Constant elementalist::app_info::built_info::GIT_HEAD_REF

pub const GIT_HEAD_REF: Option<&str>;

If the crate was compiled from within a git-repository, GIT_HEAD_REF contains full name to the reference pointed to by HEAD (e.g.: refs/heads/master). If HEAD is detached or the branch name is not valid UTF-8 None will be stored.