Guard against invalid TypeToConvert args to read methods of object and collection converter

[layomia]

Depending on the scenario, we could fail with a NRE:

[Fact]
public static void ConverterRead_VerifyInvalidTypeToConvertFails()
{
    var options = new JsonSerializerOptions();
    Type typeToConvert = typeof(KeyValuePair<int, int>);
    byte[] bytes = Encoding.UTF8.GetBytes(@"{""Key"":1,""Value"":2}");

    JsonConverter<KeyValuePair<int, int>> converter =
        (JsonConverter<KeyValuePair<int, int>>)options.GetConverter(typeToConvert);

    // Baseline
    var reader = new Utf8JsonReader(bytes);
    reader.Read();
    KeyValuePair<int, int> kvp = converter.Read(ref reader, typeToConvert, options);
    Assert.Equal(1, kvp.Key);
    Assert.Equal(2, kvp.Value);

    // Test
    reader = new Utf8JsonReader(bytes);
    reader.Read();
    try
    {
        converter.Read(ref reader, typeof(Dictionary<string, int>), options);
    }
    catch (Exception ex)
    {
        if (!(ex is InvalidOperationException))
        {
            throw ex; // NullReferenceException thrown.
        }
    }
}

Validation should take place in this method:

runtime/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonResumableConverterOfT.cs

Line 17 in ce1123f

public sealed override T Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)

The ReadStack Initialize method called downstream may also need some validation logic.

EDIT: the validation may need to take place in the individual object/collection converters.

[layomia]

Moving this to 6.0 since this is not a regression and will not be experienced if a compatible typeToConvert is passed to the converter.

[ShreyasJejurkar]

Hi, @layomia So, in this should we throw an exception like stating that type mismatched or just return null?
In case of throwing an exception, what would be appropriate exception type should be thrown (InvalidOperationException?) and with which message?

[layomia]

@MCCshreyas I believe an InvalidOperationException with a message along the lines of "Type 'NameOfType' is not compatible with converter 'ConverterName'." is appropriate.

[ShreyasJejurkar]

OK @layomia, thanks for clarification! I will get that implemented!

[eiriktsarpalis]

Moving to Future, as we won't have time to work on this in the .NET 7 timeframe.

[eiriktsarpalis]

Closing in favor of #50205 which describes the wider problem that is at play here. TL;DR built-in object converter cannot function independently of the correct JsonTypeInfo metadata associated with the type. This would need to be fixed whenever #63791 is implemented.