How to use composer (php) including cache with gitlab-ci

.gitlab-ci.yml

build:install-vendor:
  stage: build
  image: <any-image-with-composer>
  before_script:
  - composer config -g cache-dir "$(pwd)/.composer-cache"
  script:
  - composer install --ignore-platform-reqs --no-dev --optimize-autoloader --no-ansi --no-interaction --no-progress
  cache:
    paths:
    - .composer-cache/
  artifacts:
    expire_in: 30 min
    paths:
    - vendor/

Thanks for your gist! Now composer has its own image on Docker Hub.
Thus, I suggest this little modification:

image: composer:1

I know this is nothing to do with this, but why can't GitLab simply cache ~/.composer ?

probably because ~/.composer is somewhere in the container that has the composer command

I know. this is nothing to do with this, but why can't GitLab simply cache ~/.composer ?

@bertalanimre GitLab CI Caches by definition have the scope of the app aka the Git repository only. The repo resides in the working directory. This directory may be located in different locations depending of the runner setup. Broadly speaking, the CI process does not know anything else about the environment, like the existence of home directories (~ / $HOME) or which tool you use in your jobs (composer). Therefore you need to tell the tool to store its cache files in the working directory. This allows GitLab to pick them up.