fix: make sure the reactive listeners are attached as early as possible

before we would execute the use_effect that attaches event listeners
for reactive variables after those of users. Now, we execute it
before users.
Before this caused setting of reactive variables in a use_effect to
not re-render the current component.

solara/lab/toestand.py

@@ -486,7 +486,6 @@ def set(self, value):
 class AutoSubscribeContextManager:
     # a render loop might trigger a new render loop of a differtent render context
     # so we want to save, and restore the current reactive_used
-    reactive_used_before: Optional[Set[ValueBase]] = None
     reactive_used: Optional[Set[ValueBase]] = None
     reactive_added_previous_run: Optional[Set[ValueBase]] = None
     subscribed: Dict[ValueBase, Callable]
@@ -499,7 +498,6 @@ def __enter__(self):
         self.reactive_used_before = thread_local.reactive_used
         self.reactive_used = thread_local.reactive_used = set()
 
-    def __exit__(self, exc_type, exc_val, exc_tb):
         assert thread_local.reactive_used is self.reactive_used, f"{hex(id(thread_local.reactive_used))} vs {hex(id(self.reactive_used))}"
         _, set_counter = solara.use_state(0, key="auto_subscribe_force_update_counter")
 
@@ -544,7 +542,9 @@ def cleanup():
             return cleanup
 
         solara.use_effect(on_close, [])
-        thread_local.reactive_used = self.reactive_used_before
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        pass
 
 
 # alias for compatibility

tests/unit/lab/toestand_test.py

@@ -1036,3 +1036,22 @@ def Test():
     assert mock2.call_count == 1
 
     rc.close()
+
+
+def test_reactive_var_in_use_effect():
+
+    var = Reactive(1)
+
+    @solara.component
+    def Test():
+        def modify():
+            var.value = 2
+
+        solara.use_effect(modify)
+        # note: just pass the value, not the reactive variable
+        # otherwise the test passes. It is important *this*
+        # component listens to the reactive variable.
+        return solara.IntSlider("test", value=var.value)
+
+    box, rc = solara.render(Test(), handle_error=False)
+    assert rc.find(v.Slider).widget.v_model == 2