Issue 6999 - Generate style sheets in background page

lib/contentFiltering.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 228 matching lines @@
 
   if (!inline && !updateFrameStyles(sender.page.id, sender.frame.id,
                                     styleSheet.code))
   {
     inline = true;
   }
 
   let response = {trace, inline, emulatedPatterns};
 
   if (inline)
     response.rules = [...rulesFromStyleSheet(styleSheet.code)];

[Sebastian Noack, 2018/10/02 17:14:02]

Why do we have to copy this array?

[Sebastian Noack, 2018/10/02 17:15:38]

Ah, just figured it's a generator. I think I personally, might rather use
Array.from(), or does the rest-operator perform better?

[Manish Jethani, 2018/10/02 17:23:24]

Yes, the spread operator is significantly faster (actually it's much, much
faster) [1]

There's also a difference: the spread operator simply iterates over the
"iterable" (defined as an object that has a Symbol.iterator method), whereas
Array.from also additionally supports "array-like" objects (objects with a
length property and so on).

[1]: https://jsperf.com/set-iterator-vs-foreach/4

[Sebastian Noack, 2018/10/02 17:28:21]

I'd take that benchmark with a grain of salt, since it's testing against a Set
object (which it the spread operator might be optimized for), not a generic
generator. But for the case here, I guess, it doesn't matter too much.

-  else if (trace)

[Sebastian Noack, 2018/10/02 17:14:02]

Doesn't the content scripts needs the original selectors (in order for the hit
logger to find the respective filters) if tracing is active, regardless of the
"inline" flag?

[Manish Jethani, 2018/10/02 19:07:46]

Ah, you're right.

Done.

+
+  if (trace)
     response.selectors = styleSheet.selectors;
 
   return response;
 });
 
 port.on("content.injectSelectors", (message, sender) =>
 {
   let styleSheet = createStyleSheet(message.selectors);
   if (!userStyleSheetsSupported ||
       !updateFrameStyles(sender.page.id, sender.frame.id, styleSheet,
                          message.groupName, message.appendOnly))
   {
     return [...rulesFromStyleSheet(styleSheet)];
   }
 });
 
 fetch(browser.extension.getURL("/snippets.js"), {cache: "no-cache"})
 .then(response => response.ok ? response.text() : "")
 .then(text =>
 {
   snippetsLibrarySource = text;
 });