Response to IRC question

missing_extensions.rb

require 'bundler'

def lockfile
  Bundler.read_file Bundler.default_lockfile
end

def lockfile_gems
  Bundler::LockfileParser.new(lockfile).specs.map do |spec|
    [spec.name, spec.version ]
  end
end

def missing_gems
  lockfile_gems.select do |name, version|
    dep = Gem::Dependency.new name, version
    Gem::Specification.find { |spec| spec != dep }
  end
end

def missing_extensions
  missing_gems.select do |name, version|
    dep = Gem::Dependency.new name, version
    ((spec, _), _), _ = Gem::SpecFetcher.fetcher.spec_for_dependency dep
    spec.missing_extensions?
  end
end

puts missing_extensions if missing_extensions.any?