From 0bcaedc57471a22845f452d56d52c1096dab6a2a Mon Sep 17 00:00:00 2001
From: "tim.quinn@oracle.com" <tim.quinn@oracle.com>
Date: Fri, 19 Nov 2021 15:11:23 -0600
Subject: [PATCH] Need to support no-op Gauge after all

---
 .../src/main/java/io/helidon/metrics/api/NoOpMetricImpl.java | 5 +++++
 .../main/java/io/helidon/metrics/api/NoOpMetricRegistry.java | 3 +--
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/metrics/api/src/main/java/io/helidon/metrics/api/NoOpMetricImpl.java b/metrics/api/src/main/java/io/helidon/metrics/api/NoOpMetricImpl.java
index f3858e0f94c..e3fd291a6ba 100644
--- a/metrics/api/src/main/java/io/helidon/metrics/api/NoOpMetricImpl.java
+++ b/metrics/api/src/main/java/io/helidon/metrics/api/NoOpMetricImpl.java
@@ -112,6 +112,11 @@ static class NoOpGaugeImpl<T /* extends Number */> extends NoOpMetricImpl implem
             return new NoOpGaugeImpl<>(registryType, metadata, metric);
         }
 
+        static <S /* extends Number */> NoOpGaugeImpl<S> create(String registryType, Metadata metadata) {
+            // TODO uncomment above once MP metrics enforces the Number restriction
+            return new NoOpGaugeImpl<>(registryType, metadata, () -> null);
+        }
+
         private NoOpGaugeImpl(String registryType, Metadata metadata, Gauge<T> metric) {
             super(registryType, metadata);
             value = metric::getValue;
diff --git a/metrics/api/src/main/java/io/helidon/metrics/api/NoOpMetricRegistry.java b/metrics/api/src/main/java/io/helidon/metrics/api/NoOpMetricRegistry.java
index f146b01d897..9f20e33f4ed 100644
--- a/metrics/api/src/main/java/io/helidon/metrics/api/NoOpMetricRegistry.java
+++ b/metrics/api/src/main/java/io/helidon/metrics/api/NoOpMetricRegistry.java
@@ -30,9 +30,8 @@
 class NoOpMetricRegistry extends AbstractRegistry<NoOpMetric> {
 
     private static final Map<MetricType, BiFunction<String, Metadata, NoOpMetric>> NO_OP_METRIC_FACTORIES =
-            // Omit gauge because creating a gauge requires an existing delegate instance.
-            // These factory methods do not use delegates.
             Map.of(MetricType.COUNTER, NoOpMetricImpl.NoOpCounterImpl::create,
+                   MetricType.GAUGE, NoOpMetricImpl.NoOpGaugeImpl::create,
                    MetricType.HISTOGRAM, NoOpMetricImpl.NoOpHistogramImpl::create,
                    MetricType.METERED, NoOpMetricImpl.NoOpMeterImpl::create,
                    MetricType.TIMER, NoOpMetricImpl.NoOpTimerImpl::create,