Remove types deprecation warning for indices.exists

Currently we log a deprecation warning to the types removal in
RestGetIndicesAction even if the REST method is HEAD, which is used by the
indices.exists API. Since the body is empty in this case we should not need to
show the deprecation warning.

Closes elastic#43905

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

@@ -70,8 +70,8 @@ public String getName() {
     @Override
     public RestChannelConsumer prepareRequest(final RestRequest request, final NodeClient client) throws IOException {
         String[] indices = Strings.splitStringByCommaToArray(request.param("index"));
-        // starting with 7.0 we don't include types by default in the response
-        if (request.hasParam(INCLUDE_TYPE_NAME_PARAMETER)) {
+        // starting with 7.0 we don't include types by default in the response to GET requests
+        if (request.hasParam(INCLUDE_TYPE_NAME_PARAMETER) && request.method().equals(GET)) {
             deprecationLogger.deprecatedAndMaybeLog("get_indices_with_types", TYPES_DEPRECATION_MESSAGE);
         }
         final GetIndexRequest getIndexRequest = new GetIndexRequest();

server/src/test/java/org/elasticsearch/rest/action/admin/indices/RestGetIndicesActionTests.java

@@ -36,7 +36,7 @@
 public class RestGetIndicesActionTests extends RestActionTestCase {
 
     /**
-     * Test that setting the "include_type_name" parameter raises a warning
+     * Test that setting the "include_type_name" parameter raises a warning for the GET request
      */
     public void testIncludeTypeNamesWarning() throws IOException {
         Map<String, String> params = new HashMap<>();
@@ -58,4 +58,20 @@ public void testIncludeTypeNamesWarning() throws IOException {
                 .build();
         handler.prepareRequest(request, mock(NodeClient.class));
     }
+
+    /**
+     * Test that setting the "include_type_name" parameter doesn't raises a warning if the HEAD method is used (indices.exists)
+     */
+    public void testIncludeTypeNamesWarningExists() throws IOException {
+        Map<String, String> params = new HashMap<>();
+        params.put(INCLUDE_TYPE_NAME_PARAMETER, randomFrom("true", "false"));
+        RestRequest request = new FakeRestRequest.Builder(xContentRegistry())
+            .withMethod(RestRequest.Method.HEAD)
+            .withPath("/some_index")
+            .withParams(params)
+            .build();
+
+        RestGetIndicesAction handler = new RestGetIndicesAction(Settings.EMPTY, mock(RestController.class));
+        handler.prepareRequest(request, mock(NodeClient.class));
+    }
 }