Proof of Concept - Declare all dependencies in Gemfile, not in the gemspec

my_gem.gemspec

require_relative 'lib/my_gem/version'

# Proof of concept monkey-patch
class Gem::Specification
  def add_gemfile_dependencies(*groups)
    require 'bundler'
    groups = [:default] if groups.empty?

    # Quick hack to remove any gemspec call from the Gemfile to prevent a
    # circular infinite call loop. A better solution could be to patch
    # `gemspec` to do a no-op if `add_gemfile_dependencies` is running
    gemfile_content_without_gemspec = File.read('Gemfile').gsub('gemspec', '')
    dependencies = Bundler::Dsl.new.eval_gemfile('Gemfile', gemfile_content_without_gemspec)

    dependencies.select! do |dependency|
      dependency.name != name && dependency.groups.any? { |group| groups.include?(group) }
    end

    dependencies.each { |dependency| add_dependency(dependency.name, dependency.requirement) }
  end
end

Gem::Specification.new do |spec|
  # ...
  
  spec.add_gemfile_dependencies
  # or spec.add_gemfile_dependencies(:default, :release) or whatever
end