LibWeb: Handle continuation chain during hit-testing instead of after it

My previous attempt at resolving the continuation chain tried to deal
with `pointer-events: none` by repeatedly falling back to the parent
paintable until one was found that _would_ want to handle pointer
events. But since we were no longer performing hit-tests on those
paintables, false positives could pop up. This could happen for
out-of-flow block elements that did not overlap with their parent rects,
for example.

This approach works much better since it only handles the continuation
case that's relevant (the "middle" anonymous box) and it does so during
hit-testing instead of after, allowing all the other relevant logic to
come into play.

Libraries/LibWeb/Painting/PaintableBox.cpp

@@ -965,12 +965,36 @@ TraversalDecision PaintableBox::hit_test(CSSPixelPoint position, HitTestType typ
             return TraversalDecision::Break;
     }
 
+    if (!visible_for_hit_testing())
+        return TraversalDecision::Continue;
+
     if (!absolute_border_box_rect().contains(position_adjusted_by_scroll_offset))
         return TraversalDecision::Continue;
 
+    if (hit_test_continuation(callback) == TraversalDecision::Break)
+        return TraversalDecision::Break;
+
     return callback(HitTestResult { const_cast<PaintableBox&>(*this) });
 }
 
+TraversalDecision PaintableBox::hit_test_continuation(Function<TraversalDecision(HitTestResult)> const& callback) const
+{
+    // If we're hit testing the "middle" part of a continuation chain, we are dealing with an anonymous box that is
+    // linked to a parent inline node. Since our block element children did not match the hit test, but we did, we
+    // should walk the continuation chain up to the inline parent and return a hit on that instead.
+    auto continuation_node = layout_node_with_style_and_box_metrics().continuation_of_node();
+    if (!continuation_node || !layout_node().is_anonymous())
+        return TraversalDecision::Continue;
+
+    while (continuation_node->continuation_of_node())
+        continuation_node = continuation_node->continuation_of_node();
+    auto& paintable = *continuation_node->first_paintable();
+    if (!paintable.visible_for_hit_testing())
+        return TraversalDecision::Continue;
+
+    return callback(HitTestResult { paintable });
+}
+
 Optional<HitTestResult> PaintableBox::hit_test(CSSPixelPoint position, HitTestType type) const
 {
     Optional<HitTestResult> result;
@@ -985,28 +1009,6 @@ Optional<HitTestResult> PaintableBox::hit_test(CSSPixelPoint position, HitTestTy
             return TraversalDecision::Break;
         return TraversalDecision::Continue;
     });
-
-    // If our hit-testing has resulted in a hit on a paintable, we know that it is the most specific hit. If that
-    // paintable turns out to be invisible for hit-testing, we need to traverse up the paintable tree to find the next
-    // paintable that is visible for hit-testing. This implements the behavior expected for pointer-events.
-    while (result.has_value() && !result->paintable->visible_for_hit_testing()) {
-        result->index_in_node = result->paintable->dom_node() ? result->paintable->dom_node()->index() : 0;
-        result->paintable = result->paintable->parent();
-
-        // If the new parent is an anonymous box part of a continuation, we need to follow the chain to the inline node
-        // that spawned the anonymous "middle" part of the continuation, since that inline node is the actual parent.
-        if (is<PaintableBox>(*result->paintable)) {
-            auto const& box_layout_node = static_cast<PaintableBox&>(*result->paintable).layout_node_with_style_and_box_metrics();
-            if (box_layout_node.is_anonymous() && box_layout_node.continuation_of_node()) {
-                auto const* original_inline_node = &box_layout_node;
-                while (original_inline_node->continuation_of_node())
-                    original_inline_node = original_inline_node->continuation_of_node();
-
-                result->paintable = const_cast<Paintable*>(original_inline_node->first_paintable());
-            }
-        }
-    }
-
     return result;
 }
 
@@ -1048,6 +1050,9 @@ TraversalDecision PaintableWithLines::hit_test(CSSPixelPoint position, HitTestTy
             return TraversalDecision::Break;
     }
 
+    if (!visible_for_hit_testing())
+        return TraversalDecision::Continue;
+
     for (auto const& fragment : fragments()) {
         if (fragment.paintable().has_stacking_context())
             continue;

Libraries/LibWeb/Painting/PaintableBox.h

@@ -144,6 +144,7 @@ public:
 
     [[nodiscard]] virtual TraversalDecision hit_test(CSSPixelPoint position, HitTestType type, Function<TraversalDecision(HitTestResult)> const& callback) const override;
     Optional<HitTestResult> hit_test(CSSPixelPoint, HitTestType) const;
+    [[nodiscard]] TraversalDecision hit_test_continuation(Function<TraversalDecision(HitTestResult)> const& callback) const;
 
     virtual bool handle_mousewheel(Badge<EventHandler>, CSSPixelPoint, unsigned buttons, unsigned modifiers, int wheel_delta_x, int wheel_delta_y) override;
 

Tests/LibWeb/Text/expected/hit_testing/pointer-events-no-parent-extension.txt

@@ -0,0 +1,2 @@
+<HTML>
+<#document>

Tests/LibWeb/Text/input/hit_testing/pointer-events-no-parent-extension.html

@@ -0,0 +1,15 @@
+<script src="../include.js"></script>
+<body>
+    <div>
+        <!-- this div should not be hit, nor should its parent -->
+        <div id="a1" style="position: fixed; width: 100px; height: 100px; pointer-events: none"></div>
+        foobar
+    </div>
+</body>
+<script>
+    test(() => {
+        const hit = internals.hitTest(a1.offsetLeft + 50, a1.offsetTop + 80);
+        printElement(hit.node);
+        printElement(hit.node.parentNode);
+    });
+</script>