[BUG] docker compose a few env files and args section

[pmiroslawski]

Description

Here's the example of docker-compose.yml file which contains a service and has defined two files as the env_file

version: '3.9'
services:
  admin:
    ...
    build:
      context: .
      ...
      args:
        - SSH_USER=$SSH_USER
    env_file:
      - .env
      - .env.local
...

The content of .env file is:

SSH_USER="change-me"

The content of .env.local file is:

SSH_USER="change-me2"

Here's the result of docker compose config command:

services:
  admin:
    build:
      ...
      args:
        SSH_USER: change-me
    ...
    environment:
      SSH_USER: change-me2

Environment variables have been set correctly, but why hasn't the value in the args section been updated to reflect the environment variables?

Steps To Reproduce

No response

Compose Version

Docker Compose version v2.21.0

Docker Environment

Client: Docker Engine - Community
 Version:           24.0.6
 API version:       1.43
 Go version:        go1.20.7
 Git commit:        ed223bc
 Built:             Mon Sep  4 12:31:44 2023
 OS/Arch:           linux/amd64
 Context:           default

Server: Docker Engine - Community
 Engine:
  Version:          24.0.6
  API version:      1.43 (minimum version 1.12)
  Go version:       go1.20.7
  Git commit:       1a79695
  Built:            Mon Sep  4 12:31:44 2023
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.6.24
  GitCommit:        61f9fd88f79f081d64d6fa3bb1a0dc71ec870523
 runc:
  Version:          1.1.9
  GitCommit:        v1.1.9-0-gccaecfc
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

Anything else?

No response

[ndeloof]

env_file defines files used to set container environment, not those used to interpolate variables in compose.yaml. Your .env file is loaded for this purpose as the default file name.

Just a note: you don't need to repeat variable value on args, if an environment variable is defined with name it will be propagated with simpler syntax:

      args:
        - SSH_USER