Re: git: 722b16673c40 - main - acpica: Import ACPICA 20230331

On 31 Jan 2024, at 22:57, Jung-uk Kim <jkim@FreeBSD.org> wrote:
> 
> On 24. 1. 31., Gleb Smirnoff wrote:
>> On Tue, Jan 30, 2024 at 08:57:10PM -0800, Cy Schubert wrote:
>> C> > > commit 722b16673c40aedf280895f2f2f676bb494518d7
>> C> > > Author:     Jung-uk Kim <jkim@FreeBSD.org>
>> C> > > AuthorDate: 2024-01-30 21:43:45 +0000
>> C> > > Commit:     Jung-uk Kim <jkim@FreeBSD.org>
>> C> > > CommitDate: 2024-01-31 03:16:36 +0000
>> C> > >
>> C> > >    acpica: Import ACPICA 20230331
>> C> > >
>> C> > >    (cherry picked from commit 8e013e1e3b81740266738226667431cf5c28b17a)
>> C> >
>> C> > Cherry-pick not merge for a vendor merge?..
>> C>
>> C> Probably not Kosher but, a general git question about cherry-picks vs
>> C> merges. A cherry-pick, without the -x but specifying the source branch,
>> C> results in no cherry picked merge but a merge of the last commit of the
>> C> source branch to the current branch.
>> C>
>> C> Can someone explain this? And if this would be any different from a
>> C> merge from a branch that is ahead by one commit since the last merge?
>> The object hashes would be the same, but the second parent meta-data
>> is basically lost, although can be recorded in the commit text
>> message with -x.
>> The second parent is important. When searching for regressions you may
>> go into bisecting the acpica history instead of FreeBSD history once
>> you figured out that this is the merge that brough the regression. With
>> second parent this can be automated and in case of manual search still
>> easier to do.
>> So, please don't do cherry-picks instead of merges for vendor subprojects.
> 
> In very early days of git adoption, I once did "git merge" from vendor branch by the git primer and it broke git repo.  At the time, someone (imp?) had to manually fix it and I was told that I should never ever do "git merge".  Am I confused again? :-(

Yes, a plain git merge is wrong, what you’re looking for is git subtree
merge. There’s a section[1] in the Committer’s Guide documenting the
whole process. Note MFCs are different and should be cherry-picks like
normal commits, albeit with slightly special options[2].

Jess

[1] https://docs.freebsd.org/en/articles/committers-guide/#vendor-import-git
[2] https://docs.freebsd.org/en/articles/committers-guide/#_mfc_a_vendor_import