Add coercions to literal()

To prevent literal() from receiving a ClauseElement which
then leads to confusing results, add a new LiteralValueRole
coercion that does an _is_literal() check and implement
for literal().

Fixes: #5639
Change-Id: Ibd686544af2d7c013765278f984baf237de88caf

1 files changed, 13 insertions, 0 deletions

diff --git a/test/sql/test_roles.py b/test/sql/test_roles.py
index 0ef90e89e..4d905aca9 100644
--- a/test/sql/test_roles.py
+++ b/test/sql/test_roles.py
@@ -145,6 +145,19 @@ class RoleTest(fixtures.TestBase):
             )
         )
 
+    def test_no_clauseelement_in_bind(self):
+        with testing.expect_raises_message(
+            exc.ArgumentError,
+            r"Literal Python value expected, got BindParameter",
+        ):
+            literal(bindparam("x"))
+
+        with testing.expect_raises_message(
+            exc.ArgumentError,
+            r"Literal Python value expected, got .*ColumnClause",
+        ):
+            literal(column("q"))
+
     def test_scalar_select_no_coercion(self):
         with testing.expect_warnings(
             "implicitly coercing SELECT object to scalar subquery"