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

[Derrick Stolee <stolee@gmail.com>]

On 2/10/2021 7:18 AM, Filippo Valsorda wrote:
> On Mon, Feb 8, 2021 at 3:26 AM Derrick Stolee <stolee@gmail.com> 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.)
> 
> Ah, the issue indeed first showed up as I was using the internal
> version. I then installed mainline 2.30.0 to check that it reproduced
> on the same local repository before reporting a bug.

The mainline does have the BUG() statement, but it's really reflecting
bad data in the commit-graph file. That data was written by the internal
version and was not reset until you rewrote the file.

>> 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.
> 
> fetch.writecommitgraph is enabled on the internal version.
> 
> $ git version
> git version 2.30.0.478.g8a0d178c01-goog
> $ git config --get-regexp graph
> fetch.writecommitgraph true
> $ git config features.experimental
> $ ~/homebrew/bin/git version
> git version 2.30.0
> $ ~/homebrew/bin/git config --get-regexp graph
> $ ~/homebrew/bin/git config features.experimental
> 
> I zipped up the repository and the worktree before running gc, so I can
> run other commands for you if you need, but unfortunately I can't share
> the archive, as it fetched from a private branch with security fixes.

Thanks, but let me know if it reproduces again. The bug should be fixed
in ds/commit-graph-genno-fix [1], and I think the Google internal release
has been rolled back until that branch is included.

[1] https://github.com/gitster/git/commits/ds/commit-graph-genno-fix

Thanks,
-Stolee