Paper/patches/server/0439-Fix-some-rails-connecting-improperly.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Fri, 24 Jul 2020 15:56:05 -0700
Subject: [PATCH] Fix some rails connecting improperly


diff --git a/src/main/java/net/minecraft/world/level/block/BaseRailBlock.java b/src/main/java/net/minecraft/world/level/block/BaseRailBlock.java
index d8dd9f26fe4344541d0544e35bbc66c5d567a80b..dcf49e21208c78b471e6c38cdb0746a0c88fe5a7 100644
--- a/src/main/java/net/minecraft/world/level/block/BaseRailBlock.java
+++ b/src/main/java/net/minecraft/world/level/block/BaseRailBlock.java
@@ -68,6 +68,7 @@ public abstract class BaseRailBlock extends Block implements SimpleWaterloggedBl
         state = this.updateDir(world, pos, state, true);
         if (this.isStraight) {
             world.neighborChanged(state, pos, this, pos, notify);
+            state = world.getBlockState(pos); // Paper - don't desync, update again
         }
 
         return state;
diff --git a/src/main/java/net/minecraft/world/level/block/DetectorRailBlock.java b/src/main/java/net/minecraft/world/level/block/DetectorRailBlock.java
index 41452abc7b761858ff2f3ff6a833b09c16fded4f..8eff69cb70ba094f9dcc0849f0436d4a3498fceb 100644
--- a/src/main/java/net/minecraft/world/level/block/DetectorRailBlock.java
+++ b/src/main/java/net/minecraft/world/level/block/DetectorRailBlock.java
@@ -77,6 +77,7 @@ public class DetectorRailBlock extends BaseRailBlock {
 
     private void checkPressed(Level world, BlockPos pos, BlockState state) {
         if (this.canSurvive(state, world, pos)) {
+            if (state.getBlock() != this) { return; } // Paper - not our block, don't do anything
             boolean flag = (Boolean) state.getValue(DetectorRailBlock.POWERED);
             boolean flag1 = false;
             List<AbstractMinecart> list = this.getInteractingMinecartOfType(world, pos, AbstractMinecart.class, (entity) -> {
diff --git a/src/main/java/net/minecraft/world/level/block/RailState.java b/src/main/java/net/minecraft/world/level/block/RailState.java
index 0cbfad97371b59de95963a09aa16f3dad7a37222..d873625c1b8439a727d39ce207b5e84a1d86e5eb 100644
--- a/src/main/java/net/minecraft/world/level/block/RailState.java
+++ b/src/main/java/net/minecraft/world/level/block/RailState.java
@@ -17,6 +17,12 @@ public class RailState {
     private final boolean isStraight;
     private final List<BlockPos> connections = Lists.newArrayList();
 
+    // Paper start - prevent desync
+    public boolean isValid() {
+        return this.level.getBlockState(this.pos).getBlock() == this.state.getBlock();
+    }
+    // Paper end - prevent desync
+
     public RailState(Level world, BlockPos pos, BlockState state) {
         this.level = world;
         this.pos = pos;
@@ -143,6 +149,11 @@ public class RailState {
     }
 
     private void connectTo(RailState placementHelper) {
+        // Paper start - prevent desync
+        if (!this.isValid() || !placementHelper.isValid()) {
+            return;
+        }
+        // Paper end - prevent desync
         this.connections.add(placementHelper.pos);
         BlockPos blockPos = this.pos.north();
         BlockPos blockPos2 = this.pos.south();
@@ -333,10 +344,15 @@ public class RailState {
         this.state = this.state.setValue(this.block.getShapeProperty(), railShape2);
         if (forceUpdate || this.level.getBlockState(this.pos) != this.state) {
             this.level.setBlock(this.pos, this.state, 3);
+            // Paper start - prevent desync
+            if (!this.isValid()) {
+                return this;
+            }
+            // Paper end - prevent desync
 
             for(int i = 0; i < this.connections.size(); ++i) {
                 RailState railState = this.getRail(this.connections.get(i));
-                if (railState != null) {
+                if (railState != null && railState.isValid()) { // Paper - prevent desync
                     railState.removeSoftConnections();
                     if (railState.canConnectTo(this)) {
                         railState.connectTo(this);
@@ -349,6 +365,6 @@ public class RailState {
     }
 
     public BlockState getState() {
-        return this.state;
+        return this.level.getBlockState(this.pos); // Paper - prevent desync
     }
 }