No error reported when @extend fails and the extender contains certain combinators

[andrew-skybound]

I believe this should be an error, since the !optional flag is not specified here and no rules are actually being extended. The a > b.foo rule cannot be extended by c > .bar because a is not mergeable (wrong word?) with c.

It's worth noting that the same problem occurs—no error is reported—when the + combinator is used in place of the >.

Input SASS:

a > b.foo {a: b}
c > .bar {@extend .foo}

Output CSS (should just be an error):

a > b.foo {
  a: b;
}

[davidkpiano]

This looks correct. In Sass, selector unification is ignored for selectors that are impossible to unify, such as a > b.foo and c > .bar.

[andrew-skybound]

It seems to me that the fact that it's ignoring the selector is precisely the problem. This is an error:

a > b.foo {a: b}
a > c.bar {@extend .foo}

Sass::SyntaxError: "a > c.bar" failed to @extend ".foo".
No selectors matching ".foo" could be unified with "a > c.bar".

Why is my first example above not an error, when this one is?

[chriseppstein]

This should be an error.

[nex3]

We decided to make this category of things no longer be an error. See #2250.