}
		mod = r
	}

	if mustHaveSums() && !modfetch.HaveSum(mod) {
		return "", false, module.VersionError(mod, &sumMissingError{})
	}

	dir, err = modfetch.Download(ctx, mod)
	return dir, false, err
}

// mustHaveSums reports whether we require that all checksums
// needed to load or build packages are already present in the go.sum file.
func mustHaveSums() bool {

	completeFromModCache := func(m *modinfo.ModulePublic) {
		if gover.IsToolchain(m.Path) {
			return
		}

		checksumOk := func(suffix string) bool {
			return rs == nil || m.Version == "" || !mustHaveSums() ||
				modfetch.HaveSum(module.Version{Path: m.Path, Version: m.Version + suffix})
		}

		mod := module.Version{Path: m.Path, Version: m.Version}

		if m.Version != "" {

		// so assume that it requires everything.
		summary.require = vendorList
		return summary, nil
	}

	actual := resolveReplacement(m)
	if mustHaveSums() && actual.Version != "" {
		key := module.Version{Path: actual.Path, Version: actual.Version + "/go.mod"}
		if !modfetch.HaveSum(key) {