Query: Prevent querying for all terms in WP_Term_Query when include is set to [0].

This change brings the `include` parameter of `WP_Term_Query` up-to-speed with the `include` and `__in` parameters of other `_Query` classes, so that sending a value of `[0]` will not unintentionally perform an unbound query that returns all Terms.

It also introduces 3 new unit tests (for the Post, Term, and User query classes) to compare this behavior between them and ensure they remain consistent going forward.

Props audrasjb, hareesh-pillai, hellofromTonya, johnjamesjacoby, mukesh27.

Fixes #47719.

git-svn-id: https://develop.svn.wordpress.org/trunk@61048 602fd350-edb4-49c9-b593-d223f7449a82

Author: JJJ

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

@@ -470,14 +470,11 @@ public function get_terms() {
 		$exclude_tree = $args['exclude_tree'];
 		$include      = $args['include'];
 
-		$inclusions = '';
 		if ( ! empty( $include ) ) {
 			$exclude      = '';
 			$exclude_tree = '';
 			$inclusions   = implode( ',', wp_parse_id_list( $include ) );
-		}
 
-		if ( ! empty( $inclusions ) ) {
 			$this->sql_clauses['where']['inclusions'] = 't.term_id IN ( ' . $inclusions . ' )';
 		}
 
@@ -815,10 +812,13 @@ public function get_terms() {
 		$terms = $wpdb->get_results( $this->request ); // phpcs:ignore WordPress.DB.PreparedSQL.NotPrepared
 
 		if ( empty( $terms ) ) {
+			$this->terms = array();
+
 			if ( $args['cache_results'] ) {
-				wp_cache_set_salted( $cache_key, array(), 'term-queries', $last_changed );
+				wp_cache_set_salted( $cache_key, $this->terms, 'term-queries', $last_changed );
 			}
-			return array();
+
+			return $this->terms;
 		}
 
 		$term_ids = wp_list_pluck( $terms, 'term_id' );

tests/phpunit/tests/post/query.php

@@ -778,6 +778,23 @@ public function test_found_posts_should_be_integer_even_if_found_posts_filter_re
 		$this->assertIsInt( $q->found_posts );
 	}
 
+	/**
+	 * @ticket 47719
+	 */
+	public function test_post__in_should_return_no_posts_when_0() {
+		self::factory()->post->create_many( 4 );
+
+		$query = new WP_Query(
+			array(
+				'post_type' => 'post',
+				'post__in'  => array( 0 ),
+			)
+		);
+
+		$this->assertSame( array(), $query->posts );
+		$this->assertSame( 0, $query->found_posts );
+	}
+
 	/**
 	 * @ticket 57296
 	 * @covers WP_Query::get_posts

tests/phpunit/tests/term/query.php

@@ -1051,6 +1051,26 @@ public function test_hide_empty_should_include_empty_parents_of_nonempty_childre
 		$this->assertContains( $t1, $q->terms );
 	}
 
+	/**
+	 * @ticket 47719
+	 */
+	public function test_include_should_return_no_terms_when_0() {
+		register_taxonomy( 'wptests_tax', 'post' );
+
+		self::factory()->term->create_many( 3, array( 'taxonomy' => 'wptests_tax' ) );
+
+		$query = new WP_Term_Query(
+			array(
+				'taxonomy' => 'wptests_tax',
+				'include'  => array( 0 ),
+			)
+		);
+
+		$expected = array();
+		$this->assertSame( $expected, $query->terms );
+		$this->assertSame( $expected, $query->get_terms() );
+	}
+
 	/**
 	 * Ensure cache keys are generated without WPDB placeholders.
 	 *

tests/phpunit/tests/user/query.php

@@ -1740,6 +1740,20 @@ public function test_users_pre_query_filter_should_bypass_database_query() {
 		$this->assertSame( 1, $q->total_users );
 	}
 
+	/**
+	 * @ticket 47719
+	 */
+	public function test_include_should_return_no_users_when_0() {
+		$query = new WP_User_Query(
+			array(
+				'role'    => '',
+				'include' => array( 0 ),
+			)
+		);
+
+		$this->assertSame( array(), $query->get_results() );
+	}
+
 	public static function filter_users_pre_query( $posts, $query ) {
 		$query->total_users = 1;