diff --git a/gulpfile.js b/gulpfile.js
index 931bba5e7..386535042 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -36,15 +36,295 @@ var fs = require('fs');
 var rimraf = require('rimraf');
 var execSync = require('child_process').execSync;
 
-// Rebuilds Blockly, including the following:
-//  - blockly_compressed.js
-//  - blocks_compressed.js
-//  - Localization string tables in msg/js/*.js
-//  - Generators in generators/*.js
-// These files are already up-to-date in the master branch.
-gulp.task('build', gulp.shell.task([
-  'python build.py'
-]));
+var closureCompiler = require('google-closure-compiler').gulp();
+var packageJson = require('./package.json');
+var argv = require('yargs').argv;
+
+
+////////////////////////////////////////////////////////////
+//                        Build                           //
+////////////////////////////////////////////////////////////
+
+const licenseRegex = `\\/\\*\\*
+ \\* @license
+ \\* [\\w: ]+
+ \\*
+ \\* (Copyright \\d+ (Google Inc.|Massachusetts Institute of Technology))
+ \\* (https://developers.google.com/blockly/|All rights reserved.)
+ \\*
+ \\* Licensed under the Apache License, Version 2.0 \\(the "License"\\);
+ \\* you may not use this file except in compliance with the License.
+ \\* You may obtain a copy of the License at
+ \\*
+ \\*   http://www.apache.org/licenses/LICENSE-2.0
+ \\*
+ \\* Unless required by applicable law or agreed to in writing, software
+ \\* distributed under the License is distributed on an "AS IS" BASIS,
+ \\* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ \\* See the License for the specific language governing permissions and
+ \\* limitations under the License.
+ \\*\\/`;
+
+/**
+ * Helper method for stripping the Google's and MIT's Apache Licenses.
+ */
+function stripApacheLicense() {
+  // Strip out Google's and MIT's Apache licences.
+  // Closure Compiler preserves dozens of Apache licences in the Blockly code.
+  // Remove these if they belong to Google or MIT.
+  // MIT's permission to do this is logged in Blockly issue #2412.
+  return gulp.replace(new RegExp(licenseRegex, "g"), '');
+}
+
+/**
+ * Helper method for prepending the auto-generated header text.
+ */
+function prependHeader() {
+  return gulp.insert.prepend(`// Do not edit this file; automatically generated by gulp.\n`);
+}
+
+/**
+ * Helper method for calling the Closure compiler.
+ * @param {*} compilerOptions 
+ * @param {boolean=} opt_verbose Optional option for verbose logging
+ */
+function compile(compilerOptions, opt_verbose) {
+  if (!compilerOptions) compilerOptions = {};
+  compilerOptions.compilation_level = 'SIMPLE_OPTIMIZATIONS';
+  compilerOptions.warning_level = opt_verbose ? 'VERBOSE' : 'DEFAULT';
+  compilerOptions.language_out = 'ECMASCRIPT5_STRICT';
+  compilerOptions.rewrite_polyfills = false;
+  compilerOptions.generate_exports = true;
+  compilerOptions.hide_warnings_for = 'node_modules';
+
+  const platform = ['native', 'java', 'javascript'];
+
+  return closureCompiler(compilerOptions, { platform });
+}
+
+/**
+ * This task builds Blockly's core files.
+ *     blockly_compressed.js
+ */
+gulp.task('build-core', function () {
+  const defines = 'Blockly.VERSION="' + packageJson.version + '"';
+  return gulp.src([
+      'core/**/**/*.js',
+      './node_modules/google-closure-library/closure/goog/base.js'
+    ], {base: './'})
+    // Directories in Blockly are used to group similar files together
+    // but are not used to limit access with @package, instead the
+    // method means something is internal to Blockly and not a public
+    // API.
+    // Flatten all files so they're in the same directory, but ensure that
+    // files with the same name don't conflict.
+    .pipe(gulp.rename(function (p) {
+      var dirname = p.dirname.replace(new RegExp(path.sep, "g"), "-");
+      p.dirname = "";
+      p.basename = dirname + "-" + p.basename;
+    }))
+    .pipe(stripApacheLicense())
+    .pipe(compile({
+      dependency_mode: 'PRUNE',
+      entry_point: './core-blockly.js',
+      js_output_file: 'blockly_compressed.js',
+      externs: './externs/svg-externs.js',
+      define: defines
+    }, argv.verbose))
+    .pipe(prependHeader())
+    .pipe(gulp.dest('./'));
+});
+
+/**
+ * This task builds the Blockly's built in blocks.
