Build Tooling: Implement build files sourcing as stream

bin/packages/build.js

@@ -5,8 +5,9 @@ const path = require( 'path' );
 const glob = require( 'fast-glob' );
 const ProgressBar = require( 'progress' );
 const workerFarm = require( 'worker-farm' );
+const { Readable } = require( 'stream' );
 
-let files = process.argv.slice( 2 );
+const files = process.argv.slice( 2 );
 
 /**
  * Path to packages directory.
@@ -17,7 +18,13 @@ const PACKAGES_DIR = path.resolve( __dirname, '../../packages' );
 
 let onFileComplete = () => {};
 
-if ( ! files.length ) {
+let stream;
+
+if ( files.length ) {
+	stream = new Readable( { encoding: 'utf8' } );
+	files.forEach( ( file ) => stream.push( file ) );
+	stream.push( null );
+} else {
 	const bar = new ProgressBar( 'Build Progress: [:bar] :percent', {
 		width: 30,
 		incomplete: ' ',
@@ -26,7 +33,7 @@ if ( ! files.length ) {
 
 	bar.tick( 0 );
 
-	files = glob.sync( [
+	stream = glob.stream( [
 		`${ PACKAGES_DIR }/*/src/**/*.js`,
 		`${ PACKAGES_DIR }/*/src/*.scss`,
 	], {
@@ -37,7 +44,15 @@ if ( ! files.length ) {
 		onlyFiles: true,
 	} );
 
-	bar.total = files.length;
+	// Pause to avoid data flow which would begin on the `data` event binding,
+	// but should wait until worker processing below.
+	//
+	// See: https://nodejs.org/api/stream.html#stream_two_reading_modes
+	stream
+		.pause()
+		.on( 'data', ( file ) => {
+			bar.total = files.push( file );
+		} );
 
 	onFileComplete = () => {
 		bar.tick();
@@ -46,14 +61,16 @@ if ( ! files.length ) {
 
 const worker = workerFarm( require.resolve( './build-worker' ) );
 
-let complete = 0;
+let ended = false,
+	complete = 0;
 
-files.forEach( ( file ) => {
-	worker( file, () => {
+stream
+	.on( 'data', ( file ) => worker( file, () => {
 		onFileComplete();
 
-		if ( ++complete === files.length ) {
+		if ( ended && ++complete === files.length ) {
 			workerFarm.end( worker );
 		}
-	} );
-} );
+	} ) )
+	.on( 'end', () => ended = true )
+	.resume();