Add concept of "implicit boolean", treat as native

Fixed issue that is closely related to :ticket:`3639` where an expression
rendered in a boolean context on a non-native boolean backend would
be compared to 1/0 even though it is already an implcitly boolean
expression, when :meth:`.ColumnElement.self_group` were used.  While this
does not affect the user-friendly backends (MySQL, SQLite) it was not
handled by Oracle (and possibly SQL Server).   Whether or not the
expression is implicitly boolean on any database is now determined
up front as an additional check to not generate the integer comparison
within the compliation of the statement.

Fixes: #4320
Change-Id: Iae0a65e5c01bd576e64733c3651e1e1a1a1b240c

1 files changed, 33 insertions, 1 deletions

diff --git a/test/sql/test_operators.py b/test/sql/test_operators.py
index f4b3cf584..00961a2e8 100644
--- a/test/sql/test_operators.py
+++ b/test/sql/test_operators.py
@@ -2105,9 +2105,41 @@ class NegationTest(fixtures.TestBase, testing.AssertsCompiledSQL):
 
         self.assert_compile(
             expr,
-            "NOT (mytable.myid = :myid_1 OR mytable.myid = :myid_2)"
+            "NOT (mytable.myid = :myid_1 OR mytable.myid = :myid_2)",
+            dialect=default.DefaultDialect(supports_native_boolean=False)
         )
 
+    def test_negate_operator_self_group(self):
+        orig_expr = or_(
+            self.table1.c.myid == 1, self.table1.c.myid == 2).self_group()
+        expr = not_(orig_expr)
+        is_not_(expr, orig_expr)
+
+        self.assert_compile(
+            expr,
+            "NOT (mytable.myid = :myid_1 OR mytable.myid = :myid_2)",
+            dialect=default.DefaultDialect(supports_native_boolean=False)
+        )
+
+    def test_implicitly_boolean(self):
+        # test for expressions that the database always considers as boolean
+        # even if there is no boolean datatype.
+        assert not self.table1.c.myid._is_implicitly_boolean
+        assert (self.table1.c.myid == 5)._is_implicitly_boolean
+        assert (self.table1.c.myid == 5).self_group()._is_implicitly_boolean
+        assert (self.table1.c.myid == 5).label('x')._is_implicitly_boolean
+        assert not_(self.table1.c.myid == 5)._is_implicitly_boolean
+        assert or_(
+            self.table1.c.myid == 5, self.table1.c.myid == 7
+        )._is_implicitly_boolean
+        assert not column('x', Boolean)._is_implicitly_boolean
+        assert not (self.table1.c.myid + 5)._is_implicitly_boolean
+        assert not not_(column('x', Boolean))._is_implicitly_boolean
+        assert not select([self.table1.c.myid]).\
+            as_scalar()._is_implicitly_boolean
+        assert not text("x = y")._is_implicitly_boolean
+        assert not literal_column("x = y")._is_implicitly_boolean
+
 
 class LikeTest(fixtures.TestBase, testing.AssertsCompiledSQL):
     __dialect__ = 'default'