Is there any way to get the same information as the native git command
git branch --merged <sha>
via the Rugged libgit2 bindings for Ruby?
What that git commit is doing is looking at each branch and checking whether the merge-base between the branch and the commit you've given (or HEAD if none) corresponds to the one of the branch.
If they match, it's merged; if they don't, it's not. You can do this loop in ruby fairly easily
repo.branches.each(:local) # look only at local branches
.map { |b|
tgt = b.resolve.target # look at what the branch is pointing to
# and check if the target commit is included in the history of HEAD
merged = repo.merge_base(repo.head.target, tgt) == tgt.oid
[b.name, merged]
} # this will give a list with the name and whether the branch is merged
.keep_if { |name, merged| merged } # keep only the ones which are merged
.map(&:first) # get the name
You could have an merged_list << b.name if merged in the first block and make it hang off of the each, but I like composing streams of data.
You can also change whether to use :local, :remote or both for the branches depending on your need. And you can also change repo.head.target to whatever id you want to compare against.