+ *     blocks_compressed.js
+ */
+gulp.task('build-blocks', function () {
+  const provides = `goog.provide('Blockly');\ngoog.provide('Blockly.Blocks');\n`;
+  return gulp.src('blocks/*.js', {base: './'})
+    // Add Blockly.Blocks to be compatible with the compiler.
+    .pipe(gulp.replace(`goog.provide('Blockly.Constants.Colour');`,
+      `${provides}goog.provide('Blockly.Constants.Colour');`))
+    .pipe(stripApacheLicense())
+    .pipe(compile({
+      dependency_mode: 'NONE',
+      js_output_file: 'blocks_compressed.js'
+    }, argv.verbose))
+    .pipe(gulp.replace('\'use strict\';', '\'use strict\';\n\n\n'))
+    // Remove Blockly.Blocks to be compatible with Blockly.
+    .pipe(gulp.replace('var Blockly={Blocks:{}};', ''))
+    .pipe(prependHeader())
+    .pipe(gulp.dest('./'));
+});
+
+/**
+ * A helper method for building a Blockly code generator.
+ * @param {string} language Generator language.
+ * @param {string} namespace Language namespace.
+ */
+function buildGenerator(language, namespace) {
+  var provides = `goog.provide('Blockly.Generator');\ngoog.provide('Blockly.utils.string');\n`;
+  return gulp.src([`generators/${language}.js`, `generators/${language}/*.js`], {base: './'})
+    .pipe(stripApacheLicense())
+    // Add Blockly.Generator and Blockly.utils.string to be compatible with the compiler.
+    .pipe(gulp.replace(`goog.provide('Blockly.${namespace}');`,
+      `${provides}goog.provide('Blockly.${namespace}');`))
+    .pipe(compile({
+      dependency_mode: 'NONE',
+      js_output_file: `${language}_compressed.js`
+    }, argv.verbose))
+    .pipe(gulp.replace('\'use strict\';', '\'use strict\';\n\n\n'))
+    // Remove Blockly.Generator and Blockly.utils.string to be compatible with Blockly.
+    .pipe(gulp.replace('var Blockly={Generator:{},utils:{}};Blockly.utils.string={};', ''))
+    .pipe(prependHeader())
+    .pipe(gulp.dest('./'));
+};
+
+/**
+ * This task builds the javascript generator.
+ *     javascript_compressed.js
+ */
+gulp.task('build-javascript', function() {
+  return buildGenerator('javascript', 'JavaScript');
+});
+
+/**
+ * This task builds the python generator.
+ *     python_compressed.js
+ */
+gulp.task('build-python', function() {
+  return buildGenerator('python', 'Python');
+});
+
+/**
+ * This task builds the php generator.
+ *     php_compressed.js
+ */
+gulp.task('build-php', function() {
+  return buildGenerator('php', 'PHP');
+});
+
+/**
+ * This task builds the lua generator.
+ *     lua_compressed.js
+ */
+gulp.task('build-lua', function() {
+  return buildGenerator('lua', 'Lua');
+});
+
+/**
+ * This task builds the dart generator:
+ *     dart_compressed.js
+ */
+gulp.task('build-dart', function() {
+  return buildGenerator('dart', 'Dart');
+});
+
+/**
+ * This task builds Blockly's uncompressed file.
+ *     blockly_uncompressed.js
+ */
+gulp.task('build-uncompressed', function() {
+  const header = `// Do not edit this file; automatically generated by build.py.
+'use strict';
+
+this.IS_NODE_JS = !!(typeof module !== 'undefined' && module.exports);
+
+this.BLOCKLY_DIR = (function(root) {
+  if (!root.IS_NODE_JS) {
+    // Find name of current directory.
+    var scripts = document.getElementsByTagName('script');
+    var re = new RegExp('(.+)[\\\/]blockly_(.*)uncompressed\\\.js$');
+    for (var i = 0, script; script = scripts[i]; i++) {
+      var match = re.exec(script.src);
+      if (match) {
+        return match[1];
+      }
+    }
+    alert('Could not detect Blockly\\'s directory name.');
+  }
+  return '';
+})(this);
+
+this.BLOCKLY_BOOT = function(root) {
+  var dir = '';
+  if (root.IS_NODE_JS) {
+    dir = 'blockly';
+  } else {
+    dir = this.BLOCKLY_DIR.match(/[^\\/]+$/)[0];
+  }
+  // Execute after Closure has loaded.
