I’m curious, have you actually spoken with this person? Why does he do this?
Some engineers do this because they lack confidence. They’ll optimize the shit out of a solution because code reviews are a form of work inflicted torture. If this is the case, you need to think about your culture and whether this person has a reason to dread code reviews. This is not meant to insult you, but as someone who worked through his own self esteem issues decades ago, I’ve got to tell you, I didn’t appreciate the way you’ve disparaged him in this question. For example, ‘it turns out he’s been working nights at home...’ is not appropriate if you want to help someone through self esteem issues. The appropriate way to bridge that is to start with a compliment - the cat is working on his own time to help you...
Other engineers do it because they’re obsessed with learning and understanding. I see this a lot with young engineers - they have this idea that they can’t just use a library, they have to be able to build it from scratch if you give them a pile of sand.
In this case, we’ve all been there. For the love of all that’s holy, if you’re on Hacker News, you’ve gone down rabbit holes like this. Those rabbit holes make us hackers...
If this is the issue, it’s time for real talk. I wish that I understood everything but I don’t have enough time to understand everything and keep a roof over my head. At some point, you’ve got to trust in your team, your tests and your instincts. Fuck, I just resisted the urge to learn about trinary because there’s no way trinary will pay my bills this lifetime. But 21 year old Greg would have spent three years in that rabbit hole.