Code Modernization: Check the return type of wp_parse_url() in `wp_…

…mail()`.

As per the PHP manual:
> If the `component` parameter is omitted, an associative array is returned.
> If the `component` parameter is specified, `parse_url()` returns a string (or an int, in the case of `PHP_URL_PORT`) instead of an array. If the requested component doesn't exist within the given URL, `null` will be returned.

Reference: [https://www.php.net/manual/en/function.parse-url.php#refsect1-function.parse-url-returnvalues PHP Manual: parse_url(): Return Values]

In PHP 8.1, if the home URL does not have a "host" component, it would lead to a `substr(): Passing null to parameter #1 ($string) of type string is deprecated` notice.

Changing the logic around and adding validation for the return type value of `wp_parse_url()` prevents that.

Follow-up to [48601], [51606], [51622], [51626], [51629], [51630].

Props dennisatyoast, jrf.
See #54730.

git-svn-id: https://develop.svn.wordpress.org/trunk@52799 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/pluggable.php

@@ -378,12 +378,16 @@ function wp_mail( $to, $subject, $message, $headers = '', $attachments = array()
 		 */
 		if ( ! isset( $from_email ) ) {
 			// Get the site domain and get rid of www.
-			$sitename = wp_parse_url( network_home_url(), PHP_URL_HOST );
-			if ( 'www.' === substr( $sitename, 0, 4 ) ) {
-				$sitename = substr( $sitename, 4 );
-			}
+			$sitename   = wp_parse_url( network_home_url(), PHP_URL_HOST );
+			$from_email = 'wordpress@';
+
+			if ( null !== $sitename ) {
+				if ( 'www.' === substr( $sitename, 0, 4 ) ) {
+					$sitename = substr( $sitename, 4 );
+				}
 
-			$from_email = 'wordpress@' . $sitename;
+				$from_email .= $sitename;
+			}
 		}
 
 		/**

tests/phpunit/tests/mail.php

@@ -225,6 +225,28 @@ public function test_wp_mail_with_empty_from_name_for_the_from_header() {
 		$this->assertStringContainsString( $expected, $mailer->get_sent()->header );
 	}
 
+	/**
+	 * Tests that wp_mail() returns false with an empty home URL and does not error out on PHP 8.1.
+	 *
+	 * @ticket 54730
+	 */
+	public function test_wp_mail_with_empty_home_url() {
+		$to      = '[email protected]';
+		$subject = 'Testing';
+		$message = 'Test Message';
+
+		// Multisite test runs.
+		add_filter( 'network_home_url', '__return_empty_string' );
+
+		// Single site test runs.
+		add_filter( 'home_url', '__return_empty_string' );
+
+		$success = wp_mail( $to, $subject, $message );
+
+		$this->assertFalse( $success, 'wp_mail() should have returned false' );
+		$this->assertGreaterThan( 0, did_action( 'wp_mail_failed' ), 'wp_mail_failed action was not called' );
+	}
+
 	/**
 	 * @ticket 30266
 	 */