fix: run the install scripts of deps in a workspace with no root project (#4211)

close #4209

.changeset/fresh-countries-smell.md

@@ -0,0 +1,5 @@
+---
+"@pnpm/headless": patch
+---
+
+Run the install scripts of hoisted dependencies in a workspace with no root project.

packages/core/test/hoistedNodeLinker/install.ts

@@ -160,3 +160,26 @@ test('run pre/postinstall scripts. bin files should be linked in a hoisted node_
   const generatedByPostinstall = project.requireModule('pre-and-postinstall-scripts-example/generated-by-postinstall')
   expect(typeof generatedByPostinstall).toBe('function')
 })
+
+// Covers https://github.com/pnpm/pnpm/issues/4209
+test('running install scripts in a workspace that has no root project', async () => {
+  prepareEmpty()
+
+  await mutateModules([
+    {
+      buildIndex: 0,
+      manifest: {
+        name: 'project-1',
+        version: '1.0.0',
+
+        dependencies: {
+          'pre-and-postinstall-scripts-example': '1.0.0',
+        },
+      },
+      mutation: 'install',
+      rootDir: path.resolve('project-1'),
+    },
+  ], await testDefaults({ fastUnpack: false, nodeLinker: 'hoisted' }))
+
+  expect(fs.existsSync('node_modules/pre-and-postinstall-scripts-example/generated-by-preinstall.js')).toBeTruthy()
+})

packages/headless/src/index.ts

@@ -61,6 +61,7 @@ import equals from 'ramda/src/equals'
 import fromPairs from 'ramda/src/fromPairs'
 import omit from 'ramda/src/omit'
 import props from 'ramda/src/props'
+import union from 'ramda/src/union'
 import realpathMissing from 'realpath-missing'
 import linkHoistedModules from './linkHoistedModules'
 import lockfileToDepGraph, {
@@ -385,9 +386,9 @@ export default async (opts: HeadlessOptions) => {
       )
   } else {
     const directNodes = new Set<string>()
-    for (const id of importerIds) {
+    for (const id of union(importerIds, ['.'])) {
       Object
-        .values(directDependenciesByImporterId[id])
+        .values(directDependenciesByImporterId[id] ?? {})
         .filter((loc) => graph[loc])
         .forEach((loc) => {
           directNodes.add(loc)