Add some settings

src/generate.ts

@@ -103,22 +103,26 @@ export default async (project: Project, cache: Cache, report: Report) => {
           .join(``) +
         `  ]`
     );
-  const projectExprPath = ppath.join(cwd, `yarn-project.nix` as Filename);
-  xfs.writeFileSync(projectExprPath, projectExpr);
+  xfs.writeFileSync(configuration.get(`nixExprPath`), projectExpr);
 
   // Create a wrapper if it does not exist yet.
-  const defaultExprPath = ppath.join(cwd, `default.nix` as Filename);
-  if (!xfs.existsSync(defaultExprPath)) {
-    xfs.writeFileSync(defaultExprPath, defaultExprTmpl);
-    report.reportInfo(
-      0,
-      `A minimal default.nix was created. You may want to customize it.`
-    );
+  if (configuration.get(`generateDefaultNix`)) {
+    const defaultExprPath = ppath.join(cwd, `default.nix` as Filename);
+    if (!xfs.existsSync(defaultExprPath)) {
+      xfs.writeFileSync(defaultExprPath, defaultExprTmpl);
+      report.reportInfo(
+        0,
+        `A minimal default.nix was created. You may want to customize it.`
+      );
+    }
   }
 
   // Preload the cache entries into the Nix store.
-  if (xfs.existsSync(npath.toPortablePath(`/nix/store`))) {
-    xfs.mktempPromise(async (tempDir) => {
+  if (
+    configuration.get(`enableNixPreload`) &&
+    xfs.existsSync(npath.toPortablePath(`/nix/store`))
+  ) {
+    await xfs.mktempPromise(async (tempDir) => {
       const toPreload: PortablePath[] = [];
       for (const { name, filename, sha512 } of cacheEntries) {
         // Check to see if the Nix store entry already exists.

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;

src/tmpl/yarn-project.nix.in

@@ -36,6 +36,8 @@ in stdenv.mkDerivation {
   name = @@PROJECT_NAME@@;
   inherit src;
 
+  # Disable Nixify plugin to save on some unnecessary processing.
+  yarn_enable_nixify = "false";
   # Tell node-gyp to use the provided Node.js headers for native code builds.
   npm_config_nodedir = nodejs;
   # Tell node-pre-gyp to never fetch binaries / always build from source.