Fix possible non-counter warning for empty names and native histograms

Signed-off-by: Jeanette Tan <jeanette.tan@grafana.com>

promql/functions.go

@@ -88,7 +88,7 @@ func extrapolatedRate(vals []parser.Value, args parser.Expressions, enh *EvalNod
 		return enh.Out, annos.Add(annotations.NewMixedFloatsHistogramsWarning(metricName, args[0].PositionRange()))
 	}
 
-	if isCounter &&
+	if isCounter && metricName != "" && len(samples.Floats) > 0 &&
 		!strings.HasSuffix(metricName, "_total") &&
 		!strings.HasSuffix(metricName, "_sum") &&
 		!strings.HasSuffix(metricName, "_count") &&

util/annotations/annotations.go

@@ -156,8 +156,8 @@ func NewMixedClassicNativeHistogramsWarning(metricName string, pos posrange.Posi
 	}
 }
 
-// NewPossibleNonCounterInfo is used when a counter metric does not have the suffixes
-// _total, _sum, _count, or _bucket.
+// NewPossibleNonCounterInfo is used when a named counter metric with only float samples does not
+// have the suffixes _total, _sum, _count, or _bucket.
 func NewPossibleNonCounterInfo(metricName string, pos posrange.PositionRange) annoErr {
 	return annoErr{
 		PositionRange: pos,