Better handling of unknown bindings

Author: fabiocav

src/WebJobs.Script/Description/FunctionDescriptorProvider.cs

@@ -114,9 +114,15 @@ protected virtual Collection<ParameterDescriptor> GetFunctionParameters(IFunctio
 
         protected virtual ParameterDescriptor CreateTriggerParameter(BindingMetadata triggerMetadata, Type parameterType = null)
         {
-            ParameterDescriptor triggerParameter = null;
-            TryParseTriggerParameter(triggerMetadata.Raw, out triggerParameter, parameterType);
-            triggerParameter.IsTrigger = true;
+            if (TryParseTriggerParameter(triggerMetadata.Raw, out ParameterDescriptor triggerParameter, parameterType))
+            {
+                triggerParameter.IsTrigger = true;
+            }
+            else
+            {
+                throw new ScriptConfigurationException($"The binding type '{triggerMetadata.Type}' is not registered. " +
+                    $"Please ensure the type is correct and the binding extension is installed.");
+            }
 
             return triggerParameter;
         }

test/WebJobs.Script.Tests/Description/FunctionDescriptorProviderTests.cs

@@ -10,6 +10,7 @@
 using Microsoft.Azure.WebJobs.Script.Eventing;
 using Moq;
 using Xunit;
+using Newtonsoft.Json.Linq;
 
 namespace Microsoft.Azure.WebJobs.Script.Tests
 {
@@ -79,6 +80,22 @@ public void ValidateFunction_NoTriggerBinding_Throws()
             Assert.Equal("No trigger binding specified. A function must have a trigger input binding.", ex.Message);
         }
 
+        [Fact]
+        public void CreateTriggerParameter_WithNoBindingMatch_ThrowsExpectedException()
+        {
+            FunctionMetadata functionMetadata = new FunctionMetadata();
+            BindingMetadata metadata = BindingMetadata.Create(JObject.Parse("{\"type\": \"someInvalidTrigger\",\"name\": \"req\",\"direction\": \"in\"}"));
+
+            functionMetadata.Bindings.Add(metadata);
+
+            var ex = Assert.Throws<ScriptConfigurationException>(() =>
+            {
+                _provider.TryCreate(functionMetadata, out FunctionDescriptor descriptor);
+            });
+
+            Assert.Contains("someInvalidTrigger", ex.Message);
+        }
+
         [Theory]
         [InlineData(null)]
         [InlineData("")]
@@ -147,7 +164,7 @@ public TestDescriptorProvider(ScriptHost host, ScriptHostConfiguration config) :
 
             protected override IFunctionInvoker CreateFunctionInvoker(string scriptFilePath, BindingMetadata triggerMetadata, FunctionMetadata functionMetadata, Collection<FunctionBinding> inputBindings, Collection<FunctionBinding> outputBindings)
             {
-                throw new NotImplementedException();
+                return new Mock<IFunctionInvoker>().Object;
             }
         }
     }