Add backwards relation to edges

jecs.luau

@@ -1052,14 +1052,15 @@ local function archetype_destroy(world: World, archetype: Archetype)
 
 	local component_index = world.component_index
 	local archetype_edges = world.archetype_edges
-
+	local edges = archetype_edges[archetype.id]
-	for id, edge in archetype_edges[archetype.id] do
+	for id, node in edges do
-		archetype_edges[edge.id][id] = nil
+		archetype_edges[node.id][id] = nil
+		edges[id] = nil
 	end
 
 	local archetype_id = archetype.id
-	world.archetypes[archetype_id] = nil :: any
+	-- world.archetypes[archetype_id] = nil :: any
-	world.archetype_index[archetype.type] = nil :: any
+	-- world.archetype_index[archetype.type] = nil :: any
 	local columns_map = archetype.columns_map
 
 	for id in columns_map do
@@ -2330,6 +2331,8 @@ local function world_new()
 			else
 				if to.dead then
 					archetype_register(world, to)
+					edge[id] = to
+					archetype_edges[to.id][id] = src
 					to.dead = false
 				end
 				idr = component_index[id]
@@ -2539,6 +2542,7 @@ local function world_new()
 						idr = component_index[id]
 					end
 					edge[id] = to
+					archetype_edges[to.id][id] = src
 				else
 					idr = component_index[id]
 				end

test/tests.luau

@@ -24,8 +24,46 @@ type Id<T=unknown> = jecs.Id<T>
 local entity_visualiser = require("@tools/entity_visualiser")
 local dwi = entity_visualiser.stringify
 
-FOCUS()
+TEST("repeated pairs", function()
-TEST("", function()
+	local pair = jecs.pair
+	local world = jecs.world()
+	local rel = world:component() -- Does not error if this is just a tag
+
+	-- Does not happen if we delete manually instead of using this
+	world:add(rel, pair(jecs.OnDeleteTarget, jecs.Delete))
+
+	local t1 = world:entity()
+
+	local p1 = pair(rel, t1)
+
+	local e1 = world:entity()
+
+	world:set(e1, p1, true)
+
+	CHECK(world:get(e1, p1))
+	CHECK(world:each(p1)() == e1)
+
+	world:delete(t1)
+
+	local t2 = world:entity()
+	local p2 = pair(rel, t2)
+
+	local e2 = world:entity()
+
+	print("-----")
+	world:set(e2, p2, true)
+
+	CHECK(world:get(e2, p2))
+	CHECK(p1 == p2)
+	local count = 0
+	CHECK(world:has(e2, p2))
+	for _ in world:query(p2) do
+		count += 1
+	end
+	CHECK(count == 1)
+	CHECK(world:each(p2)() == e2) -- Fails
+end)
+TEST("repro", function()
 	local world = jecs.world()
 	local data = world:component()
 	local relation = world:component()