swc-project/swc · error

failed to write to temp file

Error message

failed to write to temp file

What it means

Immediately after creating the temp file, `exec_with_node_test_runner` writes the transformed source with `write!(tmp, "{src}")`. The `expect("failed to write to temp file")` panics when the write itself fails: the filesystem filled up (ENOSPC), a quota was hit mid-write, or the file handle became invalid.

Source

Thrown at crates/swc_ecma_transforms_testing/src/lib.rs:664

        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()
        .expect("failed to run mocha");

View on GitHub (pinned to 5176682b65)

Solutions

1. Check disk space (`df -h $CARGO_TARGET_DIR`) and free space or raise the quota.
2. Clean the scratch area and cargo caches (`cargo clean`, remove `$CARGO_TARGET_DIR/swc-es-exec-testing`) to reclaim room.
3. On overlayfs/container limits, raise the container's writable-layer size or bind-mount a larger volume at the target dir.
4. Skip execution tests with `EXEC=0` on space-constrained runners.

fn disk_has_space(p: &std::path::Path) -> bool {
    // Simplest portable check: write a small file and read it back.
    let probe = p.join(".space-probe");
    let ok = std::fs::write(&probe, vec![0u8; 1024]).is_ok();
    let _ = std::fs::remove_file(&probe);
    ok
}

When it happens

Trigger: Execution tests running on a full disk or quota-limited volume where the (potentially large, since it embeds the whole transformed bundle) test file cannot be fully written; flaky mounts (network filesystems, overlayfs under memory pressure).

Common situations: Build agents whose disks fill during large test batches; container overlay filesystems hitting the size limit; per-user quotas exceeded in shared CI.

Related errors

• failed to create a temp file
• failed to read file
• failed to execute transfomred code
• CARGO_MANIFEST_DIR
• test_inlined_transform does not support paths outside of the

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/a6bb878bd05914d8. Report an issue: GitHub.