Add deprecation warning for negative index.unassigned.node_left.delayed_timeout (#26832)

This was deprecated because it becomes forbidden in 7.x as per #26828.

Author: DaveCTurner

core/src/main/java/org/elasticsearch/cluster/routing/UnassignedInfo.java

@@ -30,6 +30,8 @@
 import org.elasticsearch.common.io.stream.Writeable;
 import org.elasticsearch.common.joda.FormatDateTimeFormatter;
 import org.elasticsearch.common.joda.Joda;
+import org.elasticsearch.common.logging.DeprecationLogger;
+import org.elasticsearch.common.logging.Loggers;
 import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Setting.Property;
 import org.elasticsearch.common.settings.Settings;
@@ -47,11 +49,21 @@
  */
 public final class UnassignedInfo implements ToXContentFragment, Writeable {
 
+    private static final DeprecationLogger DEPRECATION_LOGGER = new DeprecationLogger(Loggers.getLogger(UnassignedInfo.class));
+
     public static final FormatDateTimeFormatter DATE_TIME_FORMATTER = Joda.forPattern("dateOptionalTime");
 
     public static final Setting<TimeValue> INDEX_DELAYED_NODE_LEFT_TIMEOUT_SETTING =
-        Setting.timeSetting("index.unassigned.node_left.delayed_timeout", TimeValue.timeValueMinutes(1), Property.Dynamic,
-            Property.IndexScope);
+        new Setting<>("index.unassigned.node_left.delayed_timeout", (s) -> TimeValue.timeValueMinutes(1).getStringRep(), (s) -> {
+            TimeValue parsedValue = TimeValue.parseTimeValue(s, "index.unassigned.node_left.delayed_timeout");
+            if (parsedValue.getNanos() < 0) {
+                DEPRECATION_LOGGER.deprecated(
+                    "Negative values for index.unassigned.node_left.delayed_timeout [{}]" +
+                        " are deprecated and should now be set to \"0\".", s);
+            }
+            return parsedValue;
+        }, Property.Dynamic, Property.IndexScope);
+
     /**
      * Reason why the shard is in unassigned state.
      * <p>

core/src/test/java/org/elasticsearch/cluster/routing/UnassignedInfoTests.java

@@ -356,4 +356,11 @@ public void testAllocationStatusSerialization() throws IOException {
             assertThat(readStatus, equalTo(allocationStatus));
         }
     }
+
+    public void testNegativeTimeoutDeprecated() {
+        Settings settings = settings(Version.CURRENT).put(UnassignedInfo.INDEX_DELAYED_NODE_LEFT_TIMEOUT_SETTING.getKey(), "-1s").build();
+        assertThat(UnassignedInfo.INDEX_DELAYED_NODE_LEFT_TIMEOUT_SETTING.get(settings).seconds(), equalTo(-1L));
+        assertWarnings("Negative values for index.unassigned.node_left.delayed_timeout [-1s]" +
+            " are deprecated and should now be set to \"0\".");
+    }
 }