From a875f9dae7c10e313dda6b9bf5cc7bea53e493b9 Mon Sep 17 00:00:00 2001
From: "K. Adam White" <kadamwhite@git.wordpress.org>
Date: Wed, 31 Jul 2019 20:20:02 +0000
Subject: [PATCH] REST API: Skip processing fields which are not present in the
 selected context.

In `WP_REST_Controller::get_fields_for_response()`, exclude fields which are not registered to appear in the request's context.

In conjunction with r45705 this prevents the unnecessary computation of the sample permalink when making a request that is not context=edit.

Props dlh.
Fixes #45605.


git-svn-id: https://develop.svn.wordpress.org/trunk@45706 602fd350-edb4-49c9-b593-d223f7449a82
---
 .../endpoints/class-wp-rest-controller.php    | 18 +++-
 .../tests/rest-api/rest-controller.php        | 88 +++++++++++++++++++
 2 files changed, 103 insertions(+), 3 deletions(-)

diff --git a/src/wp-includes/rest-api/endpoints/class-wp-rest-controller.php b/src/wp-includes/rest-api/endpoints/class-wp-rest-controller.php
index 6188bff380..cd976f3357 100644
--- a/src/wp-includes/rest-api/endpoints/class-wp-rest-controller.php
+++ b/src/wp-includes/rest-api/endpoints/class-wp-rest-controller.php
@@ -517,18 +517,30 @@ abstract class WP_REST_Controller {
 	 * @return array Fields to be included in the response.
 	 */
 	public function get_fields_for_response( $request ) {
-		$schema = $this->get_item_schema();
-		$fields = isset( $schema['properties'] ) ? array_keys( $schema['properties'] ) : array();
+		$schema     = $this->get_item_schema();
+		$properties = isset( $schema['properties'] ) ? $schema['properties'] : array();
 
 		$additional_fields = $this->get_additional_fields();
 		foreach ( $additional_fields as $field_name => $field_options ) {
 			// For back-compat, include any field with an empty schema
 			// because it won't be present in $this->get_item_schema().
 			if ( is_null( $field_options['schema'] ) ) {
-				$fields[] = $field_name;
+				$properties[ $field_name ] = $field_options;
 			}
 		}
 
+		// Exclude fields that specify a different context than the request context.
+		$context = $request['context'];
+		if ( $context ) {
+			foreach ( $properties as $name => $options ) {
+				if ( ! empty( $options['context'] ) && ! in_array( $context, $options['context'], true ) ) {
+					unset( $properties[ $name ] );
+				}
+			}
+		}
+
+		$fields = array_keys( $properties );
+
 		if ( ! isset( $request['_fields'] ) ) {
 			return $fields;
 		}
diff --git a/tests/phpunit/tests/rest-api/rest-controller.php b/tests/phpunit/tests/rest-api/rest-controller.php
index 6301e64d9d..f130abc62d 100644
--- a/tests/phpunit/tests/rest-api/rest-controller.php
+++ b/tests/phpunit/tests/rest-api/rest-controller.php
@@ -255,6 +255,94 @@ class WP_Test_REST_Controller extends WP_Test_REST_TestCase {
 		);
 	}
 
+	public function test_get_fields_for_response_filters_by_context() {
+		$controller = new WP_REST_Test_Controller();
+
+		$request = new WP_REST_Request( 'GET', '/wp/v2/testroute' );
+		$request->set_param( 'context', 'view' );
+
+		$schema = $controller->get_item_schema();
+		$field  = 'somefield';
+
+		$listener = new MockAction();
+		$method   = 'action';
+
+		register_rest_field(
+			$schema['title'],
+			$field,
+			array(
+				'schema'       => array(
+					'type'    => 'string',
+					'context' => array( 'embed' ),
+				),
+				'get_callback' => array( $listener, $method ),
+			)
+		);
+
+		$controller->prepare_item_for_response( array(), $request );
+
+		$this->assertSame( 0, $listener->get_call_count( $method ) );
+
+		$request->set_param( 'context', 'embed' );
+
+		$controller->prepare_item_for_response( array(), $request );
+
+		$this->assertGreaterThan( 0, $listener->get_call_count( $method ) );
+	}
+
+	public function test_filtering_fields_for_response_by_context_returns_fields_with_no_context() {
+		$controller = new WP_REST_Test_Controller();
+
+		$request = new WP_REST_Request( 'GET', '/wp/v2/testroute' );
+		$request->set_param( 'context', 'view' );
+
+		$schema = $controller->get_item_schema();
+		$field  = 'somefield';
+
+		$listener = new MockAction();
+		$method   = 'action';
+
+		register_rest_field(
+			$schema['title'],
+			$field,
+			array(
+				'schema'       => array(
+					'type' => 'string',
+				),
+				'get_callback' => array( $listener, $method ),
+			)
+		);
+
+		$controller->prepare_item_for_response( array(), $request );
+
+		$this->assertGreaterThan( 0, $listener->get_call_count( $method ) );
+	}
+
+	public function test_filtering_fields_for_response_by_context_returns_fields_with_no_schema() {
+		$controller = new WP_REST_Test_Controller();
+
+		$request = new WP_REST_Request( 'GET', '/wp/v2/testroute' );
+		$request->set_param( 'context', 'view' );
+
+		$schema = $controller->get_item_schema();
+		$field  = 'somefield';
+
+		$listener = new MockAction();
+		$method   = 'action';
+
+		register_rest_field(
+			$schema['title'],
+			$field,
+			array(
+				'get_callback' => array( $listener, $method ),
+			)
+		);
+
+		$controller->prepare_item_for_response( array(), $request );
+
+		$this->assertGreaterThan( 0, $listener->get_call_count( $method ) );
+	}
+
 	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' );