Don't process cross-reference notes from forks

If a commit mentions an issue or merge request a cross-reference note will be created in the upstream issue/mr on push to a fork's default branch. This can lead to a lot of noise in the upstream project. There's no need to create a note every time a fork pushes a commit with a mention. Otherwise every fork that does a simple update from upstream operation will trigger the mention.

cc/ @DouweM @vsizov

Related(ish) to https://dev.gitlab.org/gitlab/gitlabhq/issues/2640

This is a matter of fixing the "does a cross reference for this object already exist?" check to match only on commit hash instead of project+commit hash. That way we will only get it a cross-reference for the original project in case the commit is in the original project, but we will still get fork cross references if a new commit in the fork was the first one to refer to the issue/MR.

Milestone changed to 8.5

Attempting this one!

Reassigned to @jameslopez

@DouweM I've been looking into this one today but I'm a bit stuck - not sure I'm looking at the right method. https://gitlab.com/gitlab-org/gitlab-ce/blob/master/app/services/system_note_service.rb#L294 - I thought that was the place and I can see gfm_reference has a project and a commit SHA. I can make that just a SHA by calling mentioner.gfm_reference(nil) but that doesn't seem to help to resolve the issue...

@jameslopez Right, with mentioner.gfm_reference(nil), we'll get

notes.where(note: "mentioned in SHA"

which won't match mentioned in USER/PROJECT@SHA. We can use SQL LIKE for the commit case:

notes.where("note LIKE ?", "mentioned in %SHA")

so that % matches USER/PROJECT.

Another approach would be to load all of the notes into memory, get their referenced objects (issues, MRs, commits etc), and see if the commit object is included in that list, but that'll be far less performant than using SQL.

Does that help? :)

@DouweM thanks! - that makes sense. Testing wise, what's the best way to create a commit for a fork? I'm using CreateCommitBuildsService.new and Projects::ForkService.new. Is that okay ?

mentioned in merge request !2731 (merged)

@jameslopez Looks like you've figured it out, I'll review the MR!

Status changed to closed by commit 42d088fc

mentioned in commit 42d088fc

Mentioned in commit pfjason/gitlab-ce@42d088fc