Remove DefaultSpan from public API.

api/src/jmh/java/io/opentelemetry/trace/propagation/HttpTraceContextInjectBenchmark.java

@@ -7,7 +7,7 @@
 
 import io.opentelemetry.context.Context;
 import io.opentelemetry.context.propagation.TextMapPropagator.Setter;
-import io.opentelemetry.trace.DefaultSpan;
+import io.opentelemetry.trace.Span;
 import io.opentelemetry.trace.SpanContext;
 import io.opentelemetry.trace.TraceFlags;
 import io.opentelemetry.trace.TraceState;
@@ -75,7 +75,7 @@ private static SpanContext createTestSpanContext(String traceId, String spanId)
   private static List<Context> createContexts(List<SpanContext> spanContexts) {
     List<Context> contexts = new ArrayList<>();
     for (SpanContext context : spanContexts) {
-      contexts.add(TracingContextUtils.withSpan(DefaultSpan.create(context), Context.root()));
+      contexts.add(TracingContextUtils.withSpan(Span.getPropagated(context), Context.root()));
     }
     return contexts;
   }

api/src/main/java/io/opentelemetry/trace/DefaultTracer.java

@@ -64,9 +64,7 @@ public Span startSpan() {
         spanContext = TracingContextUtils.getCurrentSpan().getContext();
       }
 
-      return spanContext != null && !SpanContext.getInvalid().equals(spanContext)
-          ? new DefaultSpan(spanContext)
-          : DefaultSpan.getInvalid();
+      return Span.getPropagated(spanContext);
     }
 
     @Override

api/src/main/java/io/opentelemetry/trace/DefaultSpan.java → api/src/main/java/io/opentelemetry/trace/PropagatedSpan.java

@@ -13,39 +13,16 @@
  * The {@code DefaultSpan} is the default {@link Span} that is used when no {@code Span}
  * implementation is available. All operations are no-op except context propagation.
  *
- * <p>Used also to stop tracing, see {@link Tracer#withSpan}.
- *
  * @since 0.1.0
  */
 @Immutable
-public final class DefaultSpan implements Span {
-
-  private static final DefaultSpan INVALID = new DefaultSpan(SpanContext.getInvalid());
-
-  /**
-   * Returns a {@link DefaultSpan} with an invalid {@link SpanContext}.
-   *
-   * @return a {@code DefaultSpan} with an invalid {@code SpanContext}.
-   * @since 0.1.0
-   */
-  public static Span getInvalid() {
-    return INVALID;
-  }
+final class PropagatedSpan implements Span {
 
-  /**
-   * Creates an instance of this class with the {@link SpanContext}.
-   *
-   * @param spanContext the {@code SpanContext}.
-   * @return a {@link DefaultSpan}.
-   * @since 0.1.0
-   */
-  public static Span create(SpanContext spanContext) {
-    return new DefaultSpan(spanContext);
-  }
+  static final PropagatedSpan INVALID = new PropagatedSpan(SpanContext.getInvalid());
 
   private final SpanContext spanContext;
 
-  DefaultSpan(SpanContext spanContext) {
+  PropagatedSpan(SpanContext spanContext) {
     this.spanContext = spanContext;
   }
 

api/src/main/java/io/opentelemetry/trace/Span.java

@@ -23,6 +23,26 @@
 @ThreadSafe
 public interface Span {
 
+  /**
+   * Returns an invalid {@link Span}. An invalid {@link Span} is used when tracing is disabled,
+   * usually because there is no OpenTelemetry SDK installed.
+   */
+  static Span getInvalid() {
+    return PropagatedSpan.INVALID;
+  }
+
+  /**
+   * Returns a non-recording {@link Span} that holds the provided {@link SpanContext} but has no
+   * functionality. It will not be exported and all tracing operations are no-op, but it can be used
+   * to propagate a valid {@link SpanContext} downstream.
+   */
+  static Span getPropagated(SpanContext spanContext) {
+    if (spanContext == null || !spanContext.isValid()) {
+      return getInvalid();
+    }
+    return new PropagatedSpan(spanContext);
+  }
+
   /**
    * Type of span. Can be used to specify additional relationships between spans in addition to a
    * parent/child relationship.
@@ -304,6 +324,15 @@ default void setAttribute(AttributeKey<Long> key, int value) {
    */
   boolean isRecording();
 
+  /**
+   * Returns whether this {@link Span} is valid.
+   *
+   * @see Span#getInvalid()
+   */
+  default boolean isValid() {
+    return getContext().isValid();
+  }
+
   /**
    * {@link Builder} is used to construct {@link Span} instances which define arbitrary scopes of
    * code that are sampled for distributed tracing as a single atomic unit.

