Check if a tag or branch is checked out by Antora

build.gradle

@@ -33,10 +33,13 @@ buildscript {
 // TODO: remove these hacks once jgit supports worktrees (nebula upgrades) and/or Antora supports full-clone
 if (project.hasProperty('antora')) {
 	'git fetch --unshallow --all --tags'.execute().text // Antora shallow-clones so there is no history (we need commit history to find the last tag in the tree)
-	String tag = 'git tag --points-at HEAD'.execute().text.trim() // jgit does not able to figure out tags in Antora's worktree
-	if (tag) {
-		println "Found release tag: $tag, using it as release.version"
-		ext['release.version'] = tag.substring(1)
+	String ref = 'git rev-parse --abbrev-ref HEAD'.execute().text.trim()
+	if (ref == 'HEAD') { // if Antora checks out a tag instead of a branch
+		String tag = 'git tag --points-at HEAD'.execute().text.trim() // jgit is not able to figure out tags in Antora's worktree
+		if (tag) {
+			println "Found release tag: $tag, using it as release.version"
+			ext['release.version'] = tag.substring(1)
+		}
 	}
 	// We need to tell the location of the .git folder since jgit does not support worktrees
 	ext['git.root'] = 'git rev-parse --path-format=absolute --git-common-dir'.execute().text.trim()