vj, fj = vj[:k], vj[k:]
		}
		if vi != vj {
			return ModCompare(mi.Path, vi, vj) < 0
		}
		return fi < fj
	})
}

// ModIsValid reports whether vers is a valid version syntax for the module with the given path.
func ModIsValid(path, vers string) bool {
	if IsToolchain(path) {
		if path == "toolchain" {
			return IsValid(FromToolchain(vers))
		}
		return IsValid(vers)
	}

	{"rsc.io/quote", "v1.2", "v1.3", -1},
	{"rsc.io/quote", "1.2", "1.3", 0}, // equal because invalid
}

func TestModIsValid(t *testing.T) { test2(t, modIsValidTests, "ModIsValid", ModIsValid) }

var modIsValidTests = []testCase2[string, string, bool]{
	{"go", "1.2", true},
	{"go", "v1.2", false},
	{"toolchain", "go1.2", true},
	{"toolchain", "v1.2", false},
	{"rsc.io/quote", "v1.2", true},

	if gover.IsToolchain(m.Path) {
		return "", ErrToolchain
	}
	dir, err := cacheDir(ctx, m.Path)
	if err != nil {
		return "", err
	}
	if !gover.ModIsValid(m.Path, m.Version) {
		return "", fmt.Errorf("non-semver module version %q", m.Version)
	}
	if module.CanonicalVersion(m.Version) != m.Version {
		return "", fmt.Errorf("non-canonical module version %q", m.Version)
	}

	case strings.HasPrefix(query, "<"):
		v := query[len("<"):]
		if !gover.ModIsValid(path, v) {
			return badVersion(v)
		}
		qm.filter = func(mv string) bool { return gover.ModCompare(qm.path, mv, v) < 0 }
		if !matchesMajor(v) {
			qm.preferIncompatible = true
		}

	case strings.HasPrefix(query, ">="):
		v := query[len(">="):]
		if !gover.ModIsValid(path, v) {
			return badVersion(v)
		}

		} else {
			data, err = lockedfile.Read(gomodActual)
		}
		if err != nil {
			return "", nil, module.VersionError(m, fmt.Errorf("reading %s: %v", base.ShortPath(name), err))
		}
	} else {
		if !gover.ModIsValid(m.Path, m.Version) {
			// Disallow the broader queries supported by fetch.Lookup.
			base.Fatalf("go: internal error: %s@%s: unexpected invalid semantic version", m.Path, m.Version)
		}
		name = "go.mod"