Ignore empty updates (#107)

src/doc.rs

@@ -116,12 +116,14 @@ impl Doc {
     pub fn observe(&mut self, py: Python<'_>, f: PyObject) -> PyResult<Py<Subscription>> {
         let sub = self.doc
             .observe_transaction_cleanup(move |txn, event| {
-                Python::with_gil(|py| {
-                    let event = TransactionEvent::new(event, txn);
-                    if let Err(err) = f.call1(py, (event,)) {
-                        err.restore(py)
-                    }
-                })
+                if event.before_state != event.after_state {
+                    Python::with_gil(|py| {
+                        let event = TransactionEvent::new(event, txn);
+                        if let Err(err) = f.call1(py, (event,)) {
+                            err.restore(py)
+                        }
+                    })
+                }
             })
             .unwrap();
         let s: Py<Subscription> = Py::new(py, Subscription::from(sub))?;

tests/test_doc.py

@@ -179,3 +179,15 @@ def test_roots():
     # assert str(roots["a"]) == "foo"
     # assert list(roots["b"]) == [5, 2, 8]
     # assert dict(roots["c"]) == None  # {"k1": 1, "k2": 2}
+
+
+def test_empty_update():
+    doc = Doc()
+    doc["text"] = Text()
+    events = []
+    sub = doc.observe(partial(callback, events))  # noqa: F841
+
+    # this triggers an empty update
+    doc["text"]
+    # empty updates should not emit an event
+    assert not events