Add description to force-merge tasks (#41365)

This is static information that is part of the force merge request.

Relates to #15975

Author: centic9

client/rest-high-level/src/test/java/org/elasticsearch/client/IndicesClientIT.java

@@ -1045,6 +1045,8 @@ public void testForceMerge() throws IOException {
             assertThat(forceMergeResponse.getSuccessfulShards(), equalTo(1));
             assertThat(forceMergeResponse.getFailedShards(), equalTo(0));
             assertThat(forceMergeResponse.getShardFailures(), equalTo(BroadcastResponse.EMPTY));
+
+            assertThat(forceMergeRequest.getDescription(), containsString(index));
         }
         {
             String nonExistentIndex = "non_existent_index";
@@ -1053,6 +1055,8 @@ public void testForceMerge() throws IOException {
             ElasticsearchException exception = expectThrows(ElasticsearchException.class,
                 () -> execute(forceMergeRequest, highLevelClient().indices()::forcemerge, highLevelClient().indices()::forcemergeAsync));
             assertEquals(RestStatus.NOT_FOUND, exception.status());
+
+            assertThat(forceMergeRequest.getDescription(), containsString(nonExistentIndex));
         }
     }
 

server/src/main/java/org/elasticsearch/action/admin/indices/forcemerge/ForceMergeRequest.java

@@ -25,6 +25,7 @@
 import org.elasticsearch.common.io.stream.StreamOutput;
 
 import java.io.IOException;
+import java.util.Arrays;
 
 import static org.elasticsearch.action.ValidateActions.addValidationError;
 
@@ -117,6 +118,14 @@ public ForceMergeRequest flush(boolean flush) {
         return this;
     }
 
+    @Override
+    public String getDescription() {
+        return "Force-merge indices " + Arrays.toString(indices()) +
+            ", maxSegments[" + maxNumSegments +
+            "], onlyExpungeDeletes[" + onlyExpungeDeletes +
+            "], flush[" + flush + "]";
+    }
+
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);

server/src/test/java/org/elasticsearch/action/admin/indices/forcemerge/ForceMergeRequestTests.java

@@ -51,4 +51,18 @@ public void testValidate() {
             assertThat(validation, nullValue());
         }
     }
+
+    public void testDescription() {
+        ForceMergeRequest request = new ForceMergeRequest();
+        assertEquals("Force-merge indices [], maxSegments[-1], onlyExpungeDeletes[false], flush[true]", request.getDescription());
+
+        request = new ForceMergeRequest("shop", "blog");
+        assertEquals("Force-merge indices [shop, blog], maxSegments[-1], onlyExpungeDeletes[false], flush[true]", request.getDescription());
+
+        request = new ForceMergeRequest();
+        request.maxNumSegments(12);
+        request.onlyExpungeDeletes(true);
+        request.flush(false);
+        assertEquals("Force-merge indices [], maxSegments[12], onlyExpungeDeletes[true], flush[false]", request.getDescription());
+    }
 }