From 244e4d4e637faa90d24a830690671064bb3fb48a Mon Sep 17 00:00:00 2001
From: Timothy Jacobs <timothyblynjacobs@git.wordpress.org>
Date: Sun, 17 Jan 2021 00:49:39 +0000
Subject: [PATCH] REST API: Allow sending an empty array to delete multi meta
 keys.

Previously, only `null` was supported.

Fixes #50790.
Props chrisvanpatten.


git-svn-id: https://develop.svn.wordpress.org/trunk@49966 602fd350-edb4-49c9-b593-d223f7449a82
---
 .../fields/class-wp-rest-meta-fields.php      |  8 +++---
 .../tests/rest-api/rest-post-meta-fields.php  | 25 +++++++++++++++++++
 2 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/src/wp-includes/rest-api/fields/class-wp-rest-meta-fields.php b/src/wp-includes/rest-api/fields/class-wp-rest-meta-fields.php
index 81806e1b65..78cef6f910 100644
--- a/src/wp-includes/rest-api/fields/class-wp-rest-meta-fields.php
+++ b/src/wp-includes/rest-api/fields/class-wp-rest-meta-fields.php
@@ -145,11 +145,15 @@ abstract class WP_REST_Meta_Fields {
 				continue;
 			}
 
+			$value = $meta[ $name ];
+
 			/*
 			 * A null value means reset the field, which is essentially deleting it
 			 * from the database and then relying on the default value.
+			 *
+			 * Non-single meta can also be removed by passing an empty array.
 			 */
-			if ( is_null( $meta[ $name ] ) ) {
+			if ( is_null( $value ) || ( array() === $value && ! $args['single'] ) ) {
 				$args = $this->get_registered_fields()[ $meta_key ];
 
 				if ( $args['single'] ) {
@@ -172,8 +176,6 @@ abstract class WP_REST_Meta_Fields {
 				continue;
 			}
 
-			$value = $meta[ $name ];
-
 			if ( ! $args['single'] && is_array( $value ) && count( array_filter( $value, 'is_null' ) ) ) {
 				return new WP_Error(
 					'rest_invalid_stored_value',
diff --git a/tests/phpunit/tests/rest-api/rest-post-meta-fields.php b/tests/phpunit/tests/rest-api/rest-post-meta-fields.php
index e3fc92d761..2b24cfc667 100644
--- a/tests/phpunit/tests/rest-api/rest-post-meta-fields.php
+++ b/tests/phpunit/tests/rest-api/rest-post-meta-fields.php
@@ -1027,6 +1027,31 @@ class WP_Test_REST_Post_Meta_Fields extends WP_Test_REST_TestCase {
 		$this->assertSame( $post_original->post_content, $post_updated->post_content );
 	}
 
+	/**
+	 * @ticket 50790
+	 */
+	public function test_remove_multi_value_with_empty_array() {
+		add_post_meta( self::$post_id, 'test_multi', 'val1' );
+		$values = get_post_meta( self::$post_id, 'test_multi', false );
+		$this->assertSame( array( 'val1' ), $values );
+
+		$this->grant_write_permission();
+
+		$data    = array(
+			'meta' => array(
+				'test_multi' => array(),
+			),
+		);
+		$request = new WP_REST_Request( 'POST', sprintf( '/wp/v2/posts/%d', self::$post_id ) );
+		$request->set_body_params( $data );
+
+		$response = rest_get_server()->dispatch( $request );
+		$this->assertSame( 200, $response->get_status() );
+
+		$meta = get_post_meta( self::$post_id, 'test_multi', false );
+		$this->assertEmpty( $meta );
+	}
+
 	public function test_remove_multi_value_db_error() {
 		add_post_meta( self::$post_id, 'test_multi', 'val1' );
 		$values = get_post_meta( self::$post_id, 'test_multi', false );