How to merge rules on a GitLab CI Job

Question

Let's suppose I have this hidden "base" job.

.base_job:
  rules:
    - if: "$CI_COMMIT_TAG"
      when: never
    - if: '$CI_PIPELINE_SOURCE == "web"'

I'd like to add these rules to a new job and be able to extend them too, e.g.:

job_1:
  rules:
    - <add .base_job here>
    - if: "$CI_MERGE_REQUEST_IID"


job_2:
  rules:
    - <add .base_job here>
    - if: "$CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH"

Note that job_1 and job_2 have different rules, including the ones from .base_job.

If I were to use extends, the jobs would have only the custom rule because according to the docs:
You can use extends to merge hashes but not arrays.

My solution so far is to copy-paste the rules for both jobs but I'd like to keep it more DRY.

Any tips on how to do it?

Answer 1

As pointed out in the question, the GitLab CI extends construct does not allow one to merge inner arrays (and more generally the expected underlying feature in YAML is not(yet) available), so basically:

.base_job:
  rules:
    - if: "$CI_COMMIT_TAG"
      when: never
    - if: '$CI_PIPELINE_SOURCE == "web"'

job_1:
  extends: .base_job
  rules:
    - if: "$CI_MERGE_REQUEST_IID"

would lead to:

job_1:
  rules:
    - if: "$CI_MERGE_REQUEST_IID"
  # ? overwritten

Alternative solution

However, if you find that the first answer posted is too hacky and too verbose, it appears you could just use the native YAML anchors construct to do the same.

Namely, you might write a GitLab CI conf-file like this:

.base_job:
  rules:
    - &rule_a
      if: "$CI_COMMIT_TAG"
      when: never
    - &rule_b
      if: '$CI_PIPELINE_SOURCE == "web"'
job_a:
  rules:
    - *rule_a
    - if: "$CI_MERGE_REQUEST_IID"
job_b:
  rules:
    - *rule_b
    - if: "$CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH"

Answer 2

So I've found a very hacky way of doing this. It is not ideal but at least I could get what I wanted working.

Warning: This is only available starting on GitLab 14.3, which as of Sep/21 is in a pre-release state.

I prepare a set of just the texts of the rules and inject them in a real rule if using !reference.

.rules_base:
  rules:
    RULE_A: "$CI_COMMIT_TAG"
    RULE_B: "$CI_MERGE_REQUEST_IID"

job_a:
  rules:
    - if: !reference [.rules_base, rules, RULE_A]
    - if: '$CI_PIPELINE_SOURCE == "web"'

job_b:
  rules:
    - if: !reference [.rules_base, rules, RULE_B]

This actually works and I can reuse the same rules on different jobs while also including new rules, if necessary.