Reduce BWC version for HotThreads.sort (#79583)

The sort by change has been merged in 7.x now and therefore
we should make 8.0 use the same BWC version.

Relates to #79392 and #79507

Co-authored-by: Nhat Nguyen <nhat.nguyen@elastic.co>

qa/mixed-cluster/src/test/java/org/elasticsearch/backwards/HotThreadsIT.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+package org.elasticsearch.backwards;
+
+import org.apache.http.util.EntityUtils;
+import org.elasticsearch.client.Request;
+import org.elasticsearch.client.Response;
+import org.elasticsearch.test.rest.ESRestTestCase;
+
+import static org.hamcrest.Matchers.equalTo;
+
+public class HotThreadsIT extends ESRestTestCase {
+
+    public void testHotThreads() throws Exception {
+        final IndexingIT.Nodes nodes = IndexingIT.buildNodeAndVersions(client());
+        assumeFalse("no new node found", nodes.getNewNodes().isEmpty());
+        assumeFalse("no bwc node found", nodes.getBWCNodes().isEmpty());
+        assumeTrue("new nodes are higher version than BWC nodes",
+            nodes.getNewNodes().get(0).getVersion().compareTo(nodes.getBWCNodes().get(0).getVersion()) > 0);
+        final Request request = new Request("GET", "/_nodes/hot_threads");
+        final Response response = client().performRequest(request);
+        final String responseString = EntityUtils.toString(response.getEntity());
+        final String[] nodeResponses = responseString.split("::: ");
+        int respondedNodes = 0;
+        for (String nodeResponse : nodeResponses) {
+            final String[] lines = nodeResponse.split("\n");
+            final String nodeId = lines[0].trim();
+            if (nodeId.isEmpty() == false) {
+                respondedNodes++;
+            }
+        }
+        assertThat(respondedNodes, equalTo(nodes.getNewNodes().size() + nodes.getBWCNodes().size()));
+    }
+}

rest-api-spec/src/main/resources/rest-api-spec/api/nodes.hot_threads.json

@@ -53,10 +53,19 @@
         "options":[
           "cpu",
           "wait",
-          "block"
+          "block",
+          "mem"
         ],
         "description":"The type to sample (default: cpu)"
       },
+      "sort":{
+        "type":"enum",
+        "options":[
+          "cpu",
+          "total"
+        ],
+        "description":"The sort order for 'cpu' type (default: total)"
+      },
       "timeout":{
         "type":"time",
         "description":"Explicit operation timeout"

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/nodes.hot_threads/10_basic.yml

@@ -0,0 +1,51 @@
+---
+"Nodes hot threads - CPU":
+  - do:
+      nodes.hot_threads:
+        type: "cpu"
+  - match:
+      $body: |
+        /Hot\ threads\ at/
+---
+"Nodes hot threads - CPU sort":
+  - do:
+      nodes.hot_threads:
+        type: "cpu"
+        sort: "cpu"
+  - match:
+      $body: |
+        /Hot\ threads\ at/
+---
+"Nodes hot threads - WAIT":
+  - do:
+      nodes.hot_threads:
+        type: "wait"
+  - match:
+      $body: |
+        /Hot\ threads\ at/
+---
+"Nodes hot threads - BLOCK":
+  - do:
+      nodes.hot_threads:
+        type: "block"
+  - match:
+      $body: |
+        /Hot\ threads\ at/
+---
+"Nodes hot threads - MEM":
+  - do:
+      nodes.hot_threads:
+        type: "mem"
+  - match:
+      $body: |
+        /Hot\ threads\ at/
+---
+"Nodes hot threads - BAD":
+  - do:
+      catch: bad_request
+      nodes.hot_threads:
+        type: "gpu"
+  - match: { status: 400 }
+  - match: { error.type: illegal_argument_exception }
+  - match: { error.reason: "type not supported [gpu]" }
+

server/src/main/java/org/elasticsearch/action/admin/cluster/node/hotthreads/NodesHotThreadsRequest.java

@@ -36,7 +36,7 @@ public NodesHotThreadsRequest(StreamInput in) throws IOException {
         type = HotThreads.ReportType.of(in.readString());
         interval = in.readTimeValue();
         snapshots = in.readInt();
-        if (in.getVersion().onOrAfter(Version.V_8_0_0)) {
+        if (in.getVersion().onOrAfter(Version.V_7_16_0)) {
             sortOrder = HotThreads.SortOrder.of(in.readString());
         }
     }
@@ -118,7 +118,7 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeString(type.getTypeValue());
         out.writeTimeValue(interval);
         out.writeInt(snapshots);
-        if (out.getVersion().onOrAfter(Version.V_8_0_0)) {
+        if (out.getVersion().onOrAfter(Version.V_7_16_0)) {
             out.writeString(sortOrder.getOrderValue());
         }
     }