add some migration api and use it

experimental/bridge/opentracing/internal/mock.go

@@ -12,6 +12,8 @@ import (
 	otelkey "go.opentelemetry.io/api/key"
 	oteltag "go.opentelemetry.io/api/tag"
 	oteltrace "go.opentelemetry.io/api/trace"
+
+	migration "go.opentelemetry.io/experimental/bridge/opentracing/migration"
 )
 
 var (
@@ -38,6 +40,9 @@ type MockTracer struct {
 	rand     *rand.Rand
 }
 
+var _ oteltrace.Tracer = &MockTracer{}
+var _ migration.DeferredContextSetupExtension = &MockTracer{}
+
 func NewMockTracer() *MockTracer {
 	return &MockTracer{
 		Resources:             oteltag.NewEmptyMap(),
@@ -94,7 +99,9 @@ func (t *MockTracer) Start(ctx context.Context, name string, opts ...oteltrace.S
 		Events:       nil,
 	}
 	ctx = oteltrace.SetCurrentSpan(ctx, span)
-	ctx = t.addSpareContextValue(ctx)
+	if !migration.SkipContextSetup(ctx) {
+		ctx = t.addSpareContextValue(ctx)
+	}
 	return ctx, span
 }
 
@@ -186,7 +193,9 @@ func (t *MockTracer) Inject(ctx context.Context, span oteltrace.Span, injector o
 	}))
 }
 
-var _ oteltrace.Tracer = &MockTracer{}
+func (t *MockTracer) DeferredContextSetupHook(ctx context.Context, span oteltrace.Span) context.Context {
+	return t.addSpareContextValue(ctx)
+}
 
 type MockEvent struct {
 	CtxAttributes oteltag.Map

experimental/bridge/opentracing/lib.go

@@ -18,9 +18,11 @@ import (
 	"context"
 	"fmt"
 	"net/http"
+	"os"
 	"reflect"
 	"strconv"
 	"strings"
+	"sync"
 
 	"google.golang.org/grpc/codes"
 
@@ -31,6 +33,8 @@ import (
 	otelcore "go.opentelemetry.io/api/core"
 	otelregistry "go.opentelemetry.io/api/registry"
 	oteltrace "go.opentelemetry.io/api/trace"
+
+	migration "go.opentelemetry.io/experimental/bridge/opentracing/migration"
 )
 
 type bridgeSpanContext struct {
@@ -233,6 +237,8 @@ func (s *bridgeSpan) Log(data ot.LogData) {
 
 type BridgeTracer struct {
 	otelTracer oteltrace.Tracer
+
+	warnOnce sync.Once
 }
 
 var _ ot.Tracer = &BridgeTracer{}
@@ -253,12 +259,19 @@ func (t *BridgeTracer) StartSpan(operationName string, opts ...ot.StartSpanOptio
 	bReference, _ := otSpanReferencesToBridgeReferenceAndLinks(sso.References)
 	// TODO: handle span kind, needs SpanData to be in the API first?
 	attributes, _, hadTrueErrorTag := otTagsToOtelAttributesKindAndError(sso.Tags)
-	_, otelSpan := t.otelTracer.Start(context.Background(), operationName, func(opts *oteltrace.SpanOptions) {
+	checkCtx := migration.WithDeferredSetup(context.Background())
+	checkCtx2, otelSpan := t.otelTracer.Start(checkCtx, operationName, func(opts *oteltrace.SpanOptions) {
 		opts.Attributes = attributes
 		opts.StartTime = sso.StartTime
 		opts.Reference = bReference.ToOtelReference()
 		opts.RecordEvent = true
 	})
+	if checkCtx != checkCtx2 {
+		t.warnOnce.Do(func() {
+			// TODO: what to use for logging?
+			fmt.Fprintf(os.Stderr, "SDK should have deferred the context setup, see the documentation of go.opentelemetry.io/experimental/bridge/opentracing/migration\n")
+		})
+	}
 	if hadTrueErrorTag {
 		otelSpan.SetStatus(codes.Unknown)
 	}
@@ -282,6 +295,9 @@ func (t *BridgeTracer) StartSpan(operationName string, opts ...ot.StartSpanOptio
 
 func (t *BridgeTracer) ContextWithSpanHook(ctx context.Context, span ot.Span) context.Context {
 	if bSpan, ok := span.(*bridgeSpan); ok {
+		if tracerWithExtension, ok := bSpan.tracer.otelTracer.(migration.DeferredContextSetupExtension); ok {
+			ctx = tracerWithExtension.DeferredContextSetupHook(ctx, bSpan.otelSpan)
+		}
 		ctx = oteltrace.SetCurrentSpan(ctx, bSpan.otelSpan)
 	}
 	return ctx

experimental/bridge/opentracing/migration/api.go

@@ -0,0 +1,11 @@
+package migration // import "go.opentelemetry.io/experimental/bridge/opentracing/migration"
+
+import (
+	"context"
+
+	oteltrace "go.opentelemetry.io/api/trace"
+)
+
+type DeferredContextSetupExtension interface {
+	DeferredContextSetupHook(ctx context.Context, span oteltrace.Span) context.Context
+}

experimental/bridge/opentracing/migration/defer.go

@@ -0,0 +1,16 @@
+package migration
+
+import (
+	"context"
+)
+
+type doDeferredContextSetupType struct{}
+
+func WithDeferredSetup(ctx context.Context) context.Context {
+	return context.WithValue(ctx, doDeferredContextSetupType{}, doDeferredContextSetupType{})
+}
+
+func SkipContextSetup(ctx context.Context) bool {
+	_, ok := ctx.Value(doDeferredContextSetupType{}).(doDeferredContextSetupType)
+	return ok
+}