# File ruby/lib/rubygems/ext/cargo_builder.rb, line 332
    def initialize(dir)
      files = Dir.glob(File.join(dir, "**", "*")).map {|f| "- #{f}" }.join "\n"

      super <<~MSG
        Dynamic library not found for Rust extension (in #{dir})

        Make sure you set "crate-type" in Cargo.toml to "cdylib"

        Found files:
        #{files}
      MSG
    end