LibWeb: Implement CSSFontFeatureValuesMap

This will be used within `CSSFontFeatureValuesRule`

Libraries/LibWeb/CMakeLists.txt

@@ -112,6 +112,7 @@ set(SOURCES
     CSS/CSSDescriptors.cpp
     CSS/CSSFontFaceDescriptors.cpp
     CSS/CSSFontFaceRule.cpp
+    CSS/CSSFontFeatureValuesMap.cpp
     CSS/CSSGroupingRule.cpp
     CSS/CSSImageValue.cpp
     CSS/CSSImportRule.cpp

Libraries/LibWeb/CSS/CSSFontFeatureValuesMap.cpp

@@ -0,0 +1,80 @@
+/*
+ * Copyright (c) 2026, Callum Law <callumlaw1709@outlook.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "CSSFontFeatureValuesMap.h"
+#include <LibJS/Runtime/Array.h>
+#include <LibWeb/Bindings/Intrinsics.h>
+#include <LibWeb/WebIDL/ExceptionOr.h>
+
+namespace Web::CSS {
+
+GC_DEFINE_ALLOCATOR(CSSFontFeatureValuesMap);
+
+GC::Ref<CSSFontFeatureValuesMap> CSSFontFeatureValuesMap::create(JS::Realm& realm, size_t max_value_count)
+{
+    return realm.create<CSSFontFeatureValuesMap>(realm, max_value_count);
+}
+
+CSSFontFeatureValuesMap::CSSFontFeatureValuesMap(JS::Realm& realm, size_t max_value_count)
+    : Bindings::PlatformObject(realm)
+    , m_map_entries(JS::Map::create(realm))
+    , m_max_value_count(max_value_count)
+{
+}
+
+WebIDL::ExceptionOr<void> CSSFontFeatureValuesMap::set(String const& feature_value_name, Variant<u32, Vector<u32>> const& values)
+{
+    // https://drafts.csswg.org/css-fonts-4/#cssfontfeaturevaluesmap
+    // The CSSFontFeatureValuesMap interface uses the default map class methods but the set method has different
+    // behavior. It takes a sequence of unsigned integers and associates it with a given featureValueName. The method
+    // behaves the same as the default map class method except that
+
+    // a single unsigned long value is treated as a sequence of a single value.
+    Vector<u32> value_vector = values.visit(
+        [](u32 single_value) { return Vector<u32> { single_value }; },
+        [](Vector<u32> value_vector) { return value_vector; });
+
+    // The method throws an exception if an invalid number of values is passed in.
+    if (value_vector.is_empty())
+        return WebIDL::InvalidAccessError::create(realm(), "CSSFontFeatureValuesMap.set requires at least one value."_utf16);
+
+    // If the associated feature value block only allows a limited number of values, the set method throws an
+    // InvalidAccessError exception when the input sequence to set contains more than the limited number of values. See
+    // the description of multi-valued feature value definitions for details on the maximum number of values allowed for
+    // a given type of feature value block.
+    if (value_vector.size() > m_max_value_count)
+        return WebIDL::InvalidAccessError::create(realm(), Utf16String::formatted("CSSFontFeatureValuesMap.set only allows a maximum of {} values for the associated feature", m_max_value_count));
+
+    Vector<JS::Value> wrapped_values;
+    wrapped_values.ensure_capacity(value_vector.size());
+
+    for (auto const& value : value_vector)
+        wrapped_values.append(JS::Value { value });
+
+    m_map_entries->map_set(JS::PrimitiveString::create(vm(), feature_value_name), JS::Array::create_from(realm(), wrapped_values.span()));
+    // TODO: Clear the relevant caches
+
+    return {};
+}
+
+void CSSFontFeatureValuesMap::on_map_modified_from_js(Badge<Bindings::CSSFontFeatureValuesMapPrototype>)
+{
+    // TODO: Clear the relevant caches
+}
+
+void CSSFontFeatureValuesMap::initialize(JS::Realm& realm)
+{
+    WEB_SET_PROTOTYPE_FOR_INTERFACE(CSSFontFeatureValuesMap);
+    Base::initialize(realm);
+}
+
+void CSSFontFeatureValuesMap::visit_edges(Cell::Visitor& visitor)
+{
+    Base::visit_edges(visitor);
+    visitor.visit(m_map_entries);
+}
+
+}

