From f1811c57e9e1fadb761e9e40643eab9ad56c9bfc Mon Sep 17 00:00:00 2001
From: achingbrain <alex@achingbrain.net>
Date: Sat, 26 Oct 2024 08:35:21 +0100
Subject: [PATCH] fix: fix metric group timers

We need to pass the metric label as the object key, otherwise trying
to stop a group timer throws.
---
 .../metrics-prometheus/src/metric-group.ts    |  2 +-
 .../test/metric-groups.spec.ts                | 20 +++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/packages/metrics-prometheus/src/metric-group.ts b/packages/metrics-prometheus/src/metric-group.ts
index 9909ffdd70..fc3cb6a496 100644
--- a/packages/metrics-prometheus/src/metric-group.ts
+++ b/packages/metrics-prometheus/src/metric-group.ts
@@ -72,7 +72,7 @@ export class PrometheusMetricGroup implements MetricGroup, CalculatedMetric<Reco
 
   timer (key: string): StopTimer {
     return this.gauge.startTimer({
-      key: 0
+      [this.label]: key
     })
   }
 }
diff --git a/packages/metrics-prometheus/test/metric-groups.spec.ts b/packages/metrics-prometheus/test/metric-groups.spec.ts
index 33ce50d4b8..257e897c40 100644
--- a/packages/metrics-prometheus/test/metric-groups.spec.ts
+++ b/packages/metrics-prometheus/test/metric-groups.spec.ts
@@ -183,4 +183,24 @@ describe('metric groups', () => {
     expect(reportedMetrics).to.include(`${metricName}{${metricLabel}="${metricKey1}"} ${metricValue1}`, 'did not include updated metric')
     expect(reportedMetrics).to.include(`${metricName}{${metricLabel}="${metricKey2}"} ${metricValue2}`, 'did not include updated metric')
   })
+
+  it('should allow grouped timers', async () => {
+    const metricName = randomMetricName()
+    const metricLabel = randomMetricName('label_')
+    const metricKey = randomMetricName('key_')
+    const metrics = prometheusMetrics()({
+      logger: defaultLogger()
+    })
+    const metric1 = metrics.registerMetricGroup(metricName, {
+      label: metricLabel
+    })
+
+    const timer = metric1.timer(metricKey)
+
+    timer()
+
+    const reportedMetrics = await client.register.metrics()
+
+    expect(reportedMetrics).to.include(`${metricName}{${metricLabel}="${metricKey}"}`, 'did not include updated metric')
+  })
 })