Don't blindly send unlit chunks when lighting updates are allowed

Spigot, by default, disables several mechanisms around how chunks are
lit, if ever, which has forced them to always send chunks before vanilla
would consider them ready to send, causing for lots of issues around
lighting glitches.

Shamefully, the amount of work to relight chunks can be detremental
to some servers, meaning that forcibily disabling light updates can
cause major performance issues.

as such, we make a compromise; if this "feature" is disabled, we will
only send chunks which are actually ready to be sent, otherwise, we
will always send chunks.

Spigot-Server-Patches/0256-Don-t-blindly-send-unlit-chunks-when-lighting-update.patch

@@ -0,0 +1,48 @@
+From 055189fd7e43d4c4bec00f501fb3d66fcc192e0c Mon Sep 17 00:00:00 2001
+From: Shane Freeder <theboyetronic@gmail.com>
+Date: Mon, 18 Dec 2017 07:26:56 +0000
+Subject: [PATCH] Don't blindly send unlit chunks when lighting updates are
+ allowed
+
+Spigot, by default, disables several mechanisms around how chunks are
+lit, if ever, which has forced them to always send chunks before vanilla
+would consider them ready to send, causing for lots of issues around
+lighting glitches.
+
+Shamefully, the amount of work to relight chunks can be detremental
+to some servers, meaning that forcibily disabling light updates can
+cause major performance issues.
+
+as such, we make a compromise; if this "feature" is disabled, we will
+only send chunks which are actually ready to be sent, otherwise, we
+will always send chunks.
+
+diff --git a/src/main/java/net/minecraft/server/Chunk.java b/src/main/java/net/minecraft/server/Chunk.java
+index 33018fa3d..4b1b236a7 100644
+--- a/src/main/java/net/minecraft/server/Chunk.java
++++ b/src/main/java/net/minecraft/server/Chunk.java
+@@ -39,7 +39,7 @@ public class Chunk {
+     final PaperLightingQueue.LightingQueue lightingQueue = new PaperLightingQueue.LightingQueue(this); // Paper
+     private boolean done;
+     private boolean lit;
+-    private boolean r;
++    private boolean r; private boolean isTicked() { return r; }; // Paper - OBFHELPER
+     private boolean s;
+     private boolean t;
+     private long lastSaved;
+@@ -1135,7 +1135,11 @@ public class Chunk {
+          * We cannot unfortunately do this lighting stage during chunk gen as it appears to put a lot more noticeable load on the server, than when it is done at play time.
+          * For now at least we will simply send all chunks, in accordance with pre 1.7 behaviour.
+          */
+-        return true;
++        // Paper Start
++        // if randomLightUpdates are enabled, we should always return true, otherwise chunks may never send
++        // to the client due to not being lit, otherwise retain standard behavior and only send properly lit chunks.
++        return !this.world.spigotConfig.randomLightUpdates || (this.isTicked() && this.done && this.lit);
++        // Paper End
+         // Spigot End
+     }
+ 
+-- 
+2.15.1
+