Feature/gem updates

[dazza-codes]

This PR is designed to cleanup and clarify how to update the gemsets for triannon and the engine cart app that will test triannon.

• The Gemfile change removes all constraints that are not in the triannon.gemset file when the engine cart is not installed yet (i.e. it removes the 'else' clause that the engine_cart:prepare task creates; this is potentially a moot point, but IMO that all belongs within the engine_cart:generate process and should not 'taint' the parent project Gemfile).
• The Rakefile changes consolidate the logic for updating the gemset of the triannon parent project and the engine cart test app, allowing the latter to resolve third-party gemsets that should not be defined by the triannon Gemfile. The key to this solution is removing the triannon parent 'Gemfile.lock' file before running the engine_cart:generate task. This avoids having to modify the triannon parent Gemfile to handle mysterious third-party conflicts between the parent Gemfile.lock and the engine cart gem requirements (such as the prior 'tilt' pin that really had nothing to do with triannon itself).

These changes have been evaluated by repeatedly running rake ci on my laptop and the same task has been run on travis with successful results.

Comments and feedback are especially appreciated from @ndushay and @cbeer. Please bear in mind that a guiding principle of this PR is to avoid using Gemfile.lock, as much as possible, by containing gem pins solely in triannon.gemspec (i.e. removing them from the triannon Gemspec file).

[dazza-codes]

@ndushay might appreciate some git rebase -i work that went into this PR (although it's not obvious now that it's done).

[dazza-codes]

One important thing to discuss is what happens if the ENV['RAILS_VERSION'] is set. Having removed the code that uses this in the triannon Gemfile, will it be used anyway by the engine cart generate process? So, I have yet to evaluate what happens when we run, say:

RAILS_VERSION=4.2.1 rake ci

[dazza-codes]

BTW, the gemnasium badge on master indicates the gemsets are outdated, but this seems to be only because of 'tilt' at 1.1 (latest is 2.x), see https://gemnasium.com/sul-dlss/triannon

[dazza-codes]

Pushing changes that result from discussion with @cbeer to clarify how and why engine cart modifies the triannon Gemfile. The file change is something like this pseudocode:

if engine_cart_gemfile_exists
  load_it
else
  define_development_dependencies
end

The 'else' clause is designed for defining dependencies to be tweaked and evaluated in development (this might be used to specify or update a dependency in triannon.gemspec). By separating these out into a :development group, they cannot have side-effects on the :test environment. The goal is to ensure that the :test environment mimics how the triannon gem will behave in third-party rails applications.

When the 'else' clause is available to the :test environment, it can have side effects. For example, when travis runs tests, it first runs a bundle install on triannon to get the engine cart gem and other triannon gem and test dependencies. This creates a new Gemfile.lock file with dependencies specific to triannon, without any 'consideration' for the engine cart dependencies. The next step is to create the engine cart app, which should only use the explicit dependencies in triannon.gemspec. However, when the Gemfile.lock file exists, the engine cart generation process will use it to resolve the app dependencies and this can result in unnecessary conflicts. In the :test environmnent, the engine cart app should be created without regard to the triannon Gemfile.lock file.

[cbeer]

It might be useful if you added a comment in your Gemfile to document the approach and deviations from the pattern provided by the engine_cart install generator , e.g.:

  file = File.expand_path("Gemfile", ENV['ENGINE_CART_DESTINATION'] || ENV['RAILS_ROOT'] || File.expand_path("../spec/internal", __FILE__))
  if File.exists?(file)
    puts "Loading #{file} ..." if $DEBUG # `ruby -d` or `bundle -v`
    instance_eval File.read(file)
  else
    gem 'rails', ENV['RAILS_VERSION'] if ENV['RAILS_VERSION']
    if ENV['RAILS_VERSION'] and ENV['RAILS_VERSION'] =~ /^4.2/
      gem 'responders', "~> 2.0"
      gem 'sass-rails', ">= 5.0"
    else
      gem 'sass-rails', "< 5.0"
    end
  end

https://github.com/cbeer/engine_cart/blob/23de7e3b7978577bec8c575954038ae99efd4672/lib/generators/engine_cart/install_generator.rb#L52-65

[dazza-codes]

@cbeer - good suggestion and, with further testing, the most recent revision to this PR gets a lot closer to the desired goals, including added commentary. (Note the commit messages are no longer generated with commit -m 'xyz comment' and should provide more useful information.)

[dazza-codes]

After team discussion today, this PR will be abandoned. The changes proposed here may be useful reference at some later date (so the PR should be available in the github PR view when the pr:open filter is removed).