MSBuild.SDK.SystemWeb VS ReferenceAssemblyAnnotator

I have some projects stuck on that, but not a lot. For web stuff, https://github.com/CZEMacLeod/MSBuild.SDK.SystemWeb does most of the heavy lifting, although things like publishing are broken.

I’ve had great luck with this on older ASP.NET projects https://github.com/CZEMacLeod/MSBuild.SDK.SystemWeb

You can use this unofficial project to modernize your .NET Framework project and take advantage of things like PackageReferences.

Sdk at least works with .net standard so shared projects can be converted to that, we also had some success using the MSBuild.SDK.SystemWeb sdk nuget package for our MVC5 projects which I found from the github issue discussions on adding official support for it on older projects.

I've been a bit luckier in that regard, but I'm not sure if your path wouldn't have taken less effort. I use https://github.com/hvanbakel/CsprojToVs2017 (dotnet migrate-2019 wizard) to modernize the projects, then further tweak them by hand. For ASP.NET projects, it's indeed a very difficult road. WebForms outright doesn't exist, and Core is very different from MVC in some areas. https://github.com/CZEMacLeod/MSBuild.SDK.SystemWeb helps somewhat.

Even for .NET Framework code, I tend to use recent C# versions. I reference https://github.com/jnm2/ReferenceAssemblyAnnotator to get nullable support and https://github.com/manuelroemer/IsExternalInit for records, and that takes care of most of the features I care about.

In the case of NRT, most of the feature lives in the compiler. Annotations, of course, live in the BCL, which is why I recommend https://github.com/jnm2/ReferenceAssemblyAnnotator — that way, you can use something like Dictionary.TryGetValue() in your .NET Standard 2.0 code, and the compiler will know that the out value is null if the method returns false.