[1.12.2 Fix] Race condition on player loading

src/main/java/cam72cam/mod/MinecraftClient.java

@@ -8,12 +8,20 @@
 import net.minecraft.client.Minecraft;
 import net.minecraft.client.entity.EntityPlayerSP;
 import net.minecraft.util.math.RayTraceResult;
+import org.jetbrains.annotations.ApiStatus;
 
 /** Static Minecraft Client props, don't touch server side */
 public class MinecraftClient {
     /** Minecraft is loaded and has a loaded world */
+    private static boolean clientReady;
+
     public static boolean isReady() {
-        return Minecraft.getMinecraft().player != null;
+        return clientReady;
+    }
+
+    @ApiStatus.Internal
+    public static void setReady(boolean newState) {
+        clientReady = newState;
     }
 
     private static Player playerCache;

src/main/java/cam72cam/mod/mixin/fix/client_player_handling/MixinMinecraft.java

@@ -0,0 +1,35 @@
+package cam72cam.mod.mixin.fix.client_player_handling;
+
+import cam72cam.mod.MinecraftClient;
+import net.minecraft.client.Minecraft;
+import net.minecraft.client.multiplayer.WorldClient;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+/**
+ * Manually track loading state to avoid race condition on {@link MinecraftClient#isReady()} and actual player spawn
+ */
+@Mixin(Minecraft.class)
+public class MixinMinecraft {
+    @Inject(method = "loadWorld(Lnet/minecraft/client/multiplayer/WorldClient;Ljava/lang/String;)V", at = @At(value = "INVOKE_ASSIGN", target = "Lnet/minecraft/client/multiplayer/WorldClient;spawnEntity(Lnet/minecraft/entity/Entity;)Z"))
+    public void markReadyWhenLoaded(WorldClient worldClientIn, String loadingMessage, CallbackInfo ci) {
+        MinecraftClient.setReady(true);
+    }
+
+    @Inject(method = "loadWorld(Lnet/minecraft/client/multiplayer/WorldClient;Ljava/lang/String;)V", at = @At(value = "INVOKE", target = "Lnet/minecraft/world/storage/ISaveFormat;flushCache()V"))
+    public void markNotReadyWhenUnloaded(WorldClient worldClientIn, String loadingMessage, CallbackInfo ci) {
+        MinecraftClient.setReady(false);
+    }
+
+    @Inject(method = "setDimensionAndSpawnPlayer", at = @At(value = "INVOKE_ASSIGN", target = "Lnet/minecraft/client/multiplayer/WorldClient;spawnEntity(Lnet/minecraft/entity/Entity;)Z"))
+    public void markReadyWhenLoaded(int dimension, CallbackInfo ci) {
+        MinecraftClient.setReady(true);
+    }
+
+    @Inject(method = "setDimensionAndSpawnPlayer", at = @At(value = "INVOKE", target = "Lnet/minecraft/client/entity/EntityPlayerSP;getEntityId()I"))
+    public void markNotReadyWhenTransfer(int dimension, CallbackInfo ci) {
+        MinecraftClient.setReady(false);
+    }
+}

src/main/resources/mixins.fix.universalmodcore.json

@@ -13,5 +13,6 @@
     "multi_release.MixinJarDiscoverer"
   ],
   "client": [
+    "client_player_handling.MixinMinecraft"
   ]
 }