shell.nix improvements, and fix problems on Darwin (qmk#9551)

shell.nix

@@ -1,25 +1,40 @@
 { avr ? true, arm ? true, teensy ? true }:
 
 let
- overlay = self: super:
- let addDarwinSupport = pkg: pkg.overrideAttrs (oldAttrs: {
- meta.platforms = (oldAttrs.meta.platforms or []) ++ self.lib.platforms.darwin;
- });
- in {
- dfu-programmer = addDarwinSupport super.dfu-programmer;
- teensy-loader-cli = addDarwinSupport super.teensy-loader-cli;
- };
-
  nixpkgs = builtins.fetchTarball {
  url = "https://github.com/NixOS/nixpkgs/archive/903266491b7b9b0379e88709feca0af900def0d9.tar.gz";
  sha256 = "1b5wjrfgyha6s15k1yjyx41hvrpmd5szpkpkxk6l5hyrfqsr8wip";
  };
 
- pkgs = import nixpkgs { overlays = [ overlay ]; };
+ pkgs = import nixpkgs { };
+
+ hjson = with pkgs.python3Packages; buildPythonPackage rec {
+ pname = "hjson";
+ version = "3.0.1";
+
+ src = fetchPypi {
+ inherit pname version;
+ sha256 = "1yaimcgz8w0ps1wk28wk9g9zdidp79d14xqqj9rjkvxalvx2f5qx";
+ };
+ doCheck = false;
+ };
+
+ pythonEnv = pkgs.python3.withPackages (p: with p; [
+ # requirements.txt
+ appdirs
+ argcomplete
+ colorama
+ hjson
+ # requirements-dev.txt
+ nose2
+ flake8
+ pep8-naming
+ yapf
+ ]);
 in
 
 with pkgs;
-let 
+let
  avrlibc = pkgsCross.avr.libcCross;
 
  avr_incflags = [
@@ -32,11 +47,11 @@ let
  "-L${avrlibc}/avr/lib/avr51"
  ];
 in
-stdenv.mkDerivation {
+mkShell {
  name = "qmk-firmware";
 
- buildInputs = [ dfu-programmer dfu-util diffutils git python3 ]
- ++ lib.optional avr [ 
+ buildInputs = [ dfu-programmer dfu-util diffutils git pythonEnv ]
+ ++ lib.optional avr [
  pkgsCross.avr.buildPackages.binutils
  pkgsCross.avr.buildPackages.gcc8
  avrlibc
@@ -47,4 +62,9 @@ stdenv.mkDerivation {
 
  AVR_CFLAGS = lib.optional avr avr_incflags;
  AVR_ASFLAGS = lib.optional avr avr_incflags;
+ shellHook = ''
+ # Prevent the avr-gcc wrapper from picking up host GCC flags
+ # like -iframework, which is problematic on Darwin
+ unset NIX_TARGET_CFLAGS_COMPILE
+ '';
 }