[MC-266577] Some trial spawners in trial chambers spawn mobs without persistence

Certain types of trial spawners that generate in the trial chambers will fail to set the spawned mobs as persistent, allowing the player to despawn the mobs and claim their reward without fighting.

Steps to Reproduce

Locate a trial spawner that is affected by the bug.
Example:

Seed: -3955354196018892310
/execute in minecraft:overworld run tp @s 40.00 -35.00 191.77 -643.71 17.55

Activate the trial spawner by switching to survival.
Move more than 128 blocks from the spawner and wait there for ~10s.
Return to the spawner.

Expected Result

The mobs remain inside the room.

Actual Result

All of the mobs spawned by the trial spawner despawn causing the trial spawner to eject loot.

Linked issues

is duplicated by 2

MC-266591 trial spawner poison skeleton spawning do not have persistent required 1 Resolved

MC-266593 trial spawner slimes are missing persistent required tag Resolved

relates to 1

MC-266592 Trial spawner baby zombies do not spawn with armor or other stuff Resolved

Attachments

Comments 1

ampolive 2023-11-11T22:10:02Z

Code analysis (Mojang mappings, 23w45a): In TrialSpawner#spawnMob:

...
   if ($$13 instanceof Mob) {
            Mob $$14 = (Mob)$$13;
            ...
            if ($$3.getEntityToSpawn().size() == 1 && $$3.getEntityToSpawn().contains("id", 8)) {
                $$14.finalizeSpawn($$0, $$0.getCurrentDifficultyAt($$14.blockPosition()), MobSpawnType.TRIAL_SPAWNER, null, null);
                $$14.setPersistenceRequired();
            }
        }
...

The spawner only sets persistence (and finalizes spawn) if the entity field inside spawn_data has only one tag (which is the id tag). Spawners that spawn slimes, skeletons holding poison arrows, and baby zombies have more than one tag, so the PersistenceRequired tag is not set (also, mobs cannot spawn left handed, baby zombies do not spawn with armor or as chicken jockeys, and poison skeletons do not spawn with armor, as that is done in finalizeSpawn).