Interpolated selectors list with nested selectors

[steven-pribilinskiy]

Source:

@c: .a, .b;

@{c} {
  &,
  & p {
    prop: value;
  }
}

Should be the same as if we would write:

.a, .b {
  &,
  & p {
    prop: value;
  }
}

But...

Compiled:

.a, .b,
.a, .b p {
  prop: value;
}

Expected:

.a,
.b,
.a p,
.b p {
  prop: value;
}

[seven-phases-max]

See #1421.

[seven-phases-max]

Closing as duplicate of #1421.