fix remove_index for postgresql when running legacy migrations

activerecord/lib/active_record/migration/compatibility.rb

@@ -41,8 +41,9 @@ def index_exists?(table_name, column_name, options = {})
         end
 
         def remove_index(table_name, options = {})
-          index_name = index_name_for_remove(table_name, options)
-          execute "DROP INDEX #{quote_column_name(index_name)} ON #{quote_table_name(table_name)}"
+          options = { column: options } unless options.is_a?(Hash)
+          options[:name] = index_name_for_remove(table_name, options)
+          super(table_name, options)
         end
 
         private

activerecord/test/cases/migration/compatibility_test.rb

@@ -21,6 +21,7 @@ def setup
       teardown do
         connection.drop_table :testings rescue nil
         ActiveRecord::Migration.verbose = @verbose_was
+        ActiveRecord::SchemaMigration.delete_all
       end
 
       def test_migration_doesnt_remove_named_index
@@ -37,6 +38,21 @@ def migrate(x)
         assert_raise(StandardError) { ActiveRecord::Migrator.new(:up, [migration]).migrate }
         assert connection.index_exists?(:testings, :foo, name: "custom_index_name")
       end
+
+      def test_migration_does_remove_unnamed_index
+        connection.add_index :testings, :bar
+
+        migration = Class.new(ActiveRecord::Migration[4.2]) {
+          def version; 101 end
+          def migrate(x)
+            remove_index :testings, :bar
+          end
+        }.new
+
+        assert connection.index_exists?(:testings, :bar)
+        ActiveRecord::Migrator.new(:up, [migration]).migrate
+        assert_not connection.index_exists?(:testings, :bar)
+      end
     end
   end
 end