feat: CLI event hook flags

cli/help.md

@@ -73,6 +73,11 @@ Basic options:
 --watch.skipWrite           Do not write files to disk when watching
 --watch.exclude <files>     Exclude files from being watched
 --watch.include <files>     Limit watching to specified files
+--watch.onStart <cmd>       Shell command to run on `"START"` event
+--watch.onBundleStart <cmd> Shell command to run on `"BUNDLE_START"` event
+--watch.onBundleEnd <cmd>   Shell command to run on `"BUNDLE_END"` event
+--watch.onEnd <cmd>         Shell command to run on `"END"` event
+--watch.onError <cmd>       Shell command to run on `"ERROR"` event
 --validate                  Validate output
 
 Examples:

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);
+			}
+		}
+	};
+}

docs/01-command-line-reference.md

@@ -379,6 +379,11 @@ Many options have command line equivalents. In those cases, any arguments passed
 --watch.skipWrite           Do not write files to disk when watching
 --watch.exclude <files>     Exclude files from being watched
 --watch.include <files>     Limit watching to specified files
+--watch.onStart <cmd>       Shell command to run on `"START"` event
+--watch.onBundleStart <cmd> Shell command to run on `"BUNDLE_START"` event
+--watch.onBundleEnd <cmd>   Shell command to run on `"BUNDLE_END"` event
+--watch.onEnd <cmd>         Shell command to run on `"END"` event
+--watch.onError <cmd>       Shell command to run on `"ERROR"` event
 --validate                  Validate output
 ```
 
@@ -496,6 +501,14 @@ Specify a virtual file extension when reading content from stdin. By default, Ro
 
 Do not read files from `stdin`. Setting this flag will prevent piping content to Rollup and make sure Rollup interprets `-` and `-.[ext]` as a regular file names instead of interpreting these as the name of `stdin`. See also [Reading a file from stdin](guide/en/#reading-a-file-from-stdin).
 
+#### `--watch.onStart <cmd>`, `--watch.onBundleStart <cmd>`, `--watch.onBundleEnd <cmd>`, `--watch.onEnd <cmd>`, `--watch.onError <cmd>`
+
+When in watch mode, run a shell command `<cmd>` for a watch event code. See also [rollup.watch](guide/en/#rollupwatch).
+
+```sh
+rollup -c --watch --watch.onEnd="node ./afterBuildScript.js"
+```
+
 ### Reading a file from stdin
 
 When using the command line interface, Rollup can also read content from stdin:

src/rollup/types.d.ts

@@ -864,6 +864,8 @@ export interface ChokidarOptions {
 	usePolling?: boolean;
 }
 
+export type RollupWatchHooks = 'onError' | 'onStart' | 'onBundleStart' | 'onBundleEnd' | 'onEnd';
+
 export interface WatcherOptions {
 	buildDelay?: number;
 	chokidar?: ChokidarOptions;

test/cli/samples/watch/watch-event-hooks/_config.js

@@ -0,0 +1,24 @@
+const { assertIncludes } = require('../../../../utils.js');
+
+module.exports = {
+	description: 'onStart event hoot shell command executes correctly',
+	command:
+		'rollup -cw --watch --watch.onStart "echo start" --watch.onBundleStart "echo bundleStart" --watch.onBundleEnd "echo bundleEnd" --watch.onEnd "echo onEnd" --watch.onError "echo onError"',
+	stderr(stderr) {
+		assertIncludes(
+			stderr,
+			`watch.onStart $ echo start
+start
+bundles main.js → _actual...
+watch.onBundleStart $ echo bundleStart
+bundleStart
+created _actual in 16ms
+watch.onBundleEnd $ echo bundleEnd
+bundleEnd
+watch.onEnd $ echo onEnd
+onEnd
+`
+		);
+		// assert.strictEqual(stderr.slice(0, 12), `${CLEAR_SCREEN}${UNDERLINE}rollup`);
+	}
+};

test/cli/samples/watch/watch-event-hooks/main.js

@@ -0,0 +1,3 @@
+var main = 42;
+
+export { main as default };

test/cli/samples/watch/watch-event-hooks/rollup.config.js

@@ -0,0 +1,7 @@
+export default {
+	input: 'main.js',
+	output: {
+		dir: '_actual',
+		format: 'es'
+	}
+};