Support Descending Indexes for MySQL

MySQL 8.0.1 and higher supports descending indexes: `DESC` in an index
definition is no longer ignored.

See https://dev.mysql.com/doc/refman/8.0/en/descending-indexes.html.

2 files changed, 2 insertions, 3 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 0866f58015..71fa7b929c 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -90,10 +90,8 @@ module ActiveRecord
         true
       end
 
-      # Technically MySQL allows to create indexes with the sort order syntax
-      # but at the moment (5.5) it doesn't yet implement them
       def supports_index_sort_order?
-        true
+        !mariadb? && version >= "8.0.1"
       end
 
       def supports_transaction_isolation?
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
index 1e58513387..571edffec7 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
@@ -38,6 +38,7 @@ module ActiveRecord
 
               indexes.last.columns << row[:Column_name]
               indexes.last.lengths.merge!(row[:Column_name] => row[:Sub_part].to_i) if row[:Sub_part]
+              indexes.last.orders.merge!(row[:Column_name] => :desc) if row[:Collation] == "D"
             end
           end