A set of gems for installation sourced from remote sources and local .gem files
Creates a new InstallerSet that will look for gems in domain.
 
               # File rubygems/resolver/installer_set.rb, line 32
def initialize(domain)
  super()
  @domain = domain
  @remote = consider_remote?
  @f = Gem::SpecFetcher.fetcher
  @always_install      = []
  @ignore_dependencies = false
  @ignore_installed    = false
  @local               = {}
  @local_source        = Gem::Source::Local.new
  @remote_set          = Gem::Resolver::BestSet.new
  @specs               = {}
end
             
            Looks up the latest specification for dependency and adds it to the always_install list.
 
               # File rubygems/resolver/installer_set.rb, line 53
def add_always_install(dependency)
  request = Gem::Resolver::DependencyRequest.new dependency, nil
  found = find_all request
  found.delete_if do |s|
    s.version.prerelease? and not s.local?
  end unless dependency.prerelease?
  found = found.select do |s|
    Gem::Source::SpecificFile === s.source or
      Gem::Platform::RUBY == s.platform or
      Gem::Platform.local === s.platform
  end
  if found.empty?
    exc = Gem::UnsatisfiableDependencyError.new request
    exc.errors = errors
    raise exc
  end
  newest = found.max_by do |s|
    [s.version, s.platform == Gem::Platform::RUBY ? -1 : 1]
  end
  @always_install << newest.spec
end
             
            Adds a local gem requested using dep_name with the given spec that can be loaded and installed using the source.
 
               # File rubygems/resolver/installer_set.rb, line 86
def add_local(dep_name, spec, source)
  @local[dep_name] = [spec, source]
end
             
            Errors encountered while resolving gems
 
               # File rubygems/resolver/installer_set.rb, line 107
def errors
  @errors + @remote_set.errors
end
             
            Returns an array of IndexSpecification objects matching DependencyRequest req.
 
               # File rubygems/resolver/installer_set.rb, line 115
def find_all(req)
  res = []
  dep = req.dependency
  return res if @ignore_dependencies and
            @always_install.none? { |spec| dep.match? spec }
  name = dep.name
  dep.matching_specs.each do |gemspec|
    next if @always_install.any? { |spec| spec.name == gemspec.name }
    res << Gem::Resolver::InstalledSpecification.new(self, gemspec)
  end unless @ignore_installed
  if consider_local?
    matching_local = @local.values.select do |spec, _|
      req.match? spec
    end.map do |spec, source|
      Gem::Resolver::LocalSpecification.new self, spec, source
    end
    res.concat matching_local
    begin
      if local_spec = @local_source.find_gem(name, dep.requirement)
        res << Gem::Resolver::IndexSpecification.new(
          self, local_spec.name, local_spec.version,
          @local_source, local_spec.platform)
      end
    rescue Gem::Package::FormatError
      # ignore
    end
  end
  res.delete_if do |spec|
    spec.version.prerelease? and not dep.prerelease?
  end
  res.concat @remote_set.find_all req if consider_remote?
  res
end