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, 20 insertions, 11 deletions

diff --git a/lib/sqlalchemy/engine/base.py b/lib/sqlalchemy/engine/base.py
index ce6c2e9c6..449f386ce 100644
--- a/lib/sqlalchemy/engine/base.py
+++ b/lib/sqlalchemy/engine/base.py
@@ -996,8 +996,10 @@ class Connection(Connectable):
             return self._execute_text(object_, multiparams, params)
         try:
             meth = object_._execute_on_connection
-        except AttributeError:
-            raise exc.ObjectNotExecutableError(object_)
+        except AttributeError as err:
+            util.raise_(
+                exc.ObjectNotExecutableError(object_), replace_context=err
+            )
         else:
             return meth(self, multiparams, params)
 
@@ -1400,7 +1402,7 @@ class Connection(Connectable):
         invalidate_pool_on_disconnect = not is_exit_exception
 
         if self._reentrant_error:
-            util.raise_from_cause(
+            util.raise_(
                 exc.DBAPIError.instance(
                     statement,
                     parameters,
@@ -1412,7 +1414,8 @@ class Connection(Connectable):
                     if context is not None
                     else None,
                 ),
-                exc_info,
+                with_traceback=exc_info[2],
+                from_=e,
             )
         self._reentrant_error = True
         try:
@@ -1502,11 +1505,13 @@ class Connection(Connectable):
                     self._autorollback()
 
             if newraise:
-                util.raise_from_cause(newraise, exc_info)
+                util.raise_(newraise, with_traceback=exc_info[2], from_=e)
             elif should_wrap:
-                util.raise_from_cause(sqlalchemy_exception, exc_info)
+                util.raise_(
+                    sqlalchemy_exception, with_traceback=exc_info[2], from_=e
+                )
             else:
-                util.reraise(*exc_info)
+                util.raise_(exc_info[1], with_traceback=exc_info[2])
 
         finally:
             del self._reentrant_error
@@ -1573,11 +1578,13 @@ class Connection(Connectable):
                 ) = ctx.is_disconnect
 
         if newraise:
-            util.raise_from_cause(newraise, exc_info)
+            util.raise_(newraise, with_traceback=exc_info[2], from_=e)
         elif should_wrap:
-            util.raise_from_cause(sqlalchemy_exception, exc_info)
+            util.raise_(
+                sqlalchemy_exception, with_traceback=exc_info[2], from_=e
+            )
         else:
-            util.reraise(*exc_info)
+            util.raise_(exc_info[1], with_traceback=exc_info[2])
 
     def _run_ddl_visitor(self, visitorcallable, element, **kwargs):
         """run a DDL visitor.
@@ -2329,7 +2336,9 @@ class Engine(Connectable, log.Identified):
                     e, dialect, self
                 )
             else:
-                util.reraise(*sys.exc_info())
+                util.raise_(
+                    sys.exc_info()[1], with_traceback=sys.exc_info()[2]
+                )
 
     def raw_connection(self, _connection=None):
         """Return a "raw" DBAPI connection from the connection pool.