[1.12.2] Mods that use Sponge Mixins interfere with CatServer patches

[AngryCarrot789]

Environment

Minecraft version(1.12.2): Build version(Get from /version command): Mods/Plugins:

• All of the mods from The 1.12.2 Pack
• EssentialsX

Describe the bug I'm building the CatServer jar from source (I run genPatches after modifying the actual game code) and then I run build, and finally run outputJar, and then I use that .jar file as my server's main jar (e.g. found in build/distributions/<jar>).

However, it seems like code patches don't seem to get applied, specially the player data patch: whenever a player joins, the CraftPlayer's readExtraData never gets called, meaning hasPlayedBefore is always false, meaning plugins like EssentialsX think a player is always joining for the first time.

I also further know this because in the saved .dat file for each player, there's no compound called bukkit which according to the code should always be created when a player's data is saved (I even tried leaving then re-joining, but that didn't help)

I also just downloaded the jar from the cat server website (which has a smaller file size if that matters), but that also did not work; no bukkit data is saved or loaded, hasPlayedBefore is always false

Expected behavior CraftPlayer.readExtraData() should get called by the EntityPlayerMP.readEntityFromNBT function, but that doesn't seem to happen.

To Reproduce Download The 1.12.2 Pack's server, then just run the cat server jar instead of the forge jar. The server loads normally and doesn't crash, but as mentioned above, player data loading does not work correctly

Screenshot/Video (If it doesn't exist you can ignore it)