Checkout: prevent error from get_value method when WC has not been properly initialized (#50692)

* Ensure WC's customer and cart props are initialized

If the customer or cart property of the main WooCommerce class is
accessed before the `woocommerce_init` action has fired, those
properties will be `null` instead of containing their respective
classes, which can cause a fatal error if you then try to access a
method on one of the classes. This makes sure the props will always
return a class.

Fixes #50245

* Revert "Ensure WC's customer and cart props are initialized"

This approach unexpectedly breaks a lot of things...

This reverts commit 310fd2c118.

* Alternate solution

The attempt to fix the problem wholistically ended up causing a lot of
things to break, so this is the band-aid approach instead.

* Add changelog file

* Remove unnecessary assignment to global POST var

This was polluting the results of the new test, causing it to fail.

plugins/woocommerce/changelog/fix-50245-fatal-error-checkout-customer

@@ -0,0 +1,4 @@
+Significance: patch
+Type: fix
+
+Prevent an error in the WC_Checkout class when WooCommerce has not been properly initialized yet

plugins/woocommerce/includes/class-wc-checkout.php

@@ -1357,7 +1357,7 @@ class WC_Checkout {
 
 		if ( is_callable( array( $customer_object, "get_$input" ) ) ) {
 			$value = $customer_object->{"get_$input"}();
-		} elseif ( $customer_object->meta_exists( $input ) ) {
+		} elseif ( is_callable( array( $customer_object, 'meta_exists' ) ) && $customer_object->meta_exists( $input ) ) {
 			$value = $customer_object->get_meta( $input, true );
 		}
 

plugins/woocommerce/tests/php/includes/class-wc-checkout-test.php

@@ -46,12 +46,11 @@ class WC_Checkout_Test extends \WC_Unit_Test_Case {
 	 * @param bool $expect_error_message_for_shipping_country True to expect an error to be generated for the shipping country.
 	 */
 	public function test_validate_posted_data_adds_error_for_non_existing_country( $ship_to_different_address, $expect_error_message_for_shipping_country ) {
-		$_POST = array(
+		$data = array(
 			'billing_country'           => 'XX',
 			'shipping_country'          => 'YY',
 			'ship_to_different_address' => $ship_to_different_address,
 		);
-		$data  = $_POST; // phpcs:ignore WordPress.Security.NonceVerification.Missing
 
 		add_filter(
 			'woocommerce_cart_needs_shipping_address',
@@ -75,12 +74,11 @@ class WC_Checkout_Test extends \WC_Unit_Test_Case {
 	 * @testdox the customer notes are correctly sanitized.
 	 */
 	public function test_order_notes() {
-		$_POST = array(
+		$data = array(
 			'ship_to_different_address' => false,
 			'order_comments'             => '<a href="http://attackerpage.com/csrf.html">This text should not save inside an anchor.</a><script>alert("alert")</script>',
 			'payment_method'            => 'bacs',
 		);
-		$data  = $_POST; // phpcs:ignore WordPress.Security.NonceVerification.Missing
 
 		$errors = new WP_Error();
 
@@ -108,12 +106,11 @@ class WC_Checkout_Test extends \WC_Unit_Test_Case {
 	 * @param bool $ship_to_different_address True to simulate shipping to a different address than the billing address.
 	 */
 	public function test_validate_posted_data_does_not_add_error_for_existing_country( $ship_to_different_address ) {
-		$_POST = array(
+		$data = array(
 			'billing_country'           => 'ES',
 			'shipping_country'          => 'ES',
 			'ship_to_different_address' => $ship_to_different_address,
 		);
-		$data  = $_POST; // phpcs:ignore WordPress.Security.NonceVerification.Missing
 
 		$errors = new WP_Error();
 
@@ -132,12 +129,11 @@ class WC_Checkout_Test extends \WC_Unit_Test_Case {
 	 * @param bool $ship_to_different_address True to simulate shipping to a different address than the billing address.
 	 */
 	public function test_validate_posted_data_does_not_add_error_for_empty_country( $ship_to_different_address ) {
-		$_POST = array(
+		$data = array(
 			'billing_country'           => '',
 			'shipping_country'          => '',
 			'ship_to_different_address' => $ship_to_different_address,
 		);
-		$data  = $_POST; // phpcs:ignore WordPress.Security.NonceVerification.Missing
 
 		$errors = new WP_Error();
 
@@ -186,12 +182,11 @@ class WC_Checkout_Test extends \WC_Unit_Test_Case {
 			)
 		);
 
-		$_POST = array(
+		$data = array(
 			'billing_country'           => $country,
 			'shipping_country'          => $country,
 			'ship_to_different_address' => false,
 		);
-		$data  = $_POST; // phpcs:ignore WordPress.Security.NonceVerification.Missing
 
 		$errors = new WP_Error();
 
@@ -202,5 +197,20 @@ class WC_Checkout_Test extends \WC_Unit_Test_Case {
 			$errors->get_error_message( 'shipping' )
 		);
 	}
+
+	/**
+	 * @testdox If the WooCommerce class's customer object is null (like if WC has not been fully initialized yet),
+	 *          calling WC_Checkout::get_value should not throw an error.
+	 */
+	public function test_get_value_no_error_on_null_customer() {
+		$sut = WC_Checkout::instance();
+
+		$orig_customer = WC()->customer;
+		WC()->customer = null;
+
+		$this->assertNull( $sut->get_value( 'billing_country' ) );
+
+		WC()->customer = $orig_customer;
+	}
 }