fix #445: Create undefined monitor variables and lists

Author: adazem009

src/engine/internal/engine.cpp

@@ -161,10 +161,23 @@ void Engine::resolveIds()
             }
 
             // TODO: Move field information out of Engine
-            if (field->name() == "VARIABLE")
-                field->setValuePtr(target->variableAt(target->findVariable(field->value().toString())));
-            else if (field->name() == "LIST")
-                field->setValuePtr(target->listAt(target->findList(field->value().toString())));
+            if (field->name() == "VARIABLE") {
+                std::string name = field->value().toString();
+                int index = target->findVariable(name);
+
+                if (index == -1)
+                    index = target->addVariable(std::make_shared<Variable>(monitor->id(), name));
+
+                field->setValuePtr(target->variableAt(index));
+            } else if (field->name() == "LIST") {
+                std::string name = field->value().toString();
+                int index = target->findList(name);
+
+                if (index == -1)
+                    index = target->addList(std::make_shared<List>(monitor->id(), name));
+
+                field->setValuePtr(target->listAt(index));
+            }
         }
 
         block->updateInputMap();

test/engine/engine_test.cpp

@@ -1702,3 +1702,27 @@ TEST(EngineTest, StopBeforeStarting)
     ASSERT_VAR(stage, "test");
     ASSERT_TRUE(GET_VAR(stage, "test")->value().toBool());
 }
+
+TEST(EngineTest, NoCrashWhenLoadingUndefinedVariableOrListMonitor)
+{
+    // Regtest for #445
+    Project p("regtest_projects/445_undefined_variable_or_list_monitor_crash.sb3");
+    ASSERT_TRUE(p.load());
+
+    auto engine = p.engine();
+
+    // The undefined variable and list should now be defined
+    Stage *stage = engine->stage();
+    ASSERT_TRUE(stage);
+    ASSERT_VAR(stage, "test");
+    auto var = GET_VAR(stage, "test");
+    ASSERT_EQ(var->id(), "E,r`5qYWCdXa~yj7nDS]");
+    ASSERT_EQ(var->value(), Value());
+
+    Target *sprite = engine->targetAt(engine->findTarget("Sprite1"));
+    ASSERT_TRUE(sprite);
+    ASSERT_LIST(sprite, "test");
+    auto list = GET_LIST(sprite, "test");
+    ASSERT_EQ(list->id(), "7a5rAs|X2_[1APT7@B1V");
+    ASSERT_TRUE(list->empty());
+}