Get rid of unnecessarily strict _doing_it_wrong().

src/wp-includes/functions.php

@@ -4702,26 +4702,14 @@ function _mce_set_direction( $mce_init ) {
  * being made. It does not return true when a REST endpoint is hit as part of another request, e.g. for preloading a
  * REST response. See {@see wp_is_rest_endpoint()} for that purpose.
  *
- * This function must not be called until the {@see 'parse_request'} action.
+ * This function should not be called until the {@see 'parse_request'} action, as the constant is only defined then,
+ * even for an actual REST request.
  *
  * @since 6.5.0
  *
  * @return bool True if it's a WordPress REST API request, false otherwise.
  */
 function wp_is_rest_request(): bool {
-	if ( ! defined( 'REST_REQUEST' ) && ! did_action( 'parse_request' ) ) {
-		_doing_it_wrong(
-			__FUNCTION__,
-			sprintf(
-				/* translators: %s: parse_request */
-				__( 'Detecting whether the current request is a REST API request is not possible until the %s hook.' ),
-				'parse_request'
-			),
-			'6.5.0'
-		);
-		return false;
-	}
-
 	return defined( 'REST_REQUEST' ) && REST_REQUEST;
 }
 

src/wp-includes/rest-api.php

@@ -3405,13 +3405,8 @@ function wp_is_rest_endpoint(): bool {
 	/* @var WP_REST_Server $wp_rest_server */
 	global $wp_rest_server;
 
-	/*
-	 * Check whether this is a standalone REST request.
-	 * This check is not using the `wp_is_rest_request()` function as it may be called before the constant is actually
-	 * available. Since this is only one way of determining whether a REST endpoint is being handled, there is no need
-	 * to be as strict here as in the check for whether this is an actual standalone REST request.
-	 */
-	$is_rest_endpoint = defined( 'REST_REQUEST' ) && REST_REQUEST;
+	// Check whether this is a standalone REST request.
+	$is_rest_endpoint = wp_is_rest_request();
 	if ( ! $is_rest_endpoint ) {
 		// Otherwise, check whether an internal REST request is currently being handled.
 		$is_rest_endpoint = isset( $wp_rest_server )