LibWeb/CSS: Implement Element.computedStyleMap()

Currently the map doesn't return any values, so it's not very useful,
but this does make a few tests pass just by existing. :^)

Libraries/LibWeb/CSS/StylePropertyMapReadOnly.idl

@@ -10,3 +10,8 @@ interface StylePropertyMapReadOnly {
     boolean has(USVString property);
     readonly attribute unsigned long size;
 };
+
+// https://drafts.css-houdini.org/css-typed-om-1/#computed-stylepropertymapreadonly-objects
+partial interface Element {
+    [SameObject] StylePropertyMapReadOnly computedStyleMap();
+};

Libraries/LibWeb/DOM/Element.cpp

@@ -122,6 +122,7 @@ void Element::visit_edges(Cell::Visitor& visitor)
     visitor.visit(m_custom_state_set);
     visitor.visit(m_cascaded_properties);
     visitor.visit(m_computed_properties);
+    visitor.visit(m_computed_style_map_cache);
     if (m_pseudo_element_data) {
         for (auto& pseudo_element : *m_pseudo_element_data) {
             visitor.visit(pseudo_element.value);
@@ -4096,4 +4097,27 @@ void Element::set_had_duplicate_attribute_during_tokenization(Badge<HTML::HTMLPa
     m_had_duplicate_attribute_during_tokenization = true;
 }
 
+// https://drafts.css-houdini.org/css-typed-om-1/#dom-element-computedstylemap
+GC::Ref<CSS::StylePropertyMapReadOnly> Element::computed_style_map()
+{
+    // The computedStyleMap() method must, when called on an Element this, perform the following steps:
+
+    // 1. If this’s [[computedStyleMapCache]] internal slot is set to null, set its value to a new
+    //    StylePropertyMapReadOnly object, whose [[declarations]] internal slot are the name and computed value of
+    //    every longhand CSS property supported by the User Agent, every registered custom property, and every
+    //    non-registered custom property which is not set to its initial value on this, in the standard order.
+    //
+    //    The computed values in the [[declarations]] of this object must remain up-to-date, changing as style
+    //    resolution changes the properties on this and how they’re computed.
+    //
+    // NOTE: In practice, since the values are "hidden" behind a .get() method call, UAs can delay computing anything
+    //    until a given property is actually requested.
+    if (m_computed_style_map_cache == nullptr) {
+        m_computed_style_map_cache = CSS::StylePropertyMapReadOnly::create_computed_style(realm(), AbstractElement { *this });
+    }
+
+    // 2. Return this’s [[computedStyleMapCache]] internal slot.
+    return *m_computed_style_map_cache;
+}
+
 }

Libraries/LibWeb/DOM/Element.h

@@ -19,6 +19,7 @@
 #include <LibWeb/CSS/Selector.h>
 #include <LibWeb/CSS/StyleInvalidation.h>
 #include <LibWeb/CSS/StyleProperty.h>
+#include <LibWeb/CSS/StylePropertyMapReadOnly.h>
 #include <LibWeb/DOM/ChildNode.h>
 #include <LibWeb/DOM/NonDocumentTypeChildNode.h>
 #include <LibWeb/DOM/ParentNode.h>
@@ -521,6 +522,8 @@ public:
     void set_had_duplicate_attribute_during_tokenization(Badge<HTML::HTMLParser>);
     bool had_duplicate_attribute_during_tokenization() const { return m_had_duplicate_attribute_during_tokenization; }
 
+    GC::Ref<CSS::StylePropertyMapReadOnly> computed_style_map();
+
 protected:
     Element(Document&, DOM::QualifiedName);
     virtual void initialize(JS::Realm&) override;
@@ -603,6 +606,11 @@ private:
     // Element objects have an internal [[RegisteredIntersectionObservers]] slot, which is initialized to an empty list.
     OwnPtr<Vector<IntersectionObserver::IntersectionObserverRegistration>> m_registered_intersection_observers;
 
