Fields API: Add the server-side registry and REST route

backport-changelog/7.2/13911.md

@@ -0,0 +1,3 @@
+https://github.com/WordPress/wordpress-develop/pull/13911
+
+* https://github.com/WordPress/gutenberg/pull/84078

lib/compat/wordpress-7.1/class-gutenberg-rest-view-config-controller-7-1.php

@@ -142,88 +142,15 @@ public function get_items( $request ) {
 			'kind'            => $kind,
 			'name'            => $name,
 			'version'         => Gutenberg_View_Config_Data::LATEST_VERSION,
-			'default_view'    => $this->cast_empty_objects( $config['default_view'], $schema['properties']['default_view'] ),
-			'default_layouts' => $this->cast_empty_objects( $config['default_layouts'], $schema['properties']['default_layouts'] ),
-			'view_list'       => $this->cast_empty_objects( $config['view_list'], $schema['properties']['view_list'] ),
-			'form'            => $this->cast_empty_objects( $config['form'], $schema['properties']['form'] ),
+			'default_view'    => gutenberg_rest_cast_empty_objects_from_schema( $config['default_view'], $schema['properties']['default_view'] ),
+			'default_layouts' => gutenberg_rest_cast_empty_objects_from_schema( $config['default_layouts'], $schema['properties']['default_layouts'] ),
+			'view_list'       => gutenberg_rest_cast_empty_objects_from_schema( $config['view_list'], $schema['properties']['view_list'] ),
+			'form'            => gutenberg_rest_cast_empty_objects_from_schema( $config['form'], $schema['properties']['form'] ),
 		);
 
 		return rest_ensure_response( $response );
 	}
 
-	/**
-	 * Recursively casts empty arrays to objects where the schema types them as
-	 * objects.
-	 *
-	 * PHP cannot distinguish an empty associative array from an empty list, so
-	 * `json_encode()` always serializes `array()` as a JSON array (`[]`). The
-	 * REST schema, however, types several values as objects, which must encode
-	 * as `{}`. This walks the value against its schema and casts any empty,
-	 * object-typed array to an object. Non-empty associative arrays already
-	 * encode as objects, so they are left as arrays and only recursed into to
-	 * fix any nested empty objects.
-	 *
-	 * Union schemas (`oneOf`/`anyOf`) are handled only for the empty-array case:
-	 * an empty value is cast to an object when any branch allows an object. Such
-	 * values are not recursed into, which is sufficient for the form schema
-	 * where they never contain empty nested objects.
-	 *
-	 * @param mixed $value  The value to normalize.
-	 * @param array $schema The schema node describing the value.
-	 * @return mixed The normalized value, with empty object-typed arrays cast to objects.
-	 */
-	protected function cast_empty_objects( $value, $schema ) {
-		if ( ! is_array( $value ) || ! is_array( $schema ) ) {
-			return $value;
-		}
-
-		if ( isset( $schema['oneOf'] ) || isset( $schema['anyOf'] ) ) {
-			$branches = isset( $schema['oneOf'] ) ? $schema['oneOf'] : $schema['anyOf'];
-			if ( array() === $value ) {
-				foreach ( $branches as $branch ) {
-					if ( is_array( $branch ) && in_array( 'object', (array) ( isset( $branch['type'] ) ? $branch['type'] : array() ), true ) ) {
-						return (object) array();
-					}
-				}
-			}
-			return $value;
-		}
-
-		$types = (array) ( isset( $schema['type'] ) ? $schema['type'] : array() );
-
-		if ( in_array( 'array', $types, true ) && isset( $schema['items'] ) ) {
-			foreach ( $value as $index => $item ) {
-				$value[ $index ] = $this->cast_empty_objects( $item, $schema['items'] );
-			}
-			return $value;
-		}
-
-		if ( in_array( 'object', $types, true ) ) {
-			if ( isset( $schema['properties'] ) ) {
-				foreach ( $schema['properties'] as $property => $property_schema ) {
-					if ( array_key_exists( $property, $value ) ) {
-						$value[ $property ] = $this->cast_empty_objects( $value[ $property ], $property_schema );
-					}
-				}
-			}
-			if ( isset( $schema['additionalProperties'] ) && is_array( $schema['additionalProperties'] ) ) {
-				foreach ( $value as $key => $item ) {
-					if ( isset( $schema['properties'][ $key ] ) ) {
-						continue;
-					}
-					$value[ $key ] = $this->cast_empty_objects( $item, $schema['additionalProperties'] );
-				}
-			}
-
-			// Empty object-typed arrays must serialize as {} to match the schema.
-			if ( array() === $value ) {
-				return (object) array();
-			}
-		}
-
-		return $value;
-	}
-
 	/**
 	 * Retrieves the item's schema, conforming to JSON Schema.
 	 *