Add more label checksn during gathering

Including check for an invalid "quantile" label in summaries.

Also, improve error messages.

Signed-off-by: beorn7 <beorn@soundcloud.com>

prometheus/examples_test.go

@@ -740,7 +740,7 @@ temperature_kelvin 4.5
 	// temperature_kelvin{location="outside"} 273.14
 	// temperature_kelvin{location="somewhere else"} 4.5
 	// ----------
-	// collected metric temperature_kelvin label:<name:"location" value:"outside" > gauge:<value:265.3 >  was collected before with the same name and label values
+	// collected metric "temperature_kelvin" { label:<name:"location" value:"outside" > gauge:<value:265.3 > } was collected before with the same name and label values
 	// # HELP humidity_percent Humidity in %.
 	// # TYPE humidity_percent gauge
 	// humidity_percent{location="inside"} 33.2

prometheus/registry.go

@@ -783,14 +783,28 @@ func checkMetricConsistency(
 		metricFamily.GetType() == dto.MetricType_HISTOGRAM && dtoMetric.Histogram == nil ||
 		metricFamily.GetType() == dto.MetricType_UNTYPED && dtoMetric.Untyped == nil {
 		return fmt.Errorf(
-			"collected metric %s %s is not a %s",
+			"collected metric %q { %s} is not a %s",
 			metricFamily.GetName(), dtoMetric, metricFamily.GetType(),
 		)
 	}
 
 	for _, labelPair := range dtoMetric.GetLabel() {
+		if !checkLabelName(labelPair.GetName()) {
+			return fmt.Errorf(
+				"collected metric %q { %s} has a label with an invalid name: %s",
+				metricFamily.GetName(), dtoMetric, labelPair.GetName(),
+			)
+		}
+		if dtoMetric.Summary != nil && labelPair.GetName() == quantileLabel {
+			return fmt.Errorf(
+				"collected metric %q { %s} must not have an explicit %q label",
+				metricFamily.GetName(), dtoMetric, quantileLabel,
+			)
+		}
 		if !utf8.ValidString(labelPair.GetValue()) {
-			return fmt.Errorf("collected metric's label %s is not utf8: %#v", labelPair.GetName(), labelPair.GetValue())
+			return fmt.Errorf(
+				"collected metric %q { %s} has a label named %q whose value is not utf8: %#v",
+				metricFamily.GetName(), dtoMetric, labelPair.GetName(), labelPair.GetValue())
 		}
 	}
 
@@ -809,7 +823,7 @@ func checkMetricConsistency(
 	}
 	if _, exists := metricHashes[h]; exists {
 		return fmt.Errorf(
-			"collected metric %s %s was collected before with the same name and label values",
+			"collected metric %q { %s} was collected before with the same name and label values",
 			metricFamily.GetName(), dtoMetric,
 		)
 	}

prometheus/registry_test.go

@@ -249,7 +249,7 @@ metric: <
 
 	expectedMetricFamilyInvalidLabelValueAsText := []byte(`An error has occurred during metrics gathering:
 
-collected metric's label constname is not utf8: "\xff"
+collected metric "name" { label:<name:"constname" value:"\377" > label:<name:"labelname" value:"different_val" > counter:<value:42 > } has a label named "constname" whose value is not utf8: "\xff"
 `)
 
 	type output struct {