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    use std::collections::hash_map::HashMap;
    use std::env;
    use std::hash::{Hash, Hasher};
    use std::path::{Path, PathBuf};
    use std::sync::Mutex;

    use anyhow::Context as _;
    use cargo_util::{paths, ProcessBuilder, ProcessError};
    use serde::{Deserialize, Serialize};
    use tracing::{debug, info, warn};

    use crate::core::compiler::apply_env_config;
    use crate::util::interning::InternedString;
    use crate::util::{CargoResult, GlobalContext, StableHasher};

    /// Information on the `rustc` executable
    #[derive(Debug)]
    pub struct Rustc {
        /// The location of the exe
        pub path: PathBuf,
        /// An optional program that will be passed the path of the rust exe as its first argument, and
        /// rustc args following this.
        pub wrapper: Option<PathBuf>,
        /// An optional wrapper to be used in addition to `rustc.wrapper` for workspace crates
        pub workspace_wrapper: Option<PathBuf>,
        /// Verbose version information (the output of `rustc -vV`)
        pub verbose_version: String,
        /// The rustc version (`1.23.4-beta.2`), this comes from verbose_version.
        pub version: semver::Version,
        /// The host triple (arch-platform-OS), this comes from verbose_version.
        pub host: InternedString,
        /// The rustc full commit hash, this comes from `verbose_version`.
        pub commit_hash: Option<String>,
        cache: Mutex<Cache>,
    }

    impl Rustc {
        /// Runs the compiler at `path` to learn various pieces of information about
        /// it, with an optional wrapper.
        ///
        /// If successful this function returns a description of the compiler along
        /// with a list of its capabilities.
        #[tracing::instrument(skip(gctx))]
        pub fn new(
            path: PathBuf,
            wrapper: Option<PathBuf>,
            workspace_wrapper: Option<PathBuf>,
            rustup_rustc: &Path,
            cache_location: Option<PathBuf>,
            gctx: &GlobalContext,
        ) -> CargoResult<Rustc> {
            let mut cache = Cache::load(
                wrapper.as_deref(),
                workspace_wrapper.as_deref(),
                &path,
                rustup_rustc,
                cache_location,
                gctx,
            );

            let mut cmd = ProcessBuilder::new(&path)
                .wrapped(workspace_wrapper.as_ref())
                .wrapped(wrapper.as_deref());
            apply_env_config(gctx, &mut cmd)?;
            cmd.arg("-vV");
            let verbose_version = cache.cached_output(&cmd, 0)?.0;

            let extract = |field: &str| -> CargoResult<&str> {
                verbose_version
                    .lines()
                    .find_map(|l| l.strip_prefix(field))
                    .ok_or_else(|| {
                        anyhow::format_err!(
                            "`rustc -vV` didn't have a line for `{}`, got:\n{}",
                            field.trim(),
                            verbose_version
                        )
                    })
            };

            let host = InternedString::new(extract("host: ")?);
            let version = semver::Version::parse(extract("release: ")?).with_context(|| {
                format!(
                    "rustc version does not appear to be a valid semver version, from:\n{}",
                    verbose_version
                )
            })?;
            let commit_hash = extract("commit-hash: ").ok().map(|hash| {
                // Possible commit-hash values from rustc are SHA hex string and "unknown". See:
                // * https://github.com/rust-lang/rust/blob/531cb83fc/src/bootstrap/src/utils/channel.rs#L73
                // * https://github.com/rust-lang/rust/blob/531cb83fc/compiler/rustc_driver_impl/src/lib.rs#L911-L913
                #[cfg(debug_assertions)]
                if hash != "unknown" {
                    debug_assert!(
                        hash.chars().all(|ch| ch.is_ascii_hexdigit()),
                        "commit hash must be a hex string, got: {hash:?}"
                    );
                    debug_assert!(
                        hash.len() == 40 || hash.len() == 64,
                        "hex string must be generated from sha1 or sha256 (i.e., it must be 40 or 64 characters long)\ngot: {hash:?}"
                    );
                }
                hash.to_string()
            });

            Ok(Rustc {
                path,
                wrapper,
                workspace_wrapper,
                verbose_version,
                version,
                host,
                commit_hash,
                cache: Mutex::new(cache),
            })
        }

        /// Gets a process builder set up to use the found rustc version, with a wrapper if `Some`.
        pub fn process(&self) -> ProcessBuilder {
            let mut cmd = ProcessBuilder::new(self.path.as_path()).wrapped(self.wrapper.as_ref());
            cmd.retry_with_argfile(true);
            cmd
        }

