[WIP] Add schema URL support to Tracer

[Do not merge, this is a draft to get maintainers' feedback]

This adds support for schema URL according to the specification:
open-telemetry/opentelemetry-specification#1666
(Link to replaced by the link to the spec after that PR is merged)

TODO:
- Populate the schema_url field in the OTLP after this PR
  open-telemetry/opentelemetry-proto#298
  is merged and the field is available in the proto message.

exporters/otlp/internal/transform/span.go

@@ -61,6 +61,8 @@ func Spans(sdl []tracesdk.ReadOnlySpan) []*tracepb.ResourceSpans {
 				InstrumentationLibrary: instrumentationLibrary(sd.InstrumentationLibrary()),
 				Spans:                  []*tracepb.Span{},
 			}
+			// TODO: set schema_url field of ils when it is available in the proto.
+			_ = sd.InstrumentationLibrary().SchemaURL
 		}
 		ils.Spans = append(ils.Spans, span(sd))
 		ilsm[iKey] = ils

exporters/otlp/internal/transform/span_test.go

@@ -262,8 +262,9 @@ func TestSpanData(t *testing.T) {
 		DroppedLinks:      3,
 		Resource:          resource.NewWithAttributes(attribute.String("rk1", "rv1"), attribute.Int64("rk2", 5)),
 		InstrumentationLibrary: instrumentation.Library{
-			Name:    "go.opentelemetry.io/test/otel",
-			Version: "v0.0.1",
+			Name:      "go.opentelemetry.io/test/otel",
+			Version:   "v0.0.1",
+			SchemaURL: "https://opentelemetry.io/schemas/1.2.0",
 		},
 	}
 
@@ -294,6 +295,7 @@ func TestSpanData(t *testing.T) {
 	assert.Equal(t, got[0].GetResource(), Resource(spanData.Resource))
 	ilSpans := got[0].GetInstrumentationLibrarySpans()
 	require.Len(t, ilSpans, 1)
+	// TODO: Add SchemaURL field checking once the field is added to the proto.
 	assert.Equal(t, ilSpans[0].GetInstrumentationLibrary(), instrumentationLibrary(spanData.InstrumentationLibrary))
 	require.Len(t, ilSpans[0].Spans, 1)
 	actualSpan := ilSpans[0].Spans[0]

exporters/stdout/trace_test.go

@@ -177,7 +177,8 @@ func TestExporter_ExportSpan(t *testing.T) {
 		],
 		"InstrumentationLibrary": {
 			"Name": "",
-			"Version": ""
+			"Version": "",
+			"SchemaURL": ""
 		}
 	}
 ]

sdk/instrumentation/library.go

@@ -32,4 +32,6 @@ type Library struct {
 	Name string
 	// Version is the version of the instrumentation library.
 	Version string
+	// SchemaURL of the telemetry emitted by the library.
+	SchemaURL string
 }

sdk/trace/provider.go

@@ -115,8 +115,9 @@ func (p *TracerProvider) Tracer(name string, opts ...trace.TracerOption) trace.T
 		name = defaultTracerName
 	}
 	il := instrumentation.Library{
-		Name:    name,
-		Version: c.InstrumentationVersion,
+		Name:      name,
+		Version:   c.InstrumentationVersion,
+		SchemaURL: c.SchemaURL,
 	}
 	t, ok := p.namedTracer[il]
 	if !ok {

sdk/trace/provider_test.go

@@ -20,6 +20,8 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+
+	"go.opentelemetry.io/otel/trace"
 )
 
 type basicSpanProcesor struct {
@@ -82,3 +84,13 @@ func TestFailedProcessorShutdownInUnregister(t *testing.T) {
 	err := stp.Shutdown(context.Background())
 	assert.NoError(t, err)
 }
+
+func TestSchemaURL(t *testing.T) {
+	stp := NewTracerProvider()
+	schemaURL := "https://opentelemetry.io/schemas/1.2.0"
+	tracerIface := stp.Tracer("tracername", trace.WithSchemaURL(schemaURL))
+
+	// Verify that the SchemaURL of the constructed Tracer is correctly populated.
+	tracerStruct := tracerIface.(*tracer)
+	assert.EqualValues(t, schemaURL, tracerStruct.instrumentationLibrary.SchemaURL)
+}

trace/config.go

@@ -25,6 +25,8 @@ type TracerConfig struct {
 	// InstrumentationVersion is the version of the library providing
 	// instrumentation.
 	InstrumentationVersion string
+	// SchemaURL of the telemetry emitted by the Tracer.
+	SchemaURL string
 }
 
 // NewTracerConfig applies all the options to a returned TracerConfig.
@@ -203,3 +205,16 @@ func (i instrumentationVersionOption) ApplyTracer(config *TracerConfig) {
 }
 
 func (instrumentationVersionOption) private() {}
+
+// WithSchemaURL sets the schema URL for Tracer.
+func WithSchemaURL(schemaURL string) InstrumentationOption {
+	return schemaURLOption(schemaURL)
+}
+
+type schemaURLOption string
+
+func (i schemaURLOption) ApplyTracer(config *TracerConfig) {
+	config.SchemaURL = string(i)
+}
+
+func (schemaURLOption) private() {}

trace/config_test.go

@@ -177,6 +177,7 @@ func TestNewSpanConfig(t *testing.T) {
 func TestTracerConfig(t *testing.T) {
 	v1 := "semver:0.0.1"
 	v2 := "semver:1.0.0"
+	schemaURL := "https://opentelemetry.io/schemas/1.2.0"
 	tests := []struct {
 		options  []TracerOption
 		expected *TracerConfig
@@ -204,6 +205,14 @@ func TestTracerConfig(t *testing.T) {
 				InstrumentationVersion: v2,
 			},
 		},
+		{
+			[]TracerOption{
+				WithSchemaURL(schemaURL),
+			},
+			&TracerConfig{
+				SchemaURL: schemaURL,
+			},
+		},
 	}
 	for _, test := range tests {
 		config := NewTracerConfig(test.options...)