Remote Containers on WSL shadows DISPLAY variable when invoking docker-compose

[i-ky]

Somewhat related to #550 and #3841.

I have a project that uses zenity in auxiliary scripts to interact with developer. For it to work in Docker Compose environment I forward DISPLAY environment variable and tell service to use host network stack. This works fine on Linux (both using docker-compose CLI directly and using VS Code with Remote Containers) and it works in WSL with GWSL when containers are managed using docker-compose CLI, but it does not work in VS Code in WSL. The root cause seems to be that Remote Containers in WSL shadows DISPLAY variable with DISPLAY='1' when invoking docker-compose:

[8424 ms] Start: Run: wsl -d Ubuntu-18.04 -e /bin/sh -c cd '/tmp/display' && ... DISPLAY='1' ... docker-compose '--project-name' 'display' '-f' '/tmp/display/docker-compose.yml' 'up' '-d'
Recreating display_main_1 ... done

• VSCode Version: 1.56.1
• Remote Containers: 0.177.2
• Local OS Version: WSL Ubuntu 18.04
• Remote OS Version: official Ubuntu 18.04 Docker image
• Remote Extension/Connection Type: Docker (on WSL)

Minimal project to reproduce:

• .devcontainer/devcontainer.json:

{
    "dockerComposeFile": "../docker-compose.yml",
    "service": "main",
    "workspaceFolder": "/code"
}

• docker-compose.yml:

services:
  main:
    init: true
    command: sleep infinity
    build:
      context: ./
    environment:
      DISPLAY:
    network_mode: host
    volumes:
    - ./:/code

• Dockerfile:

FROM ubuntu:bionic

RUN apt-get update && apt-get --assume-yes --no-install-recommends install \
        zenity \
    && apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/*

WORKDIR /code

Steps to reproduce:

1. Open folder in WSL.
2. Click "Reopen in container" when prompted (assuming Remote Containers is installed).
3. Open integrated terminal and run

$ echo $DISPLAY

4. Observe result:

1

5. Run on WSL:

$ docker-compose exec main zenity --info --text "Hello, world!"

6. Observe failure:

Unable to init server: Could not connect: Connection refused

(zenity:328): Gtk-WARNING **: 13:10:43.286: cannot open display: 1

If you have GWSL integrated with WSL distro, DISPLAY should be set to <ip>:<port> and zenity should successfully display a window with text. However, the issue isn't necessarily specific to X forwarding, any other value of DISPLAY will be shadowed as well. It just happens that this particular variable name is very important for X forwarding and cannot be changed or worked around.

[i-ky]

Sorry, the issue turned out to be that DISPLAY was missing from WSLENV.