Add a new `.trionics._tn` for "task nursery stuff"

Since I'd like to decouple the new "task-manager-nursery" lowlevel
primitives/abstractions from the higher-level
`TaskManagerNursery`-supporting API(s) and default per-task
supervision-strat and because `._mngr` is already purposed for
higher-level "on-top-of-nursery" patterns as it is.

Deats,
- move `maybe_open_nursery()` into the new mod.
- adjust the pkg-mod's import to the new sub-mod.
- also draft up this idea for an API which stacks `._beg.collapse_eg()`
  onto a nursery with the WIP name `open_loose_tn()` but more then
  likely i'll just discard this idea bc i think the explicit `@acm`
  stacking is more explicit/pythonic/up-front-grokable despite the extra
  LoC.

tractor/trionics/__init__.py

@@ -21,7 +21,6 @@ Sugary patterns for trio + tractor designs.
 from ._mngrs import (
     gather_contexts as gather_contexts,
     maybe_open_context as maybe_open_context,
-    maybe_open_nursery as maybe_open_nursery,
 )
 from ._broadcast import (
     AsyncReceiver as AsyncReceiver,
@@ -37,3 +36,6 @@ from ._beg import (
 from ._taskc import (
     maybe_raise_from_masking_exc as maybe_raise_from_masking_exc,
 )
+from ._tn import (
+    maybe_open_nursery as maybe_open_nursery,
+)

tractor/trionics/_mngrs.py

@@ -23,7 +23,6 @@ from contextlib import (
     asynccontextmanager as acm,
 )
 import inspect
-from types import ModuleType
 from typing import (
     Any,
     AsyncContextManager,
@@ -34,21 +33,18 @@ from typing import (
     Optional,
     Sequence,
     TypeVar,
-    TYPE_CHECKING,
 )
 
 import trio
 from tractor._state import current_actor
 from tractor.log import get_logger
+from ._tn import maybe_open_nursery
 # from ._beg import collapse_eg
 # from ._taskc import (
 #     maybe_raise_from_masking_exc,
 # )
 
 
-if TYPE_CHECKING:
-    from tractor import ActorNursery
-
 
 log = get_logger(__name__)
 
@@ -56,30 +52,6 @@ log = get_logger(__name__)
 T = TypeVar("T")
 
 
-@acm
-async def maybe_open_nursery(
-    nursery: trio.Nursery|ActorNursery|None = None,
-    shield: bool = False,
-    lib: ModuleType = trio,
-
-    **kwargs,  # proxy thru
-
-) -> AsyncGenerator[trio.Nursery, Any]:
-    '''
-    Create a new nursery if None provided.
-
-    Blocks on exit as expected if no input nursery is provided.
-
-    '''
-    if nursery is not None:
-        yield nursery
-    else:
-        async with lib.open_nursery(**kwargs) as nursery:
-            if lib == trio:
-                nursery.cancel_scope.shield = shield
-            yield nursery
-
-
 async def _enter_and_wait(
     mngr: AsyncContextManager[T],
     unwrapped: dict[int, T],

tractor/trionics/_tn.py

@@ -0,0 +1,94 @@
+# tractor: structured concurrent "actors".
+# Copyright 2018-eternity Tyler Goodlet.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+'''
+`trio.Nursery` wrappers which we short-hand refer to as
+`tn`: "task nursery".
+
+(whereas we refer to `tractor.ActorNursery` as the short-hand `an`)
+
+'''
+from __future__ import annotations
+from contextlib import (
+    asynccontextmanager as acm,
+)
+from types import ModuleType
+from typing import (
+    Any,
+    AsyncGenerator,
+    TYPE_CHECKING,
+)
+
+import trio
+from tractor.log import get_logger
+
+# from ._beg import (
+#     collapse_eg,
+# )
+
+if TYPE_CHECKING:
+    from tractor import ActorNursery
+
+log = get_logger(__name__)
+
+
+# ??TODO? is this even a good idea??
+# it's an extra LoC to stack `collapse_eg()` vs.
+# a new/foreign/bad-std-named very thing wrapper..?
+# -[ ] is there a better/simpler name?
+# @acm
+# async def open_loose_tn() -> trio.Nursery:
+#     '''
+#     Implements the equivalent of the old style loose eg raising
+#     task-nursery from `trio<=0.25.0` ,
+
+#     .. code-block:: python
+
+#         async with trio.open_nursery(
+#             strict_exception_groups=False,
+#         ) as tn:
+#             ...
+
+#     '''
+#     async with (
+#         collapse_eg(),
+#         trio.open_nursery() as tn,
+#     ):
+#         yield tn
+
+
+@acm
+async def maybe_open_nursery(
+    nursery: trio.Nursery|ActorNursery|None = None,
+    shield: bool = False,
+    lib: ModuleType = trio,
+    loose: bool = False,
+
+    **kwargs,  # proxy thru
+
+) -> AsyncGenerator[trio.Nursery, Any]:
+    '''
+    Create a new nursery if None provided.
+
+    Blocks on exit as expected if no input nursery is provided.
+
+    '''
+    if nursery is not None:
+        yield nursery
+    else:
+        async with lib.open_nursery(**kwargs) as tn:
+            tn.cancel_scope.shield = shield
+            yield tn