Taxonomy: Don't pass results of 'count' query through 'get_terms' filter.

Use of the 'get_terms' filter was consolidated in [37572], with the
introduction of `WP_Term_Query`. At that time, the result of 'count=true'
queries began being filtered by 'get_terms'. This breaks existing 'get_terms'
callbacks, which often assume that the returned value will be an array or a
`WP_Error` object.

Props JustinSainton.
Fixes #36992.

git-svn-id: https://develop.svn.wordpress.org/trunk@37623 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/taxonomy.php

@@ -1208,6 +1208,11 @@ function get_terms( $args = array(), $deprecated = '' ) {
 
 	$terms = $term_query->query( $args );
 
+	// Count queries are not filtered, for legacy reasons.
+	if ( $term_query->query_vars['count'] ) {
+		return $terms;
+	}
+
 	/**
 	 * Filters the found terms.
 	 *

tests/phpunit/tests/term/getTerms.php

@@ -2179,6 +2179,27 @@ class Tests_Term_getTerms extends WP_UnitTestCase {
 		$this->assertEqualSets( array(), $found );
 	}
 
+	/**
+	 * @ticket 36992
+	 * @ticket 35381
+	 */
+	public function test_count_should_pass_through_main_get_terms_filter() {
+		add_filter( 'get_terms', array( __CLASS__, 'maybe_filter_count' ) );
+
+		$found = get_terms( array(
+			'hide_empty' => 0,
+			'count' => true,
+		) );
+
+		remove_filter( 'get_terms', array( __CLASS__, 'maybe_filter_count' ) );
+
+		$this->assertNotEquals( 'foo', $found );
+	}
+
+	public static function maybe_filter_count() {
+		return 'foo';
+	}
+
 	protected function create_hierarchical_terms_and_posts() {
 		$terms = array();