make annotations use an interface

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

promql/engine.go

@@ -3471,7 +3471,7 @@ func handleVectorBinopError(err error, e *parser.BinaryExpr) annotations.Annotat
 	metricName := ""
 	pos := e.PositionRange()
 	if errors.Is(err, annotations.PromQLInfo) || errors.Is(err, annotations.PromQLWarning) {
-		return annotations.New().Add(err)
+		return annotations.New().AddRaw(err)
 	}
 	if errors.Is(err, histogram.ErrHistogramsIncompatibleSchema) {
 		return annotations.New().Add(annotations.NewMixedExponentialCustomHistogramsWarning(metricName, pos))

promql/engine_internal_test.go

@@ -65,7 +65,7 @@ func TestRecoverEvaluatorErrorWithWarnings(t *testing.T) {
 	var err error
 	var ws annotations.Annotations
 
-	warnings := annotations.New().Add(errors.New("custom warning"))
+	warnings := annotations.New().AddRaw(errors.New("custom warning"))
 	e := errWithWarnings{
 		err:      errors.New("custom error"),
 		warnings: warnings,

storage/merge_test.go

@@ -1540,7 +1540,7 @@ func TestMergeQuerierWithSecondaries_ErrorHandling(t *testing.T) {
 				&mockQuerier{resp: []string{"b"}, warnings: nil, err: errStorage},
 			},
 			expectedLabels:   []string{},
-			expectedWarnings: annotations.New().Add(errStorage),
+			expectedWarnings: annotations.New().AddRaw(errStorage),
 		},
 		{
 			name:      "nil primary querier with two failed secondaries",
@@ -1550,7 +1550,7 @@ func TestMergeQuerierWithSecondaries_ErrorHandling(t *testing.T) {
 				&mockQuerier{resp: []string{"c"}, warnings: nil, err: errStorage},
 			},
 			expectedLabels:   []string{},
-			expectedWarnings: annotations.New().Add(errStorage),
+			expectedWarnings: annotations.New().AddRaw(errStorage),
 		},
 		{
 			name: "one successful primary querier with failed secondaries",
@@ -1565,30 +1565,30 @@ func TestMergeQuerierWithSecondaries_ErrorHandling(t *testing.T) {
 				labels.FromStrings("test", "a"),
 			},
 			expectedLabels:   []string{"a"},
-			expectedWarnings: annotations.New().Add(errStorage),
+			expectedWarnings: annotations.New().AddRaw(errStorage),
 		},
 		{
 			name: "successful queriers with warnings",
 			primaries: []Querier{
-				&mockQuerier{resp: []string{"a"}, warnings: annotations.New().Add(warnStorage), err: nil},
+				&mockQuerier{resp: []string{"a"}, warnings: annotations.New().AddRaw(warnStorage), err: nil},
 			},
 			secondaries: []Querier{
-				&mockQuerier{resp: []string{"b"}, warnings: annotations.New().Add(warnStorage), err: nil},
+				&mockQuerier{resp: []string{"b"}, warnings: annotations.New().AddRaw(warnStorage), err: nil},
 			},
 			expectedSelectsSeries: []labels.Labels{
 				labels.FromStrings("test", "a"),
 				labels.FromStrings("test", "b"),
 			},
 			expectedLabels:   []string{"a", "b"},
-			expectedWarnings: annotations.New().Add(warnStorage),
+			expectedWarnings: annotations.New().AddRaw(warnStorage),
 		},
 		{
 			name: "successful queriers with limit",
 			primaries: []Querier{
-				&mockQuerier{resp: []string{"a", "d"}, warnings: annotations.New().Add(warnStorage), err: nil},
+				&mockQuerier{resp: []string{"a", "d"}, warnings: annotations.New().AddRaw(warnStorage), err: nil},
 			},
 			secondaries: []Querier{
-				&mockQuerier{resp: []string{"b", "c"}, warnings: annotations.New().Add(warnStorage), err: nil},
+				&mockQuerier{resp: []string{"b", "c"}, warnings: annotations.New().AddRaw(warnStorage), err: nil},
 			},
 			limit: 2,
 			expectedSelectsSeries: []labels.Labels{
@@ -1596,7 +1596,7 @@ func TestMergeQuerierWithSecondaries_ErrorHandling(t *testing.T) {
 				labels.FromStrings("test", "b"),
 			},
 			expectedLabels:   []string{"a", "b"},
-			expectedWarnings: annotations.New().Add(warnStorage),
+			expectedWarnings: annotations.New().AddRaw(warnStorage),
 		},
 	} {
 		var labelHints *LabelHints

