Fix Failing Multi-Language worker in case of dotnet runtime (#9085)

Resolves Issue where Multi Language will fail to start if `FUNCTION_WORKER_RUNTIME` is set to `dotnet`.
Error:
```
System.InvalidOperationException : Sequence contains no elements
at System.Linq.ThrowHelper.ThrowNoElementsException()
at System.Linq.Enumerable.Max[TSource,TResult](IEnumerable`1 source,Func`2 selector)
at Microsoft.Azure.WebJobs.Script.ScriptHost.AddFunctionDescriptors(IEnumerable`1 functionMetadata) at /_/src/WebJobs.Script/Host/ScriptHost.cs : 553
at async Microsoft.Azure.WebJobs.Script.ScriptHost.InitializeFunctionDescriptorsAsync(IEnumerable`1 functionMetadata,CancellationToken cancellationToken) at /_/src/WebJobs.Script/Host/ScriptHost.cs : 527
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at async Microsoft.Azure.WebJobs.Script.ScriptHost.InitializeAsync(CancellationToken cancellationToken) at /_/src/WebJobs.Script/Host/ScriptHost.cs : 314
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at async Microsoft.Azure.WebJobs.Script.ScriptHost.StartAsyncCore(CancellationToken cancellationToken) at /_/src/WebJobs.Script/Host/ScriptHost.cs : 258
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at async Microsoft.Extensions.Hosting.Internal.Host.StartAsync(CancellationToken cancellationToken)
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at async Microsoft.Azure.WebJobs.Script.WebHost.WebJobsScriptHostService.UnsynchronizedStartHostAsync(ScriptHostStartupOperation activeOperation,Int32 attemptCount,JobHostStartupMode startupMode) at /_/src/WebJobs.Script.WebHost/WebJobsScriptHostService.cs : 311
```

Author: Siddharth

src/WebJobs.Script/Environment/EnvironmentExtensions.cs

@@ -390,7 +390,7 @@ public static bool IsMultiLanguageRuntimeEnvironment(this IEnvironment environme
         {
             if (!isMultiLanguageEnabled.HasValue)
             {
-                isMultiLanguageEnabled = environment.IsLogicApp() && FeatureFlags.IsEnabled(ScriptConstants.FeatureFlagEnableMultiLanguageWorker, environment);
+                isMultiLanguageEnabled = environment.IsLogicApp();
             }
             return isMultiLanguageEnabled.Value;
         }

src/WebJobs.Script/ScriptConstants.cs

@@ -123,7 +123,6 @@ public static class ScriptConstants
         public const string FeatureFlagDisableMergedWebHostScriptHostConfiguration = "DisableMergedConfiguration";
         public const string FeatureFlagDisableWorkerIndexing = "DisableWorkerIndexing";
         public const string FeatureFlagEnableDebugTracing = "EnableDebugTracing";
-        public const string FeatureFlagEnableMultiLanguageWorker = "EnableMultiLanguageWorker";
         public const string FeatureFlagEnableProxies = "EnableProxies";
         public const string HostingConfigDisableLinuxAppServiceDetailedExecutionEvents = "DisableLinuxExecutionDetails";
         public const string HostingConfigDisableLinuxAppServiceExecutionEventLogBackoff = "DisableLinuxLogBackoff";

src/WebJobs.Script/Workers/Rpc/Configuration/LanguageWorkerOptionsSetup.cs

@@ -41,7 +41,11 @@ public LanguageWorkerOptionsSetup(IConfiguration configuration,
         public void Configure(LanguageWorkerOptions options)
         {
             string workerRuntime = _environment.GetEnvironmentVariable(RpcWorkerConstants.FunctionWorkerRuntimeSettingName);
-            if (!string.IsNullOrEmpty(workerRuntime) && workerRuntime.Equals(RpcWorkerConstants.DotNetLanguageWorkerName, System.StringComparison.OrdinalIgnoreCase))
+
+            // Parsing worker.config.json should always be done in case of multi language worker
+            if (!string.IsNullOrEmpty(workerRuntime) &&
+                workerRuntime.Equals(RpcWorkerConstants.DotNetLanguageWorkerName, StringComparison.OrdinalIgnoreCase) &&
+                !_environment.IsMultiLanguageRuntimeEnvironment())
             {
                 // Skip parsing worker.config.json files for dotnet in-proc apps
                 options.WorkerConfigs = new List<RpcWorkerConfig>();

test/WebJobs.Script.Tests.Integration/WebHostEndToEnd/MultiLanguageEndToEndTests.cs

@@ -39,7 +39,6 @@ public async Task CodelessFunction_CanUse_MultipleLanguageProviders()
             var settings = new Dictionary<string, string>()
             {
                 [EnvironmentSettingNames.AppKind] = "workflowApp",
-                [EnvironmentSettingNames.AzureWebJobsFeatureFlags] = $"{ScriptConstants.FeatureFlagEnableMultiLanguageWorker}",
             };
             var testEnvironment = new TestEnvironment(settings);
 
@@ -86,7 +85,6 @@ public async Task CodelessFunction_CanUse_SingleJavaLanguageProviders()
             var settings = new Dictionary<string, string>()
             {
                 [EnvironmentSettingNames.AppKind] = "workflowApp",
-                [EnvironmentSettingNames.AzureWebJobsFeatureFlags] = $"{ScriptConstants.FeatureFlagEnableMultiLanguageWorker}",
             };
             var testEnvironment = new TestEnvironment(settings);
 
@@ -126,7 +124,6 @@ public async Task CodelessFunction_CanUse_SingleJavascriptLanguageProviders()
             var settings = new Dictionary<string, string>()
             {
                 [EnvironmentSettingNames.AppKind] = "workflowApp",
-                [EnvironmentSettingNames.AzureWebJobsFeatureFlags] = $"{ScriptConstants.FeatureFlagEnableMultiLanguageWorker}",
             };
             var testEnvironment = new TestEnvironment(settings);
 
@@ -166,7 +163,6 @@ public async Task CodelessFunction_CanUse_NoLanguageProviders()
             var settings = new Dictionary<string, string>()
             {
                 [EnvironmentSettingNames.AppKind] = "workflowApp",
-                [EnvironmentSettingNames.AzureWebJobsFeatureFlags] = $"{ScriptConstants.FeatureFlagEnableMultiLanguageWorker}",
             };
             var testEnvironment = new TestEnvironment(settings);