Tag Lifecycle Events (#10993)

* wip tags

* use generics in tag registrars

* comment out varargs methods for now

* split up patch

* cache loaded service provider

* finish renames

* use builderWithExpectedSize

* finalize

patches/server/Add-Lifecycle-Event-system.patch

@@ -468,6 +468,8 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +        }
 +    }
 +
++    public abstract boolean hasHandlers();
++
 +    public abstract void forEachHandler(E event, Consumer<RegisteredHandler<O, E>> consumer, Predicate<RegisteredHandler<O, E>> predicate);
 +
 +    public abstract void removeMatching(Predicate<RegisteredHandler<O, E>> predicate);
@@ -505,7 +507,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +public final class LifecycleEventTypeProviderImpl implements LifecycleEventTypeProvider {
 +
 +    public static LifecycleEventTypeProviderImpl instance() {
-+        return (LifecycleEventTypeProviderImpl) LifecycleEventTypeProvider.PROVIDER;
++        return (LifecycleEventTypeProviderImpl) LifecycleEventTypeProvider.provider();
 +    }
 +
 +    @Override
@@ -550,6 +552,11 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +    }
 +
 +    @Override
++    public boolean hasHandlers() {
++        return !this.handlers.isEmpty();
++    }
++
++    @Override
 +    public MonitorLifecycleEventHandlerConfigurationImpl<O, E> newHandler(final LifecycleEventHandler<? super E> handler) {
 +        return new MonitorLifecycleEventHandlerConfigurationImpl<>(handler, this);
 +    }
@@ -652,6 +659,11 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +    }
 +
 +    @Override
++    public boolean hasHandlers() {
++        return !this.handlers.isEmpty();
++    }
++
++    @Override
 +    protected void register(final O owner, final AbstractLifecycleEventHandlerConfiguration<O, E> config) {
 +        Preconditions.checkArgument(config instanceof PrioritizedLifecycleEventHandlerConfigurationImpl<?, ?>, "Configuration must be a PrioritizedLifecycleEventHandlerConfiguration");
 +        this.handlers.add(new RegisteredHandler<>(owner, config));

patches/server/Add-registry-entry-and-builders.patch

@@ -96,7 +96,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +    protected HolderSet<Enchantment> exclusiveWith = HolderSet.empty(); // Paper added default to empty.
 +
 +    // Effects
-+    protected final DataComponentMap effects;
++    protected DataComponentMap effects;
 +
 +    protected final Conversions conversions;
 +

