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, 14 insertions, 8 deletions

diff --git a/lib/sqlalchemy/sql/selectable.py b/lib/sqlalchemy/sql/selectable.py
index b8d88e160..b972c13be 100644
--- a/lib/sqlalchemy/sql/selectable.py
+++ b/lib/sqlalchemy/sql/selectable.py
@@ -2620,10 +2620,13 @@ class GenerativeSelect(DeprecatedSelectBaseGenerations, SelectBase):
             return None
         try:
             value = clause._limit_offset_value
-        except AttributeError:
-            raise exc.CompileError(
-                "This SELECT structure does not use a simple "
-                "integer value for %s" % attrname
+        except AttributeError as err:
+            util.raise_(
+                exc.CompileError(
+                    "This SELECT structure does not use a simple "
+                    "integer value for %s" % attrname
+                ),
+                replace_context=err,
             )
         else:
             return util.asint(value)
@@ -3489,10 +3492,13 @@ class Select(
 
         try:
             cols_present = bool(columns)
-        except TypeError:
-            raise exc.ArgumentError(
-                "columns argument to select() must "
-                "be a Python list or other iterable"
+        except TypeError as err:
+            util.raise_(
+                exc.ArgumentError(
+                    "columns argument to select() must "
+                    "be a Python list or other iterable"
+                ),
+                from_=err,
             )
 
         if cols_present: