Re: fast forward merge overwriting my code

["brian m. carlson" <sandals@crustytoothpaste.net>]

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On 2021-05-23 at 09:48:55, Johannes Sixt wrote:
> [resending, as I forgot to include git@vger]
> 
> Am 22.05.21 um 17:48 schrieb Andre Ulrich:
> > Let's say I have a .txt file on my master branch. I used
> > 
> > git add .
> > 
> > and
> > 
> > git commit -m "blabla"
> > 
> > so everything is staged and in the history. Now I check out a new branch
> > 
> > git checkout -b testing
> > 
> > and edit the .txt file. I add some new lines at the end, but I also
> > change some of the already existing lines. Then again I add and commit
> > everything. Then I use
> > 
> > git checkout master
> > 
> > and
> > 
> > git merge testing
> > 
> > I would expect git to tell me "hey, wait, you have changed some of the
> > first lines in the .txt file. When you merge, your code on master will
> > be altered". But git just merges everything in.
> > Just imagine this was working code, and changing some of the first lines
> > breaks everything in the following lines.
> > I think I have found out what is the problem: git considers this a fast
> > forward merge (since there were no commits on master between the
> > creation and the merging of the test branch).

Yes.  However, if Git did an actual merge, the result would be the same.
In a three-way merge, if one side changes, and the other does not, the
change is adopted.  A fast-forward merge just avoids the merge commit.

> > But this is annoying. I want to be able to choose, what changes I want
> > to keep, when I do the merge (just as in case of a 3way merge, when you
> > can call a graphical merge tool to decide what lines to keep).
> 
> But in a 3-way merge, you only get to choose which changes you take if
> there is a conflict. If, in your example, you had committed a change to
> a different file on master before the merge, you would get a
> non-fast-forward (3-way) merge, and still no opportunity to choose which
> changes you take because there would be no conflict.
> 
> And why do you think we need a general warning "when you merge, your
> code on master will be altered"? Why would I want to make a merge into
> master if not to change the code on master?

I suspect Andre has a goal here or a specific use case that we're not
understanding.  If we got some more explanation about what's going on,
we could probably offer a more useful response addressing that specific
use case or goal.  It might not be a use case we support, but at least
we could address it directly.
-- 
brian m. carlson (he/him or they/them)
Houston, Texas, US

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