Remove RestGetAllAliasesAction (#31308)

We currently have a specific REST action to retrieve all aliaes, which
uses internally the get index API. This doesn't seem to be required
anymore though as the existing RestGetAliaesAction could as well take
the requests with no indices and aliases specified.

This commit removes the RestGetAllAliasesAction in favour of using
RestGetAliasesAction also for requests that don't specify indices nor
aliases. Similar to #31129.

server/src/main/java/org/elasticsearch/action/ActionModule.java

@@ -254,7 +254,6 @@
 import org.elasticsearch.rest.action.admin.indices.RestFlushAction;
 import org.elasticsearch.rest.action.admin.indices.RestForceMergeAction;
 import org.elasticsearch.rest.action.admin.indices.RestGetAliasesAction;
-import org.elasticsearch.rest.action.admin.indices.RestGetAllAliasesAction;
 import org.elasticsearch.rest.action.admin.indices.RestGetFieldMappingAction;
 import org.elasticsearch.rest.action.admin.indices.RestGetIndexTemplateAction;
 import org.elasticsearch.rest.action.admin.indices.RestGetIndicesAction;
@@ -553,8 +552,6 @@ public void initRestHandlers(Supplier<DiscoveryNodes> nodesInCluster) {
         registerHandler.accept(new RestRestoreSnapshotAction(settings, restController));
         registerHandler.accept(new RestDeleteSnapshotAction(settings, restController));
         registerHandler.accept(new RestSnapshotsStatusAction(settings, restController));
-
-        registerHandler.accept(new RestGetAllAliasesAction(settings, restController));
         registerHandler.accept(new RestGetIndicesAction(settings, restController, indexScopedSettings, settingsFilter));
         registerHandler.accept(new RestIndicesStatsAction(settings, restController));
         registerHandler.accept(new RestIndicesSegmentsAction(settings, restController));

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestGetAliasesAction.java

@@ -60,6 +60,8 @@ public class RestGetAliasesAction extends BaseRestHandler {
 
     public RestGetAliasesAction(final Settings settings, final RestController controller) {
         super(settings);
+        controller.registerHandler(GET, "/_alias", this);
+        controller.registerHandler(GET, "/_aliases", this);
         controller.registerHandler(GET, "/_alias/{name}", this);
         controller.registerHandler(HEAD, "/_alias/{name}", this);
         controller.registerHandler(GET, "/{index}/_alias", this);

x-pack/qa/core-rest-tests-with-security/build.gradle

@@ -15,6 +15,7 @@ integTestRunner {
     ['cat.aliases/10_basic/Empty cluster',
      'index/10_with_id/Index with ID',
      'indices.get_alias/10_basic/Get alias against closed indices',
+     'indices.get_alias/20_empty/Check empty aliases when getting all aliases via /_alias',
      'cat.templates/10_basic/No templates',
      'cat.templates/10_basic/Sort templates',
      'cat.templates/10_basic/Multiple template',