Don't fail version inference if no commits

Fix #112 by falling back to 0.0.0 if no commits exist.

src/main/groovy/org/ajoberstar/gradle/git/release/semver/NearestVersionLocator.groovy

@@ -19,6 +19,7 @@ import com.github.zafarkhaja.semver.Version
 
 import org.ajoberstar.grgit.Commit
 import org.ajoberstar.grgit.Grgit
+import org.ajoberstar.grgit.exception.GrgitException
 
 import org.slf4j.Logger
 import org.slf4j.LoggerFactory
@@ -73,7 +74,14 @@ class NearestVersionLocator {
 	 */
 	NearestVersion locate(Grgit grgit) {
 		logger.debug('Locate beginning on branch: {}', grgit.branch.current.fullName)
-		Commit head = grgit.head()
+
+		Commit head
+		try {
+			head = grgit.head()
+		} catch (GrgitException e) {
+			head = null
+		}
+
 		List versionTags = grgit.tag.list().inject([]) { list, tag ->
 			Version version = TagUtil.parseAsVersion(tag)
 			logger.debug('Tag {} ({}) parsed as {} version.', tag.name, tag.commit.abbreviatedId, version)
@@ -113,10 +121,25 @@ class NearestVersionLocator {
 			a.distance <=> b.distance ?: (a.version <=> b.version) * -1
 		}
 
-		Version anyVersion = any ? any.version : Version.valueOf('0.0.0')
-		Version normalVersion = normal ? normal.version : Version.valueOf('0.0.0')
-		int distanceFromAny = any ? any.distance : grgit.log(includes: [head.id]).size()
-		int distanceFromNormal = normal ? normal.distance : grgit.log(includes: [head.id]).size()
+		Version anyVersion
+		int distanceFromAny
+		if (any) {
+			anyVersion = any.version
+			distanceFromAny = any.distance
+		} else {
+			anyVersion = Version.valueOf('0.0.0')
+			distanceFromAny = head ? grgit.log(includes: [head.id]).size() : 0
+		}
+
+		Version normalVersion
+		int distanceFromNormal
+		if (normal) {
+			normalVersion = normal.version
+			distanceFromNormal = normal.distance
+		} else {
+			normalVersion = Version.valueOf('0.0.0')
+			distanceFromNormal = head ? grgit.log(includes: [head.id]).size() : 0
+		}
 
 		return new NearestVersion(anyVersion, normalVersion, distanceFromAny, distanceFromNormal)
 	}

src/test/groovy/org/ajoberstar/gradle/git/release/semver/NearestVersionLocatorSpec.groovy

@@ -116,6 +116,17 @@ class NearestVersionLocatorSpec extends Specification {
 		'unreachable' | '0.0.0'            | '0.0.0'                     | 2
 	}
 
+	def 'locator returns 0.0.0 when no commits'() {
+		given:
+		repoDir = Files.createTempDirectory('empty-repo').toFile()
+		grgit = Grgit.init(dir: repoDir)
+		expect:
+		def nearest = new NearestVersionLocator().locate(grgit)
+		nearest.any == Version.valueOf('0.0.0')
+		nearest.normal == Version.valueOf('0.0.0')
+		nearest.distanceFromNormal == 0
+	}
+
 	private void commit() {
 		byte[] bytes = new byte[128]
 		random.nextBytes(bytes)