how to get the direct parent in sass interpolation of & - css

Question

Is there a way to use {$} to get the most direct parent?
In the example below '&#{&}' is not working as I expected, I managed to work around it using mixin.
#mixin modifier($modifier, $block: &) {
&#{"."+$block}--#{$modifier} {
#content;
}
}
.namespace{
$button : 'btn';
.#{$button} {
line-height: 1;
#include modifier('big', $button){ // working but not clean
padding-top: 8px;
}
&#{&}--big{ // not working as {&} is interpolated to namespace .btn
padding-top: 12px;
}
}
}
Compiled to:
.namespace .btn {
line-height: 1;
}
.namespace .btn.btn--big {
padding-top: 8px;
}
.namespace .btn.namespace .btn--big {
padding-top: 12px;
}

Answer 1

The construct looks a bit odd to me – but you could do it like:
.namespace {
$class: ".btn";
#{$class} { line-height: 1; }
#{$class}#{$class}--big { padding-top: 8px; }
& #{$class}#{&} #{$class}--big { padding-top: 12px; }
}
...or using selector append
.namespace .btn {
line-height: 1;
#at-root {
#{selector-append(&,".btn")}--big{ padding-top: 8px; }
#{selector-append(&,&)}--big{ padding-top: 12px; }
}
}
both compiling to:
.namespace .btn { line-height: 1; }
.namespace .btn.btn--big { padding-top: 8px; }
.namespace .btn.namespace .btn--big { padding-top: 12px; }