storage/remote/otlptranslator/prometheusremotewrite/histograms.go

@@ -127,7 +127,7 @@ func exponentialToNativeHistogram(p pmetric.ExponentialHistogramDataPoint) (prom
 		}
 		h.Count = &prompb.Histogram_CountInt{CountInt: p.Count()}
 		if p.Count() == 0 && h.Sum != 0 {
-			annots.Add(fmt.Errorf("exponential histogram data point has zero count, but non-zero sum: %f", h.Sum))
+			annots.AddRaw(fmt.Errorf("exponential histogram data point has zero count, but non-zero sum: %f", h.Sum))
 		}
 	}
 	return h, annots, nil

storage/secondary.go

@@ -52,7 +52,7 @@ func newSecondaryQuerierFromChunk(cq ChunkQuerier) genericQuerier {
 func (s *secondaryQuerier) LabelValues(ctx context.Context, name string, hints *LabelHints, matchers ...*labels.Matcher) ([]string, annotations.Annotations, error) {
 	vals, w, err := s.genericQuerier.LabelValues(ctx, name, hints, matchers...)
 	if err != nil {
-		return nil, w.Add(err), nil
+		return nil, w.AddRaw(err), nil
 	}
 	return vals, w, nil
 }
@@ -60,7 +60,7 @@ func (s *secondaryQuerier) LabelValues(ctx context.Context, name string, hints *
 func (s *secondaryQuerier) LabelNames(ctx context.Context, hints *LabelHints, matchers ...*labels.Matcher) ([]string, annotations.Annotations, error) {
 	names, w, err := s.genericQuerier.LabelNames(ctx, hints, matchers...)
 	if err != nil {
-		return nil, w.Add(err), nil
+		return nil, w.AddRaw(err), nil
 	}
 	return names, w, nil
 }
@@ -84,7 +84,7 @@ func (s *secondaryQuerier) Select(ctx context.Context, sortSeries bool, hints *S
 				if err := set.Err(); err != nil {
 					// One of the sets failed, ensure current one returning errors as warnings, and rest of the sets return nothing.
 					// (All or nothing logic).
-					s.asyncSets[curr] = warningsOnlySeriesSet(ws.Add(err))
+					s.asyncSets[curr] = warningsOnlySeriesSet(ws.AddRaw(err))
 					for i := range s.asyncSets {
 						if curr == i {
 							continue

util/annotations/annotations.go

@@ -27,7 +27,7 @@ import (
 // Each individual annotation is modeled by a Go error.
 // They are deduplicated based on the string returned by error.Error().
 // The zero value is usable without further initialization, see New().
-type Annotations map[string]error
+type Annotations map[string]annoErr
 
 // New returns new Annotations ready to use. Note that the zero value of
 // Annotations is also fully usable, but using this method is often more
@@ -38,14 +38,24 @@ func New() *Annotations {
 
 // Add adds an annotation (modeled as a Go error) in-place and returns the
 // modified Annotations for convenience.
-func (a *Annotations) Add(err error) Annotations {
+func (a *Annotations) Add(err annoErr) Annotations {
 	if *a == nil {
 		*a = Annotations{}
 	}
+	prevErr, exists := (*a)[err.Error()]
+	if exists {
+		err = err.merge(prevErr)
+	}
 	(*a)[err.Error()] = err
 	return *a
 }
 
