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, 19 insertions, 3 deletions

diff --git a/test/sql/test_compiler.py b/test/sql/test_compiler.py
index b49fb455c..b53acf61e 100644
--- a/test/sql/test_compiler.py
+++ b/test/sql/test_compiler.py
@@ -70,7 +70,9 @@ from sqlalchemy.ext.compiler import compiles
 from sqlalchemy.sql import column
 from sqlalchemy.sql import compiler
 from sqlalchemy.sql import label
+from sqlalchemy.sql import operators
 from sqlalchemy.sql import table
+from sqlalchemy.sql.elements import BooleanClauseList
 from sqlalchemy.sql.expression import ClauseList
 from sqlalchemy.sql.expression import HasPrefixes
 from sqlalchemy.testing import assert_raises
@@ -1393,10 +1395,20 @@ class SelectTest(fixtures.TestBase, AssertsCompiledSQL):
         )
         self.assert_compile(
             select([t]).where(
+                and_(or_(or_(t.c.x == 12), and_(or_(and_(t.c.x == 8)))))
+            ),
+            "SELECT t.x FROM t WHERE t.x = :x_1 OR t.x = :x_2",
+        )
+        self.assert_compile(
+            select([t]).where(
                 and_(
                     or_(
                         or_(t.c.x == 12),
-                        and_(or_(), or_(and_(t.c.x == 8)), and_()),
+                        and_(
+                            BooleanClauseList._construct_raw(operators.or_),
+                            or_(and_(t.c.x == 8)),
+                            BooleanClauseList._construct_raw(operators.and_),
+                        ),
                     )
                 )
             ),
@@ -1451,11 +1463,15 @@ class SelectTest(fixtures.TestBase, AssertsCompiledSQL):
 
     def test_where_empty(self):
         self.assert_compile(
-            select([table1.c.myid]).where(and_()),
+            select([table1.c.myid]).where(
+                BooleanClauseList._construct_raw(operators.and_)
+            ),
             "SELECT mytable.myid FROM mytable",
         )
         self.assert_compile(
-            select([table1.c.myid]).where(or_()),
+            select([table1.c.myid]).where(
+                BooleanClauseList._construct_raw(operators.or_)
+            ),
             "SELECT mytable.myid FROM mytable",
         )