Summon and select ominous item spawners

Co-Authored-By: Claude Opus 5.5 <[email protected]>

crates/horizon-client/src/entity_nbt.rs

@@ -2089,7 +2089,14 @@ pub fn ominous_item_spawner_to_nbt(
         fall_distance: 0.0,
     };
     let mut tag = base.tag(raw);
-    put(&mut tag, "item", item_to_nbt(item));
+    // `ItemStack.CODEC` can't encode `ItemStack.EMPTY`, so an empty item
+    // writes no key.
+    if let Tag::Compound(map) = &mut tag {
+        map.remove(&"item".into());
+    }
+    if &*item.item != "minecraft:air" {
+        put(&mut tag, "item", item_to_nbt(item));
+    }
     put(
         &mut tag,
         "spawn_item_after_ticks",
@@ -2101,7 +2108,11 @@ pub fn ominous_item_spawner_to_nbt(
 /// and `spawn_item_after_ticks` (0 when absent). None without an item:
 /// such a spawner would spawn nothing.
 pub fn ominous_item_spawner_from_nbt(tag: &Tag) -> Option<(crate::items::ItemStack, Vec3, i64)> {
-    let item = tag.get("item").and_then(item_from_nbt)?;
+    // `readAdditionalSaveData`: `ItemStack.EMPTY` when it has none.
+    let item = tag
+        .get("item")
+        .and_then(item_from_nbt)
+        .unwrap_or_else(|| crate::items::ItemStack::new("minecraft:air", 1));
     let after = number(tag.get("spawn_item_after_ticks")).unwrap_or(0);
     Some((item, position(tag)?, after))
 }
@@ -3037,6 +3048,17 @@ mod tests {
         );
         assert_eq!((pos, after), (at, 97));
         assert!(ominous_item_spawner_from_nbt(&raw).is_none());
+        // No item is `ItemStack.EMPTY`, which writes no key back.
+        let empty = ominous_item_spawner_to_nbt(
+            &crate::items::ItemStack::new("minecraft:air", 1),
+            at,
+            0,
+            [1, 2, 3, 4],
+            Some(&tag),
+        );
+        assert!(empty.get("item").is_none());
+        let (back, pos, after) = ominous_item_spawner_from_nbt(&empty).unwrap();
+        assert_eq!((back.item.as_ref(), pos, after), ("minecraft:air", at, 0));
     }
 
     #[test]

crates/horizon-client/src/game/commands.rs

@@ -67,6 +67,8 @@ pub(super) enum Target {
     Tnt(u32),
     /// A falling block, by its entity id (`minecraft:falling_block`).
     Falling(u32),
+    /// An ominous item spawner, by its entity id (`minecraft:ominous_item_spawner`).
+    Spawner(u32),
 }
 /// An entity of a type Horizon does not simulate: its compound lives in the
 /// entity memory (`persist.raw`), its position and rotation here.
@@ -141,7 +143,8 @@ fn non_player_entity_id(t: Target) -> Option<i32> {
     | Target::Crystal(id)
     | Target::Dragon(id)
     | Target::Tnt(id)
-    | Target::Falling(id)) = t
+    | Target::Falling(id)
+    | Target::Spawner(id)) = t
     else {
         return None;
     };
@@ -525,6 +528,11 @@ impl Game<'_> {
                 .iter()
                 .find(|f| f.id == id)
                 .map(|f| [f.position.x, f.position.y, f.position.z]),
+            Target::Spawner(id) => self
+                .ominous_spawners
+                .iter()
+                .find(|s| s.id == id)
+                .map(|s| s.position),
         }
     }
     pub(super) fn target_type(&self, t: Target) -> String {
@@ -573,6 +581,7 @@ impl Game<'_> {
             Target::Dragon(_) => "minecraft:ender_dragon".into(),
             Target::Tnt(_) => "minecraft:tnt".into(),
             Target::Falling(_) => "minecraft:falling_block".into(),
+            Target::Spawner(_) => "minecraft:ominous_item_spawner".into(),
         }
     }
     /// The name of the player the game acts for: a guest's own while their
@@ -864,6 +873,7 @@ impl Game<'_> {
         }
         candidates.extend(self.tnts.iter().map(|t| Target::Tnt(t.id)));
         candidates.extend(self.falling.iter().map(|f| Target::Falling(f.id)));
+        candidates.extend(self.ominous_spawners.iter().map(|s| Target::Spawner(s.id)));
         candidates
     }
     /// The loaded levels, in the order the server holds them: the
@@ -897,6 +907,7 @@ impl Game<'_> {
             Target::Dragon(id),
             Target::Tnt(id),
             Target::Falling(id),
+            Target::Spawner(id),
         ]
         .into_iter()
         .find(|t| self.level_holds(*t))
@@ -920,6 +931,7 @@ impl Game<'_> {
             Target::Dragon(id) => self.dragon.as_ref().is_some_and(|d| d.id == id),
             Target::Tnt(id) => self.tnts.iter().any(|t| t.id == id),
             Target::Falling(id) => self.falling.iter().any(|f| f.id == id),
+            Target::Spawner(id) => self.ominous_spawners.iter().any(|s| s.id == id),
         }
     }
     /// Run `f` with the level that holds the entity a target names in place
@@ -1542,6 +1554,11 @@ impl Game<'_> {
                     f.previous = v;
                 }
             }
+            Target::Spawner(id) => {
+                if let Some(s) = self.ominous_spawners.iter_mut().find(|s| s.id == id) {
+                    s.position = [v.x, v.y, v.z];
+                }
+            }
             // Wall-mounted entities do not move.
             Target::Frame(_) | Target::Painting(_) => {}
         }
@@ -2041,6 +2058,7 @@ impl Game<'_> {
             Target::Dragon(id) => self.kill_dragon(id),
             Target::Tnt(id) => self.tnts.retain(|t| t.id != id),
             Target::Falling(id) => self.falling.retain(|f| f.id != id),
+            Target::Spawner(id) => self.ominous_spawners.retain(|s| s.id != id),
         }
         // The orbs marked for removal are gone (Entity.kill removes them).
         let before = self.orb_ids();
@@ -3714,6 +3732,7 @@ mod look_at_tests {
             Target::Dragon(7),
             Target::Tnt(7),
             Target::Falling(7),
+            Target::Spawner(7),
         ] {
             assert_eq!(non_player_entity_id(t), Some(7), "{t:?}");
         }