+// AddRaw is like Add, but a convenience wrapper for adding raw errors instead of annoErrs
+// that have query and position information and possibly a custom merge function.
+func (a *Annotations) AddRaw(err error) Annotations {
+	return a.Add(&rawErr{Err: err})
+}
+
 // Merge adds the contents of the second annotation to the first, modifying
 // the first in-place, and returns the merged first Annotation for convenience.
 func (a *Annotations) Merge(aa Annotations) Annotations {
@@ -56,6 +66,10 @@ func (a *Annotations) Merge(aa Annotations) Annotations {
 		*a = Annotations{}
 	}
 	for key, val := range aa {
+		prevVal, exists := (*a)[key]
+		if exists {
+			val = val.merge(prevVal)
+		}
 		(*a)[key] = val
 	}
 	return *a
@@ -82,11 +96,7 @@ func (a Annotations) AsStrings(query string, maxWarnings, maxInfos int) (warning
 	warnSkipped := 0
 	infoSkipped := 0
 	for _, err := range a {
-		var anErr annoErr
+		err.setQuery(query)
-		if errors.As(err, &anErr) {
-			anErr.Query = query
-			err = anErr
-		}
 		switch {
 		case errors.Is(err, PromQLInfo):
 			if maxInfos == 0 || len(infos) < maxInfos {
@@ -150,27 +160,65 @@ var (
 	HistogramIgnoredInAggregationInfo       = fmt.Errorf("%w: ignored histogram in", PromQLInfo)
 )
 
-type annoErr struct {
+type annoErr interface {
+	error
+	// We can define custom merge functions to merge annoErrs with the same raw error string.
+	merge(annoErr) annoErr
+	// Necessary when we want to show position info. Also, this is only called at the end when we call
+	// AsStrings(), so before that we deduplicate based on the raw error string when query is empty,
+	// and the full error string with details will only be shown in the end when query is set.
+	setQuery(string)
+	// Necessary so we can use errors.Is() to disambiguate between warning and info.
+	Unwrap() error
+}
+
+type rawErr struct {
+	Err error
+}
+
+func (e *rawErr) merge(_ annoErr) annoErr {
+	return e
+}
+
+func (e *rawErr) setQuery(query string) {}
+
+func (e *rawErr) Error() string {
+	return e.Err.Error()
+}
+
+func (e *rawErr) Unwrap() error {
+	return e.Err
+}
+
+type genericAnnoErr struct {
 	PositionRange posrange.PositionRange
 	Err           error
 	Query         string
 }
 
-func (e annoErr) Error() string {
+func (e *genericAnnoErr) merge(_ annoErr) annoErr {
+	return e
+}
+
+func (e *genericAnnoErr) setQuery(query string) {
+	e.Query = query
+}
+
+func (e *genericAnnoErr) Error() string {
 	if e.Query == "" {
 		return e.Err.Error()
 	}
 	return fmt.Sprintf("%s (%s)", e.Err, e.PositionRange.StartPosInput(e.Query, 0))
 }
 
-func (e annoErr) Unwrap() error {
+func (e *genericAnnoErr) Unwrap() error {
 	return e.Err
 }
 
 // NewInvalidQuantileWarning is used when the user specifies an invalid quantile
 // value, i.e. a float that is outside the range [0, 1] or NaN.
-func NewInvalidQuantileWarning(q float64, pos posrange.PositionRange) error {
+func NewInvalidQuantileWarning(q float64, pos posrange.PositionRange) annoErr {
-	return annoErr{
+	return &genericAnnoErr{
 		PositionRange: pos,
 		Err:           fmt.Errorf("%w, got %g", InvalidQuantileWarning, q),
 	}
@@ -178,8 +226,8 @@ func NewInvalidQuantileWarning(q float64, pos posrange.PositionRange) error {
 
 // NewInvalidRatioWarning is used when the user specifies an invalid ratio
 // value, i.e. a float that is outside the range [-1, 1] or NaN.
-func NewInvalidRatioWarning(q, to float64, pos posrange.PositionRange) error {
+func NewInvalidRatioWarning(q, to float64, pos posrange.PositionRange) annoErr {
-	return annoErr{
+	return &genericAnnoErr{
 		PositionRange: pos,
 		Err:           fmt.Errorf("%w, got %g, capping to %g", InvalidRatioWarning, q, to),
 	}
@@ -187,8 +235,8 @@ func NewInvalidRatioWarning(q, to float64, pos posrange.PositionRange) error {
 
