[CI Variables] Add Merge Request Variable

Description

Use case

Setting up a build task that posts the coverage report for a merge request as a comment on the merge request (filtered by the files that the merge request modified).

Issue

The problem is that I have no way of associating the build with the merge request that triggered it.

• The CI variables do not contain a reference to the merge request
• The Build API does not contain a reference to the merge request
• The Pipeline API does not contain a reference to the merge request

Observations

The build page provides a link to the merge request in the job details, so the information is readily available.

Proposal

Expose a CI variable for the merge request as CI_MERGE_REQUEST_ID when applicable.

Workaround

Iterate through all the merge requests using the API until the build's commit is found. I do not plan on resorting to this.

Links / references

• https://docs.gitlab.com/ce/ci/variables/#predefined-variables-environment-variables
• https://docs.gitlab.com/ce/api/builds.html#get-a-single-build
• https://docs.gitlab.com/ce/api/pipelines.html#get-a-single-pipeline

/cc @grzesiek

added ~19173 feature proposal ~13921 labels

I think we need a "CI Variables" label soon. There are lot's of feature proposals for CI Variables now

@deckar01 @markglenfletcher This makes a lot of sense, but we would need https://gitlab.com/gitlab-org/gitlab-ce/issues/23902 first.

There is already logic in the build service to look up the merge request for the build.

I don't really need a special only trigger since my use case is integrating it into an existing task.

If I had a variable I could just check to see if it existed to conditionally execute the behavior:

if env.CI_MERGE_REQUEST_ID:
    mr = MergeRequest.get(env.CI_MERGE_REQUEST_ID)
    mr.addComment(coverage_report.to_md())

Is there a reason this variable couldn't be the first iteration of #23902 (moved)?

I think I see the issue now. The CI variables currently contain info for the source repo, but not the target repo. You would have to have the full URL to the merge request or additional variables to make it work.

#23902 (moved) already proposes adding CI variables for CI_MERGE_REQUEST_IID and CI_MERGE_REQUEST_TARGET_BRANCH. All that would be needed is a CI_MERGE_REQUEST_TARGET_REPO to make it useful now. It would not be useful after #23902 (moved) lands though.

changed title from [CI] Merge Request ID Variable to [CI Variables] Add Merge Request Variable

Closing in favor of #23902 (moved) since it will solve my use case.

closed