// WriteGoSum writes the go.sum file if it needs to be updated.
//
// keep is used to check whether a newly added sum should be saved in go.sum.
// It should have entries for both module content sums and go.mod sums
// (version ends with "/go.mod"). Existing sums will be preserved unless they
// have been marked for deletion with TrimGoSum.

func commitRequirements(ctx context.Context, opts WriteOpts) (err error) {
	if inWorkspaceMode() {
		// go.mod files aren't updated in workspace mode, but we still want to
		// update the go.work.sum file.
		return modfetch.WriteGoSum(ctx, keepSums(ctx, loaded, requirements, addBuildListZipSums), mustHaveCompleteRequirements())
	}
	_, updatedGoMod, modFile, err := UpdateGoModFromReqs(ctx, opts)
	if err != nil {
		if errors.Is(err, errNoChange) {

			// commitRequirements below will also call WriteGoSum, but the "keep" map
			// we have here could be strictly larger: commitRequirements only commits
			// loaded.requirements, but here we may have also loaded (and want to
			// preserve checksums for) additional entities from compatRS, which are
			// only needed for compatibility with ld.TidyCompatibleVersion.
			if err := modfetch.WriteGoSum(ctx, keep, mustHaveCompleteRequirements()); err != nil {