 // NewBadBucketLabelWarning is used when there is an error parsing the bucket label
 // of a classic histogram.
-func NewBadBucketLabelWarning(metricName, label string, pos posrange.PositionRange) error {
+func NewBadBucketLabelWarning(metricName, label string, pos posrange.PositionRange) annoErr {
-	return annoErr{
+	return &genericAnnoErr{
 		PositionRange: pos,
 		Err:           fmt.Errorf("%w of %q for metric name %q", BadBucketLabelWarning, label, metricName),
 	}
@@ -197,8 +245,8 @@ func NewBadBucketLabelWarning(metricName, label string, pos posrange.PositionRan
 // NewMixedFloatsHistogramsWarning is used when the queried series includes both
 // float samples and histogram samples for functions that do not support mixed
 // samples.
-func NewMixedFloatsHistogramsWarning(metricName string, pos posrange.PositionRange) error {
+func NewMixedFloatsHistogramsWarning(metricName string, pos posrange.PositionRange) annoErr {
-	return annoErr{
+	return &genericAnnoErr{
 		PositionRange: pos,
 		Err:           fmt.Errorf("%w metric name %q", MixedFloatsHistogramsWarning, metricName),
 	}
@@ -206,8 +254,8 @@ func NewMixedFloatsHistogramsWarning(metricName string, pos posrange.PositionRan
 
 // NewMixedFloatsHistogramsAggWarning is used when the queried series includes both
 // float samples and histogram samples in an aggregation.
-func NewMixedFloatsHistogramsAggWarning(pos posrange.PositionRange) error {
+func NewMixedFloatsHistogramsAggWarning(pos posrange.PositionRange) annoErr {
-	return annoErr{
+	return &genericAnnoErr{
 		PositionRange: pos,
 		Err:           fmt.Errorf("%w aggregation", MixedFloatsHistogramsWarning),
 	}
@@ -215,8 +263,8 @@ func NewMixedFloatsHistogramsAggWarning(pos posrange.PositionRange) error {
 
 // NewMixedClassicNativeHistogramsWarning is used when the queried series includes
 // both classic and native histograms.
-func NewMixedClassicNativeHistogramsWarning(metricName string, pos posrange.PositionRange) error {
+func NewMixedClassicNativeHistogramsWarning(metricName string, pos posrange.PositionRange) annoErr {
-	return annoErr{
+	return &genericAnnoErr{
 		PositionRange: pos,
 		Err:           fmt.Errorf("%w %q", MixedClassicNativeHistogramsWarning, metricName),
 	}
@@ -224,8 +272,8 @@ func NewMixedClassicNativeHistogramsWarning(metricName string, pos posrange.Posi
 
 // NewNativeHistogramNotCounterWarning is used when histogramRate is called
 // with isCounter set to true on a gauge histogram.
-func NewNativeHistogramNotCounterWarning(metricName string, pos posrange.PositionRange) error {
+func NewNativeHistogramNotCounterWarning(metricName string, pos posrange.PositionRange) annoErr {
-	return annoErr{
+	return &genericAnnoErr{
 		PositionRange: pos,
 		Err:           fmt.Errorf("%w %q", NativeHistogramNotCounterWarning, metricName),
 	}
@@ -233,8 +281,8 @@ func NewNativeHistogramNotCounterWarning(metricName string, pos posrange.Positio
 
 // NewNativeHistogramNotGaugeWarning is used when histogramRate is called
 // with isCounter set to false on a counter histogram.
-func NewNativeHistogramNotGaugeWarning(metricName string, pos posrange.PositionRange) error {
+func NewNativeHistogramNotGaugeWarning(metricName string, pos posrange.PositionRange) annoErr {
-	return annoErr{
+	return &genericAnnoErr{
 		PositionRange: pos,
 		Err:           fmt.Errorf("%w %q", NativeHistogramNotGaugeWarning, metricName),
 	}
@@ -242,8 +290,8 @@ func NewNativeHistogramNotGaugeWarning(metricName string, pos posrange.PositionR
 
 // NewMixedExponentialCustomHistogramsWarning is used when the queried series includes
 // histograms with both exponential and custom buckets schemas.
-func NewMixedExponentialCustomHistogramsWarning(metricName string, pos posrange.PositionRange) error {
+func NewMixedExponentialCustomHistogramsWarning(metricName string, pos posrange.PositionRange) annoErr {
-	return annoErr{
+	return &genericAnnoErr{
 		PositionRange: pos,
 		Err:           fmt.Errorf("%w %q", MixedExponentialCustomHistogramsWarning, metricName),
 	}
@@ -251,8 +299,8 @@ func NewMixedExponentialCustomHistogramsWarning(metricName string, pos posrange.
 
