Add a OnDatapackSyncEvent, useful as a notification for modders to send extra data to the client (#7912)

patches/minecraft/net/minecraft/server/players/PlayerList.java.patch

@@ -16,8 +16,11 @@
        GameRules gamerules = serverlevel1.m_46469_();
        boolean flag = gamerules.m_46207_(GameRules.f_46156_);
        boolean flag1 = gamerules.m_46207_(GameRules.f_46145_);
-@@ -160,6 +_,7 @@
+@@ -158,8 +_,10 @@
+       servergamepacketlistenerimpl.m_141995_(new ClientboundChangeDifficultyPacket(leveldata.m_5472_(), leveldata.m_5474_()));
+       servergamepacketlistenerimpl.m_141995_(new ClientboundPlayerAbilitiesPacket(p_11263_.m_150110_()));
        servergamepacketlistenerimpl.m_141995_(new ClientboundSetCarriedItemPacket(p_11263_.m_150109_().f_35977_));
++      net.minecraftforge.common.MinecraftForge.EVENT_BUS.post(new net.minecraftforge.event.OnDatapackSyncEvent(this, p_11263_));
        servergamepacketlistenerimpl.m_141995_(new ClientboundUpdateRecipesPacket(this.f_11195_.m_129894_().m_44051_()));
        servergamepacketlistenerimpl.m_141995_(new ClientboundUpdateTagsPacket(this.f_11195_.m_129895_().m_144442_(this.f_11206_)));
 +      net.minecraftforge.fmllegacy.network.NetworkHooks.syncCustomTagTypes(p_11263_, this.f_11195_.m_129895_());
@@ -110,9 +113,11 @@
     }
  
     @Nullable
-@@ -786,6 +_,7 @@
+@@ -785,7 +_,9 @@
+          playeradvancements.m_135981_(this.f_11195_.m_129889_());
        }
  
++      net.minecraftforge.common.MinecraftForge.EVENT_BUS.post(new net.minecraftforge.event.OnDatapackSyncEvent(this, null));
        this.m_11268_(new ClientboundUpdateTagsPacket(this.f_11195_.m_129895_().m_144442_(this.f_11206_)));
 +      net.minecraftforge.fmllegacy.network.NetworkHooks.syncCustomTagTypes(this.f_11195_.m_129895_());
        ClientboundUpdateRecipesPacket clientboundupdaterecipespacket = new ClientboundUpdateRecipesPacket(this.f_11195_.m_129894_().m_44051_());

src/main/java/net/minecraftforge/event/OnDatapackSyncEvent.java

@@ -0,0 +1,43 @@
+package net.minecraftforge.event;
+
+import javax.annotation.Nullable;
+
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.server.players.PlayerList;
+import net.minecraftforge.eventbus.api.Event;
+
+/**
+ * Fires when a player joins the server or when the reload command is ran,
+ * before tags and crafting recipes are sent to the client. Send datapack data
+ * to clients when this event fires.
+ */
+public class OnDatapackSyncEvent extends Event
+{
+    private final PlayerList playerList;
+    @Nullable
+    private final ServerPlayer player;
+
+    public OnDatapackSyncEvent(PlayerList playerList, @Nullable ServerPlayer player)
+    {
+        this.playerList = playerList;
+        this.player = player;
+    }
+
+    /**
+     * @return The server's player list to get a view of all players.
+     */
+    public PlayerList getPlayerList()
+    {
+        return this.playerList;
+    }
+
+    /**
+     * @return The player to sync datapacks to. Null when syncing for all players,
+     *         such as when the reload command runs.
+     */
+    @Nullable
+    public ServerPlayer getPlayer()
+    {
+        return this.player;
+    }
+}

src/test/java/net/minecraftforge/debug/misc/OnDatapackSynctEventTest.java

@@ -0,0 +1,32 @@
+package net.minecraftforge.debug.misc;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraftforge.event.OnDatapackSyncEvent;
+import net.minecraftforge.eventbus.api.SubscribeEvent;
+import net.minecraftforge.fml.common.Mod;
+
+@Mod("send_datapacks_to_client")
+@Mod.EventBusSubscriber
+public class OnDatapackSynctEventTest
+{
+    private static final Logger LOGGER = LogManager.getLogger();
+
+    @SubscribeEvent
+    protected static void onSendDataToClient(final OnDatapackSyncEvent event)
+    {
+        // Fire for a specific player on login
+        if (event.getPlayer() != null)
+            syncData(event.getPlayer());
+        // Fire for all players on /reload
+        else
+            event.getPlayerList().getPlayers().forEach(OnDatapackSynctEventTest::syncData);
+    }
+
+    private static void syncData(ServerPlayer player)
+    {
+        LOGGER.info("Sending modded datapack data to {}", player.getName().getString());
+    }
+}

src/test/resources/META-INF/mods.toml

@@ -142,5 +142,7 @@ license="LGPL v2.1"
     modId="overlay_layers_test"
 [[mods]]
     modId="entity_renderer_events_test"
+[[mods]]
+    modId="send_datapacks_to_client"
 
 # ADD ABOVE THIS LINE