api/src/main/java/io/opentelemetry/trace/Tracer.java

@@ -81,7 +81,8 @@ public interface Tracer {
    *
    * <p>Supports try-with-resource idiom.
    *
-   * <p>Can be called with {@link DefaultSpan} to enter a scope of code where tracing is stopped.
+   * <p>Can be called with {@code Span.getPropagated(span.getContext())} to enter a scope of code
+   * where tracing is stopped.
    *
    * <p>Example of usage:
    *

api/src/main/java/io/opentelemetry/trace/TracingContextUtils.java

@@ -54,7 +54,7 @@ public static Span getCurrentSpan() {
    */
   public static Span getSpan(Context context) {
     Span span = context.getValue(CONTEXT_SPAN_KEY);
-    return span == null ? DefaultSpan.getInvalid() : span;
+    return span == null ? Span.getInvalid() : span;
   }
 
   /**

api/src/main/java/io/opentelemetry/trace/propagation/HttpTraceContext.java

@@ -10,7 +10,7 @@
 import io.opentelemetry.context.Context;
 import io.opentelemetry.context.propagation.TextMapPropagator;
 import io.opentelemetry.internal.TemporaryBuffers;
-import io.opentelemetry.trace.DefaultSpan;
+import io.opentelemetry.trace.Span;
 import io.opentelemetry.trace.SpanContext;
 import io.opentelemetry.trace.SpanId;
 import io.opentelemetry.trace.TraceFlags;
@@ -149,7 +149,7 @@ public <C> void inject(Context context, C carrier, Setter<C> setter) {
       return context;
     }
 
-    return TracingContextUtils.withSpan(DefaultSpan.create(spanContext), context);
+    return TracingContextUtils.withSpan(Span.getPropagated(spanContext), context);
   }
 
   private static <C> SpanContext extractImpl(C carrier, Getter<C> getter) {

api/src/test/java/io/opentelemetry/trace/DefaultTracerTest.java

@@ -31,16 +31,16 @@ class DefaultTracerTest {
 
   @Test
   void defaultGetCurrentSpan() {
-    assertThat(defaultTracer.getCurrentSpan()).isInstanceOf(DefaultSpan.class);
+    assertThat(defaultTracer.getCurrentSpan().isValid()).isFalse();
   }
 
   @Test
   void getCurrentSpan_WithSpan() {
-    assertThat(defaultTracer.getCurrentSpan()).isInstanceOf(DefaultSpan.class);
-    try (Scope ws = defaultTracer.withSpan(DefaultSpan.getInvalid())) {
-      assertThat(defaultTracer.getCurrentSpan()).isInstanceOf(DefaultSpan.class);
+    assertThat(defaultTracer.getCurrentSpan().isValid()).isFalse();
+    try (Scope ws = defaultTracer.withSpan(Span.getInvalid())) {
+      assertThat(defaultTracer.getCurrentSpan().isValid()).isFalse();
     }
-    assertThat(defaultTracer.getCurrentSpan()).isInstanceOf(DefaultSpan.class);
+    assertThat(defaultTracer.getCurrentSpan().isValid()).isFalse();
   }
 
   @Test
@@ -50,7 +50,7 @@ void spanBuilderWithName_NullName() {
 
   @Test
   void defaultSpanBuilderWithName() {
-    assertThat(defaultTracer.spanBuilder(SPAN_NAME).startSpan()).isInstanceOf(DefaultSpan.class);
+    assertThat(defaultTracer.spanBuilder(SPAN_NAME).startSpan().isValid()).isFalse();
   }
 
   @Test
@@ -65,7 +65,7 @@ void testInProcessContext() {
         assertThat(defaultTracer.getCurrentSpan()).isEqualTo(span);
       }
     }
-    assertThat(defaultTracer.getCurrentSpan()).isInstanceOf(DefaultSpan.class);
+    assertThat(defaultTracer.getCurrentSpan().isValid()).isFalse();
   }
 
   @Test
@@ -74,14 +74,14 @@ void testSpanContextPropagationExplicitParent() {
         defaultTracer
             .spanBuilder(SPAN_NAME)
             .setParent(
-                TracingContextUtils.withSpan(DefaultSpan.create(spanContext), Context.root()))
+                TracingContextUtils.withSpan(Span.getPropagated(spanContext), Context.root()))
             .startSpan();
     assertThat(span.getContext()).isSameAs(spanContext);
   }
 
   @Test
   void testSpanContextPropagation() {
-    DefaultSpan parent = new DefaultSpan(spanContext);
+    Span parent = Span.getPropagated(spanContext);
 
     Span span =
         defaultTracer
@@ -106,31 +106,34 @@ void testSpanContextPropagation_nullContext() {
 
