Re: surprising behavior from merge

[Michael Witten <mfwitten@gmail.com>]

On Fri, 11 May 2012 16:25:29 -0600, Sebastian Kuzminsky wrote:

> Hi folks, I just ran in to a strange behavior with git merge.
>
> Things start out with two branches (let's call them 'master' and
> 'other') pointing at a particular commit. In master I commit a
> small one-line change, then make a second commit that adds some
> stuff just after the line changed in the previous commit. In the
> other branch, i cherry-pick the second commit from master (the
> one that adds the new stuff). The cherry-pick succeeds, despite
> the fuzzy context. So far, so good.
>
> Next I try to merge other into master. I expected it to notice
> there was nothing to do and leave the master tree unchanged,
> but it applied the "add new stuff" patch to master (even though
> that patch is already in master) and made a commit from that. So
> it silently did the wrong thing, and now the file contains two
> copies of stuff I added.
>
> That is a simplified version of what happened, in my real repo
> there were several (unrelated and unimportant) commits on both
> master and the other branch. When the surprising double-add
> happened, i simplified the repo to remove distractions.
> The simplified repo is here if anyone wants to inspect it:
> https://github.com/SebKuzminsky/merge-problem

It would obviously be helpful to supply:

  * Explicit commands that anyone on the list can try and discuss.
    For example:

      git init repo
      cd repo
      echo a  > a; git add a; git commit -m 'small one-line change'
      echo b >> a; git commit -am 'adds some stuff after'
      ...

  * Expected behavior from those commands.

  * Actual behavior from those commands.

In other words, rather than burdening people with the task of
constructing a mental picture of what you have done, you should
show them as directly and precisely as possible; in this way,
people can go about the business of discussing your issue much
more quickly and, most importantly, PRECISELY.

Sincerely,
Michael Witten