Deprecate empty or_() and and_()

Creating an :func:`.and_` or :func:`.or_` construct with no arguments or
empty ``*args`` will now emit a deprecation warning, as the SQL produced is
a no-op (i.e. it renders as a blank string). This behavior is considered to
be non-intuitive, so for empty or possibly empty :func:`.and_` or
:func:`.or_` constructs, an appropriate default boolean should be included,
such as ``and_(True, *args)`` or ``or_(False, *args)``.   As has been the
case for many major versions of SQLAlchemy, these particular boolean
values will not render if the ``*args`` portion is non-empty.

As there are some internal cases where an empty and_() construct is used
in order to build an optional WHERE expression, a private
utility function is added to suit this use case.

Co-authored-by: Mike Bayer <mike_mp@zzzcomputing.com>
Fixes: #5054
Closes: #5062
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/5062
Pull-request-sha: 5ca2f27281977d74e390148c0fb8deaa0e0e4ad9

Change-Id: I599b9c8befa64d9a59a35ad7dd84ff400e3aa647

1 files changed, 8 insertions, 4 deletions

diff --git a/test/sql/test_update.py b/test/sql/test_update.py
index e625b7d9c..0313db832 100644
--- a/test/sql/test_update.py
+++ b/test/sql/test_update.py
@@ -1,4 +1,3 @@
-from sqlalchemy import and_
 from sqlalchemy import bindparam
 from sqlalchemy import column
 from sqlalchemy import exc
@@ -8,7 +7,6 @@ from sqlalchemy import func
 from sqlalchemy import Integer
 from sqlalchemy import literal
 from sqlalchemy import MetaData
-from sqlalchemy import or_
 from sqlalchemy import select
 from sqlalchemy import String
 from sqlalchemy import table
@@ -18,6 +16,8 @@ from sqlalchemy import update
 from sqlalchemy import util
 from sqlalchemy.dialects import mysql
 from sqlalchemy.engine import default
+from sqlalchemy.sql import operators
+from sqlalchemy.sql.elements import BooleanClauseList
 from sqlalchemy.testing import assert_raises
 from sqlalchemy.testing import assert_raises_message
 from sqlalchemy.testing import AssertsCompiledSQL
@@ -634,12 +634,16 @@ class UpdateTest(_UpdateFromTestBase, fixtures.TablesTest, AssertsCompiledSQL):
     def test_where_empty(self):
         table1 = self.tables.mytable
         self.assert_compile(
-            table1.update().where(and_()),
+            table1.update().where(
+                BooleanClauseList._construct_raw(operators.and_)
+            ),
             "UPDATE mytable SET myid=:myid, name=:name, "
             "description=:description",
         )
         self.assert_compile(
-            table1.update().where(or_()),
+            table1.update().where(
+                BooleanClauseList._construct_raw(operators.or_)
+            ),
             "UPDATE mytable SET myid=:myid, name=:name, "
             "description=:description",
         )