   @Test
   void testSpanContextPropagation_fromContext() {
-    Context context = TracingContextUtils.withSpan(new DefaultSpan(spanContext), Context.current());
+    Context context =
+        TracingContextUtils.withSpan(Span.getPropagated(spanContext), Context.current());
 
     Span span = defaultTracer.spanBuilder(SPAN_NAME).setParent(context).startSpan();
     assertThat(span.getContext()).isSameAs(spanContext);
   }
 
   @Test
   void testSpanContextPropagation_fromContextAfterNoParent() {
-    Context context = TracingContextUtils.withSpan(new DefaultSpan(spanContext), Context.current());
+    Context context =
+        TracingContextUtils.withSpan(Span.getPropagated(spanContext), Context.current());
 
     Span span = defaultTracer.spanBuilder(SPAN_NAME).setNoParent().setParent(context).startSpan();
     assertThat(span.getContext()).isSameAs(spanContext);
   }
 
   @Test
   void testSpanContextPropagation_fromContextThenNoParent() {
-    Context context = TracingContextUtils.withSpan(new DefaultSpan(spanContext), Context.current());
+    Context context =
+        TracingContextUtils.withSpan(Span.getPropagated(spanContext), Context.current());
 
     Span span = defaultTracer.spanBuilder(SPAN_NAME).setParent(context).setNoParent().startSpan();
     assertThat(span.getContext()).isEqualTo(SpanContext.getInvalid());
   }
 
   @Test
   void testSpanContextPropagationCurrentSpan() {
-    DefaultSpan parent = new DefaultSpan(spanContext);
+    Span parent = Span.getPropagated(spanContext);
     try (Scope scope = defaultTracer.withSpan(parent)) {
       Span span = defaultTracer.spanBuilder(SPAN_NAME).startSpan();
       assertThat(span.getContext()).isSameAs(spanContext);
@@ -140,7 +143,7 @@ void testSpanContextPropagationCurrentSpan() {
   @Test
   void testSpanContextPropagationCurrentSpanContext() {
     Context context =
-        TracingContextUtils.withSpan(DefaultSpan.create(spanContext), Context.current());
+        TracingContextUtils.withSpan(Span.getPropagated(spanContext), Context.current());
     try (Scope scope = context.makeCurrent()) {
       Span span = defaultTracer.spanBuilder(SPAN_NAME).startSpan();
       assertThat(span.getContext()).isSameAs(spanContext);

api/src/test/java/io/opentelemetry/trace/DefaultSpanTest.java → api/src/test/java/io/opentelemetry/trace/PropagatedSpanTest.java

@@ -17,19 +17,18 @@
 import io.opentelemetry.common.Attributes;
 import org.junit.jupiter.api.Test;
 
-/** Unit tests for {@link DefaultSpan}. */
-class DefaultSpanTest {
+class PropagatedSpanTest {
 
   @Test
   void hasInvalidContextAndDefaultSpanOptions() {
-    SpanContext context = DefaultSpan.getInvalid().getContext();
+    SpanContext context = Span.getInvalid().getContext();
     assertThat(context.getTraceFlags()).isEqualTo(TraceFlags.getDefault());
     assertThat(context.getTraceState()).isEqualTo(TraceState.getDefault());
   }
 
   @Test
   void doNotCrash() {
-    Span span = DefaultSpan.getInvalid();
+    Span span = Span.getInvalid();
     span.setAttribute(stringKey("MyStringAttributeKey"), "MyStringAttributeValue");
     span.setAttribute(booleanKey("MyBooleanAttributeKey"), true);
     span.setAttribute(longKey("MyLongAttributeKey"), 123L);
@@ -56,7 +55,7 @@ void doNotCrash() {
 
   @Test
   void defaultSpan_ToString() {
-    Span span = DefaultSpan.getInvalid();
+    Span span = Span.getInvalid();
     assertThat(span.toString()).isEqualTo("DefaultSpan");
   }
 }

api/src/test/java/io/opentelemetry/trace/SpanBuilderTest.java

@@ -22,18 +22,18 @@ class SpanBuilderTest {
   void doNotCrash_NoopImplementation() {
     Span.Builder spanBuilder = tracer.spanBuilder("MySpanName");
     spanBuilder.setSpanKind(Kind.SERVER);
-    spanBuilder.setParent(TracingContextUtils.withSpan(DefaultSpan.create(null), Context.root()));
+    spanBuilder.setParent(TracingContextUtils.withSpan(Span.getPropagated(null), Context.root()));
     spanBuilder.setParent(Context.root());
     spanBuilder.setNoParent();
-    spanBuilder.addLink(DefaultSpan.getInvalid().getContext());
-    spanBuilder.addLink(DefaultSpan.getInvalid().getContext(), Attributes.empty());
+    spanBuilder.addLink(Span.getInvalid().getContext());
+    spanBuilder.addLink(Span.getInvalid().getContext(), Attributes.empty());
     spanBuilder.setAttribute("key", "value");
     spanBuilder.setAttribute("key", 12345L);
     spanBuilder.setAttribute("key", .12345);
     spanBuilder.setAttribute("key", true);
     spanBuilder.setAttribute(stringKey("key"), "value");
     spanBuilder.setStartTimestamp(12345L);
-    assertThat(spanBuilder.startSpan()).isInstanceOf(DefaultSpan.class);
+    assertThat(spanBuilder.startSpan().isValid()).isFalse();
   }
 
