The 0.19 compiler requires that an OSI approved SPDX license is used, the list is here:
I notice that AGPL (or Affero) licences are on that list. These are a more restrictive form of viral GPL, that require the entire source of an application be published under the terms of the licence, even when only the object form of the code is being distributed; if you unwittingly include such a package in your project, you could be forced to open source all of it.
I don’t know if any packages currently use this licence - should packages with this licence be allowed to be published?
Are there other potentially problematic licences in the list?
Most packages seem to use BSD or MIT. It would be worth displaying the licence type on the package site. It would also be worth doing a licence survey to see what is actually being used.