Consider cross-compiling projects to target DefaultNetCoreTargetFramework

[pranavkm]

We have a handful of projects in the repo that do not cross-compile to .NET Core. The reference assemblies in .NET Core carry nullability and platform compatibility annotations and there are currently no plans to make this work on down level tfms.

Updating these projects to additionally cross-compile to $(DefaultNetCoreTargetFramework) seems like a small cost for the richer compile time we gain:

• https://github.com/dotnet/aspnetcore/blob/ce16ff0a51a74811674228835696e5cc78494fd7/src/SignalR/clients/csharp/Client/src/Microsoft.AspNetCore.SignalR.Client.csproj
• https://github.com/dotnet/aspnetcore/blob/ce16ff0a51a74811674228835696e5cc78494fd7/src/SignalR/clients/csharp/Client.Core/src/Microsoft.AspNetCore.SignalR.Client.Core.csproj
• https://github.com/dotnet/aspnetcore/blob/ce16ff0a51a74811674228835696e5cc78494fd7/src/SignalR/clients/csharp/Http.Connections.Client/src/Microsoft.AspNetCore.Http.Connections.Client.csproj
• https://github.com/dotnet/aspnetcore/blob/ce16ff0a51a74811674228835696e5cc78494fd7/src/SignalR/common/Protocols.NewtonsoftJson/src/Microsoft.AspNetCore.SignalR.Protocols.NewtonsoftJson.csproj
• https://github.com/dotnet/aspnetcore/blob/ce16ff0a51a74811674228835696e5cc78494fd7/src/SignalR/common/Protocols.MessagePack/src/Microsoft.AspNetCore.SignalR.Protocols.MessagePack.csproj
• https://github.com/dotnet/aspnetcore/blob/ce16ff0a51a74811674228835696e5cc78494fd7/src/SignalR/server/StackExchangeRedis/src/Microsoft.AspNetCore.SignalR.StackExchangeRedis.csproj
• https://github.com/dotnet/aspnetcore/blob/ce16ff0a51a74811674228835696e5cc78494fd7/src/Features/JsonPatch/src/Microsoft.AspNetCore.JsonPatch.csproj
• https://github.com/dotnet/aspnetcore/blob/ce16ff0a51a74811674228835696e5cc78494fd7/src/Logging.AzureAppServices/src/Microsoft.Extensions.Logging.AzureAppServices.csproj

[ghost]

Thanks for contacting us.
We're moving this issue to the Next sprint planning milestone for future evaluation / consideration. We will evaluate the request when we are planning the work for the next milestone. To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

[wtgodbe]

The only 2 that still don't target DefaultNetCoreTargetFramework are https://github.com/dotnet/aspnetcore/blob/master/src/Features/JsonPatch/src/Microsoft.AspNetCore.JsonPatch.csproj and https://github.com/dotnet/aspnetcore/blob/master/src/Logging.AzureAppServices/src/Microsoft.Extensions.Logging.AzureAppServices.csproj - the rest were done by #26140