func findFunction(name string, tmpl *Template) (v reflect.Value, isBuiltin, ok bool) {
	if tmpl != nil && tmpl.common != nil {
		tmpl.muFuncs.RLock()
		defer tmpl.muFuncs.RUnlock()
		if fn := tmpl.execFuncs[name]; fn.IsValid() {
			return fn, false, true
		}
	}
	if fn := builtinFuncs()[name]; fn.IsValid() {
		return fn, true, true
	}
	return reflect.Value{}, false, false
}