Fix #4908: Prevent artist entries from being made on disambiguation tags.

Don't allow artist entries to be created for deprecated tags.

app/models/artist.rb

@@ -174,6 +174,10 @@ class Artist < ApplicationRecord
         errors.add(:name, "'#{name}' is a #{tag.category_name.downcase} tag; artist entries can only be created for artist tags")
       end
 
+      if tag&.is_deprecated?
+        errors.add(:name, "'#{name}' is an ambiguous tag; try another name")
+      end
+
       if tag_alias.present?
         errors.add(:name, "'#{name}' is aliased to '#{tag_alias.consequent_name}'")
       end

test/unit/artist_test.rb

@@ -549,6 +549,14 @@ class ArtistTest < ActiveSupport::TestCase
         assert_equal(true, artist.invalid?)
         assert_match(/'foo' is aliased to 'bar'/, artist.errors.full_messages.join)
       end
+
+      should "not allow creating artist entries for deprecated tags" do
+        create(:tag, name: "orange", is_deprecated: true)
+        artist = build(:artist, name: "orange")
+
+        assert_equal(true, artist.invalid?)
+        assert_match(/'orange' is an ambiguous tag/, artist.errors.full_messages.join)
+      end
     end
 
     context "when renaming" do