"extends" and multiple yml files don't work together

[codablock]

I'm currently trying to use the new "multiple files" (#2051) feature and got stuck on extends not working anymore when used together.

Example:

# common.yml
baseservice:
  labels:
    - "my.label=my-value"
  environment:
    MY_ENV: "MY_VALUE"

# base.yml
service1:
  extends:
    file: common.yml
    service: baseservice
...more stuff...

# dev.yml
service2:
  extends:
    file: common.yml
    service: baseservice
...more stuff...

When started with:

docker-compose -f base.yml -f dev.yml up

the services do not include the labels and env vars from "baseservice".

Just for testing purposes, I tried to use a random name for the extends/file field in dev.yml and it did not complain about not found files, which looks like it doesn't even try to open the file.

[dnephin]

Found the bug. extends is not copied over from the override file. So the labels/environment worked on service1, but not service2.