How to recover from a git push -force?

Here is what happened:

I have two remote git branches: master and feature1. For some reason I have to use git push --force for the feature1 branch, but I didn't know when I use git push --force it will also push the master branch. Then, a disaster happened, as I pushed my local master branch to the remote repository.

Luckily, my local branch is not too far away from the remote. Basically, my remote master has two pull requests merged ahead of my local master.

So my problem is: can I reopen the pull request and remerge? I noticed that there is commit version for merge request, so I am worried if I simply make new pull request it will mess up something? Ideally I just want to redo the merging of the two requests.

Is there some other way to recover from this disaster? I learned the --force is a really, really bad choice. :(

Update, example of what happened:

I have following branches:

master
feature1
origin/master
origin/feature1

I integrate two pull requests by using the GitHub's Auto merge pull requests. Then, I didn't fetch the master branch on my local machine. Thus, I think my origin/master is two versions behind the remote master.

Then I accidentally used git -f push, which overwrote the remote branch and now I lost the commits from the pull requests on remote repository.

How can I recover from it without messing up other contributors' history?

Solution

When working with github, refer to GHugo's answer which gives a foolproof procedure with github. If you're on an in-house (or other non-github) installation, read on.

You can always restore the previously observed state of master, by resetting to the old commit and issuing another push -f. The steps involved typically look like this:

# work on local master
git checkout master

# reset to the previous state of origin/master, as recorded by reflog
git reset --hard origin/master@{1}

# at this point verify that this is indeed the desired commit.
# (if necessary, use git reflog to find the right one, and
# git reset --hard to that one)

# finally, push the master branch (and only the master branch) to the server
git push -f origin master

Note, however, that this restores remote master to the state most recently retrieved by git fetch or equivalent. Any commits pushed by others after the last time you fetched will be lost. However, those commits will still be available in their reflogs, so they can restore them using steps like the above.