yarn: add module (#7526)

modules/programs/yarn/default.nix

@@ -0,0 +1,53 @@
+{
+  lib,
+  pkgs,
+  config,
+  ...
+}:
+let
+  inherit (lib)
+    mkIf
+    mkEnableOption
+    mkOption
+    ;
+
+  cfg = config.programs.yarn;
+
+  yamlFormat = pkgs.formats.yaml { };
+in
+{
+  meta.maintainers = [ lib.maintainers.friedrichaltheide ];
+
+  options.programs.yarn = {
+    enable = mkEnableOption "management of yarn config";
+
+    settings = mkOption {
+      type = yamlFormat.type;
+      default = { };
+      example = ''
+        {
+          httpProxy = "http://proxy.example.org:3128";
+          httpsProxy = "http://proxy.example.org:3128";
+        }
+      '';
+      description = ''
+        Available configuration options for yarn see:
+        <https://yarnpkg.com/configuration/yarnrc>
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    home = {
+      file =
+        let
+          yarnRcFileName = ".yarnrc.yml";
+        in
+        {
+          "${yarnRcFileName}" = {
+            source = yamlFormat.generate "${yarnRcFileName}" cfg.settings;
+          };
+        };
+    };
+  };
+}