Rails 5: support schema t.index for mysql

changelogs/unreleased/rails5-mysql-binary-column-index-length.yml

+---
+title: 'Rails 5: support schema t.index for mysql'
+merge_request: 21485
+author: Jasper Maes
+type: other

config/initializers/mysql_set_length_for_binary_indexes.rb

@@ -2,6 +2,9 @@
 # MySQL adapter apply a length of 20. Otherwise MySQL can't create an index on
 # binary columns.
 
+# This module can be removed once a Rails 5 schema is used.
+# It can't be wrapped in a check that checks Gitlab.rails5? because
+# the old Rails 4 schema layout is still used
 module MysqlSetLengthForBinaryIndex
   def add_index(table_name, column_names, options = {})
     Array(column_names).each do |column_name|
@@ -19,3 +22,28 @@ end
 if defined?(ActiveRecord::ConnectionAdapters::Mysql2Adapter)
   ActiveRecord::ConnectionAdapters::Mysql2Adapter.send(:prepend, MysqlSetLengthForBinaryIndex)
 end
+
+if Gitlab.rails5?
+  module MysqlSetLengthForBinaryIndexAndIgnorePostgresOptionsForSchema
+    # This method is used in Rails 5 schema loading as t.index
+    def index(column_names, options = {})
+      Array(column_names).each do |column_name|
+        column = columns.find { |c| c.name == column_name }
+
+        if column&.type == :binary
+          options[:length] = 20
+        end
+      end
+
+      # Ignore indexes that use opclasses,
+      # also see config/initializers/mysql_ignore_postgresql_options.rb
+      unless options[:opclasses]
+        super(column_names, options)
+      end
+    end
+  end
+
+  if defined?(ActiveRecord::ConnectionAdapters::MySQL::TableDefinition)
+    ActiveRecord::ConnectionAdapters::MySQL::TableDefinition.send(:prepend, MysqlSetLengthForBinaryIndexAndIgnorePostgresOptionsForSchema)
+  end
+end