From 03d89503617a1e0fa2b20c7e189b7c204057b9a5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?G=C3=B6kalp=20=C3=96zcan?= <gokalp@mail.com>
Date: Sat, 3 Jan 2026 12:44:00 +1100
Subject: [PATCH] Add child-prefab-matching repro

remove binaries
---
 _REPRO/child-prefab-matching/.gitignore     |  2 +
 _REPRO/child-prefab-matching/Troll.flecs    |  3 +
 _REPRO/child-prefab-matching/build-repro.sh |  5 ++
 _REPRO/child-prefab-matching/repro.cpp      | 63 +++++++++++++++++++++
 4 files changed, 73 insertions(+)
 create mode 100644 _REPRO/child-prefab-matching/.gitignore
 create mode 100644 _REPRO/child-prefab-matching/Troll.flecs
 create mode 100755 _REPRO/child-prefab-matching/build-repro.sh
 create mode 100644 _REPRO/child-prefab-matching/repro.cpp

diff --git a/_REPRO/child-prefab-matching/.gitignore b/_REPRO/child-prefab-matching/.gitignore
new file mode 100644
index 0000000000..cddf6bb0d6
--- /dev/null
+++ b/_REPRO/child-prefab-matching/.gitignore
@@ -0,0 +1,2 @@
+flecs.o
+repro
diff --git a/_REPRO/child-prefab-matching/Troll.flecs b/_REPRO/child-prefab-matching/Troll.flecs
new file mode 100644
index 0000000000..5979d45d98
--- /dev/null
+++ b/_REPRO/child-prefab-matching/Troll.flecs
@@ -0,0 +1,3 @@
+prefab Troll : Enemy {
+	HitPoints: {value: 20}
+}
diff --git a/_REPRO/child-prefab-matching/build-repro.sh b/_REPRO/child-prefab-matching/build-repro.sh
new file mode 100755
index 0000000000..fa8351b614
--- /dev/null
+++ b/_REPRO/child-prefab-matching/build-repro.sh
@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+set -ex
+
+gcc-15 -c ../../distr/flecs.c -std=c99 -O1 -o flecs.o
+g++-15 repro.cpp flecs.o -o repro -std=c++17 -lpthread
diff --git a/_REPRO/child-prefab-matching/repro.cpp b/_REPRO/child-prefab-matching/repro.cpp
new file mode 100644
index 0000000000..1d7a17215f
--- /dev/null
+++ b/_REPRO/child-prefab-matching/repro.cpp
@@ -0,0 +1,63 @@
+#include <iostream>
+#include <cstdint>
+
+#include "../../distr/flecs.h"
+
+int main(int argc, char* argv[]) {
+    flecs::world world;
+
+    struct HitPoints {
+        float value;
+    };
+    world.component<HitPoints>("HitPoints")
+        .member<float>("value")
+        .set<HitPoints>({ float(10.0) });
+
+    flecs::entity enemy = world.prefab("Enemy");
+
+    if (world.script_run_file("Troll.flecs") != 0) {
+        std::cerr << "Error running script" << std::endl;
+        return 1;
+    }
+
+    flecs::entity Troll = world.lookup("Troll");
+    flecs::entity instance = world.entity().is_a(Troll);
+
+    auto q = world.query_builder()
+        .with(flecs::IsA, enemy);
+
+    // The original pattern as in https://github.com/VoxInteractive/Surwave/blob/4aa069c7fb4ccb292ffe0cd4690ec6023ccb1be6/Game/cpp/systems/enemy_death.h#L44
+    q.each([](flecs::entity e) {
+        std::cout << e.target(flecs::IsA).name() << std::endl; // prints Troll
+    });
+
+    // Recommended pattern (faster) - https://discord.com/channels/633826290415435777/1455553733978099763/1455641967605059854
+    q.each([](flecs::iter& it, size_t row) {
+        std::cout << it.pair(0).second().name() << std::endl; // prints Troll
+    });
+
+    auto repro_system = world.system<const HitPoints>("Repro")
+        .with(flecs::IsA, enemy)
+        .kind(0)
+        .run([](flecs::iter& it) {
+
+        while (it.next()) {
+            for (auto entity_index : it) {
+                flecs::entity entity = it.entity(static_cast<std::int32_t>(entity_index));
+
+                // The original pattern
+                const flecs::entity prefab_entity_via_entity_target = entity.target(flecs::IsA);
+
+                // Recommended pattern
+                const flecs::entity prefab_entity_via_it_pair = it.pair(1).second();
+
+                std::cout << prefab_entity_via_entity_target.name() << std::endl; // prints Troll
+                std::cout << prefab_entity_via_it_pair.name() << std::endl; // !!! prints Enemy
+            }
+        }
+    });
+
+    repro_system.run();
+
+    return 0;
+}