aliases/implications: change automatic retirement rules.

Change the rules for automatically retiring aliases and implications:

* Retire aliases to tags that are empty, or that are for a general or
  artist tag that hasn't received any new posts in the last two years.
* Retire implications from tags that are empty.
* Don't retire aliases or implications for character, copyright, or
  meta tags any more, unless the tags are empty.

app/logical/tag_relationship_retirement_service.rb

@@ -1,6 +1,9 @@
-# Removes tag aliases and implications if they haven't had any new uploads in
-# the last two years. Runs weekly. Posts a message to the forum when aliases or
-# implications are retired.
+# Removes inactive aliases and implications. 'Inactive' means aliases to empty
+# tags, implications from empty tags, and gentag and artist aliases that
+# haven't had any new posts in the last two years.
+#
+# Runs weekly. Posts a message to the forum when aliases or implications are
+# retired.
 #
 # @see DanbooruMaintenance#weekly
 module TagRelationshipRetirementService
@@ -8,20 +11,15 @@ module TagRelationshipRetirementService
 
   THRESHOLD = 2.years
 
-  def forum_topic_title
-    "Retired tag aliases & implications"
-  end
-
-  def forum_topic_body
-    "This topic deals with tag relationships created two or more years ago that have not been used since. They will be retired. This topic will be updated as an automated system retires expired relationships."
-  end
+  FORUM_TOPIC_TITLE = "Retired tag aliases & implications"
+  FORUM_TOPIC_BODY = "This topic deals with tag relationships created two or more years ago that have not been used since. They will be retired. This topic will be updated as an automated system retires expired relationships."
 
   def forum_topic
-    topic = ForumTopic.where(title: forum_topic_title).first
+    topic = ForumTopic.where(title: FORUM_TOPIC_TITLE).first
     if topic.nil?
       CurrentUser.scoped(User.system) do
-        topic = ForumTopic.create!(creator: User.system, title: forum_topic_title, category_id: 1)
-        ForumPost.create!(creator: User.system, body: forum_topic_body, topic: topic)
+        topic = ForumTopic.create!(creator: User.system, title: FORUM_TOPIC_TITLE, category_id: 1)
+        ForumPost.create!(creator: User.system, body: FORUM_TOPIC_BODY, topic: topic)
       end
     end
     topic
@@ -30,26 +28,23 @@ module TagRelationshipRetirementService
   def find_and_retire!
     messages = []
 
-    [TagAlias, TagImplication].each do |model|
-      each_candidate(model) do |rel|
-        rel.update(status: "retired")
-        messages << rel.retirement_message
-      end
+    inactive_relationships.each do |rel|
+      rel.update!(status: "retired")
+      messages << "The #{rel.relationship} [[#{rel.antecedent_name}]] -> [[#{rel.consequent_name}]] has been retired."
     end
 
     updater = ForumUpdater.new(forum_topic)
     updater.update(messages.sort.join("\n"))
   end
 
-  def each_candidate(model)
-    model.active.where("created_at < ?", THRESHOLD.ago).find_each do |rel|
-      if is_unused?(rel.consequent_name)
-        yield(rel)
-      end
-    end
+  def inactive_relationships
+    (inactive_aliases + TagAlias.active.empty + TagImplication.active.empty).uniq
   end
 
-  def is_unused?(name)
-    !Post.raw_tag_match(name).exists?(["created_at > ?", THRESHOLD.ago])
+  def inactive_aliases
+    aliases = TagAlias.general.or(TagAlias.artist).active.where("tag_aliases.created_at < ?", THRESHOLD.ago)
+    aliases.select do |tag_alias|
+      !tag_alias.consequent_tag.posts.exists?(["created_at > ?", THRESHOLD.ago])
+    end
   end
 end

app/models/tag_alias.rb

@@ -6,6 +6,8 @@ class TagAlias < TagRelationship
 
   before_create :delete_conflicting_relationships
 
+  scope :empty, -> { joins(:consequent_tag).merge(Tag.empty) }
+
   def self.to_aliased(names)
     names = Array(names).map(&:to_s)
     return [] if names.empty?

app/models/tag_implication.rb

@@ -15,6 +15,8 @@ class TagImplication < TagRelationship
   validate :meets_tag_size_requirements, on: :request
   validate :has_wiki_page, on: :request
 
+  scope :empty, -> { joins(:antecedent_tag).merge(Tag.empty) }
+
   concerning :HierarchyMethods do
     class_methods do
       def ancestors_of(names)

app/models/tag_relationship.rb

@@ -16,6 +16,12 @@ class TagRelationship < ApplicationRecord
   scope :deleted, -> {where(status: "deleted")}
   scope :retired, -> {where(status: "retired")}
 
+  # TagAlias.artist, TagAlias.general, TagAlias.character, TagAlias.copyright, TagAlias.meta
+  # TagImplication.artist, TagImplication.general, TagImplication.character, TagImplication.copyright, TagImplication.meta
+  TagCategory.categories.each do |category|
+    scope category, -> { joins(:consequent_tag).where(consequent_tag: { category: TagCategory.mapping[category] }) }
+  end
+
   before_validation :normalize_names
   validates :status, inclusion: { in: STATUSES }
   validates :antecedent_name, presence: true
@@ -103,10 +109,6 @@ class TagRelationship < ApplicationRecord
       # "TagAlias" -> "tag alias", "TagImplication" -> "tag implication"
       self.class.name.underscore.tr("_", " ")
     end
-
-    def retirement_message
-      "The #{relationship} [[#{antecedent_name}]] -> [[#{consequent_name}]] has been retired."
-    end
   end
 
   def antecedent_and_consequent_are_different