Memory leak caused by diffs?

I'm using Rugged in an application that uses Rugged to generate thousands of diffs in quick succession, and I'm noticing memory growing steadily as it runs.

I've managed to reproduce the problem in this reduced test case, which just generates a lot of diffs with a big repo (rails/rails). You can run this script and watch the memory consumption just go up and up and up.

require "rugged"

def diff_parents(commit)
  puts commit.oid
  commit.parents.each { |parent| parent.diff(commit) }
  commit.parents.each { |parent| diff_parents(parent) }
rescue SystemStackError # This can hit Ruby's recursion limit. Just move on.
end

path = "#{__dir__}/rails"
if File.directory?(path)
  repo = Rugged::Repository.new(path)
else
  print "Cloning rails…"
  repo = Rugged::Repository.clone_at("https://github.com/rails/rails", path)
  puts " done"
end

diff_parents repo.head.target

I don't have the C knowledge to figure out the cause of the leak, so this could be a libgit2 issue rather than a Rugged-specific one.

Start by running the reduced Ruby script against the Rails repository and monitoring memory while repeated parent.diff calls execute. Then trace the Rugged/libgit2 diff path to identify which allocations remain live between iterations. Done means repeated diff generation no longer shows steady memory growth, with the reproduction used to verify the result.