A change list for the compiler

[mhauru]

Changes to the compiler in 1.12, while very welcome, caused work for some packages that interface with the compiler. I'm aware of chalk-lab/Mooncake.jl#714 and TuringLang/Libtask.jl#196, there are probably others. This is of course understandable and unavoidable when packages interface with internals that aren't public.

However, as discussed on Slack a few times, it would be very useful for package maintainers if there was even a rough list of changes, and advice on how to adapt to them. To kickstart this, I started a draft with changes I encountered in 1.12. It is very incomplete (reflecting my very superficial understanding of the compiler), and I would be grateful and happy if those who know this stuff better would be up for completing it, merging it, and adding to it as more things happen in 1.13.

[JeffBezanson]

This is great, thank you. I think it should probably go in devdocs?

[yebai]

Since this is meant to be like HISTORY.md, it would be good to keep it as is. More compiler docs in devdocs can be fixed separately.

[JeffBezanson]

OK I guess this is fine.

[fingolfin]

This is a great idea, thank you for getting it started.

Is the plan to fill in the TODOs next? Or are you looking for help with that? Or should we just merge this and gradually fill in the TODOs if someone has time to work on 'em?

[mhauru]

Yep, I'm looking for help for someone to fill in the TODOs, and to add any bits that I'm not aware of. For how to do that, I'm happy with whatever the maintainers prefer: Merge this and open more PRs to improve it, merge PRs into my branch, move my branch to this repo and start a new PR from it, all fine by me.