Remove wall-time / unused skip tick protection (#11412)

Spigot still maintains some partial implementation of "tick skipping", a
practice in which the MinecraftServer.currentTick field is updated not
by an increment of one per actual tick, but instead set to
System.currentTimeMillis() / 50. This behaviour means that the tracked
tick may "skip" a tick value in case a previous tick took more than the
expected 50ms.

To compensate for this in important paths, spigot/craftbukkit
implements "wall-time". Instead of incrementing/decrementing ticks on
block entities/entities by one for each call to their tick() method,
they instead increment/decrement important values, like
an ItemEntity's age or pickupDelay, by the difference of
`currentTick - lastTick`, where `lastTick` is the value of
`currentTick` during the last tick() call.

These "fixes" however do not play nicely with minecraft's simulation
distance as entities/block entities implementing the above behaviour
would "catch up" their values when moving from a non-ticking chunk to a
ticking one as their `lastTick` value remains stuck on the last tick in
a ticking chunk and hence lead to a large "catch up" once ticked again.

Paper completely removes the "tick skipping" behaviour (See patch
"Further-improve-server-tick-loop"), making the above precautions
completely unnecessary, which also rids paper of the previous described
incompatibility with non-ticking chunks.

1 files changed, 59 insertions, 0 deletions

diff --git a/patches/server/0944-Fix-creation-of-invalid-block-entity-during-world-ge.patch b/patches/server/0944-Fix-creation-of-invalid-block-entity-during-world-ge.patch
new file mode 100644
index 0000000000..8e09c4fb05
--- /dev/null
+++ b/patches/server/0944-Fix-creation-of-invalid-block-entity-during-world-ge.patch
@@ -0,0 +1,59 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Pierpaolo Coletta <[email protected]>
+Date: Sat, 30 Mar 2024 21:06:10 +0100
+Subject: [PATCH] Fix creation of invalid block entity during world generation
+
+
+diff --git a/src/main/java/net/minecraft/server/level/WorldGenRegion.java b/src/main/java/net/minecraft/server/level/WorldGenRegion.java
+index 682c8cfbd917c086072f1756861a340800ea40da..b26a4a38144ec1b171db911bbf949b53ed35708f 100644
+--- a/src/main/java/net/minecraft/server/level/WorldGenRegion.java
++++ b/src/main/java/net/minecraft/server/level/WorldGenRegion.java
+@@ -324,7 +324,7 @@ public class WorldGenRegion implements WorldGenLevel {
+             return false;
+         } else {
+             ChunkAccess ichunkaccess = this.getChunk(pos);
+-            BlockState iblockdata1 = ichunkaccess.setBlockState(pos, state, false);
++            BlockState iblockdata1 = ichunkaccess.setBlockState(pos, state, false); final BlockState previousBlockState = iblockdata1; // Paper - Clear block entity before setting up a DUMMY block entity - obfhelper
+ 
+             if (iblockdata1 != null) {
+                 this.level.onBlockStateChange(pos, iblockdata1, state);
+@@ -340,6 +340,17 @@ public class WorldGenRegion implements WorldGenLevel {
+                         ichunkaccess.removeBlockEntity(pos);
+                     }
+                 } else {
++                    // Paper start - Clear block entity before setting up a DUMMY block entity
++                    // The concept of removing a block entity when the block itself changes is generally lifted
++                    // from LevelChunk#setBlockState.
++                    // It is however to note that this may only run if the block actually changes.
++                    // Otherwise a chest block entity generated by a structure template that is later "updated" to
++                    // be waterlogged would remove its existing block entity (see PaperMC/Paper#10750)
++                    // This logic is *also* found in LevelChunk#setBlockState.
++                    if (previousBlockState != null && !java.util.Objects.equals(previousBlockState.getBlock(), state.getBlock())) {
++                        ichunkaccess.removeBlockEntity(pos);
++                    }
++                    // Paper end - Clear block entity before setting up a DUMMY block entity
+                     CompoundTag nbttagcompound = new CompoundTag();
+ 
+                     nbttagcompound.putInt("x", pos.getX());
+diff --git a/src/main/java/net/minecraft/world/level/chunk/LevelChunk.java b/src/main/java/net/minecraft/world/level/chunk/LevelChunk.java
+index 59f9ff720e92c69e11afe7f6ccecd81b0e54a74d..86eb9029969f4de3ada7be9e135e9764172b85f5 100644
+--- a/src/main/java/net/minecraft/world/level/chunk/LevelChunk.java
++++ b/src/main/java/net/minecraft/world/level/chunk/LevelChunk.java
+@@ -961,9 +961,14 @@ public class LevelChunk extends ChunkAccess {
+                         if (this.blockEntity.getType().isValid(iblockdata)) {
+                             this.ticker.tick(LevelChunk.this.level, this.blockEntity.getBlockPos(), iblockdata, this.blockEntity);
+                             this.loggedInvalidBlockState = false;
+-                        } else if (!this.loggedInvalidBlockState) {
+-                            this.loggedInvalidBlockState = true;
+-                            LevelChunk.LOGGER.warn("Block entity {} @ {} state {} invalid for ticking:", new Object[]{LogUtils.defer(this::getType), LogUtils.defer(this::getPos), iblockdata});
++                        // Paper start - Remove the Block Entity if it's invalid
++                        } else {
++                            LevelChunk.this.removeBlockEntity(this.getPos());
++                            if (!this.loggedInvalidBlockState) {
++                                this.loggedInvalidBlockState = true;
++                                LevelChunk.LOGGER.warn("Block entity {} @ {} state {} invalid for ticking:", new Object[]{LogUtils.defer(this::getType), LogUtils.defer(this::getPos), iblockdata});
++                            }
++                            // Paper end - Remove the Block Entity if it's invalid
+                         }
+ 
+                         gameprofilerfiller.pop();