npm: add module

modules/programs/npm.nix

@@ -0,0 +1,74 @@
+# https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/programs/npm.nix
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+let
+  cfg = config.programs.npm;
+
+  xdgConfigHome = lib.removePrefix config.home.homeDirectory config.xdg.configHome;
+  configFile = if config.home.preferXdgDirectories then "${xdgConfigHome}/npm/npmrc" else ".npmrc";
+
+  iniFormat = pkgs.formats.ini {
+    listsAsDuplicateKeys = true;
+  };
+
+  toNpmrc =
+    let
+      mkLine = lib.generators.mkKeyValueDefault { } "=";
+      mkLines = k: v: if lib.isList v then map (x: mkLine "${k}[]" x) v else [ (mkLine k v) ];
+    in
+    attrs: lib.concatLines (lib.concatLists (lib.mapAttrsToList mkLines attrs));
+in
+{
+  meta.maintainers = with lib.maintainers; [ mirkolenz ];
+
+  options = {
+    programs.npm = {
+      enable = lib.mkEnableOption "{command}`npm` user config";
+
+      package = lib.mkPackageOption pkgs [ "nodejs" ] {
+        example = "nodejs_24";
+        nullable = true;
+      };
+
+      settings = lib.mkOption {
+        type = lib.types.attrsOf iniFormat.lib.types.atom;
+        description = ''
+          The user-specific npm configuration.
+          See <https://docs.npmjs.com/cli/using-npm/config> and
+          <https://docs.npmjs.com/cli/configuring-npm/npmrc>
+          for more information.
+        '';
+        default = {
+          prefix = "\${HOME}/.npm";
+        };
+        example = lib.literalExpression ''
+          {
+            color = true;
+            include = [
+              "dev"
+              "prod"
+            ];
+            init-license = "MIT";
+            prefix = "''${HOME}/.npm";
+          }
+        '';
+      };
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    home = {
+      packages = lib.mkIf (cfg.package != null) [ cfg.package ];
+      file.${configFile} = lib.mkIf (cfg.settings != { }) {
+        text = toNpmrc cfg.settings;
+      };
+      sessionVariables = lib.mkIf (cfg.settings != { }) {
+        NPM_CONFIG_USERCONFIG = "${config.home.homeDirectory}/${configFile}";
+      };
+    };
+  };
+}