Digging around and looking into the GitLab API for this, I think that this could be done with the Hubot approach (or any other Bot), but there are two more issues that I can see so far:
- Authentication: If the bot were to push the comment to an issue, it looks like a comment by the Bot in GitLab and not the real user who posted the comment in Mattermost. Not sure how to resolve that.
- Also, such a new comment would trigger another push to Mattermost from GitLab service which then makes this a duplicate of the comment which is already there. That would certainly feel like spam and we would have to find a solution for that as well.
Any other thoughts? Or even proposals on how to solve these?