Fix issue where `sum` over mixed exponential and custom buckets, or incompatible custom buckets, produces incorrect results

Signed-off-by: Charles Korn <charles.korn@grafana.com>

promql/engine.go

@@ -2784,6 +2784,7 @@ type groupedAggregation struct {
 	seen              bool // Was this output groups seen in the input at this timestamp.
 	hasFloat          bool // Has at least 1 float64 sample aggregated.
 	hasHistogram      bool // Has at least 1 histogram sample aggregated.
+	abandonHistogram  bool // If true, group has seen mixed exponential and custom buckets, or incompatible custom buckets.
 	groupAggrComplete bool // Used by LIMITK to short-cut series loop when we've reached K elem on every group.
 	incrementalMean   bool // True after reverting to incremental calculation of the mean value.
 }
@@ -2809,10 +2810,11 @@ func (ev *evaluator) aggregation(e *parser.AggregateExpr, q float64, inputMatrix
 		// Initialize this group if it's the first time we've seen it.
 		if !group.seen {
 			*group = groupedAggregation{
-				seen:       true,
+				seen:             true,
-				floatValue: f,
+				floatValue:       f,
-				floatMean:  f,
+				floatMean:        f,
-				groupCount: 1,
+				abandonHistogram: false,
+				groupCount:       1,
 			}
 			switch op {
 			case parser.AVG, parser.SUM:
@@ -2833,6 +2835,10 @@ func (ev *evaluator) aggregation(e *parser.AggregateExpr, q float64, inputMatrix
 			continue
 		}
 
+		if group.abandonHistogram {
+			continue
+		}
+
 		switch op {
 		case parser.SUM:
 			if h != nil {
@@ -2841,6 +2847,7 @@ func (ev *evaluator) aggregation(e *parser.AggregateExpr, q float64, inputMatrix
 					_, err := group.histogramValue.Add(h)
 					if err != nil {
 						handleAggregationError(err, e, inputMatrix[si].Metric.Get(model.MetricNameLabel), &annos)
+						group.abandonHistogram = true
 					}
 				}
 				// Otherwise the aggregation contained floats
@@ -2987,7 +2994,9 @@ func (ev *evaluator) aggregation(e *parser.AggregateExpr, q float64, inputMatrix
 				annos.Add(annotations.NewMixedFloatsHistogramsAggWarning(e.Expr.PositionRange()))
 				continue
 			}
-			if aggr.hasHistogram {
+			if aggr.abandonHistogram {
+				continue
+			} else if aggr.hasHistogram {
 				aggr.histogramValue.Compact(0)
 			} else {
 				aggr.floatValue += aggr.floatKahanC

promql/promqltest/testdata/native_histograms.test

@@ -762,3 +762,30 @@ eval_warn instant at 30s rate(some_metric[30s])
 # Test the case where we have more than two points for rate
 eval_warn instant at 1m rate(some_metric[1m])
     {} {{count:0.03333333333333333 sum:0.03333333333333333 buckets:[0.03333333333333333]}}
+
+# Test mixing exponential and custom buckets.
+load 6m
+  metric{series="exponential"}         {{sum:4 count:3 buckets:[1 2 1]}}  _                                                                 {{sum:4 count:3 buckets:[1 2 1]}}
+  metric{series="other-exponential"}   {{sum:3 count:2 buckets:[1 1 1]}}  _                                                                 {{sum:3 count:2 buckets:[1 1 1]}}
+  metric{series="custom"}              _                                  {{schema:-53 sum:1 count:1 custom_values:[5 10] buckets:[1]}}     {{schema:-53 sum:1 count:1 custom_values:[5 10] buckets:[1]}}
+  metric{series="other-custom"}        _                                  {{schema:-53 sum:15 count:2 custom_values:[5 10] buckets:[0 2]}}  {{schema:-53 sum:15 count:2 custom_values:[5 10] buckets:[0 2]}}
+
+# T=0: only exponential
+# T=6: only custom
+# T=12: mixed, should be ignored and emit an warning
+eval_warn range from 0 to 12m step 6m sum(metric)
+  {} {{sum:7 count:5 buckets:[2 3 2]}} {{schema:-53 sum:16 count:3 custom_values:[5 10] buckets:[1 2]}} _
+
+clear
+
+# Test incompatible custom bucket schemas.
+load 6m
+  metric{series="1"} _                                                             {{schema:-53 sum:1 count:1 custom_values:[5 10] buckets:[1]}} {{schema:-53 sum:1 count:1 custom_values:[5 10] buckets:[1]}}
+  metric{series="2"} {{schema:-53 sum:1 count:1 custom_values:[2] buckets:[1]}}    _                                                             {{schema:-53 sum:1 count:1 custom_values:[2] buckets:[1]}}
+  metric{series="3"} {{schema:-53 sum:1 count:1 custom_values:[5 10] buckets:[1]}} {{schema:-53 sum:1 count:1 custom_values:[5 10] buckets:[1]}} {{schema:-53 sum:1 count:1 custom_values:[5 10] buckets:[1]}}
+
+# T=0: incompatible, should be ignored and emit a warning
+# T=6: compatible
+# T=12: incompatible followed by compatible, should be ignored and emit a warning
+eval_warn range from 0 to 12m step 6m sum(metric)
+  {} _ {{schema:-53 sum:2 count:2 custom_values:[5 10] buckets:[2]}} _