Fail fast on issues with viewmodel serialization

[cafour]

Currently, DotVVM reports serialization issues only if an instance of a type that cannot be serialized is sent to the client. This means that a lot of issues are discovered very late.

A sample:

public class Position
{
    public int X { get; set; }
    public int Y { get; set; }

    public Position(int x, int y)
    {
        X = x;
        Y = y;
    }
}

public class ViewModel
{
    public List<Position> Positions { get; set; }
}

DotVVM currently complains about a missing parameterless constructor in Position only when the Positions list is non-empty. It would be beneficial to learn about serialization issues as soon as possible, during any request to the page at the latest.

[exyi]

1. The current version should support putting data into the constructor.

2. That's not easy to do, if we don't want to report false positives. We currently have don't have a way to analyze the entire object tree, and adding such analyzer would most likely report many errors which don't occur in practice. Specifically the missing constructor is only a problem if you need to deserialize the object.

3. There is the analyzer which is designed to do something like this, but it won't fail the page entirely