There are many idioms in nixpkgs which beginner packagers might not be aware of. This is a set of nit-picky rules that aim to point out and explain common mistakes in nixpkgs package pull requests.
This repository contains a bunch of overlays that add extra checks to stdenv.mkDerivation and other similar nixpkgs tools. The nixpkgs-hammer command will try to evaluate the specified attributes with the overlays, making sure the warnings only touch the attributes you care about, not their dependencies.
Note that while these rules almost always apply, there are some exceptions. Please read the explanations before taking an action.
Run the following command in your nixpkgs directory:
nix run -f https://github.com/jtojnar/nixpkgs-hammering/archive/master.tar.gz -c nixpkgs-hammer <attr-path>...
or with Flakes-enabled Nix:
nix run github:jtojnar/nixpkgs-hammering <attr-path>...
In order to make the checks not apply to unwanted derivations, we need to pass the information about our targets to the overlays. Unfortunately, we cannot use the attribute paths, since the mkDerivation function is not aware of them. Nix does offer minor meta-programming facility through builtins.unsafeGetAttrPos but we cannot use the positions of the attributes for the same reason. We could try matching the name attributes but there might be multiple packages with the same name depending on each other. But we can combine the two approaches and get the position of name attribute within the expression – this should uniquely identify the expression and be available among the mkDerivation arguments.
We could try to analyse the syntax of an expression but outside of context of nixpkgs we would have no semantics (perhaps we do not care and syntax only rules would be sufficient). Also I was too lazy to parse the syntax with hnix.
The code is licensed under MIT, the explanations are licensed under CC BY 4.0.