def add(path)
      return true unless File.exist?(path)

      metadata[path] = {
        "mtime" => File.mtime(path),
        "deps"  => [],
      }
      cache[path] = true
    end
def add(path)
      return true unless File.exist?(path)

      metadata[path] = {
        "mtime" => File.mtime(path),
        "deps"  => [],
      }
      cache[path] = true
    end
Add a path to the metadata

 Returns true, also on failure.