cranpose-core 0.1.96

//! Where a test writes real files.
//!
//! Enabled by the `test-helpers` feature. Every crate in the workspace that
//! needs a file on disk during a test asks here, so there is one answer to
//! where those files go rather than one per crate that drifts from the rest.

use std::path::{Path, PathBuf};
use std::sync::atomic::{AtomicU32, Ordering};

/// A unique, empty directory under the workspace `target/test-output`.
///
/// Never the system temporary directory: on Linux that is tmpfs, so a test
/// writing a payload there writes it to RAM, and a failure leaves nothing
/// under `target` to look at afterwards.
/// `apps/desktop-demo/tests/source_hygiene_aliases.rs` enforces that across
/// the workspace.
///
/// `manifest_dir` is the caller's own `env!("CARGO_MANIFEST_DIR")`. Its last
/// component names the subdirectory, so two crates asking for the same `tag`
/// get different directories; the workspace root is found by walking up to
/// the directory holding `Cargo.lock` rather than by counting `..` hops,
/// which differ per crate and are wrong the moment one moves.
pub fn test_scratch_dir(manifest_dir: &str, tag: &str) -> PathBuf {
    static COUNTER: AtomicU32 = AtomicU32::new(0);
    let unique = COUNTER.fetch_add(1, Ordering::Relaxed);
    let manifest = PathBuf::from(manifest_dir);
    let owner = manifest
        .file_name()
        .map(|name| name.to_string_lossy().into_owned())
        .unwrap_or_else(|| "workspace".to_string());
    let path = workspace_root(&manifest)
        .join("target/test-output")
        .join(owner)
        .join(format!("{tag}-{}-{unique}", std::process::id()));
    let _ = std::fs::remove_dir_all(&path);
    std::fs::create_dir_all(&path).expect("a scratch directory under target/test-output");
    path
}

/// The nearest ancestor of `manifest` holding a `Cargo.lock`, which is the
/// workspace root; the manifest directory itself when there is none, so a
/// crate built outside a workspace still writes somewhere it owns.
fn workspace_root(manifest: &Path) -> PathBuf {
    manifest
        .ancestors()
        .find(|directory| directory.join("Cargo.lock").is_file())
        .unwrap_or(manifest)
        .to_path_buf()
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn a_scratch_directory_is_empty_under_the_workspace_target() {
        let path = test_scratch_dir(env!("CARGO_MANIFEST_DIR"), "scratch");
        assert!(path.is_dir());
        assert_eq!(std::fs::read_dir(&path).expect("read").count(), 0);
        assert!(
            path.components().any(|part| part.as_os_str() == "target"),
            "the scratch directory belongs under the workspace target: {}",
            path.display()
        );
        let _ = std::fs::remove_dir_all(&path);
    }

    #[test]
    fn two_calls_do_not_share_a_directory() {
        let first = test_scratch_dir(env!("CARGO_MANIFEST_DIR"), "scratch");
        let second = test_scratch_dir(env!("CARGO_MANIFEST_DIR"), "scratch");
        assert_ne!(first, second);
        let _ = std::fs::remove_dir_all(&first);
        let _ = std::fs::remove_dir_all(&second);
    }
}