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    //! Code for building the standard library.

    use crate::core::compiler::unit_dependencies::IsArtifact;
    use crate::core::compiler::UnitInterner;
    use crate::core::compiler::{CompileKind, CompileMode, RustcTargetData, Unit};
    use crate::core::profiles::{Profiles, UnitFor};
    use crate::core::resolver::features::{CliFeatures, FeaturesFor, ResolvedFeatures};
    use crate::core::resolver::HasDevUnits;
    use crate::core::{Dependency, PackageId, PackageSet, Resolve, SourceId, Workspace};
    use crate::ops::{self, Packages};
    use crate::util::errors::CargoResult;
    use crate::GlobalContext;
    use std::collections::{HashMap, HashSet};
    use std::path::PathBuf;
    use std::rc::Rc;

    use super::BuildConfig;

    /// Parse the `-Zbuild-std` flag.
    pub fn parse_unstable_flag(value: Option<&str>) -> Vec<String> {
        // This is a temporary hack until there is a more principled way to
        // declare dependencies in Cargo.toml.
        let value = value.unwrap_or("std");
        let mut crates: HashSet<&str> = value.split(',').collect();
        if crates.contains("std") {
            crates.insert("core");
            crates.insert("alloc");
            crates.insert("proc_macro");
            crates.insert("panic_unwind");
            crates.insert("compiler_builtins");
        } else if crates.contains("core") {
            crates.insert("compiler_builtins");
        }
        crates.into_iter().map(|s| s.to_string()).collect()
    }

    pub(crate) fn std_crates(gctx: &GlobalContext, units: Option<&[Unit]>) -> Option<Vec<String>> {
        let crates = gctx.cli_unstable().build_std.as_ref()?.clone();

        // Only build libtest if it looks like it is needed.
        let mut crates = crates.clone();
        // If we know what units we're building, we can filter for libtest depending on the jobs.
        if let Some(units) = units {
            if units
                .iter()
                .any(|unit| unit.mode.is_rustc_test() && unit.target.harness())
            {
                // Only build libtest when libstd is built (libtest depends on libstd)
                if crates.iter().any(|c| c == "std") && !crates.iter().any(|c| c == "test") {
                    crates.push("test".to_string());
                }
            }
        } else {
            // We don't know what jobs are going to be run, so download libtest just in case.
            if !crates.iter().any(|c| c == "test") {
                crates.push("test".to_string())
            }
        }

        Some(crates)
    }

    /// Resolve the standard library dependencies.
    pub fn resolve_std<'gctx>(
        ws: &Workspace<'gctx>,
        target_data: &mut RustcTargetData<'gctx>,
        build_config: &BuildConfig,
        crates: &[String],
    ) -> CargoResult<(PackageSet<'gctx>, Resolve, ResolvedFeatures)> {
        if build_config.build_plan {
            ws.gctx()
                .shell()
                .warn("-Zbuild-std does not currently fully support --build-plan")?;
        }

        let src_path = detect_sysroot_src_path(target_data)?;
        let to_patch = [
            "rustc-std-workspace-core",
            "rustc-std-workspace-alloc",
            "rustc-std-workspace-std",
        ];
        let patches = to_patch
            .iter()
            .map(|&name| {
                let source_path = SourceId::for_path(&src_path.join("library").join(name))?;
                let dep = Dependency::parse(name, None, source_path)?;
                Ok(dep)
            })
            .collect::<CargoResult<Vec<_>>>()?;
        let crates_io_url = crate::sources::CRATES_IO_INDEX.parse().unwrap();
        let patch = HashMap::from([(crates_io_url, patches)]);
        let members = vec![
            String::from("library/std"),
            String::from("library/core"),
            String::from("library/alloc"),
            String::from("library/sysroot"),
        ];
        let ws_config = crate::core::WorkspaceConfig::Root(crate::core::WorkspaceRootConfig::new(
            &src_path,
            &Some(members),
            /*default_members*/ &None,
            /*exclude*/ &None,
            /*inheritable*/ &None,
            /*custom_metadata*/ &None,
        ));
        let virtual_manifest = crate::core::VirtualManifest::new(
            Rc::default(),
            Rc::new(toml_edit::ImDocument::parse("".to_owned()).expect("empty is valid TOML")),
            Rc::default(),
            Rc::default(),
            /*replace*/ Vec::new(),
            patch,
            ws_config,
            crate::core::Features::default(),
            None,
        );

