Merge pull request #1591 from davep/compose-error-expand

Reraise compose TypeError from the error rather than None

CHANGELOG.md

@@ -28,6 +28,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - `COMPONENT_CLASSES` are now inherited from base classes https://github.com/Textualize/textual/issues/1399
 - Watch methods may now take no parameters
 - Added `compute` parameter to reactive
+- A `TypeError` raised during `compose` now carries the full traceback.
 
 ### Fixed
 

src/textual/app.py

@@ -1569,7 +1569,7 @@ class App(Generic[ReturnType], DOMNode):
         except TypeError as error:
             raise TypeError(
                 f"{self!r} compose() returned an invalid response; {error}"
-            ) from None
+            ) from error
         await self.mount_all(widgets)
 
     def _on_idle(self) -> None:

src/textual/widget.py

@@ -2395,7 +2395,7 @@ class Widget(DOMNode):
         except TypeError as error:
             raise TypeError(
                 f"{self!r} compose() returned an invalid response; {error}"
-            ) from None
+            ) from error
         except Exception:
             self.app.panic(Traceback())
         else: