Handles loading extensions.json with empty extensions (#11174)

* Handle empty extensions array usecase.

* release notes.

* Liniting - remove empty line.

* Fixed typo in test comment.

* Update test/WebJobs.Script.Tests/ScriptStartupTypeDiscovererTests.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: kshyju

release_notes.md

@@ -7,3 +7,4 @@
 - Add JitTrace Files for v4.1041
 - Fix startup deadlock on transient exceptions (#11142)
 - Add warning log for end of support bundle version, any bundle version < 4 (#11075), (#11160)
+- Handles loading extensions.json with empty extensions(#11174)

src/WebJobs.Script/DependencyInjection/ScriptStartupTypeLocator.cs

@@ -235,7 +235,7 @@ private async Task<ExtensionReference[]> ParseExtensionsAsync(string metadataFil
                     await using var stream = File.OpenRead(metadataFilePath);
                     var extensionReferences = await JsonSerializer.DeserializeAsync(stream, ExtensionReferencesJsonContext.Default.ExtensionReferences);
 
-                    if (extensionReferences?.Extensions == null || extensionReferences.Extensions.Length == 0)
+                    if (extensionReferences?.Extensions == null)
                     {
                         _logger.ScriptStartUpUnableParseMetadataMissingProperty(metadataFilePath);
                         return [];

test/WebJobs.Script.Tests/ScriptStartupTypeDiscovererTests.cs

@@ -182,6 +182,7 @@ public async Task GetExtensionsStartupTypes_AcceptsRequiredBundleVersions(string
                     Assert.True(traces.Any(m => m.FormattedMessage.Contains($"Loading extension bundle")));
                 }
                 Assert.True(traces.Any(m => m.FormattedMessage.Contains($"Loading startup extension 'Storage")));
+                AssertNoErrors(traces);
             }
         }
 
@@ -310,6 +311,7 @@ public async Task GetExtensionsStartupTypes_AcceptsRequiredExtensionVersions(str
                 {
                     Assert.True(traces.Any(m => m.FormattedMessage.Contains($"Loading startup extension 'Storage")));
                 }
+                AssertNoErrors(traces);
             }
         }
 
@@ -423,6 +425,7 @@ void CopyToBin(string path)
                 Assert.Equal(typeof(AzureStorageWebJobsStartup).FullName, types.Single().FullName);
                 Assert.True(traces.Any(m => string.Equals(m.FormattedMessage, $"The extension startup type '{references[0].TypeName}' belongs to a builtin extension")));
                 Assert.True(traces.Any(m => string.Equals(m.FormattedMessage, $"The extension startup type '{references[1].TypeName}' belongs to a builtin extension")));
+                AssertNoErrors(traces);
             }
         }
 
@@ -516,6 +519,7 @@ void CopyToBin(string path)
                 Assert.Equal(typeof(AzureStorageWebJobsStartup).FullName, types.Single().FullName);
                 Assert.True(traces.Any(m => string.Equals(m.FormattedMessage, $"The extension startup type '{references[0].TypeName}' belongs to a builtin extension")));
                 Assert.True(traces.Any(m => string.Equals(m.FormattedMessage, $"The extension startup type '{references[1].TypeName}' belongs to a builtin extension")));
+                AssertNoErrors(traces);
             }
         }
 
@@ -592,11 +596,13 @@ void CopyToBin(string path)
 
                 // Act
                 var types = await discoverer.GetExtensionsStartupTypesAsync();
+                var traces = testLoggerProvider.GetAllLogMessages();
 
                 // Assert
                 AreExpectedMetricsGenerated(testMetricsLogger);
                 Assert.Equal(types.Count(), 2);
                 Assert.Equal(typeof(AzureStorageWebJobsStartup).FullName, types.FirstOrDefault().FullName);
+                AssertNoErrors(traces);
             }
         }
 
@@ -644,11 +650,13 @@ void CopyToBin(string path)
 
                 // Act
                 var types = await discoverer.GetExtensionsStartupTypesAsync();
+                var traces = testLoggerProvider.GetAllLogMessages();
 
                 // Assert
                 AreExpectedMetricsGenerated(testMetricsLogger);
                 Assert.Single(types);
                 Assert.Equal(typeof(AzureStorageWebJobsStartup).FullName, types.Single().FullName);
+                AssertNoErrors(traces);
             }
         }
 
@@ -698,11 +706,13 @@ void CopyToBin(string path)
 
