Aspnetcore: TagHelpers don't work in 2.2 runtime with 3.0 preview sdk

[nattthebear]

Describe the bug

Depending on what dotnet sdk I build with, my taghelpers fail to be picked up.

To Reproduce

Steps to reproduce the behavior:

1. Using sdk 3.0.100-preview-009812 and with runtime Microsoft.AspNetCore.App 2.2.1 installed
2. Build and run this project https://github.com/adelikat/tasvideos (I can try to make a smaller reproducing test case if it will help) (Note: project targets netcoreapp2.2)
3. The application will run, but the custom TagHelpers will not be picked up

Expected behavior

Repeating the same steps, but building with sdk 2.2.102, the TagHelpers work.

Additional context

C:\Develop\TasVideos> dotnet --info
.NET Core SDK (reflecting any global.json):
 Version:   2.2.102
 Commit:    96ff75a873

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.17763
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\2.2.102\

Host (useful for support):
  Version: 3.0.0-preview-27122-01
  Commit:  00c5c8bc40

.NET Core SDKs installed:
  2.1.302 [C:\Program Files\dotnet\sdk]
  2.2.102 [C:\Program Files\dotnet\sdk]
  3.0.100-preview-009812 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.2.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.0.0-preview-18579-0056 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.2 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.0-preview-27122-01 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.0.0-alpha-27128-4 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

To install additional .NET Core runtimes or SDKs:
  https://aka.ms/dotnet-download

[pranavkm]

@nattthebear thanks for the issue report. The fix for this should most likely be available as part of the 3.0-preview3 release. In the meanwhile, I'd recommend staying on the 2.2 SDK (using a global.json to specify an exact version) until we get a resolution for this.

[nattthebear]

Thanks for the prompt response and resolution!