Libraries/LibWeb/CSS/CSSFontFeatureValuesMap.h

@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2026, Callum Law <callumlaw1709@outlook.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibJS/Runtime/MapIterator.h>
+#include <LibWeb/Bindings/CSSFontFeatureValuesMapPrototype.h>
+#include <LibWeb/Bindings/PlatformObject.h>
+#include <LibWeb/Forward.h>
+
+namespace Web::CSS {
+
+class CSSFontFeatureValuesMap final : public Bindings::PlatformObject {
+    WEB_PLATFORM_OBJECT(CSSFontFeatureValuesMap, Bindings::PlatformObject);
+    GC_DECLARE_ALLOCATOR(CSSFontFeatureValuesMap);
+
+public:
+    static GC::Ref<CSSFontFeatureValuesMap> create(JS::Realm&, size_t max_value_count);
+
+    virtual GC::Ref<JS::Map> map_entries() { return m_map_entries; }
+
+    WebIDL::ExceptionOr<void> set(String const& feature_value_name, Variant<u32, Vector<u32>> const& values);
+
+    void on_map_modified_from_js(Badge<Bindings::CSSFontFeatureValuesMapPrototype>);
+
+private:
+    CSSFontFeatureValuesMap(JS::Realm&, size_t max_value_count);
+
+    virtual void initialize(JS::Realm&) override;
+    virtual void visit_edges(Cell::Visitor&) override;
+
+    GC::Ref<JS::Map> m_map_entries;
+    size_t m_max_value_count;
+};
+
+}

Libraries/LibWeb/CSS/CSSFontFeatureValuesMap.idl

@@ -0,0 +1,5 @@
+[Exposed=Window]
+interface CSSFontFeatureValuesMap {
+    maplike<CSSOMString, sequence<unsigned long>>;
+    undefined set(CSSOMString featureValueName, (unsigned long or sequence<unsigned long>) values);
+};

Libraries/LibWeb/Forward.h

@@ -246,6 +246,7 @@ class CSSCounterStyleRule;
 class CSSDescriptors;
 class CSSFontFaceDescriptors;
 class CSSFontFaceRule;
+class CSSFontFeatureValuesMap;
 class CSSGroupingRule;
 class CSSImageValue;
 class CSSImportRule;

Libraries/LibWeb/idl_files.cmake

@@ -29,6 +29,7 @@ libweb_js_bindings(CSS/CSSConditionRule)
 libweb_js_bindings(CSS/CSSCounterStyleRule)
 libweb_js_bindings(CSS/CSSFontFaceDescriptors)
 libweb_js_bindings(CSS/CSSFontFaceRule)
+libweb_js_bindings(CSS/CSSFontFeatureValuesMap)
 libweb_js_bindings(CSS/CSSGroupingRule)
 libweb_js_bindings(CSS/CSSImageValue)
 libweb_js_bindings(CSS/CSSImportRule)

Tests/LibWeb/Text/expected/all-window-properties.txt

@@ -41,6 +41,7 @@ CSSConditionRule
 CSSCounterStyleRule
 CSSFontFaceDescriptors
 CSSFontFaceRule
+CSSFontFeatureValuesMap
 CSSGroupingRule
 CSSImageValue
 CSSImportRule

Tests/LibWeb/Text/expected/wpt-import/css/css-fonts/idlharness.txt

@@ -2,8 +2,8 @@ Harness status: OK
 
 Found 97 tests
 
-48 Pass
-49 Fail
+56 Pass
+41 Fail
 Pass	idl_test setup
 Pass	idl_test validation
 Pass	Partial interface CSSRule: original interface defined
@@ -80,14 +80,14 @@ Fail	CSSFontFeatureValuesRule interface: attribute swash
 Fail	CSSFontFeatureValuesRule interface: attribute characterVariant
 Fail	CSSFontFeatureValuesRule interface: attribute styleset
 Fail	CSSFontFeatureValuesRule interface: attribute historicalForms
-Fail	CSSFontFeatureValuesMap interface: existence and properties of interface object
-Fail	CSSFontFeatureValuesMap interface object length
-Fail	CSSFontFeatureValuesMap interface object name
-Fail	CSSFontFeatureValuesMap interface: existence and properties of interface prototype object
-Fail	CSSFontFeatureValuesMap interface: existence and properties of interface prototype object's "constructor" property
-Fail	CSSFontFeatureValuesMap interface: existence and properties of interface prototype object's @@unscopables property
-Fail	CSSFontFeatureValuesMap interface: maplike<CSSOMString, [object Object]>
-Fail	CSSFontFeatureValuesMap interface: operation set(CSSOMString, (unsigned long or sequence<unsigned long>))
+Pass	CSSFontFeatureValuesMap interface: existence and properties of interface object
+Pass	CSSFontFeatureValuesMap interface object length
+Pass	CSSFontFeatureValuesMap interface object name
+Pass	CSSFontFeatureValuesMap interface: existence and properties of interface prototype object
+Pass	CSSFontFeatureValuesMap interface: existence and properties of interface prototype object's "constructor" property
+Pass	CSSFontFeatureValuesMap interface: existence and properties of interface prototype object's @@unscopables property
+Pass	CSSFontFeatureValuesMap interface: maplike<CSSOMString, [object Object]>
+Pass	CSSFontFeatureValuesMap interface: operation set(CSSOMString, (unsigned long or sequence<unsigned long>))
 Fail	CSSFontPaletteValuesRule interface: existence and properties of interface object
 Fail	CSSFontPaletteValuesRule interface object length
 Fail	CSSFontPaletteValuesRule interface object name