So in this case, all the requisite codeql suites exist (i.e. ruby-code-scanning.qls, ruby-security-extended.qls, ruby-security-and-quality.qls) but they are empty? Otherwise I would have expected codeql to error trying to resolve the suite, but maybe it doesn't.

Another thing to consider to make the error message better is there's a chunk of code at the end of loadConfig that does

// The list of queries should not be empty for any language. If it is then
// it is a user configuration error.
for (const language of languages) {
  if (
    queries[language] === undefined ||
    (queries[language].builtin.length === 0 &&
      queries[language].custom.length === 0)
  ) {
    throw new Error(
      `Did not detect any queries to run for ${language}. ` +
        "Please make sure that the default queries are enabled, or you are specifying queries to run."
    );
  }
}

If you move that to initConfig so it runs when using the default config too then it'll give you a friendly error message quicker before it tries to build any code or run any queries.

So in this case, all the requisite codeql suites exist (i.e. ruby-code-scanning.qls, ruby-security-extended.qls, ruby-security-and-quality.qls) but they are empty?

@robertbrignull Exactly. We don't have any queries yet that match the default query selectors.

@robertbrignull Thanks for the quick review. I addressed your comments.