Implement global default non-recording span (#1901)

* Remove the Tracer method from the Span API

* Update CHANGELOG with changes

* Update CHANGELOG.md

* Fix misspell

* Address feedback

* Implement global default non-recording span

* Add changes to CHANGELOG

* Update PR number in changelog

CHANGELOG.md

@@ -40,6 +40,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - The `ExportSpans` method of the`SpanExporter` interface type was updated to accept `ReadOnlySpan`s instead of the removed `SpanSnapshot`.
   This brings the export interface into compliance with the specification in that it now accepts an explicitly immutable type instead of just an implied one. (#1873)
 - Unembed `SpanContext` in `Link`. (#1877)
+- Spans created by the global `Tracer` obtained from `go.opentelemetry.io/otel`, prior to a functioning `TracerProvider` being set, now propagate the span context from their parent if one exists. (#1901)
 
 ### Deprecated
 

internal/global/trace.go

@@ -36,7 +36,8 @@ import (
 	"sync"
 	"sync/atomic"
 
-	"go.opentelemetry.io/otel/internal/trace/noop"
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/codes"
 	"go.opentelemetry.io/otel/trace"
 )
 
@@ -143,5 +144,44 @@ func (t *tracer) Start(ctx context.Context, name string, opts ...trace.SpanOptio
 	if delegate != nil {
 		return delegate.(trace.Tracer).Start(ctx, name, opts...)
 	}
-	return noop.Tracer.Start(ctx, name, opts...)
+
+	s := nonRecordingSpan{sc: trace.SpanContextFromContext(ctx)}
+	ctx = trace.ContextWithSpan(ctx, s)
+	return ctx, s
 }
+
+// nonRecordingSpan is a minimal implementation of a Span that wraps a
+// SpanContext. It performs no operations other than to return the wrapped
+// SpanContext.
+type nonRecordingSpan struct {
+	sc trace.SpanContext
+}
+
+var _ trace.Span = nonRecordingSpan{}
+
+// SpanContext returns the wrapped SpanContext.
+func (s nonRecordingSpan) SpanContext() trace.SpanContext { return s.sc }
+
+// IsRecording always returns false.
+func (nonRecordingSpan) IsRecording() bool { return false }
+
+// SetStatus does nothing.
+func (nonRecordingSpan) SetStatus(codes.Code, string) {}
+
+// SetError does nothing.
+func (nonRecordingSpan) SetError(bool) {}
+
+// SetAttributes does nothing.
+func (nonRecordingSpan) SetAttributes(...attribute.KeyValue) {}
+
+// End does nothing.
+func (nonRecordingSpan) End(...trace.SpanOption) {}
+
+// RecordError does nothing.
+func (nonRecordingSpan) RecordError(error, ...trace.EventOption) {}
+
+// AddEvent does nothing.
+func (nonRecordingSpan) AddEvent(string, ...trace.EventOption) {}
+
+// SetName does nothing.
+func (nonRecordingSpan) SetName(string) {}

internal/global/trace_test.go

@@ -213,3 +213,19 @@ func TestTraceProviderDelegatesSameInstance(t *testing.T) {
 
 	assert.NotSame(t, tracer, gtp.Tracer("abc", trace.WithInstrumentationVersion("xyz")))
 }
+
+func TestSpanContextPropagatedWithNonRecordingSpan(t *testing.T) {
+	global.ResetForTest()
+
+	sc := trace.NewSpanContext(trace.SpanContextConfig{
+		TraceID:    [16]byte{0x01},
+		SpanID:     [8]byte{0x01},
+		TraceFlags: trace.FlagsSampled,
+		Remote:     true,
+	})
+	ctx := trace.ContextWithSpanContext(context.Background(), sc)
+	_, span := otel.Tracer("test").Start(ctx, "test")
+
+	assert.Equal(t, sc, span.SpanContext())
+	assert.False(t, span.IsRecording())
+}