Andrew Carver wrote

Oh my -- the rabbit-hole goes even deeper:
To run something with asciidoctor-bibliography, of course I had to change my PATH variable back to Ruby 2.5 -- in which I've got these relevant gems installed:

asciidoctor (2.0.10, 1.5.7.1, 1.5.7)
asciidoctor-bibliography (0.10.0, 0.8.0, 0.7.2)
...
bibtex-ruby (5.0.0, 4.4.6)

But when I ran it, I got this:

Traceback (most recent call last):
        14: from C:/tools/ruby25/bin/asciidoctor:23:in `<main>'
        13: from C:/tools/ruby25/bin/asciidoctor:23:in `load'
        12: from C:/tools/ruby25/lib/ruby/gems/2.5.0/gems/asciidoctor-2.0.10/bin/asciidoctor:13:in `<top (required)>'
        11: from C:/tools/ruby25/lib/ruby/gems/2.5.0/gems/asciidoctor-2.0.10/bin/asciidoctor:13:in `new'
        10: from C:/tools/ruby25/lib/ruby/gems/2.5.0/gems/asciidoctor-2.0.10/lib/asciidoctor/cli/invoker.rb:24:in `initialize'
         9: from C:/tools/ruby25/lib/ruby/gems/2.5.0/gems/asciidoctor-2.0.10/lib/asciidoctor/cli/options.rb:34:in `parse!'
         8: from C:/tools/ruby25/lib/ruby/gems/2.5.0/gems/asciidoctor-2.0.10/lib/asciidoctor/cli/options.rb:274:in `parse!'
         7: from C:/tools/ruby25/lib/ruby/gems/2.5.0/gems/asciidoctor-2.0.10/lib/asciidoctor/cli/options.rb:274:in `each'
         6: from C:/tools/ruby25/lib/ruby/gems/2.5.0/gems/asciidoctor-2.0.10/lib/asciidoctor/cli/options.rb:276:in `block in parse!'
         5: from C:/tools/ruby25/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:39:in `require'
         4: from C:/tools/ruby25/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:128:in `rescue in require'
         3: from C:/tools/ruby25/lib/ruby/2.5.0/rubygems.rb:217:in `try_activate'
         2: from C:/tools/ruby25/lib/ruby/2.5.0/rubygems.rb:224:in `rescue in try_activate'
         1: from C:/tools/ruby25/lib/ruby/2.5.0/rubygems/specification.rb:1438:in `activate'
C:/tools/ruby25/lib/ruby/2.5.0/rubygems/specification.rb:2325:in `raise_if_conflicts': Unable to activate asciidoctor-bibliography-0.10.0, because asciidoctor-2.0.10 conflicts with asciidoctor (~> 1.5.6) (Gem::ConflictError)

What -- if you know -- does that last line mean??

Andrew Carver wrote

P.S. I'm also baffled by asciidoctor 2.0.10 installing just fine without installing nokogiri...??
(I think the below warning about "the last version of nokogiri ... to support your Ruby & RubyGems  was 1.8.5" was probably because I'd already installed asciidoctor 1.5.8, which depends on that version.)

Andrew Carver wrote

Thanks Dan.
May I ask you, then, whether the below sequence run just now on Ruby 2.6.x indicates the nokogiri dependency needs upgrading in asciidoctor-bibliography?

C:\Users\acarver>gem install nokogiri -v 1.8.5
ERROR:  Error installing nokogiri:
        The last version of nokogiri (= 1.8.5) to support your Ruby & RubyGems was 1.8.5. Try installing it with `gem install nokogiri -v 1.8.5`
        nokogiri requires Ruby version >= 2.2, < 2.6. The current ruby version is 2.6.3.62.

C:\Users\acarver>gem install asciidoctor
Fetching asciidoctor-2.0.10.gem
Successfully installed asciidoctor-2.0.10
Parsing documentation for asciidoctor-2.0.10
Installing ri documentation for asciidoctor-2.0.10
Done installing documentation for asciidoctor after 15 seconds
1 gem installed

C:\Users\acarver>gem install asciidoctor-bibliography
ERROR:  Error installing asciidoctor-bibliography:
        The last version of nokogiri (~> 1.8.1) to support your Ruby & RubyGems was 1.8.5. Try installing it with `gem install nokogiri -v 1.8.5` and then running the current command again
        nokogiri requires Ruby version >= 2.2, < 2.6. The current ruby version is 2.6.3.62.