   @Test

api/src/test/java/io/opentelemetry/trace/TracingContextUtilsTest.java

@@ -16,12 +16,12 @@ class TracingContextUtilsTest {
   @Test
   void testGetCurrentSpan_Default() {
     Span span = TracingContextUtils.getCurrentSpan();
-    assertThat(span).isSameAs(DefaultSpan.getInvalid());
+    assertThat(span).isSameAs(Span.getInvalid());
   }
 
   @Test
   void testGetCurrentSpan_SetSpan() {
-    Span span = DefaultSpan.create(SpanContext.getInvalid());
+    Span span = Span.getPropagated(SpanContext.getInvalid());
     try (Scope ignored = TracingContextUtils.withSpan(span, Context.current()).makeCurrent()) {
       assertThat(TracingContextUtils.getCurrentSpan()).isSameAs(span);
     }
@@ -30,12 +30,12 @@ void testGetCurrentSpan_SetSpan() {
   @Test
   void testGetSpan_DefaultContext() {
     Span span = TracingContextUtils.getSpan(Context.current());
-    assertThat(span).isSameAs(DefaultSpan.getInvalid());
+    assertThat(span).isSameAs(Span.getInvalid());
   }
 
   @Test
   void testGetSpan_ExplicitContext() {
-    Span span = DefaultSpan.create(SpanContext.getInvalid());
+    Span span = Span.getPropagated(SpanContext.getInvalid());
     Context context = TracingContextUtils.withSpan(span, Context.current());
     assertThat(TracingContextUtils.getSpan(context)).isSameAs(span);
   }
@@ -48,7 +48,7 @@ void testGetSpanWithoutDefault_DefaultContext() {
 
   @Test
   void testGetSpanWithoutDefault_ExplicitContext() {
-    Span span = DefaultSpan.create(SpanContext.getInvalid());
+    Span span = Span.getPropagated(SpanContext.getInvalid());
     Context context = TracingContextUtils.withSpan(span, Context.current());
     assertThat(TracingContextUtils.getSpanWithoutDefault(context)).isSameAs(span);
   }

api/src/test/java/io/opentelemetry/trace/propagation/HttpTraceContextTest.java

@@ -13,7 +13,7 @@
 import io.opentelemetry.context.Context;
 import io.opentelemetry.context.propagation.TextMapPropagator.Getter;
 import io.opentelemetry.context.propagation.TextMapPropagator.Setter;
-import io.opentelemetry.trace.DefaultSpan;
+import io.opentelemetry.trace.Span;
 import io.opentelemetry.trace.SpanContext;
 import io.opentelemetry.trace.SpanId;
 import io.opentelemetry.trace.TraceFlags;
@@ -52,7 +52,7 @@ private static SpanContext getSpanContext(Context context) {
   }
 
   private static Context withSpanContext(SpanContext spanContext, Context context) {
-    return TracingContextUtils.withSpan(DefaultSpan.create(spanContext), context);
+    return TracingContextUtils.withSpan(Span.getPropagated(spanContext), context);
   }
 
   @Test

extensions/trace_propagators/src/jmh/java/io/opentelemetry/extensions/trace/propagation/PropagatorContextInjectBenchmark.java

@@ -7,7 +7,7 @@
 
 import io.opentelemetry.context.Context;
 import io.opentelemetry.context.propagation.TextMapPropagator;
-import io.opentelemetry.trace.DefaultSpan;
+import io.opentelemetry.trace.Span;
 import io.opentelemetry.trace.SpanContext;
 import io.opentelemetry.trace.TraceFlags;
 import io.opentelemetry.trace.TraceState;
@@ -63,7 +63,7 @@ public abstract static class AbstractContextInjectBenchmark {
     @Fork(1)
     public Map<String, String> measureInject() {
       Context context =
-          TracingContextUtils.withSpan(DefaultSpan.create(contextToTest), Context.current());
+          TracingContextUtils.withSpan(Span.getPropagated(contextToTest), Context.current());
       doInject(context, carrier);
       return carrier;
     }