Add subshell level section

[panurg]

Env

Pure

echo $pure_version
4.11.0

Fish

fish --version
fish, version 3.7.1

OS/distribution

lsb_release -a
No LSB modules are available.
Distributor ID:	NixOS
Description:	NixOS 24.05 (Uakari)
Release:	24.05
Codename:	uakari

Background

I frequently use nix shell to make an environment with some additional tools in NixOS. I want some indication of that environment. There is a pure_enable_nixdevshell option, but it is only applicable for nix develop shell. Unfortunately there is no way to determine nix shell environment (see NixOS/nix#6677). Luckily fish provides SHLVL variable for subshell counting. It can be a solution for my problem. It is also can be somehow applicable in non-NixOS distributions.

Solution

Add a feature to display subshell level when it is greater than 2 by inspecting SHLVL variable.

I wanted to implement it by myself, but seems pure does not offer custom section. BTW it could be a great feature too. Probably there is other way without patching code which I would like to avoid?

[MarcelCoding]

Starships implements a workaround which works while upstream nix does not provide an implementation yet: https://github.com/starship/starship/blob/9ab8b84ea6cd40f83a34836111c6bda2203dccfe/src/modules/nix_shell.rs#L15-L40

[edouard-lopez]

@MarcelCoding Thanks for sharing, I'm not a Nix user myself, but I'm open to reviewing a pull request on the matter.

You can check:

1. contributing guide to get familiar for the code convention and the use of docker to dev (We have a build-pure-on-nix and dev-pure-on-nix target you can use with make) ;
2. .github/pull_request_template.md to guide you in the process
3. and tests/_pure_prompt_nixdevshell.test.fish to write the tests

[jenav]

Hi, I'm also interested in this feature and wanted to add that the lf file manager uses the LF_LEVEL env var for the same purpose and you can accomplish the same in vifm, so maybe a more generic approach could be taken.

[edouard-lopez]

Hello,
It would be best to split the work here, with PR focusing

1. On a pure function to display subshell level when it is greater than 2 by inspecting SHLVL variable.
2. Another one that will introduce custom sections. Could be a simple call to a _pure_custom_section.fish that user edit at first.

[edouard-lopez]

Started a conversation in Support add-ons #392