From f44db6a28b77a2f17a7d2e0d929fe194f1b88b52 Mon Sep 17 00:00:00 2001
From: Brian Smith <brian@dbsoft.org>
Date: Mon, 15 Jan 2024 05:54:48 -0600
Subject: [PATCH] Issue #2456 - Intersection Observer - Accept a Document as an
 explicit root. https://bugzilla.mozilla.org/show_bug.cgi?id=1617154

---
 dom/base/DOMIntersectionObserver.cpp   | 75 ++++++++++++++++----------
 dom/base/DOMIntersectionObserver.h     |  4 +-
 dom/webidl/IntersectionObserver.webidl |  4 +-
 3 files changed, 50 insertions(+), 33 deletions(-)

diff --git a/dom/base/DOMIntersectionObserver.cpp b/dom/base/DOMIntersectionObserver.cpp
index 7ee1a4c938..aaa1609b33 100644
--- a/dom/base/DOMIntersectionObserver.cpp
+++ b/dom/base/DOMIntersectionObserver.cpp
@@ -80,7 +80,14 @@ DOMIntersectionObserver::Constructor(const mozilla::dom::GlobalObject& aGlobal,
   RefPtr<DOMIntersectionObserver> observer =
     new DOMIntersectionObserver(window.forget(), aCb);
 
-  observer->mRoot = aOptions.mRoot;
+  if (!aOptions.mRoot.IsNull()) {
+    if (aOptions.mRoot.Value().IsElement()) {
+      observer->mRoot = aOptions.mRoot.Value().GetAsElement();
+    } else {
+      MOZ_ASSERT(aOptions.mRoot.Value().IsDocument());
+      observer->mRoot = aOptions.mRoot.Value().GetAsDocument();
+    }
+  }
 
   if (!observer->SetRootMargin(aOptions.mRootMargin)) {
     aRv.ThrowDOMException(NS_ERROR_DOM_SYNTAX_ERR,
@@ -258,6 +265,30 @@ EdgeInclusiveIntersection(const nsRect& aRect, const nsRect& aOtherRect)
   return Some(nsRect(left, top, right - left, bottom - top));
 }
 
+// NOTE: This returns nullptr if |aDocument| is in a cross process.
+static nsIDocument* GetTopLevelDocument(const nsIDocument& aDocument) {
+  nsCOMPtr<nsIPresShell> presShell = aDocument.GetShell();
+
+  if (presShell) {
+    nsIFrame* rootFrame = presShell->GetRootScrollFrame();
+    if (rootFrame) {
+      nsPresContext* presContext = rootFrame->PresContext();
+      while (!presContext->IsRootContentDocument()) {
+        // Walk up the tree
+        presContext = presContext->GetParentPresContext();
+        if (!presContext) {
+          break;
+        }
+      }
+      if(presContext && presContext->IsRootContentDocument()) {
+          return presContext->Document();
+      }
+    }
+  }
+
+  return nullptr;
+}
+
 enum class BrowsingContextInfo {
   SimilarOriginBrowsingContext,
   DifferentOriginBrowsingContext,
@@ -267,14 +298,12 @@ enum class BrowsingContextInfo {
 void
 DOMIntersectionObserver::Update(nsIDocument* aDocument, DOMHighResTimeStamp time)
 {
-  Element* root = nullptr;
+  nsINode* root = mRoot;
   nsIFrame* rootFrame = nullptr;
   nsRect rootRect;
 
-  if (mRoot) {
-    root = mRoot;
-    rootFrame = root->GetPrimaryFrame();
-    if (rootFrame) {
+  if (mRoot && mRoot->IsElement()) {
+    if ((rootFrame = mRoot->AsElement()->GetPrimaryFrame())) {
       nsRect rootRectRelativeToRootFrame;
       if (rootFrame->GetType() == nsGkAtoms::scrollFrame) {
         // rootRectRelativeToRootFrame should be the content rect of rootFrame, not including the scrollbars.
@@ -292,30 +321,18 @@ DOMIntersectionObserver::Update(nsIDocument* aDocument, DOMHighResTimeStamp time
                                                     containingBlock);
     }
   } else {
-    nsCOMPtr<nsIPresShell> presShell = aDocument->GetShell();
-    if (presShell) {
-      rootFrame = presShell->GetRootScrollFrame();
-      if (rootFrame) {
-        nsPresContext* presContext = rootFrame->PresContext();
-        while (!presContext->IsRootContentDocument()) {
-          // Walk up the tree
-          presContext = presContext->GetParentPresContext();
-          if (!presContext) {
-            break;
+    MOZ_ASSERT(!mRoot || mRoot->IsInUncomposedDoc());
+    nsIDocument* rootDocument =
+        mRoot ? mRoot->GetUncomposedDoc() : GetTopLevelDocument(*aDocument);
+    if (rootDocument) {
+      if (nsIPresShell* presShell = rootDocument->GetShell()) {
+        rootFrame = presShell->GetRootScrollFrame();
+        if (rootFrame) {
+          root = rootFrame->GetContent()->AsElement();
+          nsIScrollableFrame* scrollFrame = do_QueryFrame(rootFrame);
+          if (scrollFrame) {
+            rootRect = scrollFrame->GetScrollPortRect();
           }
-          nsIFrame* rootScrollFrame = presContext->PresShell()->GetRootScrollFrame();
-          if (rootScrollFrame) {
-            rootFrame = rootScrollFrame;
-          } else {
-            break;
-          }
-        }
-        root = rootFrame->GetContent()->AsElement();
-        nsIScrollableFrame* scrollFrame = do_QueryFrame(rootFrame);
-        // If we end up with a null root frame for some reason, we'll proceed
-        // with an empty root intersection rect.
-        if (scrollFrame) {
-          rootRect = scrollFrame->GetScrollPortRect();
         }
       }
     }
diff --git a/dom/base/DOMIntersectionObserver.h b/dom/base/DOMIntersectionObserver.h
index a72454007c..f309544978 100644
--- a/dom/base/DOMIntersectionObserver.h
+++ b/dom/base/DOMIntersectionObserver.h
@@ -145,7 +145,7 @@ public:
     return mOwner;
   }
 
-  Element* GetRoot() const {
+  nsINode* GetRoot() const {
     return mRoot;
   }
 
@@ -178,7 +178,7 @@ protected:
   nsCOMPtr<nsPIDOMWindowInner>                    mOwner;
   RefPtr<nsIDocument>                             mDocument;
   RefPtr<mozilla::dom::IntersectionCallback>      mCallback;
-  RefPtr<Element>                                 mRoot;
+  RefPtr<nsINode>                                 mRoot;
   nsCSSRect                                       mRootMargin;
   nsTArray<double>                                mThresholds;
   
diff --git a/dom/webidl/IntersectionObserver.webidl b/dom/webidl/IntersectionObserver.webidl
index 83200d950d..b5c904c139 100644
--- a/dom/webidl/IntersectionObserver.webidl
+++ b/dom/webidl/IntersectionObserver.webidl
@@ -30,7 +30,7 @@ interface IntersectionObserverEntry {
  Pref="dom.intersectionObserver.enabled"]
 interface IntersectionObserver {
   [Constant]
-  readonly attribute Element? root;
+  readonly attribute Node? root;
   [Constant]
   readonly attribute DOMString rootMargin;
   [Constant,Cached]
@@ -56,7 +56,7 @@ dictionary IntersectionObserverEntryInit {
 };
 
 dictionary IntersectionObserverInit {
-  Element?  root = null;
+  (Element or Document)?  root = null;
   DOMString rootMargin = "0px";
   (double or sequence<double>) threshold = 0;
 };