docker compose v2 config --no-interpolate should not escape environment variables

[zapoig]

When checking the validity of a compose file with the docker compose config command, passing the --no-interpolate option to avoid interpolating environment variables, docker compose v2 turns all the $ characters into $$, making the normalized resulting compose file unable to later be provided with values for the environment variables.

This is different from the behaviour of docker-compose config v1 which was not escaping the environment variables dollar sign in that way.

Steps to reproduce the issue:
1.

$ cat compose_with_env_vars.yml 
services:
  service:
    image: 'some.image/that/will/need/environment/variables:v1.0'
    environment:
      - MY_ENV_VAR=$ENV_VAR

$ docker compose --compatibility -f compose_with_env_vars.yml config --no-interpolate 
services:
  service:
    environment:
      MY_ENV_VAR: $$ENV_VAR
    image: some.image/that/will/need/environment/variables:v1.0

Describe the results you received:
MY_ENV_VAR: $$ENV_VAR

Describe the results you expected:
MY_ENV_VAR: $ENV_VAR

Note that the --compatibility flag doesn't change that behaviour.

Output of docker compose version:

$ docker compose version
Docker Compose version v2.2.3

Output of docker info:

$ docker info
Client:
 Context:    default
 Debug Mode: false
 Plugins:
  app: Docker App (Docker Inc., v0.9.1-beta3)
  buildx: Docker Buildx (Docker Inc., v0.7.1-docker)
  compose: Docker Compose (Docker Inc., v2.2.3)
  scan: Docker Scan (Docker Inc., v0.12.0)

Server:
 Containers: 2
  Running: 1
  Paused: 0
  Stopped: 1
 Images: 49
 Server Version: 20.10.12
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Cgroup Version: 1
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 io.containerd.runtime.v1.linux runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 7b11cfaabd73bb80907dd23182b9347b4245eb5d
 runc version: v1.0.2-0-g52b36a2
 init version: de40ad0
 Security Options:
  apparmor
  seccomp
   Profile: default
 Kernel Version: 5.4.0-99-generic
 Operating System: Ubuntu 18.04.6 LTS
 OSType: linux
 Architecture: x86_64
 CPUs: 4
 Total Memory: 5.79GiB
 Name: ubunturlututu
 ID: DQFW:JUJT:P37M:BQTT:AVXP:SQJZ:ZV6Z:KYYY:BSYY:SJK6:HTQE:VT7W
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 No Proxy: localhost,127.0.0.1
 Username: *****
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: false
 Insecure Registries:
  LinuxDev:5000
  127.0.0.0/8
 Live Restore Enabled: false

WARNING: No swap limit support

Behavior of docker-compose v1 for comparizon:
1.

$ docker-compose version
docker-compose version 1.27.4, build 40524192
docker-py version: 4.3.1
CPython version: 3.7.7
OpenSSL version: OpenSSL 1.1.0l  10 Sep 2019

$ docker-compose --compatibility -f compose_with_env_vars.yml config --no-interpolate
services:
  service:
    environment:
      MY_ENV_VAR: $ENV_VAR
    image: some.image/that/will/need/environment/variables:v1.0
version: '3.9'

[BergLucas]

I have the same problem and have been trying to figure out what it is. After some research, it seems that it comes from the Convert function in pkg/compose/compose.go. This function calls escapeDollarSign and that's the reason why the $ is escaped. I compiled docker-compose without the call to escapeDollarSign and the behavior returned as in v1.

[zapoig]

Great, thank you all.