Implement a fallback.

modules/git/git.go

@@ -20,9 +20,38 @@ func GetCurrentBranchName(t testing.TestingT) string {
 
 // GetCurrentBranchNameE retrieves the current branch name or
 // empty string in case of detached state.
+// Uses branch --show-current, which was introduced in git v2.22.
+// Falls back to rev-parse for users of the older version, like Ubuntu 18.04.
 func GetCurrentBranchNameE(t testing.TestingT) (string, error) {
 	cmd := exec.Command("git", "branch", "--show-current")
 	bytes, err := cmd.Output()
+	if err != nil {
+		cmd := exec.Command("git", "rev-parse", "--abbrev-ref", "HEAD")
+		bytes, err := cmd.Output()
+		if err != nil {
+			return "", err
+		}
+		name := strings.TrimSpace(string(bytes))
+		if name == "HEAD" {
+			return "", nil
+		}
+
+		return name, nil
+	}
+
+	name := strings.TrimSpace(string(bytes))
+	if name == "HEAD" {
+		return "", nil
+	}
+
+	return name, nil
+}
+
+// GetCurrentBranchNameOldE retrieves the current branch name or
+// empty string in case of detached state.
+func GetCurrentBranchNameOldE(t testing.TestingT) (string, error) {
+	cmd := exec.Command("git", "rev-parse", "--abbrev-ref", "HEAD")
+	bytes, err := cmd.Output()
 	if err != nil {
 		return "", err
 	}