Add nix flake

Signed-off-by: Finn Behrens <me@kloenk.dev>

.gitignore

@@ -5,3 +5,4 @@ kalk/Cargo.lock
 cli/Cargo.lock
 cli/test
 .vscode/
+result*

flake.lock

@@ -0,0 +1,25 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1632255010,
+        "narHash": "sha256-p/BYR6qhbCtDpOfw9uMYwjwyhuCVKgiSUpKZaV/63UE=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "bfc38d3d0d22c528e8abc46c5dd5f3f50fc4554b",
+        "type": "github"
+      },
+      "original": {
+        "id": "nixpkgs",
+        "type": "indirect"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,55 @@
+{
+  description = "A very basic flake";
+
+  outputs = { self, nixpkgs }:
+    let
+      systems = [
+        "x86_64-linux"
+        "aarch64-linux"
+        "x86_64-darwin"
+        #"aarch64-darwin" # currently not building due to gmp
+      ];
+
+      forAllSystems = f: nixpkgs.lib.genAttrs systems (system: f system);
+
+      nixpkgsFor = forAllSystems (system:
+        import nixpkgs {
+          inherit system;
+          overlays = [ self.overlay ];
+        });
+    in {
+      overlay = final: prev: {
+        kalker = final.rustPlatform.buildRustPackage {
+          pname = "kalker";
+          version = "unstable";
+
+          src = self;
+
+          nativeBuildInputs = with final; [ m4 ];
+
+          outputs = [ "out" "lib" ];
+
+          postInstall = ''
+            moveToOutput "lib" "$lib"
+          '';
+
+          cargoLock = { lockFile = self + "/Cargo.lock"; };
+
+        }
+        # FIXME: fix aarch64-darwin builds
+        /* // (if (final.stdenv.isDarwin && final.stdenv.isAarch64) then {
+             CARGO_FEATURE_USE_SYSTEM_LIBS = "1";
+             RUST_BACKTRACE = "1";
+             buildInputs = with final; [ gmp mpfr libmpc ];
+           } else
+             { })
+        */
+        ;
+      };
+
+      packages = forAllSystems (system: nixpkgsFor.${system});
+
+      defaultPackage = forAllSystems (system: self.packages.${system}.kalker);
+
+    };
+}