patches/server/Registry-Modification-API.patch

@@ -134,12 +134,12 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +import org.checkerframework.checker.nullness.qual.Nullable;
 +import org.intellij.lang.annotations.Subst;
 +
-+public final class PaperRegistryListenerManager {
++public class PaperRegistryListenerManager {
 +
 +    public static final PaperRegistryListenerManager INSTANCE = new PaperRegistryListenerManager();
 +
-+    public final RegistryEventMap valueAddHooks = new RegistryEventMap("value add");
-+    public final RegistryEventMap freezeHooks = new RegistryEventMap("freeze");
++    public final RegistryEventMap valueAddEventTypes = new RegistryEventMap("value add");
++    public final RegistryEventMap freezeEventTypes = new RegistryEventMap("freeze");
 +
 +    private PaperRegistryListenerManager() {
 +    }
@@ -200,7 +200,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +    ) {
 +        Preconditions.checkState(LaunchEntryPointHandler.INSTANCE.hasEntered(Entrypoint.BOOTSTRAPPER), registry.key() + " tried to run modification listeners before bootstrappers have been called"); // verify that bootstrappers have been called
 +        final @Nullable RegistryEntryInfo<M, T> entry = PaperRegistries.getEntry(registry.key());
-+        if (!RegistryEntry.Modifiable.isModifiable(entry) || !this.valueAddHooks.hasHooks(entry.apiKey())) {
++        if (!RegistryEntry.Modifiable.isModifiable(entry) || !this.valueAddEventTypes.hasHandlers(entry.apiKey())) {
 +            return registerMethod.register((WritableRegistry<M>) registry, key, nms, registrationInfo);
 +        }
 +        final RegistryEntry.Modifiable<M, T, B> modifiableEntry = RegistryEntry.Modifiable.asModifiable(entry);
@@ -217,7 +217,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +        final RegistrationInfo registrationInfo,
 +        final Conversions conversions
 +    ) {
-+        if (!RegistryEntry.Modifiable.isModifiable(entry) || !this.valueAddHooks.hasHooks(entry.apiKey())) {
++        if (!RegistryEntry.Modifiable.isModifiable(entry) || !this.valueAddEventTypes.hasHandlers(entry.apiKey())) {
 +            registry.register(key, builder.build(), registrationInfo);
 +            return;
 +        }
@@ -237,7 +237,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +        @Subst("namespace:key") final ResourceLocation beingAdded = key.location();
 +        @SuppressWarnings("PatternValidation") final TypedKey<T> typedKey = TypedKey.create(entry.apiKey(), Key.key(beingAdded.getNamespace(), beingAdded.getPath()));
 +        final RegistryEntryAddEventImpl<T, B> event = entry.createEntryAddEvent(typedKey, builder, conversions);
-+        LifecycleEventRunner.INSTANCE.callEvent(this.valueAddHooks.getHook(entry.apiKey()), event);
++        LifecycleEventRunner.INSTANCE.callEvent(this.valueAddEventTypes.getEventType(entry.apiKey()), event);
 +        if (oldNms != null) {
 +            ((MappedRegistry<M>) registry).clearIntrusiveHolder(oldNms);
 +        }
@@ -261,27 +261,27 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +
 +    public <M, T extends org.bukkit.Keyed, B extends PaperRegistryBuilder<M, T>> void runFreezeListeners(final ResourceKey<? extends Registry<M>> resourceKey, final Conversions conversions) {
 +        final @Nullable RegistryEntryInfo<M, T> entry = PaperRegistries.getEntry(resourceKey);
-+        if (!RegistryEntry.Addable.isAddable(entry) || !this.freezeHooks.hasHooks(entry.apiKey())) {
++        if (!RegistryEntry.Addable.isAddable(entry) || !this.freezeEventTypes.hasHandlers(entry.apiKey())) {
 +            return;
 +        }
 +        final RegistryEntry.Addable<M, T, B> writableEntry = RegistryEntry.Addable.asAddable(entry);
 +        final WritableCraftRegistry<M, T, B> writableRegistry = PaperRegistryAccess.instance().getWritableRegistry(entry.apiKey());
 +        final RegistryFreezeEventImpl<T, B> event = writableEntry.createFreezeEvent(writableRegistry, conversions);
-+        LifecycleEventRunner.INSTANCE.callEvent(this.freezeHooks.getHook(entry.apiKey()), event);
++        LifecycleEventRunner.INSTANCE.callEvent(this.freezeEventTypes.getEventType(entry.apiKey()), event);
 +    }
 +
 +    public <T, B extends RegistryBuilder<T>> RegistryEntryAddEventType<T, B> getRegistryValueAddEventType(final RegistryEventProvider<T, B> type) {
 +        if (!RegistryEntry.Modifiable.isModifiable(PaperRegistries.getEntry(type.registryKey()))) {
 +            throw new IllegalArgumentException(type.registryKey() + " does not support RegistryEntryAddEvent");
 +        }
-+        return this.valueAddHooks.getOrCreate(type, RegistryEntryAddEventTypeImpl::new);
++        return this.valueAddEventTypes.getOrCreate(type.registryKey(), RegistryEntryAddEventTypeImpl::new);
 +    }
 +
 +    public <T, B extends RegistryBuilder<T>> LifecycleEventType.Prioritizable<BootstrapContext, RegistryFreezeEvent<T, B>> getRegistryFreezeEventType(final RegistryEventProvider<T, B> type) {
 +        if (!RegistryEntry.Addable.isAddable(PaperRegistries.getEntry(type.registryKey()))) {
 +            throw new IllegalArgumentException(type.registryKey() + " does not support RegistryFreezeEvent");
 +        }
-+        return this.freezeHooks.getOrCreate(type, RegistryLifecycleEventType::new);
++        return this.freezeEventTypes.getOrCreate(type.registryKey(), RegistryLifecycleEventType::new);
 +    }
 +}
 diff --git a/src/main/java/io/papermc/paper/registry/WritableCraftRegistry.java b/src/main/java/io/papermc/paper/registry/WritableCraftRegistry.java
@@ -702,9 +702,10 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +package io.papermc.paper.registry.event;
 +
 +import io.papermc.paper.plugin.bootstrap.BootstrapContext;
++import io.papermc.paper.plugin.lifecycle.event.LifecycleEvent;
