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    //! Utilities for building with rustdoc.

    use crate::core::compiler::context::Context;
    use crate::core::compiler::unit::Unit;
    use crate::core::compiler::{BuildContext, CompileKind};
    use crate::sources::CRATES_IO_REGISTRY;
    use crate::util::errors::{internal, CargoResult};
    use cargo_util::ProcessBuilder;
    use std::collections::HashMap;
    use std::fmt;
    use std::hash;
    use url::Url;

    use super::CompileMode;

    const DOCS_RS_URL: &'static str = "https://docs.rs/";

    /// Mode used for `std`. This is for unstable feature [`-Zrustdoc-map`][1].
    ///
    /// [1]: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#rustdoc-map
    #[derive(Debug, Hash)]
    pub enum RustdocExternMode {
        /// Use a local `file://` URL.
        Local,
        /// Use a remote URL to <https://doc.rust-lang.org/> (default).
        Remote,
        /// An arbitrary URL.
        Url(String),
    }

    impl From<String> for RustdocExternMode {
        fn from(s: String) -> RustdocExternMode {
            match s.as_ref() {
                "local" => RustdocExternMode::Local,
                "remote" => RustdocExternMode::Remote,
                _ => RustdocExternMode::Url(s),
            }
        }
    }

    impl fmt::Display for RustdocExternMode {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            match self {
                RustdocExternMode::Local => "local".fmt(f),
                RustdocExternMode::Remote => "remote".fmt(f),
                RustdocExternMode::Url(s) => s.fmt(f),
            }
        }
    }

    impl<'de> serde::de::Deserialize<'de> for RustdocExternMode {
        fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
        where
            D: serde::de::Deserializer<'de>,
        {
            let s = String::deserialize(deserializer)?;
            Ok(s.into())
        }
    }

    /// A map of registry names to URLs where documentations are hosted.
    /// This is for unstable feature [`-Zrustdoc-map`][1].
    ///
    /// [1]: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#rustdoc-map
    #[derive(serde::Deserialize, Debug)]
    #[serde(default)]
    pub struct RustdocExternMap {
        #[serde(deserialize_with = "default_crates_io_to_docs_rs")]
        /// * Key is the registry name in the configuration `[registries.<name>]`.
        /// * Value is the URL where the documentation is hosted.
        registries: HashMap<String, String>,
        std: Option<RustdocExternMode>,
    }

    impl Default for RustdocExternMap {
        fn default() -> Self {
            Self {
                registries: HashMap::from([(CRATES_IO_REGISTRY.into(), DOCS_RS_URL.into())]),
                std: None,
            }
        }
    }

    fn default_crates_io_to_docs_rs<'de, D: serde::Deserializer<'de>>(
        de: D,
    ) -> Result<HashMap<String, String>, D::Error> {
        use serde::Deserialize;
        let mut registries = HashMap::deserialize(de)?;
        if !registries.contains_key(CRATES_IO_REGISTRY) {
            registries.insert(CRATES_IO_REGISTRY.into(), DOCS_RS_URL.into());
        }
        Ok(registries)
    }

    impl hash::Hash for RustdocExternMap {
        fn hash<H: hash::Hasher>(&self, into: &mut H) {
            self.std.hash(into);
            for (key, value) in &self.registries {
                key.hash(into);
                value.hash(into);
            }
        }
    }

    /// Adds unstable flag [`--extern-html-root-url`][1] to the given `rustdoc`
    /// invocation. This is for unstable feature [`-Zrustdoc-map`][2].
    ///
    /// [1]: https://doc.rust-lang.org/nightly/rustdoc/unstable-features.html#--extern-html-root-url-control-how-rustdoc-links-to-non-local-crates
    /// [2]: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#rustdoc-map
    pub fn add_root_urls(
        cx: &Context<'_, '_>,
        unit: &Unit,
        rustdoc: &mut ProcessBuilder,
    ) -> CargoResult<()> {
        let config = cx.bcx.config;
        if !config.cli_unstable().rustdoc_map {
            tracing::debug!("`doc.extern-map` ignored, requires -Zrustdoc-map flag");
            return Ok(());
        }
        let map = config.doc_extern_map()?;
        let mut unstable_opts = false;
        // Collect mapping of registry name -> index url.
        let name2url: HashMap<&String, Url> = map
            .registries
            .keys()
            .filter_map(|name| {
                if let Ok(index_url) = config.get_registry_index(name) {
                    Some((name, index_url))
                } else {
                    tracing::warn!(
                        "`doc.extern-map.{}` specifies a registry that is not defined",
                        name
                    );
                    None
                }
            })
            .collect();
        for dep in cx.unit_deps(unit) {
            if dep.unit.target.is_linkable() && !dep.unit.mode.is_doc() {
                for (registry, location) in &map.registries {
                    let sid = dep.unit.pkg.package_id().source_id();
                    let matches_registry = || -> bool {
                        if !sid.is_registry() {
                            return false;
                        }
                        if sid.is_crates_io() {
                            return registry == CRATES_IO_REGISTRY;
                        }
                        if let Some(index_url) = name2url.get(registry) {
                            return index_url == sid.url();
                        }
                        false
                    };
                    if matches_registry() {
                        let mut url = location.clone();
                        if !url.contains("{pkg_name}") && !url.contains("{version}") {
                            if !url.ends_with('/') {
                                url.push('/');
                            }
                            url.push_str("{pkg_name}/{version}/");
                        }
                        let url = url
                            .replace("{pkg_name}", &dep.unit.pkg.name())
                            .replace("{version}", &dep.unit.pkg.version().to_string());
                        rustdoc.arg("--extern-html-root-url");
                        rustdoc.arg(format!("{}={}", dep.unit.target.crate_name(), url));
                        unstable_opts = true;
                    }
                }
            }
        }
        let std_url = match &map.std {
            None | Some(RustdocExternMode::Remote) => None,
            Some(RustdocExternMode::Local) => {
                let sysroot = &cx.bcx.target_data.info(CompileKind::Host).sysroot;
                let html_root = sysroot.join("share").join("doc").join("rust").join("html");
                if html_root.exists() {
                    let url = Url::from_file_path(&html_root).map_err(|()| {
                        internal(format!(
                            "`{}` failed to convert to URL",
                            html_root.display()
                        ))
                    })?;
                    Some(url.to_string())
                } else {
                    tracing::warn!(
                        "`doc.extern-map.std` is \"local\", but local docs don't appear to exist at {}",
                        html_root.display()
                    );
                    None
                }
            }
            Some(RustdocExternMode::Url(s)) => Some(s.to_string()),
        };
        if let Some(url) = std_url {
            for name in &["std", "core", "alloc", "proc_macro"] {
                rustdoc.arg("--extern-html-root-url");
                rustdoc.arg(format!("{}={}", name, url));
                unstable_opts = true;
            }
        }

