if v1 == "" {
			return 0
		}
		return -1
	}
	if v1 == "" {
		return 1
	}
	return gover.ModCompare(p, v1, v2)
}

// mvsReqs implements mvs.Reqs for module semantic versions,
// with any exclusions or replacements applied internally.
type mvsReqs struct {
	roots []module.Version
}

func (r *mvsReqs) Required(mod module.Version) ([]module.Version, error) {
	if mod.Version == "" && MainModules.Contains(mod.Path) {

type retraction struct {
	modfile.VersionInterval
	Rationale string
}

// goModSummary returns a summary of the go.mod file for module m,
// taking into account any replacements for m, exclusions of its dependencies,
// and/or vendoring.
//
// m must be a version in the module graph, reachable from the Target module.
// In readonly mode, the go.sum file must contain an entry for m's go.mod file

// Users should prefer 'go get toolchain@version'.
//
// The -exclude=path@version and -dropexclude=path@version flags
// add and drop an exclusion for the given module path and version.
// Note that -exclude=path@version is a no-op if that exclusion already exists.
//
// The -replace=old[@v]=new[@v] flag adds a replacement of the given
// module path and version pair. If the @v in old@v is omitted, a

Users should prefer 'go get toolchain@version'.

The -exclude=path@version and -dropexclude=path@version flags
add and drop an exclusion for the given module path and version.
Note that -exclude=path@version is a no-op if that exclusion already exists.

The -replace=old[@v]=new[@v] flag adds a replacement of the given
module path and version pair. If the @v in old@v is omitted, a