Razor Runtime Compilation appears to be loading views of other apps

[Piedone]

Please note that this is not yet a full bug report (hence not an issue), more like we have hunches that point in a strange direction. Any help in narrowing it down would be appreciated.

We're seeing signs of concurrently running apps getting their views mixed up, i.e. App A using App B's views with Razor Runtime Compilation. Precompiled views without Razor Runtime Compilation don't have this issue.

Details

Our CI environment runs multiple versions of the same app (from multiple branches) in parallel for UI testing. dotnet build is used to build the app, dotnet publish to publish it to a folder. Then, dotnet test executes UI tests (xUnit tests) which all will start the same app's web app project with dotnet My.App.dll (which is then interacted with from an automated browser).

We see occasions that two concurrently running instances of the app (which are built from slightly different codebases, from different branches of the same repository) get mixed up views if Razor Runtime Compilation is enabled. I.e. App A loads App B's views (so views built from the templates with modifications from App B's branch). Note that the two running apps mostly only differ in a few lines, so e.g. all the DLLs are named the same.

If we turn off Razor Runtime Compilation the issue goes away.

Is this something that can actually happen within Razor Runtime Compilation? We've resolved the issue by turning it off (it was a mistake having it on anyway since the views are actually precompiled) but we figured this is worth bringing it up if there is a chance we encountered a bug.

Further technical details

• ASP.NET Core version: The app targets 3.1.
• IDE: VS 2019 16.7.2 but where the app is built in our CI environment there's only Visual Studio Build Tools 2019
• Output of dotnet --info:

.NET Core SDK (reflecting any global.json):
 Version:   3.1.302
 Commit:    41faccf259

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.14393
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\3.1.302\

Host (useful for support):
  Version: 3.1.6
  Commit:  3acd9b0cd1

.NET Core SDKs installed:
  3.1.302 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.20 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.20 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.20 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.1.6 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

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

[benaadams]

#20328 ?

[Piedone]

I'm not sure how that would be related. The app is not served via IIS.

Could it be though that somehow the apps clash due to some environment variables? The build doesn't set any (well, it sets one custom one for our own code but nothing else).