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    use super::{Config, ConfigKey, ConfigRelativePath, OptValue, PathAndArgs, StringList, CV};
    use crate::core::compiler::{BuildOutput, LinkArgTarget};
    use crate::util::CargoResult;
    use serde::Deserialize;
    use std::collections::{BTreeMap, HashMap};
    use std::path::PathBuf;

    /// Config definition of a `[target.'cfg(…)']` table.
    ///
    /// This is a subset of `TargetConfig`.
    #[derive(Debug, Deserialize)]
    pub struct TargetCfgConfig {
        pub runner: OptValue<PathAndArgs>,
        pub rustflags: OptValue<StringList>,
        // This is here just to ignore fields from normal `TargetConfig` because
        // all `[target]` tables are getting deserialized, whether they start with
        // `cfg(` or not.
        #[serde(flatten)]
        pub other: BTreeMap<String, toml::Value>,
    }

    /// Config definition of a `[target]` table or `[host]`.
    #[derive(Debug, Clone)]
    pub struct TargetConfig {
        /// Process to run as a wrapper for `cargo run`, `test`, and `bench` commands.
        pub runner: OptValue<PathAndArgs>,
        /// Additional rustc flags to pass.
        pub rustflags: OptValue<StringList>,
        /// The path of the linker for this target.
        pub linker: OptValue<ConfigRelativePath>,
        /// Build script override for the given library name.
        ///
        /// Any package with a `links` value for the given library name will skip
        /// running its build script and instead use the given output from the
        /// config file.
        pub links_overrides: BTreeMap<String, BuildOutput>,
    }

    /// Loads all of the `target.'cfg()'` tables.
    pub(super) fn load_target_cfgs(config: &Config) -> CargoResult<Vec<(String, TargetCfgConfig)>> {
        // Load all [target] tables, filter out the cfg() entries.
        let mut result = Vec::new();
        // Use a BTreeMap so the keys are sorted. This is important for
        // deterministic ordering of rustflags, which affects fingerprinting and
        // rebuilds. We may perhaps one day wish to ensure a deterministic
        // ordering via the order keys were defined in files perhaps.
        let target: BTreeMap<String, TargetCfgConfig> = config.get("target")?;
        tracing::debug!("Got all targets {:#?}", target);
        for (key, cfg) in target {
            if key.starts_with("cfg(") {
                // Unfortunately this is not able to display the location of the
                // unused key. Using config::Value<toml::Value> doesn't work. One
                // solution might be to create a special "Any" type, but I think
                // that will be quite difficult with the current design.
                for other_key in cfg.other.keys() {
                    config.shell().warn(format!(
                        "unused key `{}` in [target] config table `{}`",
                        other_key, key
                    ))?;
                }
                result.push((key, cfg));
            }
        }
        Ok(result)
    }

    /// Returns true if the `[target]` table should be applied to host targets.
    pub(super) fn get_target_applies_to_host(config: &Config) -> CargoResult<bool> {
        if config.cli_unstable().target_applies_to_host {
            if let Ok(target_applies_to_host) = config.get::<bool>("target-applies-to-host") {
                Ok(target_applies_to_host)
            } else {
                Ok(!config.cli_unstable().host_config)
            }
        } else if config.cli_unstable().host_config {
            anyhow::bail!(
                "the -Zhost-config flag requires the -Ztarget-applies-to-host flag to be set"
            );
        } else {
            Ok(true)
        }
    }

    /// Loads a single `[host]` table for the given triple.
    pub(super) fn load_host_triple(config: &Config, triple: &str) -> CargoResult<TargetConfig> {
        if config.cli_unstable().host_config {
            let host_triple_prefix = format!("host.{}", triple);
            let host_triple_key = ConfigKey::from_str(&host_triple_prefix);
            let host_prefix = match config.get_cv(&host_triple_key)? {
                Some(_) => host_triple_prefix,
                None => "host".to_string(),
            };
            load_config_table(config, &host_prefix)
        } else {
            Ok(TargetConfig {
                runner: None,
                rustflags: None,
                linker: None,
                links_overrides: BTreeMap::new(),
            })
        }
    }

    /// Loads a single `[target]` table for the given triple.
    pub(super) fn load_target_triple(config: &Config, triple: &str) -> CargoResult<TargetConfig> {
        load_config_table(config, &format!("target.{}", triple))
    }