 +import io.papermc.paper.plugin.lifecycle.event.LifecycleEventRunner;
++import io.papermc.paper.plugin.lifecycle.event.types.AbstractLifecycleEventType;
 +import io.papermc.paper.plugin.lifecycle.event.types.LifecycleEventType;
-+import io.papermc.paper.registry.RegistryBuilder;
 +import io.papermc.paper.registry.RegistryKey;
 +import java.util.HashMap;
 +import java.util.Map;
@@ -713,7 +714,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +
 +public final class RegistryEventMap {
 +
-+    private final Map<RegistryKey<?>, LifecycleEventType<BootstrapContext, ? extends RegistryEvent<?>, ?>> hooks = new HashMap<>();
++    private final Map<RegistryKey<?>, LifecycleEventType<BootstrapContext, ? extends LifecycleEvent, ?>> eventTypes = new HashMap<>();
 +    private final String name;
 +
 +    public RegistryEventMap(final String name) {
@@ -721,25 +722,26 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +    }
 +
 +    @SuppressWarnings("unchecked")
-+    public <T, B extends RegistryBuilder<T>, E extends RegistryEvent<T>, ET extends LifecycleEventType<BootstrapContext, E, ?>> ET getOrCreate(final RegistryEventProvider<T, B> type, final BiFunction<? super RegistryEventProvider<T, B>, ? super String, ET> eventTypeCreator) {
-+        final ET registerHook;
-+        if (this.hooks.containsKey(type.registryKey())) {
-+            registerHook = (ET) this.hooks.get(type.registryKey());
++    public <T, E extends LifecycleEvent, ET extends LifecycleEventType<BootstrapContext, E, ?>> ET getOrCreate(final RegistryKey<T> registryKey, final BiFunction<? super RegistryKey<T>, ? super String, ET> eventTypeCreator) {
++        final ET eventType;
++        if (this.eventTypes.containsKey(registryKey)) {
++            eventType = (ET) this.eventTypes.get(registryKey);
 +        } else {
-+            registerHook = eventTypeCreator.apply(type, this.name);
-+            LifecycleEventRunner.INSTANCE.addEventType(registerHook);
-+            this.hooks.put(type.registryKey(), registerHook);
++            eventType = eventTypeCreator.apply(registryKey, this.name);
++            LifecycleEventRunner.INSTANCE.addEventType(eventType);
++            this.eventTypes.put(registryKey, eventType);
 +        }
-+        return registerHook;
++        return eventType;
 +    }
 +
 +    @SuppressWarnings("unchecked")
-+    public <T, E extends RegistryEvent<T>> LifecycleEventType<BootstrapContext, E, ?> getHook(final RegistryKey<T> registryKey) {
-+        return (LifecycleEventType<BootstrapContext, E, ?>) Objects.requireNonNull(this.hooks.get(registryKey), "No hook for " + registryKey);
++    public <T, E extends LifecycleEvent> LifecycleEventType<BootstrapContext, E, ?> getEventType(final RegistryKey<T> registryKey) {
++        return (LifecycleEventType<BootstrapContext, E, ?>) Objects.requireNonNull(this.eventTypes.get(registryKey), "No hook for " + registryKey);
 +    }
 +
-+    public boolean hasHooks(final RegistryKey<?> registryKey) {
-+        return this.hooks.containsKey(registryKey);
++    public boolean hasHandlers(final RegistryKey<?> registryKey) {
++        final AbstractLifecycleEventType<?, ?, ?> type = ((AbstractLifecycleEventType<?, ?, ?>) this.eventTypes.get(registryKey));
++        return type != null && type.hasHandlers();
 +    }
 +
 +}
@@ -830,15 +832,15 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +import io.papermc.paper.plugin.lifecycle.event.handler.LifecycleEventHandler;
 +import io.papermc.paper.plugin.lifecycle.event.types.PrioritizableLifecycleEventType;
 +import io.papermc.paper.registry.RegistryBuilder;
++import io.papermc.paper.registry.RegistryKey;
 +import io.papermc.paper.registry.event.RegistryEntryAddEvent;
-+import io.papermc.paper.registry.event.RegistryEventProvider;
 +import java.util.function.Consumer;
 +import java.util.function.Predicate;
 +
 +public class RegistryEntryAddEventTypeImpl<T, B extends RegistryBuilder<T>> extends PrioritizableLifecycleEventType<BootstrapContext, RegistryEntryAddEvent<T, B>, RegistryEntryAddConfiguration<T>> implements RegistryEntryAddEventType<T, B> {
 +
-+    public RegistryEntryAddEventTypeImpl(final RegistryEventProvider<T, B> type, final String eventName) {
-+        super(type.registryKey() + " / " + eventName, BootstrapContext.class);
++    public RegistryEntryAddEventTypeImpl(final RegistryKey<T> registryKey, final String eventName) {
++        super(registryKey + " / " + eventName, BootstrapContext.class);
 +    }
 +
 +    @Override
@@ -914,14 +916,13 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +
 +import io.papermc.paper.plugin.bootstrap.BootstrapContext;
 +import io.papermc.paper.plugin.lifecycle.event.types.PrioritizableLifecycleEventType;
-+import io.papermc.paper.registry.RegistryBuilder;
++import io.papermc.paper.registry.RegistryKey;
 +import io.papermc.paper.registry.event.RegistryEvent;
-+import io.papermc.paper.registry.event.RegistryEventProvider;
 +
-+public final class RegistryLifecycleEventType<T, B extends RegistryBuilder<T>, E extends RegistryEvent<T>> extends PrioritizableLifecycleEventType.Simple<BootstrapContext, E> {
++public final class RegistryLifecycleEventType<T, E extends RegistryEvent<T>> extends PrioritizableLifecycleEventType.Simple<BootstrapContext, E> {
 +
-+    public RegistryLifecycleEventType(final RegistryEventProvider<T, B> type, final String eventName) {
-+        super(type.registryKey() + " / " + eventName, BootstrapContext.class);
++    public RegistryLifecycleEventType(final RegistryKey<T> registryKey, final String eventName) {
++        super(registryKey + " / " + eventName, BootstrapContext.class);
 +    }
 +}
 diff --git a/src/main/java/io/papermc/paper/registry/legacy/DelayedRegistry.java b/src/main/java/io/papermc/paper/registry/legacy/DelayedRegistry.java

