LibJS+Clients: Add JS::VM object, separate Heap from Interpreter

Taking a big step towards a world of multiple global object, this patch
adds a new JS::VM object that houses the JS::Heap.

This means that the Heap moves out of Interpreter, and the same Heap
can now be used by multiple Interpreters, and can also outlive them.

The VM keeps a stack of Interpreter pointers. We push/pop on this
stack when entering/exiting execution with a given Interpreter.
This allows us to make this change without disturbing too much of
the existing code.

There is still a 1-to-1 relationship between Interpreter and the
global object. This will change in the future.

Ultimately, the goal here is to make Interpreter a transient object
that only needs to exist while you execute some code. Getting there
will take a lot more work though. :^)

Note that in LibWeb, the global JS::VM is called main_thread_vm(),
to distinguish it from future worker VM's.

1 files changed, 3 insertions, 2 deletions

diff --git a/Userland/js.cpp b/Userland/js.cpp
index f08b336184..08271c95d6 100644
--- a/Userland/js.cpp
+++ b/Userland/js.cpp
@@ -552,6 +552,7 @@ int main(int argc, char** argv)
 
     bool syntax_highlight = !disable_syntax_highlight;
 
+    auto vm = JS::VM::create();
     OwnPtr<JS::Interpreter> interpreter;
 
     interrupt_interpreter = [&] {
@@ -561,7 +562,7 @@ int main(int argc, char** argv)
 
     if (script_path == nullptr) {
         s_print_last_result = true;
-        interpreter = JS::Interpreter::create<ReplObject>();
+        interpreter = JS::Interpreter::create<ReplObject>(*vm);
         ReplConsoleClient console_client(interpreter->console());
         interpreter->console().set_client(console_client);
         interpreter->heap().set_should_collect_on_every_allocation(gc_on_every_allocation);
@@ -842,7 +843,7 @@ int main(int argc, char** argv)
         s_editor->on_tab_complete = move(complete);
         repl(*interpreter);
     } else {
-        interpreter = JS::Interpreter::create<JS::GlobalObject>();
+        interpreter = JS::Interpreter::create<JS::GlobalObject>(*vm);
         ReplConsoleClient console_client(interpreter->console());
         interpreter->console().set_client(console_client);
         interpreter->heap().set_should_collect_on_every_allocation(gc_on_every_allocation);