Don't delete all the existing styles if we reprocess

lib/paperclip/attachment.rb

@@ -90,7 +90,7 @@ module Paperclip
       ensure_required_accessors!
       file = Paperclip.io_adapters.for(uploaded_file)
 
-      self.clear
+      self.clear(*@options[:only_process])
       return nil if file.nil?
 
       @queued_for_write[:original]   = file
@@ -202,10 +202,14 @@ module Paperclip
     # Clears out the attachment. Has the same effect as previously assigning
     # nil to the attachment. Does NOT save. If you wish to clear AND save,
     # use #destroy.
-    def clear
-      queue_existing_for_delete
-      @queued_for_write  = {}
-      @errors            = {}
+    def clear(*styles_to_clear)
+      if styles_to_clear.any?
+        queue_some_for_delete(*styles_to_clear)
+      else
+        queue_all_for_delete
+        @queued_for_write  = {}
+        @errors            = {}
+      end
     end
 
     # Destroys the attachment. Has the same effect as previously assigning
@@ -406,7 +410,13 @@ module Paperclip
       interpolator.interpolate(pattern, self, style_name)
     end
 
-    def queue_existing_for_delete #:nodoc:
+    def queue_some_for_delete(*styles)
+      @queued_for_delete += styles.uniq.map do |style|
+        path(style) if exists?(style)
+      end.compact
+    end
+
+    def queue_all_for_delete #:nodoc:
       return if @options[:preserve_files] || !file?
       @queued_for_delete += [:original, *styles.keys].uniq.map do |style|
         path(style) if exists?(style)

lib/paperclip/instance_methods.rb

@@ -28,7 +28,7 @@ module Paperclip
     def prepare_for_destroy
       Paperclip.log("Scheduling attachments for deletion.")
       each_attachment do |name, attachment|
-        attachment.send(:queue_existing_for_delete)
+        attachment.send(:queue_all_for_delete)
       end
     end
   end

test/attachment_test.rb

@@ -19,6 +19,26 @@ class AttachmentTest < Test::Unit::TestCase
     file.close
   end
 
+  should "not delete styles that don't get reprocessed" do
+    file = File.new(File.join(File.dirname(__FILE__), "fixtures", "50x50.png"), 'rb')
+    rebuild_class :styles => { :small => '100x>',
+                               :large => '500x>',
+                               :original => '42x42#' }
+    dummy = Dummy.new
+    dummy.avatar = file
+    dummy.save
+
+    assert File.exists?(dummy.avatar.path(:small))
+    assert File.exists?(dummy.avatar.path(:large))
+    assert File.exists?(dummy.avatar.path(:original))
+
+    dummy.avatar.reprocess!(:small)
+
+    assert File.exists?(dummy.avatar.path(:small))
+    assert File.exists?(dummy.avatar.path(:large))
+    assert File.exists?(dummy.avatar.path(:original))
+  end
+
   should "handle a boolean second argument to #url" do
     mock_url_generator_builder = MockUrlGeneratorBuilder.new
     attachment = Paperclip::Attachment.new(:name, :instance, :url_generator => mock_url_generator_builder)