Intern Property instances so reference equality is guaranteed

src/main/java/me/jellysquid/mods/hydrogen/common/state/property/WeakPropertyCache.java

@@ -0,0 +1,37 @@
+package me.jellysquid.mods.hydrogen.common.state.property;
+
+import net.minecraft.state.property.Property;
+
+import java.lang.ref.WeakReference;
+import java.util.WeakHashMap;
+
+public class WeakPropertyCache {
+
+    /**
+     * Values are {@link WeakReference} because values in {@link WeakHashMap} are strongly-referenced by default.
+     */
+    private static final WeakHashMap<Property<?>, WeakReference<Property<?>>> CACHE = new WeakHashMap<>();
+
+    /**
+     * Caches properties passed into it in a {@link WeakHashMap}.
+     *
+     * @param newProperty the property to cache
+     * @param <T>         the property type (checked by the property's equals method)
+     * @return the cached property
+     */
+    @SuppressWarnings("unchecked")
+    public static <T extends Property<?>> T tryCacheProperty(T newProperty) {
+        // Synchronized to prevent interleaving of separated contains-put pattern
+        synchronized (CACHE) {
+            T cachedProperty = (T) CACHE.computeIfAbsent(newProperty, WeakReference::new).get();
+
+            // Check if the reference was cleared by GC before WeakReference::get() was called.
+            if (cachedProperty == null) {
+                CACHE.put(newProperty, new WeakReference<>(newProperty));
+                return newProperty;
+            } else {
+                return cachedProperty;
+            }
+        }
+    }
+}

src/main/java/me/jellysquid/mods/hydrogen/mixin/state/property/MixinBooleanProperty.java

@@ -0,0 +1,16 @@
+package me.jellysquid.mods.hydrogen.mixin.state.property;
+
+import me.jellysquid.mods.hydrogen.common.state.property.WeakPropertyCache;
+import net.minecraft.state.property.BooleanProperty;
+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.CallbackInfoReturnable;
+
+@Mixin(BooleanProperty.class)
+public class MixinBooleanProperty {
+    @Inject(method = "of", at = @At("TAIL"), cancellable = true)
+    private static void internOf(CallbackInfoReturnable<BooleanProperty> cir) {
+        cir.setReturnValue(WeakPropertyCache.tryCacheProperty(cir.getReturnValue()));
+    }
+}

src/main/java/me/jellysquid/mods/hydrogen/mixin/state/property/MixinDirectionProperty.java

@@ -0,0 +1,16 @@
+package me.jellysquid.mods.hydrogen.mixin.state.property;
+
+import me.jellysquid.mods.hydrogen.common.state.property.WeakPropertyCache;
+import net.minecraft.state.property.DirectionProperty;
+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.CallbackInfoReturnable;
+
+@Mixin(DirectionProperty.class)
+public class MixinDirectionProperty {
+    @Inject(method = "of(Ljava/lang/String;Ljava/util/Collection;)Lnet/minecraft/state/property/DirectionProperty;", at = @At("TAIL"), cancellable = true)
+    private static void internOf(CallbackInfoReturnable<DirectionProperty> cir) {
+        cir.setReturnValue(WeakPropertyCache.tryCacheProperty(cir.getReturnValue()));
+    }
+}

src/main/java/me/jellysquid/mods/hydrogen/mixin/state/property/MixinEnumProperty.java

@@ -0,0 +1,16 @@
+package me.jellysquid.mods.hydrogen.mixin.state.property;
+
+import me.jellysquid.mods.hydrogen.common.state.property.WeakPropertyCache;
+import net.minecraft.state.property.EnumProperty;
+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.CallbackInfoReturnable;
+
+@Mixin(EnumProperty.class)
+public class MixinEnumProperty {
+    @Inject(method = "of(Ljava/lang/String;Ljava/lang/Class;Ljava/util/Collection;)Lnet/minecraft/state/property/EnumProperty;", at = @At("TAIL"), cancellable = true)
+    private static void internOf(CallbackInfoReturnable<EnumProperty<?>> cir) {
+        cir.setReturnValue(WeakPropertyCache.tryCacheProperty(cir.getReturnValue()));
+    }
+}

src/main/java/me/jellysquid/mods/hydrogen/mixin/state/property/MixinIntProperty.java

@@ -0,0 +1,16 @@
+package me.jellysquid.mods.hydrogen.mixin.state.property;
+
+import me.jellysquid.mods.hydrogen.common.state.property.WeakPropertyCache;
+import net.minecraft.state.property.IntProperty;
+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.CallbackInfoReturnable;
+
+@Mixin(IntProperty.class)
+public class MixinIntProperty {
+    @Inject(method = "of", at = @At("TAIL"), cancellable = true)
+    private static void internOf(CallbackInfoReturnable<IntProperty> cir) {
+        cir.setReturnValue(WeakPropertyCache.tryCacheProperty(cir.getReturnValue()));
+    }
+}

src/main/resources/hydrogen.mixins.json

@@ -22,6 +22,10 @@
     "chunk.MixinChunkSerializer",
     "chunk.MixinWorldChunk",
     "nbt.MixinCompoundTag",
-    "state.MixinState"
+    "state.MixinState",
+    "state.property.MixinBooleanProperty",
+    "state.property.MixinDirectionProperty",
+    "state.property.MixinEnumProperty",
+    "state.property.MixinIntProperty"
   ]
-}
+}