Confusing "invalid compose project" Error Message From Compose v2

[mccarthy]

Docker Desktop quietly updated me to Compose v2 (v2.0.0-rc.1 specifically), and now I'm getting this error message when I run most any docker-compose command (e.g. docker-compose top) for a complicated project:

service "extensions" has neither an image nor a build context specified: invalid compose project

I'm guessing v2 doesn't like something in my compose files, but as best I can tell I don't have a service named "extensions" so this error message is not very helpful. I saw another issue (https://github.com/docker/compose-cli/issues/1968) related to empty strings and quotes that referenced a similar error message, but it appeared in that case the service mentioned in the error message was a real service from the person's docker-compose file.

I do also get a number of warnings about a variable that is not set, but these warnings occurred (and didn't cause issues) in v1.
WARN[0000] The "REDACTED" variable is not set. Defaulting to a blank string.

[ndeloof]

Could you please post your compose file so I can check ?

[mccarthy]

Unfortunately the file is ~1300 lines (plus another file via extends) and I'm not able to share it. If I had an indicator of where this error was coming from, I could create a test/repro docker-compose file.

I tried to set the log level (docker-compose top --log-level DEBUG) to provide some more information, but ran into this issue:
#1891

What else can I do to help debug? Can you provide some insight into how I can validate my docker-compose files against v2? I would settle for a more helpful error message indicating what file/line this error occurred on.

[ndeloof]

Can you try running docker compose config to get the actual compose model being applied after merge/interpolation? (assuming this doesn't fail with same error)

[mccarthy]

docker compose config fails with same error.

[ndeloof]

ok, as docker compose config also fail, you can try to bisect your compose modela and don't need a running compose app to reproduce the issue:

Try to remove some of your services definition, remove extends etc until the error dissapears

[mccarthy]

Figured it out. v2 is incompatible with the names of some of our services. To repro, run docker compose config on this minimal compose file:

version: '2.3'

services:

  x-redacted:
    image: "REDACTED"

[ndeloof]

nice catch.
x-* is reserved by the compose specification to define model extensions. But I don't think we would expect extension to apply to the services dictionary. I'm checking how we could remove this constraint in compose-go ...