        let gctx = ws.gctx();
        // This is a delicate hack. In order for features to resolve correctly,
        // the resolver needs to run a specific "current" member of the workspace.
        // Thus, in order to set the features for `std`, we need to set `sysroot`
        // to be the "current" member. `sysroot` is the root, and all other
        // standard library crates are dependencies from there. Since none of the
        // other crates need to alter their features, this should be fine, for
        // now. Perhaps in the future features will be decoupled from the resolver
        // and it will be easier to control feature selection.
        let current_manifest = src_path.join("library/sysroot/Cargo.toml");
        // TODO: Consider doing something to enforce --locked? Or to prevent the
        // lock file from being written, such as setting ephemeral.
        let mut std_ws = Workspace::new_virtual(src_path, current_manifest, virtual_manifest, gctx)?;
        // Don't require optional dependencies in this workspace, aka std's own
        // `[dev-dependencies]`. No need for us to generate a `Resolve` which has
        // those included because we'll never use them anyway.
        std_ws.set_require_optional_deps(false);
        // `sysroot` is not in the default set because it is optional, but it needs
        // to be part of the resolve in case we do need it or `libtest`.
        let mut spec_pkgs = Vec::from(crates);
        spec_pkgs.push("sysroot".to_string());
        let spec = Packages::Packages(spec_pkgs);
        let specs = spec.to_package_id_specs(&std_ws)?;
        let features = match &gctx.cli_unstable().build_std_features {
            Some(list) => list.clone(),
            None => vec![
                "panic-unwind".to_string(),
                "backtrace".to_string(),
                "default".to_string(),
            ],
        };
        let cli_features = CliFeatures::from_command_line(
            &features, /*all_features*/ false, /*uses_default_features*/ false,
        )?;
        let resolve = ops::resolve_ws_with_opts(
            &std_ws,
            target_data,
            &build_config.requested_kinds,
            &cli_features,
            &specs,
            HasDevUnits::No,
            crate::core::resolver::features::ForceAllTargets::No,
        )?;
        Ok((
            resolve.pkg_set,
            resolve.targeted_resolve,
            resolve.resolved_features,
        ))
    }

    /// Generate a list of root `Unit`s for the standard library.
    ///
    /// The given slice of crate names is the root set.
    pub fn generate_std_roots(
        crates: &[String],
        std_resolve: &Resolve,
        std_features: &ResolvedFeatures,
        kinds: &[CompileKind],
        package_set: &PackageSet<'_>,
        interner: &UnitInterner,
        profiles: &Profiles,
    ) -> CargoResult<HashMap<CompileKind, Vec<Unit>>> {
        // Generate the root Units for the standard library.
        let std_ids = crates
            .iter()
            .map(|crate_name| std_resolve.query(crate_name))
            .collect::<CargoResult<Vec<PackageId>>>()?;
        // Convert PackageId to Package.
        let std_pkgs = package_set.get_many(std_ids)?;
        // Generate a map of Units for each kind requested.
        let mut ret = HashMap::new();
        for pkg in std_pkgs {
            let lib = pkg
                .targets()
                .iter()
                .find(|t| t.is_lib())
                .expect("std has a lib");
            // I don't think we need to bother with Check here, the difference
            // in time is minimal, and the difference in caching is
            // significant.
            let mode = CompileMode::Build;
            let features = std_features.activated_features(pkg.package_id(), FeaturesFor::NormalOrDev);
            for kind in kinds {
                let list = ret.entry(*kind).or_insert_with(Vec::new);
                let unit_for = UnitFor::new_normal(*kind);
                let profile = profiles.get_profile(
                    pkg.package_id(),
                    /*is_member*/ false,
                    /*is_local*/ false,
                    unit_for,
                    *kind,
                );
                list.push(interner.intern(
                    pkg,
                    lib,
                    profile,
                    *kind,
                    mode,
                    features.clone(),
                    /*is_std*/ true,
                    /*dep_hash*/ 0,
                    IsArtifact::No,
                    None,
                ));
            }
        }
        Ok(ret)
    }

    fn detect_sysroot_src_path(target_data: &RustcTargetData<'_>) -> CargoResult<PathBuf> {
        if let Some(s) = target_data.gctx.get_env_os("__CARGO_TESTS_ONLY_SRC_ROOT") {
            return Ok(s.into());
        }

        // NOTE: This is temporary until we figure out how to acquire the source.
        let src_path = target_data
            .info(CompileKind::Host)
            .sysroot
            .join("lib")
            .join("rustlib")
            .join("src")
            .join("rust");
        let lock = src_path.join("Cargo.lock");
        if !lock.exists() {
            let msg = format!(
                "{:?} does not exist, unable to build with the standard \
                 library, try:\n        rustup component add rust-src",
                lock
            );
            match target_data.gctx.get_env("RUSTUP_TOOLCHAIN") {
                Ok(rustup_toolchain) => {
                    anyhow::bail!("{} --toolchain {}", msg, rustup_toolchain);
                }
                Err(_) => {
                    anyhow::bail!(msg);
                }
            }
        }
        Ok(src_path)
    }