Re: BUG: commit-reach.c:66: bad generation skip

On 2/7/2021 5:31 PM, Filippo Valsorda wrote:

_This_ is interesting. I haven't heard of this problem happening in a released version of Git.

I'm CC'ing Jonathan Nieder who recently saw this happening, but that was on a newer version than 2.30.0 with a topic that is not part of 2.30.0. But maybe the version shipped internally is versioned without extra information on top of the latest tag? (I see your @google.com email, which makes me think you have an internal version.)

This was recently reported, but it was thought to be due to an in-process topic branch. If you recently had that version installed, then your data would have needed a rewrite anyway.

This hints towards more problems with generation numbers across split commit-graph layers. (The child has generation number 7, so it is likely part of a thin layer.)

This might be sufficient evidence to convert this BUG() to a warning with something like:

  warning: The commit-graph file has incorrect reachability index
  warning: information. Results may be incorrect until commit-graph
  warning: is rewritten with 'git commit-graph write'.

This could also be a die() instead of warning(), as that command itself might return incorrect results.

Yes, this will delete (and possibly replace) your commit-graph file where the bad data lies.

To better understand your situation, could you please run the following commands?

	git config --get-regexp graph
	git config features.experimental

I'm specifically looking for values of fetch.writeCommitGraph and gc.writeCommitGraph.

Thanks, -Stolee