Bundler/Gemfile: Gem version declaration presence cop

[timlkelly]

Hello, I've recently created a custom cop for a private project which I think is applicable to most codebases. I want to gauge if there's interest to include this in Rubocop. If so, I'd love to open up a pull to add it!

This cop checks that gems listed in the Gemfile include a version declaration. The reason is to prevent any unintended side effects from bundling and updating gems to new versions that weren't intended to change. I also think it's best practice to specify versions of dependencies. Here are the comments I wrote to give a little more context:

# This cop checks that Gems specify a Version number.
# @example
#  # bad
#  gem 'rubocop'
#
#  # good
#  gem 'rubocop', '~> 1.12'
#
#  # good
#  gem 'rubocop', '>= 1.10.0'
#
#  # good
#  gem 'rubocop', '>= 1.5.0', '< 1.10.0'
#

[koic]

JFYI, this proposal is discussed in #7669.

[timlkelly]

Ah, thank you. I missed that while searching for existing issues. I'll post there.

[timlkelly]

Pull request link for discoverability: #9727