Root Cause Analysis

[mornfire]

Description

Sable's LevelAccelerator.getBlockState() is called during getCollisionShape() of Twilight Forest's ForceFieldBlock. The ForceFieldBlock.getShape() method queries neighboring blocks to determine its visual shape. This query triggers Sable's physics pipeline again, which recursively calls getCollisionShape() again, creating an infinite loop.

The call chain:

1. Sable handles block change event
2. Sable calls RapierVoxelColliderBakery.buildPhysicsDataForBlock()
3. buildPhysicsDataForBlock() calls BlockStateBase.getCollisionShape()
4. Twilight Forest's ForceFieldBlock.getShape() is executed
5. ForceFieldBlock calls Level.getBlockState() on neighboring positions
6. Sable's mixin intercepts this and triggers the physics pipeline again
7. Go back to step 2 → Recursive update

How to Reproduce

1. Install Sable 1.2.2 + Twilight Forest 4.8.3345 on NeoForge 1.21.1
2. Generate a world with Twilight Forest dimension
3. Load a chunk containing a force field block (found in Aurora Palace structures)
4. Server crashes during chunk loading

Expected Behavior

Sable should ignore or skip physics processing for Twilight Forest's force field blocks, or handle them without recursively querying block states during collision shape building.

Suggested Fix

Add Twilight Forest's force field blocks to Sable's internal block blacklist, or modify RapierVoxelColliderBakery to cache/cancel recursive calls when the same block state is being processed.

Affected block IDs:

• twilightforest:force_field
• twilightforest:force_field_pink
• twilightforest:force_field_orange
• twilightforest:force_field_green
• twilightforest:force_field_blue
• twilightforest:force_field_violet
• twilightforest:force_field_yellow
• twilightforest:force_field_red

Workaround

Temporarily remove Sable from the mods folder, or manually disable Twilight Forest force field generation (not recommended as it breaks Aurora Palace structures).

Additional Context

• Full crash report:
  at TRANSFORMER/twilightforest@4.8.3345/twilightforest.block.ForceFieldBlock.fullFaceOrSimilarForceField(ForceFieldBlock.java:69)
  at TRANSFORMER/twilightforest@4.8.3345/twilightforest.block.ForceFieldBlock.cornerConnects(ForceFieldBlock.java:64)
  at TRANSFORMER/twilightforest@4.8.3345/twilightforest.block.ForceFieldBlock.getShape(ForceFieldBlock.java:99)
  at TRANSFORMER/minecraft@1.21.1/net.minecraft.world.level.block.state.BlockBehaviour$BlockStateBase.getShape(BlockBehaviour.java:650)
  at TRANSFORMER/minecraft@1.21.1/net.minecraft.world.level.block.state.BlockBehaviour$BlockStateBase.getCollisionShape(BlockBehaviour.java:658)
• This may affect other mods that query block states inside getCollisionShape() or getShape(), not just Twilight Forest.

Game Log

https://mclo.gs/LN83lGY

[mornfire]

Actually, it's about the Final Castle

To be more precise, the crash occurs when the game attempts to load or tick chunks containing the Final Castle (located in the Final Plateau biome) in the Twilight Forest dimension.

This structure is heavily composed of Force Field blocks (twilightforest:force_field and its colored variants). These blocks have a dynamic shape that depends on adjacent blocks, and Sable's physics engine fails to handle this properly.

Where the crash happens

The crash occurs during chunk loading/post-processing when the game tries to:

1. Load a chunk that contains part of the Final Castle
2. Sable attempts to build collision data for the force field blocks
3. The force field block's getShape() method checks neighboring blocks
4. This triggers Sable's block state interceptor again
5. → Infinite recursive loop → Recursive update

How to reproduce

1. Enter the Twilight Forest dimension
2. Locate the Final Castle in the Final Plateau biome
3. Approach or load the chunks containing it
4. Server crashes immediately

Workaround

Temporarily removing Sable allows the castle to load normally without crashes. However, this also removes all physics features from the game.