[BUG] `docker compose config --no-interpolate` breaks when using `:` in variables and short-form volumes

[Raphtor]

Description

Example compose.yml

services:
  test:
    image: ubuntu:latest
    volumes:
      - ./${DIRECTORY:?error}/:/home/data

Here, I am using the interpolation that throws an error if DIRECTORY is empty (see docs) When running docker compose config --no-interpolate, I would expect to see:

name: test
networks:
  default:
    name: test_default
services:
  test:
    image: ubuntu:latest
    networks:
      default: null
    volumes:
      - bind:
          create_host_path: true
        source: /home/user/test/${DIRECTORY:?error}
        target: /home/data
        type: bind

What I actually get:

name: test
networks:
  default:
    name: test_default
services:
  test:
    image: ubuntu:latest
    networks:
      default: null
    volumes:
      - bind:
          create_host_path: true
        source: /home/user/test/${DIRECTORY
        target: ?error}
        type: bind

There must be a naive splitting of the volume string by :, as it doesn't happen when using the required value that allows empty values, e.g ./${DIRECTORY?error}/:/home/data produces the correct output

volumes:
      - bind:
          create_host_path: true
        source: /home/user/test/${DIRECTORY?error}
        target: /home/data
        type: bind

Steps To Reproduce

1. Use the above compose file
2. Run docker compose config --no-interpolate

Compose Version

Docker Compose version v2.28.1-desktop.1

Docker Environment

Client:
 Version:    27.0.3
 Context:    desktop-linux
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.15.1-desktop.1
    Path:     /Users/normar1/.docker/cli-plugins/docker-buildx
  compose: Docker Compose (Docker Inc.)
    Version:  v2.28.1-desktop.1
    Path:     /Users/normar1/.docker/cli-plugins/docker-compose
  debug: Get a shell into any image or container (Docker Inc.)
    Version:  0.0.32
    Path:     /Users/normar1/.docker/cli-plugins/docker-debug
  desktop: Docker Desktop commands (Alpha) (Docker Inc.)
    Version:  v0.0.14
    Path:     /Users/normar1/.docker/cli-plugins/docker-desktop
  dev: Docker Dev Environments (Docker Inc.)
    Version:  v0.1.2
    Path:     /Users/normar1/.docker/cli-plugins/docker-dev
  extension: Manages Docker extensions (Docker Inc.)
    Version:  v0.2.25
    Path:     /Users/normar1/.docker/cli-plugins/docker-extension
  feedback: Provide feedback, right in your terminal! (Docker Inc.)
    Version:  v1.0.5
    Path:     /Users/normar1/.docker/cli-plugins/docker-feedback
  init: Creates Docker-related starter files for your project (Docker Inc.)
    Version:  v1.3.0
    Path:     /Users/normar1/.docker/cli-plugins/docker-init
  sbom: View the packaged-based Software Bill Of Materials (SBOM) for an image (Anchore Inc.)
    Version:  0.6.0
    Path:     /Users/normar1/.docker/cli-plugins/docker-sbom
  scout: Docker Scout (Docker Inc.)
    Version:  v1.10.0
    Path:     /Users/normar1/.docker/cli-plugins/docker-scout

Server:
 Containers: 107
  Running: 2
  Paused: 0
  Stopped: 105
 Images: 211
 Server Version: 27.0.3
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Using metacopy: false
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Cgroup Version: 2
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: ae71819c4f5e67bb4d5ae76a6b735f29cc25774e
 runc version: v1.1.13-0-g58aa920
 init version: de40ad0
 Security Options:
  seccomp
   Profile: unconfined
  cgroupns
 Kernel Version: 6.6.32-linuxkit
 Operating System: Docker Desktop
 OSType: linux
 Architecture: aarch64
 CPUs: 8
 Total Memory: 7.755GiB
 Name: docker-desktop
 ID: 0a7123d2-ddf6-414f-88db-e89d232a13b1
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 HTTP Proxy: http.docker.internal:3128
 HTTPS Proxy: http.docker.internal:3128
 No Proxy: hubproxy.docker.internal
 Labels:
  com.docker.desktop.address=unix:///Users/normar1/Library/Containers/com.docker.docker/Data/docker-cli.sock
 Experimental: false
 Insecure Registries:
  hubproxy.docker.internal:5555
  127.0.0.0/8
 Live Restore Enabled: false

WARNING: daemon is not using the default seccomp profile

Anything else?

No response

[ndeloof]

There must be a naive splitting of the volume string by :

indeed, as variable syntax has many subtle rules, it makes it hard to split string without actual interpolation. Also volume could be set by a single variable to both declare source and destination, which would prevent expanding to "long syntax":

volumes:
   - ${STRING}

[ndeloof]

Closing as "not planned". There's unfortunately no way to manage ambiguous : in short volume syntax when interpolation is disabled.

[Raphtor]

Wouldn't this be possible using a regex capture group?

1. Find all variables using (\$\{.*\})
2. Sub them out with a standard alphanumeric string and create a mapping (e.g $VAR1 -> ${DIRECTORY:?error})
3. Do short to long form conversion as normal
4. Re-substitute the variables using the mapping

I suppose as a workaround for users, this could be done outside of compose with another script.

[ndeloof]

nope, variables can be nested, which makes this way more complicated. Maybe feasible, but for a limited benefits.

What do you rely on config --no-interpolate for ?