patches/server/Tag-Lifecycle-Events.patch

@@ -0,0 +1,537 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Jake Potrebic <jake.m.potrebic@gmail.com>
+Date: Thu, 20 Jun 2024 09:40:57 -0700
+Subject: [PATCH] Tag Lifecycle Events
+
+== AT ==
+public net/minecraft/tags/TagEntry id
+public net/minecraft/tags/TagEntry tag
+public net/minecraft/tags/TagEntry required
+
+diff --git a/src/main/java/io/papermc/paper/plugin/lifecycle/event/types/LifecycleEventTypeProviderImpl.java b/src/main/java/io/papermc/paper/plugin/lifecycle/event/types/LifecycleEventTypeProviderImpl.java
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
+--- a/src/main/java/io/papermc/paper/plugin/lifecycle/event/types/LifecycleEventTypeProviderImpl.java
++++ b/src/main/java/io/papermc/paper/plugin/lifecycle/event/types/LifecycleEventTypeProviderImpl.java
+@@ -0,0 +0,0 @@ public final class LifecycleEventTypeProviderImpl implements LifecycleEventTypeP
+         return (LifecycleEventTypeProviderImpl) LifecycleEventTypeProvider.provider();
+     }
+ 
++    private final PaperTagEventTypeProvider provider = new PaperTagEventTypeProvider();
++
+     @Override
+     public <O extends LifecycleEventOwner, E extends LifecycleEvent> LifecycleEventType.Monitorable<O, E> monitor(final String name, final Class<? extends O> ownerType) {
+         return LifecycleEventRunner.INSTANCE.addEventType(new MonitorableLifecycleEventType<>(name, ownerType));
+@@ -0,0 +0,0 @@ public final class LifecycleEventTypeProviderImpl implements LifecycleEventTypeP
+     public <O extends LifecycleEventOwner, E extends LifecycleEvent> LifecycleEventType.Prioritizable<O, E> prioritized(final String name, final Class<? extends O> ownerType) {
+         return LifecycleEventRunner.INSTANCE.addEventType(new PrioritizableLifecycleEventType.Simple<>(name, ownerType));
+     }
++
++    @Override
++    public PaperTagEventTypeProvider tagProvider() {
++        return this.provider;
++    }
+ }
+diff --git a/src/main/java/io/papermc/paper/plugin/lifecycle/event/types/PaperTagEventTypeProvider.java b/src/main/java/io/papermc/paper/plugin/lifecycle/event/types/PaperTagEventTypeProvider.java
+new file mode 100644
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
+--- /dev/null
++++ b/src/main/java/io/papermc/paper/plugin/lifecycle/event/types/PaperTagEventTypeProvider.java
+@@ -0,0 +0,0 @@
++package io.papermc.paper.plugin.lifecycle.event.types;
++
++import io.papermc.paper.plugin.bootstrap.BootstrapContext;
++import io.papermc.paper.plugin.lifecycle.event.registrar.ReloadableRegistrarEvent;
++import io.papermc.paper.registry.RegistryKey;
++import io.papermc.paper.tag.PaperTagListenerManager;
++import io.papermc.paper.tag.PostFlattenTagRegistrar;
++import io.papermc.paper.tag.PreFlattenTagRegistrar;
++import org.checkerframework.checker.nullness.qual.NonNull;
++import org.checkerframework.framework.qual.DefaultQualifier;
++
++@DefaultQualifier(NonNull.class)
++public class PaperTagEventTypeProvider implements TagEventTypeProvider {
++
++    @Override
++    public <T> PrioritizableLifecycleEventType.Simple<BootstrapContext, ReloadableRegistrarEvent<PreFlattenTagRegistrar<T>>> preFlatten(final RegistryKey<T> registryKey) {
++        return PaperTagListenerManager.INSTANCE.getPreFlattenType(registryKey);
++    }
++
++    @Override
++    public <T> PrioritizableLifecycleEventType.Simple<BootstrapContext, ReloadableRegistrarEvent<PostFlattenTagRegistrar<T>>> postFlatten(final RegistryKey<T> registryKey) {
++        return PaperTagListenerManager.INSTANCE.getPostFlattenType(registryKey);
++    }
++}
+diff --git a/src/main/java/io/papermc/paper/tag/PaperPostFlattenTagRegistrar.java b/src/main/java/io/papermc/paper/tag/PaperPostFlattenTagRegistrar.java
+new file mode 100644
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
+--- /dev/null
++++ b/src/main/java/io/papermc/paper/tag/PaperPostFlattenTagRegistrar.java
+@@ -0,0 +0,0 @@
++package io.papermc.paper.tag;
++
++import com.google.common.collect.Collections2;
++import com.google.common.collect.ImmutableMap;
++import io.papermc.paper.adventure.PaperAdventure;
++import io.papermc.paper.plugin.bootstrap.BootstrapContext;
++import io.papermc.paper.plugin.lifecycle.event.registrar.PaperRegistrar;
++import io.papermc.paper.registry.RegistryKey;
++import io.papermc.paper.registry.TypedKey;
++import io.papermc.paper.registry.tag.TagKey;
++import java.util.ArrayList;
++import java.util.Collection;
++import java.util.Collections;
++import java.util.List;
++import java.util.Map;
++import java.util.NoSuchElementException;
++import java.util.Optional;
++import java.util.function.Function;
++import net.minecraft.resources.ResourceLocation;
++import org.bukkit.craftbukkit.util.CraftNamespacedKey;
++import org.checkerframework.checker.nullness.qual.NonNull;
++import org.checkerframework.checker.nullness.qual.Nullable;
++import org.checkerframework.framework.qual.DefaultQualifier;
++
++@SuppressWarnings("BoundedWildcard")
++@DefaultQualifier(NonNull.class)
++public class PaperPostFlattenTagRegistrar<M, T> implements PaperRegistrar<BootstrapContext>, PostFlattenTagRegistrar<T> {
++
++    public final Map<ResourceLocation, Collection<M>> tags;
++    private final Function<ResourceLocation, Optional<? extends M>> fromIdConverter;
++    private final Function<M, ResourceLocation> toIdConverter;
++    private final RegistryKey<T> registryKey;
++
++    public PaperPostFlattenTagRegistrar(
++        final Map<ResourceLocation, Collection<M>> tags,
