Administration: Add last fatal PHP error to auto-update failure emails

src/wp-admin/includes/class-wp-automatic-updater.php

@@ -1540,6 +1540,16 @@ protected function send_plugin_theme_email( $type, $successful_updates, $failed_
 		 */
 		$email = apply_filters( 'auto_plugin_theme_update_email', $email, $type, $successful_updates, $failed_updates );
 
+		if ( WP_DEBUG && ( 'fail' === $type || 'mixed' === $type ) ) {
+			$fatal_error = get_transient( 'wp_updater_last_fatal_error' );
+			if ( $fatal_error ) {
+				$email['body'] .= "\n\n=== " . __( 'LAST FATAL PHP ERROR' ) . " ===\n";
+				$email['body'] .= '• ' . $fatal_error . "\n";
+				$email['body'] .= "========================================\n";
+				delete_transient( 'wp_updater_last_fatal_error' );
+			}
+		}
+
 		$result = wp_mail( $email['to'], wp_specialchars_decode( $email['subject'] ), $email['body'], $email['headers'] );
 
 		if ( $result ) {
@@ -1828,6 +1838,58 @@ protected function has_fatal_error() {
 			$result       = json_decode( trim( $error_output ), true );
 		}
 
+		if ( WP_DEBUG ) {
+			$fatal_error = null;
+
+			$last_error = error_get_last();
+			if ( $last_error && in_array( $last_error['type'], array( E_ERROR, E_PARSE, E_COMPILE_ERROR, E_USER_ERROR ) ) ) {
+				$fatal_error = "PHP Fatal error: {$last_error['message']} in {$last_error['file']} on line {$last_error['line']}";
+			} else {
+				$log_file = ini_get( 'error_log' );
+
+				if ( ! $log_file ) {
+					error_log( 'WP Auto-Update: error_log is empty, falling back to debug.log' );
+					$log_file = WP_CONTENT_DIR . '/debug.log';
+				}
+
+				if ( $log_file && file_exists( $log_file ) && is_readable( $log_file ) ) {
+					$handle = fopen( $log_file, 'r' );
+					if ( $handle ) {
+						$pos = -2;
+						$current_line = '';
+						while ( $pos > -filesize( $log_file ) ) {
+							fseek( $handle, $pos, SEEK_END );
+							$char = fgetc( $handle );
+							if ( "\n" === $char ) {
+								if ( '' !== $current_line ) {
+									$line = strrev( $current_line );
+									if ( false !== strpos( $line, 'PHP Fatal error' ) ) {
+										$fatal_error = trim( $line );
+										break;
+									}
+									$current_line = '';
+								}
+							} else {
+								$current_line .= $char;
+							}
+							$pos--;
+						}
+						if ( '' !== $current_line && null === $fatal_error ) {
+							$line = strrev( $current_line );
+							if ( false !== strpos( $line, 'PHP Fatal error' ) ) {
+								$fatal_error = trim( $line );
+							}
+						}
+						fclose( $handle );
+					}
+				}
+			}
+
+			if ( $fatal_error ) {
+				set_transient( 'wp_updater_last_fatal_error', $fatal_error, 5 * MINUTE_IN_SECONDS );
+			}
+		}
+
 		delete_transient( $transient );
 
 		// Only fatal errors will result in a 'type' key.