Merge request pipeline does not accept CI variables from git push option

Summary

The merge request pipelines do not accept push options for CI/CD variables. This also makes the variable conditions in rules unusable.

Note: It is known that passing variables and CI.SKIP only work for Branch pipelines today. This request is to extend the behavior to merge request pipelines as well.

Steps to reproduce

1. Create a pipeline using the following configuration:

   # .gitlab-ci.yml
   
   always_job:
     rules:
       - if: '$CI'
     script:
       - env | grep -E '^CI_(PIPELINE|JOB)_' | sort
       - echo "SKIP_MY_EXAMPLE_JOB = $SKIP_MY_EXAMPLE_JOB"
   
   my_example:
     rules:
       - if: '$SKIP_MY_EXAMPLE_JOB != "true"'
     script:
       - echo "SKIP_MY_EXAMPLE_JOB = $SKIP_MY_EXAMPLE_JOB"

2. Create a test branch and add a dummy commit:

   git checkout -b test
   git commit --allow-empty --message='Test trigger pipeline'

3. Push the test branch with a variable in a git push option:

   git push origin test --push-option=ci.variable=SKIP_MY_EXAMPLE_JOB=true

4. Create a merge request for this branch

5. Look at the pipeline page and notice the two pipelines where my_example job is absent in the branch pipeline, but not absent in the merge request pipeline. Also notice the SKIP_MY_EXAMPLE_JOB variable is empty in the merge request pipeline.

branch pipeline	merge request pipeline

Example Project

https://gitlab.com/maikelv/test-push-option-variables-merge-request-pipeline-bug

What is the current bug behavior?

The CI push option variable SKIP_MY_EXAMPLE_JOB is not passed to the merge request pipeline:

What is the expected behavior?

The CI push option variable SKIP_MY_EXAMPLE_JOB also being passed to the merge request pipeline:

This is not an existing log, but a photoshopped screenshot to communicate the desired output

Output of checks

This bug happens on GitLab.com (currently v15.4.0-pre 48afc24c73f)

Potential workarounds

• Some customers have found success using the CI_COMMIT_MESSAGE (forum post) and rules to skip CI with Merge Request pipelines but we know this is not a great solution.