feat(linter): support eslint.config.cjs and *.cjs extension with flat config (#26637)

(cherry picked from commit 81fe132)

Author: benpsnyder

packages/eslint/src/executors/lint/utility/eslint-utils.spec.ts

@@ -162,11 +162,11 @@ describe('eslint-utils', () => {
   });
 
   describe('ESLint Flat Config', () => {
-    it('should throw if a non eslint.config.js file is used with ESLint Flat Config', async () => {
+    it('should throw if a non eslint.config.js or eslint.config.cjs file is used with ESLint Flat Config', async () => {
       await expect(
         resolveAndInstantiateESLint('./.eslintrc.json', {} as any, true)
       ).rejects.toThrowErrorMatchingInlineSnapshot(
-        `"When using the new Flat Config with ESLint, all configs must be named eslint.config.js and .eslintrc files may not be used. See https://eslint.org/docs/latest/use/configure/configuration-files-new"`
+        `"When using the new Flat Config with ESLint, all configs must be named eslint.config.js or eslint.config.cjs and .eslintrc files may not be used. See https://eslint.org/docs/latest/use/configure/configuration-files"`
       );
     });
 

packages/eslint/src/executors/lint/utility/eslint-utils.ts

@@ -10,7 +10,8 @@ export async function resolveAndInstantiateESLint(
 ) {
   if (useFlatConfig && eslintConfigPath && !isFlatConfig(eslintConfigPath)) {
     throw new Error(
-      'When using the new Flat Config with ESLint, all configs must be named eslint.config.js and .eslintrc files may not be used. See https://eslint.org/docs/latest/use/configure/configuration-files-new'
+      // todo: add support for eslint.config.mjs,
+      'When using the new Flat Config with ESLint, all configs must be named eslint.config.js or eslint.config.cjs and .eslintrc files may not be used. See https://eslint.org/docs/latest/use/configure/configuration-files'
     );
   }
   const ESLint = await resolveESLintClass(useFlatConfig);

packages/eslint/src/generators/utils/eslint-file.ts

@@ -7,7 +7,10 @@ import {
 } from '@nx/devkit';
 import type { Tree } from '@nx/devkit';
 import type { Linter } from 'eslint';
-import { useFlatConfig } from '../../utils/flat-config';
+import {
+  flatConfigEslintFilename,
+  useFlatConfig,
+} from '../../utils/flat-config';
 import {
   addBlockToFlatConfigExport,
   addCompatToFlatConfig,
@@ -174,7 +177,7 @@ export function addOverrideToLintConfig(
   if (useFlatConfig(tree)) {
     const fileName = joinPathFragments(
       root,
-      isBase ? baseEsLintFlatConfigFile : 'eslint.config.js'
+      isBase ? baseEsLintFlatConfigFile : flatConfigEslintFilename(tree)
     );
     const flatOverride = generateFlatOverride(override);
     let content = tree.read(fileName, 'utf8');
@@ -220,7 +223,7 @@ export function updateOverrideInLintConfig(
   ) => Linter.ConfigOverride<Linter.RulesRecord>
 ) {
   if (useFlatConfig(tree)) {
-    const fileName = joinPathFragments(root, 'eslint.config.js');
+    const fileName = joinPathFragments(root, flatConfigEslintFilename(tree));
     let content = tree.read(fileName, 'utf8');
     content = replaceOverride(content, root, lookup, update);
     tree.write(fileName, content);
@@ -262,7 +265,7 @@ export function lintConfigHasOverride(
   if (useFlatConfig(tree)) {
     const fileName = joinPathFragments(
       root,
-      isBase ? baseEsLintFlatConfigFile : 'eslint.config.js'
+      isBase ? baseEsLintFlatConfigFile : flatConfigEslintFilename(tree)
     );
     const content = tree.read(fileName, 'utf8');
     return hasOverride(content, lookup);
@@ -282,7 +285,7 @@ export function replaceOverridesInLintConfig(
   overrides: Linter.ConfigOverride<Linter.RulesRecord>[]
 ) {
   if (useFlatConfig(tree)) {
-    const fileName = joinPathFragments(root, 'eslint.config.js');
+    const fileName = joinPathFragments(root, flatConfigEslintFilename(tree));
     let content = tree.read(fileName, 'utf8');
     // we will be using compat here so we need to make sure it's added
     if (overrides.some(overrideNeedsCompat)) {
@@ -311,7 +314,7 @@ export function addExtendsToLintConfig(
 ) {
   const plugins = Array.isArray(plugin) ? plugin : [plugin];
   if (useFlatConfig(tree)) {
-    const fileName = joinPathFragments(root, 'eslint.config.js');
+    const fileName = joinPathFragments(root, flatConfigEslintFilename(tree));
     const pluginExtends = generatePluginExtendsElement(plugins);
     let content = tree.read(fileName, 'utf8');
     content = addCompatToFlatConfig(content);
@@ -341,7 +344,7 @@ export function addPluginsToLintConfig(
 ) {
   const plugins = Array.isArray(plugin) ? plugin : [plugin];
   if (useFlatConfig(tree)) {
-    const fileName = joinPathFragments(root, 'eslint.config.js');
+    const fileName = joinPathFragments(root, flatConfigEslintFilename(tree));
     let content = tree.read(fileName, 'utf8');
     const mappedPlugins: { name: string; varName: string; imp: string }[] = [];
     plugins.forEach((name) => {
@@ -369,7 +372,7 @@ export function addIgnoresToLintConfig(
   ignorePatterns: string[]
 ) {
   if (useFlatConfig(tree)) {
-    const fileName = joinPathFragments(root, 'eslint.config.js');
+    const fileName = joinPathFragments(root, flatConfigEslintFilename(tree));
     const block = generateAst<ts.ObjectLiteralExpression>({
       ignores: ignorePatterns.map((path) => mapFilePath(path)),
     });

packages/eslint/src/utils/config-file.ts

@@ -1,8 +1,8 @@
 import { existsSync, statSync } from 'fs';
 import { basename, dirname, join, resolve } from 'path';
+import { eslintFlatConfigFilenames } from './flat-config';
 
-// TODO(leo): add support for eslint.config.mjs and eslint.config.cjs
-export const ESLINT_FLAT_CONFIG_FILENAMES = ['eslint.config.js'];
+export const ESLINT_FLAT_CONFIG_FILENAMES = eslintFlatConfigFilenames;
 
 export const ESLINT_OLD_CONFIG_FILENAMES = [
   '.eslintrc',
@@ -40,6 +40,7 @@ export function findFlatConfigFile(
       ESLINT_FLAT_CONFIG_FILENAMES
     );
     if (configFilePath) {
+      console.log(`Found eslint flat config file at: ${configFilePath}`);
       return configFilePath;
     }
     if (currentDir === workspaceRoot) {

packages/eslint/src/utils/flat-config.ts

@@ -1,5 +1,24 @@
 import { Tree } from '@nx/devkit';
 
+// todo: add support for eslint.config.mjs,
+export const eslintFlatConfigFilenames = [
+  'eslint.config.js',
+  'eslint.config.cjs',
+];
+
+export function flatConfigEslintFilename(tree: Tree): string {
+  for (const file of eslintFlatConfigFilenames) {
+    if (tree.exists(file)) {
+      return file;
+    }
+  }
+  throw new Error('Could not find flat config file');
+}
+
 export function useFlatConfig(tree: Tree): boolean {
-  return tree.exists('eslint.config.js');
+  try {
+    return !!flatConfigEslintFilename(tree);
+  } catch {
+    return false;
+  }
 }