Record setting updater

Author: prdoyle

server/src/main/java/org/elasticsearch/common/settings/Setting.java

@@ -1319,10 +1319,6 @@ private static class RecordSetting<R extends Record> extends Setting<R> {
             Property... properties
         ) {
             super(new GroupKey(keyWithDot(key)), (s) -> "", (s) -> null, properties);
-            if (isDynamic()) {
-                // TODO
-                throw new IllegalArgumentException("Dynamic record settings not supported");
-            }
             this.key = key;
             this.recordClass = recordClass;
             this.validator = r -> {}; // TODO: validator
@@ -1391,7 +1387,30 @@ public void diff(Settings.Builder builder, Settings source, Settings defaultSett
 
         @Override
         public AbstractScopedSettings.SettingUpdater<R> newUpdater(Consumer<R> consumer, Logger logger, Consumer<R> validator) {
-            throw new IllegalStateException("setting [" + getKey() + "] is not dynamic");
+            return new AbstractScopedSettings.SettingUpdater<R>() {
+                @Override
+                public boolean hasChanged(Settings current, Settings previous) {
+                    return false == get(current).equals(get(previous));
+                }
+
+                @Override
+                public R getValue(Settings current, Settings previous) {
+                    // TODO: What am I supposed to do with previous? Javadocs don't say
+                    R result = get(current);
+                    validator.accept(result);
+                    return result;
+                }
+
+                @Override
+                public void apply(R value, Settings current, Settings previous) {
+                    consumer.accept(value);
+                }
+
+                @Override
+                public String toString() {
+                    return "Updater for record: " + recordClass.getName();
+                }
+            };
         }
 
         @SuppressForbidden(reason = "To support arbitrary record types, we must invoke the constructor with invokeWithArguments")

server/src/test/java/org/elasticsearch/common/settings/SettingTests.java

@@ -1610,7 +1610,50 @@ public void testLongSettingBounds() {
     public void testRecordSetting() {
         record TestSetting(int intSetting) {}
         Setting<TestSetting> setting = Setting.recordSetting("record.setting", TestSetting.class, MethodHandles.lookup(), List.of());
-        assertEquals(new TestSetting(123), setting.get(Settings.builder().put("record.setting.int_setting", 123).build()));
+        Settings settings123 = Settings.builder().put("record.setting.int_setting", 123).build();
+        Settings settings456 = Settings.builder().put("record.setting.int_setting", 456).build();
+
+        assertEquals(new TestSetting(123), setting.get(settings123));
         assertThrows(IllegalStateException.class, () -> setting.get(Settings.EMPTY));
+
+        var watcher = new AtomicReference<TestSetting>(null);
+        var updater = setting.newUpdater(watcher::set, logger);
+        assertNull("Creating an updater does not call set", watcher.get());
+        updater.apply(settings456, settings123);
+        assertEquals("Updater called when value changed", new TestSetting(456), watcher.get());
+        assertThrows("Throws when there's no default", IllegalStateException.class, ()->updater.apply(Settings.EMPTY, settings456));
+
+        watcher.set(null);
+        updater.apply(settings123, settings123);
+        assertNull("Updater NOT called when value unchanged", watcher.get());
+        updater.apply(settings456, settings456);
+        assertNull("Updater again not called when value unchanged", watcher.get());
+    }
+
+    public void testRecordWithDefaults() {
+        record TestSetting(int i1, int i2) {}
+        Setting<Integer> i1Setting = Setting.intSetting("record.setting.i1", -1);
+        Setting<Integer> i2Setting = Setting.intSetting("record.setting.i2", -2);
+        Setting<TestSetting> setting = Setting.recordSetting("record.setting", TestSetting.class, MethodHandles.lookup(), List.of(i1Setting, i2Setting));
+        Settings settings123 = Settings.builder().put("record.setting.i1", 123).build();
+
+        assertEquals(new TestSetting(123, 456), setting.get(Settings.builder().put("record.setting.i1", 123).put("record.setting.i2", 456).build()));
+        assertEquals(new TestSetting(-1, 456), setting.get(Settings.builder().put("record.setting.i2", 456).build()));
+        assertEquals(new TestSetting(-1, -2), setting.get(Settings.EMPTY));
+
+        var watcher = new AtomicReference<TestSetting>(null);
+        var updater = setting.newUpdater(watcher::set, logger);
+        updater.apply(settings123, Settings.EMPTY);
+        assertEquals(new TestSetting(123, -2), watcher.get());
+        updater.apply(Settings.EMPTY, settings123);
+        assertEquals(new TestSetting(-1, -2), watcher.get());
+
+        Settings explicitDefaults = Settings.builder().put("record.setting.i1", -1).put("record.setting.i2", -2).build();
+        watcher.set(null);
+        updater.apply(Settings.EMPTY, explicitDefaults);
+        assertNull("Updater NOT called when value deleted from the default", watcher.get());
+        updater.apply(explicitDefaults, Settings.EMPTY);
+        assertNull("Updater NOT called when value 'changed' to the default from nothing", watcher.get());
     }
+
 }