Cherry-pick 58a2cf8. rdar://problem/113605121

    Cherry-pick e41f567. rdar://problem/110872395

        [UI-side compositing] REGRESSION: empty Mail compose window always shows a scrollbar
        https://bugs.webkit.org/show_bug.cgi?id=259323
        rdar://110872395

        Reviewed by Simon Fraser.

        To properly set NSScrollerImps as enabled in the UI-process, send accross the web
        process state from the Scrollbar class. It is also necessary to set the state in
        setScrollingNodeScrollableAreaGeometry because the first time setting this state
        on the Scrollbar class can happen before the corresponding scrollable area has been
        added to the scrolling tree.

        * Source/WebCore/page/scrolling/AsyncScrollingCoordinator.cpp:
        (WebCore::AsyncScrollingCoordinator::setScrollbarEnabled):
        (WebCore::AsyncScrollingCoordinator::setScrollingNodeScrollableAreaGeometry):
        * Source/WebCore/page/scrolling/AsyncScrollingCoordinator.h:
        * Source/WebCore/page/scrolling/ScrollingCoordinator.h:
        (WebCore::ScrollingCoordinator::setScrollbarEnabled):
        * Source/WebCore/page/scrolling/ScrollingStateNode.h:
        * Source/WebCore/page/scrolling/ScrollingStateScrollingNode.cpp:
        (WebCore::ScrollingStateScrollingNode::ScrollingStateScrollingNode):
        (WebCore::ScrollingStateScrollingNode::setScrollbarEnabledState):
        * Source/WebCore/page/scrolling/ScrollingStateScrollingNode.h:
        (WebCore::ScrollingStateScrollingNode::scrollbarEnabledState const):
        * Source/WebCore/page/scrolling/mac/ScrollerMac.h:
        (WebCore::ScrollerMac::setEnabled):
        * Source/WebCore/page/scrolling/mac/ScrollerMac.mm:
        (WebCore::ScrollerMac::updateValues):
        * Source/WebCore/page/scrolling/mac/ScrollingTreeScrollingNodeDelegateMac.mm:
        (WebCore::ScrollingTreeScrollingNodeDelegateMac::updateFromStateNode):
        * Source/WebCore/platform/Scrollbar.cpp:
        (WebCore::Scrollbar::setEnabled):
        * Source/WebCore/platform/ScrollbarsController.h:
        (WebCore::ScrollbarsController::setScrollbarEnabledSate):
        * Source/WebKit/Shared/RemoteLayerTree/RemoteScrollingCoordinatorTransaction.cpp:
        (ArgumentCoder<ScrollingStateScrollingNode>::encode):
        (ArgumentCoder<ScrollingStateScrollingNode>::decode):
        * Source/WebKit/Shared/WebCoreArgumentCoders.serialization.in:
        * Source/WebKit/WebProcess/WebPage/RemoteLayerTree/RemoteScrollbarsController.h:
        * Source/WebKit/WebProcess/WebPage/RemoteLayerTree/RemoteScrollbarsController.mm:
        (WebKit::RemoteScrollbarsController::setScrollbarEnabledSate):

        Canonical link: https://commits.webkit.org/266261@main

Identifier: 265870.263@safari-7616-branch

Source/WebCore/page/scrolling/AsyncScrollingCoordinator.cpp

@@ -423,6 +423,20 @@ void AsyncScrollingCoordinator::setMouseMovedInContentArea(ScrollableArea& scrol
     stateNode->setMouseMovedInContentArea(state);
 }
 
