[build] allow main to be built with a .NET 8 SDK

[jonathanpeppers]

I've been testing our latest .NET 8 release, and I noticed it was not currently possible to build dotnet/maui/main if you only have .NET 8 installed.

The first issue to get past is global.json:

"sdk": {
    "version": "7.0.200",
    "allowPrerelease": true,
    "rollForward": "latestMinor"
}

latestMinor does not allow it to "roll forward" to a .NET 8 SDK as it stops at any 7.0.x version. I changed this to major, so it can use 8.x or future versions. Alternatively we could completely remove the sdk block here, but I thought this was a reasonable change for now.

The next error I got was:

The "CheckForImplicitPackageReferenceOverrides" task could not be loaded from the assembly C:\Program Files\dotnet\sdk\8.0.100-preview.7.23376.3\Sdks\Microsoft.NET.Sdk\targets\..\tools\net8.0\Microsoft.NET.Build.Tasks.dll. Could not load file or assembly 'System.Runtime, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'.
The system cannot find the file specified. Confirm that the <UsingTask> declaration is correct, that the assembly and all its dependencies are available, and that the task contains a public class that implements Microsoft.Build.Framework.ITask.

This was quite confusing, but what I found was:

• dotnet cake -> uses .NET 8 SDK from my system

• A .NET 7 SDK is provisioned in .\bin\dotnet\

• An <Exec/> task runs:

• .\bin\dotnet\dotnet restore src\DotNet\Dependencies\Workloads.csproj which fails

It looks like the issue is the outer/system .NET SDK passes the $MSBuildSDKsPath environment variable. This makes a .NET 7 SDK import .NET 8 MSBuild targets files -- and everything breaks. I could get past this error by clearing the env var. I also fixed the .binlog location for this command, so it goes in artifacts/logs now.

The last issue I found was:

========================================
dotnet-pack-maui
========================================
Process terminated. The type initializer for 'System.Management.Automation.PSObject' threw an exception.
at System.Environment.FailFast(System.String, System.Exception)
at Microsoft.PowerShell.UnmanagedPSEntry.Start(System.String[], Int32)
at Microsoft.PowerShell.ManagedPSEntry.Main(System.String[])
System.TypeInitializationException: The type initializer for 'System.Management.Automation.PSObject' threw an exception.
---> System.IO.FileNotFoundException: Could not load file or assembly 'Microsoft.Management.Infrastructure, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'. The system cannot find the file specified.
File name: 'Microsoft.Management.Infrastructure, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'
at System.Management.Automation.PSObject..cctor()
--- End of inner exception stack trace ---
at System.Management.Automation.PSObject.get_Properties()
at System.Management.Automation.HostUtilities.GetDollarProfile(String allUsersAllHosts, String allUsersCurrentHost, String currentUserAllHosts, String currentUserCurrentHost)
at Microsoft.PowerShell.ConsoleHost.DoRunspaceInitialization(RunspaceCreationEventArgs args)
at Microsoft.PowerShell.ConsoleHost.DoCreateRunspace(RunspaceCreationEventArgs args)
at Microsoft.PowerShell.ConsoleHost.CreateRunspace(RunspaceCreationEventArgs runspaceCreationArgs)
at Microsoft.PowerShell.ConsoleHost.DoRunspaceLoop(String initialCommand, Boolean skipProfiles, Collection`1 initialCommandArgs, Boolean staMode, String configurationName, String configurationFilePath)
at Microsoft.PowerShell.ConsoleHost.Run(CommandLineParameterParser cpp, Boolean isPrestartWarned)
at Microsoft.PowerShell.ConsoleHost.Start(String bannerText, String helpText, Boolean issProvidedExternally)
at Microsoft.PowerShell.UnmanagedPSEntry.Start(String[] args, Int32 argc)

It appears that the pwsh .NET global tool basically doesn't run at all on .NET 8 yet?

https://www.nuget.org/packages/PowerShell/7.3.6

This fails in this way (if you have .NET 8):

dotnet pwsh eng/package.ps1

While this one succeeds:

./bin/dotnet/dotnet pwsh eng/package.ps1

I could fix this in MAUI's build by setting ToolPath in dotnet.cake:

DotNetTool("pwsh", new DotNetToolSettings
{
    ToolPath = dotnetPath,
    //...
});

This makes the command use ./bin/dotnet/dotnet pwsh, which works.

This last change we might have to undo/revert on the net8.0 branch until they fix the pwsh global tool.