fix: fork bomb when pnpm self-manages its version (#8679)

* fix: prevent fork bombing if .tools dir had an incomplete download

* refactor: factor out reusable `VersionSwitchFail` class

* fix: avoid swallowing errors from spawn.sync()

* test: fix

.changeset/great-onions-matter.md

@@ -0,0 +1,5 @@
+---
+"pnpm": patch
+---
+
+Fix a bug causing pnpm to infinitely spawn itself when `manage-package-manager-versions=true` is set and the `.tools` directory is corrupt.

.changeset/swift-panthers-matter.md

@@ -0,0 +1,5 @@
+---
+"pnpm": patch
+---
+
+When `manage-package-manager-versions` is set to `true`, errors spawning a self-managed version of `pnpm` will now be shown (instead of being silent).

pnpm/src/switchCliVersion.ts

@@ -42,14 +42,44 @@ export async function switchCliVersion (config: Config): Promise<void> {
   const pnpmEnv = prependDirsToPath([wantedPnpmBinDir])
   if (!pnpmEnv.updated) {
     // We throw this error to prevent an infinite recursive call of the same pnpm version.
-    throw new PnpmError('VERSION_SWITCH_FAIL', `Failed to switch pnpm to v${pm.version}. Looks like pnpm CLI is missing at "${wantedPnpmBinDir}" or is incorrect`)
+    throw new VersionSwitchFail(pm.version, wantedPnpmBinDir)
   }
-  const { status } = spawn.sync('pnpm', process.argv.slice(2), {
+
+  // Specify the exact pnpm file path that's expected to execute to spawn.sync()
+  //
+  // It's not safe spawn 'pnpm' (without specifying an absolute path) and expect
+  // it to resolve to the same file path computed above due to the $PATH
+  // environment variable. While that does happen in most cases, there's a
+  // scenario where the wanted pnpm bin dir exists, but no pnpm binary is
+  // present within that directory. If that's the case, a different pnpm bin can
+  // get executed, causing infinite spawn and fork bombing the user. See details
+  // at https://github.com/pnpm/pnpm/pull/8679.
+  const pnpmBinPath = path.join(wantedPnpmBinDir, 'pnpm')
+
+  const { status, error } = spawn.sync(pnpmBinPath, process.argv.slice(2), {
     stdio: 'inherit',
     env: {
       ...process.env,
       [pnpmEnv.name]: pnpmEnv.value,
     },
   })
+
+  if (error) {
+    throw new VersionSwitchFail(pm.version, wantedPnpmBinDir, error)
+  }
+
   process.exit(status ?? 0)
 }
+
+class VersionSwitchFail extends PnpmError {
+  constructor (version: string, wantedPnpmBinDir: string, cause?: unknown) {
+    super(
+      'VERSION_SWITCH_FAIL',
+      `Failed to switch pnpm to v${version}. Looks like pnpm CLI is missing at "${wantedPnpmBinDir}" or is incorrect`,
+      { hint: cause instanceof Error ? cause?.message : undefined })
+
+    if (cause != null) {
+      this.cause = cause
+    }
+  }
+}

pnpm/test/switchingVersions.test.ts

@@ -1,8 +1,10 @@
 import path from 'path'
 import fs from 'fs'
 import { prepare } from '@pnpm/prepare'
+import { getToolDirPath } from '@pnpm/tools.path'
 import { sync as writeJsonFile } from 'write-json-file'
 import { execPnpmSync } from './utils'
+import isWindows from 'is-windows'
 
 test('switch to the pnpm version specified in the packageManager field of package.json, when manager-package-manager=versions is true', async () => {
   prepare()
@@ -58,3 +60,27 @@ test('do not switch to pnpm version when a range is specified', async () => {
 
   expect(stdout.toString()).toContain('Cannot switch to pnpm@^9.3.0')
 })
+
+test('throws error if pnpm tools dir is corrupt', () => {
+  prepare()
+  const pnpmHome = path.resolve('pnpm')
+  const env = { PNPM_HOME: pnpmHome }
+  const version = '9.3.0'
+  fs.writeFileSync('.npmrc', 'manage-package-manager-versions=true')
+  writeJsonFile('package.json', {
+    packageManager: `pnpm@${version}`,
+  })
+
+  // Run pnpm once to ensure the tools dir is created.
+  execPnpmSync(['help'], { env })
+
+  // Intentionally corrupt the tool dir.
+  const toolDir = getToolDirPath({ pnpmHomeDir: pnpmHome, tool: { name: 'pnpm', version } })
+  fs.rmSync(path.join(toolDir, 'bin/pnpm'))
+  if (isWindows()) {
+    fs.rmSync(path.join(toolDir, 'bin/pnpm.cmd'))
+  }
+
+  const { stderr } = execPnpmSync(['help'], { env })
+  expect(stderr.toString()).toContain('Failed to switch pnpm to v9.3.0. Looks like pnpm CLI is missing')
+})