feat: add PredefinedConfig for flat config

src/flat-config/index.d.ts

@@ -1,5 +1,6 @@
 import type { ESLint, Linter } from 'eslint';
 import type { Rules } from '../rules';
+import type { LiteralUnion } from '../utility-types';
 import type { LanguageOptions } from './language-options';
 import type { LinterOptions } from './linter-options';
 
@@ -56,3 +57,9 @@ export interface FlatESLintConfig {
    */
   rules?: Rules;
 }
+
+export type PredefinedConfig = LiteralUnion<
+  'eslint:recommended' | 'eslint:all'
+>;
+
+export type FlatESLintConfigs = Array<FlatESLintConfig | PredefinedConfig>;

src/index.d.ts

@@ -1,5 +1,5 @@
 import type { ESLintConfig } from './config';
-import type { FlatESLintConfig } from './flat-config';
+import type { FlatESLintConfigs } from './flat-config';
 
 /**
  * Define an ESLint config.
@@ -17,4 +17,4 @@ export function defineConfig(config: ESLintConfig): ESLintConfig;
  * @param config Flat ESLint config.
  * @returns Flat ESLint config.
  */
-export function defineConfig(config: FlatESLintConfig[]): FlatESLintConfig[];
+export function defineConfig(config: FlatESLintConfigs[]): FlatESLintConfigs[];