Add FakePlayer damage source system as alternative to FakePlayer.

Author: Darkhax

Common/src/main/java/net/darkhax/bookshelf/api/damagesource/FakePlayerDamageSource.java

@@ -0,0 +1,62 @@
+package net.darkhax.bookshelf.api.damagesource;
+
+import net.minecraft.network.chat.Component;
+import net.minecraft.network.chat.TranslatableComponent;
+import net.minecraft.resources.ResourceLocation;
+import net.minecraft.world.damagesource.DamageSource;
+import net.minecraft.world.entity.LivingEntity;
+import net.minecraft.world.level.storage.loot.LootContext;
+
+/**
+ * A damage source that is tied to a fake player. Mobs killed by this damage source type can potentially drop loot even
+ * when no player was present.
+ */
+public class FakePlayerDamageSource extends DamageSource {
+
+    /**
+     * A unique namespaced ID that is tied to the fake player damage source. This is used to provide debug info and
+     * generate player death messages.
+     */
+    private final ResourceLocation sourceId;
+
+    public FakePlayerDamageSource(ResourceLocation sourceId) {
+
+        super(sourceId.toString());
+        this.sourceId = sourceId;
+    }
+
+    @Override
+    public Component getLocalizedDeathMessage(LivingEntity deadMob) {
+
+        return new TranslatableComponent("death.attack." + this.sourceId.getNamespace() + "." + this.sourceId.getPath(), deadMob.getDisplayName());
+    }
+
+    /**
+     * Checks if the corresponding loot roll should forcefully allow player only loot drops to be produced. The default
+     * behaviour is to always allow these drops when this damage source is used.
+     * <p>
+     * When this method returns true the result of {@link net.minecraft.world.level.storage.loot.predicates.LootItemKilledByPlayerCondition#test(LootContext)}
+     * will be forcefully true.
+     *
+     * @param context Additional loot table context that can be used for additional context checks.
+     * @return Should the corresponding loot roll be able to allow player only loot drops.
+     */
+    public boolean shouldDropPlayerLoot(LootContext context) {
+
+        return true;
+    }
+
+    /**
+     * A helper method that will cause damage to a mob using the source.
+     *
+     * @param entity The entity to damage.
+     * @param damage The amount of damage to do.
+     */
+    public void causeDamage(LivingEntity entity, float damage) {
+
+        entity.hurt(this, damage);
+
+        // Sets the last tick the mob was hurt by a "player". This is required for EXP to drop.
+        entity.setLastHurtByPlayer(null);
+    }
+}

Common/src/main/java/net/darkhax/bookshelf/mixin/loot/MixinLootItemKilledByPlayerCondition.java

@@ -0,0 +1,26 @@
+package net.darkhax.bookshelf.mixin.loot;
+
+import net.darkhax.bookshelf.api.damagesource.FakePlayerDamageSource;
+import net.minecraft.world.level.storage.loot.LootContext;
+import net.minecraft.world.level.storage.loot.parameters.LootContextParams;
+import net.minecraft.world.level.storage.loot.predicates.LootItemKilledByPlayerCondition;
+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(LootItemKilledByPlayerCondition.class)
+public class MixinLootItemKilledByPlayerCondition {
+
+    @Inject(method = "test(Lnet/minecraft/world/level/storage/loot/LootContext;)Z", at = @At("HEAD"), cancellable = true)
+    public void test(LootContext context, CallbackInfoReturnable<Boolean> callback) {
+
+        if (context != null && context.hasParam(LootContextParams.DAMAGE_SOURCE) && context.getParam(LootContextParams.DAMAGE_SOURCE) instanceof FakePlayerDamageSource fakePlayerSource) {
+
+            if (fakePlayerSource.shouldDropPlayerLoot(context)) {
+
+                callback.setReturnValue(true);
+            }
+        }
+    }
+}