nix develop: Ignore stdenv's $SHELL

[edolstra]

Stdenv sets this to a bash that doesn't have readline/completion support, so running nix shell inside a nix develop gives you a crippled shell. So let's just ignore the derivation's $SHELL.

This could break interactive use of build phases that use $SHELL, butthey appear to be fairly rare.

[thufschmitt]

A small change, but such a qol improvement :)

[thufschmitt]

Should we instead set $SHELL to the interactive bash we fetch from nixpkgs? that way most stuff will just work as expected since it will still point to bash

[ncfavier]

What does this fix exactly? The only place I see SHELL used in the Nix codebase is in nix shell.

As far as I can tell, nix develop already runs an interactive bash, so the only remaining problem is when running bash directly in a nix develop shell. I don't know if/how we can fix that.

[edolstra]

@ncfavier It fixes this:

[eelco@localhost:~/Dev/nix]$ nix develop
[eelco@localhost:~/Dev/nix]$ nix shell
\[\][eelco@localhost:~/Dev/nix]$\[\] 

i.e. the inner shell doesn't have readline/completion support.

[ShamrockLee]

@ncfavier It would also fix the misinterpreted prompt in VSCode terminal IIUC.

[Hoverbear]

I encountered this particular bug often when using starship and using nix develop then launching either vscode or neovim inside, and referring to their terminals.

Eg. (If you use `starship)

nix develop
nvim .

Then run :terminal