From 046e987456d4e22e691413e4221b9177a1406ba3 Mon Sep 17 00:00:00 2001
From: Tanishq Choudhary <tanishqchoudhary007@gmail.com>
Date: Thu, 22 Oct 2026 20:57:14 +0530
Subject: [PATCH] fix(config): keep metric name case in metric-specific
 properties

normalizePropertyKey() lowercases the whole key, so settings for a
metric with uppercase letters, such as
io.prometheus.metrics.myLatency.histogram_classic_upper_bounds, are
stored under my_latency and never found for myLatency. Normalize only
the property name in io.prometheus.metrics.<metric>.<property> keys,
so metric names keep their case as they did before 1.5.0.

Signed-off-by: Tanishq Choudhary <tanishqchoudhary007@gmail.com>
---
 .../config/PrometheusPropertiesLoader.java    |  8 ++++++++
 .../PrometheusPropertiesLoaderTest.java       | 20 +++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/prometheus-metrics-config/src/main/java/io/prometheus/metrics/config/PrometheusPropertiesLoader.java b/prometheus-metrics-config/src/main/java/io/prometheus/metrics/config/PrometheusPropertiesLoader.java
index 04bbfe4a53..26334a6ba4 100644
--- a/prometheus-metrics-config/src/main/java/io/prometheus/metrics/config/PrometheusPropertiesLoader.java
+++ b/prometheus-metrics-config/src/main/java/io/prometheus/metrics/config/PrometheusPropertiesLoader.java
@@ -210,10 +210,18 @@ private static Map<Object, Object> loadPropertiesFromEnvironment() {
    * <p>For example: exemplarsEnabled → exemplars_enabled exemplars_enabled → exemplars_enabled
    * (unchanged)
    *
+   * <p>In metric-specific keys like {@code io.prometheus.metrics.<metric>.<property>} only the
+   * property name is normalized, because metric names are case-sensitive.
+   *
    * @param key the property key
    * @return the normalized property key
    */
   static String normalizePropertyKey(String key) {
+    String metricsPrefix = "io.prometheus.metrics.";
+    int lastDot = key.lastIndexOf('.');
+    if (key.startsWith(metricsPrefix) && lastDot >= metricsPrefix.length()) {
+      return key.substring(0, lastDot + 1) + normalizePropertyKey(key.substring(lastDot + 1));
+    }
     // Insert underscores before uppercase letters to convert camelCase to snake_case
     String withUnderscores = key.replaceAll("([a-z])([A-Z])", "$1_$2");
     return withUnderscores.toLowerCase(java.util.Locale.ROOT);
diff --git a/prometheus-metrics-config/src/test/java/io/prometheus/metrics/config/PrometheusPropertiesLoaderTest.java b/prometheus-metrics-config/src/test/java/io/prometheus/metrics/config/PrometheusPropertiesLoaderTest.java
index 8f910ccebd..f7b3f9505e 100644
--- a/prometheus-metrics-config/src/test/java/io/prometheus/metrics/config/PrometheusPropertiesLoaderTest.java
+++ b/prometheus-metrics-config/src/test/java/io/prometheus/metrics/config/PrometheusPropertiesLoaderTest.java
@@ -56,6 +56,22 @@ void externalPropertiesShouldOverridePropertiesFile() {
         .isFalse();
   }
 
+  @Test
+  void metricSpecificPropertiesShouldKeepMetricNameCase() {
+    Properties properties = new Properties();
+    properties.setProperty(
+        "io.prometheus.metrics.myLatency.histogram_classic_upper_bounds", ".005, .01, .015");
+    properties.setProperty("io.prometheus.metrics.HTTP_duration.histogramNativeOnly", "true");
+
+    PrometheusProperties prometheusProperties = PrometheusPropertiesLoader.load(properties);
+    assertThat(
+            prometheusProperties.getMetricProperties("myLatency").getHistogramClassicUpperBounds())
+        .containsExactly(0.005, 0.01, 0.015);
+    assertThat(prometheusProperties.getMetricProperties("HTTP_duration").getHistogramNativeOnly())
+        .isTrue();
+    assertThat(prometheusProperties.getMetricProperties("my_latency")).isNull();
+  }
+
   @Test
   void environmentVariablesShouldConfigureMetrics() {
     // Simulate environment variables as they would be loaded
@@ -160,6 +176,10 @@ void normalizePropertyKeyShouldConvertCamelCaseToSnakeCase() {
             PrometheusPropertiesLoader.normalizePropertyKey(
                 "io.prometheus.exporter.openTelemetry.serviceName"))
         .isEqualTo("io.prometheus.exporter.open_telemetry.service_name");
+    assertThat(
+            PrometheusPropertiesLoader.normalizePropertyKey(
+                "io.prometheus.metrics.myLatency.histogramNativeOnly"))
+        .isEqualTo("io.prometheus.metrics.myLatency.histogram_native_only");
 
     // Test that snake_case keys remain unchanged
     assertThat(