unify transactional context managers

Applied consistent behavior to the use case of
calling ``.commit()`` or ``.rollback()`` inside of an existing
``.begin()`` context manager, with the addition of potentially
emitting SQL within the block subsequent to the commit or rollback.
This change continues upon the change first added in
:ticket:`6155` where the use case of calling "rollback" inside of
a ``.begin()`` contextmanager block was proposed:

* calling ``.commit()`` or ``.rollback()`` will now be allowed
without error or warning within all scopes, including
that of legacy and future :class:`_engine.Engine`, ORM
:class:`_orm.Session`, asyncio :class:`.AsyncEngine`.  Previously,
the :class:`_orm.Session` disallowed this.

* The remaining scope of the context manager is then closed;
when the block ends, a check is emitted to see if the transaction
was already ended, and if so the block returns without action.

* It will now raise **an error** if subsequent SQL of any kind
is emitted within the block, **after** ``.commit()`` or
``.rollback()`` is called.   The block should be closed as
the state of the executable object would otherwise be undefined
in this state.

Fixes: #6288
Change-Id: I8b21766ae430f0fa1ac5ef689f4c0fb19fc84336

1 files changed, 5 insertions, 0 deletions

diff --git a/lib/sqlalchemy/util/concurrency.py b/lib/sqlalchemy/util/concurrency.py
index e26f305d9..60db9cfff 100644
--- a/lib/sqlalchemy/util/concurrency.py
+++ b/lib/sqlalchemy/util/concurrency.py
@@ -24,6 +24,11 @@ if not have_greenlet:
     asyncio = None  # noqa F811
 
     def _not_implemented():
+        # this conditional is to prevent pylance from considering
+        # greenlet_spawn() etc as "no return" and dimming out code below it
+        if have_greenlet:
+            return None
+
         if not compat.py3k:
             raise ValueError("Cannot use this function in py2.")
         else: