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use std::fs::File;
use std::path::Path;
use std::path::PathBuf;
use log::info;
use merc_utilities::MercError;
/// A utility for dumping files, mostly used for testing and debugging
///
/// # Details
/// The given name is used to create a dedicated directory for the output files,
/// this is especially useful for files dumped from (random) tests.
/// Uses the `MERC_DUMP=1` environment variable to enable or disable dumping files
/// to disk, to avoid unnecessary writes during normal runs. In combination with
/// `MERC_SEED` we can reproduce specific tests cases for random runs.
pub struct DumpFiles {
// None when dumping is disabled.
directory: Option<PathBuf>,
}
impl DumpFiles {
/// Creates a new `DumpFiles` instance with the given directory as output.
pub fn new(directory: &str) -> Self {
if let Ok(dump_dir) = std::env::var("MERC_DUMP") {
// Check if the directory is an absolute path
if !Path::new(dump_dir.as_str()).is_absolute() {
panic!("MERC_DUMP must be an absolute path, because tests write relative to their source file.");
Self {
directory: Some(Path::new(&dump_dir).join(directory)),
} else {
// Dumping disabled.
Self { directory: None }
/// Dumps a file with the given filename suffix by calling the provided function
/// to write the contents.
pub fn dump<F>(&mut self, filename: &str, mut write: F) -> Result<(), MercError>
where
F: FnMut(&mut File) -> Result<(), MercError>,
{
if let Some(directory) = &self.directory {
// Ensure the dump directory exists.
let _ = std::fs::create_dir_all(directory);
let path = Path::new(&directory).join(filename);
let mut file = File::create(&path)?;
write(&mut file)?;
info!("Dumped file: {}", path.to_string_lossy());
info!("No MERC_DUMP set, skipping dump: {}", filename);
Ok(())