prometheus exporter ignores metrics from the Prometheus bridge

exporters/prometheus/exporter.go

@@ -35,6 +35,11 @@ const (
 	scopeNameLabel    = scopeLabelPrefix + "name"
 	scopeVersionLabel = scopeLabelPrefix + "version"
 	scopeSchemaLabel  = scopeLabelPrefix + "schema_url"
+	// metrics from the prometehus bridge are ignored because this produces
+	// errors. Users should directly register prometheus metrics with the
+	// Registerer, rather than round-tripping them through the bridge and
+	// exporter.
+	bridgeScopeName = "go.opentelemetry.io/contrib/bridges/prometheus"
 )
 
 var metricsPool = sync.Pool{
@@ -229,6 +234,9 @@ func (c *collector) Collect(ch chan<- prometheus.Metric) {
 	}
 
 	for j, scopeMetrics := range metrics.ScopeMetrics {
+		if scopeMetrics.Scope.Name == bridgeScopeName {
+			continue
+		}
 		n := len(c.resourceKeyVals.keys) + 2 // resource attrs + scope name + scope version
 		kv := keyVals{
 			keys: make([]string, 0, n),

exporters/prometheus/exporter_test.go

@@ -797,6 +797,46 @@ func TestMultiScopes(t *testing.T) {
 	require.NoError(t, err)
 }
 
+func TestBridgeScopeIgnored(t *testing.T) {
+	ctx := t.Context()
+	registry := prometheus.NewRegistry()
+	exporter, err := New(
+		WithTranslationStrategy(otlptranslator.UnderscoreEscapingWithSuffixes),
+		WithRegisterer(registry),
+	)
+	require.NoError(t, err)
+
+	res, err := resource.New(ctx,
+		// always specify service.name because the default depends on the running OS
+		resource.WithAttributes(semconv.ServiceName("prometheus_test")),
+		// Overwrite the semconv.TelemetrySDKVersionKey value so we don't need to update every version
+		resource.WithAttributes(semconv.TelemetrySDKVersion("latest")),
+	)
+	require.NoError(t, err)
+	res, err = resource.Merge(resource.Default(), res)
+	require.NoError(t, err)
+
+	provider := metric.NewMeterProvider(
+		metric.WithReader(exporter),
+		metric.WithResource(res),
+	)
+
+	fooCounter, err := provider.Meter(bridgeScopeName, otelmetric.WithInstrumentationVersion("v0.1.0")).
+		Int64Counter(
+			"foo",
+			otelmetric.WithUnit("s"),
+			otelmetric.WithDescription("meter foo counter"))
+	assert.NoError(t, err)
+	fooCounter.Add(ctx, 100, otelmetric.WithAttributes(attribute.String("type", "foo")))
+
+	file, err := os.Open("testdata/just_target_info.txt")
+	require.NoError(t, err)
+	t.Cleanup(func() { require.NoError(t, file.Close()) })
+
+	err = testutil.GatherAndCompare(registry, file)
+	require.NoError(t, err)
+}
+
 func TestDuplicateMetrics(t *testing.T) {
 	ab := attribute.NewSet(attribute.String("A", "B"))
 	withAB := otelmetric.WithAttributeSet(ab)

exporters/prometheus/testdata/just_target_info.txt

@@ -0,0 +1,3 @@
+# HELP target_info Target metadata
+# TYPE target_info gauge
+target_info{service_name="prometheus_test",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="latest"} 1