Readd JS API function Engine.Exit()

Requested in #8244 for scripting purposes and automated testing. Extend
the original design by adding a means to pass an exit status. This also
comes in handy in case one wants to cleanly error out from JS on parsing
errors of command line arguments as reported in #7967.

Fixes: #8244
Signed-off-by: Ralph Sennhauser <ralph.sennhauser@gmail.com>

source/main.cpp

@@ -165,6 +165,7 @@ enum ShutdownType
 };
 
 static ShutdownType g_Shutdown = ShutdownType::None;
+static int g_ExitStatus{EXIT_SUCCESS};
 
 // to avoid redundant and/or recursive resizing, we save the new
 // size after VIDEORESIZE messages and only update the video mode
@@ -181,9 +182,10 @@ bool IsQuitRequested()
 	return g_Shutdown == ShutdownType::Quit;
 }
 
-void QuitEngine()
+void QuitEngine(int exitStatus)
 {
 	g_Shutdown = ShutdownType::Quit;
+	g_ExitStatus = exitStatus;
 }
 
 void RestartEngine()
@@ -209,7 +211,7 @@ static InReaction MainInputHandler(const SDL_Event_* ev)
 		break;
 
 	case SDL_QUIT:
-		QuitEngine();
+		QuitEngine(EXIT_SUCCESS);
 		break;
 
 	case SDL_DROPFILE:
@@ -235,7 +237,7 @@ static InReaction MainInputHandler(const SDL_Event_* ev)
 		std::string hotkey = static_cast<const char*>(ev->ev.user.data1);
 		if (hotkey == "exit")
 		{
-			QuitEngine();
+			QuitEngine(EXIT_SUCCESS);
 			return IN_HANDLED;
 		}
 		else if (hotkey == "screenshot")
@@ -512,7 +514,7 @@ static void NonVisualFrame()
 	g_Profiler.Frame();
 
 	if (g_Game->IsGameFinished())
-		QuitEngine();
+		QuitEngine(EXIT_SUCCESS);
 }
 
 static void MainControllerInit()
@@ -832,7 +834,6 @@ int main(int argc, char* argv[])
 
 	EarlyInit();	// must come at beginning of main
 
-	int returnValue{EXIT_SUCCESS};
 	try
 	{
 		// static_cast is ok, argc is never negative.
@@ -840,7 +841,7 @@ int main(int argc, char* argv[])
 	}
 	catch (const RL::SetupError&)
 	{
-		returnValue = EXIT_FAILURE;
+		g_ExitStatus = EXIT_FAILURE;
 	}
 
 	// Shut down profiler initialised by EarlyInit
@@ -854,5 +855,5 @@ int main(int argc, char* argv[])
 	wutil_Shutdown();
 #endif
 
-	return returnValue;
+	return g_ExitStatus;
 }