From 523a115dccdee6e4f7a7e318c3fb2cdcb5a2cbb2 Mon Sep 17 00:00:00 2001
From: Hiroyuki Ikezoe <hikezoe.birchill@mozilla.com>
Date: Tue, 6 Jul 2021 07:38:06 +0000
Subject: [PATCH] Bug 1717726 - Add a debug-only assertion disallowing remote
 <browser>s or <iframe>s inside nsDeckFrame. r=tnikkel

The background to have this assertion is that nsDeckFrame::HideBox calls
PresShell::ClearMouseCapture and ClearMouseCapture checks whether the
being-hidden panel has a content capturing mouse events or not but the check
doesn't work if the content is in a remote process. In our current
mozilla-central tree, there is no such nsDeckFrame other than our browser's
tab. In the case of our browser's tab when switching tabs, i.e. hiding an
active tab, clearing the mouse capturing state has (should have) worked since
E10S (Note for Fission cases it has worked since bug 1680405). So, because
nsDeckFrame will be obsoleted sooner or later, we disallow the situation
for other cases instead of adding special handling for the other case.

Differential Revision: https://phabricator.services.mozilla.com/D119067
---
 layout/xul/nsDeckFrame.cpp | 26 ++++++++++++++++++++++++++
 layout/xul/nsDeckFrame.h   |  5 +++++
 2 files changed, 31 insertions(+)

diff --git a/layout/xul/nsDeckFrame.cpp b/layout/xul/nsDeckFrame.cpp
index e9c7484a956d..ebc6183f7c52 100644
--- a/layout/xul/nsDeckFrame.cpp
+++ b/layout/xul/nsDeckFrame.cpp
@@ -217,6 +217,14 @@ nsDeckFrame::DoXULLayout(nsBoxLayoutState& aState) {
   // do a normal layout
   nsresult rv = nsBoxFrame::DoXULLayout(aState);
 
+  // <deck> and <tabpanels> other than our browser's tab shouldn't have any
+  // <browser> or <iframe> to avoid running into troubles with Fission.
+  MOZ_ASSERT((mContent->IsXULElement(nsGkAtoms::tabpanels) &&
+              mContent->AsElement()->AttrValueIs(
+                  kNameSpaceID_None, nsGkAtoms::id, u"tabbrowser-tabpanels"_ns,
+                  eCaseMatters)) ||
+             !HasPossiblyRemoteContents());
+
   // run though each child. Hide all but the selected one
   nsIFrame* box = nsIFrame::GetChildXULBox(this);
 
@@ -236,3 +244,21 @@ nsDeckFrame::DoXULLayout(nsBoxLayoutState& aState) {
 
   return rv;
 }
+
+bool nsDeckFrame::HasPossiblyRemoteContents() const {
+  auto hasRemoteOrMayChangeRemoteNessAttribute =
+      [](dom::Element& aElement) -> bool {
+    return (aElement.AttrValueIs(kNameSpaceID_None, nsGkAtoms::remote,
+                                 nsGkAtoms::_true, eCaseMatters) ||
+            aElement.HasAttribute(u"maychangeremoteness"_ns));
+  };
+
+  for (nsIContent* node = mContent; node; node = node->GetNextNode(mContent)) {
+    if ((node->IsXULElement(nsGkAtoms::browser) ||
+         node->IsHTMLElement(nsGkAtoms::iframe)) &&
+        hasRemoteOrMayChangeRemoteNessAttribute(*(node->AsElement()))) {
+      return true;
+    }
+  }
+  return false;
+}
diff --git a/layout/xul/nsDeckFrame.h b/layout/xul/nsDeckFrame.h
index 8eba9f62389b..34ce402a8715 100644
--- a/layout/xul/nsDeckFrame.h
+++ b/layout/xul/nsDeckFrame.h
@@ -56,6 +56,11 @@ class nsDeckFrame final : public nsBoxFrame {
 
   nsIFrame* GetSelectedBox();
 
+  // Returns whether this frame has any <browser> or <iframe> elements.
+  // Note that this function traverses down all descendants so this function
+  // should be used only in debug builds.
+  bool HasPossiblyRemoteContents() const;
+
  protected:
   void IndexChanged();
   int32_t GetSelectedIndex();