IDEA fails to build when using Manifold preprocessor

[RogueLogix]

repro steps

• create fresh mod template from https://neoforged.net/mod-generator/
• set IDEA to build using IDEA instead of gradle
• ensure it builds and runs as expected
• add manifold annotation processor dependency: annotationProcessor 'systems.manifold:manifold-preprocessor:2025.1.26'
• add manifold plugin to compiler args compileJava.options.compilerArgs += '-Xplugin:Manifold'
• attempt to build, will fail with "class X is public, should be in file named X.java" errors
• switch IDEA to build with gradle
• builds/runs as expected

A standard gradle project builds with IDEA as expected
A Fabric project builds with IDEA as expected

[Technici4n]

The error comes from the merged jars with classes and sources that we use in MDG, to let IDEA find the sources. For some reason Manifold doesn't like those.