Add support for Metrics Slices to ottl len converter

Fixes open-telemetry#25868

.chloggen/ottl-len-metrics-issue-25868.yaml

@@ -0,0 +1,20 @@
+# Use this changelog template to create an entry for release notes.
+# If your change doesn't affect end users, such as a test fix or a tooling change,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+
+# 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: pkg/ottl
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add support for Metrics Slices to `Len` converter 
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [25868]
+
+# (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:

pkg/ottl/ottlfuncs/func_len.go

@@ -9,12 +9,15 @@ import (
 	"reflect"
 
 	"go.opentelemetry.io/collector/pdata/pcommon"
+	"go.opentelemetry.io/collector/pdata/pmetric"
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl"
 )
 
 const (
-	typeError = "target arg must be of type string, []any, map[string]any, pcommon.Map, pcommon.Slice, or pcommon.Value (of type String, Map, Slice)"
+	typeError = `target arg must be of type string, []any, map[string]any, pcommon.Map, pcommon.Slice, pcommon.Value (of type String, Map, Slice), 
+	pmetric.ExemplarSlice, pmetric.ExponentialHistogramDataPointSlice, pmetric.HistogramDataPointSlice, pmetric.MetricSlice, pmetric.NumberDataPointSlice, 
+	pmetric.ResourceMetricsSlice, pmetric.ScopeMetricsSlice, pmetric.SummaryDataPointSlice, pmetric.SummaryDataPointValueAtQuantileSlice`
 )
 
 type LenArguments[K any] struct {
@@ -58,6 +61,25 @@ func computeLen[K any](target ottl.Getter[K]) ottl.ExprFunc[K] {
 			return int64(valType.Len()), nil
 		case pcommon.Slice:
 			return int64(valType.Len()), nil
+
+		case pmetric.ExemplarSlice:
+			return int64(valType.Len()), nil
+		case pmetric.ExponentialHistogramDataPointSlice:
+			return int64(valType.Len()), nil
+		case pmetric.HistogramDataPointSlice:
+			return int64(valType.Len()), nil
+		case pmetric.MetricSlice:
+			return int64(valType.Len()), nil
+		case pmetric.NumberDataPointSlice:
+			return int64(valType.Len()), nil
+		case pmetric.ResourceMetricsSlice:
+			return int64(valType.Len()), nil
+		case pmetric.ScopeMetricsSlice:
+			return int64(valType.Len()), nil
+		case pmetric.SummaryDataPointSlice:
+			return int64(valType.Len()), nil
+		case pmetric.SummaryDataPointValueAtQuantileSlice:
+			return int64(valType.Len()), nil
 		}
 
 		v := reflect.ValueOf(val)

pkg/ottl/ottlfuncs/func_len_test.go

@@ -10,6 +10,7 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	"go.opentelemetry.io/collector/pdata/pcommon"
+	"go.opentelemetry.io/collector/pdata/pmetric"
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl"
 )
@@ -39,6 +40,60 @@ func Test_Len(t *testing.T) {
 		t.Error(err)
 	}
 
+	pmetricExemplarSlice := pmetric.NewExemplarSlice()
+	pmetricExemplarSlice.EnsureCapacity(5)
+	for i := 0; i < 5; i++ {
+		pmetricExemplarSlice.AppendEmpty()
+	}
+
+	pmetricExponentialHistogramDataPointSlice := pmetric.NewExponentialHistogramDataPointSlice()
+	pmetricExponentialHistogramDataPointSlice.EnsureCapacity(5)
+	for i := 0; i < 5; i++ {
+		pmetricExponentialHistogramDataPointSlice.AppendEmpty()
+	}
+
+	pmetricHistogramDataPointSlice := pmetric.NewHistogramDataPointSlice()
+	pmetricHistogramDataPointSlice.EnsureCapacity(5)
+	for i := 0; i < 5; i++ {
+		pmetricHistogramDataPointSlice.AppendEmpty()
+	}
+
+	pmetricMetricSlice := pmetric.NewMetricSlice()
+	pmetricMetricSlice.EnsureCapacity(5)
+	for i := 0; i < 5; i++ {
+		pmetricMetricSlice.AppendEmpty()
+	}
+
+	pmetricNumberDataPointSlice := pmetric.NewNumberDataPointSlice()
+	pmetricNumberDataPointSlice.EnsureCapacity(5)
+	for i := 0; i < 5; i++ {
+		pmetricNumberDataPointSlice.AppendEmpty()
+	}
+
+	pmetricResourceSlice := pmetric.NewResourceMetricsSlice()
+	pmetricResourceSlice.EnsureCapacity(5)
+	for i := 0; i < 5; i++ {
+		pmetricResourceSlice.AppendEmpty()
+	}
+
+	pmetricScopeMetricsSlice := pmetric.NewScopeMetricsSlice()
+	pmetricScopeMetricsSlice.EnsureCapacity(5)
+	for i := 0; i < 5; i++ {
+		pmetricScopeMetricsSlice.AppendEmpty()
+	}
+
+	pmetricSummaryDataPointSlice := pmetric.NewSummaryDataPointSlice()
+	pmetricSummaryDataPointSlice.EnsureCapacity(5)
+	for i := 0; i < 5; i++ {
+		pmetricSummaryDataPointSlice.AppendEmpty()
+	}
+
+	pmetricSummaryDataPointValueAtQuantileSlice := pmetric.NewSummaryDataPointValueAtQuantileSlice()
+	pmetricSummaryDataPointValueAtQuantileSlice.EnsureCapacity(5)
+	for i := 0; i < 5; i++ {
+		pmetricSummaryDataPointValueAtQuantileSlice.AppendEmpty()
+	}
+
 	tests := []struct {
 		name     string
 		value    interface{}
@@ -89,6 +144,51 @@ func Test_Len(t *testing.T) {
 			value:    pcommonValueMap,
 			expected: 5,
 		},
+		{
+			name:     "pmetric Exemplar slice",
+			value:    pmetricExemplarSlice,
+			expected: 5,
+		},
+		{
+			name:     "pmetric ExponentialHistogramDataPoint slice",
+			value:    pmetricExponentialHistogramDataPointSlice,
+			expected: 5,
+		},
+		{
+			name:     "pmetric HistogramDataPoint slice",
+			value:    pmetricHistogramDataPointSlice,
+			expected: 5,
+		},
+		{
+			name:     "pmetric Metric slice",
+			value:    pmetricMetricSlice,
+			expected: 5,
+		},
+		{
+			name:     "pmetric NumberDataPoint slice",
+			value:    pmetricNumberDataPointSlice,
+			expected: 5,
+		},
+		{
+			name:     "pmetric Resource slice",
+			value:    pmetricResourceSlice,
+			expected: 5,
+		},
+		{
+			name:     "pmetric ScopeMetrics slice",
+			value:    pmetricScopeMetricsSlice,
+			expected: 5,
+		},
+		{
+			name:     "pmetric SummaryDataPoint slice",
+			value:    pmetricSummaryDataPointSlice,
+			expected: 5,
+		},
+		{
+			name:     "pmetric SummaryDataPointValueAtQuantile slice",
+			value:    pmetricSummaryDataPointValueAtQuantileSlice,
+			expected: 5,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {