Merge pull request #4222 from davep/watcher-context

Correct the sender of a reactive-posted message

src/textual/reactive.py

@@ -24,6 +24,7 @@
 
 from . import events
 from ._callback import count_parameters
+from ._context import active_message_pump
 from ._types import (
     MessageTarget,
     WatchCallbackBothValuesType,
@@ -73,17 +74,23 @@ def invoke_watcher(
     """
     _rich_traceback_omit = True
     param_count = count_parameters(watch_function)
-    if param_count == 2:
-        watch_result = cast(WatchCallbackBothValuesType, watch_function)(
-            old_value, value
-        )
-    elif param_count == 1:
-        watch_result = cast(WatchCallbackNewValueType, watch_function)(value)
-    else:
-        watch_result = cast(WatchCallbackNoArgsType, watch_function)()
-    if isawaitable(watch_result):
-        # Result is awaitable, so we need to await it within an async context
-        watcher_object.call_next(partial(await_watcher, watcher_object, watch_result))
+    reset_token = active_message_pump.set(watcher_object)
+    try:
+        if param_count == 2:
+            watch_result = cast(WatchCallbackBothValuesType, watch_function)(
+                old_value, value
+            )
+        elif param_count == 1:
+            watch_result = cast(WatchCallbackNewValueType, watch_function)(value)
+        else:
+            watch_result = cast(WatchCallbackNoArgsType, watch_function)()
+        if isawaitable(watch_result):
+            # Result is awaitable, so we need to await it within an async context
+            watcher_object.call_next(
+                partial(await_watcher, watcher_object, watch_result)
+            )
+    finally:
+        active_message_pump.reset(reset_token)
 
 
 @rich.repr.auto

tests/test_reactive.py

@@ -5,6 +5,8 @@
 import pytest
 
 from textual.app import App, ComposeResult
+from textual.message import Message
+from textual.message_pump import MessagePump
 from textual.reactive import Reactive, TooManyComputesError, reactive, var
 from textual.widget import Widget
 
@@ -705,3 +707,40 @@ def second_callback() -> None:
         assert logs == ["first", "second"]
         app.query_one(SomeWidget).test_var = 73
         assert logs == ["first", "second", "first", "second"]
+
+
+async def test_message_sender_from_reactive() -> None:
+    """Test that the sender of a message comes from the reacting widget."""
+
+    message_senders: list[MessagePump | None] = []
+
+    class TestWidget(Widget):
+        test_var: var[int] = var(0, init=False)
+
+        class TestMessage(Message):
+            pass
+
+        def watch_test_var(self) -> None:
+            self.post_message(self.TestMessage())
+
+        def make_reaction(self) -> None:
+            self.test_var += 1
+
+    class TestContainer(Widget):
+        def compose(self) -> ComposeResult:
+            yield TestWidget()
+
+        def on_test_widget_test_message(self, event: TestWidget.TestMessage) -> None:
+            nonlocal message_senders
+            message_senders.append(event._sender)
+
+    class TestApp(App[None]):
+
+        def compose(self) -> ComposeResult:
+            yield TestContainer()
+
+    async with TestApp().run_test() as pilot:
+        assert message_senders == []
+        pilot.app.query_one(TestWidget).make_reaction()
+        await pilot.pause()
+        assert message_senders == [pilot.app.query_one(TestWidget)]