fix(select): watch reactive prompt change (#3701)

* fix(select): allow reactive prompt change

* update watcher with new is_mounted check

* update only first in option list

* update option list only if allow blank

* update changelog

CHANGELOG.md

@@ -28,6 +28,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Loading indicators and app notifications overlapped in the wrong order https://github.com/Textualize/textual/issues/3677
 - Widgets being loaded are disabled and have their scrolling explicitly disabled too https://github.com/Textualize/textual/issues/3677
 - Method render on a widget could be called before mounting said widget https://github.com/Textualize/textual/issues/2914
+- Fixed `Select` not updating after changing the `prompt` reactive https://github.com/Textualize/textual/issues/2983
 
 ### Added
 

src/textual/widgets/_select.py

@@ -492,3 +492,15 @@ def clear(self) -> None:
             raise InvalidSelectValueError(
                 "Can't clear selection if allow_blank is set to False."
             ) from None
+
+    def _watch_prompt(self, prompt: str) -> None:
+        if not self.is_mounted:
+            return
+        select_current = self.query_one(SelectCurrent)
+        select_current.placeholder = prompt
+        if not self._allow_blank:
+            return
+        if self.value == self.BLANK:
+            select_current.update(self.BLANK)
+        option_list = self.query_one(SelectOverlay)
+        option_list.replace_option_prompt_at_index(0, Text(prompt, style="dim"))

tests/select/test_prompt.py

@@ -0,0 +1,54 @@
+from rich.text import Text
+
+from textual.app import App
+from textual.widgets import Select, Static
+from textual.widgets._select import SelectCurrent, SelectOverlay
+
+
+async def test_reactive_prompt_change():
+    """Regression test for https://github.com/Textualize/textual/issues/2983"""
+
+    class SelectApp(App):
+        def compose(self):
+            yield Select[int](
+                [(str(n), n) for n in range(3)],
+                prompt="Old prompt",
+            )
+
+    app = SelectApp()
+    async with app.run_test() as pilot:
+        select_widget = pilot.app.query_one(Select)
+        select_current = select_widget.query_one(SelectCurrent)
+        select_current_label = select_current.query_one("#label", Static)
+        select_overlay = select_widget.query_one(SelectOverlay)
+
+        assert select_current_label.renderable == Text("Old prompt")
+        assert select_overlay._options[0].prompt == Text("Old prompt")
+
+        select_widget.prompt = "New prompt"
+        assert select_current_label.renderable == Text("New prompt")
+        assert select_overlay._options[0].prompt == Text("New prompt")
+
+
+async def test_reactive_prompt_change_when_allow_blank_is_false():
+    class SelectApp(App):
+        def compose(self):
+            yield Select[int](
+                [(str(n), n) for n in range(3)],
+                prompt="Old prompt",
+                allow_blank=False,
+            )
+
+    app = SelectApp()
+    async with app.run_test() as pilot:
+        select_widget = pilot.app.query_one(Select)
+        select_current = select_widget.query_one(SelectCurrent)
+        select_current_label = select_current.query_one("#label", Static)
+        select_overlay = select_widget.query_one(SelectOverlay)
+
+        assert select_current_label.renderable == Text("0")
+        assert select_overlay._options[0].prompt == "0"
+
+        select_widget.prompt = "New prompt"
+        assert select_current_label.renderable == Text("0")
+        assert select_overlay._options[0].prompt == "0"