addCssClass/mergeCssClasses mixed result for "similar" value

[bobonov]

Using "similar" (null, true, false...) value give different result.
In particular:

• if null is passed in array or as value give different results.

• int 0 give empty result, int >0 give the number

The problem is trivial since in my case affect only TestClass for widget since when applying a class with null value result in an additional space and the resulting string do not match

What steps will reproduce the problem?

The below code compare the results

$array=['null'=>null, 'false'=>false, 'true'=>true, "empty ''"=>'', 'space'=>' ',
    'str 0'=>'0', 'int 0'=>0, 'int 1'=>1];

foreach($array as $item=>$value){
    $options=['class'=>'base_class'];
    Html::addCssClass($options, [$value]);
    echo Html::tag('div', "array[$item]", $options)."\n";
    Html::addCssClass($options, $value);
    echo Html::tag('div', "$item value", $options)."\n\n";
}

The above code give as result:

<div class="base_class ">array[null]</div>
<div class="base_class">null value</div>

<div class="base_class ">array[false]</div>
<div class="base_class ">false value</div>

<div class="base_class">array[true]</div>
<div class="base_class">true value</div>

<div class="base_class ">array[empty '']</div>
<div class="base_class ">empty '' value</div>

<div class="base_class  ">array[space]</div>
<div class="base_class  ">space value</div>

<div class="base_class 0">array[str 0]</div>
<div class="base_class 0">str 0 value</div>

<div class="base_class">array[int 0]</div>
<div class="base_class">int 0 value</div>

<div class="base_class 1">array[int 1]</div>
<div class="base_class 1">int 1 value</div>

Especially for null it gives a different result but in general the result is quite mixed for values that should give same result when casted to string.
(int) 0 should be same as (str) 0
true/false should produce in both cases ''
null passed as value or value in array should give same result

###Expected result
The expected result should be:
<div class="base_class">
except for (int) 0 which should be
<div class="base_class 0">
In the above case, starting a css class name with 0 or any number is invalid, but I do not know if there is any css framewrok doing so

Additional info

I think the best place to fix this behavior is in BaseHtml::mergeCssClasses
Here the code should drop empty values and eventually non valid css class name.
Personally I would avoid the second part (csss name validation) since this would make big problem with css framework like Tailwind.
Probably the best solution is to change the code of BaseHtml::mergeCssClasses to filter out empty and "only space" string value.
Applying the following array_filter before return fix it.

$existingClasses=array_filter($existingClasses, function($value) { return !is_null($value) && trim($value) !== ''; });

Q	A
Yii version	2.0.32
PHP version	7.2.18
Operating system	Ubuntu Server 18.04

[samdark]

Interesting find. Thanks for reporting.

Can't we solve it at HTML class rendering method?