wip: better IPC messaging with the CLI

packages/webpack5/src/plugins/WatchStatePlugin.ts

@@ -0,0 +1,76 @@
+const id = 'WatchStateLoggerPlugin';
+const version = 1;
+
+export enum messages {
+	compilationComplete = 'Webpack compilation complete.',
+	startWatching = 'Webpack compilation complete. Watching for file changes.',
+	changeDetected = 'File change detected. Starting incremental webpack compilation...',
+}
+
+/**
+ * This little plugin will report the webpack state through the console.
+ * So the {N} CLI can get some idea when compilation completes.
+ */
+export class WatchStatePlugin {
+	isRunningWatching: boolean;
+
+	apply(compiler) {
+		let isWatchMode = false;
+		let prevAssets = [];
+
+		compiler.hooks.watchRun.tapAsync(id, function (compiler, callback) {
+			callback();
+
+			isWatchMode = true;
+			console.log(messages.changeDetected);
+		});
+
+		compiler.hooks.afterEmit.tapAsync(id, function (compilation, callback) {
+			callback();
+
+			console.log(
+				isWatchMode ? messages.startWatching : messages.compilationComplete
+			);
+
+			const assets =
+				compilation.getStats().toJson(
+					{
+						assets: true,
+					},
+					true
+				).assets || [];
+			const assetList = assets.map((asset) => asset.name);
+			const emittedAssets = Array.from(compilation.emittedAssets);
+			const staleAssets = prevAssets.filter((asset) => {
+				return assetList.includes(asset) === false;
+			});
+
+			// store assets for next compilation
+			prevAssets = assetList.sort();
+
+			notify({
+				type: 'compilation',
+				version,
+
+				emittedAssets,
+				staleAssets,
+				hash: compilation.hash,
+			});
+		});
+	}
+}
+
+function notify(message: any) {
+	if (!process.send) {
+		return;
+	}
+
+	console.log(`[${id}] Notify: `, message);
+	process.send(message, (error) => {
+		if (error) {
+			console.error(`[${id}] Process Send Error: `, error);
+		}
+
+		return null;
+	});
+}