Add datapack registration lifecycle event

build-data/paper.at

@@ -110,6 +110,8 @@ public net.minecraft.server.network.ServerLoginPacketListenerImpl connection
 public net.minecraft.server.network.ServerLoginPacketListenerImpl state
 public net.minecraft.server.network.ServerLoginPacketListenerImpl$State
 public net.minecraft.server.packs.VanillaPackResourcesBuilder safeGetPath(Ljava/net/URI;)Ljava/nio/file/Path;
+public net.minecraft.server.packs.repository.FolderRepositorySource$FolderPackDetector
+public net.minecraft.server.packs.repository.FolderRepositorySource$FolderPackDetector <init>(Lnet/minecraft/world/level/validation/DirectoryValidator;)V
 public net.minecraft.server.packs.repository.Pack resources
 public net.minecraft.server.players.PlayerList playerIo
 public net.minecraft.server.players.PlayerList players

paper-api/src/main/java/io/papermc/paper/datapack/Datapack.java

@@ -1,61 +1,17 @@
 package io.papermc.paper.datapack;
 
-import java.util.Set;
 import net.kyori.adventure.text.Component;
-import org.bukkit.FeatureFlag;
+import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.Contract;
-import org.jetbrains.annotations.Unmodifiable;
 import org.jspecify.annotations.NullMarked;
 
 /**
  * This is a snapshot of a datapack on the server. It
  * won't be updated as datapacks are updated.
  */
 @NullMarked
-public interface Datapack {
-
-    /**
-     * Gets the name/id of this datapack.
-     *
-     * @return the name of the pack
-     */
-    @Contract(pure = true)
-    String getName();
-
-    /**
-     * Gets the title component of this datapack.
-     *
-     * @return the title
-     */
-    Component getTitle();
-
-    /**
-     * Gets the description component of this datapack.
-     *
-     * @return the description
-     */
-    Component getDescription();
-
-    /**
-     * Gets if this datapack is required to be enabled.
-     *
-     * @return true if the pack is required
-     */
-    boolean isRequired();
-
-    /**
-     * Gets the compatibility status of this pack.
-     *
-     * @return the compatibility of the pack
-     */
-    Compatibility getCompatibility();
-
-    /**
-     * Gets the set of required features for this datapack.
-     *
-     * @return the set of required features
-     */
-    @Unmodifiable Set<FeatureFlag> getRequiredFeatures();
+@ApiStatus.NonExtendable
+public interface Datapack extends DiscoveredDatapack {
 
     /**
      * Gets the enabled state of this pack.
@@ -74,13 +30,6 @@ public interface Datapack {
      */
     void setEnabled(boolean enabled);
 
-    /**
-     * Gets the source for this datapack.
-     *
-     * @return the pack source
-     */
-    DatapackSource getSource();
-
     /**
      * Computes the component vanilla Minecraft uses
      * to display this datapack. Includes the {@link #getSource()},
@@ -96,4 +45,11 @@ enum Compatibility {
         TOO_NEW,
         COMPATIBLE,
     }
+
+    /**
+     * Position of the pack in the load order.
+     */
+    enum Position {
+        TOP, BOTTOM
+    }
 }

