[BUG] docker compose when parentheses are present in entrypoint or command strings

[mRokita]

Description

The bug effectively disables me from using traefik's providers.docker.constraints flag, which requires presence of parentheses in the command/entrypoint string:

command: "--providers.docker --providers.docker.constraints=Label(pycon.traefik, true)"

Everytime I try running docker compose up, the following decoding error is printed:

1 error(s) decoding:

* error decoding 'Command': invalid command line string

When I remove parentheses from the command it starts up, but these braces are needed there for Traefik to understand the constraint.

Using docker compose --compatibility up doesn't solve the issue.

Docker Compose v1 has no issues with decoding the same compose file.

Steps To Reproduce

1. Create a docker-compose.yml file with the following contents:

version: "3"

services:
  traefik:
    image: traefik:v2.9.4
    command: "--providers.docker --providers.docker.constraints=Label(pycon.traefik, true)"

2. Run docker compose up
3. The following error appears

1 error(s) decoding:

* error decoding 'Command': invalid command line string

4. Removing braces ( and ) removes the error, but then Traefik does not understand the syntax.

Compose Version

Docker Compose version v2.12.2

Docker Environment

Client:
 Context:    default
 Debug Mode: false
 Plugins:
  app: Docker App (Docker Inc., v0.9.1-beta3)
  buildx: Docker Buildx (Docker Inc., v0.9.1-docker)
  compose: Docker Compose (Docker Inc., v2.12.2)
  scan: Docker Scan (Docker Inc., v0.21.0)

Server:
 Containers: 21
  Running: 1
  Paused: 0
  Stopped: 20
 Images: 203
 Server Version: 20.10.21
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: systemd
 Cgroup Version: 2
 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: 1c90a442489720eec95342e1789ee8a5e1b9536f
 runc version: v1.1.4-0-g5fd4c4d
 init version: de40ad0
 Security Options:
  seccomp
   Profile: default
  cgroupns
 Kernel Version: 5.19.16-200.fc36.x86_64
 Operating System: Fedora Linux 36 (Workstation Edition)
 OSType: linux
 Architecture: x86_64
 CPUs: 16
 Total Memory: 13.38GiB
 Name: xxx
 ID: P76X:OF5F:UHWN:5K2W:C4W6:CN5Q:7DWI:PJZ7:ECNO:UCW4:PBCJ:AG7G
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

Anything else?

No response

[mRokita]

I'm sorry - this is probably a duplicate of #8512, which has been closed because of inactivity :/
I posted a workaround there: #8512 (comment)

[ndeloof]

Until we get such corner case better supported by shellwords library (see mattn/go-shellwords#54) you can use quotes:

services:
  traefik:
    image: traefik:v2.9.4
    command: "--providers.docker --providers.docker.constraints='Label(pycon.traefik, true)'"

[antichris]

Escaping with backslashes also works.

services:
  traefik:
    image: traefik:v2.9.4
    command: --providers.docker --providers.docker.constraints=Label\(pycon.traefik,\ true\)

FWIW, it seems that this behavior is compliant with the POSIX.1-2017 standard specification, where the parentheses are defined as control operators that require quoting.

[ndeloof]

Considering control operators are well defined in POSIX (thanks @antichris for the link) and quoting is both recommended and a simple workaround, I'm closing this issue as "not planned"
We still can expect mattn/go-shellwords#54 to be fixed at some point and offer more flexibility to compose users.