mount order (#2702)

* mount order

* fix test

* simplify hooks

* changelog

* docstring

CHANGELOG.md

@@ -15,7 +15,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Fix crash when `Select` widget value attribute was set in `compose` https://github.com/Textualize/textual/pull/2690
 - Issue with computing progress in workers https://github.com/Textualize/textual/pull/2686
 - Issues with `switch_screen` not updating the results callback appropriately https://github.com/Textualize/textual/issues/2650
-
+- Fixed incorrect mount order https://github.com/Textualize/textual/pull/2702
 
 ### Added
 
@@ -29,6 +29,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - `Input` has a new component class `input--suggestion` https://github.com/Textualize/textual/pull/2604
 - Added `Widget.remove_children` https://github.com/Textualize/textual/pull/2657
 - Added `Validator` framework and validation for `Input` https://github.com/Textualize/textual/pull/2600
+- Added `message_hook` to App.run_test https://github.com/Textualize/textual/pull/2702
 
 ### Changed
 

src/textual/_context.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 from contextvars import ContextVar
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Callable
 
 if TYPE_CHECKING:
     from .app import App
@@ -21,3 +21,5 @@ class NoActiveAppError(RuntimeError):
 )
 visible_screen_stack: ContextVar[list[Screen]] = ContextVar("visible_screen_stack")
 """A stack of visible screens (with background alpha < 1), used in the screen render process."""
+message_hook: ContextVar[Callable[[Message], None]] = ContextVar("message_hook")
+"""A callable that accepts a message. Used by App.run_test."""

src/textual/app.py

@@ -65,6 +65,7 @@
 from ._compose import compose
 from ._compositor import CompositorUpdate
 from ._context import active_app, active_message_pump
+from ._context import message_hook as message_hook_context_var
 from ._event_broker import NoHandler, extract_handler_actions
 from ._path import _make_path_object_relative
 from ._wait import wait_for_idle
@@ -100,6 +101,7 @@
     # Unused & ignored imports are needed for the docs to link to these objects:
     from .css.query import WrongType  # type: ignore  # noqa: F401
     from .devtools.client import DevtoolsClient
+    from .message import Message
     from .pilot import Pilot
     from .widget import MountError  # type: ignore  # noqa: F401
 
@@ -1060,6 +1062,7 @@ async def run_test(
         headless: bool = True,
         size: tuple[int, int] | None = (80, 24),
         tooltips: bool = False,
+        message_hook: Callable[[Message], None] | None = None,
     ) -> AsyncGenerator[Pilot, None]:
         """An asynchronous context manager for testing app.
 
@@ -1078,6 +1081,7 @@ async def run_test(
             size: Force terminal size to `(WIDTH, HEIGHT)`,
                 or None to auto-detect.
             tooltips: Enable tooltips when testing.
+            message_hook: An optional callback that will called with every message going through the app.
         """
         from .pilot import Pilot
 
@@ -1090,6 +1094,8 @@ def on_app_ready() -> None:
             app_ready_event.set()
 
         async def run_app(app) -> None:
+            if message_hook is not None:
+                message_hook_context_var.set(message_hook)
             app._loop = asyncio.get_running_loop()
             app._thread_id = threading.get_ident()
             await app._process_messages(
@@ -1824,6 +1830,7 @@ async def _process_messages(
         ready_callback: CallbackType | None = None,
         headless: bool = False,
         terminal_size: tuple[int, int] | None = None,
+        message_hook: Callable[[Message], None] | None = None,
     ) -> None:
         self._set_active()
         active_message_pump.set(self)
@@ -1978,7 +1985,7 @@ async def take_screenshot() -> None:
 
     async def _on_compose(self) -> None:
         try:
-            widgets = compose(self)
+            widgets = [*self.screen._nodes, *compose(self)]
         except TypeError as error:
             raise TypeError(
                 f"{self!r} compose() method returned an invalid result; {error}"

src/textual/message_pump.py

@@ -16,12 +16,9 @@
 from . import Logger, events, log, messages
 from ._asyncio import create_task
 from ._callback import invoke
-from ._context import (
-    NoActiveAppError,
-    active_app,
-    active_message_pump,
-    prevent_message_types_stack,
-)
+from ._context import NoActiveAppError, active_app, active_message_pump
+from ._context import message_hook as message_hook_context_var
+from ._context import prevent_message_types_stack
 from ._on import OnNoWidget
 from ._time import time
 from ._types import CallbackType
@@ -554,6 +551,13 @@ async def _dispatch_message(self, message: Message) -> None:
         if message.no_dispatch:
             return
 
+        try:
+            message_hook = message_hook_context_var.get()
+        except LookupError:
+            pass
+        else:
+            message_hook(message)
+
         with self.prevent(*message._prevent):
             # Allow apps to treat events and messages separately
             if isinstance(message, Event):

src/textual/widget.py

@@ -3121,7 +3121,7 @@ async def handle_key(self, event: events.Key) -> bool:
 
     async def _on_compose(self) -> None:
         try:
-            widgets = compose(self)
+            widgets = [*self._nodes, *compose(self)]
         except TypeError as error:
             raise TypeError(
                 f"{self!r} compose() method returned an invalid result; {error}"

tests/test_widget.py

@@ -1,12 +1,14 @@
 import pytest
 from rich.text import Text
 
+from textual import events
 from textual._node_list import DuplicateIds
 from textual.app import App, ComposeResult
 from textual.containers import Container
 from textual.css.errors import StyleValueError
 from textual.css.query import NoMatches
 from textual.geometry import Size
+from textual.message import Message
 from textual.widget import MountError, PseudoClasses, Widget
 from textual.widgets import Label
 
@@ -260,3 +262,46 @@ def test_render_str() -> None:
     # Text objects are passed unchanged
     text = Text("bar")
     assert widget.render_str(text) is text
+
+
+async def test_compose_order() -> None:
+    from textual.containers import Horizontal
+    from textual.screen import Screen
+    from textual.widgets import Select
+
+    class MyScreen(Screen):
+        def on_mount(self) -> None:
+            self.query_one(Select).value = 1
+
+        def compose(self) -> ComposeResult:
+            yield Horizontal(
+                Select(((str(n), n) for n in range(10)), id="select"),
+                id="screen-horizontal",
+            )
+
+    class SelectBugApp(App[None]):
+        async def on_mount(self):
+            await self.push_screen(MyScreen(id="my-screen"))
+            self.query_one(Select)
+
+    app = SelectBugApp()
+    messages: list[Message] = []
+
+    async with app.run_test(message_hook=messages.append) as pilot:
+        await pilot.pause()
+
+    mounts = [
+        message._sender.id
+        for message in messages
+        if isinstance(message, events.Mount) and message._sender.id is not None
+    ]
+
+    expected = [
+        "_default",  # default  screen
+        "label",  # A static in select
+        "select",  # The select
+        "screen-horizontal",  # The horizontal in MyScreen.compose
+        "my-screen",  # THe screen mounted in the app
+    ]
+
+    assert mounts == expected