:extend doesn't work with nested blocks

[tomek-he-him]

.mother {
  parent: rules;

  .child {
    child: rules;
  }
}

.father {
  &:extend(.mother);
}

This outputs:

.mother,
.father {
  parent: rules;
}
.mother .child {
  child: rules;
}

I'd rather expect:

.mother,
.father {
  parent: rules;
}
.mother .child,
.father .child {
  child: rules;
}

Criticism welcome :)

[seven-phases-max]

This is expected behaviour (this is just how it was implemented initially). For possible extend extensions/improvements see #2101 (we can't just change how naked extend works now because there's already a lot of code out relying on that).

[seven-phases-max]

Closing as duplicate of #2101.