Binding projects don't work in .NET 9 RC 2

[rolfbjarne]

Running bgen with dotnet from .NET 9 RC 2 yields an error like this:

/usr/local/share/dotnet/packs/Microsoft.iOS.Sdk.net9.0_18.0/18.0.9600-net9-rc2/tools/msbuild/iOS/Xamarin.Shared.targets(1776,3): error MSB6006: "dotnet" exited with code 150.

Looking at a binlog, this is the reason:

You must install or update .NET to run this application.
App: /usr/local/share/dotnet/packs/Microsoft.iOS.Sdk.net9.0_18.0/18.0.9600-net9-rc2/tools/lib/bgen/bgen.dll
Architecture: arm64
Framework: 'Microsoft.NETCore.App', version '9.0.0-rtm.24475.3' (arm64)
.NET location: /usr/local/share/dotnet/
The following frameworks were found:
  8.0.8 at [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  9.0.0-rc.2.24473.5 at [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]

Which is because bgen was built for a newer .NET runtime than RC 2:

$ cat /usr/local/share/dotnet/packs/Microsoft.iOS.Sdk.net9.0_18.0/18.0.9600-net9-rc2/tools/lib/bgen/bgen.runtimeconfig.json

{
  "runtimeOptions": {
    "tfm": "net9.0",
    "framework": {
      "name": "Microsoft.NETCore.App",
      "version": "9.0.0-rtm.24475.3"
    },
    "rollForward": "Major",
    "configProperties": {
      "System.Runtime.Serialization.EnableUnsafeBinaryFormatterSerialization": false
    }
  }
}

And that's because it's the dependency we have in eng/Version.Details.xml:

xamarin-macios/eng/Version.Details.xml

Line 16 in a6599c7

<Dependency Name="Microsoft.NETCore.App.Ref" Version="9.0.0-rtm.24475.3" CoherentParentDependency="Microsoft.NET.Sdk">

The good news is that this will automatically fix itself for the final release.

It might be possible to work around this by installing a daily .NET 9 RTM build from here: https://github.com/dotnet/sdk/blob/main/documentation/package-table.md

This is partially a side effect of the fact that there were no public .NET 9 RC 2 .NET builds we could build against:

$ darc get-latest-build --repo dotnet/sdk --channel '.NET 9.0.1xx SDK RC 2'
No latest build found matching the specified criteria

Which meant we were building with an earlier version of .NET 9 (from the .NET 9.0.1xx SDK channel).

The second part to this is that not every .NET version from the .NET 9.0.1xx SDK channel can build projects that can run on the released version of RC 2, because they may reference an rtm version of dotnet/runtime. This is evidenced by this maestro bump: f419cce, which bumps to:

• Microsoft.NET.Sdk: Version="9.0.100-rc.2.24475.4"
• Microsoft.NETCore.App.Ref: Version="9.0.0-rtm.24475.3"

This means any projects built with this version of .NET 9 will produce *.runtimeconfig.json file requiring "Microsoft.NETCore.App.Ref=9.0.0-rtm.24475.3", which the public .NET 9 RC 2 release doesn't fulfill.