/pool_versions: fix exception in pool diffs.

https://danbooru.donmai.us/forum_topics/9127?page=280#forum_post_159633

app/models/pool_archive.rb

@@ -62,19 +62,18 @@ class PoolArchive < ApplicationRecord
     sqs_service.send_message(msg, message_group_id: "pool:#{pool.id}")
   end
 
-  def build_diff(other = nil)
+  def build_diff(other = previous)
     diff = {}
-    prev = previous
 
-    if prev.nil?
+    if other.nil?
       diff[:added_post_ids] = added_post_ids
       diff[:removed_post_ids] = removed_post_ids
       diff[:added_desc] = description
     else
-      diff[:added_post_ids] = post_ids - prev.post_ids
-      diff[:removed_post_ids] = prev.post_ids - post_ids
+      diff[:added_post_ids] = post_ids - other.post_ids
+      diff[:removed_post_ids] = other.post_ids - post_ids
       diff[:added_desc] = description
-      diff[:removed_desc] = prev.description
+      diff[:removed_desc] = other.description
     end
 
     diff

app/views/pool_versions/diff.html.erb

@@ -3,7 +3,10 @@
     <h1>Pool Version Comparison: <%= @pool_version.name %></h1>
 
     <ul>
-      <li><strong>Posts</strong>: <%= pool_version_diff(@pool_version, @other_version) %></li>
+      <li>
+        <strong>Posts</strong>:
+        <%= render "pool_versions/diff", diff: @pool_version.build_diff(@other_version) %>
+      </li>
       <% if @other_version %>
         <li><strong>Old Desc</strong>: <%= @other_version.description %></li>
       <% end %>

test/functional/pool_versions_controller_test.rb

@@ -47,5 +47,16 @@ class PoolVersionsControllerTest < ActionDispatch::IntegrationTest
         assert_select "#pool-version-#{@versions[2].id}", false
       end
     end
+
+    context "diff action" do
+      should "render" do
+        @post = create(:post)
+        @pool = as (@user) { create(:pool) }
+        as (@user) { @pool.update(name: "blah", description: "desc", post_ids: [@post.id]) }
+
+        get diff_pool_version_path(@pool.versions.last.id)
+        assert_response :success
+      end
+    end
   end
 end