IdMappingEvent can't be posted successfully

[zomb-676]

Minecraft Version: 1.21.4

NeoForge Version: 21.4.91-beta

changelog here https://neoforged.net/changelog/ don't show information that may have fixed this

Steps to Reproduce:
subscribe the IdMappingEvent(on forge bus)

Description of issue:
The IdMappingEvent can't be posted successfully, the reason is as follows

The forge bus is an EventBus that is shutdown when created
as startShutdown is called

NeoForge/src/main/java/net/neoforged/neoforge/common/NeoForge.java

Lines 12 to 22 in f1d3f70

	public class NeoForge {
	/**
	* The NeoForge event bus, used for most events.
	* Also known as the "game" bus.
	*/
	public static final IEventBus EVENT_BUS = BusBuilder.builder().startShutdown().classChecker(eventType -> {
	if (IModBusEvent.class.isAssignableFrom(eventType)) {
	throw new IllegalArgumentException("IModBusEvent events are not allowed on the common NeoForge bus! Use a mod bus instead.");
	}
	}).build();
	}

the bus is enabled at this place
it is too late for IdMappingEvent, as here we have almost complete mod loading and are collecting ModLoadingIssue

NeoForge/src/main/java/net/neoforged/neoforge/client/loading/ClientModLoader.java

Lines 110 to 128 in f1d3f70

	public static Runnable completeModLoading(Runnable initialScreensTask) {
	List<ModLoadingIssue> warnings = ModLoader.getLoadingIssues();
	boolean showWarnings = true;
	try {
	showWarnings = NeoForgeConfig.CLIENT.showLoadWarnings.get();
	} catch (NullPointerException | IllegalStateException e) {
	// We're in an early error state, config is not available. Assume true.
	}
	if (error != null) {
	// Double check we have the langs loaded for forge
	LanguageHook.loadBuiltinLanguages();
	File dumpedLocation = CrashReportExtender.dumpModLoadingCrashReport(LOGGER, error.getIssues(), mc.gameDirectory);
	// Ignore incoming initial screens task, the subsequent screens are unreachable in an error state
	return () -> mc.setScreen(new LoadingErrorScreen(error.getIssues(), dumpedLocation, () -> {}));
	}
	// We can finally start the game eventbus up
	NeoForge.EVENT_BUS.start();

but the event IdMappingEvent is fired at this place, where the freezeData is called
where the mod loading Message is still REGISTERING, the bus still shutdown and haven't be started

NeoForge/src/main/java/net/neoforged/neoforge/internal/CommonModLoader.java

Lines 46 to 55 in f1d3f70

	protected static void begin(Runnable periodicTask, boolean datagen) {
	var syncExecutor = ModWorkManager.syncExecutor();
	ModLoader.gatherAndInitializeMods(syncExecutor, ModWorkManager.parallelExecutor(), periodicTask);
	ModLoader.runInitTask("Registry initialization", syncExecutor, periodicTask, () -> {
	RegistryManager.postNewRegistryEvent();
	GameData.unfreezeData();
	GameData.postRegisterEvents();
	GameData.freezeData();

[Technici4n]

As far as I can tell, this event is quite useless. It is fired a single time right after registries are frozen, and with no remaps. We should probably remove it in 1.21.5?

[marchermans]

As far as I can tell, this event is quite useless. It is fired a single time right after registries are frozen, and with no remaps. We should probably remove it in 1.21.5?

This is an amazingly usefull event during porting and migrations!
If this event is broken we have a problem. Its main purpose is to allow modders to migrate registry values from one key to another, kind of like aliases.

Do we have any kind of alternative for this system?

[Technici4n]

The alternative is to use aliases. 😛 Known registry entries are not saved to disk anymore since the registry rework, so I don't see how this event could possibly work.

[zomb-676]

I noticed this event because I wanted to do something after completing all the registries.
Perhaps this event should be renamed into a better name.

I just noticed that MissingMappingsEvent has disappeared, so is that event replaced by DeferredRegister#addAlias?

[Technici4n]

I noticed this event because I wanted to do something after completing all the registries. Perhaps this event should be renamed into a better name.

Have you tried FMLCommonSetupEvent?

I just noticed that MissingMappingsEvent has disappeared, so is that event replaced by DeferredRegister#addAlias?

Yes