1 files changed, 50 insertions, 13 deletions

diff --git a/lib/sqlalchemy/util/compat.py b/lib/sqlalchemy/util/compat.py
index 8967955cd..004b4687a 100644
--- a/lib/sqlalchemy/util/compat.py
+++ b/lib/sqlalchemy/util/compat.py
@@ -147,13 +147,42 @@ if py3k:
     def cmp(a, b):
         return (a > b) - (a < b)
 
-    def reraise(tp, value, tb=None, cause=None):
-        if cause is not None:
-            assert cause is not value, "Same cause emitted"
-            value.__cause__ = cause
-        if value.__traceback__ is not tb:
-            raise value.with_traceback(tb)
-        raise value
+    def raise_(
+        exception, with_traceback=None, replace_context=None, from_=False
+    ):
+        r"""implement "raise" with cause support.
+
+        :param exception: exception to raise
+        :param with_traceback: will call exception.with_traceback()
+        :param replace_context: an as-yet-unsupported feature.  This is
+         an exception object which we are "replacing", e.g., it's our
+         "cause" but we don't want it printed.    Basically just what
+         ``__suppress_context__`` does but we don't want to suppress
+         the enclosing context, if any.  So for now we make it the
+         cause.
+        :param from\_: the cause.  this actually sets the cause and doesn't
+         hope to hide it someday.
+
+        """
+        if with_traceback is not None:
+            exception = exception.with_traceback(with_traceback)
+
+        if from_ is not False:
+            exception.__cause__ = from_
+        elif replace_context is not None:
+            # no good solution here, we would like to have the exception
+            # have only the context of replace_context.__context__ so that the
+            # intermediary exception does not change, but we can't figure
+            # that out.
+            exception.__cause__ = replace_context
+
+        try:
+            raise exception
+        finally:
+            # credit to
+            # https://cosmicpercolator.com/2016/01/13/exception-leaks-in-python-2-and-3/
+            # as the __traceback__ object creates a cycle
+            del exception, replace_context, from_, with_traceback
 
     def u(s):
         return s
@@ -257,13 +286,13 @@ else:
         else:
             return text
 
-    # not as nice as that of Py3K, but at least preserves
-    # the code line where the issue occurred
     exec(
-        "def reraise(tp, value, tb=None, cause=None):\n"
-        "    if cause is not None:\n"
-        "        assert cause is not value, 'Same cause emitted'\n"
-        "    raise tp, value, tb\n"
+        "def raise_(exception, with_traceback=None, replace_context=None, "
+        "from_=False):\n"
+        "    if with_traceback:\n"
+        "        raise type(exception), exception, with_traceback\n"
+        "    else:\n"
+        "        raise exception\n"
     )
 
     TYPE_CHECKING = False
@@ -405,6 +434,8 @@ def nested(*managers):
 
 
 def raise_from_cause(exception, exc_info=None):
+    r"""legacy.  use raise\_()"""
+
     if exc_info is None:
         exc_info = sys.exc_info()
     exc_type, exc_value, exc_tb = exc_info
@@ -412,6 +443,12 @@ def raise_from_cause(exception, exc_info=None):
     reraise(type(exception), exception, tb=exc_tb, cause=cause)
 
 
+def reraise(tp, value, tb=None, cause=None):
+    r"""legacy.  use raise\_()"""
+
+    raise_(value, with_traceback=tb, from_=cause)
+
+
 def with_metaclass(meta, *bases):
     """Create a base class with a metaclass.