[processor/deltatocumulative]: explicit-bounds histograms (#33983)

**Description:** <Describe what has changed.>
<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->

adds aggregation support for fixed-bucket / explicit bounds histograms


**Link to tracking Issue:**
#30705

**Testing:** unit tests added

**Documentation:** none

.chloggen/deltatocumulative-histograms.yaml

@@ -0,0 +1,28 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: deltatocumulative
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: explicit-bounds histograms
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [30705]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+  implements aggregation of explicit-bounds (traditional) histograms.
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

processor/deltatocumulativeprocessor/go.mod

@@ -3,6 +3,7 @@ module github.com/open-telemetry/opentelemetry-collector-contrib/processor/delta
 go 1.22.0
 
 require (
+	github.com/google/go-cmp v0.6.0
 	github.com/open-telemetry/opentelemetry-collector-contrib/internal/exp/metrics v0.107.0
 	github.com/open-telemetry/opentelemetry-collector-contrib/pkg/pdatatest v0.107.0
 	github.com/stretchr/testify v1.9.0

processor/deltatocumulativeprocessor/internal/data/add.go

@@ -9,6 +9,7 @@ import (
 	"go.opentelemetry.io/collector/pdata/pmetric"
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/expo"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/putil/pslice"
 )
 
 func (dp Number) Add(in Number) Number {
@@ -24,9 +25,44 @@ func (dp Number) Add(in Number) Number {
 	return dp
 }
 
-// nolint
 func (dp Histogram) Add(in Histogram) Histogram {
-	panic("todo")
+	// bounds different: no way to merge, so reset observation to new boundaries
+	if !pslice.Equal(dp.ExplicitBounds(), in.ExplicitBounds()) {
+		in.MoveTo(dp.HistogramDataPoint)
+		return dp
+	}
+
+	// spec requires len(BucketCounts) == len(ExplicitBounds)+1.
+	// given we have limited error handling at this stage (and already verified boundaries are correct),
+	// doing a best-effort add of whatever we have appears reasonable.
+	n := min(dp.BucketCounts().Len(), in.BucketCounts().Len())
+	for i := 0; i < n; i++ {
+		sum := dp.BucketCounts().At(i) + in.BucketCounts().At(i)
+		dp.BucketCounts().SetAt(i, sum)
+	}
+
+	dp.SetTimestamp(in.Timestamp())
+	dp.SetCount(dp.Count() + in.Count())
+
+	if dp.HasSum() && in.HasSum() {
+		dp.SetSum(dp.Sum() + in.Sum())
+	} else {
+		dp.RemoveSum()
+	}
+
+	if dp.HasMin() && in.HasMin() {
+		dp.SetMin(math.Min(dp.Min(), in.Min()))
+	} else {
+		dp.RemoveMin()
+	}
+
+	if dp.HasMax() && in.HasMax() {
+		dp.SetMax(math.Max(dp.Max(), in.Max()))
+	} else {
+		dp.RemoveMax()
+	}
+
+	return dp
 }
 
 func (dp ExpHistogram) Add(in ExpHistogram) ExpHistogram {

processor/deltatocumulativeprocessor/internal/data/data.go

@@ -21,10 +21,28 @@ type Point[Self any] interface {
 	Add(Self) Self
 }
 
+type Typed[Self any] interface {
+	Point[Self]
+	Number | Histogram | ExpHistogram
+}
+
 type Number struct {
 	pmetric.NumberDataPoint
 }
 
+func Zero[P Typed[P]]() P {
+	var point P
+	switch ty := any(&point).(type) {
+	case *Number:
+		ty.NumberDataPoint = pmetric.NewNumberDataPoint()
+	case *Histogram:
+		ty.HistogramDataPoint = pmetric.NewHistogramDataPoint()
+	case *ExpHistogram:
+		ty.DataPoint = pmetric.NewExponentialHistogramDataPoint()
+	}
+	return point
+}
+
 func (dp Number) Clone() Number {
 	clone := Number{NumberDataPoint: pmetric.NewNumberDataPoint()}
 	if dp.NumberDataPoint != (pmetric.NumberDataPoint{}) {

