LibWeb: Don't class mousewheel as handled if scroll offset isn't updated

Before this change, you could only scroll the current hovered scroll
container, even if it was at the beginning or end and thus having no
effect.

Now, if it doesn't update, it will not be classed as handled and will
move onto the next scroll container.

Libraries/LibWeb/DOM/Element.cpp

@@ -1867,7 +1867,7 @@ void Element::set_scroll_left(double x)
     // FIXME: Implement this in terms of calling "scroll the element".
     auto scroll_offset = paintable_box()->scroll_offset();
     scroll_offset.set_x(CSSPixels::nearest_value_for(x));
-    paintable_box()->set_scroll_offset(scroll_offset);
+    (void)paintable_box()->set_scroll_offset(scroll_offset);
 }
 
 void Element::set_scroll_top(double y)
@@ -1924,7 +1924,7 @@ void Element::set_scroll_top(double y)
     // FIXME: Implement this in terms of calling "scroll the element".
     auto scroll_offset = paintable_box()->scroll_offset();
     scroll_offset.set_y(CSSPixels::nearest_value_for(y));
-    paintable_box()->set_scroll_offset(scroll_offset);
+    (void)paintable_box()->set_scroll_offset(scroll_offset);
 }
 
 // https://drafts.csswg.org/cssom-view/#dom-element-scrollwidth
@@ -3144,7 +3144,7 @@ void Element::scroll(double x, double y)
     auto scroll_offset = paintable_box()->scroll_offset();
     scroll_offset.set_x(CSSPixels::nearest_value_for(x));
     scroll_offset.set_y(CSSPixels::nearest_value_for(y));
-    paintable_box()->set_scroll_offset(scroll_offset);
+    (void)paintable_box()->set_scroll_offset(scroll_offset);
 }
 
 // https://drafts.csswg.org/cssom-view/#dom-element-scroll

Libraries/LibWeb/Layout/LayoutState.cpp

@@ -433,7 +433,7 @@ void LayoutState::commit(Box& root)
         // (scrollable overflow rect become smaller), the scroll offset would be out of bounds.
         auto& paintable_box = const_cast<Painting::PaintableBox&>(*box->paintable_box());
         if (!paintable_box.scroll_offset().is_zero())
-            paintable_box.set_scroll_offset(paintable_box.scroll_offset());
+            (void)paintable_box.set_scroll_offset(paintable_box.scroll_offset());
     }
 
     for (auto& it : used_values_per_layout_node) {

Libraries/LibWeb/Painting/PaintableBox.cpp

@@ -111,11 +111,11 @@ CSSPixelPoint PaintableBox::scroll_offset() const
     return static_cast<DOM::Element const*>(dom_node())->scroll_offset({});
 }
 
-void PaintableBox::set_scroll_offset(CSSPixelPoint offset)
+PaintableBox::ScrollHandled PaintableBox::set_scroll_offset(CSSPixelPoint offset)
 {
     auto scrollable_overflow_rect = this->scrollable_overflow_rect();
     if (!scrollable_overflow_rect.has_value())
-        return;
+        return ScrollHandled::No;
 
     document().set_needs_to_refresh_scroll_state(true);
 
@@ -128,7 +128,7 @@ void PaintableBox::set_scroll_offset(CSSPixelPoint offset)
 
     // FIXME: If there is horizontal and vertical scroll ignore only part of the new offset
     if (offset.y() < 0 || scroll_offset() == offset)
-        return;
+        return ScrollHandled::No;
 
     auto& node = layout_node();
     if (auto pseudo_element = node.generated_for_pseudo_element(); pseudo_element.has_value()) {
@@ -136,7 +136,7 @@ void PaintableBox::set_scroll_offset(CSSPixelPoint offset)
     } else if (auto* element = as_if<DOM::Element>(dom_node())) {
         element->set_scroll_offset({}, offset);
     } else {
-        return;
+        return ScrollHandled::No;
     }
 
     // https://drafts.csswg.org/cssom-view-1/#scrolling-events
@@ -154,17 +154,18 @@ void PaintableBox::set_scroll_offset(CSSPixelPoint offset)
 
     // 3. If the element is already in doc’s pending scroll event targets, abort these steps.
     if (document.pending_scroll_event_targets().contains_slow(event_target))
-        return;
+        return ScrollHandled::Yes;
 
     // 4. Append the element to doc’s pending scroll event targets.
     document.pending_scroll_event_targets().append(*layout_node_with_style_and_box_metrics().dom_node());
 
     set_needs_display(InvalidateDisplayList::No);
+    return ScrollHandled::Yes;
 }
 
-void PaintableBox::scroll_by(int delta_x, int delta_y)
+PaintableBox::ScrollHandled PaintableBox::scroll_by(int delta_x, int delta_y)
 {
-    set_scroll_offset(scroll_offset().translated(delta_x, delta_y));
+    return set_scroll_offset(scroll_offset().translated(delta_x, delta_y));
 }
 
 void PaintableBox::set_offset(CSSPixelPoint offset)
@@ -1163,7 +1164,7 @@ void PaintableBox::scroll_to_mouse_position(CSSPixelPoint position)
     if (is_viewport())
         document().navigable()->perform_scroll_of_viewport(new_scroll_offset);
     else
-        set_scroll_offset(new_scroll_offset);
+        (void)set_scroll_offset(new_scroll_offset);
 }
 
 bool PaintableBox::handle_mousewheel(Badge<EventHandler>, CSSPixelPoint, unsigned, unsigned, int wheel_delta_x, int wheel_delta_y)
@@ -1173,8 +1174,8 @@ bool PaintableBox::handle_mousewheel(Badge<EventHandler>, CSSPixelPoint, unsigne
         return false;
     }
 
-    scroll_by(wheel_delta_x, wheel_delta_y);
-    return true;
+    auto scroll_handled = scroll_by(wheel_delta_x, wheel_delta_y);
+    return scroll_handled == ScrollHandled::Yes;
 }
 
 TraversalDecision PaintableBox::hit_test_scrollbars(CSSPixelPoint position, Function<TraversalDecision(HitTestResult)> const& callback) const

Libraries/LibWeb/Painting/PaintableBox.h

@@ -63,9 +63,14 @@ public:
     // Offset from the top left of the containing block's content edge.
     [[nodiscard]] CSSPixelPoint offset() const;
 
+    enum class ScrollHandled {
+        No,
+        Yes,
+    };
+
     CSSPixelPoint scroll_offset() const;
-    void set_scroll_offset(CSSPixelPoint);
-    void scroll_by(int delta_x, int delta_y);
+    [[nodiscard]] ScrollHandled set_scroll_offset(CSSPixelPoint);
+    [[nodiscard]] ScrollHandled scroll_by(int delta_x, int delta_y);
 
     void set_offset(CSSPixelPoint);
     void set_offset(float x, float y) { set_offset({ x, y }); }