Docker-compose variable-substitution mandatory variables - docker

Question

I have a docker-compose file that uses variable substitution for some secrets and I want to get an error if they are not supplied or empty, for this purpose I have tried this:
environment:
- >-
JAVA_OPTS=
-DMYSQL_USER=${MYSQL_USER:?MYSQL_USER_NOT_SET}
-DMYSQL_PASSWORD=${MYSQL_PASSWORD:?MYSQL_PASSWORD_NOT_SET}
-DMYSQL_URL=db:3306/${MYSQL_DATABASE:?MYSQL_DATABASE_NOT_SET}
However, it gives me the error:
ERROR: Invalid interpolation format for "environment" option in service "myservice": "JAVA_OPTS= -DMYSQL_USER=${MYSQL_USER:?MYSQL_USER_NOT_SET}...
According to https://docs.docker.com/compose/compose-file/#variable-substitution this should work since it has this snippet:
Similarly, the following syntax allows you to specify mandatory
variables:
${VARIABLE:?err} exits with an error message containing err if
VARIABLE is unset or empty in the environment. ${VARIABLE?err} exits
with an error message containing err if VARIABLE is unset in the
environment.
I also have version: "3.4" in my docker-compose so that shouldn't be the issue.
Already tried it with just ${MY_VAR?MY_ERROR} but it didn't work either.
I have even gone as far as to look at the source code but found nothing helpful.
EDIT :
I tried to make a minimum size reproduction:
docker-compose.yml
version: "3.4"
services:
hello:
image: hello-world
environment:
- TEST=${TEST?err}
docker-compose up
ERROR: Invalid interpolation format for "environment" option in service "hello": "TEST=${TEST?err}

Answer 1

This depends on your docker-compose version.
With docker-compose 1.17.1 you will get
ERROR: Invalid interpolation format for "environment" option in service "my-service": ...
if you use ${TEST?"My error message"} but with
e.g. docker-compose 1.29.2 it works as expected
ERROR: Missing mandatory value for "environment" option interpolating ... in service "my-service": "My error message"