Eliminate the need for a shell

[bgrant0607]

Either replace use of the git CLI with go-git or libgit2, like ArgoCD and Flux, or otherwise eliminate the need for a shell (reimplement submodules?).

[thockin]

I tried to removed the shell and git clone failed. It doesn't pass even the most trivial e2e test.

Looking at go-git, some of what we need (rev-parse, ls-remote, and worktree at least) are not supported. Worktree is pretty important. There may be workarounds, but it's not a drop-in.

libgit2 would require CGO, which is a can of worms which we can evaluate.

[bgrant0607]

Thanks for checking, and for describing the obstacles.

I opened this as a place for interested parties to look and/or comment.

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/lifecycle stale

[thockin]

For kicks, I tried this against my current working branch, which has some huge changes, including #691

I can make it run without a shell EXCEPT FOR submodules. If I set submodules=off it seems to run.

I don't know what we want to do with that information.

[sboardwell]

What would removing the shell mean for exechook-command actions?

[thockin]

The exechooks mechanism doesn't depend on a shell, but I suspect many exechooks are written as shell scripts.

Assuming we got rid of the shell, I suspect we would want to produce 2 images - with and without shell, or make sure people could build their own images on top of the shell-free one, or something.

But as it stands, we still need the shell, so....