Its an autotoolsism, use "1" for true but "false" for, well false, and older mesons accepted it, but modern meson doesn't, at least https://github.com/geany/geany/blob/0fd68e4182bf2540249810da52382e2f1c4810aa... and https://github.com/geany/geany/blob/0fd68e4182bf2540249810da52382e2f1c4810aa...