LibWeb: Make <script src> loads partially async (by following the spec)

Instead of firing up a network request and synchronously blocking for it
to finish via a nested event loop, we now start an asynchronous request
when encountering <script src>.

Once the script load finishes (or fails), it gets executed at one of the
synchronization points in the HTML parser.

This solves some long-standing issues with random unexpected events
getting dispatched in the middle of parsing.

1 files changed, 8 insertions, 7 deletions

diff --git a/Userland/Libraries/LibWeb/HTML/Parser/HTMLDocumentParser.cpp b/Userland/Libraries/LibWeb/HTML/Parser/HTMLDocumentParser.cpp
index 88e4493257..6503eaaf49 100644
--- a/Userland/Libraries/LibWeb/HTML/Parser/HTMLDocumentParser.cpp
+++ b/Userland/Libraries/LibWeb/HTML/Parser/HTMLDocumentParser.cpp
@@ -184,8 +184,11 @@ void HTMLDocumentParser::run(const AK::URL& url)
         m_stack_of_open_elements.pop();
 
     auto scripts_to_execute_when_parsing_has_finished = m_document->take_scripts_to_execute_when_parsing_has_finished({});
+
     for (auto& script : scripts_to_execute_when_parsing_has_finished) {
-        // FIXME: Spin the event loop until the script is ready to be parser executed and there's no style sheets blocking scripts.
+        main_thread_event_loop().spin_until([&] {
+            return script.is_ready_to_be_parser_executed() && !document().has_a_style_sheet_that_is_blocking_scripts();
+        });
         script.execute_script();
     }
 
@@ -193,12 +196,10 @@ void HTMLDocumentParser::run(const AK::URL& url)
     content_loaded_event->set_bubbles(true);
     m_document->dispatch_event(content_loaded_event);
 
-    // FIXME: The document parser shouldn't execute these, it should just spin the event loop until the list becomes empty.
-    // FIXME: Once the set has been added, also spin the event loop until the set becomes empty.
-    auto scripts_to_execute_as_soon_as_possible = m_document->take_scripts_to_execute_as_soon_as_possible({});
-    for (auto& script : scripts_to_execute_as_soon_as_possible) {
-        script.execute_script();
-    }
+    // 7. Spin the event loop until the set of scripts that will execute as soon as possible and the list of scripts that will execute in order as soon as possible are empty.
+    main_thread_event_loop().spin_until([&] {
+        return m_document->scripts_to_execute_as_soon_as_possible().is_empty();
+    });
 
     // FIXME: Spin the event loop until there is nothing that delays the load event in the Document.