++        final TagEventConfig<M, T> config
++    ) {
++        this.tags = tags;
++        this.fromIdConverter = config.fromIdConverter();
++        this.toIdConverter = config.toIdConverter();
++        this.registryKey = config.apiRegistryKey();
++    }
++
++    @Override
++    public void setCurrentContext(final @Nullable BootstrapContext owner) {
++    }
++
++    @Override
++    public RegistryKey<T> registryKey() {
++        return this.registryKey;
++    }
++
++    @Override
++    public Map<TagKey<T>, Collection<TypedKey<T>>> getAllTags() {
++        final ImmutableMap.Builder<TagKey<T>, Collection<TypedKey<T>>> tags = ImmutableMap.builderWithExpectedSize(this.tags.size());
++        for (final Map.Entry<ResourceLocation, Collection<M>> entry : this.tags.entrySet()) {
++            final TagKey<T> key = TagKey.create(this.registryKey, CraftNamespacedKey.fromMinecraft(entry.getKey()));
++            tags.put(key, this.convert(entry.getValue()));
++        }
++        return tags.build();
++    }
++
++    private Collection<TypedKey<T>> convert(final Collection<M> nms) {
++        return Collections.unmodifiableCollection(
++            Collections2.transform(nms, m -> this.convert(this.toIdConverter.apply(m)))
++        );
++    }
++
++    private TypedKey<T> convert(final ResourceLocation location) {
++        return TypedKey.create(this.registryKey, CraftNamespacedKey.fromMinecraft(location));
++    }
++
++    private M convert(final TypedKey<T> key) {
++        final Optional<? extends M> optional = this.fromIdConverter.apply(PaperAdventure.asVanilla(key.key()));
++        if (optional.isEmpty()) {
++            throw new IllegalArgumentException(key + " doesn't exist");
++        }
++        return optional.get();
++    }
++
++    @Override
++    public boolean hasTag(final TagKey<T> tagKey) {
++        return this.tags.containsKey(PaperAdventure.asVanilla(tagKey.key()));
++    }
++
++    private Collection<M> getNmsTag(final TagKey<T> tagKey, final boolean create) {
++        final ResourceLocation vanillaKey = PaperAdventure.asVanilla(tagKey.key());
++        Collection<M> tag = this.tags.get(vanillaKey);
++        if (tag == null) {
++            if (create) {
++                tag = this.tags.computeIfAbsent(vanillaKey, k -> new ArrayList<>());
++            } else {
++                throw new NoSuchElementException("Tag " + tagKey + " is not present");
++            }
++        }
++        return tag;
++    }
++
++    @Override
++    public Collection<TypedKey<T>> getTag(final TagKey<T> tagKey) {
++        return this.convert(this.getNmsTag(tagKey, false));
++    }
++
++    @Override
++    public void addToTag(final TagKey<T> tagKey, final Collection<TypedKey<T>> values) {
++        final Collection<M> nmsTag = new ArrayList<>(this.getNmsTag(tagKey, true));
++        for (final TypedKey<T> key : values) {
++            nmsTag.add(this.convert(key));
++        }
++        this.tags.put(PaperAdventure.asVanilla(tagKey.key()), nmsTag);
++    }
++
++    @Override
++    public void setTag(final TagKey<T> tagKey, final Collection<TypedKey<T>> values) {
++        final List<M> newList = List.copyOf(Collections2.transform(values, this::convert));
++        this.tags.put(PaperAdventure.asVanilla(tagKey.key()), newList);
++    }
++}
+diff --git a/src/main/java/io/papermc/paper/tag/PaperPreFlattenTagRegistrar.java b/src/main/java/io/papermc/paper/tag/PaperPreFlattenTagRegistrar.java
+new file mode 100644
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
+--- /dev/null
++++ b/src/main/java/io/papermc/paper/tag/PaperPreFlattenTagRegistrar.java
+@@ -0,0 +0,0 @@
++package io.papermc.paper.tag;
++
++import com.google.common.base.Preconditions;
++import com.google.common.collect.Collections2;
++import com.google.common.collect.ImmutableMap;
++import com.google.common.collect.Lists;
++import io.papermc.paper.adventure.PaperAdventure;
++import io.papermc.paper.plugin.bootstrap.BootstrapContext;
++import io.papermc.paper.plugin.lifecycle.event.registrar.PaperRegistrar;
++import io.papermc.paper.registry.RegistryKey;
++import io.papermc.paper.registry.tag.TagKey;
++import java.util.ArrayList;
++import java.util.Collection;
++import java.util.Collections;
++import java.util.HashMap;
++import java.util.List;
++import java.util.Map;
++import java.util.NoSuchElementException;
++import net.minecraft.resources.ResourceLocation;
++import net.minecraft.tags.TagLoader;
++import org.bukkit.craftbukkit.util.CraftNamespacedKey;
++import org.checkerframework.checker.nullness.qual.NonNull;
++import org.checkerframework.checker.nullness.qual.Nullable;
++import org.checkerframework.framework.qual.DefaultQualifier;
++
++@SuppressWarnings("BoundedWildcard")
++@DefaultQualifier(NonNull.class)
++public class PaperPreFlattenTagRegistrar<T> implements PaperRegistrar<BootstrapContext>, PreFlattenTagRegistrar<T> {
++
++    public final Map<ResourceLocation, List<TagLoader.EntryWithSource>> tags;
++    private final RegistryKey<T> registryKey;
++
++    private @Nullable BootstrapContext owner;
++
++    public PaperPreFlattenTagRegistrar(
++        final Map<ResourceLocation, List<TagLoader.EntryWithSource>> tags,
++        final TagEventConfig<?, T> config
++    ) {
++        this.tags = new HashMap<>(tags);
++        this.registryKey = config.apiRegistryKey();
++    }
++
++    @Override
++    public void setCurrentContext(final @Nullable BootstrapContext owner) {
++        this.owner = owner;
++    }
++
++    @Override
