Sort requires (#4658)

* Cleanup gulp method to sort requires

scripts/gulpfiles/cleanup_tasks.js

@@ -0,0 +1,85 @@
+/**
+ * @license
+ * Copyright 2018 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @fileoverview Gulp tasks to complete various clean up tasks.
+ */
+
+const gulp = require('gulp');
+const path = require('path');
+const through2 = require('through2');
+
+/**
+ * Sorts goog.requires in core, blocks and generators.
+ */
+function sortRequires() {
+  const srcs = ['core/**/**/*.js', 'blocks/*.js', 'generators/**/*.js'];
+  const excludes = ['core/requires.js'];
+  return gulp.src(srcs, {base: './'})
+      .pipe(through2.obj((file, _enc, next) => {
+        if (file.isNull() || file.isDirectory()) {
+          next(null, file);
+          return;
+        }
+
+        if (file.extname !== '.js' && path.extname(file.history[0]) !== '.js') {
+          next(null, file);
+          return;
+        }
+
+        const relPath = path.relative(path.join(file.cwd, file.base), file.path);
+        if (excludes.indexOf(relPath) > -1) {
+          next(null, file);
+          return;
+        }
+
+        const contents = file.contents.toString();
+
+        // Capture requires.
+        const re = /goog\.(require|requireType)\('(.*)'\);/gm;
+        const requiresList = [];
+        const requireTypesList = [];
+        let firstIndex;
+        let lastIndex;
+        while ((match = re.exec(contents)) != null) {
+          if (match[1] == 'require') requiresList.push(match[2]);
+          if (match[1] == 'requireType') requireTypesList.push(match[2]);
+          if (firstIndex == undefined) {
+            firstIndex = match.index;
+          } else {
+            lastIndex = re.lastIndex;
+          }
+        }
+
+        // Sort requires.
+        requiresList.sort(
+            (a, b) => a.toLowerCase().localeCompare(b.toLowerCase()));
+        requireTypesList.sort(
+            (a, b) => a.toLowerCase().localeCompare(b.toLowerCase()));
+
+        // Replace in file.
+        const requiresSection = requiresList.length ?
+            requiresList.map(r => `goog.require('${r}');`).join('\n') + '\n\n' :
+            '';
+        const requireTypesSection = requireTypesList.length ?
+            requireTypesList.map(r => `goog.requireType('${r}');`).join('\n') +
+                '\n\n' :
+            '';
+        const requires = `${requiresSection}${requireTypesSection}\n`;
+
+        if (firstIndex != undefined & lastIndex != undefined) {
+          file.contents = Buffer.from(
+              contents.substring(0, firstIndex) + requires +
+              contents.substring(lastIndex).trimStart());
+        }
+        next(null, file);
+      }))
+      .pipe(gulp.dest('./'));
+};
+
+module.exports = {
+  sortRequires: sortRequires
+};