if err != nil {
		return nil, err
	}

	// In parallel, execute the DAG of analyzers.
	var exec func(a *analysis.Analyzer) *action
	var execAll func(analyzers []*analysis.Analyzer)
	exec = func(a *analysis.Analyzer) *action {
		act := actions[a]
		act.once.Do(func() {
			execAll(a.Requires) // prefetch dependencies in parallel

			// The inputs to this analysis are the
			// results of its prerequisites.