Fix recursive batch() use

docs/api/reactivity-utility.md

@@ -73,4 +73,22 @@ read can still be tracked inside a reactive scope.
     function read<T>(value: T | () -> T): T
     ```
 
+## batch()
+
+Runs a given function where any source updates made within the function do not
+trigger effects until after the function runs.
+
+- **Type**
+
+    ```lua
+    function batch(fn: () -> ())
+    ```
+
+- **Details**
+
+    Improves performance when an effect depends on multiple sources, and those
+    sources need to be updated. Updating those sources inside a batch call will
+    only cause the effect to run once after the batch call ends instead of after
+    each time a source is updated.
+
 --------------------------------------------------------------------------------

src/batch.luau

@@ -11,13 +11,15 @@ local function batch(setter: () -> ())
 
     local ok, err: string? = pcall(setter)
 
-    flags.batch = false
-    
-    if not ok then throw(`error occured while batching updates: {err}`) end
-
-    if not already_batching then -- todo: flush anyways?
-        graph.flush_update_queue()
+    if not already_batching then
+        flags.batch = false
+        
+        if not already_batching then
+            graph.flush_update_queue()
+        end
     end
+
+    if not ok then throw(`error occured while batching updates: {err}`) end
 end
 
 return batch

src/graph.luau

@@ -185,8 +185,11 @@ local function queue_children<T>(node: StartNode<T>)
     update_queue.n = i
 end
 
+local _flushing = false
 local function flush_update_queue()
-    -- todo: test with recursive batch sets
+    assert(not flushing, "recursive queue flush occured") -- todo
+    _flushing = true
+
     local n0 = 0
 
     local i = n0 + 1
@@ -203,6 +206,8 @@ local function flush_update_queue()
     end
 
     update_queue.n = n0
+
+    _flushing = false
 end
 
 local function update<T>(root: StartNode<T>)

test/tests.luau

@@ -1805,7 +1805,7 @@ TEST("batch()", wrap_root(function()
     local derive = vide.derive
     local batch = vide.batch
 
-    do CASE "child evaluation halted"
+    do CASE "evaluation deferred"
         local a = source(0)
 
         local count = { b = 0, b2 = 0, c = 0 }
@@ -1840,7 +1840,47 @@ TEST("batch()", wrap_root(function()
         CHECK(c() == 5)
     end
 
-    -- todo: test batch call in recursive set
+    do CASE "recursive call"
+        local a1 = source(0)
+        local a2 = source(0)
+        local a3 = source(0)
+
+        local count = { b1 = 0, b2 = 0, b3 = 0 }
+
+        local b1 = derive(function()
+            count.b1 += 1
+            return a1() + 1
+        end)
+
+        local b2 = derive(function()
+            count.b2 += 1
+            return a2() + 1
+        end)
+
+        local b3 = derive(function()
+            count.b3 += 1
+            return a3() + 1
+        end)
+
+        batch(function()
+            a1(1)
+            batch(function()
+                a2(2)
+            end)
+            a3(3)
+            CHECK(count.b1 == 1)
+            CHECK(count.b2 == 1)
+            CHECK(count.b3 == 1)
+        end)
+
+        CHECK(count.b1 == 2)
+        CHECK(count.b2 == 2)
+        CHECK(count.b3 == 2)
+
+        CHECK(b1() == 2)
+        CHECK(b2() == 3)
+        CHECK(b3() == 4)
+    end
 end))
 
 TEST("read()", wrap_root(function()

todo.md

@@ -1,10 +1,4 @@
 # todo
 
-- optimize wide graph updating
-- implement from solid:
-  - stores
-  - portals
-  - batch()
-- optimize `indexes()` double-diffing
-- cleanup source and tests
+- improve error traces
 - prevent redundant re-eval of nodes in a complex diamond graph