Compose parsing commented out yaml for env vars

[beyondmeat]

Description

I discovered that commented out yaml that contain env vars in the comment do get parsed in RC1. This seems to be a bug introduced by the recent env changes.

for example a commented out docker label, demoted by #

# traefik.http.routers.dashboard.rule: Host(`${TRAEFIK_CNAME}.localhost`, `${TRAEFIK_CNAME}.local.${DOMAIN}`)

It will output warn on pull or up about the env variable. The env var isn't used or referenced by anything that isn't commented out.

have valid yml that uses a env variable
comment out the line in the yml, (line starting with #)
run docker compose pull to
Steps to reproduce the issue:

1. Create docker compose and use env file with env var
2. Comment out a line that uses a unique env var
3. Run pull or up

Describe the results you received:
see variable is not set. Defaulting to a blank string warning.

Describe the results you expected:
Not to see a warning. Compose must be parsing commented out yaml lines in it's env parsing code as that is the likely explanation.

Additional information you deem important (e.g. issue happens only occasionally):

Output of docker-compose --version:

RC1

Output of docker version:

Docker version 20.10.8, build 3967b7d

Output of docker context show:
You can also run docker context inspect context-name to give us more details but don't forget to remove sensitive content.

Output of docker info:

(paste your output here)

Additional environment details (AWS ECS, Azure ACI, local, etc.):

[rowanparker]

This may be related. It seems lines with $ characters cause issues. I have the following line in a docker-compose.yaml

MERCURE_JWT_SECRET: ${CADDY_MERCURE_JWT_SECRET:-!ChangeMe!}

With Docker Compose V2 enabled, I get an error and my containers won't launch.

yaml: line 9: did not find expected tag URI

If I disable Docker Compose V2, the error goes away.

The worst part is I never went in and set this value to enabled. I suspect it was silently enabled as per this article:
https://docs.docker.com/compose/cli-command/

We will gradually turn this option on automatically for Docker Desktop users, so that users can seamlessly move to Docker Compose V2 without the need to upgrade any of their scripts.

So I just wasted an hour troubleshooting this because Docker just changes things on you with no notification.

[ndeloof]

Will be fixed by compose-spec/compose-go#167 AFAICT

[ulyssessouza]

I'm closing this since compose-spec/compose-go#167 is already merged.
Please feel free to reopen if the problem persists after next release.

[beyondmeat]

@ulyssessouza please reopen, bug still valid in rc3

[ulyssessouza]

@beyondmeat Could you please post a minimal docker-compose.yml to reproduce the case?

[beyondmeat]

Any compose file will do that uses extends. When the commented out variable exists in an a compose file that is referenced by another compose file via extends, it parses the commented out var and warns it's not set. This is only happening now on for extended compose files. Should I make a new issue on docker/compose since it belongs there now?

docker-compose.yml

version: "3.9"

services:
  whoami:
    extends:
      file: ./docker-compose.whoami.yml
      service: whoami

docker-compose.whoami.yml

version: "3.9"

services:
  whoami:
    image: "traefik/whoami"
    labels:
      - "traefik.enable=true"
      # - "traefik.http.routers.whoami.rule=Host(`whoami.${THIS_IS_A_BUG}`)"
      - "traefik.http.routers.whoami.entrypoints=web"

docker compose up
WARN[0000] The "THIS_IS_A_BUG" variable is not set. Defaulting to a blank string. 

[ndeloof]

Closed => docker/compose#8603