Source

File: wp-includes/rewrite.php

function wp_resolve_numeric_slug_conflicts( $query_vars = array() ) {
	if ( ! isset( $query_vars['year'] ) && ! isset( $query_vars['monthnum'] ) && ! isset( $query_vars['day'] ) ) {
		return $query_vars;
	}

	// Identify the 'postname' position in the permastruct array.
	$permastructs   = array_values( array_filter( explode( '/', get_option( 'permalink_structure' ) ) ) );
	$postname_index = array_search( '%postname%', $permastructs, true );

	if ( false === $postname_index ) {
		return $query_vars;
	}

	/*
	 * A numeric slug could be confused with a year, month, or day, depending on position. To account for
	 * the possibility of post pagination (eg 2015/2 for the second page of a post called '2015'), our
	 * `is_*` checks are generous: check for year-slug clashes when `is_year` *or* `is_month`, and check
	 * for month-slug clashes when `is_month` *or* `is_day`.
	 */
	$compare = '';
	if ( 0 === $postname_index && ( isset( $query_vars['year'] ) || isset( $query_vars['monthnum'] ) ) ) {
		$compare = 'year';
	} elseif ( $postname_index && '%year%' === $permastructs[ $postname_index - 1 ] && ( isset( $query_vars['monthnum'] ) || isset( $query_vars['day'] ) ) ) {
		$compare = 'monthnum';
	} elseif ( $postname_index && '%monthnum%' === $permastructs[ $postname_index - 1 ] && isset( $query_vars['day'] ) ) {
		$compare = 'day';
	}

	if ( ! $compare ) {
		return $query_vars;
	}

	// This is the potentially clashing slug.
	$value = $query_vars[ $compare ];

	$post = get_page_by_path( $value, OBJECT, 'post' );
	if ( ! ( $post instanceof WP_Post ) ) {
		return $query_vars;
	}

	// If the date of the post doesn't match the date specified in the URL, resolve to the date archive.
	if ( preg_match( '/^([0-9]{4})\-([0-9]{2})/', $post->post_date, $matches ) && isset( $query_vars['year'] ) && ( 'monthnum' === $compare || 'day' === $compare ) ) {
		// $matches[1] is the year the post was published.
		if ( intval( $query_vars['year'] ) !== intval( $matches[1] ) ) {
			return $query_vars;
		}

		// $matches[2] is the month the post was published.
		if ( 'day' === $compare && isset( $query_vars['monthnum'] ) && intval( $query_vars['monthnum'] ) !== intval( $matches[2] ) ) {
			return $query_vars;
		}
	}

	/*
	 * If the located post contains nextpage pagination, then the URL chunk following postname may be
	 * intended as the page number. Verify that it's a valid page before resolving to it.
	 */
	$maybe_page = '';
	if ( 'year' === $compare && isset( $query_vars['monthnum'] ) ) {
		$maybe_page = $query_vars['monthnum'];
	} elseif ( 'monthnum' === $compare && isset( $query_vars['day'] ) ) {
		$maybe_page = $query_vars['day'];
	}
	// Bug found in #11694 - 'page' was returning '/4'.
	$maybe_page = (int) trim( $maybe_page, '/' );

	$post_page_count = substr_count( $post->post_content, '<!--nextpage-->' ) + 1;

	// If the post doesn't have multiple pages, but a 'page' candidate is found, resolve to the date archive.
	if ( 1 === $post_page_count && $maybe_page ) {
		return $query_vars;
	}

	// If the post has multiple pages and the 'page' number isn't valid, resolve to the date archive.
	if ( $post_page_count > 1 && $maybe_page > $post_page_count ) {
		return $query_vars;
	}

	// If we've gotten to this point, we have a slug/date clash. First, adjust for nextpage.
	if ( '' !== $maybe_page ) {
		$query_vars['page'] = intval( $maybe_page );
	}

	// Next, unset autodetected date-related query vars.
	unset( $query_vars['year'] );
	unset( $query_vars['monthnum'] );
	unset( $query_vars['day'] );

	// Then, set the identified post.
	$query_vars['name'] = $post->post_name;

	// Finally, return the modified query vars.
	return $query_vars;
}