Initialise customer sessions on the order pay page

[mikejolley]

Submission Review Guidelines:

• I have followed the WooCommerce Contributing Guidelines and the WordPress Coding Standards.
• I have checked to ensure there aren't other open Pull Requests for the same update/change.
• I have reviewed my code for security best practices.
• Following the above guidelines will result in quick merges and clear and detailed feedback when appropriate.

Changes proposed in this Pull Request:

Logged-out customers only have a WooCommerce session initialised when they have a cart. Some pages, such as the order pay page, may require a session outside of the regular cart flow.

To negate the need for extensions to handle this case themselves, this PR sets the session on the order pay page.

Closes #23902

Because I'm not certain what payment gateways/extensions need this, I tested using a small snippet instead to ensure a session was set.

add_action(
	'wp_head',
	function () {
		var_dump( WC()->session->get( 'test_session_data' ) );
	}
);
add_action(
	'wp_footer',
	function () {

		WC()->session->set( 'test_session_data', 'Hello' );
	}
);

This will output Hello in the header after refreshing the page only if a session is set. Otherwise it will show NULL.

How to test the changes in this Pull Request:

Testers only need to test for regressions. Run through the checkout flow as a logged out guest user and ensure there are no errors.

Developer testing

1. Use the snippet above.
2. As a logged out guest with no cart (use private browser window if possible) visit the website. You should see NULL at the top of the page indicating there is no session.
3. Visit the pay page. It can be an invalid link, it doesn't matter. e.g. https://store.local/checkout/order-pay/18/?pay_for_order=true&key=123);
4. Now refresh or visit another page. See hello in the header instead of null. This means you now have a session.

Changelog entry

• Automatically create a changelog entry from the details below.

Significance

• Patch
• Minor
• Major

Type

• Fix - Fixes an existing bug
• Add - Adds functionality
• Update - Update existing functionality
• Dev - Development related task
• Tweak - A minor adjustment to the codebase
• Performance - Address performance issues
• Enhancement - Improvement to existing functionality

Message

Fix to ensure all customers have a session when visiting the order pay page.

Comment

[github-actions]

Hi @tarunvijwani,

Apart from reviewing the code changes, please make sure to review the testing instructions as well.

You can follow this guide to find out what good testing instructions should look like:
https://github.com/woocommerce/woocommerce/wiki/Writing-high-quality-testing-instructions

[github-actions]

Test Results Summary

Commit SHA: ece851b

Test 🧪	Passed ✅	Failed 🚨	Broken 🚧	Skipped ⏭️	Unknown ❔	Total 📊	Duration ⏱️
API Tests	259	0	0	2	0	261	0m 36s
E2E Tests	241	0	0	55	0	296	6m 44s

---

To view the full API test report, click here.
To view the full E2E test report, click here.
To view all test reports, visit the WooCommerce Test Reports Dashboard.

[tarunvijwani]

Works like a charm! Thank you for the fix, @mikejolley! 🎉