Shelf mushrooms generated with fallen trees replace water

Thank you for helping us improve Minecraft! We saved your files:

It can be confirmed that the cause at the code level is as follows:

tryPlaceMushroomOnFallenTree.java snippet：

private static void tryPlaceMushroomOnFallenTree(Context context, BlockPos logPos, Direction facing, RandomSource random) {
    BlockPos mushroomPos = mushroomPosFor(logPos, facing);
    
    if (!context.isReplaceable(mushroomPos)) { //The issue lies here
        return;
    }
    //......
}

isReplaceable implementation:

the Context inner class in TreeDecorator.java:

public boolean isReplaceable(BlockPos pos) {
    return this.checkBlock(pos, BlockBehaviour.BlockStateBase::canBeReplaced);
}

Cases where canBeReplaced returns true in the game include water

Similarly, regular Poplar also has this issue

tryPlaceMushroomOnStandingTree snippet：

private static boolean tryPlaceMushroomOnStandingTree(Context context, BlockPos logPos, Direction facing, RandomSource random) {
    BlockPos mushroomPos = mushroomPosFor(logPos, facing);
    
    if (!context.isReplaceable(mushroomPos)) { //The issue lies here
        return false;
    }
    if (hasShelfMushroomAt(context, mushroomPos.below())) {
        return false;
    }
    placeMushroom(context, mushroomPos, facing, random);
    return true;
}

How to fix it:

Change “if (!context.isReplaceable(mushroomPos)) {“ to “if (!context.isAir(mushroomPos)) {“.isAir returns true only for air

But this leads to another issue. The ground in the Dappled Forest has a lot of Leaf Litter, which would greatly reduce the valid placement spots. Instead of changing it to isAir, we could add an extra water-specific check