Rebuild saved component relation indexes with their target entities

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Relation components were incorrectly loaded from pickled data as pointing in the wrong direction.
+
 ## [5.5.0] - 2026-01-14
 
 ### Changed

tcod/ecs/registry.py

@@ -71,7 +71,7 @@ def _relations_lookup_from(
         for component_key, target_components in components.items():
             for target in target_components:
                 relations_lookup[(component_key, ...)].add(origin)
-                relations_lookup[(component_key, origin)].add(origin)
+                relations_lookup[(component_key, target)].add(origin)
                 relations_lookup[(origin, component_key, None)].add(target)
                 relations_lookup[(..., component_key, None)].add(target)
 

tests/test_ecs.py

@@ -16,6 +16,28 @@
 # ruff: noqa: D103
 
 
+@pytest.mark.parametrize("component_key", [int, ("distance", int)])
+@pytest.mark.parametrize("protocol", [2, 4, 5])
+def test_pickle_component_relation_targets(component_key: type[int] | tuple[str, type[int]], protocol: int) -> None:
+    world = tcod.ecs.Registry()
+    moon, planet = world["moon"], world["planet"]
+    distance = 10
+    moon.relation_components[component_key][planet] = distance
+    moon.relation_tag["LandedOn"] = planet
+    assert set(world.Q.all_of(relations=[(component_key, planet)])) == {moon}
+
+    restored: tcod.ecs.Registry = pickle.loads(pickle.dumps(world, protocol=protocol))  # noqa: S301
+    moon, planet = restored["moon"], restored["planet"]
+
+    assert moon.relation_components[component_key][planet] == distance
+    assert set(restored.Q.all_of(relations=[(component_key, planet)])) == {moon}
+    assert set(restored.Q.all_of(relations=[(component_key, moon)])) == set()
+    assert set(restored.Q.all_of(relations=[(component_key, ...)])) == {moon}
+    assert set(restored.Q.all_of(relations=[(moon, component_key, None)])) == {planet}
+    assert set(restored.Q.all_of(relations=[(..., component_key, None)])) == {planet}
+    assert set(restored.Q.all_of(relations=[("LandedOn", planet)])) == {moon}
+
+
 def test_world() -> None:
     world = tcod.ecs.Registry()
     with pytest.warns():