Documentation for `if` has innacurate/incomplete edge cases

[ismael-miguel]

Currently, there's the following list of edge cases, on https://twig.symfony.com/doc/2.x/tags/if.html

This is innacurate/incomplete, as these edge cases have edge cases.

These are my findings:

• empty string: false
• numeric zero: false
• whitespace-only string: false?
  Running echo !!' '; shows 1
  Running echo ' ' == 0; shows 1
  Running echo ' ' == '0'; doesn't display anything
  The whitespace-only string (or any string) will be casted to a number when compared for equality with a number. Otherwise, everything is casted to a string.
• empty array: false
  Everything is casted to an array when comparing to an empty array, except boolean values. In that case, the empty array is casted to the boolean value (false)
• null: false
  Null is a special value. Null will cast to a string when comparing with a string, to a number when comparing to a number but won't be cast to an empty array when comparing to an empty array.
  My guess is due to the fact that you can write function xyz(array $arg = null){ [...] }, to distinguish between an empty array and a function with an optional parameter.

Everything below is correct.

You can see it in action on http://sandbox.onlinephpfunctions.com/code/e4dc15a4f29cd6ef6a7498ad27ac202f5f874612

Should this information be added to the documentation? Is it fine the way it is?

[xabbuh]

You are mixing two things here. The table is not about comparing the values with other arbitrary values, but how they will be evaluated in a context where a boolean is expected.

So basically in a construct like this:

{% if value %}
    value evaluates to true
{% else %}
    value evaluates to false
{% endif %}

[stof]

your sandbox code is not covering the behavior of the boolean evaluation, but of the == operator, which is a totally different things (and is not what the {% if %} documentation needs)

[ismael-miguel]

Then there are some edge cases missing.

The string '0' is a falsy value in PHP, and isn't mentioned in the table.
Also, NAN and INF are truthy, which may happen from some mathematical calculations.

[xabbuh]

Would you like to contribute the missing edge cases? :) The file to edit would be https://github.com/twigphp/Twig/blob/1.x/doc/tags/if.rst.