Add some settings

src/index.ts

@@ -1,17 +1,42 @@
 import FetchOneCommand from "./FetchOneCommand";
 import InstallBinCommand from "./InstallBinCommand";
 import generate from "./generate";
-import { Hooks, Plugin } from "@yarnpkg/core";
+import { Hooks, Plugin, SettingsType } from "@yarnpkg/core";
 
 const plugin: Plugin<Hooks> = {
   commands: [FetchOneCommand, InstallBinCommand],
   hooks: {
     afterAllInstalled: async (project, opts) => {
-      if (opts.persistProject !== false) {
+      if (
+        opts.persistProject !== false &&
+        project.configuration.get(`enableNixify`)
+      ) {
         await generate(project, opts.cache, opts.report);
       }
     },
   },
+  configuration: {
+    enableNixify: {
+      description: `If false, disables the Nixify plugin hook that generates Nix expressions`,
+      type: SettingsType.BOOLEAN,
+      default: true,
+    },
+    nixExprPath: {
+      description: `Path of the file where the project Nix expression will be written to`,
+      type: SettingsType.ABSOLUTE_PATH,
+      default: `./yarn-project.nix`,
+    },
+    generateDefaultNix: {
+      description: `If true, a default.nix will be generated if it does not exist`,
+      type: SettingsType.BOOLEAN,
+      default: true,
+    },
+    enableNixPreload: {
+      description: `If true, cached packages will be preloaded into the Nix store`,
+      type: SettingsType.BOOLEAN,
+      default: true,
+    },
+  },
 };
 
 export default plugin;