General: Handle missing field in WP_List_Util::pluck().

Handles when the `$field` (i.e. key or property) is missing in one of the `$input_list` items by checking the key (array) or property (object) exists before using it for assignment.

Resolves the following bugs:

* a PHP warning for undefined key|property.
* `null` being set for that array or object within the returned list.

The changes resolve the issues in both `WP_List_Util::pluck()` (if invoked directly) and `wp_list_pluck()`.

Also includes an additional test for the scenario where the `wp_list_pluck()` `$index_key` is not `null`, the `$field` is missing in one of the `$input_list` items.

Follow-up to [55423], [51663], [42527], [38928].

Props iamarunchaitanyajami, davidbinda, hellofromTonya, helgatheviking.
Fixes #59774.

git-svn-id: https://develop.svn.wordpress.org/trunk@57698 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-list-util.php

@@ -165,9 +165,13 @@ public function pluck( $field, $index_key = null ) {
 			 */
 			foreach ( $this->output as $key => $value ) {
 				if ( is_object( $value ) ) {
-					$newlist[ $key ] = $value->$field;
+					if ( property_exists( $value, $field ) ) {
+						$newlist[ $key ] = $value->$field;
+					}
 				} elseif ( is_array( $value ) ) {
-					$newlist[ $key ] = $value[ $field ];
+					if ( array_key_exists( $field, $value ) ) {
+						$newlist[ $key ] = $value[ $field ];
+					}
 				} else {
 					_doing_it_wrong(
 						__METHOD__,
@@ -188,16 +192,20 @@ public function pluck( $field, $index_key = null ) {
 		 */
 		foreach ( $this->output as $value ) {
 			if ( is_object( $value ) ) {
-				if ( isset( $value->$index_key ) ) {
-					$newlist[ $value->$index_key ] = $value->$field;
-				} else {
-					$newlist[] = $value->$field;
+				if ( property_exists( $value, $field ) ) {
+					if ( property_exists( $value, $index_key ) ) {
+						$newlist[ $value->$index_key ] = $value->$field;
+					} else {
+						$newlist[] = $value->$field;
+					}
 				}
 			} elseif ( is_array( $value ) ) {
-				if ( isset( $value[ $index_key ] ) ) {
-					$newlist[ $value[ $index_key ] ] = $value[ $field ];
-				} else {
-					$newlist[] = $value[ $field ];
+				if ( array_key_exists( $field, $value ) ) {
+					if ( array_key_exists( $index_key, $value ) ) {
+						$newlist[ $value[ $index_key ] ] = $value[ $field ];
+					} else {
+						$newlist[] = $value[ $field ];
+					}
 				}
 			} else {
 				_doing_it_wrong(

tests/phpunit/tests/functions/wpListPluck.php

@@ -271,7 +271,6 @@ public function data_wp_list_pluck() {
 						'abc' => 'xyz',
 					),
 					array(
-						'foo'   => 'foo',
 						'123'   => '456',
 						'lorem' => 'ipsum',
 						'key'   => 'bar',
@@ -285,10 +284,34 @@ public function data_wp_list_pluck() {
 				'key',
 				array(
 					'bar',
-					'bar'   => 'foo',
 					'value' => 'baz',
 				),
 			),
+			'arrays with key missing'        => array(
+				array(
+					array(
+						'foo' => 'bar',
+						'bar' => 'baz',
+						'abc' => 'xyz',
+					),
+					array(
+						'foo'   => 'foo',
+						'123'   => '456',
+						'lorem' => 'ipsum',
+						'key'   => 'bar',
+					),
+					array(
+						'foo' => 'baz',
+						'key' => 'value',
+					),
+				),
+				'key',
+				null,
+				array(
+					1 => 'bar',
+					2 => 'value',
+				),
+			),
 			'objects'                        => array(
 				array(
 					(object) array(
@@ -342,7 +365,6 @@ public function data_wp_list_pluck() {
 						'abc' => 'xyz',
 					),
 					(object) array(
-						'foo'   => 'foo',
 						'123'   => '456',
 						'lorem' => 'ipsum',
 						'key'   => 'bar',
@@ -356,10 +378,34 @@ public function data_wp_list_pluck() {
 				'key',
 				array(
 					'bar',
-					'bar'   => 'foo',
 					'value' => 'baz',
 				),
 			),
+			'objects with field missing'     => array(
+				array(
+					(object) array(
+						'foo' => 'bar',
+						'bar' => 'baz',
+						'abc' => 'xyz',
+					),
+					(object) array(
+						'foo'   => 'foo',
+						'123'   => '456',
+						'lorem' => 'ipsum',
+						'key'   => 'bar',
+					),
+					(object) array(
+						'foo' => 'baz',
+						'key' => 'value',
+					),
+				),
+				'key',
+				null,
+				array(
+					1 => 'bar',
+					2 => 'value',
+				),
+			),
 		);
 	}
 }