fix: OM2 Info TYPE/HELP lines use full name including _info

OM2 spec requires metric name to match MetricFamily name.
The Info writer was stripping _info for TYPE/HELP lines
(OM1 convention) while keeping it on data lines.

Author: zeitlinger

prometheus-metrics-exposition-textformats/src/main/java/io/prometheus/metrics/expositionformats/OpenMetrics2TextFormatWriter.java

@@ -296,10 +296,10 @@ private void writeSummary(Writer writer, SummarySnapshot snapshot, EscapingSchem
   private void writeInfo(Writer writer, InfoSnapshot snapshot, EscapingScheme scheme)
       throws IOException {
     MetricMetadata metadata = snapshot.getMetadata();
-    // OM2 spec: Info MetricFamily name MUST end in _info
+    // OM2 spec: Info MetricFamily name MUST end in _info.
+    // In OM2, TYPE/HELP use the same name as the data lines.
     String infoName = ensureSuffix(getExpositionBaseMetadataName(metadata, scheme), "_info");
-    String baseName = removeSuffix(infoName, "_info");
-    writeMetadataWithName(writer, baseName, "info", metadata);
+    writeMetadataWithName(writer, infoName, "info", metadata);
     for (InfoSnapshot.InfoDataPointSnapshot data : snapshot.getDataPoints()) {
       writeNameAndLabels(writer, infoName, null, data.getLabels(), scheme);
       writer.write("1");
@@ -488,11 +488,4 @@ private static String ensureSuffix(String name, String suffix) {
     }
     return name + suffix;
   }
-
-  private static String removeSuffix(String name, String suffix) {
-    if (name.endsWith(suffix)) {
-      return name.substring(0, name.length() - suffix.length());
-    }
-    return name;
-  }
 }

prometheus-metrics-exposition-textformats/src/test/java/io/prometheus/metrics/expositionformats/OpenMetrics2TextFormatWriterTest.java

@@ -207,7 +207,7 @@ void testOutputIdenticalToOM1ForSummary() throws IOException {
   }
 
   @Test
-  void testOutputIdenticalToOM1ForInfo() throws IOException {
+  void testInfoHelpNameMatchesMeterName() throws IOException {
     MetricSnapshots snapshots =
         MetricSnapshots.of(
             InfoSnapshot.builder()
@@ -219,10 +219,15 @@ void testOutputIdenticalToOM1ForInfo() throws IOException {
                         .build())
                 .build());
 
-    String om1Output = writeWithOM1(snapshots);
     String om2Output = writeWithOM2(snapshots);
 
-    assertThat(om2Output).isEqualTo(om1Output);
+    // OM2: TYPE/HELP use the full name including _info (help name == meter name)
+    assertThat(om2Output)
+        .isEqualTo(
+            "# TYPE my_info info\n"
+                + "# HELP my_info Test info\n"
+                + "my_info{platform=\"linux\",version=\"1.0\"} 1\n"
+                + "# EOF\n");
   }
 
   @Test