deprecation warning on wikimedia/less.php/lib/Less/Functions.php:1022

[spoetnik]

I have updated a Processwire module to use the latest version of wikimedia Less. I get a deprecation warning on wikimedia/less.php/lib/Less/Functions.php:1022

Deprecated: file_exists(): Passing null to parameter #1 ($filename) of type string is deprecated in .../modules/Less/wikimedia/less.php/lib/Less/Functions.php:1022

I don't think this has something todo with the implementation of the less.php library in the module.

php_version: "8.2" webserver_type: apache-fpm

[Krinkle]

@spoetnik Can you share a minimal input that triggers the warning? For example, a 5-10 line .less file that one can pass to less.php/bin/lessc.

Does it function correctly / Do you get the output you expect? (Besides this warning.)

Are there other warnings or errors caused by the same input?

[spoetnik]

I find it hard to debug this, but if I remove these lines from my Less-file, the warnings are gone:

@internal-accordion-icon-close-image: "uikit-themes/master-design-escapes/images/accordion-close.svg";
@internal-accordion-icon-open-image: "uikit-themes/master-design-escapes /images/accordion-open.svg";
@internal-divider-icon-image: "uikit-themes/master-design-escapes/images/divider-icon.svg";

I get 18 warnings for these 3 lines.

[Krinkle]

@spoetnik Is there a datauri() call in one of your stylesheets?

I'm afraid you found something unrelated. The warning you reported is from the datauri() function. The code you share must at least contain a call to that function, and pass a string or variable to it.

When reducing code for a test case, make sure you keep the code that causes the warning. Whenever you suspect something as the cause, you can first remove it and observe no warnings. But, aconfirm it by keeping only that code (remove everything not needed/used by that code) and observing a warning. Then, you have a confirmed root cause. You can repeat this to make the test case smaller.

I suspect you might have logic to call datauri() only when these variables are defined. By analogy:

$options = [ 'x' => false ];

$options['x'] = true;
if ( $options['x'] ) {
  add( 2 ); // Warning: Requires two arguments
}

If I remove $options['x'] = true;, the warning goes away. However, without the rest of the code, this does not explain the problem, because the problem is not on that line. Indeed, if we ran $options['x'] = true; on its own, there would be no warning.