Add an event for when the server is about to stop

This may allow mods to perform any additional clean up of resources, or
what not.

src/main/java/net/fabricmc/fabric/events/ServerEvent.java

@@ -24,6 +24,7 @@ import java.util.function.Consumer;
 
 public final class ServerEvent {
 	public static final HandlerRegistry<Consumer<MinecraftServer>> START = new HandlerArray<>(Consumer.class);
+	public static final HandlerRegistry<Consumer<MinecraftServer>> STOP = new HandlerArray<>(Consumer.class);
 
 	private ServerEvent() {
 

src/main/java/net/fabricmc/fabric/mixin/events/server/MixinMinecraftServer.java

@@ -34,4 +34,14 @@ public class MixinMinecraftServer {
 			handler.accept((MinecraftServer) (Object) this);
 		}
 	}
+
+	@Inject(
+		at = @At(value = "INVOKE", target = "Lnet/minecraft/server/MinecraftServer;exit()V", shift = At.Shift.BY, by = -2, ordinal = 0),
+		method = "run"
+	)
+	public void beforeExitServer(CallbackInfo info) {
+		for (Consumer<MinecraftServer> handler : ((HandlerArray<Consumer<MinecraftServer>>) ServerEvent.STOP).getBackingArray()) {
+			handler.accept((MinecraftServer) (Object) this);
+		}
+	}
 }

src/test/java/net/fabricmc/fabric/events/ServerEventMod.java

@@ -0,0 +1,15 @@
+package net.fabricmc.fabric.events;
+
+import net.fabricmc.api.ModInitializer;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+
+public class ServerEventMod implements ModInitializer {
+	private static final Logger LOGGER = LogManager.getLogger();
+
+	@Override
+	public void onInitialize() {
+		ServerEvent.START.register(server -> LOGGER.info("Server starting (" + server + ")"));
+		ServerEvent.STOP.register(server -> LOGGER.info("Server stopped (" + server + ")"));
+	}
+}

src/test/resources/mod.json

@@ -6,6 +6,7 @@
   "description": "A series of test mods to check Fabric works.",
   "license": "Apache-2.0",
   "initializers": [
-    "net.fabricmc.fabric.colormapper.ColorProviderMod"
+    "net.fabricmc.fabric.colormapper.ColorProviderMod",
+    "net.fabricmc.fabric.events.ServerEventMod"
   ]
 }