crates/horizon-client/src/game/commands/data.rs

@@ -207,6 +207,17 @@ impl Game<'_> {
                 );
                 crate::game::persist::with_raw(tag, raw)
             }
+            Target::Spawner(id) => {
+                let s = self.ominous_spawners.iter().find(|s| s.id == id)?;
+                let [x, y, z] = s.position;
+                entity_nbt::ominous_item_spawner_to_nbt(
+                    &s.item,
+                    horizon_core::geometry::Vec3::new(x, y, z),
+                    s.spawn_item_after,
+                    s.uuid,
+                    s.raw.as_deref(),
+                )
+            }
         })
     }
     /// `Entity.load` of new data (`EntityDataAccessor.setData`): the entity is
@@ -811,6 +822,8 @@ impl Game<'_> {
             Some(Target::Tnt(id))
         } else if self.falling.iter().any(|f| f.id == id) {
             Some(Target::Falling(id))
+        } else if self.ominous_spawners.iter().any(|s| s.id == id) {
+            Some(Target::Spawner(id))
         } else {
             None
         }

crates/horizon-client/src/game/lan_entities.rs

@@ -344,7 +344,9 @@ impl Game<'_> {
             e.meta.push((
                 8,
                 serializer::ITEM_STACK,
-                Value::Item(hub.stack(&Some(o.item.clone()))),
+                Value::Item(
+                    hub.stack(&Some(o.item.clone()).filter(|i| &*i.item != "minecraft:air")),
+                ),
             ));
             out.push(e);
         }

crates/horizon-client/src/game/native_entities.rs

@@ -115,7 +115,8 @@ fn target_id(t: Target) -> Option<u32> {
         | Target::Crystal(id)
         | Target::Dragon(id)
         | Target::Tnt(id)
-        | Target::Falling(id) => Some(id),
+        | Target::Falling(id)
+        | Target::Spawner(id) => Some(id),
         Target::Player | Target::Guest(_) => None,
     }
 }

crates/horizon-client/src/game/ominous_item_spawner.rs

@@ -21,8 +21,10 @@ const TICKS_SCALING: f32 = 50.0;
 const ROTATION_SPEED: f32 = 40.0;
 
