libgit2 (fetch & merge & commit)

Question

I 'm trying to pull from a repo with libgit2.

My steps are these:

• git_remote_connect - OK
• git_remote_download or should I use git_remote_fetch ?
• git_remote_ls to get the of the HEAD to pass to git_annotated_commit_from_fetchhead (is this coorect?). But there are more than 1 heads, do I pass the one with "HEAD" name?
• git_merge.

This results in MERGE_HEAD in .git folder and then I am able to merge with an existing commit.

The question is, is the above sequence correct? Why git creates FETCH_HEAD whereas libgit2 has MERGE_HEAD?

Answer 1

You probably want to use git_remote_fetch, not git_remote_download. fetch is a convenience function that performs the download and updates things like the remote tracking branches to point to the data that is on the server and - more importantly for you - the FETCH_HEAD file.

You can determine which branch to feed to git_merge by examining the FETCH_HEAD lines and identifying the branch that is not marked as not-for-merge. The simplest way to do this is to iterate over them using git_repository_fetchhead_foreach. Your callback will be invoked for each line, and you simply need to make note of the one that has for_merge set to true. The branch marked as for-merge will be the remote branch corresponding to the merge line in your config.

That is to say that if your HEAD points to master, and your configuration is:

[branch "master"]
    remote = origin
    merge = refs/heads/master

Then when you fetched from origin, the corresponding remote master branch would be marked as for-merge. Once you have identified this FETCH_HEAD entry, then you can create an annotated commit from it and call git_merge.

Note that both git core and libgit2 will create FETCH_HEADs when fetching and MERGE_HEADs when merging. You will only see the latter when the merge is ongoing - so if you run merge --no-commit on the command-line or if you have a conflict. You can use this to compare the data that git core produces to ensure that you are producing the same data using libgit2.