processor/deltatocumulativeprocessor/internal/data/datatest/compare/compare.go

@@ -0,0 +1,27 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package compare // import "github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/datatest/compare"
+
+import (
+	"reflect"
+	"strings"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/google/go-cmp/cmp/cmpopts"
+)
+
+var Opts = []cmp.Option{
+	cmpopts.EquateApprox(0, 1e-9),
+	cmp.Exporter(func(ty reflect.Type) bool {
+		return strings.HasPrefix(ty.PkgPath(), "go.opentelemetry.io/collector/pdata")
+	}),
+}
+
+func Equal[T any](a, b T) bool {
+	return cmp.Equal(a, b, Opts...)
+}
+
+func Diff[T any](a, b T) string {
+	return cmp.Diff(a, b, Opts...)
+}

processor/deltatocumulativeprocessor/internal/data/expo/expotest/equal.go → processor/deltatocumulativeprocessor/internal/data/datatest/equal.go

@@ -1,17 +1,17 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
-package expotest // import "github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/expo/expotest"
+package datatest // import "github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/datatest"
 
 import (
 	"reflect"
 	"strings"
 	"testing"
 
-	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/pdatatest/pmetrictest"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/datatest/compare"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/expo"
 )
 
@@ -20,7 +20,7 @@ type T struct {
 	testing.TB
 }
 
-func Is(t testing.TB) T {
+func New(t testing.TB) T {
 	return T{TB: t}
 }
 
@@ -58,7 +58,7 @@ func equal(t testing.TB, want, got any, name string) bool {
 	vg := reflect.ValueOf(got)
 
 	if vw.Kind() != reflect.Struct {
-		ok := reflect.DeepEqual(want, got)
+		ok := compare.Equal(want, got)
 		if !ok {
 			t.Errorf("%s: %+v != %+v", name, want, got)
 		}
@@ -79,7 +79,7 @@ func equal(t testing.TB, want, got any, name string) bool {
 			continue
 		}
 		// Append(Empty) fails above heuristic, exclude it
-		if strings.HasPrefix(mname, "Append") {
+		if strings.HasPrefix(mname, "Append") || strings.HasPrefix(mname, "Clone") {
 			continue
 		}
 
@@ -111,5 +111,10 @@ func equal(t testing.TB, want, got any, name string) bool {
 	}
 
 	// fallback to a full deep-equal for rare cases (unexported fields, etc)
-	return assert.Equal(t, want, got)
+	if diff := compare.Diff(want, got); diff != "" {
+		t.Error(diff)
+		return false
+	}
+
+	return true
 }

processor/deltatocumulativeprocessor/internal/data/expo/expotest/equal_test.go → processor/deltatocumulativeprocessor/internal/data/datatest/equal_test.go

@@ -1,7 +1,7 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
-package expotest
+package datatest
 
 import (
 	"fmt"
@@ -12,39 +12,34 @@ import (
 	"testing"
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/expo"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/expo/expotest"
 )
 
 var t testing.TB = fakeT{}
 
-var expotest = struct {
-	Is      func(t testing.TB) T
-	Observe func(expo.Scale, ...float64) expo.Buckets
-}{
-	Is:      Is,
-	Observe: Observe,
-}
+var datatest = struct{ New func(t testing.TB) T }{New: New}
 
 func ExampleT_Equal() {
-	is := expotest.Is(t)
+	is := datatest.New(t)
 
-	want := Histogram{
+	want := expotest.Histogram{
 		PosNeg: expotest.Observe(expo.Scale(0), 1, 2, 3, 4),
 		Scale:  0,
 	}.Into()
 
-	got := Histogram{
+	got := expotest.Histogram{
 		PosNeg: expotest.Observe(expo.Scale(1), 1, 1, 1, 1),
 		Scale:  1,
 	}.Into()
 
 	is.Equal(want, got)
 
