2 files changed, 22 insertions, 25 deletions
diff --git a/activerecord/lib/active_record/migration/command_recorder.rb b/activerecord/lib/active_record/migration/command_recorder.rb
index 44ea756028..03103bba98 100644
--- a/activerecord/lib/active_record/migration/command_recorder.rb
+++ b/activerecord/lib/active_record/migration/command_recorder.rb
@@ -225,7 +225,7 @@ module ActiveRecord
           [:add_foreign_key, reversed_args]
         end
 
-      # Forwards any missing method call to the \target.
+        # Forwards any missing method call to the \target.
         def method_missing(method, *args, &block)
           if @delegate.respond_to?(method)
             @delegate.send(method, *args, &block)
diff --git a/activerecord/lib/active_record/migration/compatibility.rb b/activerecord/lib/active_record/migration/compatibility.rb
index 04e538baa5..2904634eb7 100644
--- a/activerecord/lib/active_record/migration/compatibility.rb
+++ b/activerecord/lib/active_record/migration/compatibility.rb
@@ -13,7 +13,27 @@ module ActiveRecord
 
       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
@@ -101,29 +121,6 @@ module ActiveRecord
             index_name
           end
       end
-
-      class V5_0 < V5_1
-      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