Comments: Cache results of `SELECT FOUND_ROWS()` query.

When comment IDs are fetched from the cache rather than the database,
the subsequent `SELECT FOUND_ROWS()` query will not return the correct value.
To avoid unnecessary queries, we cache the results of the `found_comments`
query alongside the comment IDs.

Props spacedmonkey.
Fixes #37184.

git-svn-id: https://develop.svn.wordpress.org/trunk@38001 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-comment-query.php

@@ -394,12 +394,27 @@ class WP_Comment_Query {
 			$last_changed = microtime();
 			wp_cache_set( 'last_changed', $last_changed, 'comment' );
 		}
-		$cache_key = "get_comment_ids:$key:$last_changed";
 
-		$comment_ids = wp_cache_get( $cache_key, 'comment' );
+		$cache_key   = "get_comments:$key:$last_changed";
-		if ( false === $comment_ids ) {
+		$cache_value = wp_cache_get( $cache_key, 'comment' );
+		if ( false === $cache_value ) {
 			$comment_ids = $this->get_comment_ids();
-			wp_cache_add( $cache_key, $comment_ids, 'comment' );
+			if ( $comment_ids ) {
+				$this->set_found_comments();
+			}
+
+			$cache_value = array(
+				'comment_ids'    => $comment_ids,
+				'found_comments' => $this->found_comments,
+			);
+			wp_cache_add( $cache_key, $cache_value, 'comment' );
+		} else {
+			$comment_ids          = $cache_value['comment_ids'];
+			$this->found_comments = $cache_value['found_comments'];
+		}
+
+		if ( $this->found_comments && $this->query_vars['number'] ) {
+			$this->max_num_pages = ceil( $this->found_comments / $this->query_vars['number'] );
 		}
 
 		// If querying for a count only, there's nothing more to do.
@@ -410,21 +425,6 @@ class WP_Comment_Query {
 
 		$comment_ids = array_map( 'intval', $comment_ids );
 
-		if ( $comment_ids && $this->query_vars['number'] && ! $this->query_vars['no_found_rows'] ) {
-			/**
-			 * Filters the query used to retrieve found comment count.
-			 *
-			 * @since 4.4.0
-			 *
-			 * @param string           $found_comments_query SQL query. Default 'SELECT FOUND_ROWS()'.
-			 * @param WP_Comment_Query $comment_query        The `WP_Comment_Query` instance.
-			 */
-			$found_comments_query = apply_filters( 'found_comments_query', 'SELECT FOUND_ROWS()', $this );
-			$this->found_comments = (int) $wpdb->get_var( $found_comments_query );
-
-			$this->max_num_pages = ceil( $this->found_comments / $this->query_vars['number'] );
-		}
-
 		if ( 'ids' == $this->query_vars['fields'] ) {
 			$this->comments = $comment_ids;
 			return $this->comments;
@@ -900,6 +900,32 @@ class WP_Comment_Query {
 		}
 	}
 
+	/**
+	 * Populates found_comments and max_num_pages properties for the current query if the limit clause was used.
+	 *
+	 * @since 4.6.0
+	 * @access private
+	 *
+	 * @global wpdb $wpdb WordPress database abstraction object.
+	 */
+	private function set_found_comments() {
+		global $wpdb;
+
+		if ( $this->query_vars['number'] && ! $this->query_vars['no_found_rows'] ) {
+			/**
+			 * Filters the query used to retrieve found comment count.
+			 *
+			 * @since 4.4.0
+			 *
+			 * @param string $found_comments_query SQL query. Default 'SELECT FOUND_ROWS()'.
+			 * @param WP_Comment_Query $comment_query The `WP_Comment_Query` instance.
+			 */
+			$found_comments_query = apply_filters( 'found_comments_query', 'SELECT FOUND_ROWS()', $this );
+
+			$this->found_comments = (int) $wpdb->get_var( $found_comments_query );
+		}
+	}
+
 	/**
 	 * Fetch descendants for located comments.
 	 *

tests/phpunit/tests/comment/query.php

@@ -2151,6 +2151,29 @@ class Tests_Comment_Query extends WP_UnitTestCase {
 		$this->assertEquals( 2, $q->max_num_pages );
 	}
 
+	/**
+	 * @ticket 37184
+	 */
+	public function test_found_rows_should_be_fetched_from_the_cache() {
+		$comments = self::factory()->comment->create_many( 3, array( 'comment_post_ID' => self::$post_id ) );
+
+		// Prime cache.
+		new WP_Comment_Query( array(
+			'post_id' => self::$post_id,
+			'number' => 2,
+			'no_found_rows' => false,
+		) );
+
+		$q = new WP_Comment_Query( array(
+			'post_id' => self::$post_id,
+			'number' => 2,
+			'no_found_rows' => false,
+		) );
+
+		$this->assertEquals( 3, $q->found_comments );
+		$this->assertEquals( 2, $q->max_num_pages );
+	}
+
 	/**
 	 * @ticket 8071
 	 */