narrow the check for double-paren exprs in mysql create_index

Fixed regression from SQLAlchemy 1.3.20 caused by the fix for
:ticket:`5462` which adds double-parenthesis for MySQL functional
expressions in indexes, as is required by the backend, this inadvertently
extended to include arbitrary :func:`_sql.text` expressions as well as
Alembic's internal textual component,  which are required by Alembic for
arbitrary index expressions which don't imply double parenthesis.  The
check has been narrowed to include only binary/ unary/functional
expressions directly.

Fixes: #5800
Change-Id: I40f83c6f9dd04b984d0c86eba632a588570709a1

1 files changed, 6 insertions, 4 deletions

diff --git a/lib/sqlalchemy/dialects/mysql/base.py b/lib/sqlalchemy/dialects/mysql/base.py
index f90d961d8..7a4d3261f 100644
--- a/lib/sqlalchemy/dialects/mysql/base.py
+++ b/lib/sqlalchemy/dialects/mysql/base.py
@@ -978,6 +978,7 @@ from ...engine import reflection
 from ...sql import coercions
 from ...sql import compiler
 from ...sql import elements
+from ...sql import functions
 from ...sql import operators
 from ...sql import roles
 from ...sql import util as sql_util
@@ -2027,12 +2028,13 @@ class MySQLDDLCompiler(compiler.DDLCompiler):
             self.sql_compiler.process(
                 elements.Grouping(expr)
                 if (
-                    not isinstance(expr, elements.ColumnClause)
-                    and (
-                        not isinstance(expr, elements.UnaryExpression)
-                        or expr.modifier
+                    isinstance(expr, elements.BinaryExpression)
+                    or (
+                        isinstance(expr, elements.UnaryExpression)
+                        and expr.modifier
                         not in (operators.desc_op, operators.asc_op)
                     )
+                    or isinstance(expr, functions.FunctionElement)
                 )
                 else expr,
                 include_table=False,