& + '' needs to be wrapped in parentheses

[kaelig]

el {
  @if (& + '' == 'el') {
    content: "It works!";
  }
}

Throws:

invalid selector after '' on line 2 at column 14

See: http://sassmeister.com/gist/f19f7aa4e0fbacde9549

The simplest fix (as suggested by @hugogiraudel) is to wrap & + '' in parenthesis: (& + '').

[KittyGiraudel]

Also commented Gist: http://sassmeister.com/gist/bd0834fdae880f7a65ea.

[xzyfer]

I can see why this fails. The & + '' is an attempt to make Sass coerce the Selector into a String. It would this isn't happening in LibSass.

The reason it works with the () is because it is now a List. The LibSass engine will evaluate the list values individually, the as a list. That second look at the value is likely where we turn it into a string.

[KittyGiraudel]

Of all the possible reasons for this bug, I would not have guessed that. :D

[mgreter]

IMO & doesn't work in this context, since even when inside a list, the expected result is not correct (given the test above). So I think we actually do not handle Parent_Selector correctly in Binary_Operation (which is what if will be using). But that really is just a wild guess ...

debug_ast from Expression* Eval::operator()(Binary_Expression* b)

Binary_Expression 0x2a03d40 (0@[1:8]-[1:9]) [EQ]
 left:  Parent_Selector 0x2f734f0 (0@[1:8]-[1:9]) <>
 left:  ->Selector_List 0x23c8820 (0@[1:9]-[1:10]) [block:0x2fa5df0] [@media:0] - - -
 left:  -> Complex_Selector 0x2a03b90 (0@[1:12]-[1:12]) [block:0x2fa5df0] [weight:100] [@media:0] - - - -> {+} <>
 left:  ->  Compound_Selector 0x2d87490 (0@[1:12]-[1:15]) [block:0x2fa5df0] [weight:0] [@media:0] - - - <>
 left:  ->   Selector_Reference 0x2ce8cb0 (0@[1:12]-[1:15]) @ref 0
 left:  -> -Complex_Selector 0x2a03b00 (0@[1:12]-[1:12]) [block:0x2fa5df0] [weight:100] [@media:0] - - - -> { } <>
 left:  -> - Compound_Selector 0x2d873c0 (0@[1:10]-[1:11]) [block:0x2fa5df0] [weight:100] [@media:0] - - - <>
 left:  -> -  Type_Selector 0x2ce8c30 (0@[1:12]-[1:15]) <<'a'>> - <>
 right: Parent_Selector 0x2f73560 (0@[1:21]-[1:22]) <>
 right: ->Selector_List 0x23c88e0 (0@[1:22]-[1:23]) [block:0x2fa5df0] [@media:0] - - -
 right: -> Complex_Selector 0x2a03cb0 (0@[1:25]-[1:25]) [block:0x2fa5df0] [weight:100] [@media:0] - - - -> {+} <>
 right: ->  Compound_Selector 0x2d87630 (0@[1:25]-[1:31]) [block:0x2fa5df0] [weight:0] [@media:0] - - - <>
 right: ->   Selector_Reference 0x2ce8db0 (0@[1:25]-[1:31]) @ref 0
 right: -> -Complex_Selector 0x2a03c20 (0@[1:25]-[1:25]) [block:0x2fa5df0] [weight:100] [@media:0] - - - -> { } <>
 right: -> - Compound_Selector 0x2d87560 (0@[1:23]-[1:24]) [block:0x2fa5df0] [weight:100] [@media:0] - - - <>
 right: -> -  Type_Selector 0x2ce8d30 (0@[1:25]-[1:31]) <<'aqwe'>> - <>

[xzyfer]

This fix was a false positive due to sass/sass-spec#380. The spec still fails.

[mgreter]

We now have a passing spec test since #1249 was merged 🎈