Taxonomy: Bypass clearing taxonomy hierarchy for non-hierarchical taxonomies.

Modifies `clean_taxonomy_cache()` to bypass attempting to delete the `{$taxonomy}_children` option for non-hierarchical taxonomies, such as tags.

This removes a needless database query within `delete_option()` to determine if the `{$taxonomy}_children` option is set. It isn't.

Props: chouby, mukesh27, rollybueno, sabernhardt, shailu25, spacedmonkey, westonruter.
Fixes #64090.


git-svn-id: https://develop.svn.wordpress.org/trunk@60933 602fd350-edb4-49c9-b593-d223f7449a82

Author: peterwilsoncc

src/wp-includes/taxonomy.php

@@ -3732,8 +3732,10 @@ function clean_taxonomy_cache( $taxonomy ) {
 	wp_cache_set_terms_last_changed();
 
 	// Regenerate cached hierarchy.
-	delete_option( "{$taxonomy}_children" );
-	_get_term_hierarchy( $taxonomy );
+	if ( is_taxonomy_hierarchical( $taxonomy ) ) {
+		delete_option( "{$taxonomy}_children" );
+		_get_term_hierarchy( $taxonomy );
+	}
 
 	/**
 	 * Fires after a taxonomy's caches have been cleaned.

tests/phpunit/tests/taxonomy/cleanTaxonomyCache.php

@@ -0,0 +1,74 @@
+<?php
+
+/**
+ * @group taxonomy
+ *
+ * @covers ::clean_taxonomy_cache
+ */
+class Tests_Taxonomy_CleanTaxonomyCache extends WP_UnitTestCase {
+	/**
+	 * Ensure clearing the cache of a non-hierarchical taxonomy doesn't attempt to delete the hierarchy cache.
+	 *
+	 * @ticket 64090
+	 */
+	public function test_hierarchy_cache_not_cleared_for_non_hierarchical_taxonomy() {
+		// Prime the tag cache by inserting terms.
+		wp_insert_term( 'foo', 'post_tag' );
+
+		/*
+		 * Determine if delete_option( "{$taxonomy}_children" ) is called.
+		 *
+		 * None of the actions in delete_option() or _get_term_hierarchy() fire for
+		 * non-hierarchical taxonomies, so the query filter needs to be used to determine
+		 * if an attempt to delete the option was made.
+		 */
+		$delete_post_tag_children_called = false;
+		add_filter(
+			'query',
+			static function ( $query ) use ( &$delete_post_tag_children_called ) {
+				global $wpdb;
+				if ( "SELECT autoload FROM $wpdb->options WHERE option_name = 'post_tag_children'" === $query ) {
+					$delete_post_tag_children_called = true;
+				}
+				return $query;
+			}
+		);
+
+		clean_taxonomy_cache( 'post_tag' );
+
+		$this->assertFalse( $delete_post_tag_children_called, 'An attempt to clear the post_tag_children option should not be made.' );
+	}
+
+	/**
+	 * Ensure clearing the cache of a hierarchical taxonomy does attempt to delete the hierarchy cache.
+	 *
+	 * @ticket 64090
+	 */
+	public function test_hierarchy_cache_cleared_for_hierarchical_taxonomy() {
+		// Prime the category cache by inserting terms.
+		wp_insert_term( 'foo', 'category' );
+
+		/*
+		 * Determine if delete_option( "{$taxonomy}_children" ) is called.
+		 *
+		 * None of the actions in delete_option() or _get_term_hierarchy() fire for
+		 * non-hierarchical taxonomies, so the query filter needs to be used to determine
+		 * if an attempt to delete the option was made.
+		 */
+		$delete_category_children_called = false;
+		add_filter(
+			'query',
+			static function ( $query ) use ( &$delete_category_children_called ) {
+				global $wpdb;
+				if ( "SELECT autoload FROM $wpdb->options WHERE option_name = 'category_children'" === $query ) {
+					$delete_category_children_called = true;
+				}
+				return $query;
+			}
+		);
+
+		clean_taxonomy_cache( 'category' );
+
+		$this->assertTrue( $delete_category_children_called, 'An attempt to clear the category_children option should be made.' );
+	}
+}