feat(linter): support eslint.config.cjs with flat config

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

@@ -7,7 +7,7 @@ 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 +174,7 @@ 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 +220,7 @@ 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 +262,7 @@ 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 +282,7 @@ 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 +311,7 @@ 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 +341,7 @@ 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 +369,7 @@ 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/flat-config.ts

@@ -1,5 +1,19 @@
 import { Tree } from '@nx/devkit';
 
+export function flatConfigEslintFilename(tree: Tree): string {
+  const configFiles = ['eslint.config.js', 'eslint.config.cjs'];
+  for (const file of configFiles) {
+    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;
+  }
 }