        /// Gets a process builder set up to use the found rustc version, with a wrapper if `Some`.
        pub fn workspace_process(&self) -> ProcessBuilder {
            let mut cmd = ProcessBuilder::new(self.path.as_path())
                .wrapped(self.workspace_wrapper.as_ref())
                .wrapped(self.wrapper.as_ref());
            cmd.retry_with_argfile(true);
            cmd
        }

        pub fn process_no_wrapper(&self) -> ProcessBuilder {
            let mut cmd = ProcessBuilder::new(&self.path);
            cmd.retry_with_argfile(true);
            cmd
        }

        /// Gets the output for the given command.
        ///
        /// This will return the cached value if available, otherwise it will run
        /// the command and cache the output.
        ///
        /// `extra_fingerprint` is extra data to include in the cache fingerprint.
        /// Use this if there is other information about the environment that may
        /// affect the output that is not part of `cmd`.
        ///
        /// Returns a tuple of strings `(stdout, stderr)`.
        pub fn cached_output(
            &self,
            cmd: &ProcessBuilder,
            extra_fingerprint: u64,
        ) -> CargoResult<(String, String)> {
            self.cache
                .lock()
                .unwrap()
                .cached_output(cmd, extra_fingerprint)
        }
    }

    /// It is a well known fact that `rustc` is not the fastest compiler in the
    /// world.  What is less known is that even `rustc --version --verbose` takes
    /// about a hundred milliseconds! Because we need compiler version info even
    /// for no-op builds, we cache it here, based on compiler's mtime and rustup's
    /// current toolchain.
    ///
    /// <https://github.com/rust-lang/cargo/issues/5315>
    /// <https://github.com/rust-lang/rust/issues/49761>
    #[derive(Debug)]
    struct Cache {
        cache_location: Option<PathBuf>,
        dirty: bool,
        data: CacheData,
    }

    #[derive(Serialize, Deserialize, Debug, Default)]
    struct CacheData {
        rustc_fingerprint: u64,
        outputs: HashMap<u64, Output>,
        successes: HashMap<u64, bool>,
    }

    #[derive(Serialize, Deserialize, Debug)]
    struct Output {
        success: bool,
        status: String,
        code: Option<i32>,
        stdout: String,
        stderr: String,
    }

    impl Cache {
        fn load(
            wrapper: Option<&Path>,
            workspace_wrapper: Option<&Path>,
            rustc: &Path,
            rustup_rustc: &Path,
            cache_location: Option<PathBuf>,
            gctx: &GlobalContext,
        ) -> Cache {
            match (
                cache_location,
                rustc_fingerprint(wrapper, workspace_wrapper, rustc, rustup_rustc, gctx),
            ) {
                (Some(cache_location), Ok(rustc_fingerprint)) => {
                    let empty = CacheData {
                        rustc_fingerprint,
                        outputs: HashMap::new(),
                        successes: HashMap::new(),
                    };
                    let mut dirty = true;
                    let data = match read(&cache_location) {
                        Ok(data) => {
                            if data.rustc_fingerprint == rustc_fingerprint {
                                debug!("reusing existing rustc info cache");
                                dirty = false;
                                data
                            } else {
                                debug!("different compiler, creating new rustc info cache");
                                empty
                            }
                        }
                        Err(e) => {
                            debug!("failed to read rustc info cache: {}", e);
                            empty
                        }
                    };
                    return Cache {
                        cache_location: Some(cache_location),
                        dirty,
                        data,
                    };

                    fn read(path: &Path) -> CargoResult<CacheData> {
                        let json = paths::read(path)?;
                        Ok(serde_json::from_str(&json)?)
                    }
                }
                (_, fingerprint) => {
                    if let Err(e) = fingerprint {
                        warn!("failed to calculate rustc fingerprint: {}", e);
                    }
                    debug!("rustc info cache disabled");
                    Cache {
                        cache_location: None,
                        dirty: false,
                        data: CacheData::default(),
                    }
                }
            }
        }

