Fix workspace root selection with parent lockfiles

Author: scarab-systems

packages/next/src/lib/find-root.test.ts

@@ -0,0 +1,51 @@
+import { mkdtemp, mkdir, rm, writeFile } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { findRootDirAndLockFiles, warnDuplicatedLockFiles } from './find-root'
+
+describe('findRootDirAndLockFiles()', () => {
+  it('prefers the nearest lockfile over stray parent lockfiles', async () => {
+    const rootDir = await mkdtemp(join(tmpdir(), 'nextjs-find-root-'))
+
+    try {
+      const appDir = join(rootDir, 'app')
+      const parentLockfile = join(rootDir, 'package-lock.json')
+      const appLockfile = join(appDir, 'package-lock.json')
+
+      await mkdir(appDir)
+      await writeFile(parentLockfile, '{}')
+      await writeFile(appLockfile, '{}')
+
+      const result = findRootDirAndLockFiles(appDir)
+
+      expect(result.rootDir).toBe(appDir)
+      expect(result.lockFiles).toEqual([appLockfile, parentLockfile])
+    } finally {
+      await rm(rootDir, { recursive: true, force: true })
+    }
+  })
+})
+
+describe('warnDuplicatedLockFiles()', () => {
+  it('reports the nearest lockfile as the selected root marker', () => {
+    const appLockfile = '/repo/app/package-lock.json'
+    const parentLockfile = '/repo/package-lock.json'
+    const warn = jest.spyOn(console, 'warn').mockImplementation(() => {})
+
+    try {
+      warnDuplicatedLockFiles([appLockfile, parentLockfile])
+
+      const message = String(warn.mock.calls[0][0])
+
+      expect(message).toContain(
+        `selected the directory of ${appLockfile} as the root directory`
+      )
+      expect(message).toContain(`* ${parentLockfile}`)
+      expect(message).not.toContain(
+        `selected the directory of ${parentLockfile} as the root directory`
+      )
+    } finally {
+      warn.mockRestore()
+    }
+  })
+})

packages/next/src/lib/find-root.ts

@@ -60,21 +60,21 @@ export function findRootDirAndLockFiles(cwd: string): {
 
   return {
     lockFiles,
-    rootDir: dirname(lockFiles[lockFiles.length - 1]),
+    rootDir: dirname(lockFiles[0]),
   }
 }
 
 export function warnDuplicatedLockFiles(lockFiles: string[]) {
   if (lockFiles.length > 1) {
     const additionalLockFiles = lockFiles
-      .slice(0, -1)
+      .slice(1)
       .map((str) => `\n   * ${str}`)
       .join('')
 
     if (process.env.TURBOPACK) {
       Log.warnOnce(
         `Warning: Next.js inferred your workspace root, but it may not be correct.\n` +
-          ` We detected multiple lockfiles and selected the directory of ${lockFiles[lockFiles.length - 1]} as the root directory.\n` +
+          ` We detected multiple lockfiles and selected the directory of ${lockFiles[0]} as the root directory.\n` +
           ` To silence this warning, set \`turbopack.root\` in your Next.js config, or consider ` +
           `removing one of the lockfiles if it's not needed.\n` +
           `   See https://nextjs.org/docs/app/api-reference/config/next-config-js/turbopack#root-directory for more information.\n` +
@@ -83,7 +83,7 @@ export function warnDuplicatedLockFiles(lockFiles: string[]) {
     } else {
       Log.warnOnce(
         `Warning: Next.js inferred your workspace root, but it may not be correct.\n` +
-          ` We detected multiple lockfiles and selected the directory of ${lockFiles[lockFiles.length - 1]} as the root directory.\n` +
+          ` We detected multiple lockfiles and selected the directory of ${lockFiles[0]} as the root directory.\n` +
           ` To silence this warning, set \`outputFileTracingRoot\` in your Next.js config, or consider ` +
           `removing one of the lockfiles if it's not needed.\n` +
           `   See https://nextjs.org/docs/app/api-reference/config/next-config-js/output#caveats for more information.\n` +