Merge a Pull request which is one commit behind

Question

I forked a Github repository and made a few changes for a few days, without ever doing a pull from the original repo(the repo of which I made a fork).

Now I issued a pull request to the original repo. I found that the repo got another commit after I had forked it.

So my question is, If the owner of the repo accepts the pull request, will the commit he made afterwards stay or will his repo become a identical copy of my fork?

If it's the latter, then can you tell me how can I not delete the commit he had made?

Answer 1

All changes from both branches will appear in the history:

A-B------C----M--...
   \-X-Y---Z-/

where X, Y and Z are your commits and C is the commit you're missing. The commit M is a merge-commit that will contain all your changes in it (and potentially fixes any merge conflicts with C). Your commits will remain untouched and afterwards M will contain all changes from C, X, Y and Z.

Alternatively, the repo maintainer can rebase your branch and merge it afterwards:

A-B-C---------M--...
     \-X-Y-Z-/

when everything goes right, the state of M will be exactly the same as when doing the regular merge. However X, Y and Z will individually be made to look like they originated from C (their SHA1 value will change, too).

Both methods are equally valid, rebasing is recommended if there is quite a number of commits that you're missing (i.e. after a few weeks of developing).

Be aware: The repo maintainer may ask you to do the merge or rebase if your branch does not merge cleanly and the conflict isn't easy to fix. It is your job to supply mergeable branches.

In this case, just fetch the latest version of the branch you're pull-requesting against and try the merge yourself:

git checkout your-branch
git pull upstream master

or

git checkout your-branch
git pull --rebase upstream master

Afterwards, the branch will merge cleanly into upstream. Just post a new pull-request for your newly merged branch.