Instead of throwing there, we emit diagnostics when the type is invalid.

Author: smnsht

src/Http/Http.Extensions/gen/DiagnosticDescriptors.cs

@@ -125,4 +125,13 @@ internal static class DiagnosticDescriptors
         DiagnosticSeverity.Warning,
         isEnabledByDefault: true,
         helpLinkUri: GetHelpLinkUrl("RDG013"));
+
+    public static DiagnosticDescriptor InvalidAsParametersEnumerableType { get; } = new(
+        "RDG014",
+        new LocalizableResourceString(nameof(Resources.InvalidAsParametersEnumerableType_Title), Resources.ResourceManager, typeof(Resources)),
+        new LocalizableResourceString(nameof(Resources.InvalidAsParametersEnumerableType_Message), Resources.ResourceManager, typeof(Resources)),
+        "Usage",
+        DiagnosticSeverity.Warning,
+        isEnabledByDefault: true,
+        helpLinkUri: GetHelpLinkUrl("RDG014"));
 }

src/Http/Http.Extensions/gen/Resources.resx

@@ -195,4 +195,10 @@
   <data name="KeyedAndNotKeyedServiceAttributesNotSupported_Message" xml:space="preserve">
     <value>The [FromKeyedServices] attribute is not supported on parameters that are also annotated with IFromServiceMetadata. For more information, please see https://aka.ms/aspnet/rdg-known-issues</value>
   </data>
+  <data name="InvalidAsParametersEnumerableType_Title" xml:space="preserve">
+    <value>Invalid enumerable type</value>
+  </data>
+  <data name="InvalidAsParametersEnumerableType_Message" xml:space="preserve">
+    <value>The enumerable type '{0}' is not supported. For more information, please see https://aka.ms/aspnet/rdg-known-issues</value>
+  </data>
 </root>

src/Http/Http.Extensions/gen/StaticRouteHandlerModel/EndpointParameter.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics.CodeAnalysis;
@@ -466,6 +467,12 @@ private static bool TryGetAsParametersConstructor(Endpoint endpoint, INamedTypeS
             return false;
         }
 
+        if (type.AllInterfaces.Any(x => x.ToString() == typeof(IEnumerable).FullName))
+        {
+            endpoint.Diagnostics.Add(Diagnostic.Create(DiagnosticDescriptors.InvalidAsParametersEnumerableType, location, parameterTypeString));
+            return false;
+        }
+
         var constructors = type.Constructors.Where(constructor => constructor.DeclaredAccessibility == Accessibility.Public && !constructor.IsStatic);
         var numOfConstructors = constructors.Count();
         // When leveraging parameterless constructors, we want to ensure we only emit for writable

src/Http/Http.Extensions/test/RequestDelegateGenerator/CompileTimeCreationTests.AsParameters.cs

@@ -50,13 +50,19 @@ static string GetNoContructorsError(Type type)
             static string GetInvalidConstructorError(Type type)
                 => $"The public parameterized constructor must contain only parameters that match the declared public properties for type '{TypeNameHelper.GetTypeDisplayName(type, fullName: false)}'. For more information, please see https://aka.ms/aspnet/rdg-known-issues";
 
+            static string GetEnumerableTypeError(Type type)
+                => $"The enumerable type '{TypeNameHelper.GetTypeDisplayName(type, fullName: false)}' is not supported. For more information, please see https://aka.ms/aspnet/rdg-known-issues";
+
             return new []
             {
                     new object[] { "BadArgumentListRecord", DiagnosticDescriptors.InvalidAsParametersSingleConstructorOnly.Id, GetMultipleContructorsError(typeof(BadArgumentListRecord)) },
                     new object[] { "BadArgumentListClass", DiagnosticDescriptors.InvalidAsParametersSignature.Id, GetInvalidConstructorError(typeof(BadArgumentListClass)) },
                     new object[] { "BadArgumentListClassMultipleCtors", DiagnosticDescriptors.InvalidAsParametersSingleConstructorOnly.Id, GetMultipleContructorsError(typeof(BadArgumentListClassMultipleCtors))  },
                     new object[] { "BadAbstractArgumentListClass", DiagnosticDescriptors.InvalidAsParametersAbstractType.Id, GetAbstractTypeError(typeof(BadAbstractArgumentListClass)) },
                     new object[] { "BadNoPublicConstructorArgumentListClass", DiagnosticDescriptors.InvalidAsParametersNoConstructorFound.Id, GetNoContructorsError(typeof(BadNoPublicConstructorArgumentListClass)) },
+                    new object[] { "List<string>", DiagnosticDescriptors.InvalidAsParametersEnumerableType.Id, GetEnumerableTypeError(typeof(List<string>)) },
+                    new object[] { "List<IFormFile>", DiagnosticDescriptors.InvalidAsParametersEnumerableType.Id, GetEnumerableTypeError(typeof(List<IFormFile>)) },
+                    new object[] { "Dictionary<string, string>", DiagnosticDescriptors.InvalidAsParametersEnumerableType.Id, GetEnumerableTypeError(typeof(Dictionary<string, string>)) }
             };
         }
     }