Support for runArgs for `docker compose` scenario

[bgloss]

As a developer, I want to point docker compose to my (the correct) .env-file.

{
	"name": "Python 3 & Poetry",
	"dockerComposeFile": [
		"../../docker-compose.yml",
		"./docker-compose.yml"
	],
        "runArgs": ["--env-file=../../.env"],      <-- New Option
        ...
}

Discussed in https://github.com/orgs/devcontainers/discussions/36

^{Originally posted by bgloss March 10, 2023}
I don't get the environment variables from my project's .env file into the docker-compose.ymlsetup with a pretty default project layout.

My project layout is as follows:

.devcontainer/
     devcontainer.json
     docker-compose.yml
     Dockerfile
.env

I want to have in docker-compose.yml a section to create a Postgres container with setting up the environment one by one: POSTGRES_USER, POSTGRES_PASSWORD, and POSTGRES_DB and fill them with variables from the project's .env file. The relevant section in docker-compose.yml is:

  postgres:
    image: postgres:latest
    environment:
      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD}
      POSTGRES_USER: ${POSTGRES_USER}
      POSTGRES_DB: ${POSTGRES_DB}

I do NOT want to have a copy of my .env file in the .devcontainer/ folder, as it is the case in some of the DevContainer templates. This would work, as in this case docker compose loads it by default. I don't want this organization, as the .env file is also needed by the project's code and expected in the project root.

I also don't want to expose the whole .env-file to my container, which I could do with the env_file option in the docker compose service description.

When building a container myself (just docker, no docker compose), I can add in devcontainer.json the option runArgs next to the option build giving the env-file information to docker: --env-file ../.env However, this is not possible when using a docker-compose setup in vscode and DevContainers with "dockerComposeFile": "docker-compose.yml".

https://containers.dev/implementors/json_reference/

At the command line docker compose --env-file ../.env up does the trick.

So, my questions:

• Am I missing something?
• Is this a missing feature in devcontainer.json?