#56114

Author: smnsht

src/Http/Http.Extensions/src/RequestDelegateFactory.cs

@@ -821,6 +821,15 @@ private static Expression CreateArgument(ParameterInfo parameter, RequestDelegat
                     $"Nested {nameof(AsParametersAttribute)} is not supported and should be used only for handler parameters.");
             }
 
+            // Parameters like IFormFileCollection should throw "The abstract type ... is not supported" rather than
+            // "...not supported on enumerable parameters.". It happens down the line.
+            if (!parameter.ParameterType.IsAbstract
+                    && typeof(System.Collections.IEnumerable).IsAssignableFrom(parameter.ParameterType))
+            {
+                throw new NotSupportedException(
+                    $"The {nameof(AsParametersAttribute)} is not supported on enumerable parameters.");
+            }
+
             return BindParameterFromProperties(parameter, factoryContext);
         }
         else if (parameter.ParameterType == typeof(HttpContext))

src/Http/Http.Extensions/test/RequestDelegateFactoryTests.cs

@@ -1022,6 +1022,33 @@ public void BuildRequestDelegateThrowsInvalidOperationExceptionForInvalidParamet
         Assert.Equal(errorMessage, exception.Message);
     }
 
+    public static object[][] BadArgumentEnumerableActions
+    {
+        get
+        {
+            void TestParameterStringList([AsParameters] List<string> req) { }
+            void TestParameterDictionary([AsParameters] Dictionary<string, string> req) { }
+            void TestParameterIntArray([AsParameters] int[] req) { }
+
+            return new object[][]
+            {
+                new object[] { (Action<List<string>>)TestParameterStringList },
+                new object[] { (Action<Dictionary<string, string>>)TestParameterDictionary },
+                new object[] { (Action<int[]>)TestParameterIntArray }
+            };
+        }
+    }
+
+    [Theory]
+    [MemberData(nameof(BadArgumentEnumerableActions))]
+    public void BuildRequestDelegateThrowsNotSupportedExceptionForEnumerable(Delegate @delegate)
+    {
+        var errorMessage = $"The {nameof(AsParametersAttribute)} is not supported on enumerable parameters.";
+        var exception = Assert.Throws<NotSupportedException>(() => RequestDelegateFactory.Create(@delegate));
+
+        Assert.Equal(errorMessage, exception.Message);
+    }
+
     [Fact]
     public void BuildRequestDelegateThrowsNotSupportedExceptionForNestedParametersList()
     {
@@ -2014,6 +2041,15 @@ void TestJsonAndFormWithAttribute(Todo value1, [FromForm] string value2) { }
         Assert.Throws<InvalidOperationException>(() => RequestDelegateFactory.Create(TestJsonAndFormWithAttribute));
     }
 
+    [Fact]
+    public void CreateThrowsInvalidOperationExceptionIfIFormFileCollectionHasAsParametersAttribute()
+    {
+        void TestAction([AsParameters] IFormFileCollection formFiles) {}
+
+        var ioe = Assert.Throws<InvalidOperationException>(() => RequestDelegateFactory.Create(TestAction));
+        Assert.Equal("The abstract type 'IFormFileCollection' is not supported.", ioe.Message);
+    }
+
     [Fact]
     public void CreateThrowsNotSupportedExceptionIfIFormFileCollectionHasMetadataParameterName()
     {