func addUpdate(ctx context.Context, m *modinfo.ModulePublic) {
	if m.Version == "" {
		return
	}

	info, err := Query(ctx, m.Path, "upgrade", m.Version, CheckAllowed)
	var noVersionErr *NoMatchingVersionError
	if errors.Is(err, ErrDisallowed) ||
		errors.Is(err, fs.ErrNotExist) ||
		errors.As(err, &noVersionErr) {
		// Ignore "not found" and "no matching version" errors.

		// dependencies, so they cannot be pruned out.
		return unpruned
	}
	return pruned
}

// CheckAllowed returns an error equivalent to ErrDisallowed if m is excluded by
// the main module's go.mod or retracted by its author. Most version queries use
// this to filter out versions that should not be used.
func CheckAllowed(ctx context.Context, m module.Version) error {
	if err := CheckExclusions(ctx, m); err != nil {
		return err

	modload.ForceUseModules = true
	modload.RootMode = modload.NoRoot
	modload.Init()
	defer modload.Reset()

	// See internal/load.PackagesAndErrorsOutsideModule
	ctx := context.Background()
	allowed := modload.CheckAllowed
	if modload.IsRevisionQuery(path, version) {
		// Don't check for retractions if a specific revision is requested.
		allowed = nil
	}
	noneSelected := func(path string) (version string) { return "none" }

	mg, err := rs.Graph(ctx)
	if err != nil {
		return module.Version{}, err
	}

	candidates, err := QueryPackages(ctx, path, "latest", mg.Selected, CheckAllowed)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			// Return "cannot find module providing package […]" instead of whatever
			// low-level error QueryPattern produced.