Syncing 2 branches after git merge

Question

How do I keep 2 Git branches in sync?

I currently have a master branch and a gh-pages branch as well as the respective remotes. Both, master and gh-pages branch shared the same commit id whenever I committed as follows:

git checkout master
git commit -am "message"
git checkout gh-pages
git merge master

My log looked like so (achieved with git log --graph --oneline --all --decorate):

After a merge conflict, which I resolved, each merge receives its own commit as such:

My question is, how can I align the 2 branches so that merges will happen as previously on a single 'graph-track'?

I have tried to pull according to this answer, but to no avail.

Answer 1

It looks like commit 50b6dec was added to the gh-pages branch, and commit e43c01f was made on master at the same time, and this is what caused the merge conflict.

Because of that, gh-pages had 1 commit that master did not have. So any time you merged after that, Git was not able to do a fast-forward merge. (The fast-forward merges is what gave you the linear history you had before.) Thus, the solution is:

git checkout master
git merge gh-pages

To prevent this from happening again in the future, change your process to this:

git checkout master
git commit -am "message"
git checkout gh-pages
git merge --ff-only master

The --ff-only flag will abort the merge with an error if gh-pages has any commits that master doesn't have.

---

If you want to rewrite history so that it is as if this never happened, you can do that too.

First, ensure you are on master:

git checkout master

Now rebase:

git rebase 50b6dec

You'll have to resolve that conflict again. When finished, do:

git rebase --continue

When the rebase is complete, you will have to force-update origin:

git push --force-with-lease origin master

You'll also have to move the gh-pages branch. Do:

git branch -f gh-pages master
git push --force-with-lease origin gh-pages

This will give you a history that looks something like this:

* f218f70' (HEAD -> master) Added Scatterplot functionality to check ratings
* cb79b79' Squashed bug
* fcf0d8a' Small change
* e43c01f' Small change
* 50b6dec Small change
* a217267 Small change

Obligatory warning: Since a rebase rewrites history, this can be dangerous / disruptive for anyone else working on this branch. Be sure you clearly communicate what you have done with anyone you are collaborating with.