Fix eslint version check for older versions (#26212)

packages/next/lib/eslint/runLintCheck.ts

@@ -42,7 +42,7 @@ async function lint(
   const mod = await import(deps.resolved.get('eslint')!)
 
   const { ESLint } = mod
-  let eslintVersion = ESLint.version
+  let eslintVersion = ESLint?.version
 
   if (!ESLint) {
     eslintVersion = mod?.CLIEngine?.version

test/integration/eslint/invalid-eslint-version/.eslintrc

@@ -0,0 +1,4 @@
+{
+  "extends": "next",
+  "root": true
+}

test/integration/eslint/invalid-eslint-version/pages/index.js

@@ -0,0 +1,8 @@
+const Home = () => (
+  <div>
+    <p>Home</p>
+    /* Badly formatted comment */
+  </div>
+)
+
+export default Home

test/integration/eslint/test/index.test.js

@@ -11,6 +11,7 @@ const dirCustomConfig = join(__dirname, '../custom-config')
 const dirIgnoreDuringBuilds = join(__dirname, '../ignore-during-builds')
 const dirCustomDirectories = join(__dirname, '../custom-directories')
 const dirConfigInPackageJson = join(__dirname, '../config-in-package-json')
+const dirInvalidEslintVersion = join(__dirname, '../invalid-eslint-version')
 
 describe('ESLint', () => {
   describe('Next Build', () => {
@@ -73,6 +74,18 @@ describe('ESLint', () => {
         'Warning: External synchronous scripts are forbidden'
       )
     })
+
+    test.only('invalid eslint version', async () => {
+      const { stdout, stderr } = await nextBuild(dirInvalidEslintVersion, [], {
+        stdout: true,
+        stderr: true,
+      })
+
+      const output = stdout + stderr
+      expect(output).toContain(
+        'Your project has an older version of ESLint installed'
+      )
+    })
   })
 
   describe('Next Lint', () => {