fix: print warning when pnpmfile exports undefined

close #1615
PR #2269

packages/pnpmfile/package.json

@@ -13,7 +13,7 @@
   "scripts": {
     "lint": "tslint -c ../../tslint.json src/**/*.ts test/**/*.ts",
     "tsc": "rimraf lib && tsc",
-    "test": "pnpm run tsc",
+    "test": "pnpm run tsc && ts-node test --type-check",
     "prepublishOnly": "pnpm run tsc"
   },
   "repository": "https://github.com/pnpm/pnpm/blob/master/packages/pnpmfile",

packages/pnpmfile/src/requirePnpmfile.ts

@@ -31,6 +31,13 @@ export default (pnpmFilePath: string, prefix: string) => {
       message: `Using hooks from: ${pnpmFilePath}`,
       prefix,
     })
+    if (typeof pnpmfile === 'undefined') {
+      logger.warn({
+        message: `Ignoring the pnpmfile at "${pnpmFilePath}". It exports "undefined".`,
+        prefix,
+      })
+      return undefined
+    }
     if (pnpmfile?.hooks?.readPackage && typeof pnpmfile.hooks.readPackage !== 'function') {
       throw new TypeError('hooks.readPackage should be a function')
     }

packages/pnpmfile/test/index.ts

@@ -0,0 +1,9 @@
+import { requirePnpmfile } from '@pnpm/pnpmfile'
+import path = require('path')
+import test = require('tape')
+
+test('ignoring a pnpmfile that exports undefined', (t) => {
+  const pnpmfile = requirePnpmfile(path.join(__dirname, 'pnpmfiles/undefined.js'), __dirname)
+  t.equal(typeof pnpmfile, 'undefined')
+  t.end()
+})

packages/pnpmfile/test/pnpmfiles/undefined.js

@@ -0,0 +1 @@
+module.exports = undefined