One recurring problem in Perl modules that use Scalar::Util's
"weaken" function is that it is not present in the pure-perl variant.
So if your module uses "weaken", you can just add the following to
your Module::Install-based Makefile.PL (or equivalent):
  requires 'Task::Weaken';

Homepage:
https://metacpan.org/release/Task-Weaken
