Nested elements with attributes containing commas injects parent selector

[IdkGoodName]

I haven't really found any issue related to this, so I am sorry if it already has been submitted, but it's just something that I discovered while using Stylus for one of my projects.

When you have a selector and nest a child to it containing an attribute with a value containing comma, Stylus injects the parent selector after the comma.

To reproduce:

.a
    &[b="c, d"]
        color: red

Current behavior:

The parent selector gets injected after the comma in the attribute's value.
Output from the "To reproduce" section:

.a[b="c,.a d"] {
    color: red;
}

Expected behavior:

The attribute's value not getting touched at all, even the whitespace after the comma not being removed. Expected output:

.a[b="c, d"] {
    color: red;
}

Environment information:

• stylus version: 0.56.0
• nodejs version: 17.3.0