GitLab fails to start due to postgressql permissions if I use extends

I have a complicated docker-compose setup of which gitlab is only one part.

I had originally set up my compose files so that I have a top-level docker-compose.yml and then separate compose files for each of my containers, accessed via extends, e.g.:

services
  ...
 gitlab
    extends:
       file: gitlab-dfst/docker-compose.yml
       service: gitlab-dfst

    depends_on:
      - redis
      - postgresql
...

The gitlab-dfst/docker-compose.xml then has all the configuration except the depends and volumes stanzas.

When I start this, gitlab startup fails with a message about insufficient permissions to configure the pg_trgm feature of postgressql and it goes into a restart loop.

If I move the same compose statements from the separate file to the main docker-compose file then gitlab startup works fine.

My question: Why does using extends cause this failure? Is there some user error in this case or is this simply a configuration that won't work?

Compare the top-level docker-compose.yml with gitlab-dfst/docker-compose.xml, focusing on the service definition assembled through extends and the omitted depends_on and volumes sections. Reproduce the startup failure and inspect the PostgreSQL pg_trgm permission message. Done means determining whether the failure is caused by the compose configuration or whether this use of extends is unsupported.