remove multierror

src/trio/_core/_run.py

@@ -209,7 +209,7 @@ def collapse_exception_group(
     if (
         len(exceptions) == 1
         and isinstance(excgroup, BaseExceptionGroup)
-        and "collapsible" in str(excgroup)
+        and "collapsible" in getattr(excgroup, "__notes__", ())
     ):
         exceptions[0].__traceback__ = concat_tb(
             excgroup.__traceback__, exceptions[0].__traceback__
@@ -1128,10 +1128,12 @@ def aborted(raise_cancel: _core.RaiseCancelT) -> Abort:
             try:
                 if not self._strict_exception_groups and len(self._pending_excs) == 1:
                     return self._pending_excs[0]
-                return BaseExceptionGroup(
-                    "collapsible" if not self._strict_exception_groups else "TODO",
-                    self._pending_excs,
+                exception = BaseExceptionGroup(
+                    "Exceptions from Trio nursery", self._pending_excs
                 )
+                if not self._strict_exception_groups:
+                    exception.add_note("collapsible")
+                return exception
             finally:
                 # avoid a garbage cycle
                 # (see test_locals_destroyed_promptly_on_cancel)
@@ -1777,8 +1779,7 @@ async def python_wrapper(orig_coro: Awaitable[RetT]) -> RetT:
             self.instruments.call("task_spawned", task)
         # Special case: normally next_send should be an Outcome, but for the
         # very first send we have to send a literal unboxed None.
-        # TODO: remove [unused-ignore] when Outcome is typed
-        self.reschedule(task, None)  # type: ignore[arg-type, unused-ignore]
+        self.reschedule(task, None)  # type: ignore[arg-type]
         return task
 
     def task_exited(self, task: Task, outcome: Outcome[Any]) -> None:
@@ -2624,18 +2625,17 @@ def unrolled_run(
                         # protocol of unwrapping whatever outcome gets sent in.
                         # Instead, we'll arrange to throw `exc` in directly,
                         # which works for at least asyncio and curio.
-                        # TODO: remove [unused-ignore] when Outcome is typed
-                        runner.reschedule(task, exc)  # type: ignore[arg-type, unused-ignore]
+                        runner.reschedule(task, exc)  # type: ignore[arg-type]
                         task._next_send_fn = task.coro.throw
                     # prevent long-lived reference
-                    # TODO: develop test for this deletion
+                    # There's no regression test checking the necessity of this
                     del msg
 
                 if "after_task_step" in runner.instruments:
                     runner.instruments.call("after_task_step", task)
                 del GLOBAL_RUN_CONTEXT.task
                 # prevent long-lived references
-                # TODO: develop test for these deletions
+                # There's no regression test checking the necessity of this
                 del task, next_send, next_send_fn
 
     except GeneratorExit:

src/trio/_core/_tests/test_multierror.py

@@ -73,8 +73,8 @@ def test_concat_tb() -> None:
     assert extract_tb(get_tb(raiser2)) == entries2
 
 
-# I haven't managed to get this one to fail, despite removing the `del` from
-# _concat_tb.copy_tb (on a platform where the statement is executed)
+# Unclear if this can still fail, removing the `del` from _concat_tb.copy_tb does not seem
+# to trigger it (on a platform where the `del` is executed)
 @pytest.mark.skipif(
     sys.implementation.name != "cpython", reason="Only makes sense with refcounting GC"
 )

src/trio/_core/_tests/test_run.py

@@ -1210,7 +1210,7 @@ async def test_nursery_exception_chaining_doesnt_make_context_loops() -> None:
     async def crasher() -> NoReturn:
         raise KeyError
 
-    with pytest.raises(ExceptionGroup) as excinfo:
+    with pytest.raises(ExceptionGroup) as excinfo:  # noqa: PT012
         async with _core.open_nursery() as nursery:
             nursery.start_soon(crasher)
             raise ValueError
@@ -2528,7 +2528,9 @@ async def main() -> NoReturn:
         async with _core.open_nursery():
             raise Exception("foo")
 
-    with pytest.raises(ExceptionGroup) as exc:
+    with pytest.raises(
+        ExceptionGroup, match="^Exceptions from Trio nursery \\(1 sub-exception\\)$"
+    ) as exc:
         _core.run(main, strict_exception_groups=True)
 
     assert len(exc.value.exceptions) == 1
@@ -2561,6 +2563,26 @@ async def test_nursery_strict_exception_groups() -> None:
     assert exc.value.exceptions[0].args == ("foo",)
 
 
+async def test_nursery_loose_exception_groups() -> None:
+    """Test that loose exception groups can be enabled on a per-nursery basis."""
+
+    async def raise_error() -> NoReturn:
+        raise RuntimeError("test error")
+
+    with pytest.raises(  # noqa: PT012  # multiple statements
+        ExceptionGroup, match="^Exceptions from Trio nursery \\(2 sub-exceptions\\)$"
+    ) as exc:
+        async with _core.open_nursery(strict_exception_groups=False) as nursery:
+            nursery.start_soon(raise_error)
+            nursery.start_soon(raise_error)
+
+    assert exc.value.__notes__ == ["collapsible"]
+    assert len(exc.value.exceptions) == 2
+    for subexc in exc.value.exceptions:
+        assert type(subexc) is RuntimeError
+        assert subexc.args == ("test error",)
+
+
 async def test_nursery_collapse_strict() -> None:
     """
     Test that a single exception from a nested nursery with strict semantics doesn't get
@@ -2570,7 +2592,7 @@ async def test_nursery_collapse_strict() -> None:
     async def raise_error() -> NoReturn:
         raise RuntimeError("test error")
 
-    with pytest.raises(ExceptionGroup) as exc:
+    with pytest.raises(ExceptionGroup) as exc:  # noqa: PT012
         async with _core.open_nursery() as nursery:
             nursery.start_soon(sleep_forever)
             nursery.start_soon(raise_error)
@@ -2596,7 +2618,7 @@ async def test_nursery_collapse_loose() -> None:
     async def raise_error() -> NoReturn:
         raise RuntimeError("test error")
 
-    with pytest.raises(ExceptionGroup) as exc:
+    with pytest.raises(ExceptionGroup) as exc:  # noqa: PT012
         async with _core.open_nursery() as nursery:
             nursery.start_soon(sleep_forever)
             nursery.start_soon(raise_error)