Capture parsing errors in model state when binding convertible keys (#50929)

Author: captainsafia

src/Mvc/Mvc.Core/src/ModelBinding/Binders/DictionaryModelBinder.cs

@@ -163,7 +163,17 @@ public override async Task BindModelAsync(ModelBindingContext bindingContext)
         {
             // Use InvariantCulture to convert the key since ExpressionHelper.GetExpressionText() would use
             // that culture when rendering a form.
-            var convertedKey = ModelBindingHelper.ConvertTo<TKey>(kvp.Key, culture: null);
+            TKey? convertedKey;
+            try
+            {
+                convertedKey = ModelBindingHelper.ConvertTo<TKey>(kvp.Key, culture: null);
+            }
+            catch (Exception ex)
+            {
+                bindingContext.Result = ModelBindingResult.Failed();
+                bindingContext.ModelState.AddModelError(bindingContext.ModelName, ex.Message);
+                return;
+            }
 
             using (bindingContext.EnterNestedScope(
                 modelMetadata: valueMetadata,

src/Mvc/test/Mvc.IntegrationTests/DictionaryModelBinderIntegrationTest.cs

@@ -1352,6 +1352,79 @@ public async Task DictionaryModelBinder_ValuesIsNonNullableType_AppliesImplicitR
         Assert.False(modelState.IsValid);
     }
 
+    [Fact]
+    public async Task DictionaryModelBinder_BindsDictionaryOfSimpleValueAndEnumKey_WithError()
+    {
+        // Arrange
+        var expectedDictionary = new Dictionary<DayOfWeek, string>
+        {
+            { DayOfWeek.Monday, "hello" },
+            { DayOfWeek.Tuesday, "world" },
+        };
+        var parameterBinder = ModelBindingTestHelper.GetParameterBinder();
+        var parameter = new ParameterDescriptor()
+        {
+            Name = "parameter",
+            ParameterType = typeof(Dictionary<DayOfWeek, string>)
+        };
+
+        var testContext = ModelBindingTestHelper.GetTestContext(request =>
+        {
+            request.QueryString = new QueryString("?parameter[Monday]=hello&parameter[Tuesday]=world&parameter[Invalid]=exclamation");
+        });
+
+        var modelState = testContext.ModelState;
+
+        // Act
+        var modelBindingResult = await parameterBinder.BindModelAsync(parameter, testContext);
+
+        // Assert
+        Assert.False(modelBindingResult.IsModelSet);
+
+        Assert.NotEmpty(modelState);
+        Assert.Equal(1, modelState.ErrorCount);
+        Assert.False(modelState.IsValid);
+        Assert.Equal("Invalid is not a valid value for DayOfWeek.", modelState["parameter"].Errors[0].ErrorMessage);
+    }
+
+    [Fact]
+    public async Task DictionaryModelBinder_BindsDictionaryOfSimpleValueAndEnumValue_WithError()
+    {
+        // Arrange
+        var expectedDictionary = new Dictionary<string, DayOfWeek>
+        {
+            { "hello", DayOfWeek.Monday },
+            { "world", DayOfWeek.Tuesday },
+            { "exclamation", DayOfWeek.Sunday },
+        };
+        var parameterBinder = ModelBindingTestHelper.GetParameterBinder();
+        var parameter = new ParameterDescriptor()
+        {
+            Name = "parameter",
+            ParameterType = typeof(Dictionary<string, DayOfWeek>)
+        };
+
+        var testContext = ModelBindingTestHelper.GetTestContext(request =>
+        {
+            request.QueryString = new QueryString("?parameter[hello]=Monday&parameter[world]=Tuesday&parameter[exclamation]=BadEnumValue");
+        });
+
+        var modelState = testContext.ModelState;
+
+        // Act
+        var modelBindingResult = await parameterBinder.BindModelAsync(parameter, testContext);
+        var model = Assert.IsType<Dictionary<string, DayOfWeek>>(modelBindingResult.Model);
+
+        // Assert
+        Assert.True(modelBindingResult.IsModelSet);
+        // Assert.Equal(expectedDictionary, model);
+
+        Assert.NotEmpty(modelState);
+        Assert.Equal(1, modelState.ErrorCount);
+        Assert.False(modelState.IsValid);
+        Assert.Equal("The value 'BadEnumValue' is not valid for Value.", modelState["parameter[exclamation]"].Errors[0].ErrorMessage);
+    }
+
 #nullable enable
     public class NonNullPersonWithRequiredProperties
     {