Issue 6504, 6458, 6446 - Update selectors based on DOM mutations

lib/content/elemHideEmulation.js

Index: lib/content/elemHideEmulation.js
===================================================================
--- a/lib/content/elemHideEmulation.js
+++ b/lib/content/elemHideEmulation.js
@@ -469,23 +469,121 @@
   return patterns.some(pattern => pattern.maybeDependsOnAttributes);
 }
 
 function shouldObserveCharacterData(patterns)
 {
   return patterns.some(pattern => pattern.dependsOnCharacterData);
 }
 
+function updateSelectorsForMutation(mutation, selectorSet, selectors,
+                                    selectorFilters, root)
+{
+  let {target} = mutation;
+
+  // Existing selectors aren't affected by non-childList mutations.
+  if (mutation.type != "childList" || !root.contains(target))
+    return false;
+
+  // Find the mutation index, i.e. the index in the parent element where the
+  // mutation has occurred.
+  let index = 0;
+  let ref = mutation.previousSibling;
+  if (ref)
+  {
+    if (!(ref instanceof Element))
+      ref = ref.previousElementSibling;
+
+    if (ref)
+      index = indexOf(ref.parentNode.children, ref) + 1;
+  }
+
+  // Count the number of elements added and removed. Both can be non-zero in
+  // some cases, e.g. when Element.innerHTML is set on the parent element to
+  // overwrite all the existing child nodes.
+  let numAddedElements = 0;
+  let numRemovedElements = 0;
+
+  for (let node of mutation.addedNodes)
+  {
+    if (node instanceof Element)
+      numAddedElements++;
+  }
+
+  for (let node of mutation.removedNodes)
+  {
+    if (node instanceof Element)
+      numRemovedElements++;
+  }
+
+  let changed = false;
+
+  // Go through all the selectors and find any that match the mutation target.
+  let targetSelector = makeSelector(target) + " > ";
+  for (let i = 0; i < selectors.length; i++)
+  {
+    let selector = selectors[i];
+    if (selector.startsWith(targetSelector))
+    {
+      // If there's a match, extract the one-based child index.
+      let subSelector = selector.substring(targetSelector.length);
+      let match = /^[^:]*:nth-child\((\d+)\)/.exec(subSelector);
+      let nthIndex = match ? +match[1] : 0;
+
+      // If the child being targeted by the selector is before the mutation
+      // index (i.e. the one-based child index is not affected), do nothing.
+      if (nthIndex <= index)
+        continue;
+
+      nthIndex -= numRemovedElements;
+
+      // After adjusting for the number of removed elements, if the one-based
+      // child index appears to be lower than the mutation index, it means the
+      // child got removed. In that case we must delete the selector.
+      if (nthIndex <= index)
+      {
+        selectorSet.delete(selector);
+
+        selectors.splice(i, 1);
+        selectorFilters.splice(i, 1);
+        i--;
+
+        changed = true;
+
+        continue;
+      }
+
+      nthIndex += numAddedElements;
+
+      // If the one-based child index has changed, we must update the selector.
+      if (nthIndex != +match[1])
+      {
+        selectorSet.delete(selector);
+        selector = targetSelector + subSelector.replace(match[1], nthIndex);
+        selectorSet.add(selector);
+        selectors[i] = selector;
+
+        changed = true;
+      }
+    }
+  }
+
+  return changed;
+}
+
 function ElemHideEmulation(addSelectorsFunc, hideElemsFunc)
 {
   this.document = document;
   this.addSelectorsFunc = addSelectorsFunc;
   this.hideElemsFunc = hideElemsFunc;
   this.observer = new MutationObserver(this.observe.bind(this));
   this.useInlineStyles = true;
+  this.selectorSet = new Set();
+  this.selectors = [];
+  this.selectorFilters = [];
 }
 
 ElemHideEmulation.prototype = {
   isSameOrigin(stylesheet)
   {
     try
     {
       return new URL(stylesheet.href).origin == this.document.location.origin;
@@ -574,16 +672,19 @@
    *    then and all rules, including the ones not dependent on the DOM.
    * @param {function} [done]
    *    Callback to call when done.
    */
   _addSelectors(stylesheets, mutations, done)
   {
     let patterns = filterPatterns(this.patterns, {stylesheets, mutations});
 
+    if (patterns.length == 0)
+      return;
+
     let selectors = [];
     let selectorFilters = [];
 
     let elements = [];
     let elementFilters = [];
 
     let cssStyles = [];
 
@@ -628,19 +729,30 @@
     {
       let cycleStart = performance.now();
 
       if (!pattern)
       {
         if (!patterns.length)
         {
           if (selectors.length > 0)
-            this.addSelectorsFunc(selectors, selectorFilters);
+          {
+            for (let selector of selectors)
+              this.selectorSet.add(selector);
+
+            this.selectors.push(...selectors);
+            this.selectorFilters.push(...selectorFilters);
+
+            this.addSelectorsFunc(this.selectors,
+                                  this.selectorFilters);
+          }
+
           if (elements.length > 0)
             this.hideElemsFunc(elements, elementFilters);
+
           if (typeof done == "function")
             done();
           return;
         }
 
         pattern = patterns.shift();
 
         generator = evaluate(pattern.selectors, 0, "",
@@ -648,18 +760,21 @@
       }
       for (let selector of generator)
       {
         if (selector != null)
         {
           if (!this.useInlineStyles ||
               pattern.isSelectorHidingOnlyPattern())
           {
-            selectors.push(selector);
-            selectorFilters.push(pattern.text);
+            if (!this.selectorSet.has(selector))
+            {
+              selectors.push(selector);
+              selectorFilters.push(pattern.text);
+            }
           }
           else
           {
             for (let element of this.document.querySelectorAll(selector))
             {
               elements.push(element);
               elementFilters.push(pattern.text);
             }
@@ -779,16 +894,29 @@
   {
     let stylesheet = event.target.sheet;
     if (stylesheet)
       this.queueFiltering([stylesheet]);
   },
 
   observe(mutations)
   {
+    let selectorsChanged = false;
+    for (let mutation of mutations)
+    {
+      if (updateSelectorsForMutation(mutation, this.selectorSet, this.selectors,
+                                     this.selectorFilters, this.document))
+      {
+        selectorsChanged = true;
+      }
+    }
+
+    if (selectorsChanged)
+      this.addSelectorsFunc(this.selectors, this.selectorFilters);
+
     this.queueFiltering(null, mutations);
   },
 
   apply(patterns)
   {
     this.patterns = [];
     for (let pattern of patterns)
     {