Mismatched shared framework versions can cause failed resolution of hostpolicy in certain circumstances

[nguerrera]

Tracking issue for dotnet/sdk#2774 (comment)

Steps to reproduce

git clone https://github.com/dsplaisted/sdk
cd sdk
git checkout a777a2c96765ae7018cecb74fafb31d176da12fb
build
eng\dogfood.cmd cmd
cd ..
mkdir repro
cd repro
dotnet new mvc
dotnet run

Expected behavior

App runs

Actual behavior

A fatal error was encountered. The library 'hostpolicy.dll' required to execute the application was not found in 'd:\src\sdk\.dotnet\shared\Microsoft.AspNetCore.App\3.0.0-preview-18579-0056'.

[vitek-karas]

The reason for the wrong behavior is this line. The code figures out that the FX dependency can be resolved using the already "ready" framework (As the dependency can soft roll forward to the version we have). Logically in that case such framework should be put to the end of the list (to make it the current root), but before that the code compares the dependency version against the newest version and if they don't match it won't perform the move. No idea why.

[nguerrera]

It seems that the workaround to omit Microsoft.NETCore.App from runtimeconfig does not work in all cases.

The following reproduces the same symptom of looking for hostpolicy.dll in the wrong shared framework:

1. Install .NET Core SDK 3.0.100-preview-010124 from https://github.com/dotnet/core-sdk
2. mkdir repro
3. cd repro
4. dotnet new web
5. edit csproj as follows:

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>netcoreapp3.0</TargetFramework>
    <AspNetCoreHostingModel>InProcess</AspNetCoreHostingModel>
  </PropertyGroup>

+  <ItemGroup>
+     <FrameworkReference Include="Microsoft.WindowsDesktop.App" />
+ </ItemGroup>

</Project>

4. dotnet run

Expected: Hello world
Actual: A fatal error was encountered. The library 'hostpolicy.dll' required to execute the application was not found in 'C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App\3.0.0-preview-27316-2

cc @DamianEdwards FYI

[nguerrera]

@steveharter Do you recall the reason for that exact version check?

[nguerrera]

I guess the workaround only worked for the common case of one leaf FR and one root FR, where we remove the explicit ref to the root. But with two leaves having conflicting roots, it still doesn't work. If I understood correctly, at some point soon the root framework will stabilize first and then both WindowsDesktop and ASP.NET will converge to same ref for Preview 2 and above should start working. If that's right, the fix still isn't urgent.

[nguerrera]

cc @swaroop-sridhar