fix: added informative root directory install error

lib/commands/ci.js

@@ -36,6 +36,15 @@ class CI extends ArboristWorkspaceCmd {
     }
 
     const where = this.npm.prefix
+
+    if (path.parse(where).root === where) {
+      const msg =
+        'The current working directory is the root directory of the filesystem.\n' +
+        'Package installs in root directories are not allowed.\n' +
+        'Please create a new folder and install your packages in there.\n'
+      throw new Error(msg)
+    }
+
     const Arborist = require('@npmcli/arborist')
     const opts = {
       ...this.npm.flatOptions,

lib/commands/install.js

@@ -6,6 +6,7 @@ const pacote = require('pacote')
 const checks = require('npm-install-checks')
 const reifyFinish = require('../utils/reify-finish.js')
 const ArboristWorkspaceCmd = require('../arborist-cmd.js')
+const path = require('node:path')
 
 class Install extends ArboristWorkspaceCmd {
   static description = 'Install a package'
@@ -104,6 +105,14 @@ class Install extends ArboristWorkspaceCmd {
     const forced = this.npm.config.get('force')
     const scriptShell = this.npm.config.get('script-shell') || undefined
 
+    if (path.parse(where).root === where) {
+      const msg =
+        'The current working directory is the root directory of the filesystem.\n' +
+        'Package installs in root directories are not allowed.\n' +
+        'Please create a new folder and install your packages in there.\n'
+      throw new Error(msg)
+    }
+
     // be very strict about engines when trying to update npm itself
     const npmInstall = args.find(arg => arg.startsWith('npm@') || arg === 'npm')
     if (isGlobalInstall && npmInstall) {

test/lib/commands/ci.js

@@ -308,3 +308,27 @@ t.test('should use --workspace flag', async t => {
   assert.packageMissing('node_modules/[email protected]')
   assert.packageInstalled('node_modules/[email protected]')
 })
+
+t.test('throw error on ci in root directory', async t => {
+  let npmError = null
+
+  const { npm } = await loadMockNpm(t, {
+    config: {
+      prefix: path.parse(process.cwd()).root,
+      'dry-run': true,
+    },
+  })
+
+  try {
+    await npm.exec('ci', ['fizzbuzz'])
+  } catch (error) {
+    npmError = error.message
+  }
+
+  const expectedMessage =
+    'The current working directory is the root directory of the filesystem.\n' +
+    'Package installs in root directories are not allowed.\n' +
+    'Please create a new folder and install your packages in there.\n'
+
+  t.strictSame(npmError, expectedMessage)
+})

test/lib/commands/install.js

@@ -400,3 +400,27 @@ t.test('should show install keeps dirty --workspace flag', async t => {
   assert.packageDirty('node_modules/[email protected]')
   assert.packageInstalled('node_modules/[email protected]')
 })
+
+t.test('throw error on package install in root directory', async t => {
+  let npmError = null
+
+  const { npm } = await loadMockNpm(t, {
+    config: {
+      prefix: path.parse(process.cwd()).root,
+      'dry-run': true,
+    },
+  })
+
+  try {
+    await npm.exec('install', ['fizzbuzz'])
+  } catch (error) {
+    npmError = error.message
+  }
+
+  const expectedMessage =
+    'The current working directory is the root directory of the filesystem.\n' +
+    'Package installs in root directories are not allowed.\n' +
+    'Please create a new folder and install your packages in there.\n'
+
+  t.strictSame(npmError, expectedMessage)
+})