Resolve an illegal offset error

In Magento 2.1 or later, when creating a new product in the Magento Admin, the following error might display:

Warning: Illegal string offset 'is_in_stock' in [...]/vendor/
magento/module-catalog-inventory/Ui/DataProvider/Product/Form/
Modifier/AdvancedInventory.php on line 87

Detail

Magento 2.1 and later use PHP code comments in the getDocComment validation call in the getExtensionAttributes method in Magento\Framework\Api\ExtensionAttributesFactory.php.

If you enabled the PHP OPcache (which we recommend), this error displays because by default, the OPcache setting opcache.save-comments is disabled.

Workaround

To solve the issue, locate your OPcache configuration settings and enable opcache.save-comments as follows:

Step 1: Locate your OPcache configuration

To find OPcache configuration settings:

PHP OPcache settings are typically located either in php.ini or opcache.ini. The location might depend on your operating system and PHP version. The OPcache configuration file might have an [opcache] section or settings like opcache.enable.

Use the following guidelines to find it:

  • Apache web server:

    For Ubuntu with Apache, OPcache settings are typically located in php.ini.

    For CentOS with Apache or nginx, OPcache settings are typically located in /etc/php.d/opcache.ini

    If not, use the following command to locate it:

    sudo find / -name 'opcache.ini'
    
  • nginx web server with PHP-FPM: /etc/php5/fpm/php.ini

If you have more than one opcache.ini, modify all of them.

Step 2: Enable opcache.save-comments

  1. Open your OPcache configuration file in a text editor.
  2. Locate opcache.save-comments and uncomment it if necessary.
  3. Make sure its value is set to 1.
  4. Save your changes and exit the text editor.
  5. Restart your web server:

    • Apache, Ubuntu: service apache2 restart
    • Apache, CentOS: service httpd restart
    • nginx, Ubuntu and CentOS: service nginx restart