Writing OS experiment from scratch and curious about Grub2 and my FS
I haven't tried very much with this just yet, at least not in practice. I've been reading about GRUB2 and how to set it up but am getting slightly lost. I apologize, I don't have any source code at the moment to offer you. I just wanted to know how to set up GRUB2 to use a File System that I have written from scratch myself.
Write a GRUB driver module for your FS, like how it has modules for XFS, ext2/3/4, and so on. https://wiki.osdev.org/Writing_GRUB_Modules
https://www.gnu.org/software/grub/manual/grub/grub.html#Images explains the different components of GRUB2. The filesystem driver is loaded as part of core.img, which is built from other images.
Keep in mind that many new filesystems don't get GRUB support right away, and having a separate /boot partition that GRUB can read is not rare. e.g. on a single disk instead of a complicated RAID (although GRUB does have some md support), not encrypted, and with a long-established filesystem that GRUB does have a driver for. And that doesn't need a complicated log replay on dirty shutdowns before even reading.
Also, the earliest stage of GRUB booting needs to load core.img from a block list that's hard-coded into the small first thing the firmware loads, so filesystems where the blocks of a file's data can move around when the file wasn't modified aren't usually a good fit for /boot at all. You'd never know when you had to re-install GRUB after any change to anything on /boot.
But if you still want to make your FS bootable in GRUB, check the GRUB source code, there's probably some documentation.