Replace filter aggregator with direct filter on measure (#4342)

* Replace filter aggregator with direct filter on measure

Part of #4220

Instead of using an aggregator to filter measured attributes, directly
filter the attributes in the constructed Measure function the Builder
creates.

Include unit and integration testing of new filtering.

* Update sdk/metric/internal/aggregate/aggregate.go

Co-authored-by: David Ashpole <[email protected]>

---------

Co-authored-by: David Ashpole <[email protected]>

sdk/metric/internal/aggregate/aggregate.go

@@ -44,7 +44,11 @@ type Builder[N int64 | float64] struct {
 
 func (b Builder[N]) input(agg aggregator[N]) Measure[N] {
 	if b.Filter != nil {
-		agg = newFilter[N](agg, b.Filter)
+		fltr := b.Filter // Copy to make it immutable after assignment.
+		return func(_ context.Context, n N, a attribute.Set) {
+			fAttr, _ := a.Filter(fltr)
+			agg.Aggregate(n, fAttr)
+		}
 	}
 	return func(_ context.Context, n N, a attribute.Set) {
 		agg.Aggregate(n, a)

sdk/metric/internal/aggregate/aggregate_test.go

@@ -0,0 +1,75 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package aggregate // import "go.opentelemetry.io/otel/sdk/metric/internal/aggregate"
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"go.opentelemetry.io/otel/attribute"
+)
+
+var (
+	keyUser   = "user"
+	userAlice = attribute.String(keyUser, "Alice")
+	adminTrue = attribute.Bool("admin", true)
+
+	alice = attribute.NewSet(userAlice, adminTrue)
+
+	// Filtered.
+	attrFltr = func(kv attribute.KeyValue) bool {
+		return kv.Key == attribute.Key(keyUser)
+	}
+	fltrAlice = attribute.NewSet(userAlice)
+)
+
+type inputTester[N int64 | float64] struct {
+	aggregator[N]
+
+	value N
+	attr  attribute.Set
+}
+
+func (it *inputTester[N]) Aggregate(v N, a attribute.Set) { it.value, it.attr = v, a }
+
+func TestBuilderInput(t *testing.T) {
+	t.Run("Int64", testBuilderInput[int64]())
+	t.Run("Float64", testBuilderInput[float64]())
+}
+
+func testBuilderInput[N int64 | float64]() func(t *testing.T) {
+	return func(t *testing.T) {
+		t.Helper()
+
+		value, attr := N(1), alice
+		run := func(b Builder[N], wantA attribute.Set) func(*testing.T) {
+			return func(t *testing.T) {
+				t.Helper()
+
+				it := &inputTester[N]{}
+				meas := b.input(it)
+				meas(context.Background(), value, attr)
+
+				assert.Equal(t, value, it.value, "measured incorrect value")
+				assert.Equal(t, wantA, it.attr, "measured incorrect attributes")
+			}
+		}
+
+		t.Run("NoFilter", run(Builder[N]{}, attr))
+		t.Run("Filter", run(Builder[N]{Filter: attrFltr}, fltrAlice))
+	}
+}

sdk/metric/internal/aggregate/aggregator_test.go

@@ -34,9 +34,8 @@ const (
 )
 
 var (
-	alice = attribute.NewSet(attribute.String("user", "alice"), attribute.Bool("admin", true))
-	bob   = attribute.NewSet(attribute.String("user", "bob"), attribute.Bool("admin", false))
-	carol = attribute.NewSet(attribute.String("user", "carol"), attribute.Bool("admin", false))
+	bob   = attribute.NewSet(attribute.String(keyUser, "bob"), attribute.Bool("admin", false))
+	carol = attribute.NewSet(attribute.String(keyUser, "carol"), attribute.Bool("admin", false))
 
 	// Sat Jan 01 2000 00:00:00 GMT+0000.
 	staticTime    = time.Unix(946684800, 0)