registry: drop duplicate checks

In processMetrics drop duplicate checks. If the metricFamily exists we
already have a type check with the call to checkMetricConsistency. The
help string is already checked in the checkDescConsistency albeit only
if pedantic mode is enabled. However this is probably what is desired
anyway.

prometheus/registry.go

@@ -634,54 +634,7 @@ func processMetric(
 		return fmt.Errorf("error collecting metric %v: %w", desc, err)
 	}
 	metricFamily, ok := metricFamiliesByName[desc.fqName]
-	if ok { // Existing name.
-		if metricFamily.GetHelp() != desc.help {
-			return fmt.Errorf(
-				"collected metric %s %s has help %q but should have %q",
-				desc.fqName, dtoMetric, desc.help, metricFamily.GetHelp(),
-			)
-		}
-		// TODO(beorn7): Simplify switch once Desc has type.
-		switch metricFamily.GetType() {
-		case dto.MetricType_COUNTER:
-			if dtoMetric.Counter == nil {
-				return fmt.Errorf(
-					"collected metric %s %s should be a Counter",
-					desc.fqName, dtoMetric,
-				)
-			}
-		case dto.MetricType_GAUGE:
-			if dtoMetric.Gauge == nil {
-				return fmt.Errorf(
-					"collected metric %s %s should be a Gauge",
-					desc.fqName, dtoMetric,
-				)
-			}
-		case dto.MetricType_SUMMARY:
-			if dtoMetric.Summary == nil {
-				return fmt.Errorf(
-					"collected metric %s %s should be a Summary",
-					desc.fqName, dtoMetric,
-				)
-			}
-		case dto.MetricType_UNTYPED:
-			if dtoMetric.Untyped == nil {
-				return fmt.Errorf(
-					"collected metric %s %s should be Untyped",
-					desc.fqName, dtoMetric,
-				)
-			}
-		case dto.MetricType_HISTOGRAM:
-			if dtoMetric.Histogram == nil {
-				return fmt.Errorf(
-					"collected metric %s %s should be a Histogram",
-					desc.fqName, dtoMetric,
-				)
-			}
-		default:
-			panic("encountered MetricFamily with invalid type")
-		}
-	} else { // New name.
+	if !ok { // New name.
 		metricFamily = &dto.MetricFamily{}
 		metricFamily.Name = proto.String(desc.fqName)
 		metricFamily.Help = proto.String(desc.help)