chore: warn when running tests against stale build

jest.config.js

@@ -7,6 +7,7 @@ const createJestConfig = nextJest()
 const customJestConfig = {
   displayName: process.env.IS_WEBPACK_TEST ? 'webpack' : 'Turbopack',
   testMatch: ['**/*.test.js', '**/*.test.ts', '**/*.test.jsx', '**/*.test.tsx'],
+  globalSetup: '<rootDir>/jest-global-setup.ts',
   setupFilesAfterEnv: ['<rootDir>/jest-setup-after-env.ts'],
   verbose: true,
   rootDir: 'test',

packages/next/taskfile.js

@@ -2684,6 +2684,16 @@ export async function build(task, opts) {
     ['precompile', 'compile', 'check_error_codes', 'generate_types'],
     opts
   )
+  // Write git commit hash to dist for stale build detection during tests
+  try {
+    const { stdout: commitHash } = await execa('git', ['rev-parse', 'HEAD'])
+    await fs.writeFile(
+      join(__dirname, 'dist', '.build-commit'),
+      commitHash.trim()
+    )
+  } catch (err) {
+    console.warn(`Warning: Could not write build commit hash: ${err.message}`)
+  }
 }
 
 export async function generate_types(task, opts) {

run-tests.js

@@ -13,6 +13,7 @@ const glob = promisify(_glob)
 const exec = promisify(execOrig)
 const core = require('@actions/core')
 const { getTestFilter } = require('./test/get-test-filter')
+const { checkBuildFreshness } = require('./test/lib/check-build-freshness')
 
 // Do not rename or format. sync-react script relies on this line.
 // prettier-ignore
@@ -219,6 +220,9 @@ async function main() {
   // Ensure we have the arguments awaited from yargs.
   argv = await argv
 
+  // Check for stale or missing build
+  await checkBuildFreshness()
+
   // `.github/workflows/build_reusable.yml` sets this, we should use it unless
   // it's overridden by an explicit `--concurrency` argument.
   const envConcurrency =

test/jest-global-setup.ts

@@ -0,0 +1,5 @@
+import { checkBuildFreshness } from './lib/check-build-freshness'
+
+export default async function globalSetup() {
+  await checkBuildFreshness()
+}

test/lib/check-build-freshness.js

@@ -0,0 +1,59 @@
+const { existsSync } = require('fs')
+const fsp = require('fs/promises')
+const path = require('path')
+const { execSync } = require('child_process')
+
+const YELLOW = '\x1b[33m'
+const RESET = '\x1b[0m'
+
+/**
+ * Check if the Next.js build is fresh (matches current git HEAD).
+ * Prints warnings to console if build is missing or stale.
+ * @returns {Promise<void>}
+ */
+async function checkBuildFreshness() {
+  const distPath = path.join(__dirname, '../../packages/next/dist')
+  const buildCommitPath = path.join(distPath, '.build-commit')
+
+  if (!existsSync(distPath)) {
+    console.warn(`${YELLOW}⚠️  WARNING: No build found!${RESET}`)
+    console.warn(
+      `${YELLOW}   The packages/next/dist directory does not exist.${RESET}`
+    )
+    console.warn(
+      `${YELLOW}   Run \`pnpm build\` before running tests.\n${RESET}`
+    )
+    return
+  }
+
+  if (!existsSync(buildCommitPath)) {
+    console.warn(`${YELLOW}⚠️  WARNING: Build may be stale!${RESET}`)
+    console.warn(
+      `${YELLOW}   Unable to verify build freshness (no .build-commit marker).${RESET}`
+    )
+    console.warn(`${YELLOW}   Run \`pnpm build\` to rebuild.\n${RESET}`)
+    return
+  }
+
+  try {
+    const buildCommit = (await fsp.readFile(buildCommitPath, 'utf8')).trim()
+    const currentCommit = execSync('git rev-parse HEAD', {
+      encoding: 'utf8',
+    }).trim()
+
+    if (buildCommit !== currentCommit) {
+      console.warn(`${YELLOW}⚠️  WARNING: Build is stale!${RESET}`)
+      console.warn(
+        `${YELLOW}   Build was compiled at commit: ${buildCommit.slice(0, 8)}${RESET}`
+      )
+      console.warn(
+        `${YELLOW}   Current HEAD is at commit:    ${currentCommit.slice(0, 8)}${RESET}`
+      )
+      console.warn(`${YELLOW}   Run \`pnpm build\` to rebuild.\n${RESET}`)
+    }
+  } catch (err) {
+    // Ignore errors (e.g., git not available)
+  }
+}
+
+module.exports = { checkBuildFreshness }