Add feature that warns about DataWatcher ID conflicts

See makamys/DMod#9

src/main/java/makamys/coretweaks/Config.java

@@ -113,6 +113,10 @@ public class Config {
     public static FeatureSetting coreTweaksCommand = FeatureSetting.FALSE;
     @ConfigWrappedEnum(cat="Diagnostics", def=TRUE, com="Makes MapStorage's errors more informative.")
     public static FeatureSetting enhanceMapStorageErrors;
+    @ConfigWrappedEnum(cat="Diagnostics", def=TRUE, com="Emit warning when a mod registers a typed DataWatcher object in an already occupied ID slot (vanilla only warns in the typeless registration method).")
+    public static FeatureSetting detectDataWatcherIdConflicts;
+    @ConfigBoolean(cat="Diagnostics.detect_data_watcher_id_conflicts", def=false, com="Keep track of all registration stack traces, and print which ones conflict. Off by default because it adds some overhead to DataWatcher object registration.")
+    public static boolean detectDataWatcherIdConflictCulprit;
 
     //@ConfigBoolean(cat="Optimizations", def=FALSE, com="Use multi-threaded texture loading when stitching textures? Placebo.")
     public static FeatureSetting threadedTextureLoader = FeatureSetting.FALSE;

src/main/java/makamys/coretweaks/MixinConfigPlugin.java

@@ -151,6 +151,9 @@ public List<String> getMixins() {
             if(Config.enhanceMapStorageErrors.isActive()) {
                 mixins.add("diagnostics.enhancemapstorageerrors.MixinMapStorage");
             }
+            if(Config.detectDataWatcherIdConflicts.isActive()) {
+                mixins.add("diagnostics.detectdatawatcherconflict.MixinDataWatcher");
+            }
         }
         return mixins;
     }

src/main/java/makamys/coretweaks/diagnostics/DataWatcherMonitor.java

@@ -0,0 +1,38 @@
+package makamys.coretweaks.diagnostics;
+
+import static makamys.coretweaks.CoreTweaks.LOGGER;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.WeakHashMap;
+
+import org.apache.commons.lang3.exception.ExceptionUtils;
+
+import net.minecraft.entity.DataWatcher;
+
+public class DataWatcherMonitor {
+    private static WeakHashMap<DataWatcher, Map<Integer, List<AdditionRecord>>> data = new WeakHashMap<>();
+
+    public static void onAddition(DataWatcher dw, String entityClassName, int id) {
+        AdditionRecord record = new AdditionRecord();
+        List<AdditionRecord> recordsForId = data.computeIfAbsent(dw, k -> new HashMap<>()).computeIfAbsent(id, k -> new ArrayList<>());
+        recordsForId.add(record);
+
+        if(recordsForId.size() > 1) {
+            LOGGER.warn("Detected DataWatcher ID conflict at ID " + id + " for entity " + entityClassName);
+            for(int i = 0; i < recordsForId.size(); i++) {
+                LOGGER.warn("Stack trace for registration #" + (i + 1) + " (out of " + recordsForId.size() + "): ");
+                LOGGER.warn(recordsForId.get(i).stackTrace);
+            }
+        }
+    }
+
+    public static class AdditionRecord {
+        public final String stackTrace;
+        public AdditionRecord() {
+            stackTrace = ExceptionUtils.getStackTrace(new Throwable());
+        }
+    }
+}

src/main/java/makamys/coretweaks/mixin/diagnostics/detectdatawatcherconflict/MixinDataWatcher.java

@@ -0,0 +1,45 @@
+package makamys.coretweaks.mixin.diagnostics.detectdatawatcherconflict;
+
+import static makamys.coretweaks.CoreTweaks.LOGGER;
+
+import java.util.Map;
+
+import org.apache.commons.lang3.exception.ExceptionUtils;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+import makamys.coretweaks.Config;
+import makamys.coretweaks.diagnostics.DataWatcherMonitor;
+import net.minecraft.entity.DataWatcher;
+import net.minecraft.entity.Entity;
+
+@Mixin(DataWatcher.class)
+public class MixinDataWatcher {
+    @Shadow
+    private Entity field_151511_a;
+    @Shadow
+    private Map watchedObjects;
+
+    @Inject(method = "addObject", at = @At("HEAD"))
+    public void monitorObjectAddition(int id, Object object, CallbackInfo ci) {
+        if(Config.detectDataWatcherIdConflictCulprit && field_151511_a != null) {
+            DataWatcherMonitor.onAddition((DataWatcher)(Object)this, field_151511_a.getClass().getName(), id);
+        }
+    }
+
+    @Inject(method = "addObjectByDataType", at = @At("HEAD"))
+    public void monitorTypedObjectAddition(int id, int type, CallbackInfo ci) {
+        boolean printedCulprit = false;
+        if(Config.detectDataWatcherIdConflictCulprit && field_151511_a != null) {
+            printedCulprit = true;
+            DataWatcherMonitor.onAddition((DataWatcher)(Object)this, field_151511_a.getClass().getName(), id);
+        }
+        if(watchedObjects.containsKey(id)) {
+            LOGGER.warn("Detected duplicate DataWatcher object registration for entity " + (field_151511_a == null ? "null" : field_151511_a.getClass().getName()) + " at already occupied ID " + id + ". Things are likely going to break!" + (!Config.detectDataWatcherIdConflictCulprit ? " Enable `detectDataWatcherIdConflictCulprit` to gather more information." : ""));
+            if(!printedCulprit) LOGGER.warn("Last registration stack trace:\n" + ExceptionUtils.getStackTrace(new Throwable()));
+        }
+    }
+}