+void AsyncScrollingCoordinator::setScrollbarEnabled(Scrollbar& scrollbar)
+{
+    ASSERT(isMainThread());
+    ASSERT(m_page);
+    auto scrollingNodeID = scrollbar.scrollableArea().scrollingNodeID();
+    if (!scrollingNodeID)
+        return;
+
+    auto stateNode = dynamicDowncast<ScrollingStateScrollingNode>(m_scrollingStateTree->stateNodeForID(scrollingNodeID));
+    if (!stateNode)
+        return;
+    stateNode->setScrollbarEnabledState(scrollbar.orientation(), scrollbar.enabled());
+}
+
 void AsyncScrollingCoordinator::applyScrollingTreeLayerPositions()
 {
     m_scrollingTree->applyLayerPositions();
@@ -933,6 +947,10 @@ void AsyncScrollingCoordinator::setScrollingNodeScrollableAreaGeometry(Scrolling
     auto* verticalScrollbar = scrollableArea.verticalScrollbar();
     auto* horizontalScrollbar = scrollableArea.horizontalScrollbar();
     scrollingNode->setScrollerImpsFromScrollbars(verticalScrollbar, horizontalScrollbar);
+    if (horizontalScrollbar)
+        scrollingNode->setScrollbarEnabledState(ScrollbarOrientation::Horizontal, horizontalScrollbar->enabled());
+    if (verticalScrollbar)
+        scrollingNode->setScrollbarEnabledState(ScrollbarOrientation::Vertical, verticalScrollbar->enabled());
 
     scrollingNode->setScrollOrigin(scrollableArea.scrollOrigin());
     scrollingNode->setScrollPosition(scrollableArea.scrollPosition());

Source/WebCore/page/scrolling/AsyncScrollingCoordinator.h

@@ -172,6 +172,7 @@ class AsyncScrollingCoordinator : public ScrollingCoordinator {
     void wheelEventScrollDidEndForNode(ScrollingNodeID);
 
     WEBCORE_EXPORT void setMouseIsOverScrollbar(Scrollbar*, bool isOverScrollbar) override;
+    WEBCORE_EXPORT void setScrollbarEnabled(Scrollbar&) override;
 
     void hysterisisTimerFired(PAL::HysteresisState);
 

Source/WebCore/page/scrolling/ScrollingCoordinator.h

@@ -208,6 +208,7 @@ class ScrollingCoordinator : public ThreadSafeRefCountedAndCanMakeThreadSafeWeak
     WEBCORE_EXPORT virtual void setMouseIsOverContentArea(ScrollableArea&, bool) { }
     WEBCORE_EXPORT virtual void setMouseMovedInContentArea(ScrollableArea&) { }
     WEBCORE_EXPORT virtual void setMouseIsOverScrollbar(Scrollbar*, bool) { }
+    WEBCORE_EXPORT virtual void setScrollbarEnabled(Scrollbar&) { }
 
 protected:
     explicit ScrollingCoordinator(Page*);

