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 = true;
+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;
 
 function hideElements(tabId, frameId, selectors)
 {
-  let code = selectors.join(", ") + "{display: none !important;}";
-
-  try
-  {
-    chrome.tabs.insertCSS(tabId,
-      {
-        code,
-        cssOrigin: "user",
-        frameId,
-        matchAboutBlank: true,
-        runAt: "document_start"
-      }
-    );
-    return true;
-  }
-  catch (error)
-  {
-    if (/\bError processing cssOrigin\b/.test(error.message) == -1)
-      throw error;
-
-    userStylesheetsSupported = false;
-    return false;
-  }
+  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;
+  let selectors = null;
   let trace = devtools && devtools.hasPanel(sender.page);
 
   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
     );
   }
-  else
-  {
-    selectors = [];
-  }
 
-  if (selectors.length == 0 || userStylesheetsSupported &&
-      hideElements(sender.page.id, sender.frame.id, selectors))
-  {
-    if (trace)
-      return {selectors, trace: true, inject: false};
+  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.

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