[BUG] commit 163cdfd31 breaks interpolation in extended files about compose

[jolmg]

As an additional check (since the linked commit mentions empty environment variables), changing docker compose config for FOO=/dev/zero docker compose config in each of the above reproduction scripts gives the same results. Same errors. The only difference is that, in the successful one, source: /dev/zero rather than source: /dev/null, of course.

[idsulik]

@jolmg hi! I think the issue with the yaml, you should put empty space after ":"

- ${FOO:-/dev/null}: /tmp/foo:to
                    ^ here

[jolmg]

@idsulik This is the short syntax for volumes.. If I added a space, it wouldn't be a yaml string; it'd a mapping, and I'd get this error:

validating /tmp/docker-compose-interpolation-test-t9H5/docker-compose.yml: services.foo.volumes.0 type is required

Because it's then expecting the different syntax with specific keys.

[jolmg]

@idsulik Thank you, though. Your comment does show that switching to long syntax is a good workaround for this bug.

d=/tmp/docker-compose-interpolation-test-long-syntax

set -e
mkdir "$d"
cd "$d"

cat > docker-compose.yml <<EOF
services:
  foo:
    extends: { file: other.yml, service: foo }
EOF

cat > other.yml <<EOF
services:
  foo:
    image: bash
    volumes:
      - type: bind
        source: \${FOO:-/dev/null}
        target: /tmp/foo
        read_only: true
EOF

docker compose config

Result:

name: docker-compose-interpolation-test-long-syntax
services:
  foo:
    image: bash
    networks:
      default: null
    volumes:
      - type: bind
        source: /dev/null
        target: /tmp/foo
        read_only: true
networks:
  default:
    name: docker-compose-interpolation-test-long-syntax_default