Pass nextTextSibling to ::before layout rebuild.

third_party/WebKit/Source/core/dom/Element.cpp

Index: third_party/WebKit/Source/core/dom/Element.cpp
diff --git a/third_party/WebKit/Source/core/dom/Element.cpp b/third_party/WebKit/Source/core/dom/Element.cpp
index a403176069c3b352a8a11cbf448a268666686e72..75ec9446f6fd349cf5b75d86b34052a93ddd7fdd 100644
--- a/third_party/WebKit/Source/core/dom/Element.cpp
+++ b/third_party/WebKit/Source/core/dom/Element.cpp
@@ -2037,12 +2037,13 @@ void Element::rebuildLayoutTree(Text* nextTextSibling) {
     DCHECK(!needsReattachLayoutTree());
     SelectorFilterParentScope filterScope(*this);
     StyleSharingDepthScope sharingScope(*this);
-    reattachPseudoElementLayoutTree(PseudoIdBefore);
-    rebuildShadowRootLayoutTree();
-    rebuildChildrenLayoutTrees();
-    reattachPseudoElementLayoutTree(PseudoIdAfter);
-    reattachPseudoElementLayoutTree(PseudoIdBackdrop);
-    reattachPseudoElementLayoutTree(PseudoIdFirstLetter);
+    Text* nextTextSibling = nullptr;
+    rebuildPseudoElementLayoutTree(PseudoIdAfter);
+    rebuildShadowRootLayoutTree(nextTextSibling);
+    rebuildChildrenLayoutTrees(nextTextSibling);
+    rebuildPseudoElementLayoutTree(PseudoIdBefore, nextTextSibling);

[esprehn, 2017/03/28 20:56:51]

Why do we only need this for ::before?

[rune, 2017/03/29 10:39:47]

We always evaluate the need for a whitespace layout object based on the
preceding sibling layout object or its parent layout object. Without support for
display:contents, you cannot have ::after as the preceding layout object sibling
of a text layout object, but you can have a ::before as the preceding layout
object sibling:

<span><span::before>A</span::before> <span::after>B</span></span>

+    rebuildPseudoElementLayoutTree(PseudoIdBackdrop);
+    rebuildPseudoElementLayoutTree(PseudoIdFirstLetter);
   }
   DCHECK(!needsStyleRecalc());
   DCHECK(!childNeedsStyleRecalc());
@@ -2050,19 +2051,31 @@ void Element::rebuildLayoutTree(Text* nextTextSibling) {
   DCHECK(!childNeedsReattachLayoutTree());
 }
 
-void Element::rebuildShadowRootLayoutTree() {
+void Element::rebuildShadowRootLayoutTree(Text*& nextTextSibling) {
   for (ShadowRoot* root = youngestShadowRoot(); root;
        root = root->olderShadowRoot()) {
+    // TODO(rune@opera.com): nextTextSibling is not set correctly when we have
+    // slotted nodes (crbug.com/648931). Also, it may be incorrect when we have
+    // multiple shadow roots (for V0 shadow hosts).
+    //
+    // When we call this method and neither this, nor our child nodes are marked
+    // for re-attachment, it means one or more pseudo elements needs re-
+    // attachment. In that case, find the first text node sibling not preceeded
+    // by any in-flow children as the nextTextSibling to allow correct
+    // whitespace re-attachment if the ::before element display changes.
     if (root->needsReattachLayoutTree() || root->childNeedsReattachLayoutTree())
-      root->rebuildLayoutTree();
+      root->rebuildLayoutTree(nextTextSibling);
+    else
+      nextTextSibling = root->findNextTextSibling();

[esprehn, 2017/03/28 20:56:51]

ShadowRoot can't have siblings so this doesn't make sense.

[rune, 2017/03/29 10:39:47]

Rewrote this for PS2.

   }
 }
 
-void Element::reattachPseudoElementLayoutTree(PseudoId pseudoId) {
+void Element::rebuildPseudoElementLayoutTree(PseudoId pseudoId,
+                                             Text* nextTextSibling) {
   if (PseudoElement* element = pseudoElement(pseudoId)) {
     if (element->needsReattachLayoutTree() ||
         element->childNeedsReattachLayoutTree())
-      element->rebuildLayoutTree();
+      element->rebuildLayoutTree(nextTextSibling);
   } else {
     createPseudoElementIfNeeded(pseudoId);
   }