shellcheck-nix-attributes

When writing derivations with nix, the underlying language that gets executed in Bash, which means we can end up with many Bash snippets in our nix files. It may be desirable to check these snippets with the excellent shellcheck script such that we know that nothing strange is going to happen late into the build.

By applying the nix expression here to your derivation, an additional set of phases will run an the very start of the build. These phases will check each of the specified attributes and exit the build with failure if necessary.

Let's consider a file example-fail.nix that defines a simple derivation and runs shellcheck on installPhase:

{ pkgs ? import <nixpkgs> {} }:

let shellchecked = pkgs.callPackage ./default.nix {};
    someDerivation = pkgs.stdenvNoCC.mkDerivation {
      name = "someDerivation";
      phases = [ "installPhase" ];
      installPhase = ''
        mkdir $out
        echo foo > $out/some-output
      '';
    };
in shellchecked someDerivation

If we try to build it, we may see something like:

$ nix-build example-fail.nix --no-out-link
these derivations will be built:
  /nix/store/pywslpazmnqaqjk03qia051qyxfcc2z4-someDerivation_shellcheck_installPhase.drv
  /nix/store/bgfxd8kwcq6k5c9prprppdc3ym78fzky-someDerivation.drv
building '/nix/store/pywslpazmnqaqjk03qia051qyxfcc2z4-someDerivation_shellcheck_installPhase.drv'...
building '/nix/store/bgfxd8kwcq6k5c9prprppdc3ym78fzky-someDerivation.drv'...
shellcheck_installPhase

In /nix/store/f4lzcsyqfmnf9x4hswql7mijxsysngsn-someDerivation_shellcheck_installPhase line 1:
mkdir $out
      ^--^ SC2086: Double quote to prevent globbing and word splitting.

Did you mean:
mkdir "$out"


In /nix/store/f4lzcsyqfmnf9x4hswql7mijxsysngsn-someDerivation_shellcheck_installPhase line 2:
echo foo > $out/some-output
           ^--^ SC2086: Double quote to prevent globbing and word splitting.

Did you mean:
echo foo > "$out"/some-output

For more information:
  https://www.shellcheck.net/wiki/SC2086 -- Double quote to prevent globbing ...
builder for '/nix/store/bgfxd8kwcq6k5c9prprppdc3ym78fzky-someDerivation.drv' failed with exit code 1
error: build of '/nix/store/bgfxd8kwcq6k5c9prprppdc3ym78fzky-someDerivation.drv' failed

Great.

See default.nix for some things you can configure and few comments.

Your nixpkgs has to be recent-ish enough to support all the used library functions, such as getAttrs. If you'd like to support older versions or would like to pin a known-working nixpkgs, feel free to open an issue.