Re: commit-graph overflow generation chicken and egg

[Jeff King <peff@peff.net>]

On Thu, Jun 09, 2022 at 09:49:15AM +0200, Ævar Arnfjörð Bjarmason wrote:

> It's certainly interesting to see *how* we got to this state, but just
> so we're on the same page: I fundimentally don't think it matters to the
> *real* bug here.
> 
> Which is that at the very least f90fca638e9 (commit-graph: consolidate
> fill_commit_graph_info, 2021-01-16) and e8b63005c48 (commit-graph:
> implement generation data chunk, 2021-01-16) (CC'd author) have a bad
> regression on earlier fixes that read-only operations of the
> commit-graph *must not die*. I.e. the "parse" and "verify" paths of the
> commit-graph.c code shouldn't call exit(), die() etc.

Yeah, I'd agree that this is a good philosophy to follow. The
commit-graph data is meant to be an optimization, and we can always
continue without it.

> If you replace your graph with Jeff's corrupt one and run "git status",
> "git log" etc. it's still emitting one verbose complaint, but it no
> longer does so in loops (at least for these paths, but e.g. "git gc" is
> still doing that).
> 
> But it does get us to where we can run "git gc", and while complaining
> too much along the way will write out a new & valid commit graph at the
> end ("[... comments are mine"):

Yeah, getting through "git gc" is the key thing here. Then the problem
solves itself, sometimes even automatically (via auto-gc).

-Peff