Add safe_reraise() + warnings only to Connection._autorollback

Added an exception handler that will warn for the "cause" exception on
Py2K when the "autorollback" feature of :class:`.Connection` itself
raises an exception. In Py3K, the two exceptions are naturally reported
by the interpreter as one occurring during the handling of the other.
This is continuing with the series of changes for rollback failure
handling that were last visited as part of :ticket:`2696` in 1.0.12.

Change-Id: I600ba455a14ebaea27c6189889181f97c632f179
Fixes: #3946

2 files changed, 62 insertions, 21 deletions

diff --git a/test/engine/test_execute.py b/test/engine/test_execute.py
index 54a85bf9f..eff1026cd 100644
--- a/test/engine/test_execute.py
+++ b/test/engine/test_execute.py
@@ -1,7 +1,7 @@
 # coding: utf-8
 
 from sqlalchemy.testing import eq_, assert_raises, assert_raises_message, \
-    config, is_, is_not_, le_
+    config, is_, is_not_, le_, expect_warnings
 import re
 from sqlalchemy.testing.util import picklers
 from sqlalchemy.interfaces import ConnectionProxy
@@ -1834,6 +1834,26 @@ class HandleErrorTest(fixtures.TestBase):
             )
             eq_(patched.call_count, 1)
 
+    def test_exception_autorollback_fails(self):
+        engine = engines.testing_engine()
+        conn = engine.connect()
+
+        def boom(connection):
+            raise engine.dialect.dbapi.OperationalError("rollback failed")
+
+        with expect_warnings(
+            r"An exception has occurred during handling of a previous "
+            r"exception.  The previous exception is.*i_dont_exist",
+            py2konly=True
+        ):
+            with patch.object(conn.dialect, "do_rollback", boom) as patched:
+                assert_raises_message(
+                    tsa.exc.OperationalError,
+                    "rollback failed",
+                    conn.execute,
+                    "insert into i_dont_exist (x) values ('y')"
+                )
+
     def test_exception_event_ad_hoc_context(self):
         """test that handle_error is called with a context in
         cases where _handle_dbapi_error() is normally called without
diff --git a/test/engine/test_reconnect.py b/test/engine/test_reconnect.py
index be60056a5..f798ff845 100644
--- a/test/engine/test_reconnect.py
+++ b/test/engine/test_reconnect.py
@@ -1,4 +1,5 @@
-from sqlalchemy.testing import eq_, ne_, assert_raises, assert_raises_message
+from sqlalchemy.testing import eq_, ne_, assert_raises, \
+    expect_warnings, assert_raises_message
 import time
 from sqlalchemy import (
     select, MetaData, Integer, String, create_engine, pool, exc, util)
@@ -408,11 +409,17 @@ class MockReconnectTest(fixtures.TestBase):
         self.dbapi.shutdown("rollback_no_disconnect")
 
         # raises error
-        assert_raises_message(
-            tsa.exc.DBAPIError,
-            "something broke on rollback but we didn't lose the connection",
-            conn.execute, select([1])
-        )
+        with expect_warnings(
+            "An exception has occurred during handling .*"
+            "something broke on execute but we didn't lose the connection",
+            py2konly=True
+        ):
+            assert_raises_message(
+                tsa.exc.DBAPIError,
+                "something broke on rollback but we didn't "
+                "lose the connection",
+                conn.execute, select([1])
+            )
 
         assert conn.closed
         assert not conn.invalidated
@@ -433,11 +440,16 @@ class MockReconnectTest(fixtures.TestBase):
         self.dbapi.shutdown("rollback")
 
         # raises error
-        assert_raises_message(
-            tsa.exc.DBAPIError,
-            "Lost the DB connection on rollback",
-            conn.execute, select([1])
-        )
+        with expect_warnings(
+            "An exception has occurred during handling .*"
+            "something broke on execute but we didn't lose the connection",
+            py2konly=True
+        ):
+            assert_raises_message(
+                tsa.exc.DBAPIError,
+                "Lost the DB connection on rollback",
+                conn.execute, select([1])
+            )
 
         assert not conn.closed
         assert conn.invalidated
@@ -448,11 +460,16 @@ class MockReconnectTest(fixtures.TestBase):
         self.dbapi.shutdown("rollback")
 
         # raises error
-        assert_raises_message(
-            tsa.exc.DBAPIError,
-            "Lost the DB connection on rollback",
-            conn.execute, select([1])
-        )
+        with expect_warnings(
+            "An exception has occurred during handling .*"
+            "something broke on execute but we didn't lose the connection",
+            py2konly=True
+        ):
+            assert_raises_message(
+                tsa.exc.DBAPIError,
+                "Lost the DB connection on rollback",
+                conn.execute, select([1])
+            )
 
         assert conn.closed
         assert conn.invalidated
@@ -765,10 +782,14 @@ class RealReconnectTest(fixtures.TestBase):
         self.engine.dialect.is_disconnect = is_disconnect
         conn = self.engine.connect()
         self.engine.test_shutdown()
-        assert_raises(
-            tsa.exc.DBAPIError,
-            conn.execute, select([1])
-        )
+        with expect_warnings(
+            "An exception has occurred during handling .*",
+            py2konly=True
+        ):
+            assert_raises(
+                tsa.exc.DBAPIError,
+                conn.execute, select([1])
+            )
 
     def test_rollback_on_invalid_plain(self):
         conn = self.engine.connect()