Warning: Use of undefined constant all - assumed 'all' (this will throw an Error in a future version of PHP) in ............ on line 8

Question

// adding the CSS and JS files
function gt_setup(){
    wp_enqueue_style('google-fonts',  '//fonts.googleapis.com/css?family=Roboto|Roboto+Condensed|Roboto+Slab');
    wp_enqueue_style('fontawesome', '//href="font-awesome-4.7.0/css/font-awesome.min.css');
    wp_enqueue_style('style', get_stylesheet_uri('style.css'), NULL, microtime(), all);
    wp_enqueue_script("main", get_theme_file_uri('/js/main.js' ), NULL, microtime(), true);
}

add_action('wp_enqueue_scripts', 'gt_setup');

?>

Answer 1

It is a valid error...

So I went to Google and typed in wp_enqueue_style to check the function and it says...

wp_enqueue_style( string $handle, string $src = '', string[] $deps = array(), string|bool|null $ver = false, string $media = 'all' )

So that means that all is a valid parameter value but you failed to define it as a string by wrapping it in single (or double) quotes.

PHP Treats all as a constant and could not find it - hence the error.

PHP Treats 'all' as a string, which in this case is a valid parameter value.