如何在不重复选择器的情况下为具有不同祖先的后代编写Sass？

.parent {
  color: blue;

  .child {
    font-weight: bold;
    &:hover {
      color: red;
    }
  }
}

.parent {
  color: blue;
}
.parent .child {
  font-weight: bold;
}
.parent .child:hover {
  color: red;
}

.parent {
  color: blue;

  @at-root .child {
    font-weight: bold;
  }
}

.parent {
  color: blue;
}
.child {
  font-weight: bold;
}

.parent {
  color: blue;
}

.child {
  @extend .parent;
  font-weight: bold;
}

.parent, .child {
  color: blue;
}

.child {
  font-weight: bold;
}