Re: What's cooking in git.git (Oct 2020, #02; Fri, 9)

[Derrick Stolee <stolee@gmail.com>]

On 10/9/2020 11:59 AM, Junio C Hamano wrote:
> * ds/commit-graph-merging-fix (2020-10-08) 1 commit
>  - commit-graph: ignore duplicates when merging layers
> 
>  When "git commit-graph" detects the same commit recorded more than
>  once while it is merging the layers, it used to die.  The code now
>  ignores all but one of them and continues.
> 
>  Shouldn't it make sure all copies match, or discard all of them, to
>  avoid random corruptions kept in the repository?

Making sure each copy matches is a bigger change than I would be
comfortable with in the rc window. If you intend for this to at
least be in a better state than before, then the current fix is
safer than doing that harder work. If we had a clear repro that
was testable, then I might have a different opinion. (I see that
Thomas updated the thread with a possible repro, I will get back
to him soon.)

As for discarding them all: we would need to add code to "reparse"
a commit from the object database. Perhaps that is doable, but we
have so far not removed data from a parsed 'struct commit'. This
is probably the easiest way forward to guarantee correct data here.
Again, let's find a way to test this before committing.

Thanks,
-Stolee