LibWeb: Add CSS.escape() JS function

This is the `CSS` namespace defined in IDL here:
https://www.w3.org/TR/cssom-1/#namespacedef-css , not to be confused
with our `Web::CSS` namespace. Words are hard.

`CSS.escape()` lets you escape identifiers that can then be used to
create a CSS string.

I've also stubbed out the `CSS.supports()` function.

Userland/Libraries/LibWeb/Bindings/CSSNamespace.cpp

@@ -0,0 +1,75 @@
+/*
+ * Copyright (c) 2021, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Runtime/ErrorTypes.h>
+#include <LibJS/Runtime/GlobalObject.h>
+#include <LibJS/Runtime/VM.h>
+#include <LibJS/Runtime/Value.h>
+#include <LibWeb/Bindings/CSSNamespace.h>
+
+namespace Web::Bindings {
+
+CSSNamespace::CSSNamespace(JS::GlobalObject& global_object)
+    : JS::Object(*global_object.object_prototype())
+{
+}
+
+CSSNamespace::~CSSNamespace()
+{
+}
+
+void CSSNamespace::initialize(JS::GlobalObject& global_object)
+{
+    Object::initialize(global_object);
+    u8 attr = JS::Attribute::Enumerable;
+    define_native_function("escape", escape, 1, attr);
+    define_native_function("supports", supports, 2, attr);
+}
+
+// https://www.w3.org/TR/cssom-1/#dom-css-escape
+JS_DEFINE_NATIVE_FUNCTION(CSSNamespace::escape)
+{
+    if (!vm.argument_count()) {
+        vm.throw_exception<JS::TypeError>(global_object, JS::ErrorType::BadArgCountAtLeastOne, "CSS.escape");
+        return {};
+    }
+
+    String result = Web::CSS::serialize_an_identifier(vm.argument(0).to_string(global_object));
+    if (vm.exception())
+        return {};
+
+    return JS::Value(JS::js_string(vm, result));
+}
+
+// https://www.w3.org/TR/css-conditional-3/#dom-css-supports
+JS_DEFINE_NATIVE_FUNCTION(CSSNamespace::supports)
+{
+    if (!vm.argument_count()) {
+        vm.throw_exception<JS::TypeError>(global_object, JS::ErrorType::BadArgCountAtLeastOne, "CSS.supports");
+        return {};
+    }
+
+    if (vm.argument_count() >= 2) {
+        // When the supports(property, value) method is invoked with two arguments property and value:
+        //     If property is an ASCII case-insensitive match for any defined CSS property that the UA supports, and value successfully parses according to that property’s grammar, return true.
+        //
+        //     Otherwise, if property is a custom property name string, return true.
+        //
+        //     Otherwise, return false.
+        return JS::Value(false);
+    } else {
+        // When the supports(conditionText) method is invoked with a single conditionText argument:
+        //
+        //    If conditionText, parsed and evaluated as a <supports-condition>, would return true, return true.
+        //
+        //    Otherwise, If conditionText, wrapped in parentheses and then parsed and evaluated as a <supports-condition>, would return true, return true.
+        //
+        //    Otherwise, return false.
+        return JS::Value(false);
+    }
+}
+
+}

Userland/Libraries/LibWeb/Bindings/CSSNamespace.h

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2021, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibJS/Runtime/Object.h>
+#include <LibWeb/CSS/Serialize.h>
+
+namespace Web::Bindings {
+
+// The `CSS` namespace object in IDL. https://www.w3.org/TR/cssom-1/#namespacedef-css
+class CSSNamespace final : public JS::Object {
+    JS_OBJECT(CSSNamespace, JS::Object)
+
+public:
+    explicit CSSNamespace(JS::GlobalObject&);
+    virtual void initialize(JS::GlobalObject&) override;
+    virtual ~CSSNamespace() override;
+
+private:
+    JS_DECLARE_NATIVE_FUNCTION(escape);
+    JS_DECLARE_NATIVE_FUNCTION(supports);
+};
+
+}

Userland/Libraries/LibWeb/Bindings/WindowObject.cpp

@@ -13,6 +13,7 @@
 #include <LibJS/Runtime/FunctionObject.h>
 #include <LibJS/Runtime/Shape.h>
 #include <LibTextCodec/Decoder.h>
+#include <LibWeb/Bindings/CSSNamespace.h>
 #include <LibWeb/Bindings/CSSStyleDeclarationWrapper.h>
 #include <LibWeb/Bindings/CryptoWrapper.h>
 #include <LibWeb/Bindings/DocumentWrapper.h>
@@ -104,6 +105,8 @@ void WindowObject::initialize_global_object()
     define_native_accessor("screenLeft", screen_left_getter, {}, attr);
     define_native_accessor("screenTop", screen_top_getter, {}, attr);
 
