Using nix within Positron in a remote session (and fix docs about IDE)

[joelnitta]

I would like to connect to a remote server in Positron using the Remote-SSH: Connect to host command, then start an R Interpreter that is from a nix shell. Can you help me with this?

My first attempt has been starting from Configuring Positron installed on macOS to interact with Nix shells. I first ran "Install 'positron' command in PATH". Next, I connected to the server using my local Positron install, then ran nix-shell from a terminal in the remote session, but I don't see the nix instance in the menu of interpreters like I do when running locally.

Thanks!

[b-rodrigues]

I have no experience with this, but this thread might help: #387 (reply in thread)

[joelnitta]

Thanks for the suggestion @b-rodrigues .

I had a look at that post. I'm hoping to avoid the container route, because that is why I switched to rix/nix in the first place - no need to deal with root in the container, missing symlinks, etc.

Honestly now I would be happy to get R within nix running in either VS Code or Positron, as long as I can access it via SSH. I have heavy computations that I can't run on my laptop.

I think I need to use the local install of my IDE, because I had the same experience as @atsyplenkov with the frustratingly (IMHO unusably) slow response of the IDE within nix over SSH GUI.

I've been testing with this repo: https://github.com/joelnitta/2025-04-18_nix. It works fine locally - from a terminal in VS Code I run nix-shell, then R, then attach it to the current session with .vsc.attach().

However, when I try to do the same thing remotely (over SSH), although .vsc.attach() does not throw an error, I am in doubt that the session is really attached, because plots and help windows don't show up.

I know this is diverging from the OP, but if you have any ideas that would be great...

[b-rodrigues]

Did you install direnv on the server and the corresponding extension on your local IDE? that seems to be the solution https://docs.ropensci.org/rix/articles/e-configuring-ide.html#configuring-native-vs-codecodium-on-your-operating-system

[joelnitta]

So I did try that, but it doesn't seem to do anything. That is, I don't get the lag that you would expect while direnv runs nix-shell, and nothing seems to change (still same local shell).

I noticed there are multiple versions of direnv around, some seem to use use nix in .envrc. May that have something to do with it?

[b-rodrigues]

maybe is it working locally when you switch folders, do you get the shell started?

[joelnitta]

You mean something like this:

(base) jnitta:~$ cd 2025-04-18_nix/
(base) jnitta:~/2025-04-18_nix$ 

Should drop me into the nix shell? (where 2025-04-18_nix is this repo)

That isn't happening.

[b-rodrigues]

yes if direnv is configured correctly

[b-rodrigues]

opened a pr, it should be "use nix"

[joelnitta]

OK got that.

So at a minimum (not bothering with VS Code here), I should be able to:

1. Put the line use nix in .envrc in the folder with a functioning default.nix
2. run direnv allow in that folder
3. cd into the folder from somewhere else, and it will drop me into the nix-shell

?

That is what I have tried, and I still see only my local shell.

FYI,

$ direnv --version
2.35.0

[b-rodrigues]

did you hook your shell https://direnv.net/docs/hook.html

[joelnitta]

No (it wasn't in the rix docs). Doing that does indeed seem to get direnv functioning as expected, so I can now do R: Create R Terminal from the VS Code command palette in my SSH session and immediately get to R running in the nix shell. So that's pretty great! But unfortunately help() and plot() still do not result in any output. I'm beginning to suspect the reason lies somewhere in the R extension...

Anyways, I would recommend a few (more) updates to the docs - clarifying about direnv vs nix-direnv (is either OK? does only one work?) and adding the part about hooking the shell.

[b-rodrigues]

I'll update the docs, thanks

so is it working then? can we close this ?

[b-rodrigues]

Regarding your question about direnv vs nix-direnv, seems like both should be ok, but nix-direnv should be faster for nix based projects. However, it requires a modern bash, so they recommend direnv instead on macOS: https://github.com/nix-community/nix-direnv?tab=readme-ov-file#installation

EDIT: no that's wrong: nix-direnv is actually an extension to direnv. So you need to install both! direnv alone works, but is not optimized for nix shells. With nix-direnv, it's actually much faster!

[b-rodrigues]

fyi: 0cc73af

[joelnitta]

I get the feeling this is out-of-scope for {rix}: I've confirmed (using local R install instead of R in nix) that the lack of plots or help menus when using R in VS Code remotely via SSH is due to the VS Code R extension, and it seems getting the nix env to show up in Positron's list of interpreters is a Positron thing.

So let's consider the update to the docs sufficient to close this for now.

[b-rodrigues]

OK but when positron connects does it now see the nix-managed R from the server with direnv ? or at least with VS code ?

[joelnitta]

Positron: No, with a local (i.e., not from nix) install of Positron, even when opening the dir with .envrc, I don't see the R from nix in the list of interpreters.

VS Code: Local install of VS Code, connecting to the server with SSH then running R on the server in nix via direnv "works" (I can start an R terminal with R: Create R Terminal), but as previously mentioned help and plot windows don't appear. I also noticed that the "Workspace" tab that shows up when I click the R extension icon says "R workspace viewer requires that session watcher be enabled". I followed all instructions on that page, and it doesn't work. As I said, I think this is an VS Code R extension problem, but given the large number of similar stale issues, I have little hope of getting an answer if I file another...

[b-rodrigues]

In vscode, did you install the direnv extension as well ?

[b-rodrigues]

(on a sidenote, I'm not confronted by such issues because because I use emacs in terminal mode directly from the server)

[joelnitta]

In vscode, did you install the direnv extension as well ?

Yes, that is working as expected. As soon as I open the project folder, I'm in the nix env, and the R terminal I open is from nix.

[b-rodrigues]

so to summarize

• direnv and nix-direnv on the server
• vscode with direnv extension locally
• local vscode is able to work with remote nix shell through ssh and thanks to direnv
• but plots aren't being shown ?

[joelnitta]

yep.

but plots aren't being shown ?

I think this is because the VS Code R extension session watcher is not working when I connect via SSH. (as you can see the screenshot above)

[b-rodrigues]

thanks a lot, this issue improved my understanding of remote ssh connections with a local editor and also the documentation

[joelnitta]

FYI filed an issue about the VS Code R extension problem: REditorSupport/vscode-R#1604