Re: who's on first? - following first parent and merge-management

From: Johannes Sixt <j.sixt@viscovery.net>
Date: Mar 8, 2012, 08:03 UTC
Message-ID: <4F5867D4.1010904@viscovery.net>
In-Reply-To: <20120308071403.GE7643@sigill.intra.peff.net>

Am 3/8/2012 8:14, schrieb Jeff King:

Show 13 quoted lines

> What if the user could specify a partial ordering of refs, and we used
> that order when listing merge parents in the resulting commit. So for
> example, if you said that:
> 
>   refs/remotes/origin/master > refs/heads/master
> 
> then doing:
> 
>   $ git checkout master
>   $ git pull origin master
> 
> would result in a "flipped" merge commit, with origin/master as the
> first parent, and master as the second.

I have wished for such a thing several times already.

It happens when I have a topic with changes that trigger a complete rebuild of the project. When I merge it to master, I have to

   # on topic
   git checkout master   #1
   git merge topic       #2

#1 triggers a rebuild, but I don't do a build. Then #2 again triggers a rebuild, but in reality the only changes since the last build are those from master since the topic forked (no, I can't use ccache).

To avoid the situation, I jump through hoops by preparing an index and worktree with the merge result while I am on topic:

   # on topic
   git checkout --detach
   git merge master      # triggers rebuild of only master's changes
   # merge result ready; carry it over to master and repeat the merge
   git reset --soft master
   git checkout master
   git merge topic       # fails if content merge is necessary
   git checkout master -- file/needing/content/merge # (*)
   git merge topic       # now succeeds

This would not be necessary if the order of the merge parents could be specified, e.g.:

   # on topic
   git merge --into master

(*) Jumping through these hoops make sense only if file/needing/content/merge is _not_ the one that triggers the complete rebuild.

-- Hannes