FIX: Skip shared drafts logic if disabled (#11918)

It always showed shared drafts if no category was set.

Follow-up to dd175537f3fb5f4a62a5935f65443fc9bedb37e3.

app/controllers/list_controller.rb

@@ -58,7 +58,7 @@ class ListController < ApplicationController
 
       list = TopicQuery.new(user, list_opts).public_send("list_#{filter}")
 
-      if guardian.can_see_shared_draft? && @category.present?
+      if guardian.can_create_shared_draft? && @category.present?
         if @category.id == SiteSetting.shared_drafts_category.to_i
           # On shared drafts, show the destination category
           list.topics.each do |t|

spec/requests/list_controller_spec.rb

@@ -779,4 +779,37 @@ RSpec.describe ListController do
       end
     end
   end
+
+  describe "shared drafts" do
+    fab!(:category1) { Fabricate(:category) }
+    fab!(:category2) { Fabricate(:category) }
+
+    fab!(:topic1) { Fabricate(:topic, category: category1) }
+    fab!(:topic2) { Fabricate(:topic, category: category2) }
+
+    fab!(:shared_draft_topic) { Fabricate(:topic, category: category1) }
+    fab!(:shared_draft) { Fabricate(:shared_draft, topic: shared_draft_topic, category: category2) }
+
+    it "are not displayed if they are disabled" do
+      SiteSetting.shared_drafts_category = ""
+      sign_in(admin)
+
+      get "/c/#{category1.slug}/#{category1.id}.json"
+      expect(response.parsed_body['topic_list']['shared_drafts']).to eq(nil)
+      expect(response.parsed_body['topic_list']['topics'].map { |t| t['id'] }).to contain_exactly(topic1.id, shared_draft_topic.id)
+    end
+
+    it "are displayed in both shared drafts category and target category" do
+      SiteSetting.shared_drafts_category = category1.id
+      sign_in(admin)
+
+      get "/c/#{category1.slug}/#{category1.id}.json"
+      expect(response.parsed_body['topic_list']['shared_drafts']).to be_nil
+      expect(response.parsed_body['topic_list']['topics'].map { |t| t['id'] }).to contain_exactly(topic1.id, shared_draft_topic.id)
+
+      get "/c/#{category2.slug}/#{category2.id}.json"
+      expect(response.parsed_body['topic_list']['shared_drafts'].map { |t| t['id'] }).to contain_exactly(shared_draft_topic.id)
+      expect(response.parsed_body['topic_list']['topics'].map { |t| t['id'] }).to contain_exactly(topic2.id)
+    end
+  end
 end