Environment interpolation regression in docker-compose.yml

[ashb]

I #1765 caused a small regression in behaviour. My docker-compose.yml looks like this:

postgres:
  container_name: mailserverdocker_postgres
  build: postgres
  environment:
    POSTGRES_PASSWORD:
    PGDATA: /var/lib/postgresql/data/pgdata
  volumes:
    # This is not on the host but on the docker-machine. Cos VMHGFS permissions
    # are fail. FULL OF FAIL AND PERMISSIONS ERRORS
    - /docker-volumes/run/pg-data:/var/lib/postgresql/data

On docker-compose 1.4.2 this would use the POSTGRES_PASSWORD env var from runtime at docker-compose up - now it gives this error:

Service 'postgres' configuration key 'environment' 'POSTGRES_PASSWORD' contains None, which is an invalid type, it should be a stringnumber or a boolean

I can fix it by changing to POSTGRES_PASSWORD: ${POSTGRES_PASSWORD} -- I'm just not sure if this regression was intentional or not? It wasn't clear from the Changelog that this would break.

(Maybe just a documentation change and a note in the changelog about this being a (small) breaking change is enough here?)

[ashb]

I didn't say that very clearly: Both of these worked in v1.4.2:

• POSTGRES_PASSWORD=foo docker-compose up postgres password is "foo"
• docker-compose up postgres password is empty string (but nothing complained about it's absence)

With v1.5.0rc1 only the first works.

[aanand]

I believe this was caused not by #1765 but by #1808.

[mnowster]

@aanand @ashb I'm fixing it, I'm fixing it!