Put migration methods into a separate folder and let just ActiveRecord dependency in ActiveRecord models.

railties/lib/generators/active_record.rb

@@ -1,47 +1,16 @@
 require 'generators/named_base'
+require 'generators/migration'
 require 'active_record'
 
 module ActiveRecord
   module Generators
-    module Migration
-
-      # Creates a migration template at the given destination. The difference
-      # to the default template method is that the migration number is appended
-      # to the destination file name.
-      #
-      # The migration number, migration file name, migration class name are
-      # available as instance variables in the template to be rendered.
-      #
-      # ==== Examples
-      #
-      #   migration_template "migration.rb", "db/migrate/add_foo_to_bar.rb"
-      #
-      def migration_template(source, destination=nil, log_status=true)
-        destination = File.expand_path(destination || source, self.destination_root)
-
-        migration_dir = File.dirname(destination)
-        @migration_number     = next_migration_number(migration_dir)
-        @migration_file_name  = File.basename(destination).sub(/\.rb$/, '')
-        @migration_class_name = @migration_file_name.camelize
-
-        if existing = migration_exists?(migration_dir, @migration_file_name)
-          raise Rails::Generators::Error, "Another migration is already named #{@migration_file_name}: #{existing}"
-        end
-
-        destination = File.join(migration_dir, "#{@migration_number}_#{@migration_file_name}.rb")
-        template(source, destination, log_status)
-      end
+    class Base < Rails::Generators::NamedBase
+      include Rails::Generators::Migration
 
       protected
 
-        def migration_exists?(dirname, file_name) #:nodoc:
-          Dir.glob("#{dirname}/[0-9]*_*.rb").grep(/\d+_#{file_name}.rb$/).first
-        end
-
-        def current_migration_number(dirname) #:nodoc:
-          Dir.glob("#{dirname}/[0-9]*_*.rb").collect{ |f| f.split("_").first.to_i }.max
-        end
-
+        # Implement the required interface for Rails::Generators::Migration.
+        #
         def next_migration_number(dirname) #:nodoc:
           if ActiveRecord::Base.timestamped_migrations
             Time.now.utc.strftime("%Y%m%d%H%M%S")
@@ -49,10 +18,7 @@ module ActiveRecord
             "%.3d" % (current_migration_number(dirname) + 1)
           end
         end
-    end
 
-    class Base < Rails::Generators::NamedBase
-      include Migration
     end
   end
 end

railties/lib/generators/migration.rb

@@ -0,0 +1,56 @@
+module Rails
+  module Generators
+    # Holds common methods for migrations. It assumes that migrations has the
+    # [0-9]*_name format and can be used by another frameworks (like Sequel)
+    # just by implementing the next migration number method.
+    #
+    module Migration
+
+      # Creates a migration template at the given destination. The difference
+      # to the default template method is that the migration number is appended
+      # to the destination file name.
+      #
+      # The migration number, migration file name, migration class name are
+      # available as instance variables in the template to be rendered.
+      #
+      # ==== Examples
+      #
+      #   migration_template "migration.rb", "db/migrate/add_foo_to_bar.rb"
+      #
+      def migration_template(source, destination=nil, log_status=true)
+        destination = File.expand_path(destination || source, self.destination_root)
+
+        migration_dir = File.dirname(destination)
+        @migration_number     = next_migration_number(migration_dir)
+        @migration_file_name  = File.basename(destination).sub(/\.rb$/, '')
+        @migration_class_name = @migration_file_name.camelize
+
+        if existing = migration_exists?(migration_dir, @migration_file_name)
+          raise Rails::Generators::Error, "Another migration is already named #{@migration_file_name}: #{existing}"
+        end
+
+        destination = File.join(migration_dir, "#{@migration_number}_#{@migration_file_name}.rb")
+        template(source, destination, log_status)
+      end
+
+      protected
+
+        def migration_lookup_at(dirname) #:nodoc:
+          Dir.glob("#{dirname}/[0-9]*_*.rb")
+        end
+
+        def migration_exists?(dirname, file_name) #:nodoc:
+          migration_lookup_at(dirname).grep(/\d+_#{file_name}.rb$/).first
+        end
+
+        def current_migration_number(dirname) #:nodoc:
+          migration_lookup_at(dirname).collect{ |f| f.split("_").first.to_i }.max
+        end
+
+        def next_migration_number(dirname) #:nodoc:
+          raise NotImplementError
+        end
+
+    end
+  end
+end

railties/lib/generators/named_base.rb

@@ -92,7 +92,7 @@ module Rails
         end
     end
 
-    # Deal with controller named base on scaffold
+    # Deal with controller named base on scaffold.
     #
     module ControllerNamedBase
       def self.included(base) #:nodoc:

railties/lib/generators/rails/scaffold_controller/USAGE

@@ -1,18 +1,20 @@
 Description:
-    Stubs out a scaffolded controller and its views. Pass the controller name,
+    Stubs out a scaffolded controller and its views. Pass the model name,
     either CamelCased or under_scored, and a list of views as arguments.
+    The controller name is retrieved as a pluralized version of the model
+    name.
 
-    To create a controller within a module, specify the controller name as a
+    To create a controller within a module, specify the model name as a
     path like 'parent_module/controller_name'.
 
     This generates a controller class in app/controllers and invokes helper,
     template engine and test framework generators.
 
 Example:
-    `./script/generate scaffold_controller CreditCard open debit credit close`
+    `./script/generate scaffold_controller CreditCard`
 
     Credit card controller with URLs like /credit_card/debit.
-        Controller:      app/controllers/credit_card_controller.rb
-        Functional Test: test/functional/credit_card_controller_test.rb
-        Views:           app/views/credit_card/debit.html.erb [...]
-        Helper:          app/helpers/credit_card_helper.rb
+        Controller:      app/controllers/credit_cards_controller.rb
+        Functional Test: test/functional/credit_cards_controller_test.rb
+        Views:           app/views/credit_cards/index.html.erb [...]
+        Helper:          app/helpers/credit_cards_helper.rb

railties/lib/generators/test_unit.rb

@@ -3,7 +3,6 @@ require 'generators/named_base'
 module TestUnit
   module Generators
     class Base < Rails::Generators::NamedBase
-      check_class_collision :suffix => "Test"
     end
   end
 end

railties/lib/generators/test_unit/mailer/mailer_generator.rb

@@ -4,6 +4,7 @@ module TestUnit
   module Generators
     class MailerGenerator < Base
       argument :actions, :type => :array, :default => [], :banner => "method method"
+      check_class_collision :suffix => "Test"
 
       def create_test_files
         template "unit_test.rb", File.join('test', 'unit', class_path, "#{file_name}_test.rb")

railties/lib/generators/test_unit/observer/observer_generator.rb

@@ -3,6 +3,8 @@ require 'generators/test_unit'
 module TestUnit
   module Generators
     class ObserverGenerator < Base
+      check_class_collision :suffix => "ObserverTest"
+
       def create_test_files
         template 'unit_test.rb',  File.join('test', 'unit', class_path, "#{file_name}_observer_test.rb")
       end

railties/lib/generators/test_unit/plugin/plugin_generator.rb

@@ -3,6 +3,8 @@ require 'generators/test_unit'
 module TestUnit
   module Generators
     class PluginGenerator < Base
+      check_class_collision :suffix => "Test"
+
       def create_test_files
         directory 'test'
       end