go/src/cmd/go/internal/modload/mvs.go

// cmpVersion implements the comparison for versions in the module loader.
//
// It is consistent with gover.ModCompare except that as a special case,
// the version "" is considered higher than all other versions.
// The main module (also known as the target) has no version and must be chosen
// over other versions of the same module in the module dependency graph.
func cmpVersion(p string, v1, v2 string) int { … }

type mvsReqs …

func (r *mvsReqs) Required(mod module.Version) ([]module.Version, error) { … }

// Max returns the maximum of v1 and v2 according to gover.ModCompare.
//
// As a special case, the version "" is considered higher than all other
// versions. The main module (also known as the target) has no version and must
// be chosen over other versions of the same module in the module dependency
// graph.
func (*mvsReqs) Max(p, v1, v2 string) string { … }

// Upgrade is a no-op, here to implement mvs.Reqs.
// The upgrade logic for go get -u is in ../modget/get.go.
func (*mvsReqs) Upgrade(m module.Version) (module.Version, error) { … }

func versions(ctx context.Context, path string, allowed AllowedFunc) (versions []string, origin *codehost.Origin, err error) { … }

// previousVersion returns the tagged version of m.Path immediately prior to
// m.Version, or version "none" if no prior version is tagged.
//
// Since the version of a main module is not found in the version list,
// it has no previous version.
func previousVersion(ctx context.Context, m module.Version) (module.Version, error) { … }

func (*mvsReqs) Previous(m module.Version) (module.Version, error) { … }