LibWeb: Keep CSS sheets sorted in document tree order

This ensures that style is applied consistently, even if the document
has external CSS resources that don't always arrive in the same order.

Userland/Libraries/LibWeb/CSS/StyleComputer.cpp

@@ -141,7 +141,7 @@ void StyleComputer::for_each_stylesheet(CascadeOrigin cascade_origin, Callback c
     }
     if (cascade_origin == CascadeOrigin::Author) {
         for (auto const& sheet : document().style_sheets().sheets()) {
-            callback(sheet);
+            callback(*sheet);
         }
     }
 }

Userland/Libraries/LibWeb/CSS/StyleSheetList.cpp

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/QuickSort.h>
 #include <LibWeb/Bindings/StyleSheetListPrototype.h>
 #include <LibWeb/CSS/StyleSheetList.h>
 #include <LibWeb/DOM/Document.h>
@@ -15,6 +16,8 @@ void StyleSheetList::add_sheet(CSSStyleSheet& sheet)
     sheet.set_style_sheet_list({}, this);
     m_sheets.append(sheet);
 
+    sort_sheets();
+
     m_document.style_computer().invalidate_rule_cache();
     m_document.style_computer().load_fonts_from_sheet(sheet);
     m_document.invalidate_style();
@@ -23,7 +26,9 @@ void StyleSheetList::add_sheet(CSSStyleSheet& sheet)
 void StyleSheetList::remove_sheet(CSSStyleSheet& sheet)
 {
     sheet.set_style_sheet_list({}, nullptr);
-    m_sheets.remove_first_matching([&](auto& entry) { return &entry == &sheet; });
+    m_sheets.remove_first_matching([&](auto& entry) { return entry.ptr() == &sheet; });
+
+    sort_sheets();
 
     m_document.style_computer().invalidate_rule_cache();
     m_document.invalidate_style();
@@ -45,8 +50,8 @@ void StyleSheetList::visit_edges(Cell::Visitor& visitor)
 {
     Base::visit_edges(visitor);
     visitor.visit(m_document);
-    for (auto& sheet : m_sheets)
-        visitor.visit(&sheet);
+    for (auto sheet : m_sheets)
+        visitor.visit(sheet.ptr());
 }
 
 // https://www.w3.org/TR/cssom/#ref-for-dfn-supported-property-indices%E2%91%A1
@@ -65,7 +70,14 @@ JS::Value StyleSheetList::item_value(size_t index) const
     if (index >= m_sheets.size())
         return JS::js_undefined();
 
-    return &m_sheets[index];
+    return m_sheets[index].ptr();
+}
+
+void StyleSheetList::sort_sheets()
+{
+    quick_sort(m_sheets, [](JS::NonnullGCPtr<StyleSheet> a, JS::NonnullGCPtr<StyleSheet> b) {
+        return a->owner_node()->is_before(*b->owner_node());
+    });
 }
 
 }

Userland/Libraries/LibWeb/CSS/StyleSheetList.h

@@ -20,14 +20,14 @@ public:
     void add_sheet(CSSStyleSheet&);
     void remove_sheet(CSSStyleSheet&);
 
-    Vector<CSSStyleSheet&> const& sheets() const { return m_sheets; }
-    Vector<CSSStyleSheet&>& sheets() { return m_sheets; }
+    Vector<JS::NonnullGCPtr<CSSStyleSheet>> const& sheets() const { return m_sheets; }
+    Vector<JS::NonnullGCPtr<CSSStyleSheet>>& sheets() { return m_sheets; }
 
     CSSStyleSheet* item(size_t index) const
     {
         if (index >= m_sheets.size())
             return {};
-        return &const_cast<CSSStyleSheet&>(m_sheets[index]);
+        return const_cast<CSSStyleSheet*>(m_sheets[index].ptr());
     }
 
     size_t length() const { return m_sheets.size(); }
@@ -43,8 +43,10 @@ private:
 
     virtual void visit_edges(Cell::Visitor&) override;
 
+    void sort_sheets();
+
     DOM::Document& m_document;
-    Vector<CSSStyleSheet&> m_sheets;
+    Vector<JS::NonnullGCPtr<CSSStyleSheet>> m_sheets;
 };
 
 }

Userland/Libraries/LibWeb/DOM/Document.cpp

@@ -1582,7 +1582,7 @@ void Document::evaluate_media_rules()
 {
     bool any_media_queries_changed_match_state = false;
     for (auto& style_sheet : style_sheets().sheets()) {
-        if (style_sheet.evaluate_media_queries(window()))
+        if (style_sheet->evaluate_media_queries(window()))
             any_media_queries_changed_match_state = true;
     }