[Github Actions Importer] How to write a custom transformer for GitLab CI when workflow rules are complex

[davidng-dac]

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Hi team 👋

I’m currently migrating a GitLab CI pipeline to GitHub Actions using GitHub Actions Importer, and I’ve hit a roadblock related to custom transformation.

My .gitlab-ci.yml includes a top-level workflow: block with complex conditional rules, for example:

workflow:
  rules:
    - if: $CI_PIPELINE_SOURCE == "merge_request_event"
      when: never
    - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH
      when: always
    - if: $CI_COMMIT_BRANCH !~ /^hotfix\//
      when: always

When I run the importer:
gh actions-importer dry-run gitlab ...

I get warnings like:
Unable to map conditional expression to GitHub Actions equivalent in jobs.<job_id>.if and nothing there

and the stages information doesn’t appear correctly in the generated workflow file.

on:
  push:
  workflow_dispatch:

while my gitlab-ci has

stages:
- ".pre"
- "BUILD"
- "UPDATE"
- "DEPLOY"
- ".post"

What I’m trying to achieve

• Write a custom transformer to:
  • Map these workflow.rules conditions into proper if: expressions in GitHub Actions.
  • Preserve or reconstruct the GitLab stages order as sequential job dependencies.

I already tried with custom transform with identifiers [workflow, if, workflow.if, push, manual,...] but nothing work properly

[sinavm]

How This Maps Your Example
• Rules Output: Generates something like:

on:
  push:
    branches: [main]
  workflow_dispatch:
jobs:
  build-job:  # Example job
    if: github.ref == 'refs/heads/main' || !startsWith(github.ref, 'refs/heads/hotfix/')
    # ... steps

Stages Output: Adds needs like:

jobs:
  BUILD:
    needs: .pre  # Or skip if .pre is hidden
  UPDATE:
    needs: BUILD
  DEPLOY:
    needs: UPDATE
  .post:
    needs: DEPLOY

Adjust the reject in the code if you want hidden stages (starting with .) to be implicit.

Next Steps & Tips
• Run a Dry-Run: Peek at tmp/dry-run/.github/workflows/your-pipeline.yml to verify. If the item structure differs (e.g., rules nested differently), tweak the extraction (puts item.to_yaml for debugging).
• Edge Cases: If your jobs have per-job rules overriding the workflow ones, add another transform "job.rules" block. For regex like !~ /^hotfix//, GitHub’s startsWith is a close match—test on branches like hotfix/bugfix to confirm.

Migrate: Once happy, run:

gh actions-importer migrate ... --custom-transformers gitlab-custom-transformer.rb

This will create a PR with the workflows. Review the “Manual steps” in the PR description for secrets/runners.

Docs for More: Check the official extending with custom transformers guide for advanced stuff like runner/env mappings.

If this doesn’t quite nail it (e.g., paste your full dry-run output or the exact item debug), drop more details and I’ll refine the script. Happy migrating—GitHub Actions will feel snappier once you’re over the hump! 🚀

Best, @sinavm

[github-actions[bot]]

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