[1.10] ForgeMappingsMerger.resolveConflicts throws UnsupportedOperationException for Forge 1.20.1

[Qendolin]

I have a stonecutter project with yarn mappings, you can find it here (note: I've removed forge 1.20.1 for now, see settings.gradle)
Today I updated from Loom 1.7 to 1.10 and can no longer load the Forge 1.20.1 project.
I get this error:

java.lang.UnsupportedOperationException
        at net.fabricmc.loom.util.srg.ForgeMappingsMerger.resolveConflicts(ForgeMappingsMerger.java:321)
        at net.fabricmc.loom.util.srg.ForgeMappingsMerger.merge(ForgeMappingsMerger.java:178)
        at net.fabricmc.loom.util.srg.ForgeMappingsMerger.mergeSrg(ForgeMappingsMerger.java:391)
        at net.fabricmc.loom.configuration.providers.forge.ForgeLibrariesProvider.remapObjectHolder(ForgeLibrariesProvider.java:220)
        at net.fabricmc.loom.configuration.providers.forge.ForgeLibrariesProvider.remapFmlLoader(ForgeLibrariesProvider.java:185)
        at net.fabricmc.loom.configuration.providers.forge.ForgeLibrariesProvider.provide(ForgeLibrariesProvider.java:135)
        at net.fabricmc.loom.configuration.CompileConfiguration.setupMinecraft(CompileConfiguration.java:234)
        at net.fabricmc.loom.configuration.CompileConfiguration.lambda$run$2(CompileConfiguration.java:130)

Full output:
https://paste.ee/p/ZtB21Cun

[Riflusso]

Same problem here D:

[cassiancc]

Same situation on my Stonecutter project.

[gniftygnome]

I wonder if this is related to the fix for Neoforge mapping conflicts...

[Kira-NT]

Yup, Loom >1.7 just doesn't work with Forge. And that's quite problematic, since Loom 1.7 doesn't support NeoForge 1.21.5 🙃

[meza]

I've used Loom 1.10 with forge 1.21.4 and below. It's only an issue with 1.21.5

[cassiancc]

What mappings? The issue reported here is focused on Yarn, and I can confirm 1.20.1 and 1.19.2 were crashing.

[gniftygnome]

Yesss I don't recall that far back but there was probably a reason I had stuck with Loom 1.7 all the way through 1.21.4...

[meza]

This is 1.9.424 for 1.20.2 and above: https://github.com/meza/ServerRedstoneBlock/blob/main/settings.gradle.kts

And I'm working with 1.10.430 right now in updating to 1.21.5. It's working perfectly aside from this issue with forge :D

And yes, I'm using Yarn

[cassiancc]

Strange, checking again and it's suddenly fixed itself for me. @Qendolin, is it still broken for your project?

[Qendolin]

Yes, it did. How is that possible😂? All shedaniel had to do was make this issue a high priority and it fixed itself?