fix recursive queue flush (#28)

* fix recursive queue flush

* remove print from test

* swap order of flush

* simplified test case and remove error

* write more in-depth tests

* change approach flush_update_queue

* double diamond test case

* fix indent

* change naming of function

* subsequent updates do not batch test case

* simplify test case

src/batch.luau

@@ -6,17 +6,18 @@ local graph = require(script.Parent.graph)
 
 local function batch(setter: () -> ())
     local already_batching = flags.batch
+    local from
 
-    flags.batch = true
+    if not already_batching then
+        flags.batch = true
+        from = graph.get_update_queue_length()
+    end
 
     local ok, err: string? = pcall(setter)
 
     if not already_batching then
         flags.batch = false
-        
-        if not already_batching then
-            graph.flush_update_queue()
-        end
+        graph.flush_update_queue(from)
     end
 
     if not ok then throw(`error occured while batching updates: {err}`) end

src/graph.luau

@@ -184,14 +184,12 @@ local function queue_children_for_update<T>(node: SourceNode<T>)
     update_queue.n = i
 end
 
-local _flushing = false
-local function flush_update_queue()
-    assert(not _flushing, "recursive queue flush occured") -- todo
-    _flushing = true
+local function get_update_queue_length()
+    return update_queue.n
+end
 
-    local n0 = 0
-
-    local i = n0 + 1
+local function flush_update_queue(from: number)
+    local i = from + 1
     while i <= update_queue.n do
         local node = update_queue[i]
         --assert(node.effect)
@@ -203,10 +201,8 @@ local function flush_update_queue()
         update_queue[i] = false :: any
         i += 1
     end
-
-    update_queue.n = n0
-
-    _flushing = false
+    
+    update_queue.n = from
 end
 
 local function update_descendants<T>(root: SourceNode<T>)
@@ -286,5 +282,6 @@ return table.freeze {
     create_source_node = create_source_node,
     get_children = get_children,
     flush_update_queue = flush_update_queue,
+    get_update_queue_length = get_update_queue_length,
     scopes = scopes
 }