catch exceptions from post mount

CHANGELOG.md

@@ -5,6 +5,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## Unreleased
+
+### Fixed
+
+- Fix exceptions in watch methods being hidden on startup https://github.com/Textualize/textual/issues/1886
 
 ## [0.12.1] - 2023-02-25
 

src/textual/dom.py

@@ -221,6 +221,7 @@ def get_component_styles(self, name: str) -> RenderStyles:
 
     def _post_mount(self):
         """Called after the object has been mounted."""
+        _rich_traceback_omit = True
         Reactive._initialize_object(self)
 
     def notify_style_update(self) -> None:

src/textual/message_pump.py

@@ -429,12 +429,12 @@ async def _pre_process(self) -> None:
         try:
             await self._dispatch_message(events.Compose(sender=self))
             await self._dispatch_message(events.Mount(sender=self))
+            self._post_mount()
         except Exception as error:
             self.app._handle_exception(error)
         finally:
             # This is critical, mount may be waiting
             self._mounted_event.set()
-        self._post_mount()
 
     def _post_mount(self):
         """Called after the object has been mounted."""

src/textual/reactive.py

@@ -89,10 +89,12 @@ def _initialize_reactive(self, obj: Reactable, name: str) -> None:
             obj: An object with reactive attributes.
             name: Name of attribute.
         """
+        _rich_traceback_omit = True
         internal_name = f"_reactive_{name}"
         if hasattr(obj, internal_name):
             # Attribute already has a value
             return
+
         compute_method = getattr(obj, f"compute_{name}", None)
         if compute_method is not None and self._init:
             default = getattr(obj, f"compute_{name}")()
@@ -114,7 +116,7 @@ def _initialize_object(cls, obj: Reactable) -> None:
         Args:
             obj: An object with Reactive descriptors
         """
-
+        _rich_traceback_omit = True
         for name, reactive in obj._reactives.items():
             reactive._initialize_reactive(obj, name)