[benreesman]

So there is more than one way to skin this cat. ‘nixpkgs’ as handed to you as part of a flakes ‘inputs’ is (jargon alert) partially applied, which is to say you have to put a battery in it. In this instance what you have to pass is ‘system’ because nixpkgs supports many systems (e.g. ‘linux-x86_64’ or ‘darwin-aarach64’). It sort of makes sense that it wouldn’t know what GCC you want without that information.

You can do this up top by hand, e.g. P = inputs.nixpkgs { inherit system; }, but more commonly you would use a library like ‘flake-utils’ or ‘flake-utils-plus’ to issue system configuration for all supported packages to all your packages/derivations/devShells.

[baby]

Ah right, I saw that library but it didn’t have examples and I didn’t manage to use it. Do you know a page that would explain that?

[benreesman]

The ‘flake-utils’ readme is a pretty good jumping off point: https://github.com/numtide/flake-utils

I have this or that nitpick with FL and FLP but overall it’s very solid stuff. FLP is a little more “magical”, and that’s not always the best starting out, but you really can’t go wrong with either.