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, 59 insertions, 4 deletions

diff --git a/test/sql/test_operators.py b/test/sql/test_operators.py
index a90b03b38..d3afc2dee 100644
--- a/test/sql/test_operators.py
+++ b/test/sql/test_operators.py
@@ -42,6 +42,7 @@ from sqlalchemy.sql import sqltypes
 from sqlalchemy.sql import table
 from sqlalchemy.sql import true
 from sqlalchemy.sql.elements import BindParameter
+from sqlalchemy.sql.elements import BooleanClauseList
 from sqlalchemy.sql.elements import Label
 from sqlalchemy.sql.expression import BinaryExpression
 from sqlalchemy.sql.expression import ClauseList
@@ -51,6 +52,7 @@ from sqlalchemy.sql.expression import tuple_
 from sqlalchemy.sql.expression import UnaryExpression
 from sqlalchemy.sql.expression import union
 from sqlalchemy.testing import assert_raises_message
+from sqlalchemy.testing import combinations
 from sqlalchemy.testing import eq_
 from sqlalchemy.testing import expect_warnings
 from sqlalchemy.testing import fixtures
@@ -1062,14 +1064,67 @@ class ConjunctionTest(fixtures.TestBase, testing.AssertsCompiledSQL):
 
     __dialect__ = default.DefaultDialect(supports_native_boolean=True)
 
-    def test_one(self):
+    def test_single_bool_one(self):
         self.assert_compile(~and_(true()), "false")
 
-    def test_two(self):
+    def test_single_bool_two(self):
+        self.assert_compile(~and_(True), "false")
+
+    def test_single_bool_three(self):
         self.assert_compile(or_(~and_(true())), "false")
 
-    def test_three(self):
-        self.assert_compile(or_(and_()), "")
+    def test_single_bool_four(self):
+        self.assert_compile(~or_(false()), "true")
+
+    def test_single_bool_five(self):
+        self.assert_compile(~or_(False), "true")
+
+    def test_single_bool_six(self):
+        self.assert_compile(and_(~or_(false())), "true")
+
+    def test_single_bool_seven(self):
+        self.assert_compile(and_(True), "true")
+
+    def test_single_bool_eight(self):
+        self.assert_compile(or_(False), "false")
+
+    def test_single_bool_nine(self):
+        self.assert_compile(
+            and_(True),
+            "1 = 1",
+            dialect=default.DefaultDialect(supports_native_boolean=False),
+        )
+
+    def test_single_bool_ten(self):
+        self.assert_compile(
+            or_(False),
+            "0 = 1",
+            dialect=default.DefaultDialect(supports_native_boolean=False),
+        )
+
+    @combinations((and_, "and_", "True"), (or_, "or_", "False"))
+    def test_empty_clauses(self, op, str_op, str_continue):
+        # these warning classes will change to ArgumentError when the
+        # deprecated behavior is disabled
+        assert_raises_message(
+            exc.SADeprecationWarning,
+            r"Invoking %(str_op)s\(\) without arguments is deprecated, and "
+            r"will be disallowed in a future release.   For an empty "
+            r"%(str_op)s\(\) construct, use "
+            r"%(str_op)s\(%(str_continue)s, \*args\)\."
+            % {"str_op": str_op, "str_continue": str_continue},
+            op,
+        )
+
+    def test_empty_and_raw(self):
+        self.assert_compile(
+            BooleanClauseList._construct_raw(operators.and_), ""
+        )
+
+    def test_empty_or_raw(self):
+        self.assert_compile(
+            BooleanClauseList._construct_raw(operators.and_), ""
+        )
 
     def test_four(self):
         x = column("x")