    /// Loads a single table for the given prefix.
    fn load_config_table(config: &Config, prefix: &str) -> CargoResult<TargetConfig> {
        // This needs to get each field individually because it cannot fetch the
        // struct all at once due to `links_overrides`. Can't use `serde(flatten)`
        // because it causes serde to use `deserialize_map` which means the config
        // deserializer does not know which keys to deserialize, which means
        // environment variables would not work.
        let runner: OptValue<PathAndArgs> = config.get(&format!("{}.runner", prefix))?;
        let rustflags: OptValue<StringList> = config.get(&format!("{}.rustflags", prefix))?;
        let linker: OptValue<ConfigRelativePath> = config.get(&format!("{}.linker", prefix))?;
        // Links do not support environment variables.
        let target_key = ConfigKey::from_str(prefix);
        let links_overrides = match config.get_table(&target_key)? {
            Some(links) => parse_links_overrides(&target_key, links.val, config)?,
            None => BTreeMap::new(),
        };
        Ok(TargetConfig {
            runner,
            rustflags,
            linker,
            links_overrides,
        })
    }

    fn parse_links_overrides(
        target_key: &ConfigKey,
        links: HashMap<String, CV>,
        config: &Config,
    ) -> CargoResult<BTreeMap<String, BuildOutput>> {
        let mut links_overrides = BTreeMap::new();
        let extra_check_cfg = match config.cli_unstable().check_cfg {
            Some((_, _, _, output)) => output,
            None => false,
        };

        for (lib_name, value) in links {
            // Skip these keys, it shares the namespace with `TargetConfig`.
            match lib_name.as_str() {
                // `ar` is a historical thing.
                "ar" | "linker" | "runner" | "rustflags" => continue,
                _ => {}
            }
            let mut output = BuildOutput::default();
            let table = value.table(&format!("{}.{}", target_key, lib_name))?.0;
            // We require deterministic order of evaluation, so we must sort the pairs by key first.
            let mut pairs = Vec::new();
            for (k, value) in table {
                pairs.push((k, value));
            }
            pairs.sort_by_key(|p| p.0);
            for (key, value) in pairs {
                match key.as_str() {
                    "rustc-flags" => {
                        let flags = value.string(key)?;
                        let whence = format!("target config `{}.{}` (in {})", target_key, key, flags.1);
                        let (paths, links) = BuildOutput::parse_rustc_flags(flags.0, &whence)?;
                        output.library_paths.extend(paths);
                        output.library_links.extend(links);
                    }
                    "rustc-link-lib" => {
                        let list = value.list(key)?;
                        output
                            .library_links
                            .extend(list.iter().map(|v| v.0.clone()));
                    }
                    "rustc-link-search" => {
                        let list = value.list(key)?;
                        output
                            .library_paths
                            .extend(list.iter().map(|v| PathBuf::from(&v.0)));
                    }
                    "rustc-link-arg-cdylib" | "rustc-cdylib-link-arg" => {
                        let args = extra_link_args(LinkArgTarget::Cdylib, key, value)?;
                        output.linker_args.extend(args);
                    }
                    "rustc-link-arg-bins" => {
                        let args = extra_link_args(LinkArgTarget::Bin, key, value)?;
                        output.linker_args.extend(args);
                    }
                    "rustc-link-arg" => {
                        let args = extra_link_args(LinkArgTarget::All, key, value)?;
                        output.linker_args.extend(args);
                    }
                    "rustc-link-arg-tests" => {
                        let args = extra_link_args(LinkArgTarget::Test, key, value)?;
                        output.linker_args.extend(args);
                    }
                    "rustc-link-arg-benches" => {
                        let args = extra_link_args(LinkArgTarget::Bench, key, value)?;
                        output.linker_args.extend(args);
                    }
                    "rustc-link-arg-examples" => {
                        let args = extra_link_args(LinkArgTarget::Example, key, value)?;
                        output.linker_args.extend(args);
                    }
                    "rustc-cfg" => {
                        let list = value.list(key)?;
                        output.cfgs.extend(list.iter().map(|v| v.0.clone()));
                    }
                    "rustc-check-cfg" => {
                        if extra_check_cfg {
                            let list = value.list(key)?;
                            output.check_cfgs.extend(list.iter().map(|v| v.0.clone()));
                        } else {
                            config.shell().warn(format!(
                                "target config `{}.{}` requires -Zcheck-cfg=output flag",
                                target_key, key
                            ))?;
                        }
                    }
                    "rustc-env" => {
                        for (name, val) in value.table(key)?.0 {
                            let val = val.string(name)?.0;
                            output.env.push((name.clone(), val.to_string()));
                        }
                    }
                    "warning" | "rerun-if-changed" | "rerun-if-env-changed" => {
                        anyhow::bail!("`{}` is not supported in build script overrides", key);
                    }
                    _ => {
                        let val = value.string(key)?.0;
                        output.metadata.push((key.clone(), val.to_string()));
                    }
                }
            }
            links_overrides.insert(lib_name, output);
        }
        Ok(links_overrides)
    }

    fn extra_link_args<'a>(
        link_type: LinkArgTarget,
        key: &str,
        value: &'a CV,
    ) -> CargoResult<impl Iterator<Item = (LinkArgTarget, String)> + 'a> {
        let args = value.list(key)?;
        Ok(args.iter().map(move |v| (link_type.clone(), v.0.clone())))
    }