 // NewIncompatibleCustomBucketsHistogramsWarning is used when the queried series includes
 // custom buckets histograms with incompatible custom bounds.
-func NewIncompatibleCustomBucketsHistogramsWarning(metricName string, pos posrange.PositionRange) error {
+func NewIncompatibleCustomBucketsHistogramsWarning(metricName string, pos posrange.PositionRange) annoErr {
-	return annoErr{
+	return &genericAnnoErr{
 		PositionRange: pos,
 		Err:           fmt.Errorf("%w %q", IncompatibleCustomBucketsHistogramsWarning, metricName),
 	}
@@ -260,8 +308,8 @@ func NewIncompatibleCustomBucketsHistogramsWarning(metricName string, pos posran
 
 // 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) error {
+func NewPossibleNonCounterInfo(metricName string, pos posrange.PositionRange) annoErr {
-	return annoErr{
+	return &genericAnnoErr{
 		PositionRange: pos,
 		Err:           fmt.Errorf("%w %q", PossibleNonCounterInfo, metricName),
 	}
@@ -269,8 +317,8 @@ func NewPossibleNonCounterInfo(metricName string, pos posrange.PositionRange) er
 
 // NewHistogramQuantileForcedMonotonicityInfo is used when the input (classic histograms) to
 // histogram_quantile needs to be forced to be monotonic.
-func NewHistogramQuantileForcedMonotonicityInfo(metricName string, pos posrange.PositionRange) error {
+func NewHistogramQuantileForcedMonotonicityInfo(metricName string, pos posrange.PositionRange) annoErr {
-	return annoErr{
+	return &genericAnnoErr{
 		PositionRange: pos,
 		Err:           fmt.Errorf("%w %q", HistogramQuantileForcedMonotonicityInfo, metricName),
 	}
@@ -278,8 +326,8 @@ func NewHistogramQuantileForcedMonotonicityInfo(metricName string, pos posrange.
 
 // NewIncompatibleTypesInBinOpInfo is used if binary operators act on a
 // combination of types that doesn't work and therefore returns no result.
-func NewIncompatibleTypesInBinOpInfo(lhsType, operator, rhsType string, pos posrange.PositionRange) error {
+func NewIncompatibleTypesInBinOpInfo(lhsType, operator, rhsType string, pos posrange.PositionRange) annoErr {
-	return annoErr{
+	return &genericAnnoErr{
 		PositionRange: pos,
 		Err:           fmt.Errorf("%w %q: %s %s %s", IncompatibleTypesInBinOpInfo, operator, lhsType, operator, rhsType),
 	}
@@ -287,8 +335,8 @@ func NewIncompatibleTypesInBinOpInfo(lhsType, operator, rhsType string, pos posr
 
 // NewHistogramIgnoredInAggregationInfo is used when a histogram is ignored by
 // an aggregation operator that cannot handle histograms.
-func NewHistogramIgnoredInAggregationInfo(aggregation string, pos posrange.PositionRange) error {
+func NewHistogramIgnoredInAggregationInfo(aggregation string, pos posrange.PositionRange) annoErr {
-	return annoErr{
+	return &genericAnnoErr{
 		PositionRange: pos,
 		Err:           fmt.Errorf("%w %s aggregation", HistogramIgnoredInAggregationInfo, aggregation),
 	}

util/annotations/annotations_test.go

@@ -15,6 +15,7 @@ package annotations
 
 import (
 	"errors"
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -26,11 +27,16 @@ func TestAnnotations_AsStrings(t *testing.T) {
 	var annos Annotations
 	pos := posrange.PositionRange{Start: 3, End: 8}
 
-	annos.Add(errors.New("this is a non-annotation error"))
+	annos.AddRaw(errors.New("this is a non-annotation error"))
 
 	annos.Add(NewInvalidRatioWarning(1.1, 100, pos))
 	annos.Add(NewInvalidRatioWarning(1.2, 123, pos))
 