Source/WebCore/page/scrolling/ScrollingStateNode.h

@@ -228,37 +228,38 @@ enum class ScrollingStateNodeProperty : uint64_t {
     ContentAreaHoverState                       = 1LLU << 19,
     MouseActivityState                          = 1LLU << 20,
     ScrollbarHoverState                         = 1LLU << 21,
+    ScrollbarEnabledState                       = 1LLU << 22,
     // ScrollingStateFrameScrollingNode
-    FrameScaleFactor                            = 1LLU << 22,
-    EventTrackingRegion                         = 1LLU << 23,
-    RootContentsLayer                           = 1LLU << 24,
-    CounterScrollingLayer                       = 1LLU << 25,
-    InsetClipLayer                              = 1LLU << 26,
-    ContentShadowLayer                          = 1LLU << 27,
-    HeaderHeight                                = 1LLU << 28,
-    FooterHeight                                = 1LLU << 29,
-    HeaderLayer                                 = 1LLU << 30,
-    FooterLayer                                 = 1LLU << 31,
-    BehaviorForFixedElements                    = 1LLU << 32,
-    TopContentInset                             = 1LLU << 33,
-    FixedElementsLayoutRelativeToFrame          = 1LLU << 34,
-    VisualViewportIsSmallerThanLayoutViewport   = 1LLU << 35,
-    AsyncFrameOrOverflowScrollingEnabled        = 1LLU << 36,
-    WheelEventGesturesBecomeNonBlocking         = 1LLU << 37,
-    ScrollingPerformanceTestingEnabled          = 1LLU << 38,
-    LayoutViewport                              = 1LLU << 39,
-    MinLayoutViewportOrigin                     = 1LLU << 40,
-    MaxLayoutViewportOrigin                     = 1LLU << 41,
-    OverrideVisualViewportSize                  = 1LLU << 42,
-    OverlayScrollbarsEnabled                    = 1LLU << 43,
+    FrameScaleFactor                            = 1LLU << 23,
+    EventTrackingRegion                         = 1LLU << 24,
+    RootContentsLayer                           = 1LLU << 25,
+    CounterScrollingLayer                       = 1LLU << 26,
+    InsetClipLayer                              = 1LLU << 27,
+    ContentShadowLayer                          = 1LLU << 28,
+    HeaderHeight                                = 1LLU << 29,
+    FooterHeight                                = 1LLU << 30,
+    HeaderLayer                                 = 1LLU << 31,
+    FooterLayer                                 = 1LLU << 32,
+    BehaviorForFixedElements                    = 1LLU << 33,
+    TopContentInset                             = 1LLU << 34,
+    FixedElementsLayoutRelativeToFrame          = 1LLU << 35,
+    VisualViewportIsSmallerThanLayoutViewport   = 1LLU << 36,
+    AsyncFrameOrOverflowScrollingEnabled        = 1LLU << 37,
+    WheelEventGesturesBecomeNonBlocking         = 1LLU << 38,
+    ScrollingPerformanceTestingEnabled          = 1LLU << 39,
+    LayoutViewport                              = 1LLU << 40,
+    MinLayoutViewportOrigin                     = 1LLU << 41,
+    MaxLayoutViewportOrigin                     = 1LLU << 42,
+    OverrideVisualViewportSize                  = 1LLU << 43,
+    OverlayScrollbarsEnabled                    = 1LLU << 44,
     // ScrollingStatePositionedNode
-    RelatedOverflowScrollingNodes               = 1LLU << 44,
-    LayoutConstraintData                        = 1LLU << 45,
+    RelatedOverflowScrollingNodes               = 1LLU << 45,
+    LayoutConstraintData                        = 1LLU << 46,
     // ScrollingStateFixedNode, ScrollingStateStickyNode
-    ViewportConstraints                         = 1LLU << 46,
+    ViewportConstraints                         = 1LLU << 47,
     // ScrollingStateOverflowScrollProxyNode
-    OverflowScrollingNode                       = 1LLU << 47,
-    KeyboardScrollData                          = 1LLU << 48,
+    OverflowScrollingNode                       = 1LLU << 48,
+    KeyboardScrollData                          = 1LLU << 49,
 };
 
 class ScrollingStateNode : public ThreadSafeRefCountedAndCanMakeThreadSafeWeakPtr<ScrollingStateNode> {

Source/WebCore/page/scrolling/ScrollingStateScrollingNode.cpp

@@ -50,6 +50,7 @@ ScrollingStateScrollingNode::ScrollingStateScrollingNode(const ScrollingStateScr
 #if PLATFORM(MAC)
     , m_scrollbarHoverState(stateNode.scrollbarHoverState())
     , m_mouseLocationState(stateNode.mouseLocationState())
+    , m_scrollbarEnabledState(stateNode.scrollbarEnabledState())
     , m_verticalScrollerImp(stateNode.verticalScrollerImp())
     , m_horizontalScrollerImp(stateNode.horizontalScrollerImp())
 #endif
@@ -302,6 +303,19 @@ void ScrollingStateScrollingNode::setScrollbarHoverState(ScrollbarHoverState hov
     setPropertyChanged(Property::ScrollbarHoverState);
 }
 
+void ScrollingStateScrollingNode::setScrollbarEnabledState(ScrollbarOrientation orientation, bool enabled)
+{
+    if ((orientation == ScrollbarOrientation::Horizontal ? m_scrollbarEnabledState.horizontalScrollbarIsEnabled : m_scrollbarEnabledState.verticalScrollbarIsEnabled) == enabled)
+        return;
+
+    if (orientation == ScrollbarOrientation::Horizontal)
+        m_scrollbarEnabledState.horizontalScrollbarIsEnabled = enabled;
+    else
+        m_scrollbarEnabledState.verticalScrollbarIsEnabled = enabled;
+
+    setPropertyChanged(Property::ScrollbarEnabledState);
+}
+
 void ScrollingStateScrollingNode::dumpProperties(TextStream& ts, OptionSet<ScrollingStateTreeAsTextBehavior> behavior) const
 {
     ScrollingStateNode::dumpProperties(ts, behavior);

Source/WebCore/page/scrolling/ScrollingStateScrollingNode.h

@@ -54,6 +54,11 @@ struct MouseLocationState {
     IntPoint locationInVerticalScrollbar;
 };
 
