Allow to run migrations with given scope, with SCOPE=<scope>

Scope in migrations can be defined by adding suffix in filename,
like: 01_a_migration.blog.rb. Such migration have blog scope.

Scope is automatically added while copying migrations from engine,
so if you want to revert all of the migrations from given engine,
you can just run db:migrate with SCOPE, like:

    rake db:migrate SCOPE=blog

activerecord/CHANGELOG.md

@@ -1,5 +1,17 @@
 ## Rails 3.2.0 (unreleased) ##
 
+*   Added ability to run migrations only for given scope, which allows
+    to run migrations only from one engine (for example to revert changes
+    from engine that you want to remove).
+
+    Example:
+      rake db:migrate SCOPE=blog
+
+   *Piotr Sarnacki*
+
+*   Migrations copied from engines are now scoped with engine's name,
+    for example 01_create_posts.blog.rb. *Piotr Sarnacki*
+
 *   Implements `AR::Base.silence_auto_explain`. This method allows the user to
     selectively disable automatic EXPLAINs within a block. *fxn*
 

activerecord/lib/active_record/railties/databases.rake

@@ -149,7 +149,9 @@ db_namespace = namespace :db do
   desc "Migrate the database (options: VERSION=x, VERBOSE=false)."
   task :migrate => [:environment, :load_config] do
     ActiveRecord::Migration.verbose = ENV["VERBOSE"] ? ENV["VERBOSE"] == "true" : true
-    ActiveRecord::Migrator.migrate(ActiveRecord::Migrator.migrations_paths, ENV["VERSION"] ? ENV["VERSION"].to_i : nil)
+    ActiveRecord::Migrator.migrate(ActiveRecord::Migrator.migrations_paths, ENV["VERSION"] ? ENV["VERSION"].to_i : nil) do |migration|
+      ENV["SCOPE"].blank? || (ENV["SCOPE"] == migration.scope)
+    end
     db_namespace['_dump'].invoke
   end
 

railties/test/application/rake/migrations_test.rb

@@ -12,6 +12,30 @@ module ApplicationTests
       def teardown
         teardown_app
       end
+
+      test 'running migrations with given scope' do
+        Dir.chdir(app_path) do
+          `rails generate model user username:string password:string`
+        end
+        app_file "db/migrate/01_a_migration.bukkits.rb", <<-MIGRATION
+          class AMigration < ActiveRecord::Migration
+          end
+        MIGRATION
+
+        output = Dir.chdir(app_path) { `rake db:migrate SCOPE=bukkits` }
+        assert_no_match(/create_table\(:users\)/, output)
+        assert_no_match(/CreateUsers/, output)
+        assert_no_match(/add_column\(:users, :email, :string\)/, output)
+
+        assert_match(/AMigration: migrated/, output)
+
+        output = Dir.chdir(app_path) { `rake db:migrate SCOPE=bukkits VERSION=0` }
+        assert_no_match(/drop_table\(:users\)/, output)
+        assert_no_match(/CreateUsers/, output)
+        assert_no_match(/remove_column\(:users, :email\)/, output)
+
+        assert_match(/AMigration: reverted/, output)
+      end
       
       test 'model and migration generator with change syntax' do
          Dir.chdir(app_path) do