message: Error when the absence of any crates with files
diff: @@ -20,7 +20,10 @@ pub fn doc(ws: &Workspace<'_>, options: &DocOptions) -> CargoResult<()> {
  let compilation = ops::compile(ws, &options.compile_opts)?;
  if options.open_result {
  - let name = &compilation.root_crate_names[0];
  + let name = &compilation
  + .root_crate_names
  + .get(0)
  + .ok_or_else(|| anyhow::anyhow!("no crates with documentation"))?;
  let kind = options.compile_opts.build_config.single_requested_kind()?;
  let path = compilation.root_output[&kind]
  .with_file_name("doc")
  