2619.1.less

// usage:

.button {
    .lib.button(A);
}

.button {
    .lib.button(--compact, B);
}

// impl:

.lib {

    .button(@subclass, @x) {
        &@{subclass}          {style: @x}
        &@{subclass} > &-text {text-style: @x}
    }
    
    // a syntactic-sugar for the empty subclass.
    // *if* there're some optional args in the base mixin you'll
    // need some condition here or there like `iskeyword(@subclass)` or so:
    .button(@x) {.lib.button(~'', @x)}
}