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1 files changed, 80 insertions, 0 deletions

diff --git a/patches/server/0369-Fix-piston-physics-inconsistency-MC-188840.patch b/patches/server/0369-Fix-piston-physics-inconsistency-MC-188840.patch
new file mode 100644
index 0000000000..44f85960c4
--- /dev/null
+++ b/patches/server/0369-Fix-piston-physics-inconsistency-MC-188840.patch
@@ -0,0 +1,80 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Spottedleaf <[email protected]>
+Date: Thu, 11 Jun 2020 17:29:42 -0700
+Subject: [PATCH] Fix piston physics inconsistency - MC-188840
+
+Pistons invoke physics when they move blocks. The physics can cause
+tnt blocks to ignite. However, pistons (when storing the blocks they "moved")
+don't actually go back to the world state sometimes to check if something
+like that happened. As a result they end up moving the tnt like it was
+never ignited. This resulted in the ability to create machines
+that can duplicate tnt, called "world eaters".
+This patch makes the piston logic retrieve the block state from the world
+prevent this from occuring.
+
+This patch also sets the moved pos to air immediately after creating
+the moving piston TE. This prevents the block from being updated from
+other physics calls by the piston.
+
+Tested against the following tnt duper design:
+https://www.youtube.com/watch?v=mS7xxNGhjxs
+
+This patch also affects every type of machine that utilises
+this mechanic. For example, dead coral is removed by a physics
+update when being moved while it is attached to slimeblocks.
+
+Standard piston machines that don't destroy or modify the
+blocks they move by physics updates should be entirely
+unaffected.
+
+This patch fixes https://bugs.mojang.com/browse/MC-188840
+
+This patch also fixes rail duping and carpet duping.
+
+diff --git a/src/main/java/net/minecraft/world/level/block/piston/PistonBaseBlock.java b/src/main/java/net/minecraft/world/level/block/piston/PistonBaseBlock.java
+index 530b6af1ca2e0ac81c0a8a55dbc7cf5c796c93ce..4aa34b7df734bb755906b228e0df9eb629569ea0 100644
+--- a/src/main/java/net/minecraft/world/level/block/piston/PistonBaseBlock.java
++++ b/src/main/java/net/minecraft/world/level/block/piston/PistonBaseBlock.java
+@@ -414,14 +414,26 @@ public class PistonBaseBlock extends DirectionalBlock {
+             }
+ 
+             for (j = list.size() - 1; j >= 0; --j) {
+-                blockposition3 = (BlockPos) list.get(j);
+-                iblockdata1 = world.getBlockState(blockposition3);
++                // Paper start - fix a variety of piston desync dupes
++                boolean allowDesync = io.papermc.paper.configuration.GlobalConfiguration.get().unsupportedSettings.allowPistonDuplication;
++                BlockPos oldPos = blockposition3 = (BlockPos) list.get(j);
++                iblockdata1 = allowDesync ? world.getBlockState(oldPos) : null;
++                // Paper end - fix a variety of piston desync dupes
+                 blockposition3 = blockposition3.relative(enumdirection1);
+                 map.remove(blockposition3);
+                 BlockState iblockdata2 = (BlockState) Blocks.MOVING_PISTON.defaultBlockState().setValue(PistonBaseBlock.FACING, dir);
+ 
+                 world.setBlock(blockposition3, iblockdata2, 68);
+-                world.setBlockEntity(MovingPistonBlock.newMovingBlockEntity(blockposition3, iblockdata2, (BlockState) list1.get(j), dir, retract, false));
++                // Paper start - fix a variety of piston desync dupes
++                if (!allowDesync) {
++                    iblockdata1 = world.getBlockState(oldPos);
++                    map.replace(oldPos, iblockdata1);
++                }
++                world.setBlockEntity(MovingPistonBlock.newMovingBlockEntity(blockposition3, iblockdata2, allowDesync ? list1.get(j) : iblockdata1, dir, retract, false));
++                if (!allowDesync) {
++                    world.setBlock(oldPos, Blocks.AIR.defaultBlockState(), Block.UPDATE_CLIENTS | Block.UPDATE_KNOWN_SHAPE | Block.UPDATE_MOVE_BY_PISTON | 1024); // set air to prevent later physics updates from seeing this block
++                }
++                // Paper end - fix a variety of piston desync dupes
+                 aiblockdata[i++] = iblockdata1;
+             }
+ 
+diff --git a/src/main/java/net/minecraft/world/level/block/piston/PistonMovingBlockEntity.java b/src/main/java/net/minecraft/world/level/block/piston/PistonMovingBlockEntity.java
+index 8ea7d7da26e7d5644a8ee1a8d9e4c828c6b70a00..d7b963571c900f0f68005d6954bcd9ef1d9e0b7c 100644
+--- a/src/main/java/net/minecraft/world/level/block/piston/PistonMovingBlockEntity.java
++++ b/src/main/java/net/minecraft/world/level/block/piston/PistonMovingBlockEntity.java
+@@ -297,7 +297,7 @@ public class PistonMovingBlockEntity extends BlockEntity {
+                 if (world.getBlockState(pos).is(Blocks.MOVING_PISTON)) {
+                     BlockState blockState = Block.updateFromNeighbourShapes(blockEntity.movedState, world, pos);
+                     if (blockState.isAir()) {
+-                        world.setBlock(pos, blockEntity.movedState, 84);
++                        world.setBlock(pos, blockEntity.movedState, io.papermc.paper.configuration.GlobalConfiguration.get().unsupportedSettings.allowPistonDuplication ? 84 : (84 | Block.UPDATE_CLIENTS)); // Paper - fix a variety of piston desync dupes; force notify (flag 2), it's possible the set type by the piston block (which doesn't notify) set this block to air
+                         Block.updateOrDestroy(blockEntity.movedState, blockState, world, pos, 3);
+                     } else {
+                         if (blockState.hasProperty(BlockStateProperties.WATERLOGGED) && blockState.getValue(BlockStateProperties.WATERLOGGED)) {