Make _Unbound special in all loaded built-in modules

Author: tekknolagi

runtime/bytecode.cpp

@@ -340,7 +340,7 @@ void rewriteBytecode(Thread* thread, const Function& function) {
   RawObject module = function.moduleObject();
   bool is_builtin_module =
       module.isModule() &&
-      Module::cast(module).id() == thread->runtime()->builtinsModuleId();
+      Module::cast(module).id() <= runtime->lastBuiltinModuleId();
   for (word i = 0; i < num_opcodes;) {
     BytecodeOp op = nextBytecodeOp(bytecode, &i);
     word previous_index = i - 1;

runtime/runtime.cpp

@@ -2185,6 +2185,10 @@ void Runtime::initializeModules(Thread* thread) {
           "failed to initialize built-in module %s",
           Symbols::predefinedSymbolAt(id));
   }
+  last_builtin_module_id_ =
+      Module::cast(
+          findModuleById(kRequiredModules[ARRAYSIZE(kRequiredModules) - 1]))
+          .id();
 }
 
 RawObject Runtime::initialize(Thread* thread) {

runtime/runtime.h

@@ -297,6 +297,8 @@ class Runtime {
     builtins_module_id_ = builtins_module_id;
   }
 
+  word lastBuiltinModuleId() { return last_builtin_module_id_; }
+
   RawObject moduleDunderGetattribute() { return module_dunder_getattribute_; }
   RawObject objectDunderClass() { return object_dunder_class_; }
   RawObject objectDunderEq() { return object_dunder_eq_; }
@@ -954,6 +956,9 @@ class Runtime {
   // The ID of builtins module.
   // TODO(T64005113): Remove this once we mark individual functions.
   word builtins_module_id_ = -1;
+  // The ID of the last built-in module initialized by the runtime. Used to
+  // give special properties to built-in modules.
+  word last_builtin_module_id_ = -1;
 
   // Internal-only types, for which the Layout has a different described type
   RawObject large_bytes_ = NoneType::object();