+    // https://drafts.css-houdini.org/css-typed-om-1/#dom-element-computedstylemapcache-slot
+    // Every Element has a [[computedStyleMapCache]] internal slot, initially set to null, which caches the result of
+    // the computedStyleMap() method when it is first called.
+    GC::Ptr<CSS::StylePropertyMapReadOnly> m_computed_style_map_cache;
+
     CSSPixelPoint m_scroll_offset;
 
     bool m_in_top_layer : 1 { false };

Libraries/LibWeb/DOM/Element.idl

@@ -1,5 +1,6 @@
 #import <Animations/Animatable.idl>
 #import <ARIA/ARIAMixin.idl>
+#import <CSS/StylePropertyMapReadOnly.idl>
 #import <DOM/Attr.idl>
 #import <DOM/ChildNode.idl>
 #import <DOM/DOMTokenList.idl>

Tests/LibWeb/Text/expected/wpt-import/css/css-typed-om/the-stylepropertymap/computed/computed.tentative.txt

@@ -1,3 +1,12 @@
-Harness status: Error
+Harness status: OK
 
-Found 0 tests
+Found 7 tests
+
+7 Fail
+Fail	Computed StylePropertyMap contains every CSS property
+Fail	Computed StylePropertyMap contains CSS property declarations in style rules
+Fail	Computed StylePropertyMap contains custom property declarations in style rules
+Fail	Computed StylePropertyMap contains CSS property declarations in inline styles
+Fail	Computed StylePropertyMap contains custom property declarations in inline rules
+Fail	Computed StylePropertyMap contains computed values and not resolved values
+Fail	Computed StylePropertyMap is live

Tests/LibWeb/Text/expected/wpt-import/css/css-typed-om/the-stylepropertymap/computed/get-invalid.txt

@@ -2,5 +2,5 @@ Harness status: OK
 
 Found 1 tests
 
-1 Fail
-Fail	Calling StylePropertyMap.get with an unsupported property throws a TypeError
+1 Pass
+Pass	Calling StylePropertyMap.get with an unsupported property throws a TypeError

Tests/LibWeb/Text/expected/wpt-import/css/css-typed-om/the-stylepropertymap/computed/get.txt

@@ -2,8 +2,9 @@ Harness status: OK
 
 Found 6 tests
 
-6 Fail
-Fail	Getting a custom property not in the computed style returns undefined
+1 Pass
+5 Fail
+Pass	Getting a custom property not in the computed style returns undefined
 Fail	Getting a valid property from computed style returns the correct entry
 Fail	Getting a valid custom property from computed style returns the correct entry
 Fail	Getting a list-valued property from computed style returns only the first value

Tests/LibWeb/Text/expected/wpt-import/css/css-typed-om/the-stylepropertymap/computed/getAll.tentative.txt

@@ -2,9 +2,10 @@ Harness status: OK
 
 Found 6 tests
 
-6 Fail
-Fail	Calling StylePropertyMap.getAll with an unsupported property throws a TypeError
-Fail	Calling StylePropertyMap.getAll with a custom property not in the property model returns an empty list
+2 Pass
+4 Fail
+Pass	Calling StylePropertyMap.getAll with an unsupported property throws a TypeError
+Pass	Calling StylePropertyMap.getAll with a custom property not in the property model returns an empty list
 Fail	Calling StylePropertyMap.getAll with a valid property returns a single element list with the correct entry
 Fail	StylePropertyMap.getAll is case-insensitive
 Fail	Calling StylePropertyMap.getAll with a valid custom property returns a single element list with the correct entry

Tests/LibWeb/Text/expected/wpt-import/css/css-typed-om/the-stylepropertymap/computed/has.tentative.txt

@@ -2,9 +2,10 @@ Harness status: OK
 
 Found 7 tests
 
-7 Fail
-Fail	Calling StylePropertyMap.has with an unsupported property throws a TypeError
-Fail	Calling StylePropertyMap.has with a custom property not in the property model returns false
+2 Pass
+5 Fail
+Pass	Calling StylePropertyMap.has with an unsupported property throws a TypeError
+Pass	Calling StylePropertyMap.has with a custom property not in the property model returns false
 Fail	Calling StylePropertyMap.has with a valid property returns true
 Fail	Calling StylePropertyMap.has with a valid property in mixed case returns true
 Fail	Calling StylePropertyMap.has with a valid shorthand property returns true