+`;
+  const footer = `
+delete root.BLOCKLY_DIR;
+delete root.BLOCKLY_BOOT;
+delete root.IS_NODE_JS;
+};
+
+if (this.IS_NODE_JS) {
+  this.BLOCKLY_BOOT(this);
+  module.exports = Blockly;
+} else {
+  // Delete any existing Closure (e.g. Soy's nogoog_shim).
+  document.write('<script>var goog = undefined;</script>');
+  // Load fresh Closure Library.
+  document.write('<script src="' + this.BLOCKLY_DIR +
+      '/closure-library/base.js"></script>');
+  document.write('<script>this.BLOCKLY_BOOT(this);</script>');
+}
+`;
+  const file = 'blockly_uncompressed.js';
+  // Run depswriter.py and which scans the core directory and writes out a ``goog.addDependency`` line for each file.
+  const cmd = `python ./node_modules/google-closure-library/closure/bin/build/depswriter.py \
+    --root_with_prefix="./core ../core" > ${file}`;
+  execSync(cmd, { stdio: 'inherit' });
+
+  let providesBuilder = `\n// Load Blockly.\n`;
+  const provides = new Set();
+  const dependencies = fs.readFileSync(file, "utf8");
+  const re = /\'(Blockly[^\']*)\'/gi;
+  let m;
+  while (m = re.exec(dependencies)) {
+    provides.add(`goog.require('${m[1]}');`);
+  }
+  providesBuilder += Array.from(provides).sort().join('\n') + '\n';
+
+  return gulp.src(file)
+    // Remove comments so we're compatible with the build.py script
+    .pipe(gulp.replace(/\/\/.*\n/gm, ''))
+    // Replace quotes to be compatible with build.py
+    .pipe(gulp.replace(/\'(.*\.js)\'/gm, '"$1"'))
+    // Find the Blockly directory name and replace it with a JS variable.
+    // This allows blockly_uncompressed.js to be compiled on one computer and be
+    // used on another, even if the directory name differs.
+    .pipe(gulp.replace(/\.\.\/core/gm, `../../" + dir + "/core`))
+    .pipe(gulp.insert.wrap(header, providesBuilder + footer))
+    .pipe(gulp.dest('./'));
+});
+
+/**
+ * This task builds all of Blockly:
+ *     blockly_compressed.js
+ *     blocks_compressed.js
+ *     javascript_compressed.js
+ *     python_compressed.js
+ *     php_compressed.js
+ *     lua_compressed.js
+ *     dart_compressed.js
+ */
+gulp.task('build', gulp.parallel(
+  'build-core',
+  'build-blocks',
+  'build-javascript',
+  'build-python',
+  'build-php',
+  'build-lua',
+  'build-dart'
+));
+
+////////////////////////////////////////////////////////////
+//                         Node                           //
+////////////////////////////////////////////////////////////
 
 // Concatenates the necessary files to load Blockly in a Node.js VM.  Blockly's
 // individual libraries target use in a browser, where globals (via the window
diff --git a/package.json b/package.json
index 27f9b77b1..5e2890abb 100644
--- a/package.json
+++ b/package.json
@@ -17,12 +17,13 @@
     "name": "Neil Fraser"
   },
   "scripts": {
-    "prepare": "gulp blockly_node_javascript_en",
+    "build": "gulp build",
     "lint": "eslint .",
-    "typings": "gulp typings",
-    "test": "tests/run_all_tests.sh",
     "package": "gulp package",
-    "release": "gulp release"
+    "prepare": "gulp blockly_node_javascript_en",
+    "release": "gulp release",
+    "test": "tests/run_all_tests.sh",
+    "typings": "gulp typings"
   },
   "main": "./index.js",
   "umd": "./blockly.min.js",
@@ -54,7 +55,8 @@
     "pngjs": "^3.4.0",
     "rimraf": "^2.6.3",
     "typescript-closure-tools": "^0.0.7",
-    "webdriverio": "^5.11.5"
+    "webdriverio": "^5.11.5",
+    "yargs": "^14.0.0"
   },
   "jshintConfig": {
     "globalstrict": true,