Razor runtime view compilation via environment variable not working in .NET 6

[AndrewTriesToCode]

Runtime view compilation appears to not be working in .NET 6 Razor Pages projects when using the environment variable to specify this behavior as described here:

https://docs.microsoft.com/en-us/aspnet/core/mvc/views/view-compilation?view=aspnetcore-6.0&tabs=visual-studio#conditionally-enable-runtime-compilation-in-an-existing-project

If I manually add AddRazorRuntimeCompilation() in ConfigureServices it does work though.

I'm including v6.0.0 of the assembly package:
<PackageReference Include="Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation" Version="6.0.0" />

And my launch profile has the following section:

"environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development",
        "ASPNETCORE_HOSTINGSTARTUPASSEMBLIES": "Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation"
      }

Worked as expected in .NET 5 on the same project.

[davidfowl]

cc @halter73 (might be a hosting problem)

[javiercn]

@AndrewTriesToCode thanks for contacting us.

@pranavkm do you have any thoughts?

Thanks for contacting us.

We're moving this issue to the .NET 7 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

[pranavkm]

This was introduced as a result of my attempt to refactor the way action descriptors are registered for Razor. Runtime compilation requires adding a matcher policy and a different ADP, which is currently contingent on the default one being already registered: https://github.com/dotnet/aspnetcore/blob/main/src/Mvc/Mvc.Razor.RuntimeCompilation/src/DependencyInjection/RazorRuntimeCompilationMvcCoreBuilderExtensions.cs#L88-L99. This unfortunately does not happen with the env variable since the hosting startup runs before ConfigureServices. My guess is one way to fix it would be to reduce the check to only remove the ADP on Line 90, and do everything else all the time.

That said, for 6.0, we intentionally removed the option of conditionally enabling runtime compilation from our project templates because we believe hot reload is a better dev time alternative. Particularly for .cshtml files, you get really high fidelity for the kinds of edits that are supported, so there generally shouldn't be a reason to require this feature.

[AndrewTriesToCode]

Thanks for the details. My experience on Mac has been that hot reload only works on non-debug runs, causes an error, and is disabled for the rest of the session. It might be due to the fact that I use Rider so I’ll try it in VS code.

[SteveSandersonMS]

@pranavkm Should this go on the backlog then? I'm putting it there but please feel free to move it if you disagree.