# class Gem::Resolver

Given a set of `Gem::Dependency` objects as `needed` and a way to query the set of available specs via `set`, calculates a set of `ActivationRequest` objects which indicate all the specs that should be activated to meet the all the requirements.

### Constants

DEBUG_RESOLVER

  If the `DEBUG_RESOLVER` environment variable is set then debugging mode is enabled for the resolver. This will display information about the state of the resolver while a set of dependencies is being resolved.

SINGLE_POSSIBILITY_CONSTRAINT_PENALTY

### Attributes

development [RW]

`Set` to true if all development dependencies should be considered.

development_shallow [RW]

`Set` to true if immediate development dependencies should be considered.

ignore_dependencies [RW]

When true, no dependencies are looked up for requested gems.

skip_gems [RW]

`Hash` of gems to skip resolution. Keyed by gem name, with arrays of gem specifications as values.

soft_missing [RW]
stats [R]

List of dependencies that could not be found in the configured sources.

### Public Class Methods

compose_sets (*sets)
Source

    # File lib/rubygems/resolver.rb, line 59
    def self.compose_sets(*sets)
      sets.compact!

      sets = sets.flat_map do |set|
        case set
        when Gem::Resolver::BestSet then
          set
        when Gem::Resolver::ComposedSet then
          set.sets
        else
          set
        end
      end

      case sets.length
      when 0 then
        raise ArgumentError, "one set in the composition must be non-nil"
      when 1 then
        sets.first
      else
        Gem::Resolver::ComposedSet.new(*sets)
      end
    end

Combines `sets` into a `ComposedSet` that allows specification lookup in a uniform manner. If one of the `sets` is itself a `ComposedSet` its sets are flattened into the result `ComposedSet`.

for_current_gems (needed)
Source

    # File lib/rubygems/resolver.rb, line 87
    def self.for_current_gems(needed)
      new needed, Gem::Resolver::CurrentSet.new
    end

Creates a `Resolver` that queries only against the already installed gems for the `needed` dependencies.

new (needed, set = nil)
Source

    # File lib/rubygems/resolver.rb, line 99
    def initialize(needed, set = nil)
      @set = set || Gem::Resolver::IndexSet.new
      @needed = needed

      @development         = false
      @development_shallow = false
      @ignore_dependencies = false
      @skip_gems           = {}
      @soft_missing        = false
      @stats               = Gem::Resolver::Stats.new
    end

Create `Resolver` object which will resolve the tree starting with `needed` Dependency objects.

`set` is an object that provides where to look for specifications to satisfy the Dependencies. This defaults to `IndexSet`, which will query rubygems.org.

### Public Instance Methods

allow_missing? (dependency)
Source

    # File lib/rubygems/resolver.rb, line 271
    def allow_missing?(dependency)
      @soft_missing
    end

debug? ()
Source

    # File lib/rubygems/resolver.rb, line 176
    def debug?
      DEBUG_RESOLVER
    end

dependencies_for (specification)
Source

    # File lib/rubygems/resolver.rb, line 252
    def dependencies_for(specification)
      return [] if @ignore_dependencies
      spec = specification.spec
      requests(spec, specification)
    end

name_for (dependency)
Source

    # File lib/rubygems/resolver.rb, line 267
    def name_for(dependency)
      dependency.name
    end

output ()
Source

    # File lib/rubygems/resolver.rb, line 172
    def output
      @output ||= debug? ? $stdout : File.open(IO::NULL, "w")
    end

requirement_satisfied_by? (requirement, activated, spec)
Source

    # File lib/rubygems/resolver.rb, line 258
    def requirement_satisfied_by?(requirement, activated, spec)
      matches_spec = requirement.matches_spec? spec
      return matches_spec if @soft_missing

      matches_spec &&
        spec.spec.required_ruby_version.satisfied_by?(Gem.ruby_version) &&
        spec.spec.required_rubygems_version.satisfied_by?(Gem.rubygems_version)
    end

resolve ()
Source

    # File lib/rubygems/resolver.rb, line 185
    def resolve
      Gem::Molinillo::Resolver.new(self, self).resolve(@needed.map {|d| DependencyRequest.new d, nil }).tsort.filter_map(&:payload)
    rescue Gem::Molinillo::VersionConflict => e
      conflict = e.conflicts.values.first
      raise Gem::DependencyResolutionError, Conflict.new(conflict.requirement_trees.first.first, conflict.existing, conflict.requirement)
    ensure
      @output.close if defined?(@output) && !debug?
    end

Proceed with resolution! Returns an array of `ActivationRequest` objects.

search_for (dependency)
Source

    # File lib/rubygems/resolver.rb, line 223
    def search_for(dependency)
      possibles, all = find_possible(dependency)
      if !@soft_missing && possibles.empty?
        exc = Gem::UnsatisfiableDependencyError.new dependency, all
        exc.errors = @set.errors
        raise exc
      end

      groups = Hash.new {|hash, key| hash[key] = [] }

      # create groups & sources in the same loop
      sources = possibles.map do |spec|
        source = spec.source
        groups[source] << spec
        source
      end.uniq.reverse

      activation_requests = []

      sources.each do |source|
        groups[source].
          sort_by {|spec| [spec.version, spec.platform =~ Gem::Platform.local ? 1 : 0] }. # rubocop:disable Performance/RegexpMatch
          map {|spec| ActivationRequest.new spec, dependency }.
          each {|activation_request| activation_requests << activation_request }
      end

      activation_requests
    end

sort_dependencies (dependencies, activated, conflicts)
Source

    # File lib/rubygems/resolver.rb, line 275
    def sort_dependencies(dependencies, activated, conflicts)
      dependencies.sort_by.with_index do |dependency, i|
        name = name_for(dependency)
        [
          activated.vertex_named(name).payload ? 0 : 1,
          amount_constrained(dependency),
          conflicts[name] ? 0 : 1,
          activated.vertex_named(name).payload ? 0 : search_for(dependency).count,
          i, # for stable sort
        ]
      end
    end

### Private Instance Methods

amount_constrained (dependency)
Source

    # File lib/rubygems/resolver.rb, line 297
    def amount_constrained(dependency)
      @amount_constrained ||= {}
      @amount_constrained[dependency.name] ||= begin
        name_dependency = Gem::Dependency.new(dependency.name)
        dependency_request_for_name = Gem::Resolver::DependencyRequest.new(name_dependency, dependency.requester)
        all = @set.find_all(dependency_request_for_name).size

        if all <= 1
          all - SINGLE_POSSIBILITY_CONSTRAINT_PENALTY
        else
          search = search_for(dependency).size
          search - all
        end
      end
    end

returns an integer in (-infty, 0] a number closer to 0 means the dependency is less constraining

dependencies w/ 0 or 1 possibilities (ignoring version requirements) are given very negative values, so they always sort first, before dependencies that are unconstrained