From fb227caed19358fd2d0b13232b27a574577a4587 Mon Sep 17 00:00:00 2001
From: Boone Gorges <boonebgorges@git.wordpress.org>
Date: Wed, 13 Sep 2017 14:47:07 +0000
Subject: [PATCH] Taxonomy: Force a `DISTINCT` term query when result count
 matters.

Generally, duplicate terms returned by a term query are eliminated in PHP,
after the database query takes place. This technique doesn't work properly
when the query parameters specify the `number` of results, since the results
of a `SELECT ... LIMIT x...` query may be deduplicated to a count less than
`x`. In these cases, we force the original query to be `DISTINCT`.

Props elvishp2006.
Fixes #41796.

git-svn-id: https://develop.svn.wordpress.org/trunk@41377 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-includes/class-wp-term-query.php | 15 ++++++-
 tests/phpunit/tests/term/query.php      | 57 +++++++++++++++++++++++++
 2 files changed, 70 insertions(+), 2 deletions(-)

diff --git a/src/wp-includes/class-wp-term-query.php b/src/wp-includes/class-wp-term-query.php
index 12e7dec242..f6f53f210c 100644
--- a/src/wp-includes/class-wp-term-query.php
+++ b/src/wp-includes/class-wp-term-query.php
@@ -551,6 +551,16 @@ class WP_Term_Query {
 			$limits = '';
 		}
 
+		$do_distinct = false;
+
+		/*
+		 * Duplicate terms are generally removed when necessary after the database query.
+		 * But when a LIMIT clause is included in the query, we let MySQL enforce
+		 * distinctness so the count is correct.
+		 */
+		if ( ! empty( $limits ) && 'all_with_object_id' !== $args['fields'] ) {
+			$do_distinct = true;
+		}
 
 		if ( ! empty( $args['search'] ) ) {
 			$this->sql_clauses['where']['search'] = $this->get_search_sql( $args['search'] );
@@ -568,8 +578,7 @@ class WP_Term_Query {
 		if ( ! empty( $meta_clauses ) ) {
 			$join .= $mq_sql['join'];
 			$this->sql_clauses['where']['meta_query'] = preg_replace( '/^\s*AND\s*/', '', $mq_sql['where'] );
-			$distinct .= "DISTINCT";
-
+			$do_distinct = true;
 		}
 
 		$selects = array();
@@ -631,6 +640,8 @@ class WP_Term_Query {
 
 		$where = implode( ' AND ', $this->sql_clauses['where'] );
 
+		$distinct = $do_distinct ? 'DISTINCT' : '';
+
 		/**
 		 * Filters the terms query SQL clauses.
 		 *
diff --git a/tests/phpunit/tests/term/query.php b/tests/phpunit/tests/term/query.php
index b2e2a27621..855db6fb28 100644
--- a/tests/phpunit/tests/term/query.php
+++ b/tests/phpunit/tests/term/query.php
@@ -427,4 +427,61 @@ class Tests_Term_Query extends WP_UnitTestCase {
 		$terms = wp_get_object_terms( $post_id, array( 'category', 'wptests_tax' ) );
 		$this->assertEquals( array( $term_ids[1], $term_ids[0], 1 ), wp_list_pluck( $terms, 'term_id' ) );
 	}
+
+	/**
+	 * @ticket 41796
+	 */
+	public function test_number_should_work_with_object_ids() {
+		register_taxonomy( 'wptests_tax', 'post' );
+
+		$term_1 = self::factory()->term->create( array(
+			'taxonomy' => 'wptests_tax',
+		) );
+		$term_2 = self::factory()->term->create( array(
+			'taxonomy' => 'wptests_tax',
+		) );
+
+		$post_1 = self::factory()->post->create();
+		$post_2 = self::factory()->post->create();
+
+		wp_set_object_terms( $post_1, array( $term_1, $term_2 ), 'wptests_tax' );
+		wp_set_object_terms( $post_2, array( $term_1 ), 'wptests_tax' );
+
+		$q = new WP_Term_Query( array(
+			'taxonomy' => 'wptests_tax',
+			'object_ids' => array( $post_1, $post_2 ),
+			'number' => 2,
+		) );
+
+		$this->assertEqualSets( array( $term_1, $term_2 ), wp_list_pluck( $q->terms, 'term_id' ) );
+	}
+
+	/**
+	 * @ticket 41796
+	 */
+	public function test_number_should_work_with_object_ids_and_all_with_object_id() {
+		register_taxonomy( 'wptests_tax', 'post' );
+
+		$term_1 = self::factory()->term->create( array(
+			'taxonomy' => 'wptests_tax',
+		) );
+		$term_2 = self::factory()->term->create( array(
+			'taxonomy' => 'wptests_tax',
+		) );
+
+		$post_1 = self::factory()->post->create();
+		$post_2 = self::factory()->post->create();
+
+		wp_set_object_terms( $post_1, array( $term_1, $term_2 ), 'wptests_tax' );
+		wp_set_object_terms( $post_2, array( $term_1 ), 'wptests_tax' );
+
+		$q = new WP_Term_Query( array(
+			'taxonomy' => 'wptests_tax',
+			'object_ids' => array( $post_1, $post_2 ),
+			'fields' => 'all_with_object_id',
+			'number' => 2,
+		) );
+
+		$this->assertEqualSets( array( $term_1, $term_1 ), wp_list_pluck( $q->terms, 'term_id' ) );
+	}
 }