From e9558f0122af5c645ba3a6dc118da7e3e100590b Mon Sep 17 00:00:00 2001
From: Matthew Denton <matt@mdbitz.com>
Date: Wed, 23 Sep 2020 15:04:00 -0400
Subject: [PATCH] props @jmdodd - filter out set_object_terms actions that
 don't perform any update. Includes unit tests. (#17171)

---
 packages/sync/src/modules/class-terms.php     | 18 ++++++++++++++++
 .../sync/test_class.jetpack-sync-terms.php    | 21 +++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/packages/sync/src/modules/class-terms.php b/packages/sync/src/modules/class-terms.php
index 394eba0708a7a..a7ab85bd4f108 100644
--- a/packages/sync/src/modules/class-terms.php
+++ b/packages/sync/src/modules/class-terms.php
@@ -104,6 +104,7 @@ public function init_listeners( $callable ) {
 		add_action( 'delete_term', $callable, 10, 4 );
 		add_action( 'set_object_terms', $callable, 10, 6 );
 		add_action( 'deleted_term_relationships', $callable, 10, 2 );
+		add_filter( 'jetpack_sync_before_enqueue_set_object_terms', array( $this, 'filter_set_object_terms_no_update' ) );
 		add_filter( 'jetpack_sync_before_enqueue_jetpack_sync_save_term', array( $this, 'filter_blacklisted_taxonomies' ) );
 		add_filter( 'jetpack_sync_before_enqueue_jetpack_sync_add_term', array( $this, 'filter_blacklisted_taxonomies' ) );
 	}
@@ -255,6 +256,23 @@ public function filter_blacklisted_taxonomies( $args ) {
 		return $args;
 	}
 
+	/**
+	 * Filter out set_object_terms actions where the terms have not changed.
+	 *
+	 * @param array $args Hook args.
+	 * @return array|boolean False if no change in terms, the original hook args otherwise.
+	 */
+	public function filter_set_object_terms_no_update( $args ) {
+		// There is potential for other plugins to modify args, therefore lets validate # of and types.
+		// $args[2] is $tt_ids, $args[5] is $old_tt_ids see wp-includes/taxonomy.php L2740.
+		if ( 6 === count( $args ) && is_array( $args[2] ) && is_array( $args[5] ) ) {
+			if ( empty( array_diff( $args[2], $args[5] ) ) && empty( array_diff( $args[5], $args[2] ) ) ) {
+				return false;
+			}
+		}
+		return $args;
+	}
+
 	/**
 	 * Expand the term taxonomy IDs to terms within a hook before they are serialized and sent to the server.
 	 *
diff --git a/tests/php/sync/test_class.jetpack-sync-terms.php b/tests/php/sync/test_class.jetpack-sync-terms.php
index dcfc26cdbcc8d..9adfefbe3403f 100644
--- a/tests/php/sync/test_class.jetpack-sync-terms.php
+++ b/tests/php/sync/test_class.jetpack-sync-terms.php
@@ -133,6 +133,27 @@ public function test_delete_object_term_relationships() {
 		$this->assertEquals( $object_terms, $server_object_terms );
 	}
 
+	/**
+	 * Validate filter_set_object_terms_no_update filters out set_object_terms without changes.
+	 */
+	public function test_filter_set_object_terms_no_update() {
+		$anther_term = wp_insert_term( 'mouse', $this->taxonomy );
+		wp_set_post_terms( $this->post_id, array( $anther_term['term_id'] ), $this->taxonomy, false );
+
+		// Sync actions.
+		$this->sender->do_sync();
+		// Verify set_object_terms was triggered.
+		$this->assertNotFalse( $this->server_event_storage->get_most_recent_event( 'set_object_terms' ) );
+		// Reset event (actions) storage.
+		$this->server_event_storage->reset();
+
+		// Re-trigger and Sync actions.
+		wp_set_post_terms( $this->post_id, array( $anther_term['term_id'] ), $this->taxonomy, false );
+		$this->sender->do_sync();
+		// Verify set_object_terms was *not* triggered.
+		$this->assertFalse( $this->server_event_storage->get_most_recent_event( 'set_object_terms' ) );
+	}
+
 	public function test_filters_out_blacklisted_taxonomies() {
 		register_taxonomy( 'bloginfo_rss', 'post' );