Bug 1569512 - Make `PresShell` ignore synthesized `mousemove` events coming from another process if the child process stores mouse location of synthesized mouse events for tests r=smaug

The reason of intermittent failure of `test_bug656379-2.html` is, synthesized
`mousemove` event coming from the parent process causes `mouseout` and
`mouseleave` events of the last synthesized `mousemove` in the test.  The
reason is, synthesized `mousemove` for tests makes `PresShell` in the content
process record the cursor location, but won't make it `PresShell` in the
parent process do it.  Therefore, parent process may synthesize `mousemove`
event for the system cursor position which does not match with the synthesized
mouse location in the content process.  Therefore, `:hover` state may be
updated unexpectedly.

This patch makes `WidgetEvent::mFlags` have a flag to indicate whether it
came from another process.  Then, makes `PresShell::HandleEvent()` ignore
synthesized `mousemove` events coming from another process only when the
recorded mouse location was set by a mouse event synthesized for tests.

Differential Revision: https://phabricator.services.mozilla.com/D65282

--HG--
extra : moz-landing-system : lando

dom/events/test/test_bug656379-2.html

@@ -28,9 +28,38 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=656379
 <pre id="test">
 <script type="application/javascript">
 
+function log(aEvent) {
+  function getPath() {
+    if (!aEvent.target) {
+      return "(null)";
+    }
+    function getNodeName(aNode) {
+      if (aNode.id) {
+        return `${aNode.nodeName}#${aNode.id}`;
+      }
+      return aNode.nodeName;
+    }
+    let path = getNodeName(aEvent.target);
+    for (let parent = aEvent.target.parentElement;
+         parent && document.body != parent;
+         parent = parent.parentElement) {
+      path = `${getNodeName(parent)} > ${path}`;
+    }
+    return path;
+  }
+  info(`${aEvent.type} on ${getPath()}`);
+}
+
+window.addEventListener("mousemove", log, {capture: true});
+window.addEventListener("mouseenter", log, {capture: true});
+window.addEventListener("mouseleave", log, {capture: true});
+window.addEventListener("mouseover", log, {capture: true});
+window.addEventListener("mouseout", log, {capture: true});
+
 /** Test for Bug 656379 **/
 SimpleTest.waitForExplicitFinish();
 function* tests() {
+  info("Synthesizing mousemove on label1...");
   synthesizeMouseAtCenter($("label1"), { type: "mousemove" });
   yield undefined;
   is($("button1").matches(":hover"), true,
@@ -41,6 +70,7 @@ function* tests() {
      "Button 2 should not be hovered after mousemove over label1");
   is($("label2").matches(":hover"), false,
      "Label 2 should not be hovered after mousemove over label1");
+  info("Synthesizing mousemove on button2...");
   synthesizeMouseAtCenter($("button2"), { type: "mousemove" });
   yield undefined;
   is($("button1").matches(":hover"), false,
@@ -51,6 +81,7 @@ function* tests() {
      "Button 2 should be hovered after mousemove over button2");
   is($("label2").matches(":hover"), false,
      "Label 2 should not be hovered after mousemove over label2");
+  info("Synthesizing mousemove on label2...");
   synthesizeMouseAtCenter($("label2"), { type: "mousemove" });
   yield undefined;
   is($("button1").matches(":hover"), false,

layout/base/PresShell.cpp

@@ -842,7 +842,8 @@ PresShell::PresShell(Document* aDocument)
       mForceUseLegacyKeyCodeAndCharCodeValues(false),
       mInitializedWithKeyPressEventDispatchingBlacklist(false),
       mForceUseLegacyNonPrimaryDispatch(false),
-      mInitializedWithClickEventDispatchingBlacklist(false) {
+      mInitializedWithClickEventDispatchingBlacklist(false),
+      mMouseLocationWasSetBySynthesizedMouseEventForTests(false) {
   MOZ_LOG(gLog, LogLevel::Debug, ("PresShell::PresShell this=%p", this));
   MOZ_ASSERT(aDocument);
 
@@ -5072,8 +5073,7 @@ nscolor PresShell::GetDefaultBackgroundColorToDraw() {
   // content JS.
   Document* doc = GetDocument();
   BrowsingContext* bc = doc->GetBrowsingContext();
-  if (bc && bc->IsTop() && !bc->HasOpener() &&
-      doc->GetDocumentURI() &&
+  if (bc && bc->IsTop() && !bc->HasOpener() && doc->GetDocumentURI() &&
       NS_IsAboutBlank(doc->GetDocumentURI()) &&
       doc->PrefersColorScheme() == StylePrefersColorScheme::Dark) {
     // Use --in-content-page-background for prefers-color-scheme: dark.
@@ -6289,6 +6289,18 @@ void PresShell::DisableNonTestMouseEvents(bool aDisable) {
   sDisableNonTestMouseEvents = aDisable;
 }
 
