `tests`,");
                        append(examples, " `examples`,");
                        append(benches, " `benches`,");
                        filters.pop();
                    }

                    return shell.warn(format!(
                        "target {}{} specified, but no targets matched; this is a no-op",
                        if miss_count > 1 { "filters" } else { "filter" },
                        filters,
                    ));
                }
            }

            Ok(())
        }

        /// Warns if a target's required-features references a feature that doesn't exist.
        ///
        /// This is a warning because historically this was not validated, and it
        /// would cause too much breakage to make it an error.
        fn validate_required_features(
            &self,
            target_name: &str,
            required_features: &[String],
            summary: &Summary,
        ) -> CargoResult<()> {
            let resolve = match self.workspace_resolve {
                None => return Ok(()),
                Some(resolve) => resolve,
            };

            let mut shell = self.ws.gctx().shell();
            for feature in required_features {
                let fv = FeatureValue::new(feature.into());
                match &fv {
                    FeatureValue::Feature(f) => {
                        if !summary.features().contains_key(f) {
                            shell.warn(format!(
                                "invalid feature `{}` in required-features of target `{}`: \
                          `{}` is not present in [features] section",
                                fv, target_name, fv
                            ))?;
                        }
                    }
                    FeatureValue::Dep { .. } => {
                        anyhow::bail!(
                            "invalid feature `{}` in required-features of target `{}`: \
                      `dep:` prefixed feature values are not allowed in required-features",
                            fv,
                            target_name
                        );
                    }
                    FeatureValue::DepFeature { weak: true, .. } => {
                        anyhow::bail!(
                            "invalid feature `{}` in required-features of target `{}`: \
                      optional dependency with `?` is not allowed in required-features",
                            fv,
                            target_name
                        );
                    }
                    // Handling of dependent_crate/dependent_crate_feature syntax
                    FeatureValue::DepFeature {
                        dep_name,
                        dep_feature,
                        weak: false,
                    } => {
                        match resolve.deps(summary.package_id()).find(|(_dep_id, deps)| {
                            deps.iter().any(|dep| dep.name_in_toml() == *dep_name)
                        }) {
                            Some((dep_id, _deps)) => {
                                let dep_summary = resolve.summary(dep_id);
                                if !dep_summary.features().contains_key(dep_feature)
                                    && !dep_summary.dependencies().iter().any(|dep| {
                                        dep.name_in_toml() == *dep_feature && dep.is_optional()
                                    })
                                {
                                    shell.warn(format!(
                                        "invalid feature `{}` in required-features of target `{}`: \
                                  feature `{}` does not exist in package `{}`",
                                        fv, target_name, dep_feature, dep_id
                                    ))?;
                                }
                            }
                            None => {
                                shell.warn(format!(
                                    "invalid feature `{}` in required-features of target `{}`: \
                              dependency `{}` does not exist",
                                    fv, target_name, dep_name
                                ))?;
                            }
                        }
                    }
                }
            }
            Ok(())
        }

        /// Converts proposals to units based on each target's required features.
        fn proposals_to_units(&self, proposals: Vec<Proposal<'_>>) -> CargoResult<Vec<Unit>> {
            // Only include targets that are libraries or have all required
            // features available.
            //
            // `features_map` is a map of &Package -> enabled_features
            // It is computed by the set of enabled features for the package plus
            // every enabled feature of every enabled dependency.
            let mut features_map = HashMap::new();
            // This needs to be a set to de-duplicate units. Due to the way the
            // targets are filtered, it is possible to have duplicate proposals for
            // the same thing.
            let mut units = HashSet::new();
            for Proposal {
                pkg,
                target,
                requires_features,
                mode,
            } in proposals
            {
                let unavailable_features = match target.required_features() {
                    Some(rf) => {
                        self.validate_required_features(target.name(), rf, pkg.summary())?;

                        let features = features_map.entry(pkg).or_insert_with(|| {
                            super::resolve_all_features(
                                self.resolve,
                                self.resolved_features,
                                self.package_set,
                                pkg.package_id(),
                            )
                        });
                        rf.iter().filter(|f| !features.contains(*f)).collect()
                    }
                    None => Vec::new(),
                };
                if target.is_lib() || unavailable_features.is_empty() {
                    units.extend(self.new_units(pkg, target, mode));
                } else if requires_features {
                    let required_features = target.required_features().unwrap();
                    let quoted_required_features: Vec<String> = required_features
                        .iter()
                        .map(|s| format!("`{}`", s))
                        .collect();
                    anyhow::bail!(
                        "target `{}` in package `{}` requires the features: {}\n\
                   Consider enabling them by passing, e.g., `--features=\"{}\"`",
                        target.name(),
                        pkg.name(),
                        quoted_required_features.join(", "),
                        required_features.join(" ")
                    );
                }
                // else, silently skip target.
            }
            let mut units: Vec<_> = units.into_iter().collect();
            self.unmatched_target_filters(&units)?;

            // Keep the roots in a consistent order, which helps with checking test output.
            units.sort_unstable();
            Ok(units)
        }

        /// Generates all the base units for the packages the user has requested to
        /// compile. Dependencies for these units are computed later in [`unit_dependencies`].
        ///
        /// [`unit_dependencies`]: crate::core::compiler::unit_dependencies
        pub fn generate_root_units(&self) -> CargoResult<Vec<Unit>> {
            let proposals = self.create_proposals()?;
            self.proposals_to_units(proposals)
        }

        /// Generates units specifically for doc-scraping.
        ///
        /// This requires a separate entrypoint from [`generate_root_units`] because it
        /// takes the documented units as input.
        ///
        /// [`generate_root_units`]: Self::generate_root_units
        pub fn generate_scrape_units(&self, doc_units: &[Unit]) -> CargoResult<Vec<Unit>> {
            let scrape_proposals = self.create_docscrape_proposals(&doc_units)?;
            let scrape_units = self.proposals_to_units(scrape_proposals)?;
            Ok(scrape_units)
        }
    }