 pub(super) struct OminousItemSpawner {
-    /// The entity id a server tracks it by (0 until it is tracked).
+    /// Its entity id: from the entity counter on the server, the server's on
+    /// a client.
     pub(super) id: u32,
+    /// `DATA_ITEM`; `minecraft:air` stands for `ItemStack.EMPTY`.
     pub(super) item: ItemStack,
     pub(super) position: [f64; 3],
     pub(super) spawn_item_after: i64,
@@ -66,8 +68,9 @@ impl Game<'_> {
         position: [f64; 3],
         delay: i32,
     ) {
+        self.next_entity += 1;
         self.ominous_spawners.push(OminousItemSpawner {
-            id: 0,
+            id: self.next_entity,
             item,
             position,
             spawn_item_after: i64::from(delay),
@@ -84,8 +87,9 @@ impl Game<'_> {
         else {
             return;
         };
+        self.next_entity += 1;
         self.ominous_spawners.push(OminousItemSpawner {
-            id: 0,
+            id: self.next_entity,
             item,
             position: [at.x, at.y, at.z],
             spawn_item_after,
@@ -154,6 +158,10 @@ impl Game<'_> {
     /// `spawnItem`: a projectile shot down, or an item entity; level event
     /// 3021 and the entity_place game event.
     fn spawn_ominous_item(&mut self, s: &OminousItemSpawner) {
+        // An empty item spawns nothing, and no event marks it.
+        if &*s.item.item == "minecraft:air" {
+            return;
+        }
         let at = block(s.position);
         let p = s.position;
         match projectile(&s.item.item) {

crates/horizon-client/src/game/scoreboard.rs

@@ -182,6 +182,12 @@ impl Game<'_> {
             | Target::Tnt(id)
             | Target::Falling(id)
             | Target::Other(id) => Some(uuid_text(self.uuid_for(id))),
+            // It keeps its UUID with itself.
+            Target::Spawner(id) => self
+                .ominous_spawners
+                .iter()
+                .find(|s| s.id == id)
+                .map(|s| uuid_text(s.uuid)),
             // Orbs and projectiles have no UUID here.
             Target::Orb(_) | Target::Projectile(_) => None,
         }
@@ -216,6 +222,11 @@ impl Game<'_> {
             | Target::Tnt(id)
             | Target::Other(id) => self.persist.raw.get(&id),
             Target::Player => self.level.player_extra.as_ref(),
+            Target::Spawner(id) => self
+                .ominous_spawners
+                .iter()
+                .find(|s| s.id == id)
+                .and_then(|s| s.raw.as_deref()),
             Target::Falling(id) => self
                 .falling
                 .iter()

tools/command_exec_corpus.py

@@ -363,6 +363,22 @@ def entities():
         cmd('/tp @e[type=minecraft:falling_block] 4.5 215 8.5'),
         cmd('/kill @e[type=minecraft:falling_block]'),
         cmd('/execute if entity @e[type=minecraft:falling_block]'),
+        # An ominous item spawner, with an item or empty (`ItemStack.EMPTY`,
+        # which saves no `item` and spawns nothing when its time comes).
+        cmd('/summon minecraft:ominous_item_spawner 4.5 210 8.5 {spawn_item_after_ticks:2000L,item:{id:"minecraft:diamond",count:2},Tags:["o"]}'),
+        cmd('/execute if entity @e[type=minecraft:ominous_item_spawner,tag=o]'),
+        cmd('/tag @e[type=minecraft:ominous_item_spawner,limit=1] list'),
+        cmd('/data get entity @e[type=minecraft:ominous_item_spawner,limit=1] item'),
+        cmd('/data get entity @e[type=minecraft:ominous_item_spawner,limit=1] spawn_item_after_ticks'),
+        cmd('/tp @e[type=minecraft:ominous_item_spawner] 4.5 215 8.5'),
+        cmd('/kill @e[type=minecraft:ominous_item_spawner]'),
+        cmd('/summon minecraft:ominous_item_spawner 4.5 210 8.5'),
+        cmd('/data get entity @e[type=minecraft:ominous_item_spawner,limit=1] item'),
+        cmd('/kill @e[type=minecraft:ominous_item_spawner]'),
+        cmd('/summon minecraft:ominous_item_spawner 4.5 210 8.5 {spawn_item_after_ticks:5L}'),
+        {'op': 'tick', 'n': 10},
+        cmd('/execute if entity @e[type=minecraft:ominous_item_spawner]'),
+        cmd('/execute if entity @e[type=minecraft:item,distance=..3]'),
         # And the thrown items.
         *[c for kind in ('snowball', 'egg', 'ender_pearl') for c in (
             cmd(f'/summon minecraft:{kind} 4.5 210 8.5 {{NoGravity:1b}}'),