Add migration guide

[vyasr]

Adding a page to the documentation about migrating from scikit-build classic. I'll keep updating this as I discover more while migrating various repos, then open it for review when I've found everything I expect to find.

[henryiii]

If it helps, I've recently helped wjakob/nanobind_example and kratsg/pylibmagic#48 convert. There's a PR to scikit-build/cmake_python_distributions too.

[vyasr]

Thanks for the review @henryiii! Before I go any further, do you agree that something like this guide could be helpful? Happy to continue investing time in it if you're interested since I will be effectively compiling this list for my own use anyway.

If it helps, I've recently helped wjakob/nanobind_example and kratsg/pylibmagic#48 convert. There's a PR to scikit-build/cmake_python_distributions too.

Thanks for the pointer. I know there were a couple other early conversions too (like awkward array) that I could look at. FWIW I've got a handful of different projects that will all probably migrate roughly in lockstep, and while they are largely similar I'll probably be playing it safe and testing many/most of them before merging the migrations. So I may end up providing you with even more data points (not sure how many projects you already have on scikit-build-core now though!).

[henryiii]

Before I go any further, do you agree that something like this guide could be helpful

Sure! Eventually it might just be a guide for converting from setuptools (possibly + CMake manually added) though, once most projects have converted from scikit-build classic. But that's well in the future.

[LecrisUT]

There will also be a weird transition back when scikit-build will be calling scikit-build-core. Still confused on what that difference will end up being later on.

[henryiii]

It will try to behave like the old scikit-build, though, and it still will work through setuptools (which is not ideal); a lot of the features you don't get access to (like auto cmake/ninja download) unless you switch to the new interface.

[henryiii]

Thanks!