Gem::Resolver#incompatibilities_for

# File tmp/rubies/ruby-4.1.0-preview1/lib/rubygems/resolver.rb, line 272
def incompatibilities_for(package, version)
  package_deps = @cached_dependencies[package]
  sorted_versions = @sorted_versions[package]
  package_deps[version].filter_map do |dep_package_name, dep_constraint|
    dep_package = dep_constraint.package

    low = high = @version_to_index[package][version]

    # find version low such that all >= low share the same dep
    while low > 0 &&
          package_deps[sorted_versions[low - 1]][dep_package_name] == dep_constraint
      low -= 1
    end
    low =
      if low == 0
        nil
      else
        sorted_versions[low]
      end

    # find version high such that all < high share the same dep
    while high < sorted_versions.length &&
          package_deps[sorted_versions[high]][dep_package_name] == dep_constraint
      high += 1
    end
    high =
      if high == sorted_versions.length
        nil
      else
        sorted_versions[high]
      end

    range = Gem::PubGrub::VersionRange.new(min: low, max: high, include_min: !low.nil?)
    self_constraint = Gem::PubGrub::VersionConstraint.new(package, range: range)

    # No specs anywhere means an unknown package. Check @unfiltered_specs, not
    # the filtered set, so a dep filtered out by platform/Ruby/prerelease falls
    # through to NoVersions for proper hints instead. The band-scoped
    # self_constraint lets clean sibling versions still resolve via backtracking.
    if @unfiltered_specs[dep_package_name].empty?
      cause = Gem::PubGrub::Incompatibility::InvalidDependency.new(dep_package, dep_constraint)
      self_term = Gem::PubGrub::Term.new(self_constraint, true)
      # PubGrub's default InvalidDependency rendering drops the version
      # requirement ("depends on unknown package bar"). Supply a custom
      # explanation so the missing dependency's constraint is preserved
      # ("depends on bar = 0.5 which could not be found in any repository"),
      # matching Molinillo's diagnostics.
      return [Gem::PubGrub::Incompatibility.new(
        [self_term],
        cause: cause,
        custom_explanation: "#{self_term.to_s(allow_every: true)} depends on #{dep_constraint} which could not be found in any repository"
      )]
    end

    # An empty range means the requirement is self-contradictory (e.g. `> 2, < 1`).
    if dep_constraint.range.empty?
      return [Gem::Resolver::Incompatibility.new(
        [Gem::PubGrub::Term.new(self_constraint, true)],
        cause: Gem::PubGrub::Incompatibility::NoVersions.new(dep_constraint),
        custom_explanation: "#{dep_package_name} cannot satisfy contradictory requirements #{dep_constraint.constraint_string}"
      )]
    end

    Gem::PubGrub::Incompatibility.new(
      [Gem::PubGrub::Term.new(self_constraint, true), Gem::PubGrub::Term.new(dep_constraint, false)],
      cause: :dependency
    )
  end
end