View file vendor/laravel/framework/src/Illuminate/View/Compilers/Concerns/CompilesInjections.php

<?php

namespace Illuminate\View\Compilers\Concerns;

trait CompilesInjections
{
    /**
     * Compile the inject statements into valid PHP.
     *
     * @param  string  $expression
     * @return string
     */
    protected function compileInject($expression)
    {
        $segments = explode(',', preg_replace("/[\(\)]/", '', $expression));

        $variable = trim($segments[0], " '\"");

        $service = trim($segments[1]);

        return "<?php \${$variable} = app({$service}); ?>";
    }
}