+struct ScrollbarEnabledState {
+    bool horizontalScrollbarIsEnabled { false };
+    bool verticalScrollbarIsEnabled { false };
+};
+
 class ScrollingStateScrollingNode : public ScrollingStateNode {
 public:
     virtual ~ScrollingStateScrollingNode();
@@ -124,6 +129,9 @@ class ScrollingStateScrollingNode : public ScrollingStateNode {
     ScrollbarHoverState scrollbarHoverState() const { return m_scrollbarHoverState; }
     WEBCORE_EXPORT void setScrollbarHoverState(ScrollbarHoverState);
 
+    ScrollbarEnabledState scrollbarEnabledState() const { return m_scrollbarEnabledState; }
+    WEBCORE_EXPORT void setScrollbarEnabledState(ScrollbarOrientation, bool);
+
     void setScrollerImpsFromScrollbars(Scrollbar* verticalScrollbar, Scrollbar* horizontalScrollbar);
 
     WEBCORE_EXPORT void setMouseIsOverContentArea(bool);
@@ -157,6 +165,7 @@ class ScrollingStateScrollingNode : public ScrollingStateNode {
 
     ScrollbarHoverState m_scrollbarHoverState;
     MouseLocationState m_mouseLocationState;
+    ScrollbarEnabledState m_scrollbarEnabledState;
 
 #if PLATFORM(MAC)
     RetainPtr<NSScrollerImp> m_verticalScrollerImp;

Source/WebCore/page/scrolling/mac/ScrollerMac.h

@@ -72,9 +72,14 @@ class ScrollerMac {
     void visibilityChanged(bool);
     void updateMinimumKnobLength(int);
     void detach();
+    void setEnabled(bool flag) { m_isEnabled = flag; }
+
 private:
     int m_minimumKnobLength { 0 };
+
+    bool m_isEnabled { false };
     bool m_isVisible { false };
+
     ScrollerPairMac& m_pair;
     const ScrollbarOrientation m_orientation;
     IntPoint m_lastKnownMousePositionInScrollbar;

Source/WebCore/page/scrolling/mac/ScrollerMac.mm

@@ -357,8 +357,7 @@ - (void)invalidate
     auto values = m_pair.valuesForOrientation(m_orientation);
 
     BEGIN_BLOCK_OBJC_EXCEPTIONS
-
-    [m_scrollerImp setEnabled:!!m_hostLayer];
+    [m_scrollerImp setEnabled:m_isEnabled];
     [m_scrollerImp setBoundsSize:NSSizeFromCGSize([m_hostLayer bounds].size)];
     [m_scrollerImp setDoubleValue:values.value];
     [m_scrollerImp setPresentationValue:values.value];

Source/WebCore/page/scrolling/mac/ScrollingTreeScrollingNodeDelegateMac.mm

@@ -82,7 +82,13 @@
         if (scrollingStateNode.scrollableAreaParameters().verticalNativeScrollbarVisibility != NativeScrollbarVisibility::Visible)
             m_scrollerPair->verticalScroller().setHostLayer(nullptr);
     }
-
+
+    if (scrollingStateNode.hasChangedProperty(ScrollingStateNode::Property::ScrollbarEnabledState)) {
+        auto scrollbarEnabledState = scrollingStateNode.scrollbarEnabledState();
+        m_scrollerPair->horizontalScroller().setEnabled(scrollbarEnabledState.horizontalScrollbarIsEnabled);
+        m_scrollerPair->verticalScroller().setEnabled(scrollbarEnabledState.verticalScrollbarIsEnabled);
+    }
+
     if (scrollingStateNode.hasChangedProperty(ScrollingStateNode::Property::ContentAreaHoverState)) {
         if (scrollingStateNode.mouseIsOverContentArea())
             m_scrollerPair->mouseEnteredContentArea();

Source/WebCore/platform/Scrollbar.cpp

@@ -442,6 +442,7 @@ void Scrollbar::setEnabled(bool e)
         return;
     m_enabled = e;
     theme().updateEnabledState(*this);
+    m_scrollableArea.scrollbarsController().updateScrollbarEnabledState(*this);
     invalidate();
 }
 