 	// Output:
-	// equal_test.go:40: Negative().BucketCounts().AsRaw(): [1 1 2] != [4]
-	// equal_test.go:40: Negative().BucketCounts().Len(): 3 != 1
-	// equal_test.go:40: Positive().BucketCounts().AsRaw(): [1 1 2] != [4]
-	// equal_test.go:40: Positive().BucketCounts().Len(): 3 != 1
-	// equal_test.go:40: Scale(): 0 != 1
+	// equal_test.go:35: Negative().BucketCounts().AsRaw(): [1 1 2] != [4]
+	// equal_test.go:35: Negative().BucketCounts().Len(): 3 != 1
+	// equal_test.go:35: Positive().BucketCounts().AsRaw(): [1 1 2] != [4]
+	// equal_test.go:35: Positive().BucketCounts().Len(): 3 != 1
+	// equal_test.go:35: Scale(): 0 != 1
 }
 
 func TestNone(*testing.T) {}

processor/deltatocumulativeprocessor/internal/data/expo/expo_test.go

@@ -7,12 +7,13 @@ import (
 	"fmt"
 	"testing"
 
+	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/datatest"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/expo"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/expo/expotest"
 )
 
 func TestAbsolute(t *testing.T) {
-	is := expotest.Is(t)
+	is := datatest.New(t)
 
 	bs := expotest.Bins{ø, 1, 2, 3, 4, 5, ø, ø}.Into()
 	abs := expo.Abs(bs)

processor/deltatocumulativeprocessor/internal/data/expo/merge_test.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"testing"
 
+	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/datatest"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/expo"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/expo/expotest"
 )
@@ -46,7 +47,7 @@ func TestMerge(t *testing.T) {
 		name := fmt.Sprintf("(%+d,%d)+(%+d,%d)=(%+d,%d)", a.Offset(), a.BucketCounts().Len(), b.Offset(), b.BucketCounts().Len(), want.Offset(), want.BucketCounts().Len())
 		t.Run(name, func(t *testing.T) {
 			expo.Merge(a, b)
-			is := expotest.Is(t)
+			is := datatest.New(t)
 			is.Equal(want, a)
 		})
 	}

processor/deltatocumulativeprocessor/internal/data/expo/scale_test.go

@@ -12,8 +12,8 @@ import (
 	"github.com/stretchr/testify/assert"
 	"go.opentelemetry.io/collector/pdata/pmetric"
 
+	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/datatest"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/expo"
-	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/expo/expotest"
 )
 
 func TestDownscale(t *testing.T) {
@@ -83,7 +83,7 @@ func TestDownscale(t *testing.T) {
 				buckets[i] = Repr[B]{scale: r.scale, bkt: bkt}
 			}
 
-			is := expotest.Is(t)
+			is := datatest.New(t)
 			for i := 0; i < len(buckets)-1; i++ {
 				expo.Downscale(buckets[i].bkt, buckets[i].scale, buckets[i+1].scale)
 

processor/deltatocumulativeprocessor/internal/data/expo/zero_test.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/stretchr/testify/assert"
 
+	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/datatest"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/expo"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/expo/expotest"
 )
@@ -56,7 +57,7 @@ func TestWidenZero(t *testing.T) {
 			}
 			expo.WidenZero(hist, zt)
 
-			is := expotest.Is(t)
+			is := datatest.New(t)
 			is.Equal(want, hist)
 		})
 	}
@@ -108,7 +109,7 @@ func TestSlice(t *testing.T) {
 
 			expo.Abs(bins).Slice(from, to)
 
-			is := expotest.Is(t)
+			is := datatest.New(t)
 			is.Equal(want, bins)
 		})
 	}

processor/deltatocumulativeprocessor/internal/data/expo_test.go

@@ -9,14 +9,15 @@ import (
 
 	"go.opentelemetry.io/collector/pdata/pmetric"
 
+	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/datatest"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/expo"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/deltatocumulativeprocessor/internal/data/expo/expotest"
 )
 
 // represents none/absent/unset in several tests
 const ø = math.MaxUint64
 
-func TestAdd(t *testing.T) {
+func TestExpoAdd(t *testing.T) {
 	type expdp = expotest.Histogram
 	type bins = expotest.Bins
 	var obs0 = expotest.Observe0
@@ -92,7 +93,7 @@ func TestAdd(t *testing.T) {
 	for _, cs := range cases {
 		run := func(dp, in expdp) func(t *testing.T) {
 			return func(t *testing.T) {
-				is := expotest.Is(t)
+				is := datatest.New(t)
 
 				var (
 					dp   = ExpHistogram{dp.Into()}