Per environment variables in gitlab-ci yaml?

GitLab CI/CD
1

Problem to solve

As CI/CD Variables we can assign variables to individual environments. It is not clear how to achieve the same in .gitlab-ci.yaml

Steps to reproduce

As per the given gitlab-ci.yml, given a job that uses parallel matrix or similar means to deploy to multiple environments, one might need different variables to apply to each. It is, however, an error to use $ENV in an extends directive.

Configuration

.environments:
  parallel:
    matrix:
      - ENV: development
      - ENV: staging
      - ENV: production

.env:development:
  variables:
    URL: http://dev.example.com
.env:staging:
  variables:
    APP_URL: http://staging.example.com
.env:production:
  variables:
    APP_URL: http://example.com

deploy:
  extends:
  - .environments
  - .env:$ENV
  environment:
    name: $ENV