paper-api/src/main/java/io/papermc/paper/datapack/DatapackRegistrar.java

@@ -0,0 +1,202 @@
+package io.papermc.paper.datapack;
+
+import io.papermc.paper.plugin.configuration.PluginMeta;
+import io.papermc.paper.plugin.lifecycle.event.registrar.Registrar;
+import java.io.IOException;
+import java.net.URI;
+import java.nio.file.Path;
+import java.util.Map;
+import java.util.function.Consumer;
+import net.kyori.adventure.text.Component;
+import org.jetbrains.annotations.ApiStatus;
+import org.jetbrains.annotations.Contract;
+import org.jetbrains.annotations.Unmodifiable;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
+
+/**
+ * The registrar for datapacks. The event for this registrar
+ * is called anytime the game tries to discover datapacks at any of the
+ * configured locations. This means that if a datapack should stay available to the server,
+ * it must always be discovered whenever this event fires.
+ * <p>An example of a plugin loading a datapack from within it's own jar is below</p>
+ * <pre>{@code
+ * public class YourPluginBootstrap implements PluginBootstrap {
+ *     @Override
+ *     public void bootstrap(BoostrapContext context) {
+ *         final LifecycleEventManager<BootstrapContext> manager = context.getLifecycleManager();
+ *         manager.registerEventHandler(LifecycleEvents.DATAPACK_DISCOVERY, event -> {
+ *             DatapackRegistrar registrar = event.registrar();
+ *             try {
+ *                 final URI uri = Objects.requireNonNull(
+ *                     YourPluginBootstrap.class.getResource("/pack")
+ *                 ).toURI();
+ *                 registrar.discoverPack(uri, "packId");
+ *             } catch (final URISyntaxException | IOException e) {
+ *                 throw new RuntimeException(e);
+ *             }
+ *         });
+ *     }
+ * }
+ * }</pre>
+ * @see io.papermc.paper.plugin.lifecycle.event.types.LifecycleEvents#DATAPACK_DISCOVERY
+ */
+@ApiStatus.NonExtendable
+@ApiStatus.Experimental
+@NullMarked
+public interface DatapackRegistrar extends Registrar {
+
+    /**
+     * Checks if a datapack with the specified name has been discovered.
+     *
+     * @param name the name of the pack
+     * @return true if the pack has been discovered
+     * @see Datapack#getName()
+     */
+    @Contract(pure = true)
+    boolean hasPackDiscovered(String name);
+
+    /**
+     * Gets a discovered datapack by its name.
+     *
+     * @param name the name of the pack
+     * @return the datapack
+     * @throws java.util.NoSuchElementException if the pack is not discovered
+     * @see Datapack#getName()
+     */
+    @Contract(pure = true)
+    DiscoveredDatapack getDiscoveredPack(String name);
+
+    /**
+     * Removes a discovered datapack by its name.
+     *
+     * @param name the name of the pack
+     * @return true if the pack was removed
+     * @see Datapack#getName()
+     */
+    @Contract(mutates = "this")
+    boolean removeDiscoveredPack(String name);
+
+    /**
+     * Gets all discovered datapacks.
+     *
+     * @return an unmodifiable map of discovered packs
+     */
+    @Contract(pure = true)
+    @Unmodifiable Map<String, DiscoveredDatapack> getDiscoveredPacks();
+
+    /**
+     * Discovers a datapack at the specified {@link URI} with the id.
+     * <p>Symlinks obey the {@code allowed_symlinks.txt} in the server root directory.</p>
+     *
+     * @param uri the location of the pack
+     * @param id a unique id (will be combined with plugin for the datapacks name)
+     * @return the discovered datapack (or null if it failed)
+     * @throws IOException if any IO error occurs
+     */
+    default @Nullable DiscoveredDatapack discoverPack(final URI uri, final String id) throws IOException {
+        return this.discoverPack(uri, id, c -> {});
+    }
+
+    /**
+     * Discovers a datapack at the specified {@link URI} with the id.
+     * <p>Symlinks obey the {@code allowed_symlinks.txt} in the server root directory.</p>
+     *
+     * @param uri the location of the pack
+     * @param id a unique id (will be combined with plugin for the datapacks name)
+     * @param configurer a configurer for extra options
+     * @return the discovered datapack (or null if it failed)
+     * @throws IOException if any IO error occurs
+     */
+    @Nullable DiscoveredDatapack discoverPack(URI uri, String id, Consumer<Configurer> configurer) throws IOException;
+
+    /**
+     * Discovers a datapack at the specified {@link Path} with the id.
+     * <p>Symlinks obey the {@code allowed_symlinks.txt} in the server root directory.</p>
+     *
+     * @param path the location of the pack
+     * @param id a unique id (will be combined with plugin for the datapacks name)
+     * @return the discovered datapack (or null if it failed)
+     * @throws IOException if any IO error occurs
+     */
+    default @Nullable DiscoveredDatapack discoverPack(final Path path, final String id) throws IOException {
+        return this.discoverPack(path, id, c -> {});
+    }
+
+    /**
+     * Discovers a datapack at the specified {@link Path} with the id.
+     * <p>Symlinks obey the {@code allowed_symlinks.txt} in the server root directory.</p>
+     *
+     * @param path the location of the pack
+     * @param id a unique id (will be combined with plugin for the datapacks name)
+     * @param configurer a configurer for extra options
+     * @return the discovered datapack (or null if it failed)
+     * @throws IOException if any IO error occurs
+     */
+    @Nullable DiscoveredDatapack discoverPack(Path path, String id, Consumer<Configurer> configurer) throws IOException;
+
+    /**
+     * Discovers a datapack at the specified {@link URI} with the id.
+     * <p>Symlinks obey the {@code allowed_symlinks.txt} in the server root directory.</p>
+     *
+     * @param pluginMeta the plugin which will be the "owner" of this datapack
+     * @param uri the location of the pack
+     * @param id a unique id (will be combined with plugin for the datapacks name)
+     * @param configurer a configurer for extra options
+     * @return the discovered datapack (or null if it failed)
+     * @throws IOException if any IO error occurs
+     */
+    @Nullable DiscoveredDatapack discoverPack(PluginMeta pluginMeta, URI uri, String id, Consumer<Configurer> configurer) throws IOException;
+
+    /**
+     * Discovers a datapack at the specified {@link Path} with the id.
+     * <p>Symlinks obey the {@code allowed_symlinks.txt} in the server root directory.</p>
+     *
+     * @param pluginMeta the plugin which will be the "owner" of this datapack
+     * @param path the location of the pack
+     * @param id a unique id (will be combined with plugin for the datapacks name)
+     * @param configurer a configurer for extra options
+     * @return the discovered datapack (or null if it failed)
+     * @throws IOException if any IO error occurs
+     */
+    @Nullable DiscoveredDatapack discoverPack(PluginMeta pluginMeta, Path path, String id, Consumer<Configurer> configurer) throws IOException;
+
+    /**
+     * Configures additional, optional, details about a datapack.
+     */
+    @ApiStatus.NonExtendable
+    @ApiStatus.Experimental
+    interface Configurer {
+
+        /**
+         * Changes the title of the datapack from the default which
+         * is just the "id" in the {@code registerPack} methods.
+         *
+         * @param title the new title
+         * @return the configurer for chaining
+         */
+        @Contract(value = "_ -> this", mutates = "this")
+        Configurer title(Component title);
+
+        /**
+         * Sets whether this pack is going to be automatically enabled on server starts even if previously disabled.
+         * Defaults to false.
+         *
+         * @param autoEnableOnServerStart true to ensure the pack is enabled on server starts.
+         * @return the configurer for chaining
+         */
+        @Contract(value = "_ -> this", mutates = "this")
+        Configurer autoEnableOnServerStart(boolean autoEnableOnServerStart);
+
+        /**
+         * Configures the position in the
+         * load order of this datapack.
+         *
+         * @param fixed won't move around in the load order as packs are added/removed
+         * @param position try to insert at the top of the order or bottom
+         * @return the configurer for chaining
+         */
+        @Contract(value = "_, _ -> this", mutates = "this")
+        Configurer position(boolean fixed, Datapack.Position position);
+    }
+}

