[pkg/ottl]: add IsRootSpan converter (#33729)

**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.-->

Introduced `IsRootSpan()` converter function which returns `true` if the
span in the corresponding context is root, that means its
`parent_span_id` equals to hexadecimal representation of zero. In all
other scenarios function returns `false`.

**Link to tracking Issue:** #32918

**Testing:** 

- unit tests
- e2e tests

**Documentation:** <Describe the documentation added.>

- README entry

---------

Signed-off-by: odubajDT <ondrej.dubaj@dynatrace.com>
Co-authored-by: Tiffany Hrabusa <30397949+tiffany76@users.noreply.github.com>

.chloggen/add-isrootspan.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: 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 IsRootSpan() converter function."
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [32918]
+
+# (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: Converter `IsRootSpan()` returns `true` if the span in the corresponding context is root, that means its `parent_span_id` equals to hexadecimal representation of zero. In all other scenarios function returns `false`.
+
+# 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: []

internal/filter/filterottl/functions.go

@@ -21,7 +21,10 @@ import (
 )
 
 func StandardSpanFuncs() map[string]ottl.Factory[ottlspan.TransformContext] {
-	return ottlfuncs.StandardConverters[ottlspan.TransformContext]()
+	m := ottlfuncs.StandardConverters[ottlspan.TransformContext]()
+	isRootSpanFactory := ottlfuncs.NewIsRootSpanFactory()
+	m[isRootSpanFactory.Name()] = isRootSpanFactory
+	return m
 }
 
 func StandardSpanEventFuncs() map[string]ottl.Factory[ottlspanevent.TransformContext] {

pkg/ottl/e2e/e2e_test.go

@@ -12,10 +12,13 @@ import (
 	"go.opentelemetry.io/collector/component/componenttest"
 	"go.opentelemetry.io/collector/pdata/pcommon"
 	"go.opentelemetry.io/collector/pdata/plog"
+	"go.opentelemetry.io/collector/pdata/ptrace"
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl/contexts/ottllog"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl/contexts/ottlspan"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl/ottlfuncs"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/pdatatest/plogtest"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/pdatatest/ptracetest"
 )
 
 var (
@@ -840,6 +843,41 @@ func Test_e2e_ottl_features(t *testing.T) {
 	}
 }
 
+func Test_ProcessTraces_TraceContext(t *testing.T) {
+	tests := []struct {
+		statement string
+		want      func(_ ottlspan.TransformContext)
+	}{
+		{
+			statement: `set(attributes["entrypoint-root"], name) where IsRootSpan()`,
+			want: func(tCtx ottlspan.TransformContext) {
+				tCtx.GetSpan().Attributes().PutStr("entrypoint-root", "operationB")
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.statement, func(t *testing.T) {
+			settings := componenttest.NewNopTelemetrySettings()
+			funcs := ottlfuncs.StandardFuncs[ottlspan.TransformContext]()
+			isRootSpanFactory := ottlfuncs.NewIsRootSpanFactory()
+			funcs[isRootSpanFactory.Name()] = isRootSpanFactory
+			spanParser, err := ottlspan.NewParser(funcs, settings)
+			assert.NoError(t, err)
+			spanStatements, err := spanParser.ParseStatement(tt.statement)
+			assert.NoError(t, err)
+
+			tCtx := constructSpanTransformContext()
+			_, _, _ = spanStatements.Execute(context.Background(), tCtx)
+
+			exTCtx := constructSpanTransformContext()
+			tt.want(exTCtx)
+
+			assert.NoError(t, ptracetest.CompareResourceSpans(newResourceSpans(exTCtx), newResourceSpans(tCtx)))
+		})
+	}
+}
+
 func constructLogTransformContext() ottllog.TransformContext {
 	resource := pcommon.NewResource()
 	resource.Attributes().PutStr("host.name", "localhost")
@@ -873,6 +911,18 @@ func constructLogTransformContext() ottllog.TransformContext {
 	return ottllog.NewTransformContext(logRecord, scope, resource, plog.NewScopeLogs(), plog.NewResourceLogs())
 }
 
+func constructSpanTransformContext() ottlspan.TransformContext {
+	resource := pcommon.NewResource()
+
+	scope := pcommon.NewInstrumentationScope()
+	scope.SetName("scope")
+
+	td := ptrace.NewSpan()
+	fillSpanOne(td)
+
+	return ottlspan.NewTransformContext(td, scope, resource, ptrace.NewScopeSpans(), ptrace.NewResourceSpans())
+}
+
 func newResourceLogs(tCtx ottllog.TransformContext) plog.ResourceLogs {
 	rl := plog.NewResourceLogs()
 	tCtx.GetResource().CopyTo(rl.Resource())
@@ -882,3 +932,19 @@ func newResourceLogs(tCtx ottllog.TransformContext) plog.ResourceLogs {
 	tCtx.GetLogRecord().CopyTo(l)
 	return rl
 }
+
+func newResourceSpans(tCtx ottlspan.TransformContext) ptrace.ResourceSpans {
+	rl := ptrace.NewResourceSpans()
+	tCtx.GetResource().CopyTo(rl.Resource())
+	sl := rl.ScopeSpans().AppendEmpty()
+	tCtx.GetInstrumentationScope().CopyTo(sl.Scope())
+	l := sl.Spans().AppendEmpty()
+	tCtx.GetSpan().CopyTo(l)
+	return rl
+}
+
+func fillSpanOne(span ptrace.Span) {
+	span.SetName("operationB")
+	span.SetSpanID(spanID)
+	span.SetTraceID(traceID)
+}

pkg/ottl/ottlfuncs/README.md

@@ -424,6 +424,7 @@ Available Converters:
 - [IsBool](#isbool)
 - [IsDouble](#isdouble)
 - [IsInt](#isint)
+- [IsRootSpan](#isrootspan)
 - [IsMap](#ismap)
 - [IsMatch](#ismatch)
 - [IsList](#islist)
@@ -744,6 +745,23 @@ Examples:
 