Source/WebCore/platform/ScrollbarsController.h

@@ -95,6 +95,7 @@ class ScrollbarsController {
 
     WEBCORE_EXPORT virtual bool shouldDrawIntoScrollbarLayer(Scrollbar&) const { return true; }
     WEBCORE_EXPORT virtual bool shouldRegisterScrollbars() const { return true; }
+    WEBCORE_EXPORT virtual void updateScrollbarEnabledState(Scrollbar&) { }
 
     WEBCORE_EXPORT virtual void setScrollbarMinimumThumbLength(WebCore::ScrollbarOrientation, int) { }
     WEBCORE_EXPORT virtual int minimumThumbLength(WebCore::ScrollbarOrientation) { return 0; }

Source/WebKit/Shared/RemoteLayerTree/RemoteScrollingCoordinatorTransaction.cpp

@@ -177,6 +177,12 @@ void ArgumentCoder<ScrollingStateScrollingNode>::encode(Encoder& encoder, const
         encoder << mouseLocationState.locationInHorizontalScrollbar;
         encoder << mouseLocationState.locationInVerticalScrollbar;
     }
+
+    if (node.hasChangedProperty(ScrollingStateNode::Property::ScrollbarEnabledState)) {
+        auto scrollbarEnabledState = node.scrollbarEnabledState();
+        encoder << scrollbarEnabledState.horizontalScrollbarIsEnabled;
+        encoder << scrollbarEnabledState.verticalScrollbarIsEnabled;
+    }
 }
 
 void ArgumentCoder<ScrollingStateFrameScrollingNode>::encode(Encoder& encoder, const ScrollingStateFrameScrollingNode& node)
@@ -322,6 +328,18 @@ bool ArgumentCoder<ScrollingStateScrollingNode>::decode(Decoder& decoder, Scroll
         node.setMouseMovedInContentArea({ locationInHorizontalScrollbar, locationInVerticalScrollbar });
     }
 
+    if (node.hasChangedProperty(ScrollingStateNode::Property::ScrollbarEnabledState)) {
+        bool horizontalScrollbarEnabled;
+        if (!decoder.decode(horizontalScrollbarEnabled))
+            return false;
+
+        bool verticalScrollbarEnabled;
+        if (!decoder.decode(verticalScrollbarEnabled))
+            return false;
+        node.setScrollbarEnabledState(ScrollbarOrientation::Horizontal, horizontalScrollbarEnabled);
+        node.setScrollbarEnabledState(ScrollbarOrientation::Vertical, verticalScrollbarEnabled);
+    }
+
     return true;
 }
 

Source/WebKit/Shared/WebCoreArgumentCoders.serialization.in

@@ -3106,6 +3106,7 @@ header: <WebCore/ScrollingStateNode.h>
     ContentAreaHoverState
     MouseActivityState
     ScrollbarHoverState
+    ScrollbarEnabledState
     FrameScaleFactor
     EventTrackingRegion
     RootContentsLayer

Source/WebKit/WebProcess/WebPage/RemoteLayerTree/RemoteScrollbarsController.h

@@ -54,6 +54,7 @@ class RemoteScrollbarsController final : public WebCore::ScrollbarsController {
     bool shouldDrawIntoScrollbarLayer(WebCore::Scrollbar&) const final;
     bool shouldRegisterScrollbars() const final { return scrollableArea().isListBox(); }
     int minimumThumbLength(WebCore::ScrollbarOrientation) final;
+    void updateScrollbarEnabledState(WebCore::Scrollbar&) final;
 
 private:
     bool m_horizontalOverlayScrollbarIsVisible { false };

Source/WebKit/WebProcess/WebPage/RemoteLayerTree/RemoteScrollbarsController.mm

@@ -107,5 +107,11 @@
     return orientation == WebCore::ScrollbarOrientation::Horizontal ? m_horizontalMinimumThumbLength : m_verticalMinimumThumbLength;
 }
 
+void RemoteScrollbarsController::updateScrollbarEnabledState(WebCore::Scrollbar& scrollbar)
+{
+    if (auto scrollingCoordinator = m_coordinator.get())
+        scrollingCoordinator->setScrollbarEnabled(scrollbar);
+}
+
 }
 #endif // PLATFORM(MAC)