ruby/rubygems · error · Gem::InstallError

extension outside of gem root

Error message

extension outside of gem root

What it means

Error "extension outside of gem root" thrown in ruby/rubygems.

Source

Thrown at lib/rubygems/ext/cargo_builder.rb:110

    cmd += [*cargo_rustc_args(dest_path, crate_name)]
    cmd
  end

  private

  def cargo
    ENV.fetch("CARGO", "cargo")
  end

  # returns the directory nesting of the extension, ignoring the first part, so
  # "ext/foo/bar/Cargo.toml" becomes "foo/bar"
  def extension_nesting(extension)
    parts = extension.to_s.split(Regexp.union([File::SEPARATOR, File::ALT_SEPARATOR].compact))

    parts = parts.each_with_object([]) do |segment, final|
      next if segment == "."
      if segment == ".."
        raise Gem::InstallError, "extension outside of gem root" if final.empty?
        next final.pop
      end
      final << segment
    end

    File.join(parts[1...-1])
  end

  def rb_config_env
    result = {}
    RbConfig::CONFIG.each {|k, v| result["RBCONFIG_#{k}"] = v }
    result
  end

  def cargo_rustc_args(dest_dir, crate_name)
    [
      *linker_args,
      *mkmf_libpath,

View on GitHub (pinned to 86cbb817a3)

When it happens

Trigger: Thrown at lib/rubygems/ext/cargo_builder.rb:110 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of ruby/rubygems@86cbb817a3 (2026-08-23). Data as JSON: /api/errors/2308aa88d41b7f9a. Report an issue: GitHub.