+    define_direct_property("CSS", heap().allocate<CSSNamespace>(*this, *this), 0);
+
     // Legacy
     define_native_accessor("event", event_getter, event_setter, JS::Attribute::Enumerable);
 

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -1,4 +1,5 @@
 set(SOURCES
+    Bindings/CSSNamespace.cpp
     Bindings/CSSRuleWrapperFactory.cpp
     Bindings/CSSStyleDeclarationWrapperCustom.cpp
     Bindings/EventListenerWrapper.cpp
@@ -14,6 +15,7 @@ set(SOURCES
     Bindings/WindowObject.cpp
     Bindings/Wrappable.cpp
     Crypto/Crypto.cpp
+    CSS/Serialize.cpp
     CSS/CSSConditionRule.cpp
     CSS/CSSGroupingRule.cpp
     CSS/CSSImportRule.cpp

Userland/Libraries/LibWeb/CSS/Serialize.cpp

@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2021, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/StringBuilder.h>
+#include <AK/Utf8View.h>
+#include <LibWeb/CSS/Serialize.h>
+
+namespace Web::CSS {
+
+// https://www.w3.org/TR/cssom-1/#escape-a-character
+String escape_a_character(u32 character)
+{
+    StringBuilder builder;
+    builder.append('\\');
+    builder.append_code_point(character);
+    return builder.to_string();
+}
+
+// https://www.w3.org/TR/cssom-1/#escape-a-character-as-code-point
+String escape_a_character_as_code_point(u32 character)
+{
+    return String::formatted("\\{:x} ", character);
+}
+
+// https://www.w3.org/TR/cssom-1/#serialize-an-identifier
+String serialize_an_identifier(StringView const& ident)
+{
+    StringBuilder builder;
+    Utf8View characters { ident };
+    auto first_character = characters.is_empty() ? 0 : *characters.begin();
+
+    // To serialize an identifier means to create a string represented by the concatenation of,
+    // for each character of the identifier:
+    for (auto character : characters) {
+        // If the character is NULL (U+0000), then the REPLACEMENT CHARACTER (U+FFFD).
+        if (character == 0) {
+            builder.append_code_point(0xFFFD);
+            continue;
+        }
+        // If the character is in the range [\1-\1f] (U+0001 to U+001F) or is U+007F,
+        // then the character escaped as code point.
+        if ((character >= 0x0001 && character <= 0x001F) || (character == 0x007F)) {
+            builder.append(escape_a_character_as_code_point(character));
+            continue;
+        }
+        // If the character is the first character and is in the range [0-9] (U+0030 to U+0039),
+        // then the character escaped as code point.
+        if (builder.is_empty() && character >= '0' && character <= '9') {
+            builder.append(escape_a_character_as_code_point(character));
+            continue;
+        }
+        // If the character is the second character and is in the range [0-9] (U+0030 to U+0039)
+        // and the first character is a "-" (U+002D), then the character escaped as code point.
+        if (builder.length() == 1 && first_character == '-' && character >= '0' && character <= '9') {
+            builder.append(escape_a_character_as_code_point(character));
+            continue;
+        }
+        // If the character is the first character and is a "-" (U+002D), and there is no second
+        // character, then the escaped character.
+        if (builder.is_empty() && character == '-' && characters.length() == 1) {
+            builder.append(escape_a_character(character));
+            continue;
+        }
+        // If the character is not handled by one of the above rules and is greater than or equal to U+0080, is "-" (U+002D) or "_" (U+005F), or is in one of the ranges [0-9] (U+0030 to U+0039), [A-Z] (U+0041 to U+005A), or \[a-z] (U+0061 to U+007A), then the character itself.
+        if ((character >= 0x0080)
+            || (character == '-') || (character == '_')
+            || (character >= '0' && character <= '9')
+            || (character >= 'A' && character <= 'Z')
+            || (character >= 'a' && character <= 'z')) {
+            builder.append_code_point(character);
+            continue;
+        }
+        // Otherwise, the escaped character.
+        builder.append(escape_a_character(character));
+    }
+    return builder.to_string();
+}
+
+}

Userland/Libraries/LibWeb/CSS/Serialize.h

@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2021, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/String.h>
+#include <AK/StringView.h>
+
+namespace Web::CSS {
+
+String escape_a_character(u32 character);
+String escape_a_character_as_code_point(u32 character);
+
+String serialize_an_identifier(StringView const& ident);
+
+}