Allow batching within a batch (#137)

reactive/src/effect.rs

@@ -70,14 +70,22 @@ pub fn untrack<T>(f: impl FnOnce() -> T) -> T {
 }
 
 pub fn batch<T>(f: impl FnOnce() -> T) -> T {
-    RUNTIME.with(|runtime| {
-        runtime.batching.set(true);
+    let already_batching = RUNTIME.with(|runtime| {
+        let batching = runtime.batching.get();
+        if !batching {
+            runtime.batching.set(true);
+        }
+
+        batching
     });
+
     let result = f();
-    RUNTIME.with(|runtime| {
-        runtime.batching.set(false);
-        runtime.run_pending_effects();
-    });
+    if !already_batching {
+        RUNTIME.with(|runtime| {
+            runtime.batching.set(false);
+            runtime.run_pending_effects();
+        });
+    }
 
     result
 }

reactive/tests/effect.rs

@@ -0,0 +1,70 @@
+use std::{cell::Cell, rc::Rc};
+
+use floem_reactive::{batch, create_effect, create_rw_signal};
+
+#[test]
+fn batch_simple() {
+    let name = create_rw_signal("John");
+    let age = create_rw_signal(20);
+
+    let count = Rc::new(Cell::new(0));
+
+    create_effect({
+        let count = count.clone();
+        move |_| {
+            name.track();
+            age.track();
+
+            count.set(count.get() + 1);
+        }
+    });
+
+    // The effect runs once immediately
+    assert_eq!(count.get(), 1);
+
+    // Setting each signal once will trigger the effect
+    name.set("Mary");
+    assert_eq!(count.get(), 2);
+
+    age.set(21);
+    assert_eq!(count.get(), 3);
+
+    // Batching will only update once
+    batch(|| {
+        name.set("John");
+        age.set(20);
+    });
+    assert_eq!(count.get(), 4);
+}
+
+#[test]
+fn batch_batch() {
+    let name = create_rw_signal("John");
+    let age = create_rw_signal(20);
+
+    let count = Rc::new(Cell::new(0));
+
+    create_effect({
+        let count = count.clone();
+        move |_| {
+            name.track();
+            age.track();
+
+            count.set(count.get() + 1);
+        }
+    });
+
+    assert_eq!(count.get(), 1);
+
+    // Batching within another batch should be equivalent to batching them all together
+    batch(|| {
+        name.set("Mary");
+        age.set(21);
+        batch(|| {
+            name.set("John");
+            age.set(20);
+        });
+    });
+
+    assert_eq!(count.get(), 2);
+}