Prevent ArgumentOutOfRangeException when handling nested generic types (#59201)

* Add unit test for the issue

* Fix typo

* Fix bug

* More efficient check with a better variable name

Author: sander1095

src/OpenApi/src/Extensions/JsonTypeInfoExtensions.cs

@@ -67,7 +67,7 @@ internal static class JsonTypeInfoExtensions
         }
 
         // Although arrays are enumerable types they are not encoded correctly
-        // with JsonTypeInfoKind.Enumerable so we handle the Enumerble type
+        // with JsonTypeInfoKind.Enumerable so we handle the Enumerable type
         // case here.
         if (jsonTypeInfo is JsonTypeInfo { Kind: JsonTypeInfoKind.Enumerable } || type.IsArray)
         {
@@ -104,7 +104,13 @@ internal static string GetSchemaReferenceId(this Type type, JsonSerializerOption
         // Generic types become a concatenation of the generic type name and the type arguments
         if (type.IsGenericType)
         {
-            var genericTypeName = type.Name[..type.Name.LastIndexOf('`')];
+            // We need to handle the case where the generic type is a nested type,
+            // so we check if the name contains a backtick already.
+            // For more information: https://github.com/dotnet/aspnetcore/issues/59092
+            var backtickIndex = type.Name.LastIndexOf('`');
+            var isNestedGenericType = backtickIndex == -1;
+
+            var genericTypeName = isNestedGenericType ? type.Name : type.Name[..backtickIndex];
             var genericArguments = type.GetGenericArguments();
             var argumentNames = string.Join("And", genericArguments.Select(arg => arg.GetSchemaReferenceId(options)));
             return $"{genericTypeName}Of{argumentNames}";

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Extensions/JsonTypeInfoExtensionsTests.cs

@@ -17,6 +17,21 @@ private class Container
         internal delegate void ContainedTestDelegate(int x, int y);
     }
 
+    /// <remarks>
+    /// https://github.com/dotnet/aspnetcore/issues/59092
+    /// </remarks>
+    public static class Foo<T>
+    {
+        public static class Bar<TT>
+        {
+            public class Baz
+            {
+                public required T One { get; set; }
+                public required TT Two { get; set; }
+            }
+        }
+    }
+
     /// <summary>
     /// This data is used to test the <see cref="TypeExtensions.GetSchemaReferenceId"/> method
     /// which is used to generate reference IDs for OpenAPI schemas in the OpenAPI document.
@@ -58,6 +73,7 @@ private class Container
         [typeof(Dictionary<string, string[]>), null],
         [typeof(Dictionary<string, List<string[]>>), null],
         [typeof(Dictionary<string, IEnumerable<string[]>>), null],
+        [typeof(Foo<int>.Bar<string>.Baz), "BazOfintAndstring"],
     ];
 
     [Theory]