From 3e704473e709479f680f3e93747cbc9a17203663 Mon Sep 17 00:00:00 2001
From: Boone Gorges <boonebgorges@git.wordpress.org>
Date: Fri, 23 Aug 2019 16:04:07 +0000
Subject: [PATCH] Taxonomy: Ensure consistency of `hide_empty` in term queries
 when `taxonomy` is excluded.

When querying for terms in hierarchical categories using `hide_empty=true`,
results have historically included parent terms which are themselves
unattached to any objects (are "empty") but which have non-empty descendent
terms. Because this process involves walking the descendant tree, we avoid it
when we detect that the queried taxonomies are not hierarchical. (This
behavior was introduced in [5525].)

When the `taxonomy` parameter of `get_terms()` was made optional - see #35495,
[36614] - it affected the mechanism for avoiding unneccessary tree walks,
since there may not be any explicitly declared taxonomies to run through
`is_taxonomy_hierarchical()`. As a result, term queries excluding `taxonomy`
did not check descendants, and empty parents with non-empty children were not
included in `hide_empty` results.

We correct the behavior by crawling term descendants when the `taxonomy`
argument is absent, which means that we're querying for terms in all taxonomies.

Props smerriman.
Fixes #37728.

git-svn-id: https://develop.svn.wordpress.org/trunk@45888 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-includes/class-wp-term-query.php |  3 +
 tests/phpunit/tests/term/query.php      | 79 +++++++++++++++++++++++++
 2 files changed, 82 insertions(+)

diff --git a/src/wp-includes/class-wp-term-query.php b/src/wp-includes/class-wp-term-query.php
index 13c0ea3f80..a7d400daa8 100644
--- a/src/wp-includes/class-wp-term-query.php
+++ b/src/wp-includes/class-wp-term-query.php
@@ -326,6 +326,9 @@ class WP_Term_Query {
 					$has_hierarchical_tax = true;
 				}
 			}
+		} else {
+			// When no taxonomies are provided, assume we have to descend the tree.
+			$has_hierarchical_tax = true;
 		}
 
 		if ( ! $has_hierarchical_tax ) {
diff --git a/tests/phpunit/tests/term/query.php b/tests/phpunit/tests/term/query.php
index 4daac1c35f..699330851b 100644
--- a/tests/phpunit/tests/term/query.php
+++ b/tests/phpunit/tests/term/query.php
@@ -767,4 +767,83 @@ class Tests_Term_Query extends WP_UnitTestCase {
 	public static function filter_terms_pre_query( $terms, $query ) {
 		return array( 555 );
 	}
+
+	/**
+	 * @ticket 37728
+	 */
+	public function test_hide_empty_should_include_empty_parents_of_nonempty_children() {
+		register_taxonomy(
+			'wptests_tax',
+			'post',
+			array(
+				'hierarchical' => true,
+			)
+		);
+
+		$t1 = self::factory()->term->create(
+			array(
+				'taxonomy' => 'wptests_tax',
+			)
+		);
+
+		$t2 = self::factory()->term->create(
+			array(
+				'taxonomy' => 'wptests_tax',
+				'parent'   => $t1,
+			)
+		);
+
+		$p = self::factory()->post->create();
+
+		wp_set_object_terms( $p, $t2, 'wptests_tax' );
+
+		$q = new WP_Term_Query(
+			array(
+				'taxonomy'   => 'wptests_tax',
+				'hide_empty' => true,
+				'fields'     => 'ids',
+			)
+		);
+
+		$this->assertContains( $t1, $q->terms );
+	}
+
+	/**
+	 * @ticket 37728
+	 */
+	public function test_hide_empty_should_include_empty_parents_of_nonempty_children_when_category_is_unspecified() {
+		register_taxonomy(
+			'wptests_tax',
+			'post',
+			array(
+				'hierarchical' => true,
+			)
+		);
+
+		$t1 = self::factory()->term->create(
+			array(
+				'taxonomy' => 'wptests_tax',
+			)
+		);
+
+		$t2 = self::factory()->term->create(
+			array(
+				'taxonomy' => 'wptests_tax',
+				'parent'   => $t1,
+			)
+		);
+
+		$p = self::factory()->post->create();
+
+		wp_set_object_terms( $p, $t2, 'wptests_tax' );
+
+		$q = new WP_Term_Query(
+			array(
+				'hide_empty' => true,
+				'fields'     => 'ids',
+			)
+		);
+
+		$this->assertContains( $t1, $q->terms );
+	}
 }