Consider automatic directory set-up using proj.yml when using devcontainers

[MiguelRodo]

Issues

• If based on working directory, can't customise as the working directory is always the same (well, by default)

• Can't use some file (e.g. "user-mrodo_devcontainer") as these have to be recreated in the devcontainer every time

• This is really a bit of a mess-up, as the environment is supposed to be "standardised" and here it isn't

Possible solutions

• Make settings depend on an environment variable
  • This will have to be set up in the Docker file
    • In this case, people would have to clone the repository, create a new docker file and then rechoose their directory
  • If they want to rechoose the directory
    • But depending on the project structure, they may have to.
• Multiple devcontainer files would help
  • VSC does not seem able to make use of that yet, but it seems like it is on track to do so.
  • This would happen either via an extends property (that just adds keys to an existing devcontainer.json file) or a ref property (that is more sophisticated in some way).
    • Add support for alternate definition configs under .devcontainer devcontainers/spec#6
    • New merge command to combine parent and child devcontainer.json configurations for inheritance  devcontainers/cli#19
• Manually select which settings to use each time, and then restart R to reflect them

[MiguelRodo]

Best solution thus far

Export the container environment variable localWorkspaceFolder to the container using these lines in .devcontainer.json:

"remoteEnv": {
  "LOCAL_WORKSPACE_FOLDER": "${localWorkspaceFolder}"
}

Then, when projr sets up the directory, it will use this variable if it exists, otherwise it will use its actual working directory.

[MiguelRodo]

I think we're going to call this PROJR_SYSTEM_ID. Better than PROJR_USER as this isn't about a specific user necessarily, it's actually about the system. Also better than PROJR_WORKING_DIRECTORY as this need not be a directory.

[MiguelRodo]

It is still useful as docker containers in VSC mount the code directory into a user-independent location, and so would be the same across many users.

[MiguelRodo]

We've already made settings depend on the environment variable, so this is actually done. What we need to do is quick and just rename it to PROJR_SYSTEM_ID.

[MiguelRodo]

Done. We have extensive profile abilities, so this is easily handled by setting the environmanent variable PROJR_PROFILE in dockerfile.