Overload defineConfig to accept a RollupOptionsFunction parameter

src/rollup/rollup.ts

@@ -29,6 +29,7 @@ import type {
 	Plugin,
 	RollupBuild,
 	RollupOptions,
+	RollupOptionsFunction,
 	RollupOutput,
 	RollupWatcher
 } from './types';
@@ -275,6 +276,8 @@ async function writeOutputFile(
  * Mainly to facilitate IDE code prompts, after all, export default does not prompt, even if you add @type annotations, it is not accurate
  * @param options
  */
-export function defineConfig<T extends RollupOptions | RollupOptions[]>(options: T): T {
+export function defineConfig<T extends RollupOptions | RollupOptions[] | RollupOptionsFunction>(
+	options: T
+): T {
 	return options;
 }

src/rollup/types.d.ts

@@ -927,3 +927,8 @@ interface AcornNode {
 
 export function defineConfig(options: RollupOptions): RollupOptions;
 export function defineConfig(options: RollupOptions[]): RollupOptions[];
+export function defineConfig(optionsFunction: RollupOptionsFunction): RollupOptionsFunction;
+
+export type RollupOptionsFunction = (
+	commandLineArguments: Record<string, any>
+) => MaybePromise<RollupOptions | RollupOptions[]>;

test/load-config-file/index.js

@@ -41,6 +41,15 @@ describe('loadConfigFile', () => {
 		assert.deepStrictEqual(JSON.parse(JSON.stringify(options)), defaultConfigs);
 	});
 
+	it('loads an ESM config file exporting a config with defineConfigFn()', async () => {
+		const { options, warnings } = await loadConfigFile(
+			path.resolve(__dirname, 'samples/defineconfigfn-as-esm/rollup.config.mjs')
+		);
+		assert.strictEqual(warnings.count, 0);
+		// Remove undefined values and functions before checking
+		assert.deepStrictEqual(JSON.parse(JSON.stringify(options)), defaultConfigs);
+	});
+
 	it('loads a CommonJS config file', async () => {
 		const { options, warnings } = await loadConfigFile(
 			path.resolve(__dirname, 'samples/cjs-via-pkg/rollup.config.js')
@@ -59,6 +68,15 @@ describe('loadConfigFile', () => {
 		assert.deepStrictEqual(JSON.parse(JSON.stringify(options)), defaultConfigs);
 	});
 
+	it('loads a CommonJS config file exporting a config with defineConfigFn()', async () => {
+		const { options, warnings } = await loadConfigFile(
+			path.resolve(__dirname, 'samples/defineconfigfn-as-cjs/rollup.config.cjs')
+		);
+		assert.strictEqual(warnings.count, 0);
+		// Remove undefined values and functions before checking
+		assert.deepStrictEqual(JSON.parse(JSON.stringify(options)), defaultConfigs);
+	});
+
 	it('throws a helpful error when loading an ES module that should actually be CommonJS', async () => {
 		let caughtError;
 		try {

test/load-config-file/samples/defineconfigfn-as-cjs/rollup.config.cjs

@@ -0,0 +1,10 @@
+// @ts-check
+const { defineConfig } = require('../../../../dist/shared/rollup')
+
+module.exports = defineConfig(args => ({
+	input: 'my-input',
+	output: {
+		file: 'my-file',
+		format: 'es'
+	}
+}))

test/load-config-file/samples/defineconfigfn-as-esm/rollup.config.mjs

@@ -0,0 +1,10 @@
+// @ts-check
+import { defineConfig } from '../../../../dist/es/rollup.js'
+
+export default defineConfig(args => ({
+	input: 'my-input',
+	output: {
+		file: 'my-file',
+		format: 'es'
+	}
+}))