fix(git_branch): Make Git branch module support bare repositories (#2522)

Co-authored-by: Kim Christensen <KMCH@simcorp.com>

src/modules/git_branch.rs

@@ -27,12 +27,13 @@ pub fn module<'a>(context: &'a Context) -> Option<Module<'a>> {
 
     let repo = context.get_repo().ok()?;
 
-    let repo_root = repo.root.as_ref()?;
-    let git_repo = Repository::open(repo_root).ok()?;
-    let is_detached = git_repo.head_detached().ok()?;
-    if config.only_attached && is_detached {
-        return None;
-    };
+    if let Some(repo_root) = repo.root.as_ref() {
+        let git_repo = Repository::open(repo_root).ok()?;
+        let is_detached = git_repo.head_detached().ok()?;
+        if config.only_attached && is_detached {
+            return None;
+        }
+    }
 
     let branch_name = repo.branch.as_ref()?;
     let mut graphemes: Vec<&str> = branch_name.graphemes(true).collect();
@@ -343,6 +344,33 @@ mod tests {
         repo_dir.close()
     }
 
+    #[test]
+    fn test_works_in_bare_repo() -> io::Result<()> {
+        let repo_dir = tempfile::tempdir()?;
+
+        Command::new("git")
+            .args(&["init", "--bare"])
+            .current_dir(&repo_dir)
+            .output()?;
+
+        Command::new("git")
+            .args(&["symbolic-ref", "HEAD", "refs/heads/main"])
+            .current_dir(&repo_dir)
+            .output()?;
+
+        let actual = ModuleRenderer::new("git_branch")
+            .path(&repo_dir.path())
+            .collect();
+
+        let expected = Some(format!(
+            "on {} ",
+            Color::Purple.bold().paint(format!("\u{e0a0} {}", "main")),
+        ));
+
+        assert_eq!(expected, actual);
+        repo_dir.close()
+    }
+
     // This test is not possible until we switch to `git status --porcelain`
     // where we can mock the env for the specific git process. This is because
     // git2 does not care about our mocking and when we set the real `GIT_DIR`