Initial support for nix shell/develop

Nix shell/develop provides similar functionality to 'magic shell' but works with the
Nix package manager (https://nixos.org/download/) and is generally used to manage
an entire operating system.
Nix does not follow the FHS standard which means that magic does not work on systems
using Nix out of the box and providing such a developer environment makes it easier
for people using Nix to use and contribute to the software provided by Modular.
On a system with a default Nix installation the shell can be entered by going to the
mojo repository path and executing 'nix-shell'.
With flake support enabled it also works with 'nix develop'.

Signed-off-by: Thomas Mader <[email protected]>

flake.nix

@@ -0,0 +1,81 @@
+{
+  description = "Magic development environment";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
+    flake-compat = {
+      url = "github:edolstra/flake-compat";
+      flake = false;
+    };
+  };
+
+  outputs = { self, nixpkgs, flake-utils, flake-compat }:
+    let
+      linuxPkgs = nixpkgs.legacyPackages."x86_64-linux";
+      darwinPkgs = nixpkgs.legacyPackages."aarch64-darwin";
+      forAllSystems = function:
+        nixpkgs.lib.genAttrs [
+          "x86_64-linux"
+          "aarch64-darwin"
+        ] (system: function nixpkgs.legacyPackages.${system});
+      version = "0.3.0";
+      getBinary = system: {
+          "x86_64-linux" = "magic-x86_64-unknown-linux-musl";
+          "aarch64-darwin" = "magic-aarch64-apple-darwin";
+      }.${system} or (throw "unsupported system: ${system}");
+      fetchMagic = pkgs: binary: pkgs.stdenv.mkDerivation rec {
+          name = "magic";
+          src = pkgs.fetchurl {
+            url = "https://dl.modular.com/public/magic/raw/versions/${version}/${binary}";
+            sha256 = "sha256-wNweaK1TPqsVv9D1x7/m5kr1tryWfftzKCKDNdVBkOc=";
+          };
+
+          dontUnpack = true;
+
+          postInstall = ''
+            mkdir -p $out/bin
+            cp $src $out/bin/magic
+            chmod +x $out/bin/magic
+          '';
+        };
+      magicEnv = pkgs: magic: (pkgs.buildFHSEnv {
+        name = "magic-shell";
+        targetPkgs = pkgs: (with pkgs; [
+          libz
+          clang
+          lit
+          llvm
+          # Magic provides currently ncurses 6.5 on it's own but libtinfo is
+          # needed and in nixpkgs this does not seem to be provided separately
+          # https://github.com/NixOS/nixpkgs/issues/89769
+          ncurses
+        ]);
+        profile = ''
+          MODULAR_HOME=$HOME/.modular
+          BIN_DIR=$MODULAR_HOME/bin
+          MAGIC=$BIN_DIR/magic
+
+          if [ ! -e $MAGIC ]; then
+            mkdir -p $BIN_DIR
+            cp ${magic}/bin/magic $BIN_DIR/magic
+            echo 37e8aeee-7585-494b-83e4-59244188c2fe > "$MODULAR_HOME/webUserId"
+          fi
+
+          export PATH=$BIN_DIR:$PATH
+          # Seems to work but prints error 'complete: command not found' when 
+          # the shell is entered.
+          # Maybe related to https://github.com/NixOS/nix/issues/6091#issuecomment-1038247010
+          eval "$(magic completion --shell bash)"
+        '';
+        runScript = ''
+          magic shell
+        '';
+      }).env;
+    in
+    {
+      devShells = forAllSystems (pkgs: {
+        default = magicEnv pkgs (fetchMagic pkgs (getBinary pkgs.system));
+      });
+    };
+}
+

shell.nix

@@ -0,0 +1,13 @@
+# To support non-flake-enabled nix instances.
+(import
+  (
+    let lock = builtins.fromJSON (builtins.readFile ./flake.lock); in
+    fetchTarball {
+      url = lock.nodes.flake-compat.locked.url or
+      "https://github.com/edolstra/flake-compat/archive/${lock.nodes.flake-compat.locked.rev}.tar.gz";
+      sha256 = lock.nodes.flake-compat.locked.narHash;
+    }
+  )
+  { src = ./.; }
+).shellNix
+