Ensure all nested exception throws have a cause

Applied an explicit "cause" to most if not all internally raised exceptions
that are raised from within an internal exception catch, to avoid
misleading stacktraces that suggest an error within the handling of an
exception.  While it would be preferable to suppress the internally caught
exception in the way that the ``__suppress_context__`` attribute would,
there does not as yet seem to be a way to do this without suppressing an
enclosing user constructed context, so for now it exposes the internally
caught exception as the cause so that full information about the context
of the error is maintained.

Fixes: #4849
Change-Id: I55a86b29023675d9e5e49bc7edc5a2dc0bcd4751

1 files changed, 18 insertions, 10 deletions

diff --git a/test/base/test_utils.py b/test/base/test_utils.py
index 48e464a01..183e157e5 100644
--- a/test/base/test_utils.py
+++ b/test/base/test_utils.py
@@ -3,7 +3,6 @@
 import copy
 import datetime
 import inspect
-import sys
 
 from sqlalchemy import exc
 from sqlalchemy import sql
@@ -2899,20 +2898,29 @@ class ReraiseTest(fixtures.TestBase):
         except MyException as err:
             is_(err.__cause__, None)
 
-    def test_reraise_disallow_same_cause(self):
+    def test_raise_from_cause_legacy(self):
         class MyException(Exception):
             pass
 
+        class MyOtherException(Exception):
+            pass
+
+        me = MyException("exc on")
+
         def go():
             try:
-                raise MyException("exc one")
-            except Exception as err:
-                type_, value, tb = sys.exc_info()
-                util.reraise(type_, err, tb, value)
+                raise me
+            except Exception:
+                util.raise_from_cause(MyOtherException("exc two"))
 
-        assert_raises_message(AssertionError, "Same cause emitted", go)
+        try:
+            go()
+            assert False
+        except MyOtherException as moe:
+            if testing.requires.python3.enabled:
+                is_(moe.__cause__, me)
 
-    def test_raise_from_cause(self):
+    def test_raise_from(self):
         class MyException(Exception):
             pass
 
@@ -2924,8 +2932,8 @@ class ReraiseTest(fixtures.TestBase):
         def go():
             try:
                 raise me
-            except Exception:
-                util.raise_from_cause(MyOtherException("exc two"))
+            except Exception as err:
+                util.raise_(MyOtherException("exc two"), from_=err)
 
         try:
             go()