&:extend Interpolated Selectors Not Working

[srsgores]

Using less-1.5.1, the it appears that LESS is unable to extend interpolated selectors, or generated mixins. The following will not work as expected:

@delay-increment: 0.3s;
@delay-maximum: 10;

/* Animation mixin */
#animation {
    .animation-delay(...) {
        -webkit-animation-delay: @arguments;
        -moz-animation-delay: @arguments;
        -o-animation-delay: @arguments;
        -ms-animation-delay: @arguments;
        animation-delay: @arguments;
    }
}

/* Animation Delays */
.delays(@index) when (@index > 0) {
    .delayed-@{index} {
        @time: @index * @delay-increment;
        #animation > .animation-delay(@time);
    }
    .delays(@index - 1);
}
.delays(0) {}
.delays(@delay-maximum);

.container {
    &:extend(.delayed-2);
}

It will yield only the generated delayed classes:

/* Animation Delays */
.delayed-10 {
    -webkit-animation-delay: 5s;
    -moz-animation-delay: 5s;
    -o-animation-delay: 5s;
    -ms-animation-delay: 5s;
    animation-delay: 5s;
}
//all the way to 1 -- nothing is extended

It's as if the generated class doesn't exist. And as you'd expect, doing delayed-2 results in .delayed-2 is undefined.

Thanks in advance for fixing.

[seven-phases-max]

Duplicate of #1325 (also see #1485, #1597 and all crosslinks there). Those issues may differ in details but in general they all are about the same: "Extend dynamically generated classes".

And as you'd expect, doing delayed-2 results in .delayed-2 is undefined.

This is another feature: #1196 (already implemented in the master).

[seven-phases-max]

Also not denying the importance of #1325, I feel like I need to express an opinion on your aproach for the particular use-case. You pregenerate ~30 CSS classes with 5 properties in each -> 150 CSS properties that may never be used, are you sure this is optimal? (Actually #1177 + (optionally) a tool like autoprefixer would be much better solution for this use-case).

[srsgores]

@seven-phases-max, that's why I use @import (reference), which was introduced in 1.5. Only when you extend, does the code appear.

[seven-phases-max]

@srsgores I see, still #1177 (provided it is implemented with > 0-parameter mixin support) would be better way to do it than #1325 on top of @import(reference). Especially taking into account that the first may have natural extend(.delay(.6s)) syntax while the latter has meaningless extend(.delay-2) (I'm just trying to weight which one would be more rational to upvote :)