Merge status lost when stashing

Question

It happens that information about a merge are lost after we do a stash. A usual merge and a stashed merge are compared below.

Right: merge + push

git merge release-2013-10-29
# Everything works, cool
git commit -am "Upgraded to release 2013-10-29"
git push origin dev

Result is as expected, a merge commit:

Wrong: merge + stash + push

Here I am in a scenario where I need to stash the merge changes just in order to have a look at the previous-to-the-merge behaviour.

git merge release-2013-11-06
# Conflicts fixed, but detected inappropriate behaviour
git stash
git stash pop
git commit -am "Upgraded to release 2013-11-06"
git push origin dev

Result: this commit is not a "merge" anymore. We also lost all single authored commits contained by the merge, just like if I would have made all these changes.

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So, shouldn't we stash anything when merging? How to avoid such behaviour then?

Answer 1

When you do a merge, git stores a reference to the branch you're merging in MERGE_HEAD. But it seems like git stash doesn't save the reference.

You can try to set the MERGE_HEAD back to the commit which you were merging after applying the stash:

Suppose you're merging release-2013-11-06 branch onto master, and the last commit there is - 3be2c99, then you can do:

git stash apply --index
git update-ref MERGE_HEAD 3be2c99
git status
# All conflicts fixed but you're still merging
# ....

Notice the usage of --index while applying the stash. That is required to get the changes back in the index, else you will get the stashed changes only in the working tree.

P.S: Ideally you should avoid stashing your uncommitted merge.