paper-api/src/main/java/io/papermc/paper/datapack/DatapackSource.java

@@ -13,6 +13,7 @@ public sealed interface DatapackSource permits DatapackSourceImpl {
     DatapackSource FEATURE = create("feature");
     DatapackSource WORLD = create("world");
     DatapackSource SERVER = create("server");
+    DatapackSource PLUGIN = create("plugin");
 
     private static DatapackSource create(final String name) {
         return new DatapackSourceImpl(name);

paper-api/src/main/java/io/papermc/paper/datapack/DiscoveredDatapack.java

@@ -0,0 +1,71 @@
+package io.papermc.paper.datapack;
+
+import java.util.Set;
+import net.kyori.adventure.text.Component;
+import org.bukkit.FeatureFlag;
+import org.jetbrains.annotations.ApiStatus;
+import org.jetbrains.annotations.Contract;
+import org.jetbrains.annotations.Unmodifiable;
+import org.jspecify.annotations.NullMarked;
+
+/**
+ * This is a snapshot of a discovered datapack on the server. It
+ * won't be updated as datapacks are updated.
+ */
+@NullMarked
+@ApiStatus.NonExtendable
+public interface DiscoveredDatapack {
+
+    /**
+     * Gets the name/id of this datapack.
+     *
+     * @return the name of the pack
+     */
+    @Contract(pure = true)
+    String getName();
+
+    /**
+     * Gets the title component of this datapack.
+     *
+     * @return the title
+     */
+    Component getTitle();
+
+    /**
+     * Gets the description component of this datapack.
+     *
+     * @return the description
+     */
+    Component getDescription();
+
+    /**
+     * Gets if this datapack is required.
+     * <p>
+     * A "required" datapack will always be enabled on server startup, even if previously disabled.
+     *
+     * @return true if the pack is required
+     */
+    boolean isRequired();
+
+    /**
+     * Gets the compatibility status of this pack.
+     *
+     * @return the compatibility of the pack
+     */
+    Datapack.Compatibility getCompatibility();
+
+    /**
+     * Gets the set of required features for this datapack.
+     *
+     * @return the set of required features
+     */
+    @Unmodifiable
+    Set<FeatureFlag> getRequiredFeatures();
+
+    /**
+     * Gets the source for this datapack.
+     *
+     * @return the pack source
+     */
+    DatapackSource getSource();
+}