Backend: Make it possible to identify a new/empty branch with workflow:rules

⚠ Solution

After implementing #293645 (closed) it appears like we have a working solution using this config

workflow:
  rules:
    - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH
      when: always
    - if: $CI_COMMIT_BRANCH
      changes:
        paths: ['**/*']
        compare_to: master
      when: always

test:
  script: exit 0

Problem to Solve

Whenever a user creates a new branch it will be picked up by GitLab and will be post-processed. In turn, a pipeline will be created.

The pipeline could be useless in cases where there is nothing different from the origin, even considering .gitlab-ci.yml conditions.

Proposed solution

test:
  script: ./run tests
  rules:
    - if: $CI_COMMIT_BRANCH
      changes:
        paths:
          - *
        compare:
          branch: master

old Proposal (not relevant)

Click to expand

By having a new variable CI_BRANCH_COMMIT_COUNT that users could add to the workflow:rules condition, the variable will be defined based on a result of using a Git command, any pipeline using can then determine whether the branch is the same as the default branch.

An example for capturing a branch commit count could look like this:

git rev-list --count $CI_COMMIT_BRANCH ^DEFAULT_BRANCH (for regular pipelines)
git rev-list --count $CI_COMMIT_BRANCH ^CI_MERGE_REQUEST_TARGET_BRANCH_NAME (for MR pipelines)

This way users could add that to the pipeline configuration as

workflow:
  rules:
    - if: $CI_BRANCH_COMMIT_COUNT == 0
      when: never

...

in case they would like to avoid a pipeline to run when a new branch is created

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