WorldGenFeatureFix

Tips: Mojang has marked this problem as fixed since 26.1 Snapshot 6, you may don't need this mod in 26.1 anymore.

What this mod fixes?

When custom world generation datapack uses minecraft:lake or minecraft:snow_and_freeze placed feature with water, The chunk generator crashes. (See MC-273228 or MC-272370 for more details).
Inspired by This pull request, This mod apply mixins to make them work.

Techinal Details

In version 1.21, chunk generation has been highly optimized, which unintentionally breaks the freeze detection of the lake feature since it may trying to access inaccessible chunks. However, since Mojang only uses the lake feature for lava lakes at now, this issue does not occur in vanilla Minecraft — but it does affect custom world generators! This mod applies mixins that fallback to getUncachedNoiseChunk, allowing the lake feature to work correctly again.

Disclaimer

However, The PR also mentioned that LakeFeature is deprecated and vanilla has moved away from using it for anything except for lava lakes. The error for unsafe chunk gets removing here is an intentional safeguard against bad code, such as that in the dead path in LakeFeature when creating water lakes. While it may appear to 'fix' the problem at hand it is not a proper solution and will cause other more serious problems to go undetected. Use at your own risk. (At least it works perfect in my server)