fixes #2009

app/models/post.rb

@@ -416,6 +416,7 @@ class Post < ActiveRecord::Base
       normalized_tags = Tag.scan_tags(tag_string)
       normalized_tags = filter_metatags(normalized_tags)
       normalized_tags = normalized_tags.map{|tag| tag.downcase}
+      normalized_tags = remove_negated_tags(normalized_tags)
       normalized_tags = normalized_tags.map {|x| Tag.find_or_create_by_name(x).name}
       normalized_tags = TagAlias.to_aliased(normalized_tags)
       normalized_tags = TagImplication.with_descendants(normalized_tags)
@@ -424,6 +425,12 @@ class Post < ActiveRecord::Base
       set_tag_string(normalized_tags.uniq.sort.join(" "))
     end
 
+    def remove_negated_tags(tags)
+      negated_tags, tags = tags.partition {|x| x =~ /\A-/i}
+      negated_tags.map!{|x| x[1..-1]}
+      return tags - negated_tags
+    end
+
     def filter_metatags(tags)
       @pre_metatags, tags = tags.partition {|x| x =~ /\A(?:rating|parent):/i}
       @post_metatags, tags = tags.partition {|x| x =~ /\A(?:-pool|pool|newpool|fav):/i}

test/unit/post_test.rb

@@ -578,6 +578,15 @@ class PostTest < ActiveSupport::TestCase
         end
       end
 
+      context "tagged with a negated tag" do
+        should "remove the tag if present" do
+          @post.update_attributes(:tag_string => "aaa bbb ccc")
+          @post.update_attributes(:tag_string => "aaa bbb ccc -bbb")
+          @post.reload
+          assert_equal("aaa ccc", @post.tag_string)
+        end
+      end
+
       should "have an array representation of its tags" do
         post = FactoryGirl.create(:post)
         post.set_tag_string("aaa bbb")