Fix crash on table creation when removing relation component (#297)

Author: mlange-42

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## [[v0.5.1]](https://github.com/mlange-42/ark/compare/v0.5.0...v0.5.1)
+
+### Bugfixes
+
+- Fixes crash on table creation when removing a relation component (#297, fixes #295)
+
 ## [[v0.5.0]](https://github.com/mlange-42/ark/compare/v0.4.8...v0.5.0)
 
 ### Breaking changes

ecs/storage.go

@@ -73,10 +73,21 @@ func (s *storage) findOrCreateTable(oldTable *table, add []ID, remove []ID, rela
 	}
 
 	var allRelations []RelationID
-	if len(relations) > 0 {
-		allRelations = appendNew(oldTable.relationIDs, relations...)
+	if len(remove) > 0 {
+		// filter out removed relations
+		allRelations = make([]RelationID, 0, len(oldTable.relationIDs)+len(relations))
+		for _, rel := range oldTable.relationIDs {
+			if arch.mask.Get(rel.component) {
+				allRelations = append(allRelations, rel)
+			}
+		}
+		allRelations = append(allRelations, relations...)
 	} else {
-		allRelations = oldTable.relationIDs
+		if len(relations) > 0 {
+			allRelations = appendNew(oldTable.relationIDs, relations...)
+		} else {
+			allRelations = oldTable.relationIDs
+		}
 	}
 	table, ok := arch.GetTable(s, allRelations)
 	if !ok {

ecs/table_test.go

@@ -35,6 +35,7 @@ func TestTableMatches(t *testing.T) {
 	posID := ComponentID[Position](&w)
 	velID := ComponentID[Velocity](&w)
 	childID := ComponentID[ChildOf](&w)
+	child2ID := ComponentID[ChildOf2](&w)
 
 	compMap := make([]int16, maskTotalBits)
 	compMap[1] = 0
@@ -48,6 +49,7 @@ func TestTableMatches(t *testing.T) {
 	)
 
 	expectTrue(t, table.MatchesExact([]RelationID{{component: childID, target: Entity{2, 0}}}))
+	expectTrue(t, table.MatchesExact([]RelationID{{component: childID, target: Entity{2, 0}}, {component: child2ID, target: Entity{2, 0}}}))
 	expectFalse(t, table.MatchesExact([]RelationID{{component: childID, target: Entity{3, 0}}}))
 
 	expectPanics(t, func() {

ecs/world_test.go

@@ -245,6 +245,30 @@ func TestWorldRelations(t *testing.T) {
 	})
 }
 
+func TestWorldRelationsBug295(t *testing.T) {
+	world := NewWorld()
+	parentMap := NewMap1[Position](&world)
+	childMap := NewMap3[Velocity, ChildOf, ChildOf2](&world)
+
+	parent1 := parentMap.NewEntity(&Position{})
+	parent2 := parentMap.NewEntity(&Position{})
+	child := childMap.NewEntity(
+		&Velocity{},
+		&ChildOf{},
+		&ChildOf2{},
+		Rel[ChildOf](parent1),
+		Rel[ChildOf2](parent2),
+	)
+
+	inFarmMap1 := NewMap[ChildOf](&world)
+	inFarmMap2 := NewMap[ChildOf2](&world)
+
+	inFarmMap1.Remove(child)
+	expectEqual(t, parent2, inFarmMap2.GetRelation(child))
+
+	inFarmMap2.Remove(child)
+}
+
 func TestWorldSetRelations(t *testing.T) {
 	w := NewWorld(16)