        if unstable_opts {
            rustdoc.arg("-Zunstable-options");
        }
        Ok(())
    }

    /// Adds unstable flag [`--output-format`][1] to the given `rustdoc`
    /// invocation. This is for unstable feature [`-Zunstable-features`].
    ///
    /// [1]: https://doc.rust-lang.org/nightly/rustdoc/unstable-features.html?highlight=output-format#-w--output-format-output-format
    pub fn add_output_format(
        cx: &Context<'_, '_>,
        unit: &Unit,
        rustdoc: &mut ProcessBuilder,
    ) -> CargoResult<()> {
        let config = cx.bcx.config;
        if !config.cli_unstable().unstable_options {
            tracing::debug!("`unstable-options` is ignored, required -Zunstable-options flag");
            return Ok(());
        }

        if let CompileMode::Doc { json: true, .. } = unit.mode {
            rustdoc.arg("-Zunstable-options");
            rustdoc.arg("--output-format=json");
        }

        Ok(())
    }

    /// Indicates whether a target should have examples scraped from it by rustdoc.
    /// Configured within Cargo.toml and only for unstable feature
    /// [`-Zrustdoc-scrape-examples`][1].
    ///
    /// [1]: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#scrape-examples
    #[derive(Clone, Hash, PartialEq, Eq, PartialOrd, Ord, Debug, Copy)]
    pub enum RustdocScrapeExamples {
        Enabled,
        Disabled,
        Unset,
    }

    impl RustdocScrapeExamples {
        pub fn is_enabled(&self) -> bool {
            matches!(self, RustdocScrapeExamples::Enabled)
        }

        pub fn is_unset(&self) -> bool {
            matches!(self, RustdocScrapeExamples::Unset)
        }
    }

    impl BuildContext<'_, '_> {
        /// Returns the set of [`Docscrape`] units that have a direct dependency on `unit`.
        ///
        /// [`RunCustomBuild`] units are excluded because we allow failures
        /// from type checks but not build script executions.
        /// A plain old `cargo doc` would just die if a build script execution fails,
        /// there is no reason for `-Zrustdoc-scrape-examples` to keep going.
        ///
        /// [`Docscrape`]: crate::core::compiler::CompileMode::Docscrape
        /// [`RunCustomBuild`]: crate::core::compiler::CompileMode::Docscrape
        pub fn scrape_units_have_dep_on<'a>(&'a self, unit: &'a Unit) -> Vec<&'a Unit> {
            self.scrape_units
                .iter()
                .filter(|scrape_unit| {
                    self.unit_graph[scrape_unit]
                        .iter()
                        .any(|dep| &dep.unit == unit && !dep.unit.mode.is_run_custom_build())
                })
                .collect()
        }

        /// Returns true if this unit is needed for doing doc-scraping and is also
        /// allowed to fail without killing the build.
        pub fn unit_can_fail_for_docscraping(&self, unit: &Unit) -> bool {
            // If the unit is not a Docscrape unit, e.g. a Lib target that is
            // checked to scrape an Example target, then we need to get the doc-scrape-examples
            // configuration for the reverse-dependent Example target.
            let for_scrape_units = if unit.mode.is_doc_scrape() {
                vec![unit]
            } else {
                self.scrape_units_have_dep_on(unit)
            };

            if for_scrape_units.is_empty() {
                false
            } else {
                // All Docscrape units must have doc-scrape-examples unset. If any are true,
                // then the unit is not allowed to fail.
                for_scrape_units
                    .iter()
                    .all(|unit| unit.target.doc_scrape_examples().is_unset())
            }
        }
    }