WIP: Reject pathes that use the wrong list indexing syntax [i] instead of /i

JsonPatchDocumentExtensionDataAdapter/JsonPatchDocumentExtensionDataAdapter/JsonPatchDocumentExtensionDataAdapter.cs

@@ -258,6 +258,10 @@ in TModel model
             }
 
             var originalError = applyError!;
+            {
+                // if the operation looks like a list operation with [<index>] instead of /<index>
+                // then log a warning
+            }
             var extensionDataKey = GetPathRelativeToExtensionData(originalOperation.path);
             if (extensionDataAlreadyExists)
             {

JsonPatchDocumentExtensionDataAdapter/UnitTest/Models.cs

@@ -24,6 +24,17 @@ internal class MyClassWithNesting
     public MyClass? MyModel { get; set; }
 }
 
+internal class MyClassWithAList
+{
+    public int? Foo { get; set; }
+    public string? Bar { get; set; }
+
+    public List<int>? SomeList { get; set; }
+
+    [System.Text.Json.Serialization.JsonExtensionData]
+    public IDictionary<string, object>? MyExtensionData { get; set; }
+}
+
 /// <summary>
 /// similar to <see cref="MyClass"/> but with JsonPropertyName attributes
 /// </summary>

JsonPatchDocumentExtensionDataAdapter/UnitTest/SimpleTests.cs

@@ -1,6 +1,7 @@
 using FluentAssertions;
 using JsonExtensionDataPatchDocumentAdapter;
 using Microsoft.AspNetCore.JsonPatch;
+using Microsoft.AspNetCore.JsonPatch.Exceptions;
 using Microsoft.AspNetCore.JsonPatch.Operations;
 
 namespace UnitTest;
@@ -126,4 +127,29 @@ bool invokeAsExtensionMethod
                 .Be("def");
         }
     }
+
+    [TestMethod]
+    public void TestPatchingExtensionData_Recognizes_Invalid_Path()
+    {
+        var myEntity = new MyClassWithAList();
+        var myPatch = new JsonPatchDocument<MyClassWithAList>();
+        myPatch.Add(x => x.Foo, 42);
+        myPatch.Add(x => x.Bar, "fgh");
+        myPatch.Operations.Add(
+            new Operation<MyClassWithAList>
+            {
+                path = "/SomeList[0]",
+                op = "add",
+                value = 17,
+            }
+        );
+        var patchingOriginal = () => myPatch.ApplyTo(myEntity);
+        patchingOriginal.Should().Throw<JsonPatchException>();
+
+        var adaptedPatch = new JsonPatchDocumentExtensionDataAdapter<MyClassWithAList>(x =>
+            x.MyExtensionData
+        ).TransformDocument(myPatch, in myEntity);
+        adaptedPatch.ApplyTo(myEntity);
+        myEntity.MyExtensionData.Should().NotContainKey("SomeList[0]");
+    }
 }