LibJS+js+test-js: Add GC debug mode that keeps cells "alive" as zombies

This patch adds a `-z` option to js and test-js. When run in this mode,
garbage cells are never actually destroyed. We instead keep them around
in a special zombie state.

This allows us to validate that zombies don't get marked in future GC
scans (since there were not supposed to be any more references!) :^)

Cells get notified when they become a zombie (via did_become_zombie())
and this is used by WeakContainer cells to deregister themselves from
the heap.

1 files changed, 4 insertions, 0 deletions

diff --git a/Userland/Utilities/js.cpp b/Userland/Utilities/js.cpp
index 0e152b7e08..25dd94ef7b 100644
--- a/Userland/Utilities/js.cpp
+++ b/Userland/Utilities/js.cpp
@@ -1079,6 +1079,7 @@ public:
 int main(int argc, char** argv)
 {
     bool gc_on_every_allocation = false;
+    bool zombify_dead_cells = false;
     bool disable_syntax_highlight = false;
     Vector<String> script_paths;
 
@@ -1091,6 +1092,7 @@ int main(int argc, char** argv)
     args_parser.add_option(s_as_module, "Treat as module", "as-module", 'm');
     args_parser.add_option(s_print_last_result, "Print last result", "print-last-result", 'l');
     args_parser.add_option(gc_on_every_allocation, "GC on every allocation", "gc-on-every-allocation", 'g');
+    args_parser.add_option(zombify_dead_cells, "Zombify dead cells (to catch missing GC marks)", "zombify-dead-cells", 'z');
     args_parser.add_option(disable_syntax_highlight, "Disable live syntax highlighting", "no-syntax-highlight", 's');
     args_parser.add_positional_argument(script_paths, "Path to script files", "scripts", Core::ArgsParser::Required::No);
     args_parser.parse(argc, argv);
@@ -1131,6 +1133,7 @@ int main(int argc, char** argv)
         ReplConsoleClient console_client(interpreter->global_object().console());
         interpreter->global_object().console().set_client(console_client);
         interpreter->heap().set_should_collect_on_every_allocation(gc_on_every_allocation);
+        interpreter->heap().set_zombify_dead_cells(zombify_dead_cells);
         interpreter->vm().set_underscore_is_last_value(true);
 
         s_editor = Line::Editor::construct();
@@ -1334,6 +1337,7 @@ int main(int argc, char** argv)
         ReplConsoleClient console_client(interpreter->global_object().console());
         interpreter->global_object().console().set_client(console_client);
         interpreter->heap().set_should_collect_on_every_allocation(gc_on_every_allocation);
+        interpreter->heap().set_zombify_dead_cells(zombify_dead_cells);
 
         signal(SIGINT, [](int) {
             sigint_handler();