swc-project/swc · error

failed to create a temp file

Error message

failed to create a temp file

What it means

`exec_with_node_test_runner` writes the generated mocha test file with `OpenOptions::new().create(true).truncate(true).write(true).open(&path)`. The `expect("failed to create a temp file")` panics when opening `{tmpdir}/{hash}.test.js` for writing fails — almost always permission or disk-space issues on the temp directory just created, since the parent directory already exists at this point.

Source

Thrown at crates/swc_ecma_transforms_testing/src/lib.rs:663

        println!("Trying cache as `SWC_CACHE_TEST` is `1`");

        if success_cache.exists() {
            println!("Cache: success");
            return Ok(());
        }
    }

    let tmp_dir = tempdir_in(&root).expect("failed to create a temp directory");
    create_dir_all(&tmp_dir).unwrap();

    let path = tmp_dir.path().join(format!("{hash}.test.js"));

    let mut tmp = OpenOptions::new()
        .create(true)
        .truncate(true)
        .write(true)
        .open(&path)
        .expect("failed to create a temp file");
    write!(tmp, "{src}").expect("failed to write to temp file");
    tmp.flush().unwrap();

    let test_runner_path = find_executable("mocha").expect("failed to find `mocha` from path");

    let mut base_cmd = if cfg!(target_os = "windows") {
        let mut c = Command::new("cmd");
        c.arg("/C").arg(&test_runner_path);
        c
    } else {
        Command::new(&test_runner_path)
    };

    let output = base_cmd
        .arg(format!("{}", path.display()))
        .arg("--color")
        .current_dir(root)
        .output()

View on GitHub (pinned to 5176682b65)

Solutions

1. Verify you can create files inside `$CARGO_TARGET_DIR/swc-es-exec-testing/` manually; fix ACLs/ownership if not.
2. Clear stale contents of the scratch dir (`rm -rf $CARGO_TARGET_DIR/swc-es-exec-testing`) to remove collided/locked files; it is a pure cache/scratch area.
3. Free disk space if ENOSPC, and disable execution tests (`EXEC=0`) in environments that cannot write there.

fn can_create_files_under(p: &std::path::Path) -> bool {
    let probe = p.join(".file-probe");
    std::fs::write(&probe, b"").is_ok() && {
        let _ = std::fs::remove_file(&probe);
        true
    }
}

When it happens

Trigger: Execution tests where the temp dir exists but is not writable (ACLs, SELinux denials), the filesystem filled up between dir creation and file creation, or antivirus/mandatory-locking environments blocking file creation on Windows.

Common situations: Hardened CI images with restrictive ACLs on the cargo target dir; disk-full agents; Windows environments where another process holds a lock on a same-named leftover file.

Related errors

• failed to create parent directory for temp directory
• failed to create a temp directory
• failed to read file
• failed to write to temp file
• failed to run mocha

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/7a2e761888eb4989. Report an issue: GitHub.