+bool PresShell::MouseLocationWasSetBySynthesizedMouseEventForTests() const {
+  if (!mPresContext) {
+    return false;
+  }
+  if (mPresContext->IsRoot()) {
+    return mMouseLocationWasSetBySynthesizedMouseEventForTests;
+  }
+  PresShell* rootPresShell = GetRootPresShell();
+  return rootPresShell &&
+         rootPresShell->mMouseLocationWasSetBySynthesizedMouseEventForTests;
+}
+
 void PresShell::RecordMouseLocation(WidgetGUIEvent* aEvent) {
   if (!mPresContext) return;
 
@@ -6315,6 +6327,8 @@ void PresShell::RecordMouseLocation(WidgetGUIEvent* aEvent) {
           nsLayoutUtils::GetEventCoordinatesRelativeTo(aEvent, rootFrame);
       mMouseEventTargetGuid = InputAPZContext::GetTargetLayerGuid();
     }
+    mMouseLocationWasSetBySynthesizedMouseEventForTests =
+        aEvent->mFlags.mIsSynthesizedForTests;
 #ifdef DEBUG_MOUSE_LOCATION
     if (aEvent->mMessage == eMouseEnterIntoWidget) {
       printf("[ps=%p]got mouse enter for %p\n", this, aEvent->mWidget);
@@ -6333,6 +6347,8 @@ void PresShell::RecordMouseLocation(WidgetGUIEvent* aEvent) {
     // the mouse exit when the mouse moves from one of our widgets into another.
     mMouseLocation = nsPoint(NS_UNCONSTRAINEDSIZE, NS_UNCONSTRAINEDSIZE);
     mMouseEventTargetGuid = InputAPZContext::GetTargetLayerGuid();
+    mMouseLocationWasSetBySynthesizedMouseEventForTests =
+        aEvent->mFlags.mIsSynthesizedForTests;
 #ifdef DEBUG_MOUSE_LOCATION
     printf("[ps=%p]got mouse exit for %p\n", this, aEvent->mWidget);
     printf("[ps=%p]clearing mouse location\n", this);
@@ -6439,6 +6455,17 @@ nsresult PresShell::HandleEvent(nsIFrame* aFrameForPresShell,
                                 bool aDontRetargetEvents,
                                 nsEventStatus* aEventStatus) {
   MOZ_ASSERT(aGUIEvent);
+  // If it's synthesized in the parent process and our mouse location was set
+  // by a mouse event which was synthesized for tests because the test does not
+  // want to change `:hover` state with the synthesized mouse event for native
+  // mouse cursor position.
+  if (aGUIEvent->mMessage == eMouseMove &&
+      aGUIEvent->CameFromAnotherProcess() && XRE_IsContentProcess() &&
+      !aGUIEvent->mFlags.mIsSynthesizedForTests &&
+      MouseLocationWasSetBySynthesizedMouseEventForTests() &&
+      aGUIEvent->AsMouseEvent()->mReason == WidgetMouseEvent::eSynthesized) {
+    return NS_OK;
+  }
   EventHandler eventHandler(*this);
   return eventHandler.HandleEvent(aFrameForPresShell, aGUIEvent,
                                   aDontRetargetEvents, aEventStatus);
@@ -10633,7 +10660,7 @@ nsresult PresShell::UpdateImageLockingState() {
   return rv;
 }
 
-PresShell* PresShell::GetRootPresShell() {
+PresShell* PresShell::GetRootPresShell() const {
   if (mPresContext) {
     nsPresContext* rootPresContext = mPresContext->GetRootPresContext();
     if (rootPresContext) {

layout/base/PresShell.h

@@ -1939,6 +1939,7 @@ class PresShell final : public nsStubDocumentObserver,
   // Check if aEvent is a mouse event and record the mouse location for later
   // synth mouse moves.
   void RecordMouseLocation(WidgetGUIEvent* aEvent);
+  inline bool MouseLocationWasSetBySynthesizedMouseEventForTests() const;
   class nsSynthMouseMoveEvent final : public nsARefreshObserver {
    public:
     nsSynthMouseMoveEvent(PresShell* aPresShell, bool aFromScroll)
@@ -2758,7 +2759,7 @@ class PresShell final : public nsStubDocumentObserver,
     static StaticRefPtr<dom::Element> sLastKeyDownEventTargetElement;
   };
 
