[nix-shell] unset shellHook?

[toraritte]

Problem

Calling nix-shell inside a "nix-shell" (a shell that is the result of a Nix expression setting shellHook) will inherit the parent's shellHook, but this is never mentioned in the nix-shell man page.

For example:

$ nix-shell -E '(import <nixpkgs> {}).mkShell { shellHook = "echo \"\n========\nWELCOME!\n========\""; }'

========
WELCOME!
========

[nix-shell:~]$ nix-shell -p jq

========
WELCOME!
========

@abathur has more examples in this Discourse thread and also mentions commit 0135fd6 for nix develop to avoid this exact issue.

Checklist

• checked latest Nix manual (source)
• checked open documentation issues and pull requests for possible duplicates (as best I could)

Proposal

I was vacillating between opening this documentation issue and filing a bug report, but I don't know if this is considered a bug. Personally, I prefer the nix develop approach for the shellHook only affecting a particular nix-shell invocation and not subsequent ones, but it is certainly not documented (or, at least, not in the nix-shell manual) so adding a note or a warning would definitely help.

$ nix-shell -E '(import <nixpkgs> {}).mkShell { shellHook = "echo \"\n========\nWELCOME!\n=======\"; unset shellHook;"; }'

========
WELCOME!
=======

[nix-shell:~]$ nix-shell -p jq
[nix-shell:~]$ 

Priorities

Add 👍 to issues you find important.

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/how-to-avoid-embedded-nix-shell-to-re-use-parent-nix-shells-shellhook/27541/6

[roberth]

The documentation says

If the derivation defines the variable shellHook,

which I think would be more than reasonable to interpret as "if and only if".

I would consider this to be a long standing bug that is still worth fixing.