Add VSCode devcontainer configuration

[idan]

This creates the a basic harness that permits users to develop with their local checkout inside the same docker container which powers the GitHub action. Does not yet contain docs and tests, but I did try it out with a clean checkout and was able to build images. 🎉

See #208 for discussion about where this can go.

Steps to use:

1. Install docker
2. Install the Remote - Containers extension either via the extensions panel, or in your favorite terminal:
   code --install-extension ms-vscode-remote.remote-containers
3. Opening the zmk folder in VS Code now displays a prompt to re-open inside a container:
   
4. Click Reopen in Container and the VS Code window will reload and do the necessary initial docker setup. This can take a little while.
5. Open a terminal in VS Code and issue the following commands to initialize your environment:

$ west init -l app
$ west update # and go make lunch, this is going to take a while
$ cd app
$ west build -b YourBoardName -- -DSHIELD=YourShieldName

That's it!

[CrossR]

Some potential to combine this with #192, and include the Docker ext as a recommended extension, though also raises the question of it the instructions provided there work for a Docker based workflow (making the compilation database, using it etc).

[joelspadin]

I suspect that the compilation database part is still correct, but you'd need to change the compiler path to match wherever it ends up being in the container. Maybe we just add Docker to the list of OSes in all the docs pages?

[petejohanson]

I suspect that the compilation database part is still correct, but you'd need to change the compiler path to match wherever it ends up being in the container. Maybe we just add Docker to the list of OSes in all the docs pages?

Yeah, if we can make this seemless, I definitely think it should be an "OS tab/option" in the dev setup docs.

[petejohanson]

One tweak, and a question around SELinux settings.

[idan]

So, the tweak above worked. Onto new issues!

Git pull/push with SSH remotes doesn't work inside the container because the docker image lacks SSH. Fixable with apt update; apt install ssh. We should probably bake that into the image? Once that's there, it Just Works™, and the devcontainers extension properly forwards things to the host's ssh-agent.

The more annoying (but less critical) thing I've run into is that GPG commit signing doesn't work. Like SSH, GPG is not installed in the image (easily fixable like above). Once it's there, it still doesn't work — the ~/.gnupg directory doesn't even exist:

Supposedly, this should work as of v118 of the remote-containers extension, but there's no documentation. However, another issue identifies a control to test against. When I try to gpg from inside the "try a sample" node container, I can see my keyring and a socket, and signing works fine:

My current hunch is that maybe the image needs to contain GPG already when it boots or the VSCode remote-containers extension doesn't try to set up forwarding.

[idan]

To be clear:

• SSH is critical, you can't git without it in many cases
• Commit signing is nice to have
• You can always commit from outside the container; this is all about quality of life at this point

[idan]

OK, it works! I brought back the dockerfile and used it to install SSH/GPG into the image. Now when VSCode comes up, everything works out of the box for me (MacOS).

[petejohanson]

One comment on the dockerfile, but certainly minor. I would love to get this in, so we can build on it, even if we aren't 100% happy with the documentation piece.

Thoughts @idan ?

[idan]

@petejohanson yes! I'll hack on the docs tonight and try to get it into a happy place, or move them to a separate branch so we can commit the docker bits and do the docs in a follow-onw

[petejohanson]

This is fabulous! Thanks sticking with this, and the docs updates.