Apply default source only when not specified

Author: mathewc

src/WebJobs.Script/Extensions/TraceWriterExtensions.cs

@@ -36,7 +36,11 @@ public static TraceWriter Apply(this TraceWriter traceWriter, IDictionary<string
             return new InterceptingTraceWriter(traceWriter, interceptor);
         }
 
-        public static TraceWriter WithSource(this TraceWriter traceWriter, string source) => new InterceptingTraceWriter(traceWriter, t => t.Source = source);
+        /// <summary>
+        /// Apply the specified default source value to all trace events
+        /// when the source is not specified.
+        /// </summary>
+        public static TraceWriter WithSource(this TraceWriter traceWriter, string source) => new InterceptingTraceWriter(traceWriter, t => t.Source = string.IsNullOrEmpty(t.Source) ? source : t.Source);
 
         public static void Verbose(this TraceWriter traceWriter, string message, IDictionary<string, object> properties)
         {

test/WebJobs.Script.Tests.Integration/SamplesEndToEndTests.cs

@@ -1015,6 +1015,8 @@ public async Task HostLog_Anonymous_Fails()
         [Fact]
         public async Task HostLog_AdminLevel_Succeeds()
         {
+            TestHelpers.ClearHostLogs();
+
             var request = new HttpRequestMessage(HttpMethod.Post, "admin/host/log");
             request.Headers.Add(AuthorizationLevelAttribute.FunctionsKeyHeaderName, MasterKey);
             var logs = new HostLogEntry[]

test/WebJobs.Script.Tests/Diagnostics/TraceWriterExtensionsTests.cs

@@ -12,6 +12,28 @@ namespace Microsoft.Azure.WebJobs.Script.Tests
 {
     public class TraceWriterExtensionsTests
     {
+        [Fact]
+        public void WithSource_AppliesDefaultSource()
+        {
+            TestTraceWriter testTraceWriter = new TestTraceWriter(TraceLevel.Verbose);
+            var wrappedTraceWriter = testTraceWriter.WithSource("TestDefault");
+
+            wrappedTraceWriter.Info("Test1");
+            wrappedTraceWriter.Info("Test2", "CustomSource");
+            wrappedTraceWriter.Info("Test3", string.Empty);
+
+            Assert.Equal(3, testTraceWriter.Traces.Count);
+
+            Assert.Equal("Test1", testTraceWriter.Traces[0].Message);
+            Assert.Equal("TestDefault", testTraceWriter.Traces[0].Source);
+
+            Assert.Equal("Test2", testTraceWriter.Traces[1].Message);
+            Assert.Equal("CustomSource", testTraceWriter.Traces[1].Source);
+
+            Assert.Equal("Test3", testTraceWriter.Traces[2].Message);
+            Assert.Equal("TestDefault", testTraceWriter.Traces[2].Source);
+        }
+
         [Fact]
         public void Apply_CreatesInterceptingTraceWriter()
         {