FEATURE: option to automatically delete unused tags (#23864)

Introduced a new site setting that enables the automatic and daily removal of unused tags.

spec/jobs/clean_up_tags_spec.rb

@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+describe Jobs::CleanUpTags do
+  subject(:job) { described_class.new }
+
+  let!(:tags) do
+    [
+      Fabricate(
+        :tag,
+        name: "used_publically",
+        staff_topic_count: 2,
+        public_topic_count: 2,
+        pm_topic_count: 0,
+        created_at: 10.minutes.ago,
+      ),
+      Fabricate(
+        :tag,
+        name: "used_privately",
+        staff_topic_count: 0,
+        public_topic_count: 0,
+        pm_topic_count: 3,
+        created_at: 10.minutes.ago,
+      ),
+      Fabricate(
+        :tag,
+        name: "used_by_staff",
+        staff_topic_count: 3,
+        public_topic_count: 0,
+        pm_topic_count: 0,
+        created_at: 10.minutes.ago,
+      ),
+    ]
+  end
+  fab!(:unused_tag) do
+    Fabricate(
+      :tag,
+      name: "unused1",
+      staff_topic_count: 0,
+      public_topic_count: 0,
+      pm_topic_count: 0,
+      created_at: 10.minutes.ago,
+    )
+  end
+
+  fab!(:tag_in_group) do
+    Fabricate(
+      :tag,
+      name: "unused_in_group",
+      public_topic_count: 0,
+      staff_topic_count: 0,
+      pm_topic_count: 0,
+    )
+  end
+  fab!(:tag_group) { Fabricate(:tag_group, tag_names: [tag_in_group.name]) }
+
+  it "deletes unused tags" do
+    SiteSetting.automatically_clean_unused_tags = true
+    expect { job.execute({}) }.to change { Tag.count }.by(-1)
+    expect { unused_tag.reload }.to raise_error(ActiveRecord::RecordNotFound)
+  end
+
+  it "does nothing when site setting is disabled by default" do
+    expect { job.execute({}) }.not_to change { Tag.count }
+  end
+end