Allow additional path parameters to be added for capabilities validat…

…ion (#108901)

server/src/main/java/org/elasticsearch/rest/BaseRestHandler.java

@@ -81,7 +81,7 @@ public final long getUsageCount() {
     @Override
     public final void handleRequest(RestRequest request, RestChannel channel, NodeClient client) throws Exception {
         // check if the query has any parameters that are not in the supported set (if declared)
-        Set<String> supported = supportedQueryParameters();
+        Set<String> supported = allSupportedParameters();
         if (supported != null) {
             var allSupported = Sets.union(ALWAYS_SUPPORTED, supported);
             if (allSupported.containsAll(request.params().keySet()) == false) {

server/src/main/java/org/elasticsearch/rest/RestHandler.java

@@ -86,6 +86,18 @@ default List<Route> routes() {
         return Collections.emptyList();
     }
 
+    /**
+     * The set of path and query parameters that could be present on this handler.
+     * This method is only required due to <a href="https://github.com/elastic/elasticsearch/issues/36785">#36785</a>,
+     * which conflates query and path parameters inside the rest handler.
+     * This method should be overridden to add path parameters to {@link #supportedQueryParameters}
+     * if the handler has path parameters.
+     * This method will be removed when {@link #supportedQueryParameters()} and {@link BaseRestHandler#responseParams()} are combined.
+     */
+    default @Nullable Set<String> allSupportedParameters() {
+        return supportedQueryParameters();
+    }
+
     /**
      * The set of query parameters accepted by this rest handler,
      * {@code null} if query parameters should not be checked nor validated.