Wrap non-AppCommandError exceptions with TransformerError

discord/app_commands/errors.py

@@ -92,10 +92,11 @@ class TransformerError(AppCommandError):
 
     This inherits from :exc:`~discord.app_commands.AppCommandError`.
 
-    .. note::
+    If an exception occurs while converting that does not subclass
-
+    :exc:`AppCommandError` then the exception is wrapped into this exception.
-        If the transformer raises a custom :exc:`AppCommandError` then it will
+    The original exception can be retrieved using the ``__cause__`` attribute.
-        be propagated rather than wrapped into this exception.
+    Otherwise if the exception derives from :exc:`AppCommandError` then it will
+    be propagated as-is.
 
     .. versionadded:: 2.0
 

discord/app_commands/transformers.py

@@ -44,7 +44,7 @@ from typing import (
     Union,
 )
 
-from .errors import TransformerError
+from .errors import AppCommandError, TransformerError
 from .models import AppCommandChannel, AppCommandThread, Choice
 from ..channel import StageChannel, StoreChannel, VoiceChannel, TextChannel, CategoryChannel
 from ..enums import AppCommandOptionType, ChannelType
@@ -136,7 +136,13 @@ class CommandParameter:
                     raise TransformerError(value, self.type, self._annotation)
                 return choice
 
-            return await self._annotation.transform(interaction, value)
+            try:
+                return await self._annotation.transform(interaction, value)
+            except AppCommandError:
+                raise
+            except Exception as e:
+                raise TransformerError(value, self.type, self._annotation) from e
+
         return value