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
(cherry picked from commit 85a88df13ab8d217331cf98392544a888b4d7df3)

1 files changed, 6 insertions, 6 deletions

diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index 667dd7d3d..330f3c3bc 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -2295,37 +2295,37 @@ class SQLCompiler(Compiled):
     def visit_contains_op_binary(self, binary, operator, **kw):
         binary = binary._clone()
         percent = self._like_percent_literal
-        binary.right = percent.__add__(binary.right).__add__(percent)
+        binary.right = percent.concat(binary.right).concat(percent)
         return self.visit_like_op_binary(binary, operator, **kw)
 
     def visit_not_contains_op_binary(self, binary, operator, **kw):
         binary = binary._clone()
         percent = self._like_percent_literal
-        binary.right = percent.__add__(binary.right).__add__(percent)
+        binary.right = percent.concat(binary.right).concat(percent)
         return self.visit_not_like_op_binary(binary, operator, **kw)
 
     def visit_startswith_op_binary(self, binary, operator, **kw):
         binary = binary._clone()
         percent = self._like_percent_literal
-        binary.right = percent.__radd__(binary.right)
+        binary.right = percent._rconcat(binary.right)
         return self.visit_like_op_binary(binary, operator, **kw)
 
     def visit_not_startswith_op_binary(self, binary, operator, **kw):
         binary = binary._clone()
         percent = self._like_percent_literal
-        binary.right = percent.__radd__(binary.right)
+        binary.right = percent._rconcat(binary.right)
         return self.visit_not_like_op_binary(binary, operator, **kw)
 
     def visit_endswith_op_binary(self, binary, operator, **kw):
         binary = binary._clone()
         percent = self._like_percent_literal
-        binary.right = percent.__add__(binary.right)
+        binary.right = percent.concat(binary.right)
         return self.visit_like_op_binary(binary, operator, **kw)
 
     def visit_not_endswith_op_binary(self, binary, operator, **kw):
         binary = binary._clone()
         percent = self._like_percent_literal
-        binary.right = percent.__add__(binary.right)
+        binary.right = percent.concat(binary.right)
         return self.visit_not_like_op_binary(binary, operator, **kw)
 
     def visit_like_op_binary(self, binary, operator, **kw):