native_summon: return experience orbs' ids, and place passengers without a Pos

Follow-up to #5408. A summoned orb spawned but native_summon returned None,
since no command Target lookup covers orbs: return the stack's first
spawned id. Passengers without Pos were not placed and got lost: share
/summon's recursive place helper (place_summoned), which also supplies
the Fire and Rotation defaults.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01XnU6QT61YPiPzVNysmVHsH

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

@@ -3,6 +3,7 @@
 mod admin;
 pub(super) mod compute;
 mod data;
+pub(super) use data::place_summoned;
 mod effects;
 pub(super) mod execute;
 pub(super) mod extra;

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

@@ -28,6 +28,36 @@ fn set_key(tag: &mut Tag, key: &str, value: Tag) {
         c.insert(JavaString::from(key), value);
     }
 }
+/// `EntityType.loadEntityRecursive` snaps every entity of the stack,
+/// passengers included, to the position (`/summon`, `native_summon`).
+pub(in crate::game) fn place_summoned(tag: &mut Tag, pos: [f64; 3]) {
+    let p = pos.map(|v| Tag::Double(v.to_bits()));
+    set_key(tag, "Pos", Tag::List(p.to_vec()));
+    // Entity.load: an absent Fire reads as 0 (until the entity moves).
+    if tag.get("Fire").is_none() {
+        set_key(tag, "Fire", Tag::Short(0));
+    }
+    if tag.get("Rotation").is_none() {
+        set_key(
+            tag,
+            "Rotation",
+            Tag::List(vec![
+                Tag::Float(0.0f32.to_bits()),
+                Tag::Float(0.0f32.to_bits()),
+            ]),
+        );
+    }
+    if let Tag::Compound(c) = tag
+        && let Some(Tag::List(riders)) = c.get_mut(&"Passengers".into())
+    {
+        for r in riders {
+            if matches!(r, Tag::Compound(_)) {
+                place_summoned(r, pos);
+            }
+        }
+    }
+}
+
 impl Game<'_> {
     // ---- entity data ---------------------------------------------------
 
@@ -762,36 +792,7 @@ impl Game<'_> {
             return Err(err("argument.nbt.expected.compound", &[]));
         }
         set_key(&mut tag, "id", Tag::String(kind.into()));
-        // EntityType.loadEntityRecursive snaps every entity of the stack,
-        // passengers included, to the position.
-        fn place(tag: &mut Tag, pos: [f64; 3]) {
-            let p = pos.map(|v| Tag::Double(v.to_bits()));
-            set_key(tag, "Pos", Tag::List(p.to_vec()));
-            // Entity.load: an absent Fire reads as 0 (until the entity moves).
-            if tag.get("Fire").is_none() {
-                set_key(tag, "Fire", Tag::Short(0));
-            }
-            if tag.get("Rotation").is_none() {
-                set_key(
-                    tag,
-                    "Rotation",
-                    Tag::List(vec![
-                        Tag::Float(0.0f32.to_bits()),
-                        Tag::Float(0.0f32.to_bits()),
-                    ]),
-                );
-            }
-            if let Tag::Compound(c) = tag
-                && let Some(Tag::List(riders)) = c.get_mut(&"Passengers".into())
-            {
-                for r in riders {
-                    if matches!(r, Tag::Compound(_)) {
-                        place(r, pos);
-                    }
-                }
-            }
-        }
-        place(&mut tag, pos);
+        place_summoned(&mut tag, pos);
         let from = self.mobs.len();
         let canceled = self.persist.joins_canceled;
         let target = self.spawn_entity_from_nbt(tag);

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

@@ -5,7 +5,10 @@
 //! `item_display` showing an item model from the mod's assets. They act where
 //! the world is simulated, in the level in place, which each names by its
 //! `dimension` (`minecraft:overworld`) as `native_set_block` does.
-use super::{Game, commands::Target};
+use super::{
+    Game,
+    commands::{Target, place_summoned},
+};
 use horizon_core::geometry::Vec3;
 use horizon_world::nbt::{Compound, Tag};
 
@@ -134,14 +137,19 @@ impl Game<'_> {
         }
         let mut tag = nbt;
         tag.insert("id".into(), Tag::String(kind.into()));
-        tag.insert(
-            "Pos".into(),
-            Tag::List(pos.map(|v| Tag::Double(v.to_bits())).to_vec()),
-        );
+        // As `/summon` does: every entity of the stack, passengers included,
+        // stands at `pos`.
+        let mut tag = Tag::Compound(tag);
+        place_summoned(&mut tag, pos);
         let from = self.mobs.len();
-        let target = self.spawn_entity_from_nbt(Tag::Compound(tag));
+        let first = self.next_entity + 1;
+        let target = self.spawn_entity_from_nbt(tag);
         self.native_mobs_joined(from, false);
-        target.and_then(target_id)
+        // The root is the first entity spawned, also for kinds no command
+        // target stands for (experience orbs).
+        target
+            .and_then(target_id)
+            .or((self.next_entity >= first).then_some(first))
     }
     /// Moves entity `id`, one Horizon keeps without simulating (a display, a
     /// marker, an interaction), to `pos` facing `yaw` and `pitch` in degrees;
@@ -281,6 +289,31 @@ mod tests {
         );
     }
 
+    #[test]
+    fn a_passenger_without_a_position_stands_where_the_stack_is_summoned() {
+        let mut rider = Compound::new();
+        rider.insert("id".into(), Tag::String("minecraft:pig".into()));
+        let mut root = Compound::new();
+        root.insert("id".into(), Tag::String("minecraft:pig".into()));
+        root.insert("Passengers".into(), Tag::List(vec![Tag::Compound(rider)]));
+        let mut tag = Tag::Compound(root);
+        place_summoned(&mut tag, [1.5, 70.0, -2.5]);
+        let pos = Tag::List(
+            [1.5, 70.0, -2.5]
+                .map(|v: f64| Tag::Double(v.to_bits()))
+                .to_vec(),
+        );
+        let Tag::Compound(root) = &tag else { panic!() };
+        assert_eq!(root.get(&"Pos".into()), Some(&pos));
+        let Some(Tag::List(riders)) = root.get(&"Passengers".into()) else {
+            panic!("no passengers");
+        };
+        let Tag::Compound(rider) = &riders[0] else {
+            panic!()
+        };
+        assert_eq!(rider.get(&"Pos".into()), Some(&pos));
+    }
+
     #[test]
     fn summon_positions_are_summons() {
         assert!(position_ok([0.5, 64.0, 0.5]));