Cron: Fix malformed cron array in wp_schedule_single_event() when _get_cron_array() returns false.

In `wp_schedule_single_event()`, the cron info array is retrieved via a call to `_get_cron_array()` and straight away cast to an array. But as the documentation for that function (correctly) states, the return type of that function is `array|false`, where `false` is returned for a site where no cron jobs have been scheduled (yet).

In the case that `_get_cron_array()` would return `false`, this would now unintentionally create an array with a single entry with key `0` and as the value `false`.

This is a bug. Fixed now by adding validation to the output of `_get_cron_array()` and initializing `$crons` to an empty array if `false` was returned.

Tests added first to prove the bug (a) was introduced in #44818 [44917] and (b) is now fixed.

Follow-up to [44917].

Props jrf, peterwilsoncc.
Fixes #53950.

git-svn-id: https://develop.svn.wordpress.org/trunk@51916 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/cron.php

@@ -118,7 +118,11 @@ function wp_schedule_single_event( $timestamp, $hook, $args = array(), $wp_error
 	 * current time) all events scheduled within the next ten minutes
 	 * are considered duplicates.
 	 */
-	$crons     = (array) _get_cron_array();
+	$crons = _get_cron_array();
+	if ( ! is_array( $crons ) ) {
+		$crons = array();
+	}
+
 	$key       = md5( serialize( $event->args ) );
 	$duplicate = false;
 

tests/phpunit/tests/cron.php

@@ -100,7 +100,6 @@ class Tests_Cron extends WP_UnitTestCase {
 		$this->assertSame( $recur, wp_get_schedule( $hook, $args ) );
 	}
 
-
 	/**
 	 * Tests that a call to wp_schedule_event() on a site without any scheduled events
 	 * does not result in a PHP deprecation warning on PHP 8.1 or higher.
@@ -125,6 +124,30 @@ class Tests_Cron extends WP_UnitTestCase {
 		$this->assertTrue( wp_schedule_event( $timestamp, 'daily', $hook ) );
 	}
 
+	/**
+	 * Tests that a call to wp_schedule_single_event() on a site without any scheduled events
+	 * does not result in the value "false" being added into the cron array.
+	 *
+	 * @ticket 53950
+	 *
+	 * @covers ::wp_schedule_single_event
+	 */
+	function test_wp_schedule_single_event_without_cron_option() {
+		delete_option( 'cron' );
+
+		// Verify that the cause of the error is in place.
+		$this->assertFalse( _get_cron_array(), '_get_cron_array() does not return false' );
+
+		$hook      = __FUNCTION__;
+		$timestamp = strtotime( '+10 minutes' );
+
+		// Add an event.
+		$this->assertTrue( wp_schedule_single_event( $timestamp, $hook ), 'Scheduling single event failed' );
+
+		// Verify that "false" is not a value in the final cron array.
+		$this->assertNotContains( false, get_option( 'cron' ), 'Resulting cron array contains the value "false"' );
+	}
+
 	function test_unschedule_event() {
 		// Schedule an event and make sure it's returned by wp_next_scheduled().
 		$hook      = __FUNCTION__;