search: move misc search parsing helpers to PostQueryBuilder.

* Move various search parser helper methods (`has_metatag?`,
  `is_single_tag?` et al) from PostSets and the Tag model to
  PostQueryBuilder.

* Fix various minor bugs stemming from trying to check if a search query
  contains certain metatags using regexes or other adhoc techniques.

app/models/post.rb

@@ -1069,7 +1069,7 @@ class Post < ApplicationRecord
     def fast_count(tags = "", timeout: 1_000, raise_on_timeout: false, skip_cache: false)
       tags = tags.to_s
       tags += " rating:s" if CurrentUser.safe_mode?
-      tags += " -status:deleted" if CurrentUser.hide_deleted_posts? && !Tag.has_metatag?(tags, "status", "-status")
+      tags += " -status:deleted" if CurrentUser.hide_deleted_posts? && !PostQueryBuilder.new(tags).has_metatag?("status", "-status")
       tags = PostQueryBuilder.new(tags).normalize_query
 
       # Optimize some cases. these are just estimates but at these
@@ -1135,7 +1135,7 @@ class Post < ApplicationRecord
     end
 
     def get_count_from_cache(tags)
-      if Tag.is_simple_tag?(tags)
+      if PostQueryBuilder.new(tags).is_simple_tag?
         count = Tag.find_by(name: tags).try(:post_count)
       else
         # this will only have a value for multi-tag searches or single metatag searches

app/models/tag.rb

@@ -227,40 +227,6 @@ class Tag < ApplicationRecord
     end
   end
 
-  module ParseMethods
-    # true if query is a single "simple" tag (not a metatag, negated tag, or wildcard tag).
-    def is_simple_tag?(query)
-      is_single_tag?(query) && !is_metatag?(query) && !is_negated_tag?(query) && !is_optional_tag?(query) && !is_wildcard_tag?(query)
-    end
-
-    def is_single_tag?(query)
-      PostQueryBuilder.new(query).split_query.size == 1
-    end
-
-    def is_metatag?(tag)
-      has_metatag?(tag, *PostQueryBuilder::METATAGS)
-    end
-
-    def is_negated_tag?(tag)
-      tag.starts_with?("-")
-    end
-
-    def is_optional_tag?(tag)
-      tag.starts_with?("~")
-    end
-
-    def is_wildcard_tag?(tag)
-      tag.include?("*")
-    end
-
-    def has_metatag?(tags, *metatags)
-      return nil if tags.blank?
-
-      tags = PostQueryBuilder.new(tags.to_str).split_query if tags.respond_to?(:to_str)
-      tags.grep(/\A(?:#{metatags.map(&:to_s).join("|")}):(.+)\z/i) { $1 }.first
-    end
-  end
-
   module SearchMethods
     # ref: https://www.postgresql.org/docs/current/static/pgtrgm.html#idm46428634524336
     def order_similarity(name)
@@ -393,6 +359,5 @@ class Tag < ApplicationRecord
   include ApiMethods
   include CountMethods
   include CategoryMethods
-  extend ParseMethods
   extend SearchMethods
 end

app/models/upload.rb

@@ -237,7 +237,7 @@ class Upload < ApplicationRecord
   include SourceMethods
 
   def assign_rating_from_tags
-    if rating = Tag.has_metatag?(tag_string, :rating)
+    if rating = PostQueryBuilder.new(tag_string).find_metatag(:rating)
       self.rating = rating.downcase.first
     end
   end