 - `IsInt(attributes["maybe a int"])`
 
+### IsRootSpan
+
+`IsRootSpan()`
+
+The `IsRootSpan` Converter returns `true` if the span in the corresponding context is root, which means
+its `parent_span_id` is equal to hexadecimal representation of zero.
+
+This function is supported with [OTTL span context](../contexts/ottlspan/README.md). In any other context it is not supported.
+
+The function returns `false` in all other scenarios, including `parent_span_id == ""` or `parent_span_id == nil`.
+
+Examples:
+
+- `IsRootSpan()`
+
+- `set(attributes["isRoot"], "true") where IsRootSpan()`
+
 ### IsMap
 
 `IsMap(value)`

pkg/ottl/ottlfuncs/func_is_root_span.go

@@ -0,0 +1,25 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package ottlfuncs // import "github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl/ottlfuncs"
+
+import (
+	"context"
+
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl/contexts/ottlspan"
+)
+
+func NewIsRootSpanFactory() ottl.Factory[ottlspan.TransformContext] {
+	return ottl.NewFactory("IsRootSpan", nil, createIsRootSpanFunction)
+}
+
+func createIsRootSpanFunction(_ ottl.FunctionContext, _ ottl.Arguments) (ottl.ExprFunc[ottlspan.TransformContext], error) {
+	return isRootSpan()
+}
+
+func isRootSpan() (ottl.ExprFunc[ottlspan.TransformContext], error) {
+	return func(_ context.Context, tCtx ottlspan.TransformContext) (any, error) {
+		return tCtx.GetSpan().ParentSpanID().IsEmpty(), nil
+	}, nil
+}

pkg/ottl/ottlfuncs/func_is_root_span_test.go

@@ -0,0 +1,40 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package ottlfuncs // import "github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl/ottlfuncs"
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"go.opentelemetry.io/collector/pdata/pcommon"
+	"go.opentelemetry.io/collector/pdata/ptrace"
+
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl/contexts/ottlspan"
+)
+
+func Test_IsRootSpan(t *testing.T) {
+	exprFunc, err := isRootSpan()
+	assert.NoError(t, err)
+
+	// root span
+	spanRoot := ptrace.NewSpan()
+	spanRoot.SetParentSpanID(pcommon.SpanID{
+		0, 0, 0, 0, 0, 0, 0, 0,
+	})
+
+	value, err := exprFunc(nil, ottlspan.NewTransformContext(spanRoot, pcommon.NewInstrumentationScope(), pcommon.NewResource(), ptrace.NewScopeSpans(), ptrace.NewResourceSpans()))
+	assert.NoError(t, err)
+	require.Equal(t, true, value)
+
+	// non root span
+	spanNonRoot := ptrace.NewSpan()
+	spanNonRoot.SetParentSpanID(pcommon.SpanID{
+		1, 0, 0, 0, 0, 0, 0, 0,
+	})
+
+	value, err = exprFunc(nil, ottlspan.NewTransformContext(spanNonRoot, pcommon.NewInstrumentationScope(), pcommon.NewResource(), ptrace.NewScopeSpans(), ptrace.NewResourceSpans()))
+	assert.NoError(t, err)
+	require.Equal(t, false, value)
+}

processor/transformprocessor/internal/traces/functions.go

@@ -12,7 +12,10 @@ import (
 
 func SpanFunctions() map[string]ottl.Factory[ottlspan.TransformContext] {
 	// No trace-only functions yet.
-	return ottlfuncs.StandardFuncs[ottlspan.TransformContext]()
+	m := ottlfuncs.StandardFuncs[ottlspan.TransformContext]()
+	isRootSpanFactory := ottlfuncs.NewIsRootSpanFactory()
+	m[isRootSpanFactory.Name()] = isRootSpanFactory
+	return m
 }
 
 func SpanEventFunctions() map[string]ottl.Factory[ottlspanevent.TransformContext] {

processor/transformprocessor/internal/traces/functions_test.go

@@ -16,6 +16,8 @@ import (
 
 func Test_SpanFunctions(t *testing.T) {
 	expected := ottlfuncs.StandardFuncs[ottlspan.TransformContext]()
+	isRootSpanFactory := ottlfuncs.NewIsRootSpanFactory()
+	expected[isRootSpanFactory.Name()] = isRootSpanFactory
 	actual := SpanFunctions()
 	require.Equal(t, len(expected), len(actual))
 	for k := range actual {

processor/transformprocessor/internal/traces/processor_test.go

@@ -344,6 +344,12 @@ func Test_ProcessTraces_TraceContext(t *testing.T) {
 				td.ResourceSpans().At(0).ScopeSpans().At(0).Spans().At(1).Attributes().PutStr("entrypoint", "operationB")
 			},
 		},
+		{
+			statement: `set(attributes["entrypoint-root"], name) where IsRootSpan()`,
+			want: func(td ptrace.Traces) {
+				td.ResourceSpans().At(0).ScopeSpans().At(0).Spans().At(1).Attributes().PutStr("entrypoint-root", "operationB")
+			},
+		},
 		{
 			statement: `set(attributes["test"], ConvertCase(name, "lower")) where name == "operationA"`,
 			want: func(td ptrace.Traces) {