Allow extending the environment for nix develop

[thufschmitt]

Is your feature request related to a problem? Please describe.

When hacking on a project, I frequently find myself wanting to throw in more stuff than what the devShell in flake.nix specifies.

For example, when working on Nix, I like having clangd and gdb (and bear and rr, etc..) available. I also set a few custom MAKEFLAGS.
Conversely, nickel’s flake has a bunch of dev tools as input of its devShell which might not be useful for everyone (so ideally shouldn't have to be in the flake)

With nix-shell, I handled this (in a non-optimal fashion) by having a (gitignored) my-shell.nix overriding the derivation in shell.nix to add everything I needed.

Now that I use nix develop, this trick isn't possible anymore. However I think flakes are also a good opportunity to make this a first-class pattern.

Describe the solution you'd like

I'm not sure how that should look like, but I'd like to be able to have a local file that would override the devShell in the flake, so that I can have all this extra-stuff without having to patch the flake itself, and ensuring that nix build still exactly builds what's specified in the flake file.

Describe alternatives you've considered

I currently have a convoluted direnv setup that loads another flake (with nix print-dev-env) in addition to the local one to bring more programs in scope. But that's both fragile, invasive, and non standard.

I guess #3978 could also enable this use-case (by having another flake that has the upstream one as input and reexports an overriden version of it), although that would still require a bunch of custom setup.

[bjornfor]

guix has a command-line variant for that: guix environment <main-package> --ad-hoc <extra> <developer> <tools>...

Ref. https://guix.gnu.org/manual/en/html_node/Invoking-guix-environment.html

[stale]

I marked this as stale due to inactivity. → More info