Fix invalid cast issue in omnisharp-roslyn by fixing LspHandlerDescriptor ctor #488
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See:
The issue (apparently) is that
LspHandlerDescriptoris constructed forDelegatingRequestthat is registered inLanguageServerHost.cs(in omnisharp-roslyn) viar.OnRequest()here:https://github.com/OmniSharp/omnisharp-roslyn/blob/b68f146a649bd6b0294894831e08bbd3b802110c/src/OmniSharp.LanguageServerProtocol/LanguageServerHost.cs#L310
The constructor attempts to resolve RPC return type based on what generic type is set on
IRequest<T>that is inherited byDelegatingRequest. HoweverDelegatingRequestimplements bothIRequestandIRequest<TResponse>and LINQ code selectsIRequest<MediatR.Unit>type as the return value -- while it should beIRequest<JToken>for LSP requests (apparently?).The issue was fixed by ordering implemented
IRequest<>interfaces by generic param type and taking the first that is notMediatR.Unit-- only then use theMediatR.Unitversion.I am not 100% sure this is the proper/correct fix for my issue (OmniSharp/omnisharp-roslyn#1995) but it seems to do the job.
I can try to write tests or change this you feel that is the wrong approach to fix the issue.