null / "" are not mapped to false / true correctly?

[ascheman]

Having an issue (asciidoctor/asciidoctor-maven-plugin#288) with building slides from asciidoc with the Maven plugin, @mojavelinux pointed out that the plugin mapping of boolean values is correct but values are not mapped correctly by the reveal converter:

E.g., setting

<revealjs_controls>true</revealjs_controls>

leads to

Reveal.initialize({
  // Display controls in the bottom right corner
  controls: ,

making JS complain about the , instead of an expected value of true or false.

This results in an empty slide show.

[mojavelinux]

The correct way to emit these values is as follows:

#{(attr 'revealjs_controls', '') ? true : false}

or

#{!!(attr 'revealjs_controls', '')}

(!! coerces the value to a boolean)

That way, the expression emits "true" if the attribute has a value (even if that value is empty string) and "false" if the value is nil or the attribute is not set.

[mojavelinux]

(we don't have to worry about converting the boolean to a string since the interpolation already takes care of that for us).

[mojavelinux]

This also shields us from being hit by other bogus values for these attributes.

[mojavelinux]

Actually, because we use default values, this isn't going to work since there's no way in what I proposed to set a false value.

That means we need the following:

#{(attr 'revealjs_controls', '') != 'false'}

[mojavelinux]

Default values for attributes are still a bit rocky in Asciidoctor, which is what is making this so difficult. There's also the legacy that true values are empty string. We're just jammed between a rock and a hard place on this one...so we have to do some extra work.

[obilodeau]

I don't understand what causes the issue. Can someone provide a simple example without the maven part?

[mojavelinux]

In AsciiDoc, empty string represents a "true" value. However, we are passing this value through "as is", thus causing the Reveal.js configuration to look like:

Reveal.initialize({
  // Display controls in the bottom right corner
  controls: ,

Instead, we should coerce the value to a boolean using a helper function. I've proposed a PR. See #126.

Here's how we now map the values:

true => true
false => false
nil => false
'true' => true
'false' => false
1 => true
0 => false
'1' => true
'0' => false

(technically, any other value is true).

[obilodeau]

Fixed pushed in master. Let me know if a release would simplify your workflow. I can make one.

[ascheman]

Thanks so far, can wait for the next release ...