Exception.HResult setter should be made public

[luqunl]

Currently The setter on Exception.HResult is protected. If customer need to set a different HResult for a specific exception, customer has to create a derived exception to override.

Rationale and Usage

It is very common to set a different HResult for interop area due to compatibility reason --- Interop should return same HResult as the code is called/implemented by native code.

For example:

https://github.com/dotnet/corefx/blob/02a26f8f417967e31bab8d96605d3d8846154e8a/src/System.Runtime.WindowsRuntime/src/System/IO/NetFxToWinRtStreamAdapter.cs#L195

Exception.SetErrorCode is an internal API. The HResult for ObjectDisposedException is 0x80131622 and RO_E_CLOSED is 0x80000013

        if (_fClosed)
        {
            return RO_E_CLOSED;
        }

With this change, you can directly assign HResult and remove SetErrorCode internal API.

ex. HResult  = __HResults.RO_E_CLOSED;

Proposed API

    public partial class Exception : System.Runtime.Serialization.ISerializable
    {
        // Existing members
        // public int HResult { get { throw null; } protected set { } }
         // Proposed members
         public int HResult { get { throw null; } set { } }
    }

Details

There are other ways to achieve this:

• Change Exception.SetErrorCode from Internal to public API 
  Pro: a lot of existing code already use this API, less code change
  Con:  More complicated than proposed one. There are two ways to change HResult(Derived from exists exception and use Exception.SetErrorCode API). 
  

• Add a new public API in Marshal which update HResult for an exception
  Pro: It works
  Con: Complicated and customer have to know this new Marshal API exists.
  

Overall, Make Exception.HResult setter to public is simpler way to do this.

[danmoseley]

@luqunl can this be closed?