How to fetch enough commits to do a merge in a shallow clone

Question

What I'm trying to do: test pull requests from github. I want to locally merge a pull request into master and run some tests on the result. Since the repository is huge, I do a shallow clone.

To be able to do the merge, I fetch more and more commits (git fetch with increasing --depth) until I have the merge-commit between master the pull request.

However, it doesn't work every time. It looks like I do not only need the merge-base, but also every commit in the master..merge_base range. I'm not sure however how to do that.

So, the question is: how do I fetch enough history to do the merge?

Answer 1

If you have the history from when feature branched from master but don't want the full history of master then you can estimate a branching date and use;

git fetch --shallow-since=<date> origin master 

It's hard to use any other form of git fetch to do what you want (query the remote for the merge-base) because git fetch fetches refs. There might not be a ref that you're looking for.

You can automate the digging using the following script.

while [ -z $( git merge-base master feature ) ]; do          git fetch -q --deepen=1 origin master feature; done 

Answer 2

What you need (I think), in a catch-22 way, is 'git describe --all --first-parent' to tell you the depth of the given commit from the appropriate branch. However I'm not sure how to get that from Github before you do your shallow fetch ;-)