Add `ErrorContext.Member` to `ErrorContext.Path` when clearly needed

- #8509

nits:
- use `ModelNames.CreatePropertyModelName(...)`
- move `exception` assignment up and reuse that variable

src/Microsoft.AspNetCore.Mvc.Formatters.Json/JsonInputFormatter.cs

@@ -261,32 +261,48 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
                     {
                         successful = false;
 
-                        // Handle path combinations such as "" + "Property", "Parent" + "Property", or "Parent" + "[12]".
+                        // When ErrorContext.Path does not include ErrorContext.Member, add Member to form full path.
-                        var key = eventArgs.ErrorContext.Path;
+                        var path = eventArgs.ErrorContext.Path;
-                        if (!string.IsNullOrEmpty(context.ModelName))
+                        var member = eventArgs.ErrorContext.Member?.ToString();
+                        var addMember = !string.IsNullOrEmpty(member);
+                        if (addMember)
                         {
-                            if (string.IsNullOrEmpty(eventArgs.ErrorContext.Path))
+                            // Path.Member case (path.Length < member.Length) needs no further checks.
+                            if (path.Length == member.Length)
                             {
-                                key = context.ModelName;
+                                // Add Member in Path.Memb case but not for Path.Path.
+                                addMember = !string.Equals(path, member, StringComparison.Ordinal);
                             }
-                            else if (eventArgs.ErrorContext.Path[0] == '[')
+                            else if (path.Length > member.Length)
                             {
-                                key = context.ModelName + eventArgs.ErrorContext.Path;
+                                // Finally, check whether Path already ends with Member.
-                            }
+                                if (member[0] == '[')
-                            else
+                                {
-                            {
+                                    addMember = !path.EndsWith(member, StringComparison.Ordinal);
-                                key = context.ModelName + "." + eventArgs.ErrorContext.Path;
+                                }
+                                else
+                                {
+                                    addMember = !path.EndsWith("." + member, StringComparison.Ordinal);
+                                }
                             }
                         }
 
-                        var metadata = GetPathMetadata(context.Metadata, eventArgs.ErrorContext.Path);
+                        if (addMember)
-                        var modelStateException = WrapExceptionForModelState(eventArgs.ErrorContext.Error);
+                        {
-                        context.ModelState.TryAddModelError(key, modelStateException, metadata);
+                            path = ModelNames.CreatePropertyModelName(path, member);
+                        }
 
-                        _logger.JsonInputException(eventArgs.ErrorContext.Error);
+                        // Handle path combinations such as ""+"Property", "Parent"+"Property", or "Parent"+"[12]".
+                        var key = ModelNames.CreatePropertyModelName(context.ModelName, path);
 
                         exception = eventArgs.ErrorContext.Error;
 
+                        var metadata = GetPathMetadata(context.Metadata, path);
+                        var modelStateException = WrapExceptionForModelState(exception);
+                        context.ModelState.TryAddModelError(key, modelStateException, metadata);
+
+                        _logger.JsonInputException(exception);
+
                         // Error must always be marked as handled
                         // Failure to do so can cause the exception to be rethrown at every recursive level and
                         // overflow the stack for x64 CLR processes

test/Microsoft.AspNetCore.Mvc.Formatters.Json.Test/JsonInputFormatterTest.cs

@@ -44,7 +44,7 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
             httpContext.Features.Set<IHttpResponseFeature>(new TestResponseFeature());
             httpContext.Request.Body = new NonSeekableReadStream(contentBytes);
             httpContext.Request.ContentType = "application/json";
-            
+
             var formatterContext = CreateInputFormatterContext(typeof(User), httpContext);
 
             // Act
@@ -531,7 +531,7 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
             // missing password property here
             var contentBytes = Encoding.UTF8.GetBytes("{ \"UserName\" : \"John\"}");
             var httpContext = GetHttpContext(contentBytes, "application/json;charset=utf-8");
-            
+
             var formatterContext = CreateInputFormatterContext(typeof(UserLogin), httpContext);
 
             // Act
@@ -571,7 +571,7 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
         [InlineData("{\"a\":{\"b\"}}", "a", "Invalid character after parsing property name. Expected ':' but got: }. Path 'a', line 1, position 9.")]
         [InlineData("{\"age\":\"x\"}", "age", "Could not convert string to decimal: x. Path 'age', line 1, position 10.")]
         [InlineData("{\"login\":1}", "login", "Error converting value 1 to type 'Microsoft.AspNetCore.Mvc.Formatters.JsonInputFormatterTest+UserLogin'. Path 'login', line 1, position 10.")]
-        [InlineData("{\"login\":{\"username\":\"somevalue\"}}", "login", "Required property 'Password' not found in JSON. Path 'login', line 1, position 33.")]
+        [InlineData("{\"login\":{\"username\":\"somevalue\"}}", "login.Password", "Required property 'Password' not found in JSON. Path 'login', line 1, position 33.")]
         public async Task ReadAsync_WithAllowInputFormatterExceptionMessages_RegistersJsonInputExceptionsAsInputFormatterException(
             string content,
             string modelStateKey,
@@ -582,7 +582,7 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
 
             var contentBytes = Encoding.UTF8.GetBytes(content);
             var httpContext = GetHttpContext(contentBytes);
-            
+
             var formatterContext = CreateInputFormatterContext(typeof(User), httpContext);
 
             // Act

test/Microsoft.AspNetCore.Mvc.FunctionalTests/InputObjectValidationTests.cs

@@ -172,8 +172,10 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
         public async Task CheckIfExcludedField_IsNotValidatedForNonBodyBoundModels()
         {
             // Arrange
-            var kvps = new List<KeyValuePair<string, string>>();
+            var kvps = new List<KeyValuePair<string, string>>
-            kvps.Add(new KeyValuePair<string, string>("Alias", "xyz"));
+            {
+                new KeyValuePair<string, string>("Alias", "xyz"),
+            };
             var content = new FormUrlEncodedContent(kvps);
 
             // Act
@@ -316,7 +318,7 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
                 validationProblemDetails.Errors,
                 error =>
                 {
-                    Assert.Empty(error.Key);
+                    Assert.Equal("isbn", error.Key);
                     Assert.Equal(new[] { "Required property 'isbn' not found in JSON. Path '', line 1, position 44." }, error.Value);
                 });
         }