use concat() directly for contains, startswith, endswith

Adjusted the SQL compilation for string containment functions
``.contains()``, ``.startswith()``, ``.endswith()`` to force the use of the
string concatenation operator, rather than relying upon the overload of the
addition operator, so that non-standard use of these operators with for
example bytestrings still produces string concatenation operators.

To accommodate this, needed to add a new _rconcat operator function,
which is private, as well as a fallback in concat_op() that works
similarly to Python builtin ops.

Fixes: #8253
Change-Id: I2b7f56492f765742d88cb2a7834ded6a2892bd7e

1 files changed, 16 insertions, 1 deletions

diff --git a/lib/sqlalchemy/sql/operators.py b/lib/sqlalchemy/sql/operators.py
index 2b888769a..44d63b398 100644
--- a/lib/sqlalchemy/sql/operators.py
+++ b/lib/sqlalchemy/sql/operators.py
@@ -615,6 +615,16 @@ class ColumnOperators(Operators):
         """
         return self.operate(concat_op, other)
 
+    def _rconcat(self, other: Any) -> ColumnOperators:
+        """Implement an 'rconcat' operator.
+
+        this is for internal use at the moment
+
+        .. versionadded:: 1.4.40
+
+        """
+        return self.reverse_operate(concat_op, other)
+
     def like(
         self, other: Any, escape: Optional[str] = None
     ) -> ColumnOperators:
@@ -1764,7 +1774,12 @@ def filter_op(a: Any, b: Any) -> Any:
 
 @_operator_fn
 def concat_op(a: Any, b: Any) -> Any:
-    return a.concat(b)
+    try:
+        concat = a.concat
+    except AttributeError:
+        return b._rconcat(a)
+    else:
+        return concat(b)
 
 
 @_operator_fn