Bug 1429656 - Implement ShadowRoot.activeElement

Tag #1375

dom/base/DocumentOrShadowRoot.cpp

@@ -6,6 +6,8 @@
 
 #include "DocumentOrShadowRoot.h"
 #include "mozilla/dom/StyleSheetList.h"
+#include "nsDocument.h"
+#include "nsFocusManager.h"
 #include "ShadowRoot.h"
 #include "XULDocument.h"
 
@@ -100,5 +102,48 @@ DocumentOrShadowRoot::GetElementsByClassName(const nsAString& aClasses)
   return nsContentUtils::GetElementsByClassName(&AsNode(), aClasses);
 }
 
+nsIContent*
+DocumentOrShadowRoot::Retarget(nsIContent* aContent) const
+{
+  for (nsIContent* cur = aContent;
+       cur;
+       cur = cur->GetContainingShadowHost()) {
+    if (cur->SubtreeRoot() == &AsNode()) {
+      return cur;
+    }
+  }
+  return nullptr;
+}
+
+Element*
+DocumentOrShadowRoot::GetRetargetedFocusedElement()
+{
+  if (nsCOMPtr<nsPIDOMWindowOuter> window = AsNode().OwnerDoc()->GetWindow()) {
+    nsCOMPtr<nsPIDOMWindowOuter> focusedWindow;
+    nsIContent* focusedContent =
+      nsFocusManager::GetFocusedDescendant(window,
+                                           false,
+                                           getter_AddRefs(focusedWindow));
+    // be safe and make sure the element is from this document
+    if (focusedContent && focusedContent->OwnerDoc() == AsNode().OwnerDoc()) {
+      if (focusedContent->ChromeOnlyAccess()) {
+        focusedContent = focusedContent->FindFirstNonChromeOnlyAccessContent();
+      }
+
+      if (focusedContent) {
+        if (!nsDocument::IsWebComponentsEnabled(focusedContent)) {
+          return focusedContent->AsElement();
+        }
+
+        if (nsIContent* retarget = Retarget(focusedContent)) {
+          return retarget->AsElement();
+        }
+      }
+    }
+  }
+
+  return nullptr;
+}
+
 }
 }