My solution to a #ruby IRC question

jekyll_plugins.rb

# frozen_string_literal: true

fetcher = Gem::SpecFetcher.fetcher

matches = fetcher.detect do |spec|
  spec.name.start_with? 'jekyll-'
end

plugins = matches.map(&:first).map(&:name).uniq

specs = plugins.map do |plugin|
  Gem.latest_spec_for plugin
end.compact

this_jekyll_version = Gem::Version.new ARGV.first || '4.0.0'

compatible_specs = specs.select do |spec|
  jekyll = spec.dependencies.find { |dependency| dependency.name == 'jekyll' }
  jekyll&.requirement&.satisfied_by? this_jekyll_version
end

compatible_plugins = compatible_specs.map(&:name)

puts compatible_plugins

output.txt

jekyll-4-picture-tag
jekyll-admin
jekyll-admin-jekyll34
jekyll-age
jekyll-algolia
jekyll-amazon
jekyll-amp
jekyll-angular
jekyll-app-engine
jekyll-archives
jekyll-asciidoc
jekyll-asciinema
jekyll-authors
jekyll-auto-image
jekyll-avatar
jekyll-beastiepress
jekyll-bitly
jekyll-bootstrap-sass
jekyll-brotli
jekyll-browserify
jekyll-browsersync
jekyll-cat
jekyll-categories
jekyll-category-pages
jekyll-category_generator
jekyll-cloudinary
jekyll-code-example-tag
jekyll-coffeescript
jekyll-commonmark
jekyll-components
jekyll-compose
jekyll-config-variables
jekyll-conrefifier
jekyll-contentblocks
jekyll-contentful
jekyll-csv
jekyll-csvy
jekyll-dark-ored
jekyll-data
jekyll-data-pages
jekyll-date-format
jekyll-diagrams
jekyll-docs
jekyll-drafts-as-metadata
jekyll-embeds
jekyll-emoji
jekyll-environment-variables
jekyll-epub
jekyll-events
jekyll-everypolitician
jekyll-extlinks
jekyll-favicon
jekyll-feed
jekyll-filepath
jekyll-firstimage
jekyll-flickr
jekyll-fridge
jekyll-frontmatter-jsonify
jekyll-ftp
jekyll-geo-pattern
jekyll-gist
jekyll-git-authors
jekyll-git-updated
jekyll-github-comments
jekyll-github-last-modified
jekyll-github-pages-search
jekyll-gitlab-letsencrypt
jekyll-google-tag-manager
jekyll-google_analytics
jekyll-graphviz
jekyll-gzip
jekyll-haml
jekyll-haml-markup
jekyll-handlebars
jekyll-hanfverband-theme
jekyll-i18n
jekyll-image-size
jekyll-imagemagick
jekyll-imageresizer
jekyll-img-srcset
jekyll-import
jekyll-include-cache
jekyll-include-with-frontmatter
jekyll-include_sass
jekyll-info
jekyll-inline-svg
jekyll-jelly
jekyll-jolt
jekyll-joule
jekyll-jsminify
jekyll-jupyter-notebook
jekyll-katex
jekyll-languages
jekyll-last-modified
jekyll-last-modified-at
jekyll-latex-block
jekyll-lazy-load-image
jekyll-less
jekyll-lin
jekyll-link-checker
jekyll-link-url-filter
jekyll-liquify
jekyll-livescript
jekyll-mail-comments
jekyll-materialdocs
jekyll-mathematical
jekyll-mentioji
jekyll-mentions
jekyll-menus
jekyll-microtypo
jekyll-minifier
jekyll-minify-html
jekyll-minimagick
jekyll-mscgen
jekyll-navigation
jekyll-nested-menu-generator
jekyll-netlify-headers
jekyll-netlify-redirects
jekyll-octicons
jekyll-oembed
jekyll-onebox
jekyll-opal
jekyll-openmoji
jekyll-optional-front-matter
jekyll-org
jekyll-page-hooks
jekyll-pages-directory
jekyll-paginate-categories
jekyll-paginate-category
jekyll-paginate-cats
jekyll-paginate-multiple
jekyll-paginate-tags
jekyll-paginate_command
jekyll-pandoc
jekyll-pandoc-multiple-formats-jekyll34
jekyll-pandoc-rouge
jekyll-pants
jekyll-pdf-embed
jekyll-picture-tag-latest
jekyll-plantastisch
jekyll-plantuml
jekyll-plantuml-url
jekyll-plugin-cloudinary
jekyll-polyglot
jekyll-postcss
jekyll-postfiles
jekyll-pre-commit
jekyll-presentations
jekyll-press
jekyll-prismjs-compile
jekyll-pseudo
jekyll-pseudocode
jekyll-purgecss
jekyll-quickstart
jekyll-ramler
jekyll-random
jekyll-read-more
jekyll-readme-index
jekyll-rebellion
jekyll-redirect-from
jekyll-regex-replace
jekyll-relative-links
jekyll-relative-urls
jekyll-remote-include
jekyll-remote-theme
jekyll-remote_csv
jekyll-remove-file-extension
jekyll-replace-img
jekyll-resizer
jekyll-responsive-image
jekyll-retinamagick
jekyll-robotstxt
jekyll-root-directory
jekyll-rpg
jekyll-sass
jekyll-scholar
jekyll-search
jekyll-seo-tag
jekyll-sharelinks
jekyll-simple-template
jekyll-site-tree
jekyll-sitemap
jekyll-smartcropper
jekyll-snippets
jekyll-spark
jekyll-srcset
jekyll-srcset-tag
jekyll-swfobject
jekyll-tagging-related_posts
jekyll-tagslist
jekyll-target-blank
jekyll-template
jekyll-test
jekyll-text-theme
jekyll-theme-apex
jekyll-theme-basically-basic
jekyll-theme-console
jekyll-theme-consulting
jekyll-theme-cvent-dev-portal
jekyll-theme-developer
jekyll-theme-drop
jekyll-theme-ethereal
jekyll-theme-glueckkanja
jekyll-theme-guides-mbland
jekyll-theme-hacker-nogh
jekyll-theme-isabelline
jekyll-theme-kindee-simple
jekyll-theme-lcsb-default
jekyll-theme-mehdix-rtl
jekyll-theme-minimal-elcymon
jekyll-theme-open-course
jekyll-theme-overflow
jekyll-theme-parallelism
jekyll-theme-portfolio
jekyll-theme-primer
jekyll-theme-rose
jekyll-theme-so-simple
jekyll-theme-space
jekyll-theme-stellar
jekyll-theme-tactile-nogh
jekyll-theme-twenty
jekyll-theme-white-xmas
jekyll-thumb
jekyll-thumbnail
jekyll-thumbor
jekyll-tidy
jekyll-time-to-read
jekyll-timeago
jekyll-titles-from-headings
jekyll-toc
jekyll-toc-helpers
jekyll-torrent
jekyll-transform
jekyll-turbolinks
jekyll-twemoji
jekyll-typogrify
jekyll-url-backport
jekyll-video-tag
jekyll-watch
jekyll-webring
jekyll-werther
jekyll-whiteglass
jekyll-writeinpublic
jekyll-youtube
jekyll-zopfli