(#170) Add ability to remove gem from appraisal

[jebentier]

Purpose of PR

This is adding the ability to use the remove_gem declaration within an appraise block. By doing so the gem will be dropped from the generated Gemfile. This is useful in cases where an appraisal require the removal of old dependencies that are still used by the mainline source.

Example Usage

Gemfile

gem 'rails', '~> 4.2'

group :test do
  gem 'rspec', '~> 4.0'
  gem 'test_after_commit'
end

Appraisals

appraise 'rails-5' do
  gem 'rails', '~> 5.2'

  group :test do
    remove_gem 'test_after_commit'
  end
end

To produce:
gemfiles/rails_5.gemfile

gem 'rails', '~> 5.2'

group :test do
  gem 'rspec', '~> 4.0'
end

Fixes #170

[nickcharlton]

Thanks! This looks good.

I think it would be useful to document this addition, do you think you could add it to the README? I'm thinking that perhaps the best approach here would be to add a new section for additional options like this

[composerinteralia]

Nice! This is definitely something I would have used before if it existed.

[jebentier]

@composerinteralia I've gone ahead and made the suggested edits to the new contract and updated the PR to reflect those changes.

@nickcharlton I've gone ahead and updated the README to include documentation for this new declaration

[jebentier]

@composerinteralia would you have some time to re-review this in the coming days? I’m looking forward to getting this feature out so that we can use it at my company. If there’s anything that I can do to help with the release management of the gem as well, just let me know and I’d be happy to help.

[nickcharlton]

Hi @jebentier! Sorry, that's on me. I was meaning to go ahead and merge this but it turned into a fairly busy week.

I'm going to merge this now and I'll take a look at doing a new release some time before this Friday. Thanks for your contribution!

[jebentier]

@nickcharlton no worries at all, it’s been rather busy here as well. Thank you for accepting this contribution.

[jebentier]

@nickcharlton any update on getting this released?

[ColinDKelley]

@nickcharlton Any update on the release that will include this PR? It seems especially important since master has been documenting this new feature for 2 months now.

[ColinDKelley]

@nickcharlton Any update on the release that will include this PR?

[nickcharlton]

Thanks for your patience everyone — I just did this now and so you should see version 2.4.0 available now.