Bug 774914/785145 - Convert divs with only a <p> element child into plain <p> elements (r=mfinkle)

mobile/android/chrome/content/Readability.js

@@ -458,18 +458,29 @@ Readability.prototype = {
 
         // Turn all divs that don't have children block level elements into p's
         if (node.tagName === "DIV") {
-          if (node.innerHTML.search(this.REGEXPS.divToPElements) === -1) {
-            let newNode = doc.createElement('p');
-            newNode.innerHTML = node.innerHTML;
+          // Sites like http://mobile.slate.com encloses each paragraph with a DIV
+          // element. DIVs with only a P element inside and no text content can be
+          // safely converted into plain P elements to avoid confusing the scoring
+          // algorithm with DIVs with are, in practice, paragraphs.
+          let pIndex = this._getSinglePIndexInsideDiv(node);
+
+          if (node.innerHTML.search(this.REGEXPS.divToPElements) === -1 || pIndex >= 0) {
+            let newNode;
+            if (pIndex >= 0) {
+              newNode = node.childNodes[pIndex];
+            } else {
+              newNode = doc.createElement('p');
+              newNode.innerHTML = node.innerHTML;
+
+              // Manually update allElements since it is not a live NodeList
+              newNode._index = nodeIndex;
+              allElements[nodeIndex] = newNode;
+
+              nodesToScore[nodesToScore.length] = newNode;
+            }
+
             node.parentNode.replaceChild(newNode, node);
-
-            // Manually update allElements since it is not a live NodeList
-            newNode._index = nodeIndex;
-            allElements[nodeIndex] = newNode;
             purgeNode(node);
-
-            nodeIndex -= 1;
-            nodesToScore[nodesToScore.length] = node;
           } else {
             // EXPERIMENTAL
             for (let i = 0, il = node.childNodes.length; i < il; i += 1) {
@@ -709,6 +720,36 @@ Readability.prototype = {
     }
   },
 
+  /**
+   * Get child index of the only P element inside a DIV with no
+   * text content. Returns -1 if the DIV node contains non-empty
+   * text nodes or if it contains other element nodes.
+   *
+   * @param Element
+  **/
+  _getSinglePIndexInsideDiv: function(e) {
+    let childNodes = e.childNodes;
+    let pIndex = -1;
+
+    for (let i = childNodes.length; --i >= 0;) {
+      let node = childNodes[i];
+
+      if (node.nodeType === Node.ELEMENT_NODE) {
+        if (node.tagName !== "P")
+          return -1;
+
+        if (pIndex >= 0)
+          return -1;
+
+        pIndex = i;
+      } else if (node.nodeType == Node.TEXT_NODE && this._getInnerText(node, false)) {
+        return -1;
+      }
+    }
+
+    return pIndex;
+  },
+
   /**
    * Get the inner text of a node - cross browser compatibly.
    * This also strips out any excess whitespace to be found.