[MC-146825] Red and brown mushrooms can't be placed on top slabs or inverted stairs

Summary:
It is not possible to place red or brown mushrooms on the top slabs or inverted stair blocks, despite the fact that they provide a suitable supporting surface. This is also in conflict with behaviour on bedrock edition, where it is possible to place mushrooms on top slabs and inverted stairs.

Code analysis:
Code analysis by @unknown can be found in this comment.

Attachments

Comments 19

migrated 2019-04-10T20:25:24Z

probably intended feature

NeunEinser 2019-10-18T13:29:07Z

I don't think this is intended. Most other things like torches only require to be placed on top of a solid face. The same should be true for mushrooms as well.

Avoma 2020-12-25T19:08:57Z

Can confirm in 20w51a.

Avoma 2021-02-10T16:02:40Z

Can confirm in 21w05b.

Avoma 2021-02-16T19:37:29Z

Can confirm in 21w06a.

9 more comments

Avoma 2021-03-08T10:37:43Z

Can confirm in 1.16.5 and 21w08b.

migrated 2021-07-04T01:38:02Z

Yes I would think this is a bug. It doesn't affect it. The stairs are upside down so it should be able to place.

Avoma 2021-08-05T13:48:00Z

Can confirm in 1.17.1.

Avoma 2021-12-27T13:40:45Z

Can confirm in 1.18.1.

Avoma 2022-05-11T16:01:13Z

Can confirm in 1.18.2 and 22w18a.

Avoma 2022-07-01T12:28:23Z

Can confirm in 1.19.

Avoma 2022-08-23T14:16:21Z

Can confirm in 1.19.2.

PurPur134 2023-08-08T21:26:45Z

Can confirm in 23w31a.

[Mod] Jingy 2023-08-24T00:38:30Z

Code Analysis:

^{(Decompiled with MCP)}
Currently, the applicable blocks for placement are ones that are "isSolidRender" (Full cube blocks)

protected boolean mayPlaceOn(BlockState blockState, BlockGetter blockGetter, BlockPos blockPos) {
      return blockState.isSolidRender(blockGetter, blockPos);
   }

Possible Fix:

One fix for this, is to use "isFaceSturdy" instead, which only checks for a certain face of the block being applicable for placement (In this case, the top face).

protected boolean mayPlaceOn(BlockState blockState, BlockGetter blockGetter, BlockPos blockPos) {
      return blockState.isFaceSturdy(blockGetter, blockPos, Direction.UP);
   }

This provides the following behavior:

[media]

PurPur134 2024-06-10T21:31:24Z

Can confirm in 1.20.6 and 1.21 Release Candidate 1.

muzikbike 2026-10-06T16:53:29Z

Would the fix for MC-312242 also cover this?

Pavel Rozhkov 2026-10-06T19:15:35Z

It is possible to place mushrooms on top slabs and inverted stairs in bedrock edition, so it is also a parity issue.

Pavel Rozhkov 2026-10-13T15:44:57Z

fixed in 26.4 Snapshot 4

muzikbike 2026-10-13T20:52:42Z

Can indeed confirm this to be fixed: