Build Tooling: Optimize build by spawning worker pool (#15230)

* Build Tooling: Create worker pool for build

* Build Tooling: Define build concurrency explicitly

* Revert "Build Tooling: Define build concurrency explicitly"

This reverts commit 4338f9e.

* Build Tooling: Implement build files sourcing as stream

* Build Tooling: Reinstate error handling to build script

* Build Tooling: Log build error to stderr

Co-Authored-By: Daniel Richards <[email protected]>

* Build: Assign non-zero exit code on build error

Co-Authored-By: Daniel Richards <[email protected]>

bin/packages/build-worker.js

@@ -0,0 +1,159 @@
+/**
+ * External dependencies
+ */
+const { promisify } = require( 'util' );
+const fs = require( 'fs' );
+const path = require( 'path' );
+const babel = require( '@babel/core' );
+const makeDir = require( 'make-dir' );
+const sass = require( 'node-sass' );
+const postcss = require( 'postcss' );
+
+/**
+ * Internal dependencies
+ */
+const getBabelConfig = require( './get-babel-config' );
+
+/**
+ * Path to packages directory.
+ *
+ * @type {string}
+ */
+const PACKAGES_DIR = path.resolve( __dirname, '../../packages' );
+
+/**
+ * Mapping of JavaScript environments to corresponding build output.
+ *
+ * @type {Object}
+ */
+const JS_ENVIRONMENTS = {
+	main: 'build',
+	module: 'build-module',
+};
+
+/**
+ * Promisified fs.readFile.
+ *
+ * @type {Function}
+ */
+const readFile = promisify( fs.readFile );
+
+/**
+ * Promisified fs.writeFile.
+ *
+ * @type {Function}
+ */
+const writeFile = promisify( fs.writeFile );
+
+/**
+ * Promisified sass.render.
+ *
+ * @type {Function}
+ */
+const renderSass = promisify( sass.render );
+
+/**
+ * Get the package name for a specified file
+ *
+ * @param  {string} file File name
+ * @return {string}      Package name
+ */
+function getPackageName( file ) {
+	return path.relative( PACKAGES_DIR, file ).split( path.sep )[ 0 ];
+}
+
+/**
+ * Get Build Path for a specified file.
+ *
+ * @param  {string} file        File to build
+ * @param  {string} buildFolder Output folder
+ * @return {string}             Build path
+ */
+function getBuildPath( file, buildFolder ) {
+	const pkgName = getPackageName( file );
+	const pkgSrcPath = path.resolve( PACKAGES_DIR, pkgName, 'src' );
+	const pkgBuildPath = path.resolve( PACKAGES_DIR, pkgName, buildFolder );
+	const relativeToSrcPath = path.relative( pkgSrcPath, file );
+	return path.resolve( pkgBuildPath, relativeToSrcPath );
+}
+
+/**
+ * Object of build tasks per file extension.
+ *
+ * @type {Object<string,Function>}
+ */
+const BUILD_TASK_BY_EXTENSION = {
+	async '.scss'( file ) {
+		const outputFile = getBuildPath( file.replace( '.scss', '.css' ), 'build-style' );
+		const outputFileRTL = getBuildPath( file.replace( '.scss', '-rtl.css' ), 'build-style' );
+
+		const [ , contents ] = await Promise.all( [
+			makeDir( path.dirname( outputFile ) ),
+			readFile( file, 'utf8' ),
+		] );
+
+		const builtSass = await renderSass( {
+			file,
+			includePaths: [ path.resolve( __dirname, '../../assets/stylesheets' ) ],
+			data: (
+				[
+					'colors',
+					'breakpoints',
+					'variables',
+					'mixins',
+					'animations',
+					'z-index',
+				].map( ( imported ) => `@import "${ imported }";` ).join( ' ' )	+
+				contents
+			),
+		} );
+
+		const result = await postcss( require( './post-css-config' ) ).process( builtSass.css, {
+			from: 'src/app.css',
+			to: 'dest/app.css',
+		} );
+
+		const resultRTL = await postcss( [ require( 'rtlcss' )() ] ).process( result.css, {
+			from: 'src/app.css',
+			to: 'dest/app.css',
+		} );
+
+		await Promise.all( [
+			writeFile( outputFile, result.css ),
+			writeFile( outputFileRTL, resultRTL.css ),
+		] );
+	},
+
+	async '.js'( file ) {
+		for ( const [ environment, buildDir ] of Object.entries( JS_ENVIRONMENTS ) ) {
+			const destPath = getBuildPath( file, buildDir );
+			const babelOptions = getBabelConfig( environment, file.replace( PACKAGES_DIR, '@wordpress' ) );
+
+			const [ , transformed ] = await Promise.all( [
+				makeDir( path.dirname( destPath ) ),
+				babel.transformFileAsync( file, babelOptions ),
+			] );
+
+			await Promise.all( [
+				writeFile( destPath + '.map', JSON.stringify( transformed.map ) ),
+				writeFile( destPath, transformed.code + '\n//# sourceMappingURL=' + path.basename( destPath ) + '.map' ),
+			] );
+		}
+	},
+};
+
+module.exports = async ( file, callback ) => {
+	const extension = path.extname( file );
+	const task = BUILD_TASK_BY_EXTENSION[ extension ];
+
+	if ( ! task ) {
+		return;
+	}
+
+	try {
+		await task( file );
+		callback();
+	} catch ( error ) {
+		callback( error );
+	}
+};