Preserve magic comments and content encoding of copied migrations.

During insertion of "# This migration comes from ... " comment at the beginning of
a migration, presence of magic comment was not considered.

activerecord/CHANGELOG.md

 ## Rails 4.0.0 (unreleased) ##
 
+*   When copying migrations, preserve their magic comments and content encoding.
+
+    *OZAWA Sakuro*
+
 *   Fix ActiveRecord `subclass_from_attrs` when `eager_load` is false.
     It cannot find subclass because all classes are loaded automatically
     when it needs.

activerecord/lib/active_record/migration.rb

@@ -634,8 +634,17 @@ def copy(destination, sources, options = {})
         source_migrations = ActiveRecord::Migrator.migrations(path)
 
         source_migrations.each do |migration|
-          source = File.read(migration.filename)
-          source = "# This migration comes from #{scope} (originally #{migration.version})\n#{source}"
+          source = File.binread(migration.filename)
+          inserted_comment = "# This migration comes from #{scope} (originally #{migration.version})\n"
+          if /\A#.*\b(?:en)?coding:\s*\S+/ =~ source
+            # If we have a magic comment in the original migration,
+            # insert our comment after the first newline(end of the magic comment line)
+            # so the magic keep working.
+            # Note that magic comments must be at the first line(except sh-bang).
+            source[/\n/] = "\n#{inserted_comment}"
+          else
+            source = "#{inserted_comment}#{source}"
+          end
 
           if duplicate = destination_migrations.detect { |m| m.name == migration.name }
             if options[:on_skip] && duplicate.scope != scope.to_s
@@ -649,7 +658,7 @@ def copy(destination, sources, options = {})
           old_path, migration.filename = migration.filename, new_path
           last = migration
 
-          File.open(migration.filename, "w") { |f| f.write source }
+          File.binwrite(migration.filename, source)
           copied << migration
           options[:on_copy].call(scope, migration, old_path) if options[:on_copy]
           destination_migrations << migration

activerecord/test/cases/migration_test.rb

@@ -738,6 +738,26 @@ def test_copying_migrations_with_timestamps_to_destination_with_timestamps_in_fu
     clear
   end
 
+  def test_copying_migrations_preserving_magic_comments
+    ActiveRecord::Base.timestamped_migrations = false
+    @migrations_path = MIGRATIONS_ROOT + "/valid"
+    @existing_migrations = Dir[@migrations_path + "/*.rb"]
+
+    copied = ActiveRecord::Migration.copy(@migrations_path, {:bukkits => MIGRATIONS_ROOT + "/magic"})
+    assert File.exists?(@migrations_path + "/4_currencies_have_symbols.bukkits.rb")
+    assert_equal [@migrations_path + "/4_currencies_have_symbols.bukkits.rb"], copied.map(&:filename)
+
+    expected = "# coding: ISO-8859-15\n# This migration comes from bukkits (originally 1)"
+    assert_equal expected, IO.readlines(@migrations_path + "/4_currencies_have_symbols.bukkits.rb")[0..1].join.chomp
+
+    files_count = Dir[@migrations_path + "/*.rb"].length
+    copied = ActiveRecord::Migration.copy(@migrations_path, {:bukkits => MIGRATIONS_ROOT + "/magic"})
+    assert_equal files_count, Dir[@migrations_path + "/*.rb"].length
+    assert copied.empty?
+  ensure
+    clear
+  end
+
   def test_skipping_migrations
     @migrations_path = MIGRATIONS_ROOT + "/valid_with_timestamps"
     @existing_migrations = Dir[@migrations_path + "/*.rb"]

activerecord/test/migrations/magic/1_currencies_have_symbols.rb

+# coding: ISO-8859-15
+
+class CurrenciesHaveSymbols < ActiveRecord::Migration
+  def self.up
+    # We use  for default currency symbol
+    add_column "currencies", "symbol", :string, :default => ""
+  end
+
+  def self.down
+    remove_column "currencies", "symbol"
+  end
+end