REST API: Don't assume all item schemas have properties.

src/wp-includes/rest-api/endpoints/class-wp-rest-controller.php

@@ -344,8 +344,10 @@ public function get_public_item_schema() {
 
 		$schema = $this->get_item_schema();
 
-		foreach ( $schema['properties'] as &$property ) {
-			unset( $property['arg_options'] );
+		if ( ! empty( $schema['properties'] ) ) {
+			foreach ( $schema['properties'] as &$property ) {
+				unset( $property['arg_options'] );
+			}
 		}
 
 		return $schema;

tests/phpunit/includes/bootstrap.php

@@ -154,6 +154,7 @@ function wp_tests_options( $value ) {
 require __DIR__ . '/utils.php';
 require __DIR__ . '/spy-rest-server.php';
 require __DIR__ . '/class-wp-rest-test-search-handler.php';
+require __DIR__ . '/class-wp-rest-test-configurable-controller.php';
 require __DIR__ . '/class-wp-fake-block-type.php';
 
 /**

tests/phpunit/includes/class-wp-rest-test-configurable-controller.php

@@ -0,0 +1,60 @@
+<?php
+/**
+ * Unit tests covering WP_REST_Controller functionality using a flexible schema.
+ *
+ * @package WordPress
+ * @subpackage REST API
+ * @since 5.4.0
+ */
+
+/**
+ * WP_REST_Test_Configurable_Controller class.
+ *
+ * @group restapi
+ *
+ * @since 5.4.0
+ */
+class WP_REST_Test_Configurable_Controller extends WP_REST_Controller {
+
+	/**
+	 * Test schema.
+	 *
+	 * @since 5.4.0
+	 *
+	 * @var array $test_schema
+	 */
+	protected $test_schema;
+
+	/**
+	 * Class constructor.
+	 *
+	 * @since 5.4.0
+	 *
+	 * @param array $test_schema Schema for use in testing.
+	 */
+	public function __construct( $test_schema ) {
+		$this->test_schema = $test_schema;
+	}
+
+	/**
+	 * Provides the test schema.
+	 *
+	 * @since 5.4.0
+	 *
+	 * @return array Test schema.
+	 */
+	public function get_test_schema() {
+		return $this->test_schema;
+	}
+
+	/**
+	 * Get the item's schema, conforming to JSON Schema.
+	 *
+	 * @since 5.4.0
+	 *
+	 * @return array
+	 */
+	public function get_item_schema() {
+		return $this->add_additional_fields_schema( $this->get_test_schema() );
+	}
+}

tests/phpunit/tests/rest-api/rest-controller.php

@@ -343,6 +343,39 @@ public function test_filtering_fields_for_response_by_context_returns_fields_wit
 		$this->assertGreaterThan( 0, $listener->get_call_count( $method ) );
 	}
 
+	/**
+	 * @ticket 48785
+	 */
+	public function test_get_public_item_schema_with_properties() {
+		$schema = ( new WP_REST_Test_Controller() )->get_public_item_schema();
+
+		// Double-check that the public item schema set in WP_REST_Test_Controller still has properties.
+		$this->assertArrayHasKey( 'properties', $schema );
+
+		// But arg_options should be removed.
+		$this->assertArrayNotHasKey( 'arg_options', $schema['properties']['someargoptions'] );
+	}
+
+	/**
+	 * @ticket 48785
+	 */
+	public function test_get_public_item_schema_no_properties() {
+		$controller = new WP_REST_Test_Configurable_Controller(
+			array(
+				'$schema'     => 'http://json-schema.org/draft-04/schema#',
+				'title'       => 'foo',
+				'type'        => 'string',
+				'description' => 'This is my magical endpoint that just returns a string.',
+			)
+		);
+
+		// Initial check that the test class is working as expected.
+		$this->assertArrayNotHasKey( 'properties', $controller->get_public_item_schema() );
+
+		// Test that the schema lacking 'properties' is returned as expected.
+		$this->assertEqualSetsWithIndex( $controller->get_public_item_schema(), $controller->get_test_schema() );
+	}
+
 	public function test_add_additional_fields_to_object_respects_fields_param() {
 		$controller = new WP_REST_Test_Controller();
 		$request    = new WP_REST_Request( 'GET', '/wp/v2/testroute' );