-  PresShell* GetRootPresShell();
+  PresShell* GetRootPresShell() const;
 
   nscolor GetDefaultBackgroundColorToDraw();
 
@@ -3160,6 +3161,10 @@ class PresShell final : public nsStubDocumentObserver,
   // Whether mForceUseLegacyNonPrimaryDispatch is initialised.
   bool mInitializedWithClickEventDispatchingBlacklist : 1;
 
+  // Set to true if mMouseLocation is set by a mouse event which is synthesized
+  // for tests.
+  bool mMouseLocationWasSetBySynthesizedMouseEventForTests : 1;
+
   struct CapturingContentInfo final {
     CapturingContentInfo()
         : mAllowed(false),

layout/base/nsPresContext.cpp

@@ -793,7 +793,7 @@ void nsPresContext::UpdateCharSet(NotNull<const Encoding*> aCharSet) {
   }
 }
 
-nsPresContext* nsPresContext::GetParentPresContext() {
+nsPresContext* nsPresContext::GetParentPresContext() const {
   mozilla::PresShell* presShell = GetPresShell();
   if (presShell) {
     nsViewManager* viewManager = presShell->GetViewManager();
@@ -848,8 +848,8 @@ nsIWidget* nsPresContext::GetRootWidget() const {
 
 // We may want to replace this with something faster, maybe caching the root
 // prescontext
-nsRootPresContext* nsPresContext::GetRootPresContext() {
-  nsPresContext* pc = this;
+nsRootPresContext* nsPresContext::GetRootPresContext() const {
+  nsPresContext* pc = const_cast<nsPresContext*>(this);
   for (;;) {
     nsPresContext* parent = pc->GetParentPresContext();
     if (!parent) break;

layout/base/nsPresContext.h

@@ -181,7 +181,7 @@ class nsPresContext : public nsISupports,
    * Returns the parent prescontext for this one. Returns null if this is a
    * root.
    */
-  nsPresContext* GetParentPresContext();
+  nsPresContext* GetParentPresContext() const;
 
   /**
    * Returns the prescontext of the toplevel content document that contains
@@ -218,7 +218,7 @@ class nsPresContext : public nsISupports,
    * hierarchy that contains this presentation context, or nullptr if it can't
    * be found (e.g. it's detached).
    */
-  nsRootPresContext* GetRootPresContext();
+  nsRootPresContext* GetRootPresContext() const;
 
   virtual bool IsRoot() { return false; }
 

widget/BasicEvents.h

@@ -176,6 +176,8 @@ struct BaseEventFlags {
   // remote process (but it's not handled yet if it's not a duplicated event
   // instance).
   bool mPostedToRemoteProcess : 1;
+  // If mCameFromAnotherProcess is true, the event came from another process.
+  bool mCameFromAnotherProcess : 1;
 
   // At lease one of the event in the event path had non privileged click
   // listener.
@@ -337,6 +339,16 @@ struct BaseEventFlags {
   inline bool HasBeenPostedToRemoteProcess() const {
     return mPostedToRemoteProcess;
   }
+  /**
+   * Return true if the event came from another process.
+   */
+  inline bool CameFromAnotherProcess() const { return mCameFromAnotherProcess; }
+  /**
+   * Mark the event as coming from another process.
+   */
+  inline void MarkAsComingFromAnotherProcess() {
+    mCameFromAnotherProcess = true;
+  }
   /**
    * Mark the event is reserved by chrome.  I.e., shouldn't be dispatched to
    * content because it shouldn't be cancelable.
@@ -700,6 +712,18 @@ class WidgetEvent : public WidgetEventTime {
   inline bool HasBeenPostedToRemoteProcess() const {
     return mFlags.HasBeenPostedToRemoteProcess();
   }
+  /**
+   * Return true if the event came from another process.
+   */
+  inline bool CameFromAnotherProcess() const {
+    return mFlags.CameFromAnotherProcess();
+  }
+  /**
+   * Mark the event as coming from another process.
+   */
+  inline void MarkAsComingFromAnotherProcess() {
+    mFlags.MarkAsComingFromAnotherProcess();
+  }
   /**
    * Mark the event is reserved by chrome.  I.e., shouldn't be dispatched to
    * content because it shouldn't be cancelable.

widget/nsGUIEventIPC.h

@@ -74,6 +74,8 @@ struct ParamTraits<mozilla::WidgetEvent> {
       // Reset cross process dispatching state here because the event has not
       // been dispatched to different process from current process.
       aResult->ResetCrossProcessDispatchingState();
+      // Mark the event comes from another process.
+      aResult->MarkAsComingFromAnotherProcess();
     }
     return ret;
   }