Revert "RFC: add SpanContext.LocalRootSpanID (#1029)" (#1031)

This reverts commit 57c0993.

It was merged without updating the spec and resolving
census-instrumentation/opencensus-specs#229

trace/export.go

@@ -73,11 +73,10 @@ func UnregisterExporter(e Exporter) {
 // SpanData contains all the information collected by a Span.
 type SpanData struct {
 	SpanContext
-	ParentSpanID    SpanID
-	LocalRootSpanID SpanID
-	SpanKind        int
-	Name            string
-	StartTime       time.Time
+	ParentSpanID SpanID
+	SpanKind     int
+	Name         string
+	StartTime    time.Time
 	// The wall clock time of EndTime will be adjusted to always be offset
 	// from StartTime by the duration of the span.
 	EndTime time.Time

trace/trace.go

@@ -39,10 +39,9 @@ type Span struct {
 	// It will be non-nil if we are exporting the span or recording events for it.
 	// Otherwise, data is nil, and the Span is simply a carrier for the
 	// SpanContext, so that the trace ID is propagated.
-	data            *SpanData
-	mu              sync.Mutex // protects the contents of *data (but not the pointer value.)
-	spanContext     SpanContext
-	localRootSpanID SpanID
+	data        *SpanData
+	mu          sync.Mutex // protects the contents of *data (but not the pointer value.)
+	spanContext SpanContext
 
 	// lruAttributes are capped at configured limit. When the capacity is reached an oldest entry
 	// is removed to create room for a new entry.
@@ -170,16 +169,14 @@ func WithSampler(sampler Sampler) StartOption {
 func StartSpan(ctx context.Context, name string, o ...StartOption) (context.Context, *Span) {
 	var opts StartOptions
 	var parent SpanContext
-	var localRoot SpanID
 	if p := FromContext(ctx); p != nil {
 		p.addChild()
 		parent = p.spanContext
-		localRoot = p.localRootSpanID
 	}
 	for _, op := range o {
 		op(&opts)
 	}
-	span := startSpanInternal(name, parent != SpanContext{}, parent, localRoot, false, opts)
+	span := startSpanInternal(name, parent != SpanContext{}, parent, false, opts)
 
 	ctx, end := startExecutionTracerTask(ctx, name)
 	span.executionTracerTaskEnd = end
@@ -198,16 +195,15 @@ func StartSpanWithRemoteParent(ctx context.Context, name string, parent SpanCont
 	for _, op := range o {
 		op(&opts)
 	}
-	span := startSpanInternal(name, parent != SpanContext{}, parent, SpanID{}, true, opts)
+	span := startSpanInternal(name, parent != SpanContext{}, parent, true, opts)
 	ctx, end := startExecutionTracerTask(ctx, name)
 	span.executionTracerTaskEnd = end
 	return NewContext(ctx, span), span
 }
 
-func startSpanInternal(name string, hasParent bool, parent SpanContext, localRoot SpanID, remoteParent bool, o StartOptions) *Span {
+func startSpanInternal(name string, hasParent bool, parent SpanContext, remoteParent bool, o StartOptions) *Span {
 	span := &Span{}
 	span.spanContext = parent
-	span.localRootSpanID = localRoot
 
 	cfg := config.Load().(*Config)
 
@@ -217,10 +213,6 @@ func startSpanInternal(name string, hasParent bool, parent SpanContext, localRoo
 	span.spanContext.SpanID = cfg.IDGenerator.NewSpanID()
 	sampler := cfg.DefaultSampler
 
-	if localRoot == (SpanID{}) {
-		span.localRootSpanID = span.spanContext.SpanID
-	}
-
 	if !hasParent || remoteParent || o.Sampler != nil {
 		// If this span is the child of a local span and no Sampler is set in the
 		// options, keep the parent's TraceOptions.
@@ -244,7 +236,6 @@ func startSpanInternal(name string, hasParent bool, parent SpanContext, localRoo
 
 	span.data = &SpanData{
 		SpanContext:     span.spanContext,
-		LocalRootSpanID: span.localRootSpanID,
 		StartTime:       time.Now(),
 		SpanKind:        o.SpanKind,
 		Name:            name,

trace/trace_test.go

@@ -230,32 +230,6 @@ func TestStartSpanWithRemoteParent(t *testing.T) {
 	}
 }
 
-func TestLocalRootSpanID(t *testing.T) {
-	ctx, span1 := StartSpan(context.Background(), "span1")
-	if span1.localRootSpanID == (SpanID{}) {
-		t.Errorf("exporting root span: expected nonzero localRootSpanID")
-	}
-
-	_, span2 := StartSpan(ctx, "span2")
-	if err := checkChild(span1.spanContext, span2); err != nil {
-		t.Error(err)
-	}
-	if got, want := span2.localRootSpanID, span1.localRootSpanID; got != want {
-		t.Errorf("span2.localRootSpanID=%q; want %q (span1.localRootSpanID)", got, want)
-	}
-
-	_, span3 := StartSpanWithRemoteParent(context.Background(), "span3", span2.SpanContext())
-	if err := checkChild(span3.spanContext, span2); err != nil {
-		t.Error(err)
-	}
-	if span3.localRootSpanID == (SpanID{}) {
-		t.Errorf("exporting span with remote parent: expected nonzero localRootSpanID")
-	}
-	if got, want := span3.localRootSpanID, span2.localRootSpanID; got == want {
-		t.Errorf("span3.localRootSpanID=%q; expected different value to span2.localRootSpanID, got same", got)
-	}
-}
-
 // startSpan returns a context with a new Span that is recording events and will be exported.
 func startSpan(o StartOptions) *Span {
 	_, span := StartSpanWithRemoteParent(context.Background(), "span0",
@@ -300,11 +274,7 @@ func endSpan(span *Span) (*SpanData, error) {
 	if got.SpanContext.SpanID == (SpanID{}) {
 		return nil, fmt.Errorf("exporting span: expected nonzero SpanID")
 	}
-	if got.LocalRootSpanID == (SpanID{}) {
-		return nil, fmt.Errorf("exporting span: expected nonzero LocalRootSpanID")
-	}
 	got.SpanContext.SpanID = SpanID{}
-	got.LocalRootSpanID = SpanID{}
 	if !checkTime(&got.StartTime) {
 		return nil, fmt.Errorf("exporting span: expected nonzero StartTime")
 	}