feat(eslint): add support for ESLint v9

package.json

@@ -27,6 +27,7 @@
     "chalk": "^4.1.0",
     "codecov-lite": "2.0.0",
     "del-cli": "^5.0.0",
+    "eslint": "^8.57.1",
     "eslint-config-rollup": "^3.0.1",
     "esm": "^3.2.25",
     "execa": "^5.1.1",

packages/eslint/package.json

@@ -54,6 +54,7 @@
     "lint"
   ],
   "peerDependencies": {
+    "eslint": "^8.57.1||^9.0.0",
     "rollup": "^1.20.0||^2.0.0||^3.0.0||^4.0.0"
   },
   "peerDependenciesMeta": {
@@ -62,18 +63,21 @@
     }
   },
   "dependencies": {
-    "@rollup/pluginutils": "^5.0.1",
-    "eslint": "^8.57.1"
+    "@rollup/pluginutils": "^5.0.1"
   },
   "devDependencies": {
     "@rollup/plugin-node-resolve": "^15.0.0",
     "@rollup/plugin-typescript": "^9.0.1",
     "@types/eslint": "^8.56.12",
+    "eslint": "^8.57.1",
+    "eslint9": "npm:eslint@^9.37.0",
+    "esmock": "^2.7.3",
     "rollup": "^4.0.0-24",
     "typescript": "^4.8.3"
   },
   "types": "./types/index.d.ts",
   "ava": {
+    "workerThreads": false,
     "files": [
       "!**/fixtures/**",
       "!**/helpers/**",

packages/eslint/test/test.mjs

@@ -1,7 +1,11 @@
 import fs from 'fs';
-
 import { createRequire } from 'module';
+import process from 'process';
+import path from 'path';
+import { fileURLToPath } from 'url';
 
+import eslint9 from 'eslint9';
+import esmock from 'esmock';
 import test from 'ava';
 import nodeResolve from '@rollup/plugin-node-resolve';
 import { rollup } from 'rollup';
@@ -241,3 +245,36 @@
 
   t.is(count, 1);
 });
+
+test.serial('works with ESLint v9', async (t) => {
+  // Load the plugin with an override to route 'eslint' imports to ESLint v9
+  const eslint = await esmock('current-package', {
+    eslint: eslint9
+  });
+
+  // ESLint v9 needs to be invoked with a flat config file in the current dir
+  const cwd = process.cwd();
+  const testDir = path.dirname(fileURLToPath(import.meta.url));
+  process.chdir(path.join(testDir, 'fixtures', 'flat-config'));
+
+  let count = 0;
+  try {
+    await rollup({
+      input: './undeclared.js',
+      plugins: [
+        eslint({
+          formatter: (results) => {
+            count += results[0].messages.length;
+            // eslint-disable-next-line prefer-destructuring
+            const { message } = results[0].messages[0];
+            t.is(message, "'x' is not defined.");
+          }
+        })
+      ]
+    });
+  } finally {
+    process.chdir(cwd);
+  }
+
+  t.is(count, 1);
+});