Add nix shell support

[gytis-ivaskevicius]

nix-shell is something similar to python virtual env but more powerful, this patchset adds support for it.

[mafredri]

I think this looks alright and would probably work in 99% of cases, only potential issue I see is that the nix shell may override an active virtualenv (if it's possible for them to be active at the same time).

[andresilva]

Would be nice to have a way to disable this.

[gytis-ivaskevicius]

unset IN_NIX_SHELL?

[andresilva]

IN_NIX_SHELL wasn't set by this code, it works but you're assuming it isn't used for anything else besides pure. I think having a NIX_SHELL_DISABLE_PROMPT makes sense, just like it's done for VIRTUAL_ENV support.

[mafredri]

IN_NIX_SHELL wasn't set by this code, it works but you're assuming it isn't used for anything else besides pure. I think having a NIX_SHELL_DISABLE_PROMPT makes sense, just like it's done for VIRTUAL_ENV support.

We don't have anything like this for virtualenvs 🤔, we simply respect the user option of VIRTUAL_ENV_DISABLE_PROMPT if it is set, it's part of regular virtualenvs though, not Pure.

Is there any similar mechanism for nix shell that we could piggy-back on? We'd like to avoid adding a new configuration option for this.

[gytis-ivaskevicius]

No, there is no such logic to piggyback on.
@andresilva Can you elaborate on your usecase? Whatever your use case it sounds pretty odd 🤔

[andresilva]

We don't have anything like this for virtualenvs 🤔, we simply respect the user option of VIRTUAL_ENV_DISABLE_PROMPT if it is set, it's part of regular virtualenvs though, not Pure.

I don't use virtualenv so I didn't know this, I assumed it was something specific to pure.

@andresilva Can you elaborate on your usecase? Whatever your use case it sounds pretty odd 🤔

My use case is quite simple: I don't like this and I want to disable it. IMO the proposed solution to unset a variable that wasn't set by pure is unsatisfactory. If I have some other script that relies on IN_NIX_SHELL for detection then it will be broken.

[mafredri]

IMO the proposed solution to unset a variable that wasn't set by pure is unsatisfactory. If I have some other script that relies on IN_NIX_SHELL for detection then it will be broken.

I 100% agree. I've not been personally able to evaluate how nix shell can/is used since this is pretty much the first I've heard of it. Obviously if it's something that's enabled 24/7, then displaying the (excess) information is not ideal.

Would it make senses to never display nix-shell (i.e. $name is unset), instead only display it when $name has a value? My thought process is that it could be valuable to know when you're in a different "environment", or whatever it is.

If we were to add a configuration option for this, perhaps it could be added as a zstyle (zstyle :prompt:pure:environment:nix-shell show yes)?

[andresilva]

Would it make senses to never display nix-shell (i.e. $name is unset), instead only display it when $name has a value? My thought process is that it could be valuable to know when you're in a different "environment", or whatever it is.

I don't want to bore you with the details but I don't use nix-shell directly but instead use lorri, this means that I'll always have a $name set even though I'm not interested in seeing it.

If we were to add a configuration option for this, perhaps it could be added as a zstyle (zstyle :prompt:pure:environment:nix-shell show yes)?

That would work for me.