Nesting issues 4.1.0

[woble]

4.1.0 seems to solve most issues, but now something else doesn't work. Unsure if according with spec. It worked prior v3 though.

The following does not compile at all. Using postcss-selector-matches to unfold matches in the example; does not affect the postcss-nesting processing as & + & is expected to work.

li {
    color: cyan;

    /* Basic */
    & + & {
        color: tomato;
    }

    /* Complex */
    &:nth-last-child(n+2):matches(:first-child, :first-child ~ &) {
        color: red;
    }
}

Expected

li {
    color: cyan;
}

li + li {
    color: tomato;
}

li:nth-last-child(n+2):first-child,
li:nth-last-child(n+2):first-child ~ li {
    color: red;
}

[Jonathan Neal]

This is on purpose, as & does not merely represent string concatenation. See this comment from the author of the spec: #17 (comment)

[Huáng Jùnliàng]

& + & is not invalid but meaningless according to the author (#17 (comment)). The idea is that & is not a selector but the element itself.

This opens to a case where

ol {
    @nest &.li + &.li {
        margin-top: 5px;
    }
}

should be valid as well as meaningful according to the spec. But as the author said (#17 (comment)), it is relatively rare and polyfilling this would need greater even expensive efforts, so we simply reject multiple & occurence in a complex selector.