Support default value for structs, such as default(CancellationToken)

[ZhouWei]

Runtime: NET6.0
IronPython: 2.7.11

In mongodb, there are many methods with default value as default(CancellationToken)

long CountDocuments(FilterDefinition<TDocument> filter, CountOptions options = null, CancellationToken cancellationToken = default(CancellationToken));

but in IronPython, when we call the method:

CountDocuments[BsonDocument]("collection")

got

IronPython.Runtime.Exceptions.TypeErrorException: expected CancellationToken, got NoneType

I seems that IronPython does't support default value for structs, such as default(CancellationToken)

[slozier]

Thanks for the report, I managed to reproduce this with something like:

public void Test(CancellationToken token = default);

A potential fix would be to add some sort of check to DefaultArgBuilder.ToExpression in the DLR (don't think this is correct but something similar may work):

if (parameterType.IsValueType) {
    // default(T)
    return AstUtils.Constant(Activator.CreateInstance(parameterType));
}

[ZhouWei]

Thanks, can we do this without modified the IronPython Souce Code?

DefaultArgBuilder.ToExpression

[slozier]

Thanks, can we do this without modified the IronPython Souce Code?

I don't have any workaround, I think you will have to explicitly pass in the argument CountDocuments[BsonDocument]("collection", cancellationToken=CancellationToken.None).