Reports of "class 'WooCommerce\Square\Gateway\Blocks_Handler' not found" fatal errors

[mattallan]

Describe the bug

We've received internal reports of some sites we manage getting the following fatal error:

PHP Fatal error:  Uncaught Error: Class "WooCommerce\Square\Gateway\Blocks_Handler" not found
in .../plugins/woocommerce-square/woocommerce-square.php:430

After looking into this, I found that we're init'ing our blocks handler code and our autoloader behind two different conditions, which results in cases where register_payment_method_block_integrations() is trying to call new WooCommerce\Square\Gateway\Blocks_Handler() without our autoloader existing.

For instance:

• Registering our blocks handler requires is_environment_compatible() to pass which checks for PHP 7.4+
• Init'ing our autoloader requires is_environment_compatible() + plugins_compatible() which also checks that WP version is 6.3+ and WC version is 8.7+.

What this difference means is if a store has WooCommerce 8.6 installed (an unsupported version), the autoloader won't be init'ed, however, the block handler code will still try to register our block integration classes resulting in the fatal error.

To reproduce

1. Install and activate WooCommerce 8.6 and the latest WooCommerce Square
2. Load any WP Admin page
3. Note the fatal error:

Environment (please complete the following information):

• WordPress Version
• WooCommerce Version
• WooCommerce Square Plugin Version
• Browser [e.g. chrome, safari] and Version
• Any other plugins installed

Additional details

System status

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[shameemreza]

Another report here: 8261040-zen Thread: https://wordpress.org/support/topic/critical-error-when-activating-plugin-4/