message: print more detailed message for cache directory creation
diff: @@ -63,10 +63,17 @@ impl FileSystemCache {
  }
  } else {
  // Create the directory and any parent directories if they don't yet exist.
  - create_dir_all(&path)?;
  + let res = create_dir_all(&path);
  + if res.is_err() {
  + Err(io::Error::new(
  + io::ErrorKind::Other,
  + format!("failed to create cache directory: {}", path.display()),
  + ))
  + } else {
  Ok(Self { path, ext: None })
  }
  }
  + }
  /// Set the extension for this cached file.
  ///
  