From 88de9a1d7cc71704153408562e54efc53bfd48a3 Mon Sep 17 00:00:00 2001
From: Jonathan Desrosiers <desrosj@git.wordpress.org>
Date: Fri, 14 Dec 2018 03:16:56 +0000
Subject: [PATCH] Meta: Allow empty strings to be set by Custom Fields meta
 box.

Because the REST API allows meta keys to have empty values, the Custom Fields meta box should permit the same behavior.

Props charlestonsw, soulseekah, danielbachhuber.

Merges [43811] to trunk.

Fixes #43559.

git-svn-id: https://develop.svn.wordpress.org/trunk@44153 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-admin/includes/ajax-actions.php     |  3 -
 src/wp-admin/includes/post.php             |  2 +-
 tests/phpunit/tests/admin/includesPost.php | 17 ++++++
 tests/phpunit/tests/ajax/AddMeta.php       | 71 ++++++++++++++++++++++
 4 files changed, 89 insertions(+), 4 deletions(-)
 create mode 100644 tests/phpunit/tests/ajax/AddMeta.php

diff --git a/src/wp-admin/includes/ajax-actions.php b/src/wp-admin/includes/ajax-actions.php
index db22db2924..f11b243e1a 100644
--- a/src/wp-admin/includes/ajax-actions.php
+++ b/src/wp-admin/includes/ajax-actions.php
@@ -1443,9 +1443,6 @@ function wp_ajax_add_meta() {
 		if ( '' == trim( $key ) ) {
 			wp_die( __( 'Please provide a custom field name.' ) );
 		}
-		if ( '' == trim( $value ) ) {
-			wp_die( __( 'Please provide a custom field value.' ) );
-		}
 		if ( ! $meta = get_metadata_by_mid( 'post', $mid ) ) {
 			wp_die( 0 ); // if meta doesn't exist
 		}
diff --git a/src/wp-admin/includes/post.php b/src/wp-admin/includes/post.php
index 2595f69f7c..adc17ba91f 100644
--- a/src/wp-admin/includes/post.php
+++ b/src/wp-admin/includes/post.php
@@ -867,7 +867,7 @@ function add_meta( $post_ID ) {
 		$metavalue = trim( $metavalue );
 	}
 
-	if ( ( '0' === $metavalue || ! empty( $metavalue ) ) && ( ( ( '#NONE#' != $metakeyselect ) && ! empty( $metakeyselect ) ) || ! empty( $metakeyinput ) ) ) {
+	if ( ( ( '#NONE#' != $metakeyselect ) && ! empty( $metakeyselect ) ) || ! empty( $metakeyinput ) ) {
 		/*
 		 * We have a key/value pair. If both the select and the input
 		 * for the key have data, the input takes precedence.
diff --git a/tests/phpunit/tests/admin/includesPost.php b/tests/phpunit/tests/admin/includesPost.php
index 289f828e4c..ee3edb8aa0 100644
--- a/tests/phpunit/tests/admin/includesPost.php
+++ b/tests/phpunit/tests/admin/includesPost.php
@@ -799,4 +799,21 @@ class Tests_Admin_Includes_Post extends WP_UnitTestCase {
 		$this->assertArrayHasKey( $name, $blocks );
 		$this->assertSame( array( 'icon' => 'text' ), $blocks[ $name ] );
 	}
+
+	/**
+	 * @ticket 43559
+	 */
+	public function test_post_add_meta_empty_is_allowed() {
+		$p = self::factory()->post->create();
+
+		$_POST = array(
+			'metakeyinput' => 'testkey',
+			'metavalue'    => '',
+		);
+
+		wp_set_current_user( self::$admin_id );
+
+		$this->assertNotFalse( add_meta( $p ) );
+		$this->assertEquals( '', get_post_meta( $p, 'testkey', true ) );
+	}
 }
diff --git a/tests/phpunit/tests/ajax/AddMeta.php b/tests/phpunit/tests/ajax/AddMeta.php
new file mode 100644
index 0000000000..6ca4f3a0f2
--- /dev/null
+++ b/tests/phpunit/tests/ajax/AddMeta.php
@@ -0,0 +1,71 @@
+<?php
+
+/**
+ * Admin ajax functions to be tested
+ */
+require_once( ABSPATH . 'wp-admin/includes/ajax-actions.php' );
+
+/**
+ * Testing Add Meta AJAX functionality.
+ *
+ * @group ajax
+ */
+class Tests_Ajax_AddMeta extends WP_Ajax_UnitTestCase {
+	/**
+	 * @ticket 43559
+	 */
+	public function test_post_add_meta_empty_is_allowed_ajax() {
+		$p = self::factory()->post->create();
+
+		// Become an administrator.
+		$this->_setRole( 'administrator' );
+
+		$_POST = array(
+			'post_id'              => $p,
+			'metakeyinput'         => 'testkey',
+			'metavalue'            => '',
+			'_ajax_nonce-add-meta' => wp_create_nonce( 'add-meta' ),
+		);
+
+		// Make the request.
+		try {
+			$this->_handleAjax( 'add-meta' );
+		} catch ( WPAjaxDieContinueException $e ) {
+			unset( $e );
+		}
+
+		$this->assertEquals( '', get_post_meta( $p, 'testkey', true ) );
+	}
+
+	/**
+	 * @ticket 43559
+	 */
+	public function test_post_update_meta_empty_is_allowed_ajax() {
+		$p = self::factory()->post->create();
+
+		$m = add_post_meta( $p, 'testkey', 'hello' );
+
+		// Become an administrator.
+		$this->_setRole( 'administrator' );
+
+		$_POST = array(
+			'_ajax_nonce-add-meta' => wp_create_nonce( 'add-meta' ),
+			'post_id'              => $p,
+			'meta'                 => array(
+				$m => array(
+					'key'   => 'testkey',
+					'value' => '',
+				),
+			),
+		);
+
+		// Make the request.
+		try {
+			$this->_handleAjax( 'add-meta' );
+		} catch ( WPAjaxDieContinueException $e ) {
+			unset( $e );
+		}
+
+		$this->assertEquals( '', get_post_meta( $p, 'testkey', true ) );
+	}
+}