Add nix environment for dependencies

nix/cmake-shell.nix

@@ -0,0 +1,17 @@
+{ pkgs ? (import <nixpkgs> {})}:
+
+let
+  zmkPkgs = (import ../default.nix { inherit pkgs; });
+  inherit (zmkPkgs) zmk zephyr;
+
+  zmkCmake = pkgs.writeShellScriptBin "zmk-cmake" ''
+    export PATH=${pkgs.lib.makeBinPath zmk.nativeBuildInputs}:$PATH
+    export CMAKE_PREFIX_PATH=${zephyr}
+
+    cmake -G Ninja ${pkgs.lib.escapeShellArgs zmk.cmakeFlags} "-DUSER_CACHE_DIR=/tmp/.cache" "$@"
+  '';
+in
+pkgs.stdenv.mkDerivation {
+  name = "zmk-cmake-shell";
+  nativeBuildInputs = zmk.nativeBuildInputs ++ [zmkCmake];
+}

nix/west-shell.nix

@@ -0,0 +1,62 @@
+{ pkgs ? (import <nixpkgs> {})}:
+
+let
+  # need a newer west than nixpkgs packages
+  pythonOverrides = self: super: {
+    west = super.west.overridePythonAttrs(old: rec {
+      inherit (old) pname;
+      version = "0.9.0";
+      src = super.fetchPypi {
+        inherit pname version;
+        sha256 = "1asgw3v3k77lvh4i1c3s0gncy2dn658py6256bzpjp1k35gs8mbg";
+      };
+    });
+  };
+
+  python = pkgs.python3.override {
+    packageOverrides = pythonOverrides;
+  };
+
+  # from zephyr/scripts/requirements-base.txt
+  pythonDependencies = ps: with ps; [
+    pyelftools
+    pyyaml
+    canopen
+    packaging
+    progress
+    anytree
+    intelhex
+    west
+  ];
+in
+with pkgs;
+# requires multiStdenv to build 32-bit test binaries
+multiStdenv.mkDerivation {
+  name = "zmk-shell";
+
+  buildInputs = [
+    # ZMK dependencies
+    gitFull
+    wget
+    autoconf
+    automake
+    bzip2
+    ccache
+    dtc # devicetree compiler
+    dfu-util
+    gcc
+    libtool
+    ninja
+    cmake
+    xz
+    (python.withPackages(pythonDependencies))
+
+    # ARM toolchain
+    gcc-arm-embedded
+  ];
+
+  ZEPHYR_TOOLCHAIN_VARIANT = "gnuarmemb";
+  GNUARMEMB_TOOLCHAIN_PATH = gcc-arm-embedded;
+
+  shellHook = "if [ ! -d \"zephyr\" ]; then west init -l app/ ; west update; west zephyr-export; fi; source zephyr/zephyr-env.sh";
+}