Gem::Installer#installed_specs

# File tmp/rubies/ruby-3.4.1/lib/rubygems/installer.rb, line 376
def installed_specs
  @installed_specs ||= begin
    specs = []

    Gem::Util.glob_files_in_dir("*.gemspec", File.join(gem_home, "specifications")).each do |path|
      spec = Gem::Specification.load path
      specs << spec if spec
    end

    specs
  end
end