Homebrew isn't recognizing the formula? about jardiff HOT 4 CLOSED

brew install retronym/formulas/jardiff
Updating Homebrew...
==> Installing jardiff from retronym/formulas
==> Downloading https://github.com/scala/jardiff/releases/download/v1.6.0/jardiff.jar
Already downloaded: /Users/jz/Library/Caches/Homebrew/downloads/8d21de597dd69

% brew untap retronym/formulas
Untapping retronym/formulas...
Untapped 2 formulae (43 files, 37.4KB).

~ % brew install retronym/formulas/jardiff                                                                  [master|✚1]
==> Tapping retronym/formulas
Cloning into '/usr/local/Homebrew/Library/Taps/retronym/homebrew-formulas'...
remote: Enumerating objects: 10, done.
remote: Counting objects: 100% (10/10), done.
remote: Compressing objects: 100% (9/9), done.
remote: Total 28 (delta 1), reused 4 (delta 0), pack-reused 18
Receiving objects: 100% (28/28), 5.45 KiB | 2.73 MiB/s, done.
Resolving deltas: 100% (5/5), done.
Error: Invalid formula: /usr/local/Homebrew/Library/Taps/retronym/homebrew-formulas/jardiff.rb
jardiff: /usr/local/Homebrew/Library/Taps/retronym/homebrew-formulas/jardiff.rb:9: `@1' is not allowed as an instance variable name
/usr/local/Homebrew/Library/Taps/retronym/homebrew-formulas/jardiff.rb:9: syntax error, unexpected end-of-input, expecting end
  depends_on openjdk@11
                    ^
Error: Cannot tap retronym/formulas: invalid syntax in tap!