From 69084521f7279841d8f011841564ded6d658d33c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Emilio=20Cobos=20=C3=81lvarez?= <emilio@crisal.io>
Date: Fri, 10 May 2024 08:08:42 +0000
Subject: [PATCH] Bug 1895928 - PresShell::ScheduleViewManagerFlush shouldn't
 set the layout flush bit. r=smaug

A version of the patch in bug 1895870 caused some WPT tests to time out
because document.fonts.ready never resolves.

This is because I made PresShell::HasPendingReflow look at
mNeedLayoutFlush, and nsIFrame::SchedulePaint() calls
PresShell::ScheduleViewManagerFlush() which sets that bit.

So we end up with mNeedLayoutFlush, but without a flush scheduled, and
the ready promise doesn't resolve until something else schedules a
flush. I fixed the original patch to preserve behavior, but requesting a
repaint shouldn't require a layout flush.

This call was added in bug 598482 part 16:

  https://hg.mozilla.org/mozilla-central/rev/71d77495b606fc145bdceabcda29181978bd9405

We only need the layout flush if there are view geometry updates, so
shift the call up to the view manager.

Differential Revision: https://phabricator.services.mozilla.com/D209938
---
 layout/base/PresShell.cpp | 4 +---
 view/nsView.cpp           | 3 +--
 view/nsViewManager.cpp    | 1 +
 3 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/layout/base/PresShell.cpp b/layout/base/PresShell.cpp
index a96335a192da..cd41da37304f 100644
--- a/layout/base/PresShell.cpp
+++ b/layout/base/PresShell.cpp
@@ -3931,11 +3931,9 @@ void PresShell::ScheduleViewManagerFlush() {
     return;
   }
 
-  nsPresContext* presContext = GetPresContext();
-  if (presContext) {
+  if (nsPresContext* presContext = GetPresContext()) {
     presContext->RefreshDriver()->ScheduleViewManagerFlush();
   }
-  SetNeedLayoutFlush();
 }
 
 void PresShell::DispatchSynthMouseMove(WidgetGUIEvent* aEvent) {
diff --git a/view/nsView.cpp b/view/nsView.cpp
index 7a9addc8e4c4..41988da30cc8 100644
--- a/view/nsView.cpp
+++ b/view/nsView.cpp
@@ -1081,8 +1081,7 @@ void nsView::DidCompositeWindow(mozilla::layers::TransactionId aTransactionId,
 }
 
 void nsView::RequestRepaint() {
-  PresShell* presShell = mViewManager->GetPresShell();
-  if (presShell) {
+  if (PresShell* presShell = mViewManager->GetPresShell()) {
     presShell->ScheduleViewManagerFlush();
   }
 }
diff --git a/view/nsViewManager.cpp b/view/nsViewManager.cpp
index b9931f0c2a02..dd2f6c77cfa9 100644
--- a/view/nsViewManager.cpp
+++ b/view/nsViewManager.cpp
@@ -455,6 +455,7 @@ void nsViewManager::PostPendingUpdate() {
   nsViewManager* rootVM = RootViewManager();
   rootVM->mHasPendingWidgetGeometryChanges = true;
   if (rootVM->mPresShell) {
+    rootVM->mPresShell->SetNeedLayoutFlush();
     rootVM->mPresShell->ScheduleViewManagerFlush();
   }
 }