Unintentional "Variable Definition Interpolation" with "Property Interpolation" syntax.

[seven-phases-max]

As revealed in #2132, Property Interpolation syntax can be used to define variables too (if the interpolation statement is wrapped into a mixin):

.mixin() {
    @name: ~"@whatever";
    @{name}: red;
}

div {
   .mixin();
    color: @whatever;
}

compiles to

div {
  color: red;
}

The problem is that this was not really intended to work at all so probably this should somehow throw a error, at least by now. We did not consider this "feature" at all and all potential side-effects and conflicts with other features (scope, lazy-loading, LDW) it may have.