# Lock parsing only reads this one file when no import token can occur. A
# conservative substring probe also sends comments/URLs containing "import"
# through the complete-source path. Fragment names may have any extension.
{ source }:
let
  regular = ((builtins.readDir source)."quixos.lock" or null) == "regular";
  text = if regular then builtins.readFile (source + "/quixos.lock") else "import";
in
if builtins.replaceStrings [ "import" ] [ "" ] text != text then
  source
else
  builtins.path {
    path = source;
    name = "qx-lock-source";
    filter = filename: _: filename == toString source || filename == "${source}/quixos.lock";
  }