feat: CLI event hook flags

cli/run/watch-cli.ts

@@ -15,6 +15,7 @@ import loadAndParseConfigFile from './loadConfigFile';
 import loadConfigFromCommand from './loadConfigFromCommand';
 import { getResetScreen } from './resetScreen';
 import { printTimings } from './timings';
+import { createWatchHooks } from './watchHooks';
 
 export async function watch(command: Record<string, any>): Promise<void> {
 	process.env.ROLLUP_WATCH = 'true';
@@ -24,6 +25,7 @@ export async function watch(command: Record<string, any>): Promise<void> {
 	let configWatcher: FSWatcher;
 	let resetScreen: (heading: string) => void;
 	const configFile = command.config ? await getConfigPath(command.config) : null;
+	const runWatchHook = createWatchHooks(command);
 
 	onExit(close);
 	process.on('uncaughtException', close);
@@ -84,6 +86,7 @@ export async function watch(command: Record<string, any>): Promise<void> {
 				case 'ERROR':
 					warnings.flush();
 					handleError(event.error, true);
+					runWatchHook('onError');
 					break;
 
 				case 'START':
@@ -93,6 +96,8 @@ export async function watch(command: Record<string, any>): Promise<void> {
 						}
 						resetScreen(underline(`rollup v${rollup.VERSION}`));
 					}
+					runWatchHook('onStart');
+
 					break;
 
 				case 'BUNDLE_START':
@@ -107,6 +112,7 @@ export async function watch(command: Record<string, any>): Promise<void> {
 							cyan(`bundles ${bold(input)} → ${bold(event.output.map(relativeId).join(', '))}...`)
 						);
 					}
+					runWatchHook('onBundleStart');
 					break;
 
 				case 'BUNDLE_END':
@@ -119,12 +125,14 @@ export async function watch(command: Record<string, any>): Promise<void> {
 								)}`
 							)
 						);
+					runWatchHook('onBundleEnd');
 					if (event.result && event.result.getTimings) {
 						printTimings(event.result.getTimings());
 					}
 					break;
 
 				case 'END':
+					runWatchHook('onEnd');
 					if (!silent && isTTY) {
 						stderr(`\n[${dateTime()}] waiting for changes...`);
 					}

cli/run/watchHooks.ts

@@ -0,0 +1,34 @@
+import { execSync } from 'child_process';
+import type { RollupWatchHooks } from '../../src/rollup/types';
+import { bold, cyan } from '../../src/utils/colors';
+import { stderr } from '../logging';
+
+function extractWatchHooks(
+	command: Record<string, any>
+): Partial<Record<RollupWatchHooks, string>> {
+	if (!Array.isArray(command.watch)) return {};
+
+	return command.watch
+		.filter(value => typeof value === 'object')
+		.reduce((acc, keyValueOption) => ({ ...acc, ...keyValueOption }), {});
+}
+
+export function createWatchHooks(command: Record<string, any>): (hook: RollupWatchHooks) => void {
+	const watchHooks = extractWatchHooks(command);
+
+	return function (hook: RollupWatchHooks): void {
+		if (watchHooks[hook]) {
+			const cmd = watchHooks[hook]!;
+
+			if (!command.silent) {
+				stderr(cyan(`watch.${hook} ${bold(`$ ${cmd}`)}`));
+			}
+
+			try {
+				execSync(cmd, { stdio: command.silent ? 'ignore' : 'inherit' });
+			} catch (e) {
+				stderr((e as Error).message);
+			}
+		}
+	};
+}

src/rollup/types.d.ts

@@ -868,6 +868,8 @@ export interface ChokidarOptions {
 	usePolling?: boolean;
 }
 
+export type RollupWatchHooks = 'onError' | 'onStart' | 'onBundleStart' | 'onBundleEnd' | 'onEnd';
+
 export interface WatcherOptions {
 	buildDelay?: number;
 	chokidar?: ChokidarOptions;