As an employee, I’ve managed to evade these clauses by negotiating them as early as possible in the interview process. With smaller companies, it hasn’t really been as difficult as I expected.
However, my local laws provide some additional protection against this type of thing. I didn’t even realize it until I consulted with a lawyer who pointed out that my state’s laws don’t allow companies to claim IP generated in off hours. Of course, consult with a lawyer to confirm which jurisdiction actually applies to your employment.
As a manager on the other side of the table, I’ve had some strange experiences: On more than one occasion, employees have tried to open-source things they wrote for us without asking. Juniors especially may not fully understand the bounds of IP ownership, to the point that they think code they wrote is theirs, even if written for their job as paid works for hire. I’m not suggesting that’s what’s happening here, but after seeing developers walk straight into situations where they’re releasing company code without permission I reserve judgment when I see situations like this. If these libraries were developed on company time for company work products then the developer may not have a particularly strong claim for his ownership.
On the other hand, if these are entirely unreleased to his work then of course this is a ridiculous request.
EDIT: A quick look at the source code suggests this situation might not be as clear-cut in favor of the developer as the comments here suggest. Both of the repos in question appear to be derivative works of projects that Badoo (aka Bumble, the developer's employer) owns. The MVIKotlin library opens with this statement:
> This project is inspired by Badoo MVICore library.
And the Decompose repo has this statement in the opening:
> This project is inspired by Badoos RIBs fork of the Uber RIBs framework.
And unless I'm missing something, the developer worked for Badoo (Bumble) during the entire period. It would be extremely difficult to argue that a derivative work of your employer's IP, written during your time of employment and possibly during work time, is fully independent of the company. If the developer used these projects in any way for their work at Bumble (e.g. actually using these tools or libraries as part of the app) or he used company equipment/time/resources while building them, then it would be virtually impossible to argue that these works were not partially work-for-hire as part of his employment.