                 // Act
                 var types = await discoverer.GetExtensionsStartupTypesAsync();
+                var traces = testLoggerProvider.GetAllLogMessages();
 
                 //Assert
                 AreExpectedMetricsGenerated(testMetricsLogger);
                 Assert.Single(types);
                 Assert.Equal(typeof(AzureStorageWebJobsStartup).FullName, types.Single().FullName);
+                AssertNoErrors(traces);
             }
         }
 
@@ -1144,13 +1154,55 @@ void CopyToBin(string path)
 
                 // Act
                 var types = await discoverer.GetExtensionsStartupTypesAsync();
+                var traces = testLoggerProvider.GetAllLogMessages();
                 Environment.SetEnvironmentVariable(EnvironmentSettingNames.AzureWebJobsFeatureFlags, null);
                 Environment.SetEnvironmentVariable(EnvironmentSettingNames.FunctionWorkerRuntime, null);
 
                 //Assert that filtering did not take place because of worker indexing
                 Assert.True(types.Count() == 1);
                 Assert.Equal(typeof(AzureStorageWebJobsStartup).FullName, types.ElementAt(0).FullName);
+                AssertNoErrors(traces);
+            }
+        }
+
+        [Fact]
+        public async Task GetExtensionsStartupTypes_EmptyExtensionsArray()
+        {
+            TestMetricsLogger testMetricsLogger = new TestMetricsLogger();
+
+            using var directory = new TempDirectory();
+            var binPath = Path.Combine(directory.Path, "bin");
+            Directory.CreateDirectory(binPath);
+
+            // extensions.json file with an empty extensions array (simulating extensions.json produced by in-proc app)
+            string extensionJson = """
+            {
+              "extensions": []
             }
+            """;
+            File.WriteAllText(Path.Combine(binPath, "extensions.json"), extensionJson);
+
+            TestLoggerProvider testLoggerProvider = new TestLoggerProvider();
+            LoggerFactory factory = new LoggerFactory();
+            factory.AddProvider(testLoggerProvider);
+            var testLogger = factory.CreateLogger<ScriptStartupTypeLocator>();
+
+            var mockExtensionBundleManager = new Mock<IExtensionBundleManager>();
+            mockExtensionBundleManager.Setup(e => e.IsExtensionBundleConfigured()).Returns(true);
+            mockExtensionBundleManager.Setup(e => e.GetExtensionBundleDetails()).Returns(Task.FromResult(new ExtensionBundleDetails() { Id = "bundleID", Version = "1.0.0" }));
+            mockExtensionBundleManager.Setup(e => e.GetExtensionBundleBinPathAsync()).Returns(Task.FromResult(binPath));
+
+            var languageWorkerOptions = new TestOptionsMonitor<LanguageWorkerOptions>(new LanguageWorkerOptions());
+            var mockFunctionMetadataManager = GetTestFunctionMetadataManager(languageWorkerOptions);
+            OptionsWrapper<ExtensionRequirementOptions> optionsWrapper = new(new ExtensionRequirementOptions());
+            var discoverer = new ScriptStartupTypeLocator(directory.Path, testLogger, mockExtensionBundleManager.Object, mockFunctionMetadataManager, testMetricsLogger, optionsWrapper);
+
+            var types = await discoverer.GetExtensionsStartupTypesAsync();
+            var traces = testLoggerProvider.GetAllLogMessages();
+
+            AreExpectedMetricsGenerated(testMetricsLogger);
+            Assert.Empty(types); // Ensure no types are loaded because the extensions array is empty
+            AssertNoErrors(traces);
         }
 
         private IFunctionMetadataManager GetTestFunctionMetadataManager(IOptionsMonitor<LanguageWorkerOptions> options, ICollection<FunctionMetadata> metadataCollection = null, bool hasPrecompiledFunction = false, bool hasNodeFunctions = false, bool hasDotnetIsolatedFunctions = false)
@@ -1234,5 +1286,10 @@ private ILogger<ScriptStartupTypeLocator> GetTestLogger()
             var testLogger = factory.CreateLogger<ScriptStartupTypeLocator>();
             return testLogger;
         }
+
+        private static void AssertNoErrors(IList<LogMessage> traces)
+        {
+            Assert.False(traces.Any(m => m.Level == LogLevel.Error || m.Level == LogLevel.Critical));
+        }
     }
 }