aggregateutil: allow filtering against empty attribute set

.chloggen/aggregate_labels_empty.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: metricstransform
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: The previously removed functionality of aggregating against an empty label set is restored.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [34430]
+
+# (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:
+
+# 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: []

cmd/otelcontribcol/go.mod

@@ -4,8 +4,6 @@ module github.com/open-telemetry/opentelemetry-collector-contrib/cmd/otelcontrib
 
 go 1.22.0
 
-toolchain go1.22.6
-
 require (
 	github.com/open-telemetry/opentelemetry-collector-contrib/confmap/provider/s3provider v0.108.0
 	github.com/open-telemetry/opentelemetry-collector-contrib/confmap/provider/secretsmanagerprovider v0.108.0

internal/coreinternal/aggregateutil/aggregate.go

@@ -33,9 +33,21 @@ func CopyMetricDetails(from, to pmetric.Metric) {
 }
 
 func FilterAttrs(metric pmetric.Metric, filterAttrKeys []string) {
-	if len(filterAttrKeys) == 0 {
+	// filterAttrKeys being nil means the filter is to be skipped.
+	if filterAttrKeys == nil {
 		return
 	}
+	// filterAttrKeys being empty means it is explicitly expected to filter
+	// against an empty label set, which is functionally the same as removing
+	// all attributes.
+	if len(filterAttrKeys) == 0 {
+		RangeDataPointAttributes(metric, func(attrs pcommon.Map) bool {
+			attrs.Clear()
+			return true
+		})
+	}
+	// filterAttrKeys having provided attributes means the filter continues
+	// as normal.
 	RangeDataPointAttributes(metric, func(attrs pcommon.Map) bool {
 		attrs.RemoveIf(func(k string, _ pcommon.Value) bool {
 			return isNotPresent(k, filterAttrKeys)

internal/coreinternal/aggregateutil/aggregate_test.go

@@ -125,9 +125,7 @@ func Test_FilterAttributes(t *testing.T) {
 			want: func() pmetric.Metric {
 				m := pmetric.NewMetric()
 				s := m.SetEmptySum()
-				d := s.DataPoints().AppendEmpty()
-				d.Attributes().PutStr("attr1", "val1")
-				d.Attributes().PutStr("attr2", "val2")
+				s.DataPoints().AppendEmpty()
 				return m
 			},
 		},