Version specific gem :platform in Gemfile doesn't do anything that I can see

[kjg]

Running Bundler Version 1.11.2

If I have a Gemfile that specifies

platforms :ruby_18 do
  gem "rake", "< 11.0"
end
platforms :ruby_20 do
  gem "rake", "> 11.0"
end

I get the error

[!] There was an error parsing `Gemfile`: You cannot specify the same gem twice with different version requirements.
You specified: rake (< 11.0) and rake (> 11.0). Bundler cannot continue.

Am I just missing the point of the version specific platform option on the gems?

Is there anyway to meet this use case of installing a different version of the gem depending on the version of ruby?

Even though rake specifies it's REQUIRED RUBY VERSION in it's gemfile, bundler still tries to install >11 when I'm on ruby 1.8.7 for example, so using platforms :ruby_20 is what I'd expect to have to do to work around this, but that doesn't seem to work either.

[segiddins]

There's no way to do this -- you'll need to stick with 10.x for 1.8 compatibility.

[kjg]

What is the intended use case for the version specific platform identifiers? The docs indicate that it does constrain the ruby version http://bundler.io/v1.11/man/gemfile.5.html#PLATFORMS-platforms-

[segiddins]

Yes, they do, but a single bundle must be self-coherent, regardless of different groups, platform blocks, install_if blocks, etc

[coilysiren]

So as far as I can tell, this is best interpreted as a feature request to allow Bundler to have different versions of the same gem on different platforms? cc @kjg

[segiddins]

If that's the feature request, we can close this -- that's simply not in the cards. It goes completely against bundler's promise of installing the same dependencies everywhere. If this functionality is something the user wants, they will have to use a regular ruby conditional and deal with the fact that their lockfile with change every time that they switch ruby versions

[kjg]

Gems inside the platforms :ruby_18 block still seem to get installed even on ruby 2.0

[antoineco]

@kjg I confirm that. The following blocks are enforced with all Ruby versions:

platforms :ruby_18 do
  # https://github.com/rspec/rspec-core/issues/1864
  gem 'rspec', '< 3.2.0',  :require => false
  gem 'rake',  '< 11.0.0', :require => false
end

platforms :ruby_18, :ruby_19 do
  gem 'json',      '< 2.0.0', :require => false
  gem 'json_pure', '< 2.0.0', :require => false
end

[segiddins]

Closing, this is how the :platform filter is intended to work -- it only changes which gems are activated at runtime and intentionally does not allow specifying different versions of the same gem.