ActivityContext Changes

src/libraries/System.Diagnostics.DiagnosticSource/src/Resources/Strings.resx

@@ -150,9 +150,6 @@
   <data name="SetParentIdOnActivityWithParent" xml:space="preserve">
     <value>"Can not set ParentId on activity which has parent"</value>
   </data>
-  <data name="SpanIdOrTraceIdInvalid" xml:space="preserve">
-    <value>"Invalid SpanId or TraceId"</value>
-  </data>
   <data name="StartTimeNotUtc" xml:space="preserve">
     <value>"StartTime is not UTC"</value>
   </data>

src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/ActivityContext.cs

@@ -21,12 +21,6 @@ namespace System.Diagnostics
         /// <param name="traceState"> Carries system-specific configuration data.</param>
         public ActivityContext(ActivityTraceId traceId, ActivitySpanId spanId, ActivityTraceFlags traceFlags, string? traceState = null)
         {
-            // We don't allow creating context with invalid span or trace Ids.
-            if (traceId == default || spanId == default)
-            {
-                throw new ArgumentException(SR.SpanIdOrTraceIdInvalid, traceId == default ? nameof(traceId) : nameof(spanId));
-            }
-
             TraceId = traceId;
             SpanId = spanId;
             TraceFlags = traceFlags;

src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/ActivitySource.cs

@@ -133,11 +133,12 @@ public bool HasListeners()
             }
             else
             {
+                ActivityContext initializedContext =  context == default && Activity.Current != null ? Activity.Current.Context : context;
                 listeners.EnumWithFunc(listener => {
                     var getRequestedDataUsingContext = listener.GetRequestedDataUsingContext;
                     if (getRequestedDataUsingContext != null)
                     {
-                        ActivityCreationOptions<ActivityContext> aco = new ActivityCreationOptions<ActivityContext>(this, name, context, kind, tags, links);
+                        ActivityCreationOptions<ActivityContext> aco = new ActivityCreationOptions<ActivityContext>(this, name, initializedContext, kind, tags, links);
                         ActivityDataRequest dr = getRequestedDataUsingContext(ref aco);
                         if (dr > dateRequest)
                         {

src/libraries/System.Diagnostics.DiagnosticSource/tests/ActivitySourceTests.cs

@@ -360,6 +360,40 @@ public void TestActivityCreationProperties()
                 }
             }).Dispose();
         }
+
+        [Fact]
+        public void TestDefaultParentContext()
+        {
+            RemoteExecutor.Invoke(() => {
+                using (ActivitySource aSource = new ActivitySource("ParentContext"))
+                {
+                    using (ActivityListener listener = new ActivityListener
+                    {
+                        ShouldListenTo = (activitySource) => activitySource.Name == "ParentContext",
+                        GetRequestedDataUsingContext = (ref ActivityCreationOptions<ActivityContext> activityOptions) =>
+                        {
+                            Activity c = Activity.Current;
+                            if (c != null)
+                            {
+                                Assert.Equal(c.Context, activityOptions.Parent);
+                            }
+
+                            return ActivityDataRequest.AllData;
+                        }
+                    })
+                    {
+                        ActivitySource.AddActivityListener(listener);
+
+                        using (Activity a = aSource.StartActivity("a", ActivityKind.Server, new ActivityContext(ActivityTraceId.CreateRandom(), ActivitySpanId.CreateRandom(), 0)))
+                        using (Activity b = aSource.StartActivity("b"))
+                        {
+                            Assert.Equal(a.Context, b.Parent.Context);
+                        }
+                    }
+                }
+            }).Dispose();
+        }
+
         public void Dispose() => Activity.Current = null;
     }
 }