Re: emacs.git 'master' reset

On Mon, Jul 27, 2026 at 02:37:44AM +0200, Michael Heerdegen via Emacs development discussions. wrote:
> [email protected] writes:
> 
> > Note that they get different hashes, because a commit's hash is
> > chained with previous commit's hashes, so if one is missing (or
> > otherwise changed) the whole history from then on gets different
> > hashes.
> 
> I wondered why there were different hashes this time.

A commit's hash is a hash over the tree hash (which is a recursive
hash over all directories and files) and other tidbits, like author,
etc. Among them is the parent's hash, thus it is linked to its
history. This [1] seems to be a good description.


> No git guru here, but: apart from that suprise just hitting F u (aka
> `magit-pull-from-upstream' in Magit) was good enough here.

I don't know what F u does. If that corresponds to "git pull" and you
were up to date before the action it should complain, since the remote
branch has changed unexpectedly (that's the "change history" part)

> My head
> commit is in the master branch, and my master is some commits ahead of
> origin/master.  The rebasing onto the new origin/master happened
> automatically.  So I expect that for most people where the situation is
> similar the procedure should not be complicated...?

It shouldn't. Usually, the rebase will do -- sometimes you need that
tougher "git reset --hard origin/master" which makes sure your local
branch matches the remote (your local repo contains copies of the
remote branches under origin/* [2]). The more drastic method will also
throw away your local commits, should you have any [3], so caveat resettor.

Cheers

[1] https://shafiul.github.io/gitbook/1_the_git_object_model.html
[2] "origin" and "master" are all names, they can be changed; I'm
   assuming defaults; "master" these days is more often spelled
   "main", but Emacs stuck with the older.
[3] Never, ever commit to master/main unless you know what you are
   doing
-- 
t

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