Gemfile in asciidoctor-epub3-1.5.1 vs Gemfile in asciidoctor-epub3-2.0.0

@@ -3,17 +3,14 @@
 source 'https://rubygems.org'
 
 # Look in asciidoctor-epub3.gemspec for runtime and development dependencies.
 gemspec
 
-if ENV.key? 'ASCIIDOCTOR_VERSION'
-  gem 'asciidoctor', ENV['ASCIIDOCTOR_VERSION'], require: false
-  # Newer asciidoctor-diagram 1.5.x require asciidoctor >=1.5.7
-  gem 'asciidoctor-diagram', '1.5.16', require: false if Gem::Version.new(ENV['ASCIIDOCTOR_VERSION']) < Gem::Version.new('2.0.0')
-end
-
 group :optional do
-  # epubcheck-ruby might be safe to be converted into runtime dependency, but could have issues when packaged into asciidoctorj-epub3
-  gem 'epubcheck-ruby', '~> 4.2.5.0'
-  # Kindlegen is unavailable neither for 64-bit MacOS nor for ARM
-  gem 'kindlegen', '~> 3.1.0' unless RbConfig::CONFIG['host_os'] =~ /darwin/
+  # epubcheck-ruby might be safe to be converted into runtime dependency,
+  # but could have issues when packaged into asciidoctorj-epub3
+  gem 'epubcheck-ruby', '~> 5.1.0.0'
+
+  # Kindlegen is unavailable neither for 64-bit x86 macOS nor for ARM
+  # Also, skip JRuby on Windows for now. See https://github.com/jruby/jruby/issues/7171
+  gem 'kindlegen', '~> 3.1.0' unless RUBY_PLATFORM =~ /darwin/ || (Gem.win_platform? && RUBY_ENGINE == 'jruby')
 end