[Artists] Fix reverting removing urls when validations fail

app/models/artist.rb

@@ -208,6 +208,11 @@ class Artist < ApplicationRecord
     end
 
     def url_string=(string)
+      # FIXME: This is a hack. Setting an association directly immediatly updates without regard for the parents validity.
+      # As a consequence, removing urls always works. This does not create a new ArtistVersion.
+      # This fix isn't great but it's the best I came up with without rather large changes.
+      return unless valid?
+
       url_string_was = url_string
 
       self.urls = string.to_s.scan(/[^[:space:]]+/).map do |url|

test/unit/artist_test.rb

@@ -337,6 +337,43 @@ class ArtistTest < ActiveSupport::TestCase
         assert_equal("artist_user_unlinked", mod_action.action)
         assert_equal({ "artist_page" => @artist.id, "user_id" => user.id }, mod_action.values)
       end
+
+      should "fail if the user is limited" do
+        @artist.url_string = "https://e621.net"
+        as(create(:user)) { @artist.save }
+
+        @artist.reload
+        assert_equal("https://e621.net", @artist.url_string)
+
+        Danbooru.config.stubs(:disable_throttles?).returns(false)
+        Danbooru.config.stubs(:artist_edit_limit).returns(0)
+
+        @artist.url_string = ""
+        assert_no_difference(-> { ArtistVersion.count }) do
+          as(create(:user)) { @artist.save }
+        end
+
+        @artist.reload
+        assert_equal("https://e621.net", @artist.url_string)
+      end
+
+      should "not change urls when locked" do
+        @artist.url_string = "https://e621.net"
+        as(create(:user)) { @artist.save }
+
+        @artist.reload
+        assert_equal("https://e621.net", @artist.url_string)
+
+        @artist.update_column(:is_locked, true)
+
+        @artist.url_string = "https://e926.net"
+        assert_no_difference(-> { ArtistVersion.count }) do
+          as(create(:user)) { @artist.save }
+        end
+
+        @artist.reload
+        assert_equal("https://e621.net", @artist.url_string)
+      end
     end
   end
 end