tags: don't allow tags with unbalanced parentheses.

Don't allow tags to have unbalanced parentheses, except for a few
emoticon tags as special exceptions to the rule.

app/logical/tag_name_validator.rb

@@ -18,6 +18,10 @@ class TagNameValidator < ActiveModel::EachValidator
       record.errors.add(attribute, "'#{value}' cannot be more than #{MAX_TAG_LENGTH} characters long")
     end
 
+    if !value.in?(Tag::PERMITTED_UNBALANCED_TAGS) && !value.has_balanced_parens?
+      record.errors.add(attribute, "'#{value}' cannot have unbalanced parentheses")
+    end
+
     case value
     when /\A_*\z/
       record.errors.add(attribute, "cannot be blank")

app/models/tag.rb

@@ -3,6 +3,9 @@
 class Tag < ApplicationRecord
   ABBREVIATION_REGEXP = /([a-z0-9])[a-z0-9']*($|[^a-z0-9']+)/
 
+  # Tags that are permitted to have unbalanced parentheses, as a special exception to the normal rule that parentheses in tags must balanced.
+  PERMITTED_UNBALANCED_TAGS = %w[:) :( ;) ;( >:) >:(]
+
   has_one :wiki_page, :foreign_key => "title", :primary_key => "name"
   has_one :artist, :foreign_key => "name", :primary_key => "name"
   has_one :antecedent_alias, -> {active}, :class_name => "TagAlias", :foreign_key => "antecedent_name", :primary_key => "name"

config/initializers/core_extensions.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Danbooru
   module Extensions
     module String
@@ -55,6 +57,22 @@ module Danbooru
 
         text
       end
+
+      # @return [Boolean] True if the string contains only balanced parentheses; false if the string contains unbalanced parentheses.
+      def has_balanced_parens?(open = "(", close = ")")
+        parens = 0
+
+        chars.each do |char|
+          if char == open
+            parens += 1
+          elsif char == close
+            parens -= 1
+            return false if parens < 0
+          end
+        end
+
+        parens == 0
+      end
     end
   end
 end

test/unit/tag_test.rb

@@ -147,6 +147,16 @@ class TagTest < ActiveSupport::TestCase
       should allow_value("foo bar").for(:name).on(:create)
       should allow_value("FOO").for(:name).on(:create)
 
+      should allow_value(":)").for(:name).on(:create)
+      should allow_value(":(").for(:name).on(:create)
+      should allow_value(";)").for(:name).on(:create)
+      should allow_value(";(").for(:name).on(:create)
+      should allow_value(">:)").for(:name).on(:create)
+      should allow_value(">:(").for(:name).on(:create)
+
+      should allow_value("foo_(bar)").for(:name).on(:create)
+      should allow_value("foo_(bar_(baz))").for(:name).on(:create)
+
       should_not allow_value("").for(:name).on(:create)
       should_not allow_value("___").for(:name).on(:create)
       should_not allow_value("~foo").for(:name).on(:create)
@@ -154,6 +164,7 @@ class TagTest < ActiveSupport::TestCase
       should_not allow_value("/foo").for(:name).on(:create)
       should_not allow_value("`foo").for(:name).on(:create)
       should_not allow_value("%foo").for(:name).on(:create)
+      should_not allow_value("(foo").for(:name).on(:create)
       should_not allow_value(")foo").for(:name).on(:create)
       should_not allow_value("{foo").for(:name).on(:create)
       should_not allow_value("}foo").for(:name).on(:create)
@@ -169,6 +180,12 @@ class TagTest < ActiveSupport::TestCase
       should_not allow_value("FAV:blah").for(:name).on(:create)
       should_not allow_value("X"*171).for(:name).on(:create)
 
+      should_not allow_value("foo)").for(:name).on(:create)
+      should_not allow_value("foo(").for(:name).on(:create)
+      should_not allow_value("foo)(").for(:name).on(:create)
+      should_not allow_value("foo(()").for(:name).on(:create)
+      should_not allow_value("foo())").for(:name).on(:create)
+
       metatags = PostQueryBuilder::METATAGS + TagCategory.mapping.keys
       metatags.each do |metatag|
         should_not allow_value("#{metatag}:foo").for(:name).on(:create)