1 files changed, 34 insertions, 16 deletions
diff --git a/config/initializers/mysql_set_length_for_binary_indexes.rb b/config/initializers/mysql_set_length_for_binary_indexes.rb
index 81ed2fb83de..0445d8fcae2 100644
--- a/config/initializers/mysql_set_length_for_binary_indexes.rb
+++ b/config/initializers/mysql_set_length_for_binary_indexes.rb
@@ -24,28 +24,46 @@ 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 = {})
-      options[:length] ||= {}
-      Array(column_names).each do |column_name|
-        column = columns.find { |c| c.name == column_name }
-
-        if column&.type == :binary
-          options[:length][column_name] = 20
-        end
-      end
+module MysqlSetLengthForBinaryIndexAndIgnorePostgresOptionsForSchema
+  # This method is used in Rails 5 schema loading as t.index
+  def index(column_names, options = {})
+    # Ignore indexes that use opclasses,
+    # also see config/initializers/mysql_ignore_postgresql_options.rb
+    if options[:opclasses]
+      warn "WARNING: index on columns #{column_names} uses unsupported option, skipping."
+      return
+    end
+
+    # when running rails 4 with rails 5 schema, rails 4 doesn't support multiple
+    # indexes on the same set of columns. Mysql doesn't support partial indexes, so if
+    # an index already exists and we add another index, skip it if it's partial:
+    # see https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21492#note_102821326
+    if !Gitlab.rails5? && indexes[column_names] && options[:where]
+      warn "WARNING: index on columns #{column_names} already exists and partial index is not supported, skipping."
+      return
+    end
+
+    options[:length] ||= {}
+    Array(column_names).each do |column_name|
+      column = columns.find { |c| c.name == column_name }
 
-      # Ignore indexes that use opclasses,
-      # also see config/initializers/mysql_ignore_postgresql_options.rb
-      unless options[:opclasses]
-        super(column_names, options)
+      if column&.type == :binary
+        options[:length][column_name] = 20
       end
     end
+
+    super(column_names, options)
   end
+end
 
+def mysql_adapter?
+  defined?(ActiveRecord::ConnectionAdapters::Mysql2Adapter) && ActiveRecord::Base.connection.is_a?(ActiveRecord::ConnectionAdapters::Mysql2Adapter)
+end
+
+if Gitlab.rails5?
   if defined?(ActiveRecord::ConnectionAdapters::MySQL::TableDefinition)
     ActiveRecord::ConnectionAdapters::MySQL::TableDefinition.send(:prepend, MysqlSetLengthForBinaryIndexAndIgnorePostgresOptionsForSchema)
   end
+elsif mysql_adapter? && defined?(ActiveRecord::ConnectionAdapters::TableDefinition)
+  ActiveRecord::ConnectionAdapters::TableDefinition.send(:prepend, MysqlSetLengthForBinaryIndexAndIgnorePostgresOptionsForSchema)
 end