++    public RegistryKey<T> registryKey() {
++        return this.registryKey;
++    }
++
++    @Override
++    public Map<TagKey<T>, Collection<TagEntry<T>>> getAllTags() {
++        final ImmutableMap.Builder<TagKey<T>, Collection<io.papermc.paper.tag.TagEntry<T>>> builder = ImmutableMap.builderWithExpectedSize(this.tags.size());
++        for (final Map.Entry<ResourceLocation, List<TagLoader.EntryWithSource>> entry : this.tags.entrySet()) {
++            final TagKey<T> key = TagKey.create(this.registryKey, CraftNamespacedKey.fromMinecraft(entry.getKey()));
++            builder.put(key, convert(entry.getValue()));
++        }
++        return builder.build();
++    }
++
++    private static <T> List<io.papermc.paper.tag.TagEntry<T>> convert(final List<TagLoader.EntryWithSource> nmsEntries) {
++        return Collections.unmodifiableList(Lists.transform(nmsEntries, PaperPreFlattenTagRegistrar::convert));
++    }
++
++    private static <T> io.papermc.paper.tag.TagEntry<T> convert(final TagLoader.EntryWithSource nmsEntry) {
++        return new TagEntryImpl<>(CraftNamespacedKey.fromMinecraft(nmsEntry.entry().id), nmsEntry.entry().tag, nmsEntry.entry().required);
++    }
++
++    private TagLoader.EntryWithSource convert(final TagEntry<T> entry) {
++        Preconditions.checkState(this.owner != null, "Owner is not set");
++        final ResourceLocation vanilla = PaperAdventure.asVanilla(entry.key());
++        final net.minecraft.tags.TagEntry nmsEntry;
++        if (entry.isTag()) {
++            if (entry.isRequired()) {
++                nmsEntry = net.minecraft.tags.TagEntry.tag(vanilla);
++            } else {
++                nmsEntry = net.minecraft.tags.TagEntry.optionalTag(vanilla);
++            }
++        } else {
++            if (entry.isRequired()) {
++                nmsEntry = net.minecraft.tags.TagEntry.element(vanilla);
++            } else {
++                nmsEntry = net.minecraft.tags.TagEntry.optionalElement(vanilla);
++            }
++        }
++        return new TagLoader.EntryWithSource(nmsEntry, this.owner.getPluginMeta().getDisplayName());
++    }
++
++    @Override
++    public boolean hasTag(final TagKey<T> tagKey) {
++        return this.tags.containsKey(PaperAdventure.asVanilla(tagKey.key()));
++    }
++
++    private List<TagLoader.EntryWithSource> getNmsTag(final TagKey<T> tagKey, boolean create) {
++        final ResourceLocation vanillaKey = PaperAdventure.asVanilla(tagKey.key());
++        List<TagLoader.EntryWithSource> tag = this.tags.get(vanillaKey);
++        if (tag == null) {
++            if (create) {
++                tag = this.tags.computeIfAbsent(vanillaKey, k -> new ArrayList<>());
++            } else {
++                throw new NoSuchElementException("Tag " + tagKey + " is not present");
++            }
++        }
++        return tag;
++    }
++
++    @Override
++    public List<TagEntry<T>> getTag(final TagKey<T> tagKey) {
++        return convert(this.getNmsTag(tagKey, false));
++    }
++
++    @Override
++    public void addToTag(final TagKey<T> tagKey, final Collection<TagEntry<T>> entries) {
++        final List<TagLoader.EntryWithSource> nmsTag = new ArrayList<>(this.getNmsTag(tagKey, true));
++        for (final TagEntry<T> tagEntry : entries) {
++            nmsTag.add(this.convert(tagEntry));
++        }
++        this.tags.put(PaperAdventure.asVanilla(tagKey.key()), nmsTag);
++    }
++
++    @Override
++    public void setTag(final TagKey<T> tagKey, final Collection<TagEntry<T>> entries) {
++        final List<TagLoader.EntryWithSource> newList = List.copyOf(Collections2.transform(entries, this::convert));
++        this.tags.put(PaperAdventure.asVanilla(tagKey.key()), newList);
++    }
++}
+diff --git a/src/main/java/io/papermc/paper/tag/PaperTagListenerManager.java b/src/main/java/io/papermc/paper/tag/PaperTagListenerManager.java
+new file mode 100644
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
+--- /dev/null
++++ b/src/main/java/io/papermc/paper/tag/PaperTagListenerManager.java
+@@ -0,0 +0,0 @@
++package io.papermc.paper.tag;
++
++import io.papermc.paper.plugin.bootstrap.BootstrapContext;
++import io.papermc.paper.plugin.lifecycle.event.LifecycleEventRunner;
++import io.papermc.paper.plugin.lifecycle.event.registrar.ReloadableRegistrarEvent;
++import io.papermc.paper.plugin.lifecycle.event.types.AbstractLifecycleEventType;
++import io.papermc.paper.plugin.lifecycle.event.types.PrioritizableLifecycleEventType;
++import io.papermc.paper.registry.PaperRegistries;
++import io.papermc.paper.registry.RegistryKey;
++import io.papermc.paper.registry.event.RegistryEventMap;
++import java.util.Collection;
++import java.util.List;
++import java.util.Map;
++import net.minecraft.core.Holder;
++import net.minecraft.core.Registry;
++import net.minecraft.resources.ResourceLocation;
++import net.minecraft.tags.TagLoader;
++import org.checkerframework.checker.nullness.qual.NonNull;
++import org.checkerframework.checker.nullness.qual.Nullable;
++import org.checkerframework.framework.qual.DefaultQualifier;
++
++@DefaultQualifier(NonNull.class)
++public class PaperTagListenerManager {
++
++    public static final String PRE_FLATTEN_EVENT_NAME = "pre-flatten";
++    public static final String POST_FLATTEN_EVENT_NAME = "post-flatten";
++
++    public static final PaperTagListenerManager INSTANCE = new PaperTagListenerManager();
++
++    public final RegistryEventMap preFlatten = new RegistryEventMap(PRE_FLATTEN_EVENT_NAME);
