Example of a hook for vcs_info for optionally displaying the git revision

vcs_info-hook-optional-rev

# Toggle this to test the hook
zstyle ':vcs_info:git:*' get-revision true

# basic 'formats' config: (git)[hash] branch
zstyle ':vcs_info:git*' formats "(%s)%i %b"

# Register new hook
zstyle ':vcs_info:git*+set-message:*' hooks git-optional-rev

# Define new hook
function +vi-git-optional-rev() {
    # If revision is a non-empty string, rewrite it with a preceeding space.
    if [[ -n "${hook_com[revision]}" ]]; then
        hook_com[revision]=" ${hook_com[revision]}"
    fi
}