LibWeb: Use DOM Selection instead of ad-hoc layout tree selection

Before this patch, we were expressing the current selection as a range
between two points in the layout tree. This was a made-up concept I
called LayoutRange (2x LayoutPosition) and as it turns out, we don't
actually need it!

Instead, we can just use the Selection API from the Selection API spec.
This API expresses selection in terms of the DOM, and we already had
many of the building blocks implemented.

To ensure that selections get visually updated when the underlying Range
of an active Selection is programmatically manipulated, Range now has
an "associated Selection". If a range is updated while associated with
a selection, we recompute layout tree selection states and repaint the
page to make it user-visible.

Userland/Libraries/LibWeb/DOM/Document.cpp

@@ -873,6 +873,8 @@ void Document::update_layout()
             page->client().page_did_layout();
     }
 
+    m_layout_root->recompute_selection_states();
+
     m_needs_layout = false;
     m_layout_update_timer->stop();
 }

Userland/Libraries/LibWeb/DOM/Range.cpp

@@ -17,6 +17,7 @@
 #include <LibWeb/DOM/Text.h>
 #include <LibWeb/Geometry/DOMRect.h>
 #include <LibWeb/HTML/Window.h>
+#include <LibWeb/Layout/InitialContainingBlock.h>
 
 namespace Web::DOM {
 
@@ -71,6 +72,28 @@ void Range::initialize(JS::Realm& realm)
     set_prototype(&Bindings::ensure_web_prototype<Bindings::RangePrototype>(realm, "Range"));
 }
 
+void Range::visit_edges(Cell::Visitor& visitor)
+{
+    Base::visit_edges(visitor);
+    visitor.visit(m_associated_selection);
+}
+
+void Range::set_associated_selection(Badge<Selection::Selection>, JS::GCPtr<Selection::Selection> selection)
+{
+    m_associated_selection = selection;
+    update_associated_selection();
+}
+
+void Range::update_associated_selection()
+{
+    if (!m_associated_selection)
+        return;
+    if (auto* layout_root = m_associated_selection->document()->layout_node()) {
+        layout_root->recompute_selection_states();
+        layout_root->set_needs_display();
+    }
+}
+
 // https://dom.spec.whatwg.org/#concept-range-root
 Node& Range::root()
 {
@@ -173,6 +196,7 @@ WebIDL::ExceptionOr<void> Range::set_start_or_end(Node& node, u32 offset, StartO
         m_end_offset = offset;
     }
 
+    update_associated_selection();
     return {};
 }
 
@@ -353,6 +377,7 @@ WebIDL::ExceptionOr<void> Range::select(Node& node)
     m_end_container = *parent;
     m_end_offset = index + 1;
 
+    update_associated_selection();
     return {};
 }
 
@@ -370,11 +395,11 @@ void Range::collapse(bool to_start)
     if (to_start) {
         m_end_container = m_start_container;
         m_end_offset = m_start_offset;
-        return;
+    } else {
+        m_start_container = m_end_container;
+        m_start_offset = m_end_offset;
     }
-
-    m_start_container = m_end_container;
-    m_start_offset = m_end_offset;
+    update_associated_selection();
 }
 
 // https://dom.spec.whatwg.org/#dom-range-selectnodecontents
@@ -395,6 +420,7 @@ WebIDL::ExceptionOr<void> Range::select_node_contents(Node const& node)
     m_end_container = node;
     m_end_offset = length;
 
+    update_associated_selection();
     return {};
 }
 

Userland/Libraries/LibWeb/DOM/Range.h

@@ -9,6 +9,7 @@
 #pragma once
 
 #include <LibWeb/DOM/AbstractRange.h>
+#include <LibWeb/Selection/Selection.h>
 
 namespace Web::DOM {
 
@@ -86,15 +87,20 @@ public:
 
     bool contains_node(Node const&) const;
 
+    void set_associated_selection(Badge<Selection::Selection>, JS::GCPtr<Selection::Selection>);
+
 private:
     explicit Range(Document&);
     Range(Node& start_container, u32 start_offset, Node& end_container, u32 end_offset);
 
     virtual void initialize(JS::Realm&) override;
+    virtual void visit_edges(Cell::Visitor&) override;
 
     Node& root();
     Node const& root() const;
 
+    void update_associated_selection();
+
     enum class StartOrEnd {
         Start,
         End,
@@ -108,6 +114,8 @@ private:
     WebIDL::ExceptionOr<void> insert(JS::NonnullGCPtr<Node>);
 
     bool partially_contains_node(Node const&) const;
+
+    JS::GCPtr<Selection::Selection> m_associated_selection;
 };
 
 }