Preserve symbols across builds, don't mangle _handle (#2687)

* Preserve symbols across builds

* let => const

gulp-tasks/build-packages.js

@@ -60,8 +60,9 @@ module.exports = {
       parallel(
           build_node_packages,
           build_node_ts_packages,
-          build_sw_packages,
-          build_window_packages,
+          // This needs to be a series, not in parallel, so that there isn't a
+          // race condition with the terser nameCache.
+          series(build_sw_packages, build_window_packages),
       ),
   ),
 };

gulp-tasks/build-sw-packages.js

@@ -158,7 +158,9 @@ function swBundleSequence() {
 
   return series(
       parallel(transpilations),
-      parallel(builds),
+      // This needs to be a series, not in parallel, so that there isn't a
+      // race condition with the terser nameCache.
+      series(builds),
   );
 }
 

gulp-tasks/build-window-packages.js

@@ -102,7 +102,9 @@ function windowBundleSequence() {
 
   return series(
       parallel(transpilations),
-      parallel(builds),
+      // This needs to be a series, not in parallel, so that there isn't a
+      // race condition with the terser nameCache.
+      series(builds),
   );
 }
 

gulp-tasks/utils/rollup-helper.js

@@ -15,6 +15,9 @@ const terserPlugin = require('rollup-plugin-terser').terser;
 const constants = require('./constants');
 const getVersionsCDNUrl = require('./versioned-cdn-url');
 
+// See https://github.com/GoogleChrome/workbox/issues/1674
+const nameCache = {};
+
 module.exports = {
   // Every use of rollup should have minification and the replace
   // plugin set up and used to ensure as consist set of tests
@@ -46,6 +49,7 @@ module.exports = {
     const minifyBuild = buildType === constants.BUILD_TYPES.prod;
     if (minifyBuild) {
       const terserOptions = {
+        nameCache,
         module: buildFormat === 'esm' ? true : false,
         mangle: {
           properties: {
@@ -54,8 +58,10 @@ module.exports = {
               '_obj',
               // We need this to be exported correctly.
               '_private',
+              // See https://github.com/GoogleChrome/workbox/issues/2686
+              '_handle',
             ],
-            // mangle > properties > regex will allow uglify-es to minify
+            // mangle > properties > regex will allow terser to minify
             // private variable and names that start with a single underscore
             // followed by a letter. This restriction to avoid mangling
             // unintentional fields in our or other libraries code.