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.
Fixes #43559.


git-svn-id: https://develop.svn.wordpress.org/branches/5.0@43811 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/ajax-actions.php

@@ -1341,8 +1341,6 @@ function wp_ajax_add_meta() {
 		$value = wp_unslash( $_POST['meta'][$mid]['value'] );
 		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
 		if ( is_protected_meta( $meta->meta_key, 'post' ) || is_protected_meta( $key, 'post' ) ||

src/wp-admin/includes/post.php

@@ -814,7 +814,7 @@ function add_meta( $post_ID ) {
 	if ( is_string( $metavalue ) )
 		$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.

tests/phpunit/tests/admin/includesPost.php

@@ -707,4 +707,21 @@ function test_get_block_editor_server_block_settings() {
 		$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 ) );
+	}
 }

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 ) );
+	}
+}