Which version of the docker-compose file is compose using?

Which version of the file specification is compose using in the case?

version: "3.0"
services:
  db:
    image: docker.feedzai.com/hub-proxy/library/postgres:11
    healthcheck:
      test: ["CMD-SHELL", "pg_isready"]
      interval: 10s
      timeout: 5s
      retries: 5

  app:
  image: docker.feedzai.com/hub-proxy/library/postgres:11
    healthcheck:
      test: ["CMD-SHELL", "app_isready"]
      interval: 10s
      timeout: 5s
      retries: 5
    depends_on:
      db:
        condition: service_healthy

According to the documentation , condition is no longer supported in docker-compose file version 3. But this configuration works and if I run docker-compose config I still see the version 3.0 there.

According to the specs, which joins version 2 and 3, this is valid syntax, but for what I understand, the file can use any syntax, and compose will select the version to fit that configuration. So, how can I know which version compose is choosing to interpret this file?


How I reproduce this issue

# Got a docker with ubuntu jammmy
docker run --rm -it --entrypoint /bin/bash ubuntu:jammy-20220531
>

#Install docker-compose inside the container (v. 1.29.2)
> apt-get update && apt-get install docker-compose
> docker-compose -v
docker-compose version 1.29.2, build unknown

# copy the above file to the container (from another terminal)
docker cp docker-compose.yml <container id>:

# run docker-compose config to validate the configuration file
> docker-compose config
services:
  app:
    depends_on:
      db:
        condition: service_healthy
    healthcheck:
      interval: 10s
      retries: 5
      test:
      - CMD-SHELL
      - app_isready
      timeout: 5s
    image: docker.feedzai.com/hub-proxy/library/postgres:11
  db:
    healthcheck:
      interval: 10s
      retries: 5
      test:
      - CMD-SHELL
      - pg_isready
      timeout: 5s
    image: docker.feedzai.com/hub-proxy/library/postgres:11
version: '3.0'