calepin 0.0.20

A Rust CLI for preprocessing Typst documents with executable code chunks
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use std::ffi::{OsStr, OsString};
use std::path::PathBuf;
use std::sync::{Mutex, MutexGuard, OnceLock};

static ENV_LOCK: OnceLock<Mutex<()>> = OnceLock::new();

pub fn env_lock() -> MutexGuard<'static, ()> {
    ENV_LOCK
        .get_or_init(|| Mutex::new(()))
        .lock()
        .expect("env lock poisoned")
}

pub struct EnvVarGuard {
    key: &'static str,
    previous: Option<OsString>,
}

impl EnvVarGuard {
    pub fn set(key: &'static str, value: impl AsRef<OsStr>) -> Self {
        let previous = std::env::var_os(key);
        std::env::set_var(key, value);
        Self { key, previous }
    }

    pub fn unset(key: &'static str) -> Self {
        let previous = std::env::var_os(key);
        std::env::remove_var(key);
        Self { key, previous }
    }

    pub fn prepend_path(path: PathBuf) -> Self {
        let previous = std::env::var_os("PATH");
        let mut paths = vec![path];
        if let Some(old_path) = &previous {
            paths.extend(std::env::split_paths(old_path));
        }
        std::env::set_var("PATH", std::env::join_paths(paths).unwrap());
        Self {
            key: "PATH",
            previous,
        }
    }
}

impl Drop for EnvVarGuard {
    fn drop(&mut self) {
        match &self.previous {
            Some(value) => std::env::set_var(self.key, value),
            None => std::env::remove_var(self.key),
        }
    }
}