ruby/rubygems · error · Gem::Ext::CargoBuilder::DylibNotFoundError

Dynamic library not found for Rust extension (in #{dir}) Ma

Error message

Dynamic library not found for Rust extension (in #{dir})

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

Found files:
#{files}

What it means

Error "Dynamic library not found for Rust extension (in #{dir}) Make sure you set "crate-type" in Cargo.toml to "cdylib" Found files: #{files}" thrown in ruby/rubygems.

Source

Thrown at lib/rubygems/ext/cargo_builder.rb:43

    # Where's the Cargo.toml of the crate we're building
    cargo_toml = File.join(cargo_dir, "Cargo.toml")
    # What's the crate's name
    crate_name = cargo_crate_name(cargo_dir, cargo_toml, results)

    begin
      # Create a tmp dir to do the build in
      tmp_dest = Dir.mktmpdir(".gem.", cargo_dir)

      # Run the build
      cmd = cargo_command(cargo_toml, tmp_dest, args, crate_name)
      runner.call(cmd, results, "cargo", cargo_dir, build_env)

      # Where do we expect Cargo to write the compiled library
      dylib_path = cargo_dylib_path(tmp_dest, crate_name)

      # Helpful error if we didn't find the compiled library
      raise DylibNotFoundError, tmp_dest unless File.exist?(dylib_path)

      # Cargo and Ruby differ on how the library should be named, rename from
      # what Cargo outputs to what Ruby expects
      dlext_name = "#{crate_name}.#{makefile_config("DLEXT")}"
      dlext_path = File.join(File.dirname(dylib_path), dlext_name)
      FileUtils.cp(dylib_path, dlext_path)

      nesting = extension_nesting(extension)

      if Gem.install_extension_in_lib && lib_dir
        nested_lib_dir = File.join(lib_dir, nesting)
        FileUtils.mkdir_p nested_lib_dir
        FileUtils.cp_r dlext_path, nested_lib_dir, remove_destination: true
      end

      # move to final destination
      nested_dest_path = File.join(dest_path, nesting)
      FileUtils.mkdir_p nested_dest_path

View on GitHub (pinned to 86cbb817a3)

When it happens

Trigger: Thrown at lib/rubygems/ext/cargo_builder.rb:43 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/9d6a5c227eecb8eb. Report an issue: GitHub.