Source
File: wp-includes/feed.php
function get_feed_build_date( $format ) {
global $wp_query;
$datetime = false;
$max_modified_time = false;
$utc = new DateTimeZone( 'UTC' );
if ( ! empty( $wp_query ) && $wp_query->have_posts() ) {
// Extract the post modified times from the posts.
$modified_times = wp_list_pluck( $wp_query->posts, 'post_modified_gmt' );
// If this is a comment feed, check those objects too.
if ( $wp_query->is_comment_feed() && $wp_query->comment_count ) {
// Extract the comment modified times from the comments.
$comment_times = wp_list_pluck( $wp_query->comments, 'comment_date_gmt' );
// Add the comment times to the post times for comparison.
$modified_times = array_merge( $modified_times, $comment_times );
}
// Determine the maximum modified time.
$datetime = date_create_immutable_from_format( 'Y-m-d H:i:s', max( $modified_times ), $utc );
}
if ( false === $datetime ) {
// Fall back to last time any post was modified or published.
$datetime = date_create_immutable_from_format( 'Y-m-d H:i:s', get_lastpostmodified( 'GMT' ), $utc );
}
if ( false !== $datetime ) {
$max_modified_time = $datetime->format( $format );
}
/**
* Filters the date the last post or comment in the query was modified.
*
* @since 5.2.0
*
* @param string|false $max_modified_time Date the last post or comment was modified in the query, in UTC.
* False on failure.
* @param string $format The date format requested in get_feed_build_date().
*/
return apply_filters( 'get_feed_build_date', $max_modified_time, $format );
}