message: Don't use `for` loop on an `Option`
diff: @@ -386,23 +386,21 @@ pub fn resolve_with_previous<'cfg>(
  let keep = |p: &PackageId| pre_patch_keep(p) && !avoid_patch_ids.contains(p);
  let dev_deps = ws.require_optional_deps() || has_dev_units == HasDevUnits::Yes;
  +
  + if let Some(r) = previous {
  + trace!("previous: {:?}", r);
  +
  // In the case where a previous instance of resolve is available, we
  // want to lock as many packages as possible to the previous version
  // without disturbing the graph structure.
  - if let Some(r) = previous {
  - trace!("previous: {:?}", r);
  register_previous_locks(ws, registry, r, &keep, dev_deps);
  - }
  // Prefer to use anything in the previous lock file, aka we want to have conservative updates.
  - for r in previous {
  - for id in r.iter() {
  - if keep(&id) {
  + for id in r.iter().filter(keep) {
  debug!("attempting to prefer {}", id);
  version_prefs.prefer_package_id(id);
  }
  }
  - }
  if register_patches {
  registry.lock_patches();
  