How to enable WSLg from within a devcontainer?

[anttikes]

I am using the following setup:

• Windows 11 Pro (10.0.22631 Build 22631)
• Docker Desktop (4.34.3, 170107), using WSL2 backend
• Visual Studio Code (1.95.0, user setup), running on the Windows host

What I want is to be able to utilize the "WSLg" feature that is present on the "docker-desktop" distribution that is running the container engine. I am using the attached simplistic Qt application to prototype it.

qt-test.zip

When I open this project in VS Code I can build the devcontainer, run it, and then use the CMake extension to build the application successfully. When I try to run the application from VS Code it will fail, stating that no Qt Platform Abstraction (QPA) plugins could be utilized.

If I open a terminal on the devcontainer and issue either env or ls -la /tmp/ the source of the problem seems clear: the folders and environment variables required by WSLg are not present or have incorrect values compared to what they are if I were to run the same commands inside the docker-desktop distribution.

As evident in the devcontainer.json file I have tried mapping these folders & variables into the devcontainer but if the sections are taken into use the build/run process will error out, stating that the folder /tmp/.X11-unix folder cannot be found. The reason for this error seems to be that the docker run command (and its --mount flag) is executed in the context of the Windows host machine instead of the docker-desktop distribution in the WSL. Furthermore, the DISPLAY environment variable on the distribution has the value :0 but if I evaluate the environment variables inside the devcontainer terminal it has the value of 1.

I came across the VS Code setting "Dev > Containers: Execute in WSL" and I tried enabling it. This did not yield any help; instead the entire devcontainers feature of VS Code ceased operating correctly. I had to disable this option in order to be able to even open the folder in the container.

I am not sure what to try next, and could use some advice.

[anttikes]

After looking into this issue a bit longer it seems that this is actually a bug in the docker-desktop distribution.

If I install e.g. "Debian" distribution onto WSL2, set it as my default distribution, and then repeat this exercise then I do not have to do anything, and the Qt application "just works", like magic.

The key setting in VS Code is "Dev > Containers: Forward WSLServices". This setting already mounts the folders and sets the environment variables. But when you only have docker-desktop distribution then it does not work correctly because for some reason this distribution uses /mnt/host/wslg/ folder to hold the files instead of /mnt/wslg like stated in the WSLg documentation.

I will probably file a bug report about this but I'll just need to figure out whose responsibility it is. Is it a bug in Docker Desktop's "system distro", or a bug in how the VS Code setting works...