Reverting to host initialization exception (#3855)

Author: maiqbal11

src/WebJobs.Script/Host/ScriptHost.cs

@@ -714,17 +714,7 @@ internal async Task<Collection<FunctionDescriptor>> GetFunctionDescriptorsAsync(
             Collection<FunctionDescriptor> functionDescriptors = new Collection<FunctionDescriptor>();
             var httpFunctions = new Dictionary<string, HttpTriggerAttribute>();
 
-            if (!Utility.IsSingleLanguage(functions, _currentRuntimeLanguage))
-            {
-                if (string.IsNullOrEmpty(_currentRuntimeLanguage))
-                {
-                    _logger.LogWarning($"Select a language for your function app by specifying {LanguageWorkerConstants.FunctionWorkerRuntimeSettingName} AppSetting");
-                }
-                else
-                {
-                    _logger.LogWarning($"Did not find functions with language [{_currentRuntimeLanguage}].");
-                }
-            }
+            Utility.VerifyFunctionsMatchSpecifiedLanguage(functions, _currentRuntimeLanguage);
 
             foreach (FunctionMetadata metadata in functions)
             {

src/WebJobs.Script/Utility.cs

@@ -439,6 +439,21 @@ internal static bool TryReadFunctionConfig(string scriptDir, out string json, IF
             return true;
         }
 
+        internal static void VerifyFunctionsMatchSpecifiedLanguage(IEnumerable<FunctionMetadata> functions, string currentRuntimeLanguage)
+        {
+            if (!IsSingleLanguage(functions, currentRuntimeLanguage))
+            {
+                if (string.IsNullOrEmpty(currentRuntimeLanguage))
+                {
+                    throw new HostInitializationException($"Found functions with more than one language. Select a language for your function app by specifying {LanguageWorkerConstants.FunctionWorkerRuntimeSettingName} AppSetting");
+                }
+                else
+                {
+                    throw new HostInitializationException($"Did not find functions with language [{currentRuntimeLanguage}].");
+                }
+            }
+        }
+
         internal static bool IsSingleLanguage(IEnumerable<FunctionMetadata> functions, string currentRuntimeLanguage)
         {
             if (functions == null)

test/WebJobs.Script.Tests/ScriptHostTests.cs

@@ -1088,6 +1088,83 @@ private static IEnumerable<FunctionMetadata> GetDotNetFunctionsMetadata()
             return functionsList;
         }
 
+        [Fact]
+        public void VerifyFunctionsMatchSpecifiedLanguage_Throws_For_UnmatchedLanguage_With_RuntimeLanguage_Specified()
+        {
+            FunctionMetadata funcJS1 = new FunctionMetadata()
+            {
+                Name = "funcJS1",
+                Language = "node"
+            };
+            IEnumerable<FunctionMetadata> functionsList = new Collection<FunctionMetadata>()
+            {
+                funcJS1
+            };
+
+            HostInitializationException ex = Assert.Throws<HostInitializationException>(() => Utility.VerifyFunctionsMatchSpecifiedLanguage(functionsList, LanguageWorkerConstants.DotNetLanguageWorkerName));
+            Assert.Equal($"Did not find functions with language [{LanguageWorkerConstants.DotNetLanguageWorkerName}].", ex.Message);
+        }
+
+        [Fact]
+        public void VerifyFunctionsMatchSpecifiedLanguage_NoThrow_For_MixedLanguageMatching_With_RuntimeLanguage_Specified()
+        {
+            FunctionMetadata funcJS1 = new FunctionMetadata()
+            {
+                Name = "funcJS1",
+                Language = "node"
+            };
+            // CSharp matches dotnet so we should be able to initialize the host
+            FunctionMetadata funcCS1 = new FunctionMetadata()
+            {
+                Name = "funcJS1",
+                Language = "csharp"
+            };
+            IEnumerable<FunctionMetadata> functionsList = new Collection<FunctionMetadata>()
+            {
+                funcJS1, funcCS1
+            };
+
+            Utility.VerifyFunctionsMatchSpecifiedLanguage(functionsList, LanguageWorkerConstants.DotNetLanguageWorkerName);
+        }
+
+        [Fact]
+        public void VerifyFunctionsMatchSpecifiedLanguage_NoThrow_For_SingleLanguage_Without_RuntimeLanguage_Specified()
+        {
+            FunctionMetadata funcJS1 = new FunctionMetadata()
+            {
+                Name = "funcJS1",
+                Language = "node"
+            };
+            IEnumerable<FunctionMetadata> functionsList = new Collection<FunctionMetadata>()
+            {
+                funcJS1
+            };
+
+            Utility.VerifyFunctionsMatchSpecifiedLanguage(functionsList, string.Empty);
+        }
+
+        [Fact]
+        public void VerifyFunctionsMatchSpecifiedLanguage_Throws_For_NotSingleLanguage_Without_RuntimeLanguage_Specified()
+        {
+            FunctionMetadata funcJS1 = new FunctionMetadata()
+            {
+                Name = "funcJS1",
+                Language = "node"
+            };
+            FunctionMetadata funcCS1 = new FunctionMetadata()
+            {
+                Name = "funcCS1",
+                Language = "csharp"
+            };
+            IEnumerable<FunctionMetadata> functionsList = new Collection<FunctionMetadata>()
+            {
+                funcJS1, funcCS1
+            };
+
+            HostInitializationException ex = Assert.Throws<HostInitializationException>(() => Utility.VerifyFunctionsMatchSpecifiedLanguage(functionsList, string.Empty));
+            Assert.Equal($"Found functions with more than one language. Select a language for your function app by specifying {LanguageWorkerConstants.FunctionWorkerRuntimeSettingName} AppSetting", ex.Message);
+        }
+
         [Fact]
         public async Task InitializeRpcService_Throws()
         {