Consume param in compat mode and add tests

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/cluster.component_template/10_basic.yml

@@ -171,3 +171,33 @@
   - match: {component_templates.0.component_template.template.lifecycle.enabled: true}
   - match: {component_templates.0.component_template.template.lifecycle.data_retention: "10d"}
   - is_true: component_templates.0.component_template.template.lifecycle.rollover
+
+---
+"Deprecated local parameter":
+  - requires:
+      capabilities:
+        - method: GET
+          path: /_component_template
+          capabilities: ["local_param_deprecated"]
+      test_runner_features: ["capabilities", "warnings"]
+      reason: Deprecation was implemented with capability
+
+  - do:
+      cluster.get_component_template:
+        local: true
+      warnings:
+        - "the [?local] query parameter to this API has no effect, is now deprecated, and will be removed in a future version"
+
+---
+"Deprecated local parameter works in v8 compat mode":
+  - requires:
+      test_runner_features: ["capabilities", "warnings", "headers"]
+
+  - do:
+      headers:
+        Content-Type: "application/vnd.elasticsearch+json;compatible-with=8"
+        Accept: "application/vnd.elasticsearch+json;compatible-with=8"
+      cluster.get_component_template:
+        local: true
+
+  - exists: component_templates

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

@@ -333,10 +333,12 @@ public static TimeValue getTimeout(RestRequest restRequest) {
     // NOTE: ensure each usage of this method has been deprecated for long enough to remove it.
     @UpdateForV10(owner = UpdateForV10.Owner.DISTRIBUTED_COORDINATION)
     public static void consumeDeprecatedLocalParameter(RestRequest request) {
-        if (request.getRestApiVersion() == RestApiVersion.V_8) {
+        if (request.hasParam("local") == false) {
             return;
         }
-        if (request.paramAsBoolean("local", false)) {
+        // Consume this param just for validation when in BWC mode.
+        final var local = request.paramAsBoolean("local", false);
+        if (request.getRestApiVersion() != RestApiVersion.V_8) {
             DeprecationLogger.getLogger(TransportLocalClusterStateAction.class)
                 .critical(
                     DeprecationCategory.API,

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

@@ -32,6 +32,8 @@
 @ServerlessScope(Scope.PUBLIC)
 public class RestGetComponentTemplateAction extends BaseRestHandler {
 
+    private static final Set<String> SUPPORTED_CAPABILITIES = Set.of("local_param_deprecated");
+
     @Override
     public List<Route> routes() {
         return List.of(
@@ -72,4 +74,8 @@ protected Set<String> responseParams() {
         return Settings.FORMAT_PARAMS;
     }
 
+    @Override
+    public Set<String> supportedCapabilities() {
+        return SUPPORTED_CAPABILITIES;
+    }
 }