[fiddlerwoaroof]

I wrote a nearly complete implementation of git file format parsers in Common Lisp over like a month of evenings and weekends. I’m sure there are hard parts between where I am and a full git implementation but you can get quite a bit of utility out of a relatively small amount of effort.

[MrJohz]

It's a case of Pareto. Parsing the git file format is relatively simple, but handling all the weird states a Git repo can be in and doing the correct things to those files in each state is a lot harder. And then adding the network protocol on top of that makes directly reproducing Git quite difficult.

I know JJ used to use Git2 for a lot of network operations like pushing and pulling, but ran into too many issues with SSH handling that they've since switched to directly invoking the Git binary for those operations.

[fiddlerwoaroof]

There aren’t that many weird states a git repository can be in: the on-disk format of the repository is too simple for that. The hard part has to do with the various protocols for transferring objects around.

[deathanatos]

I think there's more corners out there than most people would give credit to? Just off the top of my head: files in the index (but maybe this isn't "weird enough"), rebasing but paused, rebasing with conflicts, merge with conflicts, cherry-picking but conflicts, middle of a bisect with all the state that implies, alternate objects dirs, alternate working dirs, submodules and all of their weirdness, and a "bare" repo.

Heck, had my PS1 return an error this week after I created a separate working dir for a repo and cd'd into it. Did you know .git can be a normal file? I didn't when I wrote my PS1.

[fiddlerwoaroof]

I knew .git can be a normal file because of worktrees. But most of the weird states have to do with the working tree not the repository. Even rebasing isn’t weird as far as the file formats go: it just is replaying commits on top of a new base commit. Since my goal was basically to implement enough of git to serve files from a git repository as a website, the actual task was fairly small.

[lucasoshiro]

Yeah, I wrote mine in Haskell. It's a good exercise for understanding how Git works