Backport #3329 to 3-2-stable

Fix bug with autosave collection association on new record with a marked
for destroy record in autosave collection.

Fixes #6918.

activerecord/lib/active_record/autosave_association.rb

@@ -332,25 +332,31 @@ def save_collection_association(reflection)
 
         if records = associated_records_to_validate_or_save(association, @new_record_before_save, autosave)
           begin
-          records.each do |record|
-            next if record.destroyed?
+            records_to_destroy = []
+
+            records.each do |record|
+              next if record.destroyed?
+
+              saved = true
+
+              if autosave && record.marked_for_destruction?
+                records_to_destroy << record
+              elsif autosave != false && (@new_record_before_save || record.new_record?)
+                if autosave
+                  saved = association.insert_record(record, false)
+                else
+                  association.insert_record(record) unless reflection.nested?
+                end
+              elsif autosave
+                saved = record.save(:validate => false)
+              end
 
-            saved = true
+              raise ActiveRecord::Rollback unless saved
+            end
 
-            if autosave && record.marked_for_destruction?
+            records_to_destroy.each do |record|
               association.proxy.destroy(record)
-            elsif autosave != false && (@new_record_before_save || record.new_record?)
-              if autosave
-                saved = association.insert_record(record, false)
-              else
-                association.insert_record(record) unless reflection.nested?
-              end
-            elsif autosave
-              saved = record.save(:validate => false)
             end
-
-            raise ActiveRecord::Rollback unless saved
-          end
           rescue
             records.each {|x| IdentityMap.remove(x) } if IdentityMap.enabled?
             raise

activerecord/test/cases/autosave_association_test.rb

@@ -770,6 +770,16 @@ def destroy(*args)
     assert_equal before, @pirate.reload.birds
   end
 
+  def test_when_new_record_a_child_marked_for_destruction_should_not_affect_other_records_from_saving
+    @pirate = @ship.build_pirate(:catchphrase => "Arr' now I shall keep me eye on you matey!") # new record
+
+    3.times { |i| @pirate.birds.build(:name => "birds_#{i}") }
+    @pirate.birds[1].mark_for_destruction
+    @pirate.save!
+
+    assert_equal 2, @pirate.birds.reload.length
+  end
+
   # Add and remove callbacks tests for association collections.
   %w{ method proc }.each do |callback_type|
     define_method("test_should_run_add_callback_#{callback_type}s_for_has_many") do