lack of partial signature remapping

[tildejustin]

In prior versions of loom, or withuseLegacyMixinAp = true, signatures which did not exist in the minecraft version being compiled against could still be written partially with named, partially with intermediary mappings. Example:
https://github.com/RedLime/SleepBackground/blob/31fcebfba49dd36d9edfa2d53981febcbcecaef8/src/main/java/com/redlimerl/sleepbackground/mixin/MixinMinecraftClient.java#L41-L43. With useLegacyMixinAp = false, one has to manually remap the entire signature if it does not exist in the compile target jar, since the named parts of the signature are not remapped (I verified this with vineflower).

[nelind3]

This seems to also affect targets that have a method that shouldn't be remapped on a class that should. For example I ran into a problem using the mixin extension to remap a mixin that looks like this:

package com.example.mixin;

import net.minecraft.nbt.NbtList;
import net.minecraft.world.tick.ChunkTickScheduler;
import org.spongepowered.asm.mixin.Mixin;
import org.spongepowered.asm.mixin.injection.At;
import org.spongepowered.asm.mixin.injection.Inject;
import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;

import java.util.function.Function;

@Mixin(ChunkTickScheduler.class)
public class ChunkTickSchedulerMixin {
	@Inject(
		method = "toNbt",
		at = @At(
			value = "INVOKE",
			target = "Lnet/minecraft/nbt/NbtList;add(Ljava/lang/Object;)Z"
		)
	)
	private void notProperlyRemapped(long time, Function<Object, String> typeToNameFunction, CallbackInfoReturnable<NbtList> cir) {
		// The target descriptor in the @At is not properly remapped and this @Inject fails outside dev
	}
}

The target descriptor won't get remapped properly. A fernflower decompilation of the remapped .class file looks like this

package com.example.mixin;

import java.util.function.Function;
import net.minecraft.class_6755;
import org.spongepowered.asm.mixin.Mixin;
import org.spongepowered.asm.mixin.injection.At;
import org.spongepowered.asm.mixin.injection.Inject;
import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;

@Mixin({class_6755.class})
public class ChunkTickSchedulerMixin {
	@Inject(
		method = {"method_39365(JLjava/util/function/Function;)Lnet/minecraft/class_2499;"},
		at = {@At(
			value = "INVOKE",
			target = "Lnet/minecraft/nbt/NbtList;add(Ljava/lang/Object;)Z"
		)}
	)
	private void notProperlyRemapped(long time, Function typeToNameFunction, CallbackInfoReturnable cir) {
		
	}
}

Notice how the NbtList reference did not get remapped. I suspect that this happens because the boolean add(T) method on NbtList is declared higher up in the class hierarchy in the collections API and thus shouldn't be remapped and won't have and entry in the mappings file causing tiny remapper to "skip" the entire descriptor assuming that it doesn't need remapping. That's just a guess though. This seems to be related

To reproduce the bug I made a new loom project using fabric-example-mod, configured loom to use tiny remapper for remapping of mixins using useLegacyMixinAp = false in the build.gradle and made a mixin like the one shown above. Building the project and decompiling the result gave me the decompiled code shown above.