Using ModifyArgs causes a "ClassNotFoundException" under ModLauncher 9

[Speiger]

o/ so its offical too, I tried using ModifyArgs to replace values in a constructor.
While it was working on startup when the code changed started to be accessed it caused a "ClassNotFoundException"

java.lang.NoClassDefFoundError: org/spongepowered/asm/synthetic/args/Args$1
at net.minecraft.server.WorldLoader$PackConfig.createResourceManager(WorldLoader.java:44) ~[forge-1.19-41.0.30_mapped_official_1.19-recomp.jar%2390!/:?] {re:classloading}
at net.minecraft.server.WorldLoader.load(WorldLoader.java:20) ~[forge-1.19-41.0.30_mapped_official_1.19-recomp.jar%2390!/:?] {re:classloading}
at net.minecraft.client.gui.screens.worldselection.CreateWorldScreen.openFresh(CreateWorldScreen.java:116) ~[forge-1.19-41.0.30_mapped_official_1.19-recomp.jar%2390!/:?] {re:mixin,pl:runtimedistcleaner:A,re:classloading,pl:mixin:APP:chunkpregen.mixins.json:client.CreateNewWorldMixin,pl:mixin:A,pl:runtimedistcleaner:A}

Here is the mixin being used

@Mixin(MinecraftServer.class)
public class ServerSeedMixin
{
    @ModifyArgs(method = "createLevels", at = @At(value = "INVOKE", target = "Lnet/minecraft/server/level/ServerLevel;<init>", ordinal = 1))
    public void onWorldLoad(Args args)
    {
        System.out.println("Size="+args.size()+", Dimension="+args.get(4)+", Seed="+args.get(7));
    }
}

I am using the forge beta for 1.19 mappings should be visible through the crashlog.

[SizableShrimp]

This is a known bug with Forge 1.17+ and is not a bug with mixin

[Speiger]

yep fully aware (discord)

[LexManos]

Just to clarify, from what I understand this NOT a Forge bug. But more an issue with Mixin and JPMS. These synthetic accessor classes need to be in the module that they are mixing into. Instead of trying to be defined in Mixin's module. As that entire module does not go through transformers and thus can't have dynamic code. The other potential solution is to manually define the class in the correct classloader yourself. But it probably would just be easier to change the package.

[Speiger]

@LexManos might be the case or might be not the case, that is for you and @Mumfrey to figure out.
For me I already found a solution that works a lot better and does not have to deal with "Maybes or non maybes" of forge...

But my suggestion would be: Either implement a compiler warning that straight out disables that feature or actually fix the issue, whoever causes it.

[zml2008]

There's a solution long discussed and planned in McModLauncher/modlauncher#90, with a PR in McModLauncher/modlauncher#110 -it's already been figured out, just needs people to have time to review & implement. you're welcome to help out if you want things to improve.

[marchermans]

There's a solution long discussed and planned in McModLauncher/modlauncher#90, with a PR in McModLauncher/modlauncher#110 -it's already been figured out, just needs people to have time to review & implement. you're welcome to help out if you want things to improve.

Well this solves some of it, but Lexes argument still holds.
Mixin needs to generate it into the module namespace of the module it is targetting.
Even with that API you can't inject that org/spongepowered/asm/synthetic/args/ namespace into the Game layer in each module since that would violate JPMS

[Mumfrey]

The reason it generates the args classes in a central package instead of in the target package is that args classes are shared and aren't target-specific. For example an Args for two strings is just an args for 2 strings and if another mixin for a different class uses the same signature then the same Args class will be used instead of generating a new one.

If they need to be generated somewhere else then that's doable, but generating them in the same package as the first target doesn't make particular sense either.

Even with that API you can't inject that org/spongepowered/asm/synthetic/args/ namespace into the Game layer in each module since that would violate JPMS

I don't really get what you mean by this since JPMS doesn't know whether the classes are loaded off disk or generated at runtime. As far as I can see this should be a perfectly valid operation in JPMS-land like it was pre-JPMS.

[marchermans]

Even with that API you can't inject that org/spongepowered/asm/synthetic/args/ namespace into the Game layer in each module since that would violate JPMS

I don't really get what you mean by this since JPMS doesn't know whether the classes are loaded off disk or generated at runtime. As far as I can see this should be a perfectly valid operation in JPMS-land like it was pre-JPMS.

The problem is that two modules can not have classes in the same package. That violates JPMS.
You should pick a central package like: net/minecraft/mixin/asm/synthetic for example and target the minecraft module.

[Speiger]

You should pick a central package like: net/minecraft/mixin/asm/synthetic for example and target the minecraft module.

Yes that but not that package. It should be a package specific to that mod because the likelyhood of classes with anything else is to high. And that would make sense since the Class is loaded only if the mod is loaded anyways.
Best would be to move it actually into the class that has said mixins that causes it.

[Mumfrey]

The problem is that two modules can not have classes in the same package. That violates JPMS.

There are no other classes in that package, org.spongepowered.asm.synthetic is used purely for synthetic classes, so the classes can all be in one module.

You should pick a central package like: net/minecraft/mixin/asm/synthetic for example and target the minecraft module.

I don't get to pick the module, that part is handled by modlauncher.

It should be a package specific to that mod because the likelyhood of classes with anything else is to high. And that would make sense since the Class is loaded only if the mod is loaded anyways.

I already said this above, Args classes are not mod-specific, they are shared.

[marchermans]

You can not use your Mixin package, it is part of your Mixin module which is not loaded into the game layer but into the plugins layer.

If you want it to work no matter what with a single package, but ML basically requires you to pick something under net.minecraft.

You could inject a "helper" mod with its own root package and use that as package for it, but it as long as it gets loaded into the right layer.