feat: set up a basic flake

flake.nix

@@ -0,0 +1,39 @@
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  };
+  outputs = {
+    self,
+    nixpkgs,
+    ...
+  }: let
+    systems = ["x86_64-linux" "aarch64-darwin"];
+    buildEachSystem = output: builtins.map output systems;
+    buildAllSystems = output: (
+      builtins.foldl' nixpkgs.lib.recursiveUpdate {} (buildEachSystem output)
+    );
+  in
+    buildAllSystems (system: let
+      pkgs = import nixpkgs {inherit system;};
+    in {
+      packages.${system} = {
+        topiary-nushell = pkgs.callPackage ./package.nix {
+          tree-sitter-nu = builtins.fetchGit {
+            url = "https://github.com/nushell/tree-sitter-nu";
+            rev = "47d4b4f5369c0cae866724758ae88ef07e10e4f1";
+          };
+        };
+        default = self.packages.${system}.topiary-nushell;
+      };
+      apps.${system} = {
+        topiary-nushell = {
+          type = "app";
+          program = "${pkgs.lib.getExe self.packages.${system}.topiary-nushell}";
+          meta = {
+            description = "Topiary with NuShell support";
+          };
+        };
+        default = self.apps.${system}.topiary-nushell;
+      };
+    });
+}

package.nix

@@ -0,0 +1,59 @@
+{
+  stdenv,
+  lib,
+  writeShellApplication,
+  tree-sitter-nu ? fetchGit "https://github.com/nushell/tree-sitter-nu",
+  topiary,
+  nushell,
+  writeText,
+  callPackage,
+}:
+writeShellApplication (let
+  libtree-sitter-nu = callPackage ({
+    lib,
+    stdenv,
+  }:
+    stdenv.mkDerivation (finalAttrs: {
+      pname = "tree-sitter-nu";
+      version = tree-sitter-nu.rev;
+
+      src = tree-sitter-nu;
+
+      makeFlags = [
+        # The PREFIX var isn't picking up from stdenv.
+        "PREFIX=$(out)"
+      ];
+
+      meta = with lib; {
+        description = "A tree-sitter grammar for nu-lang, the language of nushell";
+        homepage = "https://github.com/nushell/tree-sitter-nu";
+        license = licenses.mit;
+      };
+    })) {};
+in {
+  name = "topiary-nushell";
+  runtimeInputs = [nushell topiary];
+  runtimeEnv = let
+    extension = with stdenv;
+      if isLinux
+      then ".so"
+      else if isDarwin
+      then ".dylib"
+      else throw "Unsupported system: ${system}";
+  in {
+    TOPIARY_CONFIG_FILE = writeText "languages.ncl" ''
+      {
+        languages = {
+          nu = {
+            extensions = ["nu"],
+            grammar.source.path = "${libtree-sitter-nu}/lib/libtree-sitter-nu${extension}",
+          },
+        },
+      }
+    '';
+    TOPIARY_LANGUAGE_DIR = ./languages;
+  };
+  text = ''
+    ${lib.getExe topiary} "$@"
+  '';
+})