Disallow creation of nested tracking scopes

src/graph.luau

@@ -10,7 +10,7 @@ export type StartNode<T> = {
 
 export type Node<T> =  {
     cache: T,
-    effect:  ((T) -> T) | false,
+    effect:  ((T) -> T) | "owner" | "untracked",
     cleanups: { () -> () } | false,
     parents: { owner: StartNode<T>?, [number]: StartNode<T> },
     [number]: Node<T>
@@ -50,8 +50,8 @@ local function get_owning_scope(): Node<unknown>
     if not scope then
         local caller_name = debug.info(2, "n")
         return throw(`cannot use {caller_name}() in non-reactive scope, must be used within a root() or mount() callback`)
-    elseif scope.effect then
-        throw("owning scope is not stable; are you trying to derive a new source from within a side-effect?")
+    elseif scope.effect ~= "owner" then
+        throw("reactive scope is not an owning scope; new effects cannot be created in side-effects")
     end
     return scope
 end
@@ -117,8 +117,6 @@ local function destroy<T>(node: Node<T>)
     run_cleanups(node)
     unparent(node)
 
-    node.effect = false
-
     if node.parents.owner then
         remove_child(node.parents.owner, node)
         node.parents.owner = nil
@@ -168,24 +166,13 @@ local function update_from<T>(node: StartNode<T>, n0: number)
 
     -- unparent all children and queue for eval
     do
-        local i = 1
-        local child = node[i]
+        local child = node[1]
         while child do
+            --assert(child.parents.owner)
             unparent(child)
-
             n += 1
             update_queue[n] = child
-
-            local next_child = node[i]
-
-            -- children who have this parent as an owner will not be unparented
-            -- if such a child is encountered then skip it
-            if next_child == child then
-                i += 1
-                next_child = node[i]
-            end
-
-            child = next_child
+            child = node[1]
         end
     end
 
@@ -194,7 +181,7 @@ local function update_from<T>(node: StartNode<T>, n0: number)
     -- evaluate all queued children
     for i = n0 + 1, n do
         local child = update_queue[i]
-        if not child.effect then continue end
+        assert(type(child.effect) == "function")
 
         if evaluate_node(child) then
             update_from(child, n)
@@ -212,12 +199,12 @@ end
 
 local function track<T>(node: StartNode<T>)
     local scope = get_scope()
-    if scope and scope.effect then -- do not track nodes with no effect
+    if scope and type(scope.effect) == "function" then -- do not track nodes with no effect
         add_child(node, scope)
     end
 end
 
-local function create_node<T>(value: T, effect: false | (T) -> T): Node<T>
+local function create_node<T>(value: T, effect: "owner" | (T) -> T): Node<T>
     return {
         cache = value,
         effect = effect,

src/maps.luau

@@ -30,7 +30,7 @@ end
 local function indexes<K, VI, VO>(input: () -> Map<K, VI>, transform: (() -> VI, K) -> VO): () -> { VO }
     local owner = get_owning_scope()
 
-    local subowner = create_node(false, false)
+    local subowner = create_node(false, "owner")
     set_owner(subowner, owner)
 
     local input_cache = {} :: Map<K, VI>
@@ -67,7 +67,7 @@ local function indexes<K, VI, VO>(input: () -> Map<K, VI>, transform: (() -> VI,
 
             if cv ~= v then
                 if cv == nil then -- create new scope and run transform
-                    local scope = create_node(false, false)
+                    local scope = create_node(false, "owner")
                     scopes[i] = scope :: Node<any>
 
                     local node = create_start_node(v)
@@ -112,6 +112,7 @@ local function indexes<K, VI, VO>(input: () -> Map<K, VI>, transform: (() -> VI,
     local node = create_node(false :: any, function()
         return update_children(input())
     end)
+    set_owner(node, owner)
 
     evaluate_node(node)
 
@@ -124,7 +125,7 @@ end
 local function values<K, VI, VO>(input: () -> Map<K, VI>, transform: (VI, () -> K) -> VO): () -> { VO }
     local owner = get_owning_scope()
 
-    local subowner = create_node(false, false)
+    local subowner = create_node(false, "owner")
     set_owner(subowner, owner)
     
     local cur_input_cache_up = {} :: Map<VI, K>
@@ -155,7 +156,7 @@ local function values<K, VI, VO>(input: () -> Map<K, VI>, transform: (VI, () ->
             local cv = cur_input_cache[v]
             
             if cv == nil then -- create new scope and run transform
-                local scope = create_node(false, false)
+                local scope = create_node(false, "owner")
                 scopes[v] = scope :: Node<any>
 
                 local node = create_start_node(i)
@@ -214,6 +215,7 @@ local function values<K, VI, VO>(input: () -> Map<K, VI>, transform: (VI, () ->
     local node = create_node(false :: any, function()
         return update_children(input())
     end)
+    set_owner(node, owner)
 
     evaluate_node(node)
 

src/root.luau

@@ -11,7 +11,7 @@ local destroy = graph.destroy
 local refs = {}
 
 local function root<T...>(fn: (destroy: () -> ()) -> T...): T...
-    local node = create_node(false, false)
+    local node = create_node(false, "owner")
 
     refs[node] = true -- prevent gc of root node
 

src/switch.luau

@@ -38,7 +38,7 @@ local function switch<T, U>(source: () -> T): (map: Map<T, ((() -> U)?)>) -> ()
                 throw("map must map a value to a function")
             end
 
-            local new_scope = create_node(false, false)
+            local new_scope = create_node(false, "owner")
             last_scope = new_scope :: Node<any>
             
             set_owner(new_scope, owner)

src/untrack.luau

@@ -13,7 +13,7 @@ local function untrack<T>(source: () -> T): T
 
     -- sources are only tracked if the node in scope has an effect
     local effect = scope.effect
-    scope.effect = false
+    scope.effect = "untracked"
 
     local ok, result = pcall(source)