fix: return minimum version from module

When versioning a go module with no matching major version tags,
gotagger should return vX.0.0, where X is the major version of the
module.

Fixes #211

gotagger.go

@@ -358,15 +358,19 @@ func (g *Gotagger) latestModule(tags []string, m module) (*semver.Version, strin
 
 	majorVersion := strings.TrimPrefix(versionRegex.FindString(m.name), goModSep)
 	if majorVersion == "" {
-		majorVersion = "v1"
+		majorVersion = "v0"
 	}
 
 	moduleVersion, err := semver.NewVersion(majorVersion + ".0.0")
 	if err != nil {
 		return nil, "", err
 	}
 
-	maximumVersion := moduleVersion.IncMajor()
+	_maximumVersion := moduleVersion.IncMajor()
+	if majorVersion == "v0" {
+		_maximumVersion = _maximumVersion.IncMajor()
+	}
+	maximumVersion := &_maximumVersion
 	logger.Info("ignoring modules greater than " + g.Config.VersionPrefix + maximumVersion.String())
 
 	var latestVersion *semver.Version
@@ -375,7 +379,11 @@ func (g *Gotagger) latestModule(tags []string, m module) (*semver.Version, strin
 		// strip the module prefix from the tag so we can parse it as a semver
 		tagName := strings.TrimPrefix(tag, m.prefix)
 		// we want the highest version that is less than the next major version
-		if tver, err := semver.NewVersion(tagName); err == nil && tver.LessThan(&maximumVersion) {
+		tver, err := semver.NewVersion(tagName)
+		if err != nil {
+			continue
+		}
+		if tver.Compare(maximumVersion) < 0 && tver.Compare(moduleVersion) >= 0 {
 			if latestVersion == nil || latestVersion.LessThan(tver) {
 				logger.Info("found newer tag", "tag", tag)
 				latestVersion = tver
@@ -384,9 +392,9 @@ func (g *Gotagger) latestModule(tags []string, m module) (*semver.Version, strin
 		}
 	}
 
-	// if there were no tags, then return 0.0.0
+	// if there were no tags, then return the base module version
 	if latestVersion == nil {
-		return semver.MustParse("0.0.0"), "", nil
+		return moduleVersion, "", nil
 	}
 
 	hash, err := g.repo.RevParse(latestTag + "^{commit}")

gotagger_test.go

@@ -44,6 +44,12 @@ func TestGotagger_latestModule(t *testing.T) {
 			repoFunc: simpleGoRepo,
 			want:     "v0.1.0",
 		},
+		{
+			title:    "new v2 module",
+			module:   module{".", "foo/v2", ""},
+			repoFunc: newV2Module,
+			want:     "v2.0.0",
+		},
 		{
 			title:    "latest foo v1 directory",
 			module:   module{".", "foo", ""},
@@ -72,7 +78,7 @@ func TestGotagger_latestModule(t *testing.T) {
 			title:    "breaking change in v1 module",
 			module:   module{".", "foo/v2", ""},
 			repoFunc: untaggedV2Repo,
-			want:     "v1.0.0",
+			want:     "v2.0.0",
 		},
 	}
 
@@ -1703,6 +1709,13 @@ func mixedTagGoRepo(t testutils.T, repo *sgit.Repository, path string) {
 	testutils.CommitFile(t, repo, path, "go.mod", "feat: add go.mod", []byte("module foo\n"))
 }
 
+func newV2Module(t testutils.T, repo *sgit.Repository, path string) {
+	t.Helper()
+
+	// create top-level go.mod with v2 module
+	testutils.CommitFile(t, repo, path, "go.mod", "feat: add go.mod", []byte("module foo/v2\n"))
+}
+
 func v2DirGitRepo(t testutils.T, repo *sgit.Repository, path string) {
 	t.Helper()