        fn cached_output(
            &mut self,
            cmd: &ProcessBuilder,
            extra_fingerprint: u64,
        ) -> CargoResult<(String, String)> {
            let key = process_fingerprint(cmd, extra_fingerprint);
            if self.data.outputs.contains_key(&key) {
                debug!("rustc info cache hit");
            } else {
                debug!("rustc info cache miss");
                debug!("running {}", cmd);
                let output = cmd.output()?;
                let stdout = String::from_utf8(output.stdout)
                    .map_err(|e| anyhow::anyhow!("{}: {:?}", e, e.as_bytes()))
                    .with_context(|| format!("`{}` didn't return utf8 output", cmd))?;
                let stderr = String::from_utf8(output.stderr)
                    .map_err(|e| anyhow::anyhow!("{}: {:?}", e, e.as_bytes()))
                    .with_context(|| format!("`{}` didn't return utf8 output", cmd))?;
                self.data.outputs.insert(
                    key,
                    Output {
                        success: output.status.success(),
                        status: if output.status.success() {
                            String::new()
                        } else {
                            cargo_util::exit_status_to_string(output.status)
                        },
                        code: output.status.code(),
                        stdout,
                        stderr,
                    },
                );
                self.dirty = true;
            }
            let output = &self.data.outputs[&key];
            if output.success {
                Ok((output.stdout.clone(), output.stderr.clone()))
            } else {
                Err(ProcessError::new_raw(
                    &format!("process didn't exit successfully: {}", cmd),
                    output.code,
                    &output.status,
                    Some(output.stdout.as_ref()),
                    Some(output.stderr.as_ref()),
                )
                .into())
            }
        }
    }

    impl Drop for Cache {
        fn drop(&mut self) {
            if !self.dirty {
                return;
            }
            if let Some(ref path) = self.cache_location {
                let json = serde_json::to_string(&self.data).unwrap();
                match paths::write(path, json.as_bytes()) {
                    Ok(()) => info!("updated rustc info cache"),
                    Err(e) => warn!("failed to update rustc info cache: {}", e),
                }
            }
        }
    }

    fn rustc_fingerprint(
        wrapper: Option<&Path>,
        workspace_wrapper: Option<&Path>,
        rustc: &Path,
        rustup_rustc: &Path,
        gctx: &GlobalContext,
    ) -> CargoResult<u64> {
        let mut hasher = StableHasher::new();

        let hash_exe = |hasher: &mut _, path| -> CargoResult<()> {
            let path = paths::resolve_executable(path)?;
            path.hash(hasher);

            paths::mtime(&path)?.hash(hasher);
            Ok(())
        };

        hash_exe(&mut hasher, rustc)?;
        if let Some(wrapper) = wrapper {
            hash_exe(&mut hasher, wrapper)?;
        }
        if let Some(workspace_wrapper) = workspace_wrapper {
            hash_exe(&mut hasher, workspace_wrapper)?;
        }

        // Rustup can change the effective compiler without touching
        // the `rustc` binary, so we try to account for this here.
        // If we see rustup's env vars, we mix them into the fingerprint,
        // but we also mix in the mtime of the actual compiler (and not
        // the rustup shim at `~/.cargo/bin/rustup`), because `RUSTUP_TOOLCHAIN`
        // could be just `stable-x86_64-unknown-linux-gnu`, i.e, it could
        // not mention the version of Rust at all, which changes after
        // `rustup update`.
        //
        // If we don't see rustup env vars, but it looks like the compiler
        // is managed by rustup, we conservatively bail out.
        let maybe_rustup = rustup_rustc == rustc;
        match (
            maybe_rustup,
            gctx.get_env("RUSTUP_HOME"),
            gctx.get_env("RUSTUP_TOOLCHAIN"),
        ) {
            (_, Ok(rustup_home), Ok(rustup_toolchain)) => {
                debug!("adding rustup info to rustc fingerprint");
                rustup_toolchain.hash(&mut hasher);
                rustup_home.hash(&mut hasher);
                let real_rustc = Path::new(&rustup_home)
                    .join("toolchains")
                    .join(rustup_toolchain)
                    .join("bin")
                    .join("rustc")
                    .with_extension(env::consts::EXE_EXTENSION);
                paths::mtime(&real_rustc)?.hash(&mut hasher);
            }
            (true, _, _) => anyhow::bail!("probably rustup rustc, but without rustup's env vars"),
            _ => (),
        }

        Ok(hasher.finish())
    }

    fn process_fingerprint(cmd: &ProcessBuilder, extra_fingerprint: u64) -> u64 {
        let mut hasher = StableHasher::new();
        extra_fingerprint.hash(&mut hasher);
        cmd.get_args().for_each(|arg| arg.hash(&mut hasher));
        let mut env = cmd.get_envs().iter().collect::<Vec<_>>();
        env.sort_unstable();
        env.hash(&mut hasher);
        hasher.finish()
    }