Get rid of MultiError in favor of ExceptionGroup

This required some changes to the tests since EdgeDb's MultiError
has some ergonomic conveniences that ExceptionGroup doesn't:

- A helper method to get the types of the exceptions
- It puts the number and types of the exceptions in the message

Also, in one case (test_taskgroup_14) an EG nested inside another
EG was raised, whereas the original code just raised one EG.
This remains to be investigated.

Author: gvanrossum

Lib/asyncio/taskgroups.py

@@ -164,8 +164,7 @@ async def __aexit__(self, et, exc, tb):
             errors = self._errors
             self._errors = None
 
-            me = TaskGroupError('unhandled errors in a TaskGroup',
-                                errors=errors)
+            me = TaskGroupError('unhandled errors in a TaskGroup', errors)
             raise me from None
 
     def create_task(self, coro):
@@ -268,29 +267,7 @@ def _on_task_done(self, task):
             self._parent_task.cancel()
 
 
-class MultiError(Exception):
-
-    def __init__(self, msg, *args, errors=()):
-        if errors:
-            types = set(type(e).__name__ for e in errors)
-            msg = f'{msg}; {len(errors)} sub errors: ({", ".join(types)})'
-            for er in errors:
-                msg += f'\n + {type(er).__name__}: {er}'
-                if er.__traceback__:
-                    er_tb = ''.join(traceback.format_tb(er.__traceback__))
-                    er_tb = textwrap.indent(er_tb, ' | ')
-                    msg += f'\n{er_tb}\n'
-        super().__init__(msg, *args)
-        self.__errors__ = tuple(errors)
-
-    def get_error_types(self):
-        return {type(e) for e in self.__errors__}
-
-    def __reduce__(self):
-        return (type(self), (self.args,), {'__errors__': self.__errors__})
-
-
-class TaskGroupError(MultiError):
+class TaskGroupError(ExceptionGroup):
     pass
 
 

Lib/test/test_asyncio/test_taskgroups.py

@@ -27,6 +27,10 @@ class MyExc(Exception):
     pass
 
 
+def get_error_types(eg):
+    return {type(exc) for exc in eg.exceptions}
+
+
 class TestTaskGroup(unittest.IsolatedAsyncioTestCase):
 
     def setUp(self):
@@ -117,10 +121,11 @@ async def runner():
 
             NUM += 10
 
-        with self.assertRaisesRegex(taskgroups.TaskGroupError,
-                                    r'1 sub errors: \(ZeroDivisionError\)'):
+        with self.assertRaises(taskgroups.TaskGroupError) as cm:
             await self.loop.create_task(runner())
 
+        self.assertEqual(get_error_types(cm.exception), {ZeroDivisionError})
+
         self.assertEqual(NUM, 0)
         self.assertTrue(t2_cancel)
         self.assertTrue(t2.cancelled())
@@ -162,12 +167,10 @@ async def runner():
 
         # The 3 foo1 sub tasks can be racy when the host is busy - if the
         # cancellation happens in the middle, we'll see partial sub errors here
-        with self.assertRaisesRegex(
-            taskgroups.TaskGroupError,
-            r'(1|2|3) sub errors: \(ZeroDivisionError\)',
-        ):
+        with self.assertRaises(taskgroups.TaskGroupError) as cm:
             await self.loop.create_task(runner())
 
+        self.assertEqual(get_error_types(cm.exception), {ZeroDivisionError})
         self.assertEqual(NUM, 0)
         self.assertTrue(t2_cancel)
         self.assertTrue(runner_cancel)
@@ -280,7 +283,7 @@ async def runner():
         try:
             await runner()
         except taskgroups.TaskGroupError as t:
-            self.assertEqual(t.get_error_types(), {ZeroDivisionError})
+            self.assertEqual(get_error_types(t), {ZeroDivisionError})
         else:
             self.fail('TaskGroupError was not raised')
 
@@ -309,7 +312,7 @@ async def runner():
         try:
             await runner()
         except taskgroups.TaskGroupError as t:
-            self.assertEqual(t.get_error_types(), {ZeroDivisionError})
+            self.assertEqual(get_error_types(t), {ZeroDivisionError})
         else:
             self.fail('TaskGroupError was not raised')
 
@@ -382,9 +385,11 @@ async def runner():
                     g2.create_task(crash_after(0.2))
 
         r = self.loop.create_task(runner())
-        with self.assertRaisesRegex(taskgroups.TaskGroupError, r'1 sub errors'):
+        with self.assertRaises(taskgroups.TaskGroupError) as cm:
             await r
 
+        self.assertEqual(get_error_types(cm.exception), {ValueError})
+
     async def test_taskgroup_14(self):
 
         async def crash_after(t):
@@ -399,9 +404,13 @@ async def runner():
                     g2.create_task(crash_after(0.1))
 
         r = self.loop.create_task(runner())
-        with self.assertRaisesRegex(taskgroups.TaskGroupError, r'1 sub errors'):
+        with self.assertRaises(taskgroups.TaskGroupError) as cm:
             await r
 
+        # TODO(guido): Check that the nested exception group is expected
+        self.assertEqual(get_error_types(cm.exception), {taskgroups.TaskGroupError})
+        self.assertEqual(get_error_types(cm.exception.exceptions[0]), {ValueError})
+
     async def test_taskgroup_15(self):
 
         async def crash_soon():
@@ -497,7 +506,7 @@ async def runner():
         try:
             await r
         except taskgroups.TaskGroupError as t:
-            self.assertEqual(t.get_error_types(), {MyExc})
+            self.assertEqual(get_error_types(t),{MyExc})
         else:
             self.fail('TaskGroupError was not raised')
 
@@ -523,7 +532,7 @@ async def runner():
         try:
             await r
         except taskgroups.TaskGroupError as t:
-            self.assertEqual(t.get_error_types(), {MyExc, ZeroDivisionError})
+            self.assertEqual(get_error_types(t), {MyExc, ZeroDivisionError})
         else:
             self.fail('TasgGroupError was not raised')