Backend: Legacy POST /ci/lint API endpoint

Introduction

The POST /ci/lint API endpoint is problematic because it does not accept a project as a parameter. So, the result is only valid as long as the CI config is basic (no includes, no rules, etc).

I haven't found the related discussions about those problems but please add if you find any.

Data

• Doc: https://docs.gitlab.com/15.5/ee/api/lint.html#validate-the-ci-yaml-configuration
• Usage: https://log.gprd.gitlab.net/goto/4a31f0e0-5e8d-11ed-8d37-e9a2f393ea2a
  • It has ~15k requests per week.
  • It has ~131 unique users: https://log.gprd.gitlab.net/goto/1c877600-5e8e-11ed-8d37-e9a2f393ea2a
• Code: https://gitlab.com/gitlab-org/gitlab/-/blob/15-5-stable-ee/lib/api/lint.rb#L24

Proposal

1. Add the deprecated notice to the documentation.
2. Initiate a deprecation flow: https://about.gitlab.com/handbook/product/gitlab-the-product/#process-for-deprecating-and-removing-a-feature
3. Reach out to the affected users.
4. Enable the removal for GitLab.com.
5. Enable the removal for self-hosted in major version.