++    public final RegistryEventMap postFlatten = new RegistryEventMap(POST_FLATTEN_EVENT_NAME);
++
++    private PaperTagListenerManager() {
++    }
++
++    public <A> Map<ResourceLocation, List<TagLoader.EntryWithSource>> firePreFlattenEvent(
++        final Map<ResourceLocation, List<TagLoader.EntryWithSource>> initial,
++        final @Nullable TagEventConfig<?, A> config
++    ) {
++        if (config == null || config.preFlatten() == null || !config.preFlatten().hasHandlers()) {
++            return initial;
++        }
++        final PaperPreFlattenTagRegistrar<A> registrar = new PaperPreFlattenTagRegistrar<>(initial, config);
++        LifecycleEventRunner.INSTANCE.callReloadableRegistrarEvent(
++            config.preFlatten(),
++            registrar,
++            BootstrapContext.class,
++            config.cause()
++        );
++        return Map.copyOf(registrar.tags);
++    }
++
++    public <M, A> Map<ResourceLocation, Collection<M>> firePostFlattenEvent(
++        final Map<ResourceLocation, Collection<M>> initial,
++        final @Nullable TagEventConfig<M, A> config
++    ) {
++        if (config == null || config.postFlatten() == null || !config.postFlatten().hasHandlers()) {
++            return initial;
++        }
++        final PaperPostFlattenTagRegistrar<M, A> registrar = new PaperPostFlattenTagRegistrar<>(initial, config);
++        LifecycleEventRunner.INSTANCE.callReloadableRegistrarEvent(
++            config.postFlatten(),
++            registrar,
++            BootstrapContext.class,
++            config.cause()
++        );
++        return Map.copyOf(registrar.tags);
++    }
++
++    public <M, B> @Nullable TagEventConfig<Holder<M>, B> createEventConfig(final Registry<M> registry, final ReloadableRegistrarEvent.Cause cause) {
++        if (PaperRegistries.getEntry(registry.key()) == null) {
++            // TODO probably should be able to modify every registry
++            return null;
++        }
++        final RegistryKey<B> registryKey = PaperRegistries.registryFromNms(registry.key());
++        @Nullable AbstractLifecycleEventType<BootstrapContext, ReloadableRegistrarEvent<PreFlattenTagRegistrar<B>>, ?> preFlatten = null;
++        if (this.preFlatten.hasHandlers(registryKey)) {
++            preFlatten = (AbstractLifecycleEventType<BootstrapContext, ReloadableRegistrarEvent<PreFlattenTagRegistrar<B>>, ?>) this.preFlatten.<B, ReloadableRegistrarEvent<PreFlattenTagRegistrar<B>>>getEventType(registryKey);
++        }
++        @Nullable AbstractLifecycleEventType<BootstrapContext, ReloadableRegistrarEvent<PostFlattenTagRegistrar<B>>, ?> postFlatten = null;
++        if (this.postFlatten.hasHandlers(registryKey)) {
++            postFlatten = (AbstractLifecycleEventType<BootstrapContext, ReloadableRegistrarEvent<PostFlattenTagRegistrar<B>>, ?>) this.postFlatten.<B, ReloadableRegistrarEvent<PostFlattenTagRegistrar<B>>>getEventType(registryKey);
++        }
++        return new TagEventConfig<>(
++            preFlatten,
++            postFlatten,
++            cause,
++            registry::getHolder,
++            h -> ((Holder.Reference<M>) h).key().location(),
++            PaperRegistries.registryFromNms(registry.key())
++        );
++    }
++
++    public <T> PrioritizableLifecycleEventType.Simple<BootstrapContext, ReloadableRegistrarEvent<PreFlattenTagRegistrar<T>>> getPreFlattenType(final RegistryKey<T> registryKey) {
++        return this.preFlatten.getOrCreate(registryKey, (ignored, name) -> {
++            return new PrioritizableLifecycleEventType.Simple<>(name, BootstrapContext.class);
++        });
++    }
++
++    public <T> PrioritizableLifecycleEventType.Simple<BootstrapContext, ReloadableRegistrarEvent<PostFlattenTagRegistrar<T>>> getPostFlattenType(final RegistryKey<T> registryKey) {
++        return this.postFlatten.getOrCreate(registryKey, (ignored, name) -> {
++            return new PrioritizableLifecycleEventType.Simple<>(name, BootstrapContext.class);
++        });
++    }
++}
+diff --git a/src/main/java/io/papermc/paper/tag/TagEventConfig.java b/src/main/java/io/papermc/paper/tag/TagEventConfig.java
+new file mode 100644
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
+--- /dev/null
++++ b/src/main/java/io/papermc/paper/tag/TagEventConfig.java
+@@ -0,0 +0,0 @@
++package io.papermc.paper.tag;
++
++import io.papermc.paper.plugin.bootstrap.BootstrapContext;
++import io.papermc.paper.plugin.lifecycle.event.registrar.ReloadableRegistrarEvent;
++import io.papermc.paper.plugin.lifecycle.event.types.AbstractLifecycleEventType;
++import io.papermc.paper.registry.RegistryKey;
++import java.util.Optional;
++import java.util.function.Function;
++import net.minecraft.resources.ResourceLocation;
++import org.checkerframework.checker.nullness.qual.NonNull;
++import org.checkerframework.checker.nullness.qual.Nullable;
++import org.checkerframework.framework.qual.DefaultQualifier;
++
++@DefaultQualifier(NonNull.class)
++public record TagEventConfig<M, A>(
++    @Nullable AbstractLifecycleEventType<BootstrapContext, ? extends ReloadableRegistrarEvent<PreFlattenTagRegistrar<A>>, ?> preFlatten,
++    @Nullable AbstractLifecycleEventType<BootstrapContext, ? extends ReloadableRegistrarEvent<PostFlattenTagRegistrar<A>>, ?> postFlatten,
++    ReloadableRegistrarEvent.Cause cause,
++    Function<ResourceLocation, Optional<? extends M>> fromIdConverter,
++    Function<M, ResourceLocation> toIdConverter,
++    RegistryKey<A> apiRegistryKey
++) {
++}
