Tests: Replace load-reference-page debug action with internals method

WPT reference tests can add metadata to tests to instruct the test
runner how to interpret the results. Because of this, it is not enough
to have an action that starts loading the (mis)match reference: we need
the test runner to receive the metadata so it can act accordingly.

This sets our test runner up for potentially supporting multiple
(mis)match references, and fuzzy rendering matches - the latter will be
implemented in the following commit.

Libraries/LibWeb/Internals/Internals.cpp

@@ -1,9 +1,11 @@
 /*
  * Copyright (c) 2023, Andreas Kling <andreas@ladybird.org>
+ * Copyright (c) 2025, Jelle Raaijmakers <jelle@ladybird.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/JsonObject.h>
 #include <LibJS/Runtime/Date.h>
 #include <LibJS/Runtime/VM.h>
 #include <LibUnicode/TimeZone.h>
@@ -12,6 +14,7 @@
 #include <LibWeb/DOM/Document.h>
 #include <LibWeb/DOM/Event.h>
 #include <LibWeb/DOM/EventTarget.h>
+#include <LibWeb/DOM/NodeList.h>
 #include <LibWeb/DOMURL/DOMURL.h>
 #include <LibWeb/HTML/HTMLElement.h>
 #include <LibWeb/HTML/Window.h>
@@ -19,7 +22,6 @@
 #include <LibWeb/Page/InputEvent.h>
 #include <LibWeb/Page/Page.h>
 #include <LibWeb/Painting/PaintableBox.h>
-#include <LibWeb/Painting/ViewportPaintable.h>
 
 namespace Web::Internals {
 
@@ -50,6 +52,39 @@ void Internals::set_test_timeout(double milliseconds)
     page().client().page_did_set_test_timeout(milliseconds);
 }
 
+// https://web-platform-tests.org/writing-tests/reftests.html#components-of-a-reftest
+WebIDL::ExceptionOr<void> Internals::load_reference_test_metadata()
+{
+    auto& vm = this->vm();
+    auto& page = this->page();
+
+    auto* document = page.top_level_browsing_context().active_document();
+    if (!document)
+        return vm.throw_completion<JS::InternalError>("No active document available"sv);
+
+    JsonObject metadata;
+
+    // Collect all <link rel="match"> and <link rel="mismatch"> references.
+    auto collect_references = [&vm, &document](StringView type) -> WebIDL::ExceptionOr<JsonArray> {
+        JsonArray references;
+        auto reference_nodes = TRY(document->query_selector_all(MUST(String::formatted("link[rel={}]", type))));
+        for (size_t i = 0; i < reference_nodes->length(); ++i) {
+            auto const* reference_node = reference_nodes->item(i);
+            auto href = as<DOM::Element>(reference_node)->get_attribute_value(HTML::AttributeNames::href);
+            auto url = document->encoding_parse_url(href);
+            if (!url.has_value())
+                return vm.throw_completion<JS::InternalError>(MUST(String::formatted("Failed to construct URL for '{}'", href)));
+            references.must_append(url->to_string());
+        }
+        return references;
+    };
+    metadata.set("match_references"sv, TRY(collect_references("match"sv)));
+    metadata.set("mismatch_references"sv, TRY(collect_references("mismatch"sv)));
+
+    page.client().page_did_receive_reference_test_metadata(metadata);
+    return {};
+}
+
 void Internals::gc()
 {
     vm().heap().collect_garbage();

Libraries/LibWeb/Internals/Internals.h

@@ -22,6 +22,7 @@ public:
 
     void signal_test_is_done(String const& text);
     void set_test_timeout(double milliseconds);
+    WebIDL::ExceptionOr<void> load_reference_test_metadata();
 
     WebIDL::ExceptionOr<String> set_time_zone(StringView time_zone);
 

Libraries/LibWeb/Internals/Internals.idl

@@ -7,6 +7,7 @@ interface Internals {
 
     undefined signalTestIsDone(DOMString text);
     undefined setTestTimeout(double milliseconds);
+    undefined loadReferenceTestMetadata();
 
     DOMString setTimeZone(DOMString timeZone);