- revert the change first made in a6fe4dc, as we are now generalizing

the warning here to all safe_reraise() cases in Python 2.
- Revisiting :ticket:`2696`, first released in 1.0.10, which attempts to
work around Python 2's lack of exception context reporting by emitting
a warning for an exception that was interrupted by a second exception
when attempting to roll back the already-failed transaction; this
issue continues to occur for MySQL backends in conjunction with a
savepoint that gets unexpectedly lost, which then causes a
"no such savepoint" error when the rollback is attempted, obscuring
what the original condition was.

The approach has been generalized to the Core "safe
reraise" function which takes place across the ORM and Core in any
place that a transaction is being rolled back in response to an error
which occurred trying to commit, including the context managers
provided by :class:`.Session` and :class:`.Connection`, and taking
place for operations such as a failure on "RELEASE SAVEPOINT".
Previously, the fix was only in place for a specific path within
the ORM flush/commit process; it now takes place for all transational
context managers as well.
fixes #2696

2 files changed, 9 insertions, 14 deletions

diff --git a/lib/sqlalchemy/orm/session.py b/lib/sqlalchemy/orm/session.py
index 56513860a..0af8f60fb 100644
--- a/lib/sqlalchemy/orm/session.py
+++ b/lib/sqlalchemy/orm/session.py
@@ -408,23 +408,11 @@ class SessionTransaction(object):
             for subtransaction in stx._iterate_parents(upto=self):
                 subtransaction.close()
 
-        if _capture_exception:
-            captured_exception = sys.exc_info()[1]
-
         boundary = self
         if self._state in (ACTIVE, PREPARED):
             for transaction in self._iterate_parents():
                 if transaction._parent is None or transaction.nested:
-                    try:
-                        transaction._rollback_impl()
-                    except Exception:
-                        if _capture_exception:
-                            util.warn(
-                                "An exception raised during a Session "
-                                "persistence operation cannot be raised "
-                                "due to an additional ROLLBACK exception; "
-                                "the exception is: %s" % captured_exception)
-                        raise
+                    transaction._rollback_impl()
                     transaction._state = DEACTIVE
                     boundary = transaction
                     break
@@ -446,7 +434,7 @@ class SessionTransaction(object):
 
         self.close()
         if self._parent and _capture_exception:
-            self._parent._rollback_exception = captured_exception
+            self._parent._rollback_exception = sys.exc_info()[1]
 
         sess.dispatch.after_soft_rollback(sess, self)
 
diff --git a/lib/sqlalchemy/util/langhelpers.py b/lib/sqlalchemy/util/langhelpers.py
index 11aa9384d..a1780536a 100644
--- a/lib/sqlalchemy/util/langhelpers.py
+++ b/lib/sqlalchemy/util/langhelpers.py
@@ -59,6 +59,13 @@ class safe_reraise(object):
             self._exc_info = None   # remove potential circular references
             compat.reraise(exc_type, exc_value, exc_tb)
         else:
+            if not compat.py3k and self._exc_info and self._exc_info[1]:
+                # emulate Py3K's behavior of telling us when an exception
+                # occurs in an exception handler.
+                warn(
+                    "An exception has occurred during handling of a "
+                    "previous exception.  The previous exception "
+                    "is:\n %s %s\n" % (self._exc_info[0], self._exc_info[1]))
             self._exc_info = None   # remove potential circular references
             compat.reraise(type_, value, traceback)