Did a first pass and proposed two changes for review upstream:

Will use that to create some jobs on our Jenkins to make sure they are working properly. I have a test git repo to exercise the jobs against.

If all fine, I will cherry pick / update on our integration/jenkins-job-builder.git fork.

I had meeting yesterday, then did some random reviews in the evening.
This morning I had to fix T128569: Zuul deadlocks if unknown repo has activity in Gerrit.

Stuff to do is craft a few jobs making use of the patchset I crafted, run them and ensure they work properly. Once confirmed, I will cherry pick both of my patches on integration/jenkins-job-builder and people can update their local installation.

I created a git repository with a /config.yaml file having:

python:
    - py27
    - py34
    - py35
database:
    - postgre
    - mysql

The dummy JJB config:

- job:
    name: hashar-jjb-yamlaxis
    project-type: matrix
    axes:
     - axis:
        type: label-expression
        name: label
        values:
         - contintLabsSlave && UbuntuTrusty
     - axis:
        name: python
        type: yaml
        filename: config.yaml
     - axis:
        name: database
        type: yaml
        filename: config.yaml
    scm:
        - git:
            url: 'https://github.com/hashar/yamlaxis'
            branches:
                - master
            wipe-workspace: false
            clean:
                after: true
    builders:
        - shell: |
            echo -e "Axis...\nPython: $python\nDatabase: $database"

Build page view:

And the echo commands shows the env variables $python and $database properly.

The patches I have proposed are very rough and I need to do a second pass on them. Namely enhance the documentation and add a few more tests.

Change 274435 had a related patch set uploaded (by Hashar):
Merge in Jenkins Yaml Axis Plugin support

https://gerrit.wikimedia.org/r/274435

Change 274435 merged by Hashar:
Merge in Jenkins Yaml Axis Plugin support

https://gerrit.wikimedia.org/r/274435

I have refreshed our fork of JJB to the latest master, carefully inspecting diff as I was rebasing commits after commits (git bisect works like a charm).

Cherry picked my two changes send upstream and I have merged them in our fork. Tip of master is cd63874ab6bccdf4e93a522ed3543c84e96c0170 you will want to update your JJB setup.

So this task is almost complete, pending review / merge of changes in upstream repository.

I have addressed the few comments that were pending in OpenStack Gerrit and rebased the serie of patches.

Upstream patch has been merged :-} So I guess I just have to update our fork.