class Bundler::Resolver

def self.resolve(requirements, index, source_requirements = {})

collection of gemspecs is returned. Otherwise, nil is returned.
,nil:: If the list of dependencies can be resolved, a
==== Returns

*dependencies:: The list of dependencies to resolve
==== Parameters

causing any gem activation errors.
the list of passed dependencies and any child dependencies without
Figures out the best possible configuration of gems that satisfies 
def self.resolve(requirements, index, source_requirements = {})
  resolver = new(index, source_requirements)
  result = catch(:success) do
    resolver.resolve(requirements, {})
    output = resolver.errors.inject("") do |o, (conflict, (origin, requirement))|
      if origin
        o << "  Conflict on: #{conflict.inspect}:\n"
        o << "    * #{conflict} (#{origin.version}) activated by #{origin.required_by.first}\n"
        o << "    * #{requirement} required"
        if requirement.required_by.first
          o << " by #{requirement.required_by.first}\n"
        else
          o << " in Gemfile\n"
        end
      else
        o << "  #{requirement} not found in any of the sources\n"
        o << "      required by #{requirement.required_by.first}\n"
      end
      o << "    All possible versions of origin requirements conflict."
    end
    raise VersionConflict, "No compatible versions could be found for required dependencies:\n  #{output}"
    nil
  end
  SpecSet.new(result.values)
end