Never output empty blocks

[xzyfer]

Under some circumstances Libsass will output blocks (selectors) without any declarations i.e.

.my-selector {

}

Specs added sass/sass-spec#199

[KittyGiraudel]

Do you have any hint about when LibSass happens to behave like this?

[xzyfer]

In Ruby sass, when a declaration's value is evaluated to null the declaration is not outputted. Libsass follows this behaviour. However when that behaviour produces an empty block, the block is still incorrectly outputted.

Compare these to Ruby Sass:
http://sassmeister.com/gist/40b92fb0a73177ac383b
http://sassmeister.com/gist/9788dfaf2fba2a7428bd

[lunelson]

I made a test for this—note however, that actually writing null directly in to a declaration still outputs. For this test I had to create a function that returns null, rather than the following which was my first try (however this is an unlikely edge case).

input:

.test {
  out: null;
}

output:

.test {
  out: null; }

[KittyGiraudel]

This is actually an intended behaviour from Sass. As far as I know, to speed up compilation times Sass does not evaluate all CSS values. It does some kind of quick match to see whether a value should be evaluated as SassScript or not.

While this behaviour leads to an issue where you can actually output prop: null if you explicitly write null as a CSS value, this scenario is very unlikely.

Anyway, this explains the need for a function. If you want to avoid having to declare a function/mixin for this, you can simply wrap null in braces to force Sass to evaluate it:

foo {
  bar: (null);
}

[lunelson]

Thanks @hugogiraudel that's what I figured ;)

[xzyfer]

As far as I know, to speed up compilation times Sass does not evaluate all CSS values. It does some kind of quick match to see whether a value should be evaluated as SassScript or not.

@hugogiraudel is correct. I recently added this is the same smarts to Libsass.

For this test I had to create a function that returns null

Both functions that return null and variables with the null value should have this behavior.