mod actions: record the subject of the mod action.

Add a polymorphic `subject` field that records the subject of the mod
action. The subject is the post, user, comment, artist, etc the mod
action is for.

* The subject for the user ban and unban actions is the user, not the ban itself.
* The subject for the user feedback update and deletion actions is the user,
  not the feedback itself.
* The subject for the post undeletion action is the post, not the approval itself.
* The subject for the move favorites action is the source post where the
  favorites were moved from, not the destination post where the favorites
  were moved to.
* The subject for the post permanent delete action is nil, because the
  post itself is hard deleted.
* When a post is permanently deleted, all mod actions related to the
  post are deleted as well.

test/unit/comment_test.rb

@@ -159,9 +159,12 @@ class CommentTest < ActiveSupport::TestCase
         end
 
         should "create a mod action" do
-          assert_difference("ModAction.count") do
-            @comment.update(body: "nope")
-          end
+          @comment.update(body: "nope")
+
+          assert_equal(1, ModAction.count)
+          assert_equal("comment_update", ModAction.last.category)
+          assert_equal(@comment, ModAction.last.subject)
+          assert_equal(@mod, ModAction.last.creator)
         end
 
         should "credit the moderator as the updater" do

test/unit/favorite_group_test.rb

@@ -27,7 +27,7 @@ class FavoriteGroupTest < ActiveSupport::TestCase
       @fav_group.add(@post)
       assert_equal([@post.id], @fav_group.post_ids)
 
-      @post.expunge!
+      @post.expunge!(create(:admin_user))
       assert_equal([], @fav_group.reload.post_ids)
     end
   end

test/unit/post_approval_test.rb

@@ -68,6 +68,8 @@ class PostApprovalTest < ActiveSupport::TestCase
           assert_equal(true, @post.reload.is_active?)
           assert_equal("post_undelete", ModAction.last.category)
           assert_equal("undeleted post ##{@post.id}", ModAction.last.description)
+          assert_equal(@post, ModAction.last.subject)
+          assert_equal(@new_approver, ModAction.last.creator)
         end
       end
 

test/unit/post_test.rb

@@ -34,6 +34,15 @@ class PostTest < ActiveSupport::TestCase
         perform_enqueued_jobs # perform IqdbAddPostJob
       end
 
+      should "log a modaction" do
+        @post.expunge!(@user)
+
+        assert_equal(1, ModAction.count)
+        assert_equal("post_permanent_delete", ModAction.last.category)
+        assert_equal(@user, ModAction.last.creator)
+        assert_nil(ModAction.last.subject)
+      end
+
       should "delete the files" do
         assert_nothing_raised { @post.file(:preview) }
         assert_nothing_raised { @post.file(:original) }
@@ -64,6 +73,20 @@ class PostTest < ActiveSupport::TestCase
         assert_equal(0, FavoriteGroup.for_post(@post.id).count)
       end
 
+      should "destroy all modactions belonging to the post" do
+        create(:mod_action, description: "deleted post ##{@post.id}", category: :post_delete, subject: @post)
+        create(:mod_action, description: "undeleted post ##{@post.id}", category: :post_undelete, subject: @post)
+        create(:mod_action, description: "banned post ##{@post.id}", category: :post_ban, subject: @post)
+        create(:mod_action, description: "unbanned post ##{@post.id}", category: :post_unban, subject: @post)
+
+        @post.expunge!(@user)
+
+        assert_equal(1, ModAction.count)
+        assert_equal("post_permanent_delete", ModAction.last.category)
+        assert_equal(@user, ModAction.last.creator)
+        assert_nil(ModAction.last.subject)
+      end
+
       should "decrement the uploader's upload count" do
         assert_difference("@post.uploader.reload.post_upload_count", -1) do
           @post.expunge!

test/unit/post_vote_test.rb

@@ -107,6 +107,8 @@ class PostVoteTest < ActiveSupport::TestCase
 
         vote.soft_delete!(updater: admin)
         assert_match(/deleted post vote #\d+ on post #\d+/, ModAction.post_vote_delete.last.description)
+        assert_equal(vote, ModAction.post_vote_delete.last.subject)
+        assert_equal(admin, ModAction.post_vote_delete.last.creator)
       end
     end
 
@@ -129,6 +131,8 @@ class PostVoteTest < ActiveSupport::TestCase
 
       should "leave a mod action" do
         assert_match(/undeleted post vote #\d+ on post #\d+/, ModAction.post_vote_undelete.last.description)
+        assert_equal(@vote, ModAction.post_vote_undelete.last.subject)
+        assert_equal(@admin, ModAction.post_vote_undelete.last.creator)
       end
     end
   end

test/unit/user_deletion_test.rb

@@ -70,6 +70,9 @@ class UserDeletionTest < ActiveSupport::TestCase
     should "generate a modaction" do
       @deletion.delete!
       assert_match(/deleted user ##{@user.id}/, ModAction.last.description)
+      assert_equal(@user, ModAction.last.subject)
+      assert_equal("user_delete", ModAction.last.category)
+      assert_equal(@deletion.deleter, ModAction.last.creator)
     end
 
     should "remove any favorites" do
@@ -90,7 +93,9 @@ class UserDeletionTest < ActiveSupport::TestCase
 
       @deletion.delete!
       assert_equal("user_#{@user.id}", @user.reload.name)
-      assert_equal(true, ModAction.exists?(description: "deleted user ##{@user.id}", creator: @deletion.deleter))
+      assert_equal("deleted user ##{@user.id}", ModAction.last.description)
+      assert_equal(@deletion.deleter, ModAction.last.creator)
+      assert_equal(@user, ModAction.last.subject)
     end
 
     should "not work for other users" do