+	annos.Add(newTestCustomWarning(1.5, pos, 12, 14))
+	annos.Add(newTestCustomWarning(1.5, pos, 10, 20))
+	annos.Add(newTestCustomWarning(1.5, pos, 5, 15))
+	annos.Add(newTestCustomWarning(1.5, pos, 12, 14))
+
 	annos.Add(NewHistogramIgnoredInAggregationInfo("sum", pos))
 
 	warnings, infos := annos.AsStrings("lorem ipsum dolor sit amet", 0, 0)
@@ -38,8 +44,65 @@ func TestAnnotations_AsStrings(t *testing.T) {
 		"this is a non-annotation error",
 		"PromQL warning: ratio value should be between -1 and 1, got 1.1, capping to 100 (1:4)",
 		"PromQL warning: ratio value should be between -1 and 1, got 1.2, capping to 123 (1:4)",
+		"PromQL warning: custom value set to 1.5, 4 instances with smallest 5 and biggest 20 (1:4)",
 	})
 	require.ElementsMatch(t, infos, []string{
 		"PromQL info: ignored histogram in sum aggregation (1:4)",
 	})
 }
+
+type testCustomError struct {
+	PositionRange posrange.PositionRange
+	Err           error
+	Query         string
+	Min           []float64
+	Max           []float64
+	Count         int
+}
+
+func (e *testCustomError) merge(other annoErr) annoErr {
+	o, ok := other.(*testCustomError)
+	if !ok {
+		return e
+	}
+	if e.Err.Error() != o.Err.Error() || len(e.Min) != len(o.Min) || len(e.Max) != len(o.Max) {
+		return e
+	}
+	for i, aMin := range e.Min {
+		if aMin < o.Min[i] {
+			o.Min[i] = aMin
+		}
+	}
+	for i, aMax := range e.Max {
+		if aMax > o.Max[i] {
+			o.Max[i] = aMax
+		}
+	}
+	o.Count += e.Count + 1
+	return o
+}
+
+func (e *testCustomError) setQuery(query string) {
+	e.Query = query
+}
+
+func (e *testCustomError) Error() string {
+	if e.Query == "" {
+		return e.Err.Error()
+	}
+	return fmt.Sprintf("%s, %d instances with smallest %g and biggest %g (%s)", e.Err, e.Count+1, e.Min[0], e.Max[0], e.PositionRange.StartPosInput(e.Query, 0))
+}
+
+func (e *testCustomError) Unwrap() error {
+	return e.Err
+}
+
+func newTestCustomWarning(q float64, pos posrange.PositionRange, smallest, largest float64) annoErr {
+	testCustomWarning := fmt.Errorf("%w: custom value set to", PromQLWarning)
+	return &testCustomError{
+		PositionRange: pos,
+		Err:           fmt.Errorf("%w %g", testCustomWarning, q),
+		Min:           []float64{smallest},
+		Max:           []float64{largest},
+	}
+}

web/api/v1/api.go

@@ -84,7 +84,11 @@ const (
 	errorNotAcceptable errorType = "not_acceptable"
 )
 
-var LocalhostRepresentations = []string{"127.0.0.1", "localhost", "::1"}
+var (
+	LocalhostRepresentations = []string{"127.0.0.1", "localhost", "::1"}
+
+	errResultsTruncatedLimit = errors.New("results truncated due to limit")
+)
 
 type apiError struct {
 	typ errorType
@@ -735,7 +739,7 @@ func (api *API) labelNames(r *http.Request) apiFuncResult {
 
 	if limit > 0 && len(names) > limit {
 		names = names[:limit]
-		warnings = warnings.Add(errors.New("results truncated due to limit"))
+		warnings = warnings.AddRaw(errResultsTruncatedLimit)
 	}
 	return apiFuncResult{names, nil, warnings, nil}
 }
@@ -833,7 +837,7 @@ func (api *API) labelValues(r *http.Request) (result apiFuncResult) {
 
 	if limit > 0 && len(vals) > limit {
 		vals = vals[:limit]
-		warnings = warnings.Add(errors.New("results truncated due to limit"))
+		warnings = warnings.AddRaw(errResultsTruncatedLimit)
 	}
 
 	return apiFuncResult{vals, nil, warnings, closer}
@@ -940,7 +944,7 @@ func (api *API) series(r *http.Request) (result apiFuncResult) {
 
 		if limit > 0 && len(metrics) > limit {
 			metrics = metrics[:limit]
-			warnings.Add(errors.New("results truncated due to limit"))
+			warnings.AddRaw(errResultsTruncatedLimit)
 			return apiFuncResult{metrics, nil, warnings, closer}
 		}
 	}