Add workdir support

[raultapia]

Closes #249

[tfoote]

Thanks for adding this with test coverage. It's great to have.

As mentioned in #249 (comment)

The user extension adjusts the workdir

rocker/src/rocker/templates/user_snippet.Dockerfile.em

Line 38 in ade9803

WORKDIR @(dir)

and it would be good to integrate this with that.

I think that there's a sort of higherarchy

• If workdir is set explicitly, then use that.
• If it's not set and you're inside of a mounted path keep the cwd
• If it's not set, and the current directour is outside of a mounted volume, default to the home directory.

[raultapia]

I've implemented the hierarchy you proposed with some minor changes. The current status is:

• If executed without --workdir, defaults to home directory.
• If executed with --workdir, the current directory is set as WORKDIR from get_user_snippet.
• If executed with --workdir=path, the directory is set and it overrides the WORKDIR from get_user_snippet.

[tfoote]

Thanks for iterating this is making progress, but it isn't dealing withthe workdir interactions with the user extension:

rocker/src/rocker/templates/user_snippet.Dockerfile.em

Line 38 in ade9803

WORKDIR @(dir)

And the workdir will need to be the last snippet to be effective for setting the workdir for the user only, and now potentially effecting the other extensions if it gets evaluated first. I think that it may make more sense to do this as a core capability versus as an extension because of that and the need for the interaction with the mounting and user mechanisms.

[tfoote]

Please see my comments in the main thread. This needs to provide sequencing protection and interact with the user and mount extensions to give the expected potential working directories.

somewhere like

rocker/src/rocker/core.py

Line 485 in ade9803

return dockerfile_str

Or else we need to add a sequencing support to extensions.