Issue 5695 - Use tabs.insertCSS if extensionTypes.CSSOrigin exists

lib/cssInjection.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
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 /** @module cssInjection */
 
 "use strict";
 
 const {RegExpFilter} = require("filterClasses");
 const {ElemHide} = require("elemHide");
 const {checkWhitelisted} = require("whitelisting");
 const {extractHostFromFrame} = require("url");
 const {port} = require("messaging");
 const devtools = require("devtools");
 
-let userStyleSheetsSupported = "extensionTypes" in chrome &&

[Sebastian Noack, 2017/09/15 22:52:44]

Use const here?

[Manish Jethani, 2017/09/17 13:51:37]

Done.

-                               "CSSOrigin" in chrome.extensionTypes;
+const userStyleSheetsSupported = "extensionTypes" in chrome &&
+                                 "CSSOrigin" in chrome.extensionTypes;
 
 function hideElements(tabId, frameId, selectors)
 {
   chrome.tabs.insertCSS(tabId, {
     code: selectors.join(", ") + "{display: none !important;}",
     cssOrigin: "user",
     frameId,
     matchAboutBlank: true,
     runAt: "document_start"
   });
 }
 
 port.on("elemhide.getSelectors", (msg, sender) =>
 {
-  let selectors = null;
+  let selectors = [];
   let trace = devtools && devtools.hasPanel(sender.page);
+  let inject = !userStyleSheetsSupported;
 
   if (!checkWhitelisted(sender.page, sender.frame,
                         RegExpFilter.typeMap.DOCUMENT |
                         RegExpFilter.typeMap.ELEMHIDE))
   {
     let specificOnly = checkWhitelisted(sender.page, sender.frame,
                                         RegExpFilter.typeMap.GENERICHIDE);
     selectors = ElemHide.getSelectorsForDomain(
       extractHostFromFrame(sender.frame),
       specificOnly ? ElemHide.SPECIFIC_ONLY : ElemHide.ALL_MATCHING
     );
   }
 
-  if (!selectors || selectors.length == 0)
-    return {};

[Sebastian Noack, 2017/09/15 22:52:44]

Actually, we have to pass "trace", even if there are no selectors here. There
might be emulation filters which are retrieved by a different message. But they
are traced as well if with return {trace:true} here.

Also "elemhide.injectSelectors" messages might still be send unless we return
{inject:true}.

Perhaps, it is simplest to just get rid of this special case here, and just
don't call hideElements() (as it would fail) if selectors are empty, and handle
that scenario for the inject=true scenario in the content script.

[Manish Jethani, 2017/09/17 13:51:37]

Done.

See my other comments.

+  if (!inject && selectors.length > 0)
+    hideElements(sender.page.id, sender.frame.id, selectors);
 
-  if (!userStyleSheetsSupported)

[Manish Jethani, 2017/09/15 21:26:09]

I've kept the userStyleSheetsSupported flag since there's no need to check the
existence of extensionTypes.CSSOrigin every time.

-    return {selectors, trace, inject: true};
+  let response = {trace, inject};
+  if (trace || inject)
+    response.selectors = selectors;
 
-  hideElements(sender.page.id, sender.frame.id, selectors);
-
-  if (trace)

[Manish Jethani, 2017/09/15 21:26:09]

This return statement could be merged into the next one but then we'd be
returning two useless properties. I like the consistency of never returning a
property that's false or null.

[Sebastian Noack, 2017/09/15 22:52:44]

I see the point for not including selectors=null (as selectors is irrelevant
unless either trace or inject is true), but only reporting a boolean state if it
is true seems inconsistent to me.

[Manish Jethani, 2017/09/17 13:51:37]

Done.

-    return {selectors, trace: true};
-
-  return {};
+  return response;
 });
 
 port.on("elemhide.injectSelectors", (msg, sender) =>
 {
   hideElements(sender.page.id, sender.frame.id, msg.selectors);
 });