Raises when `ActiveRecord::Migration` is inherited directly.

activerecord/CHANGELOG.md

+*   Raises when `ActiveRecord::Migration` is inherited directly.
+
+    *Rafael Mendonça França*
+
 *   Remove deprecated `original_exception` argument in `ActiveRecord::StatementInvalid#initialize`
     and `ActiveRecord::StatementInvalid#original_exception`.
 

activerecord/lib/active_record/migration.rb

@@ -522,7 +522,10 @@ class Current < Migration # :nodoc:
     def self.inherited(subclass) # :nodoc:
       super
       if subclass.superclass == Migration
-        subclass.include Compatibility::Legacy
+        raise StandardError, "Directly inheriting from ActiveRecord::Migration is not supported. " \
+          "Please specify the Rails release the migration was written for:\n" \
+          "\n" \
+          "  class #{self.class.name} < ActiveRecord::Migration[4.2]"
       end
     end
 

activerecord/lib/active_record/migration/compatibility.rb

@@ -13,7 +13,27 @@ def self.find(version)
 
       V5_1 = Current
 
-      module FourTwoShared
+      class V5_0 < V5_1
+        def create_table(table_name, options = {})
+          if adapter_name == "PostgreSQL"
+            if options[:id] == :uuid && !options[:default]
+              options[:default] = "uuid_generate_v4()"
+            end
+          end
+
+          # Since 5.1 Postgres adapter uses bigserial type for primary
+          # keys by default and MySQL uses bigint. This compat layer makes old migrations utilize
+          # serial/int type instead -- the way it used to work before 5.1.
+          if options[:id].blank?
+            options[:id] = :integer
+            options[:auto_increment] = true
+          end
+
+          super
+        end
+      end
+
+      class V4_2 < V5_0
         module TableDefinition
           def references(*, **options)
             options[:index] ||= false
@@ -101,46 +121,6 @@ def index_name_for_remove(table_name, options = {})
             index_name
           end
       end
-
-      class V5_0 < V5_1
-        def create_table(table_name, options = {})
-          if adapter_name == "PostgreSQL"
-            if options[:id] == :uuid && !options[:default]
-              options[:default] = "uuid_generate_v4()"
-            end
-          end
-
-          # Since 5.1 Postgres adapter uses bigserial type for primary
-          # keys by default and MySQL uses bigint. This compat layer makes old migrations utilize
-          # serial/int type instead -- the way it used to work before 5.1.
-          if options[:id].blank?
-            options[:id] = :integer
-            options[:auto_increment] = true
-          end
-
-          super
-        end
-      end
-
-      class V4_2 < V5_0
-        # 4.2 is defined as a module because it needs to be shared with
-        # Legacy. When the time comes, V5_0 should be defined straight
-        # in its class.
-        include FourTwoShared
-      end
-
-      module Legacy
-        include FourTwoShared
-
-        def migrate(*)
-          ActiveSupport::Deprecation.warn \
-            "Directly inheriting from ActiveRecord::Migration is deprecated. " \
-            "Please specify the Rails release the migration was written for:\n" \
-            "\n" \
-            "  class #{self.class.name} < ActiveRecord::Migration[4.2]"
-          super
-        end
-      end
     end
   end
 end

activerecord/test/cases/migration/compatibility_test.rb

@@ -55,7 +55,7 @@ def migrate(x)
       end
 
       def test_references_does_not_add_index_by_default
-        migration = Class.new(ActiveRecord::Migration) {
+        migration = Class.new(ActiveRecord::Migration[4.2]) {
           def migrate(x)
             create_table :more_testings do |t|
               t.references :foo
@@ -73,7 +73,7 @@ def migrate(x)
       end
 
       def test_timestamps_have_null_constraints_if_not_present_in_migration_of_create_table
-        migration = Class.new(ActiveRecord::Migration) {
+        migration = Class.new(ActiveRecord::Migration[4.2]) {
           def migrate(x)
             create_table :more_testings do |t|
               t.timestamps
@@ -90,7 +90,7 @@ def migrate(x)
       end
 
       def test_timestamps_have_null_constraints_if_not_present_in_migration_for_adding_timestamps_to_existing_table
-        migration = Class.new(ActiveRecord::Migration) {
+        migration = Class.new(ActiveRecord::Migration[4.2]) {
           def migrate(x)
             add_timestamps :testings
           end
@@ -102,15 +102,9 @@ def migrate(x)
         assert connection.columns(:testings).find { |c| c.name == "updated_at" }.null
       end
 
-      def test_legacy_migrations_get_deprecation_warning_when_run
-        migration = Class.new(ActiveRecord::Migration) {
-          def up
-            add_column :testings, :baz, :string
-          end
-        }
-
-        assert_deprecated do
-          migration.migrate :up
+      def test_legacy_migrations_raises_exception_when_inherited
+        assert_raises(StandardError) do
+          Class.new(ActiveRecord::Migration)
         end
       end
     end