+diff --git a/src/main/java/net/minecraft/server/ServerFunctionLibrary.java b/src/main/java/net/minecraft/server/ServerFunctionLibrary.java
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
+--- a/src/main/java/net/minecraft/server/ServerFunctionLibrary.java
++++ b/src/main/java/net/minecraft/server/ServerFunctionLibrary.java
+@@ -0,0 +0,0 @@ public class ServerFunctionLibrary implements PreparableReloadListener {
+                             return null;
+                         }).join());
+                     this.functions = builder.build();
+-                    this.tags = this.tagsLoader.build((Map<ResourceLocation, List<TagLoader.EntryWithSource>>)intermediate.getFirst());
++                    this.tags = this.tagsLoader.build((Map<ResourceLocation, List<TagLoader.EntryWithSource>>)intermediate.getFirst(), null); // Paper - command function tags are not implemented yet
+                 },
+                 applyExecutor
+             );
+diff --git a/src/main/java/net/minecraft/tags/TagLoader.java b/src/main/java/net/minecraft/tags/TagLoader.java
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
+--- a/src/main/java/net/minecraft/tags/TagLoader.java
++++ b/src/main/java/net/minecraft/tags/TagLoader.java
+@@ -0,0 +0,0 @@ public class TagLoader<T> {
+         return list.isEmpty() ? Either.right(builder.build()) : Either.left(list);
+     }
+ 
+-    public Map<ResourceLocation, Collection<T>> build(Map<ResourceLocation, List<TagLoader.EntryWithSource>> tags) {
++    // Paper start - fire tag registrar events
++    public Map<ResourceLocation, Collection<T>> build(Map<ResourceLocation, List<TagLoader.EntryWithSource>> tags, @Nullable io.papermc.paper.tag.TagEventConfig<T, ?> eventConfig) {
++        tags = io.papermc.paper.tag.PaperTagListenerManager.INSTANCE.firePreFlattenEvent(tags, eventConfig);
++        // Paper end - fire tag registrar events
+         final Map<ResourceLocation, Collection<T>> map = Maps.newHashMap();
+         TagEntry.Lookup<T> lookup = new TagEntry.Lookup<T>() {
+             @Nullable
+@@ -0,0 +0,0 @@ public class TagLoader<T> {
+                     )
+                     .ifRight(resolvedEntries -> map.put(id, (Collection<T>)resolvedEntries))
+         );
+-        return map;
++        return io.papermc.paper.tag.PaperTagListenerManager.INSTANCE.firePostFlattenEvent(map, eventConfig); // Paper - fire tag registrar events
+     }
+ 
+-    public Map<ResourceLocation, Collection<T>> loadAndBuild(ResourceManager manager) {
+-        return this.build(this.load(manager));
++    // Paper start - fire tag registrar events
++    public Map<ResourceLocation, Collection<T>> loadAndBuild(ResourceManager manager, @Nullable io.papermc.paper.tag.TagEventConfig<T, ?> eventConfig) {
++        return this.build(this.load(manager), eventConfig);
++        // Paper end - fire tag registrar events
+     }
+ 
+     public static record EntryWithSource(TagEntry entry, String source) {
+diff --git a/src/main/java/net/minecraft/tags/TagManager.java b/src/main/java/net/minecraft/tags/TagManager.java
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
+--- a/src/main/java/net/minecraft/tags/TagManager.java
++++ b/src/main/java/net/minecraft/tags/TagManager.java
+@@ -0,0 +0,0 @@ public class TagManager implements PreparableReloadListener {
+     ) {
+         List<? extends CompletableFuture<? extends TagManager.LoadResult<?>>> list = this.registryAccess
+             .registries()
+-            .map(registry -> this.createLoader(manager, prepareExecutor, (RegistryAccess.RegistryEntry<?>)registry))
++            .map(registry -> this.createLoader(manager, prepareExecutor, (RegistryAccess.RegistryEntry<?>)registry, applyExecutor instanceof net.minecraft.server.MinecraftServer ? io.papermc.paper.plugin.lifecycle.event.registrar.ReloadableRegistrarEvent.Cause.INITIAL : io.papermc.paper.plugin.lifecycle.event.registrar.ReloadableRegistrarEvent.Cause.RELOAD)) // Paper - add registrar event cause
+             .toList();
+         return CompletableFuture.allOf(list.toArray(CompletableFuture[]::new))
+             .thenCompose(synchronizer::wait)
+@@ -0,0 +0,0 @@ public class TagManager implements PreparableReloadListener {
+ 
+     private <T> CompletableFuture<TagManager.LoadResult<T>> createLoader(
+         ResourceManager resourceManager, Executor prepareExecutor, RegistryAccess.RegistryEntry<T> requirement
++        , io.papermc.paper.plugin.lifecycle.event.registrar.ReloadableRegistrarEvent.Cause cause // Paper - add registrar event cause
+     ) {
+         ResourceKey<? extends Registry<T>> resourceKey = requirement.key();
+         Registry<T> registry = requirement.value();
+         TagLoader<Holder<T>> tagLoader = new TagLoader<>(registry::getHolder, Registries.tagsDirPath(resourceKey));
+-        return CompletableFuture.supplyAsync(() -> new TagManager.LoadResult<>(resourceKey, tagLoader.loadAndBuild(resourceManager)), prepareExecutor);
++        // Paper start - fire tag registrar events
++        final io.papermc.paper.tag.TagEventConfig<Holder<T>, ?> config = io.papermc.paper.tag.PaperTagListenerManager.INSTANCE.createEventConfig(registry, cause);
++        return CompletableFuture.supplyAsync(() -> new TagManager.LoadResult<>(resourceKey, tagLoader.loadAndBuild(resourceManager, config)), prepareExecutor);
++        // Paper end - fire tag registrar events
+     }
+ 
+     public static record LoadResult<T>(ResourceKey<? extends Registry<T>> key, Map<ResourceLocation, Collection<Holder<T>>> tags) {