Extending self can lead to non-semanticly different output

[mgreter]

.foo[disabled] {
    @extend .foo;
    background: blue;
}
.bar[disabled] {
  foo {
    @extend .bar;
    background: blue;
  }
}
foo {
  .baz[disabled] {
    @extend .baz;
    background: blue;
  }
}

ruby sass:

.foo[disabled] { background: blue; }
.bar[disabled] foo { background: blue; }
foo [disabled].baz { background: blue; }

libsass with #2052

[disabled].foo { background: blue; }
.bar[disabled] foo { background: blue; }
foo [disabled].baz { background: blue; }

//CC @chriseppstein any idea why ruby sass differs in .bar[disabled] vs [disabled].baz?

[chriseppstein]

@mgreter I'm no expert in the extend code. But it seems like this is the reason:
https://github.com/sass/sass/blob/stable/lib/sass/selector/simple_sequence.rb#L193-L195

This is a non-semantic difference in a corner case where the @extend is pointless (it's extending itself). I wouldn't even bother to write a test for this. Just whistle and walk away.

[xzyfer]

Rescoping this to 3.4.1 since it shouldn't block 3.4.0.